Formation and Release of NO from Ruthenium Nitrosyl Ammine

Subscriber access provided by BOSTON UNIV

Article

Formation and Release of NO from Ruthenium Nitrosyl Ammine Complexes [Ru(NH)(NO)] in Aqueous Solution: A Theoretical Investigation 3

5

2+/3+

Gabriel L. S. Rodrigues, and Willian Ricardo Rocha J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.6b08813 • Publication Date (Web): 18 Oct 2016 Downloaded from http://pubs.acs.org on October 19, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry B is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Formation and Release of NO from Ruthenium Nitrosyl Ammine Complexes [Ru(NH3)5(NO)]2+/3+ in Aqueous Solution: A Theoretical Investigation.

Gabriel L. S. Rodrigues and Willian R. Rocha*

LQC-MM: Laboratório de Química Computacional e Modelagem Molecular Departamento de Química, ICEx, Universidade Federal de Minas Gerais 31270-901, Pampulha, Belo Horizonte, MG, Brazil

___________________________________________________________ * Corresponding author. E-mail address: [email protected] (W. R. Rocha) Phone: +55 31 34095766

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 50

Abstract: In this article Density Functional Theory in conjunction with Monte Carlo statistical mechanical simulation were used to investigate the electronic structure, reduction potential, solvation and solvent effects on the electronic spectra of nitrosyl ammine complexes, using [Ru(NH3)5(NO)]2+/3+ as model compounds. In addition, ligand exchange reactions with solvent water molecules were also investigated. It is shown that the complexes are involved in strong hydrogen bonds in aqueous solution, with mean average energies of (-13.5 ± 04) and (-22.4 ± 04) kcal.mol-1 for the Ru(II) and Ru(III), respectively. Interestingly, for all the complexes studied the NO ligand is not involved in hydrogen bonding interactions in aqueous solution. These strong hydrogen bonds are responsible for the high stability of these complexes in aqueous solution, showing formation constants Kf greater than 1021. The complex [Ru(NH3)5(NO)]3+ can easily be reduced by biological reducing agents in both the singlet and triplet states however, the reduction is easier in the triplet state which has a positive reduction potential of 1.70V. The formation of the [Ru(NH3)5(NO)]3+ in its most stable singlet state may takes place through at least two singlet-triplet surface crossings leading to non-adiabatic effects. The existence of the minimum energy crossing points makes the release of NO from the triplet state more favorable, with an activation energy almost seven times smaller (~ 6 kcal.mol-1).


Page 3 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction: Nitric Oxide (NO) is a molecule of great chemical and biological interest, which has stimulated the scientific community mainly due to its biochemical functions and possible therapeutic applications.1-4 NO is classified as a messenger molecule and it is well known to play important roles in several important biochemical and physiological processes in the human body as, for instance, modulation of the immune and endocrine response, cardiovascular control, regulation of blood pressure, neurotransmission, induction of apoptosis, among others.5-8 Due to the instability of NO in biological environment and its short lifetime the study of its physiological effects is not trivial. These facts have encouraged several studies in obtaining stable transition metal compounds for the in situ delivery of NO, in a controlled manner, upon chemical9,10, electrochemical11 or photochemical12-17 stimuli in the organism, acting thus as prodrugs. Ruthenium complexes have shown very promising for this purpose18,21 due to its thermodynamic stability, high affinity for NO, photodynamic reactivity, solubility in water and accessibility of different oxidation states under physiological conditions. As examples, the compounds trans[(Ru(NH3)4(L)(NO)]3+ (L= pyridine, 4-methyl-pyridine) when in aqueous solution and irradiated in the near ultraviolet (300-370 nm) result in dissociation of NO and production of the compound trans-[(Ru(NH3)4(L)(H2O)]3+.19 Cameron et al.20 reported the use of ruthenium complexes as potential and effective scavengers of NO in biological systems. Clarke and coworkers21 reported that the administration of the complex trans-[RuII(cyclam)Cl(NO)]2+ reduces blood pressure and produces an antihypertensive effect 20 times longer than that generated by sodium nitroprusside,



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

used to lower blood pressure. More recently, Nakanishi et al.

Page 4 of 50

22

incorporated Ru(salen)

complexes into liposome bilayers allowing the photoinduced release and membrane transport of NO. Despite the progress in the synthesis, characterization and biological studies, the mechanism involved in the release of NO from these transition metal nitrosyl complexes is not yet fully understood. This can, in part, be attributed to the nature of the metal-NO bond, since the non-innocent NO ligand can coordinate to the metal center as NO+, NO- and NO•23,24 and also to the short lifetime of the species released. Therefore, the way the nitrosyl species is released in solution is still a matter of controversy.8,25-28 There are experimental evidences showing that the nitrosyl can be released as NO+ 25,26, NO•27-31 and also NO-, through a biological reduction of NO. This NO- can be involved in acid-base equilibrium generating the HNO species, which has several implications in biology.32,33 In addition, these nitrosyl species reacts promptly with several compounds in the biological environment and thus the study of the nature and fate of these released species is not trivial. Computational Chemistry has contributed greatly to the understanding of the nature of the metal-NO bonds and reactivity of metal nitrosyl compounds.34-38 For instance, Caramori et al.34 have employed quantum chemical calculations at the DFT level of theory for trans-[RuII(NH3)4(L)NO]q and trans-[RuII(NH3)4(L)NO]q-1 (with q being the charge of the complex and L = NH3, Cl-, and H2O) to study the nature of the Ru-NO+ and Ru-NO chemical bonding through the energy decomposition analysis (EDA). They showed that both the orbital term and Pauli repulsion contributes to the weakening of the NO bond and, the NO ligand is more susceptible to dissociation in comparison to NO+, due to the increasing Pauli repulsion contribution. Our group have 4 ACS Paragon Plus Environment

Page 5 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


also contributed to the understanding of the M-NO bond in the complexes [M(Im)(PPIX)(L)]q, where M= Fe2+ and Ru2+, Im=Imidazole ring, PPIX= ProtoPorphyrin IX of the heme group and L=NO+, NO and NO-.37 We showed that NO coordinates preferentially through the nitrogen atom and its oxidized form NO+ produces more stable complexes. Charge and energy decomposition analysis revealed that, the interaction of NO species with the Ru2+ fragment is stronger than with Fe2+ fragment. Important contributions to the spectroscopy and photodissociation dynamics of ruthenium nitrosyl complexes have been given by González and co-workers.38,39 For instance,

they

have

studied

the

photorelease

of

NO

from

the

complex

[Ru(PaPy3)(NO)]2+ using TD-DFT based surface-hopping molecular dynamics.39 They found that intersystem crossing is ultrafast and the dissociation is initiated in less than 50 fs. Additionally, multiconfigurational spin-corrected calculations revealed that the ground state of the complex has a significant contribution of RuIIINO0 electronic configuration, in contrast to the proposed RuIINO+ configuration. Aiming at understanding the fate of the released NO species in solution, we have recently employed ab initio molecular dynamics simulations to investigate the early chemical events involved in the dynamics of nitric oxide (NO•), nitrosonium cation (NO+) and nitroxide anion (NO-) in aqueous solution.40 We showed that NO+ ion is very reactive in aqueous solution having a lifetime of ~ 4 x 10-13 s, which is shorter than the value of 3 x 10-10 s predicted experimentally. The NO+ reacts generating the nitrous acid as an intermediate and the NO2- ion as the final product. The dynamics of NO•, on the other hand revealed the reversible formation of a transient anion radical species HONO•-. The calculations with ruthenium nitrosyl complexes, reported so far, have been performed in gas phase and, despite the important contributions given by electronic



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 50

structure calculations, there are some basic aspects related to ruthenium nitrosyl complexes in aqueous solution that need to be investigated. For instance, the calculation of the reduction potential of these complexes, the magnitude of the intermolecular interactions in solution and how these interactions affect the spectroscopic properties. Additionally, since the release of NO from the complexes is followed by coordination of solvent molecules to the vacant coordination site, it is important to investigate the mechanism and energies involved in the NO exchange reactions with the solvent. In this article we have used the complexes [Ru(NH3)5(NO)]2+/3+ as a model to understand the electronic structure, reduction potential, solvation, solvent effects on the electronic spectra and ligand exchange reactions with water. To this end, Density Functional Theory in conjunction with Monte Carlo statistical mechanical simulation and implicit solvent models were used. As we shall see, despite the apparent simplicity of these complexes, their electronic structures are rather complicate. The solvation of these complexes shows surprising results concerning the magnitude of the intermolecular interactions and, due to the presence of an unpaired electron on the NO ligand and different spin states of the complexes, the modeling of the exchange reaction in solution is not a simple task, involving surface crossings leading thus to nonadiabatic effects.

Computational Details: Full unconstrained geometry optimizations and frequency calculations of all species

involved

in

this

study

([Ru(NH3)5(NO)]2+/3+,

[Ru(NH3)5(H2O)]2+/3+,

[Ru(NH3)6]2+/3+ and the free ligands) were carried out at the DFT level of theory41 with the TPSSh hybrid meta-GGA exchange-correlation functional42 as implemented in the


Page 7 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ORCA program.43 The Ahlrichs full electron def2-TZVP basis set44 was used for all atoms. Scalar relativistic effects were treated using the Zeroth Order Regular Approximation (ZORA) formalism.45-47 To speed up the calculations the resolution of the identity48 was used for the coulomb, and the chain of sphere approach49 for the exchange part of the Fock matrix, employing the def2-TZVP/J auxiliary basis set.50 We have shown that this combination of exchange-correlation functional and basis set have been shown to provide good structural and energetic results for a series of transitions metal complexes51 and also to describe the electronic spectrum of ruthenium-amine compounds.52 Calculations on the open-shell structures were carried out within the unrestricted Kohn-Sham formalism. Using the optimized geometry of the [Ru(NH3)5(NO)]2+/3+ complexes in their more stable spin state (S = 1/2 for the Ru2+ and S = 0 for the Ru3+ complex), Monte Carlo (MC) statistical mechanics simulations53 in the NVT ensemble were carried out at 298K. The simulations were composed of one solute molecule (the nitrosyl complex) and 499 water molecules in a cubic box of 30Å, applying the periodic boundary conditions and minimum image convention.53 The system was equilibrated with 50000 MC steps, followed by additional 80000 MC steps to obtain the thermodynamic properties. The energy at each MC step was evaluated using a classical intermolecular pair potential composed of the 12-6 Lennard-Jones (LJ) plus Coulomb terms.53 The water molecules were described with the TIP3P model54. The UFF force field55 was used to describe the Ru atom, using modified σ and ε parameters.56 The OPLS force field parameters57 were used for the other atoms. The atomic charges for the complexes, used to describe the Coulomb interactions, were obtained through the CHELPG



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 50

method.58 All Monte Carlo Simulations were performed using the DICE program developed by Canuto and Coutinho.59 Configurations selected along the MC simulations were used to describe the solvent effects on the electronic spectra of the complexes. The number of water molecules used in the calculations was obtained through the analysis of radial pair distribution function between the ruthenium and the oxygen atom of the water molecules. The electronic spectrum was computed using the TDDFT formalism60, employing the TPSSh42 functional and including 10 water molecules within the first solvation shell explicitly. TD-DFT excitation energies were then obtained treating the water molecules with the aug-cc-PVDZ and also, describing the water molecules as Effective Fragment Potentials (EFP) method of Gordon and co-workers.61-63 For both approaches the long range solvent effects were treated using the polarizable continuum model (PCM)

64

. The TD-DFT calculations were carried out using the GAMESS-US

program.65 The reaction mechanism and energetics involved in the ligand exchange reactions was investigated using the coordinate-driven minimum-energy path approach. In this approach, the optimized [Ru(NH3)5(H2O)]2+/3+ complexes were surrounded by 10 water molecules, obtained from the Monte Carlo simulations. The nitrosyl molecule was placed initially at 3.6 Å away from the metallic center, as is shown in figure 6, and the entire system is placed in the COSMO reaction field to describe the long range solvent interactions. The distance Ru-NO is diminished from 3.6 to 1.6 Å and, for a given r(RuNO) distance, all remaining intramolecular coordinates have been fully optimized, in each electronic spin state, without any symmetry constraint. Additional frequency calculations were performed on the stationary points located on the ligand exchange 8 ACS Paragon Plus Environment

Page 9 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reaction curves. The calculations were performed with the TPSSh functional42 and the Karlsruhe TZVP basis set44 was employed for all atoms. Relativistic effects were treated within the ZORA approach.45-47 These calculations were carried out with the ORCA program.43

Results and Discussion: Electronic structure, solvation, reduction potential and electronic spectra The optimized structures obtained for the complexes [Ru(NH3)5(NO)]2+/3+ and [Ru(NH3)6]2+/3+, in its different spin states, are shown in figure 1 and the energies of the different spin states are given in table 1. The ions Ru2+ and Ru3+ have d6 and d5 valence configuration, respectively. Thus, the complexes with ammonia will give rise to complexes with singlet and quintet multiplicities for Ru2+ and doublet and sextet for Ru3+, respectively. The nitrosyl complexes on the other hand, due to the unpaired electron on the NO ligand, will give rise to complexes with doublet and sextet multiplicities for Ru2+ and singlet and triplet for Ru3+. The singlet state of the [Ru(NH3)5(NO)]3+ is believed to have a formal coordination of the type RuII-NO+, with an electron transfer from the NO to the Ru3+ ion. As can be seen in table 1, the low spin configurations of the complexes are the most stable one and, the high spin configurations are not thermally accessible at room or body temperatures. For instance, the energy difference between the doublet and sextet spin states of the [Ru(NH3)5(NO)]2+ complex is more than 80 kcal.mol-1. The smallest energy difference was obtained for the singlet and triplet spin states of [Ru(NH3)5(NO)]3+, 43.5 kcal.mol-1, which can be considered as accessible under mild conditions of temperature.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 50

The main structural parameters computed for the nitrosyl complexes are quoted in table 2. As can be seen, the geometry of the complexes varies little with the spin state. The main difference, however, is in the coordination angle of the NO ligand. The ligand coordinates linearly to the metallic center in the singlet state of the RuIII-NO complex, with an angle 179.6°, in line with the experimental measurements.66 However, for the ground state of the RuII-NO complex and the triplet state of the RuIII-NO complex, the NO bends upon coordination, with the ∠ Ru-N-O angle of 141.8° and 139.2°, respectively. Since the singlet and triplet state of the RuIII-NO complexes differ mainly by the ∠ Ru-N-O angle, we monitored how the charge distribution over the atoms changes as a function of this angle and, the results are shown in figure 2. As it can be seen, from 100 to 120º the charges increase over nitrogen and decrease over ruthenium. This can be explained by the σ-donation from the NO to the metallic center. After this point, the back-donation from the metal to the π* orbital of the NO ligand, becomes more relevant due to the symmetry requirements and thus, the charges over ruthenium increases and decreases over nitrogen. That is, with the linearity of the NO coordination the superposition between the d orbitals of ruthenium and the π* orbital of the NO becomes more efficient and the back-donation is more pronounced, leading to a shorter Ru-NO bond. Despite that ruthenium nitrosyl complexes have being used for the in situ delivery of NO in biological systems, RuIII-NO complexes are essentially inert due to the high dissociation energy. These complexes usually need to be reduced to the RuIINO counterpart, in which the Ru-NO dissociation energy is lower. This is the base of


Page 11 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


what is known as the activation by reduction hypothesis.7,18 Therefore, the investigation of the reduction potential of the Ru-nitrosyl complexes is of great interest. However, the calculation of reduction potential of transition metal compounds in solution is not an easy task since it requires a good theoretical method to treat the electronic structure of these compounds as well as an adequate method to obtain their solvation free energies. As was shown in table 1, the singlet-triplet energy gap computed for the [Ru(NH3)5(NO)]3+ compound is 43.5 kcal.mol-1, which means that the triplet state can be

thermally

and/or

optically

accessed.

Therefore,

the

reduction

of

the

[Ru(NH3)5(NO)]3+ compound can follow two pathways, starting from the singlet or triplet states, as shown in figure 3. The reduction potential of the complexes was computed, according to Rulíšek68, using the equation 1: 0 E 0 [V] = 27.21(Gox [a.u] − Gred [a.u]) − Eabs (NHE)[V]

(1)

0 Where Gox/red is the Gibbs free energy of the oxidized/reduced forms and Eabs (NHE) is

the absolute potential of the normal hydrogen electrode which, in this work, we used the recommend value of 4.281 V suggested by Isse and Gennaro.69 The Gibbs free energy of the species is obtained using equation 2: G = Eelec-nuc + ∆Gsolv + Gterm

(2)

Where ∆Gsolv is the solvation free energy, Gterm is the thermal contribution to the Gibbs free energy, obtained within the rigid rotor/harmonic oscillator approach and Eelec-nuc is the electronic-nuclear energy of the species. As can be seen, the solvation Gibbs free energy and the electronic energy dominate the computation of the reduction potential. The reduction potentials were computed at the TPSSh/def2-TZVP level of theory. The



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 50

Gibbs free energy of Solvation were obtained using the SMD model of Truhlar and Cramer70, as implemented in the ORCA program43 in which the electrostatic contribution to the solvation free energy is obtained using the Conductor-like Screening Model (COSMO) of Klamt.71 The results showed in table 3 reveals that the TPSSh/def2-TZVP//SMD protocol gives excellent results for the reduction potential of [Ru(NH3)6]3+. The difference between the experimental72 and calculated values is just 0.03 V. Table 3 also shows that the reduction of the [Ru(NH3)5(NO)]3+ compound is more favorable in the triplet state for which the reduction potential is computed as 1.70 V. The reduction potential for the singlet state is computed as -0.01 V. It is worth mentioning that the reduction potential of many biological reducing agents such as NADH, cysteine, glutathione is around -0.3 V at biological pH.73,74 Therefore, according to the computed values for the reduction potential, the [Ru(NH3)5(NO)]3+ compound can easily be reduced by biological reducing agents in both the singlet and triplet states. However, the reduction from the triplet state is certainly more favorable. Another important aspect of the ruthenium nitrosyl complexes that, to the best of our knowledge, have never been investigated previously by computational methods is related to their interactions with the solvent in aqueous solution. Once the NO ligand is coordinated it can interact with nucleophilic species and be released as other NO species such as HNO or N2O.8 Therefore, the involvement of the coordinated NO with the solvent through, for instance, hydrogen bonding interactions can, in principle, facilitate proton transfer processes or restrict the interaction with other species. Therefore, the study of the nature and magnitude of the intermolecular interactions involving ruthenium nitrosyl complexes in aqueous solution can provide important information to the understanding of the release of NO by ruthenium nitrosyl complexes.


Page 13 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4 shows the radial pair distribution functions between the ruthenium and the oxygen atom of the water molecules, gRu-O and also between the nitrogen and oxygen atoms of the NO ligand and the water molecules, obtained in the Monte Carlo simulation. The gRu-O gives an idea of the solvation of the entire molecules and, therefore, the number of solvation shells. For both the Ru2+ and Ru3+ complexes, three well defined solvation shells are obtained. Due to the higher charge of the complex, the first solvation shell of the Ru3+ complex is slightly more compact than the Ru2+, starting at 3.55 Å, ending at 4.90 Å and having a maximum at 4.15 Å. The integration of the first peak gives 15 water molecules present in the first solvation shell of both complexes. The second solvation shell contains 49 and 43 water molecules for the Ru3+ and Ru2+ complexes, respectively. It is worth noting that the complexes can orient water molecules up to 10 Å away from the metallic center. It means that if one wants to simulate the solvent effects on, for instance, spectroscopic properties, at least 15 water molecules representing the first solvation shell are necessary. However, as we have demonstrated previously52, if the spectroscopic effect is localized, for instance, at solvent effects on d-d electronic transitions, continuum solvation models can work perfectly. The pair distribution function involving the NO ligand and the water molecules of the solvent can also be seen in figure 4. The NH3 ligands are involved in strong hydrogen bonds with the solvent as can be seen by the sharp and well defined peak, centered about 1.850 Å, in the g(r) involving the hydrogen of ammonia and the oxygen of water, g(HNH3-OW). In contrast, the NO ligand is not involved in hydrogen bonding with the solvent as is shown in figure 4. This result shows that the coordinated NO ligand is free to react with other molecules in solution. It is worth noting that upon



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 50

coordination the charges over the oxygen and nitrogen atoms of the NO ligand becomes slightly positive in the [Ru(NH3)5(NO)]3+ complex (qN = 0.116e and qO = 0.174e) and slightly negative in the [Ru(NH3)5(NO)]2+ complex (qN = -0.072e and qO = -0.049e). These charge distributions can explain the absence of hydrogen bonding interactions involving the coordinated ligand and the solvent molecules. We evaluated the magnitude of the hydrogen bonds in solution analyzing the uncorrelated configurations obtained along the Monte Carlo Simulation, using the procedure developed by Canuto and Coutinho.75 The geometric criterion used to define the hydrogen bonds were: RDA = 3.2 Å, ∠(D-H-A) ± 30°, where D and A refers to hydrogen bond donor and acceptor atoms, respectively. Additionally, an energetic criterion of ∆E < 0, was used. That is, configurations that meet the geometric criterion and stabilize the interaction energy are considered as hydrogen bonds. Within the 200 uncorrelated configurations we found 2483 and 1903 HB for the [Ru(NH3)5(NO)]3+ and [Ru(NH3)5(NO)]2+ compounds, respectively, giving an average of 12.4 and 9.5 HB per configuration. The hydrogen bonds are distributed within a range of energies, as is shown in figure 5. As can be seen, the compounds make strong hydrogen bonds with the solvent, which contributed to their high solvation energies. We found an average hydrogen bond energy of -13.5±0.4 kcal.mol-1 for the [Ru(NH3)5(NO)]2+ complex and -22.4±0.4 kcal.mol-1 for the [Ru(NH3)5(NO)]3+ complex. It is important to mention that the consequences of such strong hydrogen bonds are that the water molecules can eventually deprotonate the ammonia ligands, giving rise to a series of reactions. Unfortunately, the method we are using does not include polarization of both solute and solvent and also, does not allow chemical bonds to be broken/formed. We believe that a proper ab initio molecular dynamics study of these complexes in solution may reveal


Page 15 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


new facts regarding the interaction of these complexes with the solvent and this study is under way. Therefore, our results can be view only as an estimate of the strength of the hydrogen bonds of the complexes in solution. The electronic spectrum of the complex [Ru(NH3)5(NO)]3+, is dominated by two electronic transitions at λ1 = 460 nm (HOMO → LUMO; 1A1 → 3T1, 3T2; MLCT t2 → π*(NO)) and λ2 = 300 nm (1A1 → 3A1, 3E1; d-d) both with low intensity and oscillator strength.67 We have applied the Time Dependent Density Functional Theory (TDDFT) 60

, using the same TPSSh functional, to model the electronic spectrum in gas phase and

in solution. For the computation of the solvation effects, the water molecules of the first solvation shell were included explicitly in two different ways. First, they were treated as Effective Fragment Potentials

61-63

and the long range effects included by means of

the PCM implicit solvation model.64 In the second approach the entire system was treated at the TPSSh level, and the water molecules were described with aug-cc-PVDZ also in this approach the long range solvent effects were treated with the PCM method. The results are quoted in table 4. The second electronic transition λ2 is essentially a localized d-d transition and, suffers a hypsochromic shift upon solvation, changing from 315 nm in gas phase to 290 nm in solution. This result shows that the splitting of the d levels of the ruthenium ion increases upon solvation. On the other hand, the first electronic transition λ1, which is essentially a metal-to-ligand (d → π*(NO)) charge transfer, undergoes a bathochromic shift upon solvation. For this transition the solvatochromic shift is larger than for λ2. The computed gas phase transition was 395 nm and in solution we obtained 423 nm, treating the water molecules as Effective fragments, and 427 nm treating the entire system ab initio. The bathochromic shift can be explained by the increase in the d-levels of the ruthenium ion and also by the



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 50

stabilization of the π*(NO) orbital upon solvation, diminishing the energy difference between the d-levels of the metal and the anti-bonding orbital of the nitrosyl ligand. It is worth noting that for the internal d-d transition, we obtain a good agreement between the computed and experimental value. However, for the MLCT transition, the agreement is poor, which can in part be attributed to the inadequacy of the functional to treat such kind of charge transfer transition and also to the absence of dynamical effects of the solute that were not included. It is also important to note that the treatment of the water molecules as EFP´s gives essentially the same value (within 1% difference) as obtained treating the entire system quantum-mechanically, with a lower computational cost, showing the efficiency of the EFP approach to simulate the solvent effects on spectroscopic properties. Similar results using EFP´s were obtained previously by our group.52

3.2 Thermodynamics and reaction mechanism The Gibbs free energy (∆Gr(sol)) involved in the formation reaction of the [Ru(NH3)5(NO)]2+/3+ complexes in aqueous solution, at 300 K, starting from the [Ru(NH3)6]2+/3+ and [Ru(NH3)5(H2O)]2+/3+ complexes, were computed according to equation 3: ∆Gr(sol) = ∆Gr(g) + ∆∆Gsolv

(3)

Where ∆Gr(g) is the free energy difference computed in gas phase, through harmonic frequency calculations at the TPSSh/def2-TZVP level of theory and ∆∆Gsolv is the difference in Gibbs solvation free energies obtained with the SMD model70, as described in the theoretical details section, using the same level of theory used for the gas phase. From the Gibbs free energy of reaction in aqueous solution the formation 16 ACS Paragon Plus Environment

Page 17 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


constants (Kf) of the complexes were computed. The results are quoted in table 5 and reveals that the ruthenium nitrosyl complexes are very stable in aqueous solution, resulting in highly favorable Gibbs free energy changes (< -25 kcal.mol-1) and therefore high formation constants (> 1021). The high stability of these complexes in solution means that the release of NO, through simple ligand exchange reactions, is a very unlike process. Therefore, chemical routes for the release of NO may involve direct reaction of the coordinated nitrosyl ligand with nucleophilic species.7,8 In addition, the photochemical release of NO from the ruthenium nitrosyl complexes is also possible and, the dynamics of this process can be very complex.13,15-17 The modeling of the reaction mechanism involved in the capture/release of NO in aqueous solution, employing simple ligand exchange reactions as those listed in table 5, is not a trivial task. For instance, in equation 4 of table 5, the nitrosyl complex [Ru(NH3)5(NO)]3+ has a singlet ground state and the [Ru(NH3)5(H2O)]3+ complex has a doublet ground state. That is, the reactant and products have different spin state and thus, the reaction may proceed through surface crossings, which usually requires more sophisticated theoretical treatment to include these non-adiabatic effects.76 The released NO molecule can also react with the solvent water molecules generating different NO species as we demonstrated recently.40 Therefore, in order to investigate this reaction mechanism we must include explicit solvent water molecules at least up to the first solvation shell. Aiming at understanding the reaction mechanism and energetics involved in these reactions, the energy landscape for the ligand exchange reactions were built using the coordinate-driven minimum-energy path approach as described in the computational details section



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 50

Figure 7 shows the potential energy surface for the displacement of H2O in the [Ru(NH3)5(H2O)]2+ complex by the NO ligand, occurring in the doublet spin state. The formation of the nitrosyl complex takes place with a very small energy barrier of ~ 5 kcal.mol-1. The transition state region for this reaction shows r(Ru-NO) = 2.457 Å, the Ru-H2O bond is partially broken r(Ru-H2O) = 2.237 Å and the angle N-Ru-O = 117.4º. Further interaction of the NO molecule generates the nitrosyl complex with r(Ru-NO) = 1.886 Å, and the water molecule displaced from the coordination sphere, r(Ru-H2O) = 4.292 Å. The inverse reaction, the release of NO, has high activation energy of ~ 42 kcal.mol-1. This result suggests that the thermal release of NO from the nitrosyl complex is unlike to occur at room or body temperature. The potential energy surface for the formation of [Ru(NH3)5(NO)]3+ through the displacement of the H2O ligand in the complex [Ru(NH3)5(H2O)]3+, is shown in figure 8. This reaction is more complicated since both NO (S = 1/2) and the complex [Ru(NH3)5(H2O)]3+ (S = 1/2) have one unpaired electron. Therefore, the reaction can take place in a triplet spin surface, leading to the triplet product [Ru(NH3)5(NO)]3+ (S = 1) or, the spins can couple and the reaction occurs in a singlet (S = 0) surface, generating the most stable singlet [Ru(NH3)5(NO)]3+ product. In other words, the reactants with two unpaired electrons must generate the most stable singlet product, and this must involve at least one surface crossing point. This kind of nonradiative transition between electronic states with two different spin multiplicities can be adequately investigated using non-adiabatic transition state theory (NA-TST)76-78, which involves the determination of the Minimum-Energy crossing point (MECP). To calculate the transition probability between the two curves, it is necessary to calculate the spin-orbit coupling at the MECP, which usually requires multiconfigurational calculations to be


Page 19 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


performed, imposing restriction on the size of the system under study. However, based on the properties of the MECP, a qualitative description of the process can be obtained 77 and, this was the approach used in this work. In figure 8, from right to left, the formation of the nitrosyl complex takes place. As we can see, the formation reaction starts in the triplet surface with the spins unpaired. As the NO approaches the metallic center, the two surfaces cross at 2.80 Å, before the transition state region of the triplet surface. The structure and energy associated with this Minimum Energy Crossing Point (MECP), was obtained using the suggestions of Harvey et al.77 and implemented in the ORCA program. The structure of this MECP-I, shown in table 6, was obtained within 5x10-4 eV of energy difference between the singlet and triplet surfaces. At this point, the reaction may follow the singlet surface with a considerable small energy barrier. Further approach of NO along the singlet surface reaches the MECP-II at which another hop to the triplet surface is expected to happen. Close to the MECP-II, another hopping point is obtained at MECPIII, at which a final hop from the triplet to the singlet surface takes place, generating the final product [Ru(NH3)5(NO)]3+ in the singlet state. The main structural parameters obtained for the MECP´s are quoted in table 6. Attempts to optimize the structures of MECP-2 and MECP-3, converged to very similar structures, due to the proximity of this two crossing points. Thus, the crossing points II and III, may be seen as local minima in the seam of the intersection region, both close to the global minimum energy crossing point. It is worth noting that the reverse process, the release of NO from the nitrosyl complexes (from left to right in figure 8) have very different energy barriers. The release from the singlet [Ru(NH3)5(NO)]3+ complex have activation energy ~ 45 kcal.mol-1, very similar to the value obtained for RuII-nitrosyl complex. However, the



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 50

release from the triplet state may be very favorable through the MECP´s, having activation energy almost seven times smaller (~ 6 kcal.mol-1). This result suggests that if the singlet complex is excited to the triplet state the NO release can be enhanced greatly. Finally, it is important to mention that we were not able to fully optimize the transition states structures involved in the ligand exchange reactions reported. Therefore, the energy values reported are only good estimates and can only be used qualitatively.

4. Final Remarks In this work Density Functional Theory in conjunction with Monte Carlo simulations were employed to study the electronic structure, solvation properties and reactivity of ruthenium-amine nitrosyl complexes. It was shown that Ru(II) nitrosyl complexes have only one thermally accessible spin state and the Ru(III) complexes have the singlet ant triplet spin states both being thermally accessible. According to the computed values for the reduction potential, the [Ru(NH3)5(NO)]3+ compound can easily be reduced by biological reducing agents in both the singlet and triplet states. The reduction is easier in the triplet state which has a positive reduction potential of 1.70V. It is worth mention that the computed reduction potential using the combination of SMD and COSMO solvent model yielded very good results, in agreement with the experimental findings. The nitrosyl complexes in aqueous solution are involved in strong hydrogen bonding interactions, with mean average energies of (-13.5 ± 04) and (-22.4 ± 04) kcal.mol-1 for the Ru(II) and Ru(III) nitrosyl complexes, respectively. Interestingly, the NO ligand in the complexes does not form hydrogen bonds in solution, meaning that it remains available to react with other species.


Page 21 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The electronic spectrum of the nitrosyl complexes showed that the internal d → d transitions are little affected by the solvent. However, the transitions involving charge transfer from the metal to the NO ligand are more sensitive to the solvent. Treating the first solvation shell and the complexes at full ab initio level or treating the solvent molecules as Effective Fragment Potential provide essentially the same transition energy for the MLCT transition (tithing 1% difference). However, both solvent treatments were not able to reproduce the experimental value for the MLCT transition (about 30 nm of deviation) and we believe that this may be due to the absence of dynamics effects in the calculations, as we have shown previously.52 This result shows the effectiveness of the EFP solvent model to treat the solvent effects in electronic transitions, with a lower computational cost. The formation of the nitrosyl complexes through ligand exchange reactions involving nitrosyl/water and nitrosyl/ammonia are thermodynamically very favorable, with Gibbs free energy of reaction less than -30 kcal.mol-1 and formation constants Kf greater than 1021. The mechanism associated with the formation of the complexes and release of NO from of the nitrosyl complexes have some intrinsic difficulties associated with the existence of different spin states leading to non-adiabatic effects. We showed that the formation of the [Ru(NH3)5(NO)]3+ in its most stable singlet state may takes place through at least two MECP´s. The existence of these MECP´s, makes the release of NO from the triplet state more favorable, with an activation energy almost seven times smaller (~ 6 kcal.mol-1), suggesting that if the singlet complex is excited to the triplet state the NO release can be enhanced greatly. We believe that a non-adiabatic ab initio molecular dynamics simulation of the release of NO from these complexes can



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 50

provide important information on the dynamics of this process and, these studies are under way. Finally, it is important to mention that despite the simplicity of the complexes studied here, regarding the number of atoms and nature of the ligands, the main conclusions of the present work are of great importance for the understanding of the behavior of these complexes in aqueous solution and therefore, can serve as a model for other nitrosyl complexes. Also, we believe that the theoretical methods used in this study may be used as a reference for future theoretical works involving nitrosyl complexes in solution.

5. Acknowledgements: The authors would like to thank the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, INCT-Catálise) and FAPEMIG (Fundação de Amparo à Pesquisa do Estado de Minas Gerais) for the financial support and research grants.

6. References: (1) Ignarro, L. J.; Buga, G. M.; Wood, K. S.; Byrnes, R. E.; Chaudhuri, G. Endothelium-derived Relaxing Factor Produced and Released from Artery and Vein is Nitric Oxide. Proc. Natl. Acad. Sci. USA 1987, 84, 9265-9269. (2) Palmer, R. M. J.; Ashton, D. S.; Moncada, S.; Vascular Endothelial Cells Synthesize Nitric Oxide from L-arginine. Nature 1988, 333, 664-666. (3) Ignarro, L. J.; Murad, F. Nitric Oxide: Biochemistry, Molecular Biology and Therapeutic Implications; Academic Press: California, 1995.


Page 23 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(4) Ignarro, L. J.; Endothelium-Derived Nitric Oxide: Pharmacology and Relationship to the Actions of Organic Nitrate Esters. Pharm. Res. 1989, 6, 651-659. (5) Cullota, E.; Koshland, D. E. NO News is Good news. Science 1992, 258, 18621865. (6) Richter-Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford University Press, New York, 1992. (7) Tfouni, E.; Truzzi, D. R.; Tavares, A.; Gomes, A. J.; Figueiredo, L. E.; Franco, D. W. Biological Activity of Ruthenium Nitrosyl Complexes. Nitric Oxide-Biology and Chemistry. Nitric Oxide 2012, 26, 38-53. And references therein. (8) van Eldik, R.; Olabe, J. A. (Eds.) NO Related Chemistry. Adv. Inorg. Chem., 2015, 67, 2-375. Especial Thematic issue. (9) Tfouni, E.; Krieger, M.; McGarvey, B. R.; Franco, D. W. Structure, Chemical and Photochemical Reactivity and Biological Activity of Some Ruthenium Amine Nitrosyl Complexes. Coord. Chem. Rev. 2003, 236, 57-69. (10) Tfouni, E.; Ferreira, K. Q.; Doro, F. G.; Da Silva, R. S.; Da Rocha, Z. N. Ru(II) and Ru(III) complexes with cyclam and related species. Coord. Chem. Rev. 2005, 249, 405-418. (11) Raveh, O.; Peley, N.; Bettleheim, A.; Silberman, I.; Rishpon, J. Determination of NO Production in Melanoma Cells using an Amperometric Nitric Oxide Sensor. Bioelectrochem. Bioenerg. 1997, 43, 19-23. (12) Sauaia, M. G.; Lima, R. G. De; Tedesco, A. C.; Da Silva, R. S. Nitric Oxide Production by Visible Light Irradiation of Aqueous Solution of Nitrosyl Ruthenium Complexes. Inorg. Chem. 2005, 44, 9946-9951.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 50

(13) Ford, P. C.; Bourassa, J.; Miranda, K.; Lee, K.; Lorkovic, I.; Boggs, S.; Kudo, S.; Laverman, L. Photochemistry of Metal Nitrosyl Complexes: Delivery of Nitric Oxide to Biological Targets. Coord. Chem. Rev. 1998, 171, 185-202. (14) Szacilowski, K.; Macyk, W.; Drzewiecka-Maruszek, A.; Brindel, M.; Stochel, G. Bioinorganic Photochemistry: Frontiers and Mechanisms. Chem. Rev. 2005, 105, 26472694. (15) Rose, M. J.; Mascharak, P. K. Photoactive Ruthenium Nitrosyls: Effects of Light and Potential Application as NO Donors. Coord. Chem. Rev. 2008, 252, 2093-2114. (16) Heilman, B.; Mascharak, P. K. Light-triggered Nitric oxide Delivery to Malignant Sites and Infection. Phil. Trans. R. Soc. A 2013, 371:20120368. (17) Fry, N. L.; Mascharak, P. K. Photoactive Ruthenium Nitrosyls as NO Donors: How To Sensitize Them toward Visible Light. Acc. Chem. Res. 2011, 44, 289-298. (18) Clarke, M. J. Ruthenium Metallopharmaceuticals. Coord. Chem. Rev. 2003, 236, 209-233. (19) Carlos, R. M.; Ferro, A. A.; Silva, H. A. S.; Gomes, M. G.; Borges, S. S. S.; Ford, P. C.; Tfouni, E.; Franco, D. W. Photochemical Reactions of trans-[Ru(NH3)4L(NO)]3+ Complexes. Inorg. Chim. Acta 2004, 357, 1381-1388. (20) Cameron, B. et al. Ruthenium(III) Polyaminocarboxylate Complexes: Efficient and Effective Nitric Oxide Scavengers. Inorg. Chem. 2003, 42, 1868-1876. (21) Clarke, M. J. Ruthenium Metallopharmaceuticals. Coord. Chem. Rev. 2002, 232, 69-93. (22) Nakanishi, K.; Koshiyama, T. ; Iba, S.; Ohba, M. Lipophilic Ruthenium Salen Complexes: Incorporation into Liposome Bilayers and Photoinduced Release of Nitric Oxide. Dalton Trans. 2015, 44, 14200-14203.


Page 25 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Enemark, J. H.; Feltham, R. D. Stereochemical Control of Valence. II. Behavior of the {MNO}n [Metal Mononitrosyl] Group in Ligand Fields. J. Am. Chem. Soc. 1974, 96, 5002-5004. (24) Enemark, J. H.; Feltham, R. D. Structures of Metal Nitrosyls. Topics Stereochem.

1981, 12, 155-215. (25) Mitra, R. P.; Jain, D. V. S.; Banerjee, A. K.; Chari, K. V. R. Photolysis of Sodium Nitroprusside and Nitroprussic Acid. J. Inorg. Nucl. Chem. 1963, 25, 1263-1266. (26) Oszajca, J.; Stochel, G.; Wasielewska, E.; Stasicka, Z. ; Gryglewski, R. J.; Jakubowski, A.; Cieslik, K. Cyanonitrosylmetallates as Potential NO-donors. J. Inorg. Biochem. 1998, 69, 121-127. (27) Roncaroli, F.; Van Eldik, R.; Olabe, J. A. Release of NO from Reduced Nitroprusside Ion. Iron-Dinitrosyl Formation and NO-Disproportionation Reactions. Inorg. Chem. 2005, 44, 2781-2790. (28) Olabe, J. A. The Coordination Chemistry of Nitrosyl in Cyanoferrates. An Exhibit of Bioinorganic Relevant Reactions. Dalton Trans. 2008, 3633-3648. (29) Buxton, G. V.; Dainton, F. S.; Kalecinski, J. The Radiation Chemistry of Aqueous Solutions of Sodium Nitroprusside. Int. J. Radiat. Phys. Chem. 1969, 1, 87-98. (30) Wolfe, S. K.; Swinehart, J. H. Photochemistry of Pentacyanonitrosylferrate(2-), Nitroprusside. Inorg. Chem. 1975, 14, 1049-1053. (31) Cox, A. B.; Wallace, R. M. Photolysis of Nitrosyl Ruthenium Chloro Complexes. Inorg. Nucl. Chem. Lett., 1971, 7, 1191-1194. (32) Miranda, K. M. The Chemistry of Nitroxyl (HNO) and Implications in Biology. Coord. Chem. Rev. 2005, 249, 433-455.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 50

(33) Doctorovich, F.; Farmer, P.J. The Intricate Puzzle of HNO Chemistry. J. Inorg. Biochem 2013, 118, 107. (34) Caramori, G. F.; Frenking, G. The Nature of the Ru−NO Bond in Ruthenium Tetraammine Nitrosyl Complexes. Organometallics 2007, 26, 5815-5825. (35) Caramori, G. F.; Kunitz, A. G.; Doro, F. G.; Frenking, G.; Andriani, K. F.; Tfouni, E. The nature of Ru–NO Bonds in Ruthenium Tetraazamacrocycle Nitrosyl Complexes - A Computational Study. Dalton Trans. 2012, 41, 7327-7339. (36) Andriani, K. F.; Caramori, G. F.; Muñoz-Castro, A.; Doro, F. G. The Influence of L Ligands on the {RuNO}6/7 Bonding Situation in cis-[Ru(NO)(NO2)L1–4]q Complexes: a Theoretical Insight RSC Adv., 2015, 5, 69057-69066. (37) Aguilar, C. M.; Rocha, W. R. The Nature of the M–NO Bond in [M(Imidazole)(PPIX)(L)]q Complexes (M=Fe2+, Ru2+; L=NO+, NO and NO−; PPIX=Protoporphyrin IX). Inorg. Chim. Acta, 2013, 408, 18-26. (38) Freitag, L.; Knecht, S.; Keller, S. F.; Delcey, M. G.; Aquilante, F.; Pedersen, T. B.; Lindh, R.; Reiher, M.; González, L. Orbital Entanglement and CASSCF Analysis of the Ru–NO Bond in a Ruthenium Nitrosyl Complex. Phys. Chem. Chem. Phys. 2015, 17, 14383-14392. (39) Freitag, L.; Gonzaléz, L. Theoretical Spectroscopy and Photodynamics of a Ruthenium Nitrosyl Complex. Inorg. Chem. 2014, 53, 6415-6426. (40) Venâncio, M. F.; Rocha, W. R. Ab Initio Molecular Dynamics Simulation of Aqueous Solution of Nitric Oxide in Different Formal Oxidation States. Chem. Phys. Lett. 2015, 638, 9-14. (41) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and Molecules, Oxford University Press, 1989.


Page 27 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(42) Staroverov, V. N. ; Scuseria, G. E.; Tao, J.; Perdew, J. P. Comparative Assessment of a New Nonempirical Density Functional: Molecules and Hydrogen-Bonded Complexes. J. Chem. Phys. 2003, 119, 12129-12137. (43) Neese, F. The ORCA Program System. Wiley Interdiscip. Rev.: Comput. Mol. Sci.

2012, 2, 73-78. (44) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297-3305. (45) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. Relativistic Regular Two Component Hamiltonians. J. Chem. Phys. 1993, 99, 4597-4610. (46) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. Relativistic Total Energy Using Regular Approximations. J. Chem. Phys. 1994, 101, 9783-9792. (47) van Lenthe, E.; van Leeuwen, R.; Baerends, E. J.; Snijders, J. G. Relativistic regular Two-Component Hamiltonians Int. J. Quantum Chem. 1996, 57, 281-293. (48) Neese, F. An Improvement of the Resolution of the Identity Approximation for the Formation of the Coulomb Matrix. J. Comput. Chem. 2003, 24, 1740-1747. (49) Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U. Efficient, Approximate and Parallel Hartree–Fock and Hybrid DFT Calculations. A ‘Chain-of-Spheres’ Algorithm for the Hartree–Fock Exchange. Chem. Phys. 2009, 356, 98-109. (50) Weigend, F. Accurate Coulomb-Fitting Basis Sets for H to Rn. Phys. Chem. Chem. Phys. 2006, 8, 1057-1065.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 50

(51) Ferreira, D. E. C.; De Almeida, W. B.; Neves, A.; Rocha, W. R. DFT Study of Structural, Electronic and Magnetic Properties of Fe(Iii)-M(Ii) (M=Fe, Cu, Ni, Co and Mn) Mixed-Valence Complexes. Comput. Theor. Chem. 2012, 979, 89-95. (52) Chagas, M. A.; Rocha, W. R. Solvent Effects on the Metal-to-Ligand Charge Transfer Transition of the Complex [Ru(NH3)5(Pyrazine)]2+. Chem. Phys. Lett., 2014, 612, 78-83. (53) Allen, M. P.; Tildesley, D. J. Computer Simulation of Liquids, Oxford University Press, Oxford, 1989. (54) Jorgensen, W. L.; Chandrasekhar, J.; Madura, J. D.; Impey, R. W.; Klein, M. L. Comparison of Simple Potential Functions for Simulating Liquid Water. J. Chem. Phys.

1983, 79, 926-935 (55) Rappe, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard III, W. A.; Skiff, W. M. UFF, A Full Periodic Table Force Field for Molecular Mechanics and Molecular Dynamics Simulations. J. Am. Chem. Soc. 1992, 114,10024-10035. (56) Aguilar, C. M.; De Almeida, W. B.; Rocha, W. R. Solvation and Electronic Spectrum of Ni2+ ion in Aqueous and Ammonia Solutions: A sequential Monte Carlo/TD-DFT Study. Chem. Phys. 2008, 353, 66-72. (57) Jorgensen, W. L.; Maxwell, D. S.; Tirado-Rives, J. Development and Testing of the OPLS All-Atom Force Field on Conformational Energetics and Properties of Organic Liquids. J. Am. Chem. Soc. 1996, 118, 11225–11236. (58) Breneman, C. M.; Wiberg, K. B. Determining Atom-Centered Monopoles from Molecular Electrostatic Potentials. The Need for High Sampling Density in Formamide Conformational Analysis. J. Comp. Chem. 1990, 11, 361-373. 28 ACS Paragon Plus Environment

Page 29 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(59) Coutinho, K.; Canuto, S. DICE: A Monte Carlo Program for Liquid Simulation; University of São Paulo, 1997. (60) Ullrich, C. A. Time-Dependent Density Functional Theory: Theory and Applications, Oxford University Press, 2012. (61) Adamovic, I.; Freitag, M. A.; Gordon, M. S. Density Functional Theory Based Effective Fragment Potential Method. J. Chem. Phys. 2003, 118, 6725-6732. (62) Gordon, M. S.; Freitag, M. A.; Bandyopadhyay, P.; Jensen, J. H.; Kairys, V.; Stevens, W. J. The Effective Fragment Potential Method: A QM-Based MM Approach to Modeling Environmental Effects in Chemistry. J. Phys. Chem. A 2001, 105, 293-307. (63) Day, P. N.; Jensen, J. H.; Gordon, M. S.; Webb, S. P.; Stevens, W. J.; Krauss, M.; Garmer, D.; Basch, H.; Cohen, D. An Effective Fragment Method for Modeling Solvent Effects in Quantum Mechanical Calculations. J. Chem. Phys. 1996, 105, 1968-1986. (64) Tomasi, J.; Mennucci, B.; Cammi, R. Quantum Mechanical Continuum Solvation Models. Chem. Rev. 2005, 105, 2999-3094. (65) Schmidt, M. W. et al. General Atomic and Molecular Electronic Structure System J. Comput. Chem. 1993, 14, 1347-1363. (66) Bottomley, F. Reinvestigation of the Crystal and Molecular Structures of Pentaamminenitrosylruthenium

Trichloride

amminehydroxonitrosylruthenium Dichloride,

Hydrate

and

trans-Tetra-

J. Chem. Soc. Dalton. Trans., 1974,

1600-1605.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 50

(67) Armor, J. N.; Scheidegger, H. A.; Taube, H. A Bimolecular Mechanism for Substitution. J. Am. Chem. Soc. 1968, 90, 5928-5929. (68) Rulíšek, L. On the Accuracy of Calculated Reduction Potentials of Selected Group 8 (Fe, Ru, and Os) Octahedral Complexes. J. Phys. Chem. C, 2013, 117, 16871-16877. (69) Isse, A. A.; Gennaro, A. Absolute Potential of the Standard Hydrogen Electrode and the Problem of Interconversion of Potentials in Different Solvents. J. Phys. Chem. B, 2010, 114, 7894-7899. (70) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. Universal Solvation Model Based on Solute Electron Density and on a Continuum Model of the Solvent Defined by the Bulk Dielectric Constant and Atomic Surface Tensions. J. Phys. Chem. B, 2009, 113, 6378-6396. (71) Klamt, A.; Schuurmann, G. COSMO: A New Approach to Dielectric Screening in Solvents with Explicit Expressions for the Screening Energy and its Gradient. J. Chem. Soc., Perkin Trans 2. 1993, 799-805. (72) Lundblad, R. L.; MacDonald, F. M. (Eds.) Handbook of Biochemistry and Molecular Biology, 4th Ed., CRC Press: Boca Raton, FL, 2010. (73) Millis, K. K.; Weaver, K. H.; Rabenstein, D. L. Oxidation/Reduction Potential of Glutathione. J. Org. Chem. 1993, 58, 4144-4146. (74) Lide, D. R. (Ed.) Handbook of Chemistry and Physics, 88th Ed., CRC Press: Boca Raton, FL, 2007.


Page 31 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(75) Coutinho, K.; Canuto, S. Solvent Effects from a Sequential Monte Carlo-Quantum Mechanical Approach. Adv. Quantum Chem. 1997, 28, 89-105. (76) Harvey, J. N. Understanding the Kinetics of Spin-Forbidden Chemical Reactions. Phys. Chem. Chem. Phys. 2007, 9, 331-343. (77) Harvey, J. N.; Aschi, M.; Schwarz, H.; Koch, W. The Singlet and Triplet States of Phenyl Cation. A Hybrid Approach for Locating Minimum Energy Crossing Points Between Non-Interacting Potential Energy Surfaces. Theor Chem. Acc. 1998, 99, 95-99. (78) Lykhin, A. O.; Kaliakin, D. S.; dePolo, G. E.; Kuzubov, A. A.; Varganov, S. A. Nonadiabatic Transition State Theory: Application to Intersystem Crossings in the Active Sites of Metal-Sulfur Proteins. Int. J. Quantum Chem. 2016, 116, 750-761.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 50

Table 1: Total and relative energies, computed at the TPSSh/def2-TZVP level of theory, for the studied compounds.* Compound [Ru(NH3)6]2+

Total Spin (S)

Total Energy (Eh)

∆EZPE (kcal.mol-1)

0

-4906.25837033

0.0

(0.23621076) 2

-4906.14655218

64.5

(0.22713181) [Ru(NH3)6]3+

1/2

-4905.72432441

0.0

(0.23794179) 5/2

-4905.59334031

76.5

(0.22894333) [Ru(NH3)5(NO)]2+

1/2

-4979.72257957

0.0

(0.20455159) 5/2

-4979.58189462

83.7

(0.19717820) [Ru(NH3)5(NO)]3+

0

-4979.21238573

0.0

(0.20900719) 1

-4979.13854347

43.5

(0.20450175) * Zero point vibrational energies are given in parenthesis. ∆EZPE is the relative energy with inclusion of ZPE corrections.


Page 33 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 2: Main structural parameters obtained at the TPSSh/def2-TZVP level of theory for the Ru-nitrosyl complexes.* Parameter

r (Ru-NO)

[Ru(NH3)5(NO)]2+

[Ru(NH3)5(NO)]3+

[Ru(NH3)5(NO)]3+

(S = 1/2)

(S = 0)

(S = 1)

1.839

1.721

1.982

1.770(9) r (N-O)

1.171

1.121

1.139

1.172(14) r (Ru-(NH3)eq)av

2.155

2.160

2.149

2.017(11) r (Ru-(NH3)ax)

2.236

2.167

2.190

2.092(8) ∠(Ru-N-O)

141.8

179.6

139.2

172.8(9) * Experimental values are in italics, taken from ref. 66. Bond distances in Å and angles in degrees.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 34 of 50

Table 3: Gas phase total energy (Eel.)a, thermal corrections to the Gibbs free energy (Gterm.)b, Solvation free energy (∆Gsolv.)c, total Gibbs free energy (G)d and reduction potential reduction (E0), computed for the complexes studied. [Ru(NH3)5(NO)]3+

[Ru(NH3)5(NO)]3+

[Ru(NH3)5(NO)]2+

[Ru(NH3)6]3+

[Ru(NH3)6]2+

(S = 0)

(S = 1)

(S = 1/2)

(S = 1/2)

(S = 0)

-4979.21238573

-4979.13854347

-4979.72257957

-4905.72432441

-4906.25837033

Gterm. (a.u)

0.17113091

0.16325059

0.16487528

0.19837824

0.19662013

∆Gsolv. (a.u)

-0.6735854

-0.6767415

-0.3139994

-0.6629974

-0.2891150

G (a.u)

-4979.7148402

-4979.6520344

-4979.8717037

-4906.1889435

-4906.3508652

E0[V]

-0.01

1.70

Eel. (a.u)

0.13 (0.10)e

a

computed at the TPSSh/def2-TZVP level of theory. b Gterm. is the termal contribution to the Gibbs free energy described as ZPE – RTln(qtransqrotqvib), where ZPE is the zero point vibrational energy and RTln(qtransqrotqvib) gives the enthalpic and entropic contributions to the gas phase Gibbs free energy. c Obtained using the SMD model, with the electrostatic part computed with the COSMO solvation model. d G = Eel. + ∆Gsolv + Gterm.e Experimental value for the reduction potential of [Ru(NH3)6]3+/2+ taken from ref. 74

34

ACS Paragon Plus Environment

Page 35 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 4: TDDFT computed electronic transitions for the complex [Ru(NH3)5(NO)]3+ in aqueous solution using different solvent models. λ1 (nm)

λ2 (nm)

(1A1 →3T1,3T2; MLCT t2 →π*(NO))

(1A1 →3A1,3E1; d →d)

Gas Phase

395

315

PCM

410

314

(EFP + PCM)a

423

288

(H2O + PCM)b

427

290

Experimentalc

460

300

a

Cluster composed of [Ru(NH3)5(NO)]3+ in 18 water molecules treated as effective fragment potentials and long range interactions treated with the PCM model. bCluster composed of [Ru(NH3)5(NO)]3+ in 18 water molecules treated fully ab initio and long range interactions treated with the PCM model. c taken from ref. 67.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 50

Table 5: Gibbs free energy of reaction in solution (∆Gsol) and formation constants (Kf) for the formation reaction of the nitrosyl complexes through ligand displacement reations. ∆Gsol Reaction

Kf

(kcal.mol-1)

[Ru(NH3)6]2+ + NO → [Ru(NH3)5(NO)]2+ + NH3

-29.96

6.60 x 1021

[Ru(NH3)6]3+ + NO → [Ru(NH3)5(NO)]3+ + NH3

-33.14

1.38 x 1024

[Ru(NH3)5(H2O)]2+ + NO → [Ru(NH3)5(NO)]2+ + H2O

-41.94

3.55 x 1030

[Ru(NH3)5(H2O)]3+ + NO → [Ru(NH3)5(NO)]3+ + H2O

-46.43

6.62 x 1033


Page 37 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 6: TPSSh/TZVP optimized parameters for the minimum energy crossing points involved in the ligand exchange reaction [Ru(NH3)5(H2O)]3+

+

NO

→

[Ru(NH3)5(NO)]3+ + H2O.*

Parameter

MECP-I

MECP-II

MECP-III

r(Ru-NO)

2.922

1.960

1.961

r(N-O)

1.132

1.164

1.164

r(Ru-OH2)

2.101

3.902

3.891

r(Ru-(NH3)eq)av

2.131

2.105

2.105

r(Ru-(NH3)ax)

2.090

2.135

2.135

∠(Ru-N-O)

117.24

136.15

135.95

∠(NO-Ru-OH2)

62.51

54.93

54.51

* Bond distances in Å and bond angles in degrees.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 50

Figure Captions: Figure 1: TPSSh/def2-TZVP optimized structures for the [Ru(NH3)6]2+/3+ and [Ru(NH3)5(NO)]2+/3+ complexes in different spin states.

Figure 2: Variation of the atomic charges with the ∠(Ru-N-O) angle for the [Ru(NH3)5(NO)]3+ complex.

Figure 3: Schematic representation of the reduction reaction of [Ru(NH3)5(NO)]3+ from the singlet and triplet spin states. E0(s-d) and E0(t-d) are the standard reduction potential for the singlet and triplet structures, respectively. ∆E(s-t) is the singlet-triplet energy gap.

Figure 4: Radial pair distribution functions (RDF) for the complexes in solution. (A) RDF between the ruthenium atom and the oxygen of water. (B) RDF´s between the nitrogen of nitrosyl ligand and the hydrogen of water (NNO-HW), oxygen of nitrosyl and hydrogen of water (ONO-HW) and between the hydrogen of the ammonia ligands and oxygen of water (HNH3-OW), obtained for the [Ru(NH3)5(NO)]2+ complex. (C) RDF´s between the nitrogen of nitrosyl ligand and the hydrogen of water (NNO-HW), oxygen of nitrosyl and hydrogen of water (ONO-HW) and between the hydrogen of the ammonia ligands and oxygen of water (HNH3-OW), obtained for the [Ru(NH3)5(NO)]3+ complex.

Figure 5: Distribution of the hydrogen bond energies computed for the [Ru(NH3)5(NO)]2+ (top) and [Ru(NH3)5(NO)]3+ (bottom) complexes in aqueous solution.

Figure 6: Initial configuration of the [Ru(NH3)5(NO)]3+.10H2O cluster used to model de ligands exchange reaction mechanism.


Page 39 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7: Doublet potential energy surface for the ligand exchange reaction [Ru(NH3)5(H2O)]2+

+

NO

→ [Ru(NH3)5(NO)]2+

+

H2O, computed at the

TPSSh/TZVP level of theory.

Figure 8: Singlet and triplet potential energy surface for the ligand exchange reaction [Ru(NH3)5(H2O)]3+

+

NO

→ [Ru(NH3)5(NO)]3+

+

H2O, computed at the

TPSSh/TZVP level of theory.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

[Ru(NH3)6]2+ (S = 0)

[Ru(NH3)6]2+ (S = 2)

[Ru(NH3)6]3+ (S = 1/2)

[Ru(NH3)6]3+ (S = 5/2)

Page 40 of 50

[Ru(NH3)5(NO)]2+ (S = 1/2)


Page 41 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Ru(NH3)5(NO)]2+ (S = 5/2)

[Ru(NH3)5(NO)]3+ (S = 0)

[Ru(NH3)5(NO)]3+ (S = 1)

Figure 1:



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 50

Figure 2:


Page 43 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3:



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 50

(A)

(B)

(C) Figure 4:


Page 45 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5:



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 46 of 50

Figure 6:


Page 47 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


B A

D

C



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 48 of 50

Figure 7:

B

A


Page 49 of 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


C D Figure 8:



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

102x60mm (96 x 96 DPI)

ACS Paragon Plus Environment

Page 50 of 50

Formation and Release of NO from Ruthenium Nitrosyl Ammine

Recommend Documents