Origin of the Individual Basicity of Corrole NH-Tautomers - American

Subscriber access provided by NEW YORK UNIV

Article

On the Origin of the Individual Basicity of Corrole NHTautomers: A Quantum Chemical Study on Molecular Structure and Dynamics, Kinetics and Thermodynamics Wichard J. D. Beenken, Wouter Maes, Mikalai M. Kruk, Todd J. Martínez, and Martin Presselt J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.5b02869 • Publication Date (Web): 08 Jun 2015 Downloaded from http://pubs.acs.org on June 12, 2015

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 A 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 20

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

On the Origin of the Individual Basicity of Corrole NH-Tautomers: A Quantum Chemical Study on Molecular Structure and Dynamics, Kinetics and Thermodynamics Wichard Beenken1, Wouter Maes2, Mikalai Kruk3, Todd Martínez4, Martin Presselt1,4,5* 1

Ilmenau University of Technology, Institute of Physics, P.O. Box 100565, 98684 Ilmenau, Germany

2

Design & Synthesis of Organic Semiconductors (DSOS), Institute for Materials Research (IMO), Hasselt University, Universitaire Campus, Agoralaan 1 - Building D, B-3590 Diepenbeek, Belgium

3

Belarusian State Technological University, Physics Department, Sverdlova str. 13a, Minsk 220006 Belarus

4

Department of Chemistry and PULSE Institute, Stanford University, Stanford, California 94305, USA

5

Institute of Physical Chemistry, Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany, E-mail: [email protected], Phone: +493641 948 356

*

Corresponding author

Keywords: corrole, NH-tautomer, basicity, molecular dynamics, out-of-plane distortions, density functional theory, electrostatic potential, thermodynamics, Gibbs free energy

-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

Abstract Free-base corroles exist as individual NH-tautomers that may differ in their spectral and chemical properties. The present paper focusses on the origin of the basicity difference between two AB2-pyrimidinylcorrole NH-tautomers, which has been tentatively attributed to differences in the weak out-of-plane distortions of the pyrrolenic ring between two NHtautomers. Using DFT-geometry optimizations we show that the pyrroles which are involved in the NH-tautomerization process are approximately in-plane, while the other two pyrroles are tilted out-of-plane in opposite directions. Alternative out-of-plane distortion patterns play a minor role, as revealed by ab initio molecular dynamics simulations. Given that the protonated corrole is a unique species, the energy difference between the two NH-tautomers equals the difference in protonation driving force between them. This energy difference increases with improved theoretical level of accounting for intermolecular interactions and dielectric screening of surface charges. The different charge distributions of the two NHtautomers result in electrostatic potential distributions that effect a larger proton attraction in case of the T1 tautomer than in case of the T2 tautomer. In summary, our quantum chemical results show clearly a higher basicity of the T1 tautomer as compared to the T2 tautomer: The previously assumed pronounced out-of-plane tilt of the T1-non-protonated nitrogen is verified by ab initio molecular dynamics simulations. Together with analysis of the electrostatic potential distribution we show that the non-protonated nitrogen is not only tilted stronger, but is significantly more accessible for protons in case of T1 as compared to T2. Additionally, the thermodynamic basicity is higher for T1 than for T2.

Introduction Corroles are tetrapyrrolic macrocycles that are structurally similar to porphyrins, but contain three rather than four meso-carbons (Cm) due to one direct pyrrole-pyrrole (Ca-Ca) linkage, as shown in Scheme 1.1-3 Because of their peculiar photophysical properties and chelating abilities, corroles are investigated for numerous applications, such as novel catalysts, antitumor and imaging agents, as molecular sensors and in optoelectronic devices.4-21

-2-


Page 2 of 20

Page 3 of 20

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


Scheme 1: Energetically favorable and alternative core configurations of the corrole NH-tautomers T1 and T2 investigated in the present paper (R1 = mesityl, R2 = 4,6-dichloropyrimidin-5-yl).

Recently it was shown that the particular position of the proton-free pyrrolic ring (i.e. pyrrolenic ring) in meso-aryl-substituted corroles determines the distinct optical properties and reactivity toward protons for the corresponding NH-tautomers (T1 and T2, see Scheme 1 for the particular structures and assignments).22-26 Moreover, evidences of the coexistence of two NH-tautomers in fluid solutions at room temperature have been presented.22,26 In particular, it was found that two NH-tautomers differ in their basicity, which was supposed to be due to different out-of-plane (oop) distortions of the corrole macrocycle and, more specifically, due to out-of-plane tilting of the pyrrolenic ring to be protonated in the different NH-tautomers.22,26 In our recent work we focused on experimental assignment and quantum chemical calculations of the UV-vis absorption spectra, as well as on the static ground state geometries of the NH-tautomers of meso-pyrimidinylcorroles.22,23,25-29 We have found indeed that the pyrrole ring to be protonated in the quickly reacting T1 tautomer is tilted out of the mean macrocyclic plane approximately three times more than in the slowly reacting T2 tautomer, where it lies almost in with the mean macrocycle plane.26

In the present work we give new insights in the origin of the basicity/reactivity difference between the two corrole NH-tautomers beyond the steady state geometry differences. We show that the T1 tautomer has a slightly lower pKB-value than the T2 tautomer and we discuss kinetic reaction barriers. We investigate the dynamic structural changes in the NH-tautomers by performing ab initio molecular dynamics (MD) simulations, particularly searching for -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

further conformers that are out-of-plane distorted in a different way than the energetically most favorable structures, thus offering alternative protonation pathways. Finally, we explore the chemical features of 10-(4,6-dichloropyrimidin-5-yl)-5,15-dimesitylcorrole that cause the electrostatic potential distribution promoting protonation stronger in case of the T1 tautomer than in case of the T2 tautomer, where an electrostatic potential bottleneck is formed.

Methods For geometry optimizations the quantum chemistry program Gaussian 0930 was used, involving a polarizable continuum model (PCM) to simulate dichloromethane (CH2Cl2) solvent. Final geometries were obtained applying the CH2Cl2-PCM, the B3LYP density functional and the TZVP triple-ζ basis set, which has been shown to give excellent geometries, electron density distributions31-35 and spectroscopic properties36-38 in many cases. Ab initio molecular dynamics (AIMD) simulations were performed using the quantum chemistry program TeraChem using the B3LYP functional and the Ahlrichs pVDZ basis set.39,40 The AIMD simulations were performed with a target temperature of 1000 K to increase the probability of conformational transitions. For subsequent analysis of the trajectory and visualization a self-written program in Mathematica41 was used. For molecular representations the programs Molden42 and gOpenMol43,44 were applied. For calculations of pKB-values we used the COSMO-RS technique and the COSMOthermX graphical interface to run COSMOtherm.45-47 The underlying quantum chemical calculations were performed using the program Turbomole48,49, the BP86 gradient corrected density functional together with the marij-approximation and the def2-TZVP basis set50-53. We worked in the infinite conductor limit and used the default “isorad” technique for cavity construction to simulate a solvent environment.

Results and Discussion In our recent work we have identified the structural differences between the two mesopyrimidinylcorrole NH-tautomers, i.e. the oop-tilts of the pyrrolenic ring, as one probable origin of their different protonation rates.22,26 This reactivity difference must be reflected in the energetics of individual NH-tautomer protonation that are explored by means of quantum chemical calculations in the present paper. For reference purposes the isolated molecules are considered, whereas involving a polarizable solvent model (PCM) allows approximating the influence of a dichloromethane solvent environment that was chosen as a representative -4-


Page 4 of 20

Page 5 of 20

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


example. Different protonation paths via the top side of the molecule (front side on the figures below) or via the bottom side (backside on the figures below) of the corrole macrocycle were studied for cases when water molecules are hydrogen-bound to the corrole macrocycle.

Molecular Energies and Geometries As shown at a glance in Figure 1, the Gibbs free energy of the T1 tautomer, G(T1), is higher than that of the T2 tautomer, G(T2), by values ranging from 2.5 kJ/mol (isolated molecules) to 3.1 kJ/mol (dichloromethane PCM, see Table 1 for energies relative to G(T2)). These values are significantly lower than the energy difference reported for the unsubstituted corrole NH-tautomers with planar conformation (2.45 kcal/mol ≈ 10.2 kJ/mol).54 Thus, the out-ofplane distortions seem to diminish the energy difference between the two NH-tautomers. After protonation of either tautomer, the protonated corrole adopts essentially the same saddle-type structure. Therefore, the difference in the driving force for the protonation ΔΔGprot found between the T1 and the T2 tautomer depends on the energy difference between the T1 and the T2 tautomers only according to ΔΔGprot = ΔGprot(T1) - ΔGprot(T2) = G(T1) - G(T2).

Eq. 11

Note that Eq. 1 holds true only in case identical structures of the protonated species are considered. Even if DFT-based geometry optimizations yield a wave- and a saddle-type macrocycle geometry for each of the NH-tautomer-water clusters (see Figure 1), dependent on the side of protonation, relaxation to the energetically favored saddle-type structure is assumed to take place since the experimental data do not show any evidences for the presence of two different conformers in the protonated corrole solution, i.e. all the protonated corrole species are of the same type.22

Protonation Energies To estimate the particular ΔGprot-values for the protonation of the T1 as well as T2 tautomer, we consider the equilibrium between either of the protonated tautomers T1/2 with water according to the reaction [T1/2H∙(2-n)H2O]+ + (n+1) H2O ↔ T1/2∙(2-n)H2O + H3O+ + n H2O, with n = 0 or 2

(Eq. 2)

The n water molecules would cancel out of the equilibrium, but they facilitate energy comparison of educts and products in case of additionally involved explicitly H-bound water molecules, as shown in the equilibria at the bottom of Figure 1. All energies given in this Figure refer to one corrole and two water molecules that are either free or H-bound to the 1

The subscript „prot“ abbreviates „protonation“.

-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 6 of 20

corrole, both in the protonation state indicated in the Figure, respectively. The Gibbs free energy difference ΔGeqdeprot for the [T1/2H]+-deprotonation in the equilibrium shown in Eq. 2 is calculated according to ΔGeqdeprot(T1/2) = G(T1/2) – G([T1/2H]+) + {G(H3O+) – G(H2O)}.

(Eq. 3)

All energies used in Eq. 3 were calculated on the same level of theory. If we compare the relative G-values of the free-base and the protonated corroles in Table 1, we find that binding of a proton to the free-base and reorganization results in a Gibbs free energy gain of ΔGprot(T1/T2)=1015.0/1012.5 kJ/mol for the isolated molecules and ΔGprot(T1/T2)=1020.6/1017.5 kJ/mol if a dichloromethane-PCM is involved. Considering the equilibrium with water (Eq. 2, 3) we obtain ΔGeqprot(T1/T2)=324.4/321.9 kJ/mol for isolated molecules,

while

involving

a

dichloromethane-PCM

reduces

this

difference

to

ΔGeqprot(T1/T2)=157.0/153.8 kJ/mol. Explicit hydrogen bonding of water molecules significantly decreases the relative Gibbs free energies of both the free base and the protonated corroles, as shown in Table 1. However, if we compare the G-values of a protonated NH-tautomer with two hydrogen-bound water molecules with the same, but isolated, NH-tautomer and add the Gibbs free energy of two free water molecules we find slight destabilization due to hydrogen bonding of the water molecules by ΔGHBH2O([T1/2H]+s)=G([T1/2H]+s∙2H2O) - {G([T1/2H]+s) + 2∙G(H2O)}=28 kJ/mol for the saddle-type [T1/2H]+-structure. However, the destabilization of the free-base NHtautomers

is

slightly

higher

and

not

identical

for

the

NH-tautomers

(ΔGHBH2O(T1/T2)=53/52 kJ/mol) than for the protonated corroles. Therefore, the total energy gain due to protonation of corroles with two hydrogen bound water molecules, ΔGeqprot(T1/T2)=182.7/177.8 kJ/mol, is higher than for PC-embedded corroles, namely by the difference in the hydrogen-bound water energies between each pair of the free-base and protonated corrole.

pKB-values According to Eq. 4 and 5 (R is the gas constant and T=298.15 K) it appears to be straight forward to quantify the basicity difference between the T1 and the T2 tautomer by means of the difference of their pKB-values. However, because continuum models do not account for hydrogen bonding, the theoretically linear relation between pKB and ΔG is not sufficiently reproduced by quantum chemical calculations considering PC-embedded or isolated molecules. -6-


Page 7 of 20

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


ΔG = - RT lnK = -RT ln10 lg(KA / [H2O]) = RT ln10 (pKA + 1.74) pKB = 14 + 1.74 – ΔG/(RT ln10)

(Eq. 4)

(Eq. 5)

If we apply Eq. 5 to the ΔG-values, including consideration of explicitly hydrogen-bound water molecules, we end up at negative pKB-values in any case. Because Klamt and others obtain excellent linear relations according to Eq. 5 but with a smaller slope,46,55 we recalculated our pKB-values accordingly, but still end up with small negative pKB-values. For an improved description of polar interactions at the interface of the molecule-containing cavities, we performed COSMO-RS45-47,56-59 (Conductor-like Screening Model for Realistic Solvation) calculations, which resulted in still rather small pKB-values of pKB(T1)=4.05 and pKB(T2)=4.47. The difference between these values for T1 and T2 of ΔpKB=0.42 is exceptionally small. For the ΔG-values discussed above, we expect that, even if they might be too high, the relation between ΔGeqprot(T1) and ΔGeqprot(T2) as well as the corresponding ΔpKB=0.43 for isolated molecules and ΔpKB=0.55 for PC-embedded molecules are reliable. Due to consideration of H-bound water molecules ΔpKB further increases up to 0.81, as listed in Table 1.

NH-Tautomerization In order to investigate which of the protonations has the higher rate and whether NHtautomerization competes with protonation we searched for transition states of the corresponding reactions. As shown in Figure 1, the Gibbs free energy of the NHtautomerization transition state is higher than for the T2 tautomer reference state by 18 to 25 kJ/mol, dependent on the applied calculation conditions, corresponding to 7-10 kBT at room temperature (T: temperature, kB: Boltzmann constant). Consequently, even if NHtautomerization is expected to occur, it is slow and does not compete with the effectively diffusion controlled protonation reactions, which is in accordance with the experimentally observed individual protonation rates of the NH-tautomers. In the following we will focus on the probability for a hydronium ion to approach the non-protonated pyrrole in terms of geometric nitrogen exposure and distribution of repulsive and attractive electrostatic potentials around the non-protonated pyrrole tilted out of macrocycle plane.

-7-



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

Fig 1: Gibbs free energy differences ΔG of corrole NH-tautomers T1 (“B”) and T2 (“D”, set as reference), of the corresponding transition state [T1/2]* (“C”) and of the protonated form “A” that is formed commonly from T1 and T2. Each of the shown states is geometry optimized in the gas phase, with a polarizable continuum solvent model (PCM), respectively, and with additional explicit water molecules H-bound to the protonated corrol. ΔGvalues for reactions with free and with H-bound water molecules were calculated according to the equilibria shown at the bottom of the figure. Wave- and saddle-type structures of the protonated corrole with two H-bound water molecules, [T1/2H∙2H2O]+, are shown on the left.

Table 1: Gibbs free energies (G) of pyrimidinylcorrole free-base NH-tautomers T1 and T2, of the corresponding transition state [T1/2]*, and of the protonated form relative to G(T2), respectively. These energies were calculated considering isolated molecules without and with involvement of a polarizable solvent model (PCM) to simulate dichloromethane solvent and additional involvement of explicitly hydrogen-bound water molecules (also PCM). Gibbs free energy differences (ΔG) were calculated for all protonation scenarios involving the H2O

⇌ H3O+ equilibrium. To calculate pKB-values we used the 1/(RT ln10)-slope that is expected from thermodynamics and determines the difference pKB(T1) - pKB(T2) = ΔpKB. Note that in certain cases significantly smaller slopes were observed if solvent molecules were not explicitly included in the quantum chemical calculations. no PCM +

G([T1H] ) G(T1) G([T1/2]*) G(T2) G([T2H]+)

[kJ/mol] [kJ/mol] [kJ/mol] [kJ/mol] [kJ/mol]

-1013 2 18 0 -1013

PCM -1116 3 20 0 -1116

-8-

2 H2O H-bound -1141 5 26 0 -1141


Page 8 of 20

Page 9 of 20

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


ΔG([H3O]+-H2O)

[kJ/mol]

ΔG(T1 prot.) ΔG(T2 prot.) ΔΔG(prot.)

[kJ/mol] [kJ/mol] [kJ/mol] [kcal/mol] [eV]

ΔpKB

691

964

964

324.407 321.942 2.465 0.5893 0.02555

155.454 152.346 3.109 0.7430 0.03222

182.667 177.767 4.899 1.1709 0.05077

0.432

0.545

0.808

Corrole structure dynamics The meso-pyrimidinyl-substituted free-base corrole investigated in this study is structurally similar to meso-aryl-substituted mono-protonated porphyrins. In case of the porphyrins, the out-of-plane tilt of the non-protonated pyrrole influences its basicity.60-65 However, in corroles the steric repulsions between the hydrogens in the macrocycle core (Hcore-repulsions) are more pronounced compared to porphyrins due to the lacking of one meso-carbon, which causes a smaller macrocyclic core with three motional degrees of freedom less. Consequently, in the following special emphasis is put on determination of the weight of different Hcoreconfigurations, which might cause variations in the reactivity-influencing pyrrole oop-tilts. According to our recent work one distinct structure is obtained by DFT-geometry optimizations for each NH-tautomer.26 Briefly, in the global minima neighboring Hcore–atoms are pushing each other out-of-plane in opposite directions, while the third Hcore lies approximately in the mean macrocycle plane. Within this rather intuitive picture an alternative configuration should be possible for each of the two NH-tautomers, as shown in Scheme 1. Alternation of the Hcore-configuration would influence the Hcore-lacking pyrrole due to oop-tilt transmission via the bulky meso-aryl substituents, thus having a potential impact on the reactivities of the NH-tautomers. Even if the alternative structures do not represent the pronounced energetic minima according to our recent work,26 they might occur temporarily. Therefore, it is important to study the dynamics of the oop-deformations and the probability of conformers with alternative oop-deformations to get a comprehensive picture of the individual basicity of the two corrole NH-tautomers. We investigated the structure dynamics of the T1 and T2 tautomer by means of ab initio MD simulations at 1000 K. The Hcore-configurations were traced via the angles γNHoop between the N-H bonds and the plane defined by the three meso-carbons. The N-H bonds are highlighted by colored vectors in the T1 and T2 structures in Figure 2, respectively. The macrocycle planes are depicted as gray squares. In case of the T1 tautomer, the angle γNHoop(B) of the core-hydrogen scatters around the energetically optimal value of 36° (green horizontal line at the top panel of Figure 2), γNHoop(A)-angles of the neighboring pyrrole are distributed at significantly lower values -9-



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 20

around -24°, while γNHoop(C)-angles deviate from in-plane orientation by around -8°. In case of the T2 tautomer, the strongest oop-tilt is present for the core-hydrogen at pyrrole A with its γNHoop(A)-values scattering around -34° (median; optimized value is -39°; in what follows the median is only given if it differs from the optimized angle by more than 3°). γNHoop(B)- and γNHoop(D)-values are scattering around 21° and 3°, respectively. Thus, within the considered time the oop-distortions of the pyrroles of both tautomers T1 and T2 basically represent the energetically favorable Hcore-configurations as shown in the upper row of Scheme 1.

Fig 2: The molecules at the left represent the energetically most favorable structures for the T1 (top) and the T2 (bottom) tautomers, respectively, of the studied meso-pyrimidinylcorrole (H: white, C: gray, N: blue, Cl: yellow). The Hcore-configurations were traced via the angles γNHoop between the N-H bonds (highlighted by colored vectors drawn in the molecules) and the plane defined by the three meso-carbons (gray plane drawn in the molecules). The progress of γNHoop during the MD-runs is plotted vs. time t and the initial γNHoop-values of the optimized corroles are drawn as horizontal lines. Occasional intersections between γNHoop-traces referring to pyrroles B and C in case of the T1 tautomer and to pyrroles A and D in case of the T2 tautomer show contributions of the alternative Hcore-configuration.

- 10 -


Page 11 of 20

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


Fig 3: γNHoop-angles are plotted on a cartesian frame. Note that the blue γ NHoop(A)-axis points to negative values and that the z-axis refers to γNHoop(C)-values in case of T1 but to γNHoop(D)-values in case of the T2 tautomer. The shown MD-traces (red: T1, blue: T2) occupy only two quadrants; inversion at the origin would yield MD-traces of the corresponding enantiomers (not shown). Particularly for the T2 tautomer, γNHoop(D) and γNHoop(B) spawn to small values at the same time as shown by the MD-trace projection to the plane spawned by the γ NHoop(D)- and γNHoop(B)-axes, i.e., both the diagonal opposing core-hydrogens are occasionally close to planarity at the same time. The cases where γNHoop(D)=γNHoop(B) are indicated by a dashed black line. 2% of all data for T2 are between this line and the γNHoop(D)-axis, i.e. γNHoop(D) > γNHoop(B), and correspond to the alternative Hcoreconfiguration. In case of the T1 tautomer, this alternative Hcore-configuration (1% presence during our MD-run) is even half as probable, as seen for the projection to the γNHoop(C), γNHoop(A)-plane.

However, occasional intersections between the γNHoop(C)- and γNHoop(A)-traces referring to diagonal opposing pyrroles for T1 and between γNHoop(D)- and γNHoop(B)-traces for T2 indicate minor populations of the alternative Hcore-configuration in the course of the MDsimulations. The complete configuration space of the Hcore-oop-tilts covered during the MDruns is shown in Figure 3. The shown MD-traces (red: T1, blue: T2) occupy only two quadrants. Inversion at the origin would yield MD-traces of the corresponding enantiomers (not shown). Particularly for the T2 tautomer, γNHoop(D) and γNHoop(B) spawn to small values at the same time as shown by the MD-trace projection to the plane spawned by the γNHoop(D)and γNHoop(B)-axes. That means that both the diagonal opposing core-hydrogens are occasionally close to planarity at the same time. The |γNHoop(D,C)|>|γNHoop(B)| cases, that correspond to the alternative Hcore-configurations, are enclosed by dotted black lines on the projection planes in Figure 3 and represent very small subsets of the MD-trajectories of the T1 (1%) and the T2 (2%) tautomers.

- 11 -



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 20

To investigate whether the occasionally occurring alternative Hcore-configurations influence the oop-tilt of the pyrrolenic ring we compared the corresponding probability density function for γpyoop(D) in the T1 tautomer and for γpyoop(C) in the T2 tautomer, respectively, that are based on the total set of MD-structures with those referring to the subset of alternative structures only, as shown in Figure 4. The γpyoop-values are the angles between the corrole plane as defined by the three meso-carbons and a pyrrole-vector pointing from the center of mass of the two peripheral pyrrole carbons to the pyrrole nitrogen. First, we consider the total set of structures occurring during our MD-runs at 1000 K. There the γpyoop(D)-angles of the non-protonated pyrrole are approximately equally distributed between -10° and 0° for the T1 tautomer, though the value γpyoop(D)=-6.4° is energetically most favorable, as shown in the upper panel of Figure 4. In case of the T2 tautomer, the optimal γpyoop(C)-angle is closer to planarity (γpyoop(C)=-2.3°), thus facilitating oop-tilts in the counter direction that give rise to a peak around +2°. Since in approximately one third of all the T2 tautomer structures the non-protonated pyrrole is tilted to positive angles, back-side attacks during the course of a reaction at the corresponding nitrogen should be significantly more probable than for the T1 tautomer. Now, considering the small subset of alternative Hcore-configurations only, the probability density function referring to the T1 tautomer approximately resembles the shape of the probability density function of the total set of the T1 tautomer structures rather than showing any particular feature (see lower panel of Figure 4). In contrast, the probability density function referring to the alternative T2 tautomer structures possesses a pronounced peak close to +2°. Although both alternative Hcore-configurations have small weights, the alternative structures referring to the T2 tautomer are twice as probable as those referring to the T1 tautomer. This is important since they provide additional weight to non-protonated pyrrole oop-tilts opposite in direction to the globally energetically optimized structure. However, both the tilt at the energetically most favorable structure and the median tilt from our MD-runs are larger for the T1 tautomer (γpyoop(D, opt)=-6.4°; γpyoop(D, median)=-2.7) than for the T2 tautomer (γpyoop(C, opt)=-2.3°; γpyoop(C, median)=-1.5). This means that the non-protonated pyrrole nitrogen is more exposed in the T1 tautomer than in the T2 tautomer, thus particularly facilitating protonation at the T1 tautomer. For discovering further conformers, we investigated both the covered three-dimensional configuration space shown in Figure 3 and the four-dimensional space spawned by the four pyrrole oop-tilt angles that were defined in the same way as described above for the nonprotonated pyrrole. Neither there are obvious clusters in either of these spaces, nor does - 12 -


Page 13 of 20

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


geometry optimization of molecular structures, which are closest to one out of ten via kmeans clustering created cluster centers, yields new conformers.

Fig 4: At the upper panel the probability density functions of the γpyoop-angles of the non-protonated pyrrole in the T1 tautomer (red dashed line) and the T2 tautomer (blue solid line) during the MD-runs are shown. The lower panel shows the corresponding probability density functions if only the 1% and 2% (for the T1 and T2 tautomers, respectively) of all MD-structures that are assigned to the alternative Hcore-configurations are considered. The vertical lines indicate γpyoop-angles of the energetically most favorable structures for the considered set of structures.

Electrostatic potential distributions In the preceding sections we have shown that the T1 tautomer possesses a slightly lower pKB than the T2 tautomer. In the following we focus on repulsive and attractive electrostatic potentials φ which determine possible reaction paths guiding hydronium ions to the nitrogen binding sites.66,67 As shown in the upper row of Figure 5, repulsive positive φ values largely originate from hydrogen and chlorine atoms. Therefore, the space for a proton to approach the pyrrolenic nitrogen is more restricted in case of the T2 tautomer, where this ring is clamped between a mesityl- and the 4,6-dichloropyrimidin-5-yl group, than in case of the T1 tautomer, where this pyrrole neighbors a mesityl group only. Furthermore, the negative proton-attracting isosurface at φ=-0.01 a.u. (red colored in Figure 5), which originates from π-electrons at the corrole core and at the meso-substituents as well as from the nitrogen lone pairs at the meso-pyrimidinyl group and the corrole core, appears to spread wider around the pyrrolenic ring in case of the T1 tautomer than in case of the T2 tautomer. Particularly, the proton-attracting potentials - 13 -



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 20

induced by the π-electrons of the D-pyrrole additionally contribute largely to the protonattracting region in case of the T1 tautomer. For both NH-tautomers, proton-attracting electrostatic potentials are present at both sides of the macrocycle as shown by the φ=-0.01 a.u. surfaces in Figure 5, but in case of the T1 tautomer the side to which the pyrrolenic nitrogen is exposed to appears favorable, as shown by the spot at φ=-0.04 a.u. that is present at the exposed side only (Figure 5). In contrast, the T2 tautomer hast two similar spots at φ=-0.04 a.u. present on both sides since the tilt-angle of the pyrrolenic ring was shown to be much smaller and varies between positive and negative values in preceding section. Each of these spots corresponds to the pyrrolenic nitrogen lonepair. In summary, the isosurfaces at 0.01 a.u. clearly show the different shielding of the proton-free pyrrole for the NH-tautomers T1 and T2, respectively. This contributes significantly to the basicity difference between T1 and T2 discussed in terms of molecular energies and oopdistortions in the previous sections.

Fig 5: Backside view of the pyrimidinylcorrole NH-tautomers with isosurfaces of positive (blue – for protons repulsive) and negative (red – for protons attractive) electrostatic potentials φ that are calculated involving a dichloromethane PCM environment. Top row: At φ=±0.01 a.u. Bottom row: At φ=±0.04 a.u.

- 14 -


Page 15 of 20

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


Conclusions Free base AB2-corroles exist as two individual NH-tautomers that may differ in their spectral and chemical properties. In a simplified picture, the difference in basicity of the NHtautomers was tentatively attributed to a small difference (of 4°) in the out-of-plane distortion of the virtually in-plane oriented non-protonated pyrrolenic ring in each of the NH-tautomers. The out-of-plane distortions are basically due to steric hindrance between the hydrogens in the narrow macrocycle core. DFT-geometry optimizations show that the pyrroles C and D that are involved in the NH-tautomerization, with a barrier of ~20 kJ/mol, are approximately mutually coplanar, while the other two pyrroles (A and B) are tilted out-of-plane in opposite directions. Alternative core-hydrogen configurations, which show a different out-of-plane distortion pattern, play a minor role, as revealed by ab initio molecular dynamics simulations. Given that the protonated corroles are identical species, independent from the educt NHtautomer, the energy difference between the two NH-tautomers is the thermodynamic origin of the difference in protonation driving force between the two NH-tautomers. We could show that with improved theoretical level of considering intermolecular interactions and dielectric screening of surface charges, the energy difference between the NH-tautomers gets larger (up to 5 kJ/mol). The different charge distributions of the two NH-tautomers cause electrostatic potential distributions that effect a larger proton attraction in case of the T1 tautomer than in case of the T2 tautomer. In addition to the slightly different out-of-plane tilt of the non-protonated pyrroles and the energy difference between the corrole NH-tautomers, the T1 tautomer is a better precursor for a protonated corrole than the T2 tautomer. Furthermore, the asymmetry in the substitution pattern of the studied AB2-pyrimidinylcorrole causes a lower electrostatic shielding by the ortho-substituted meso-phenyl groups and a more widespread proton attractive potential in case of the T1 tautomer as compared to the T2 tautomer, which facilitates protonation of T1. It appears probable that with decreasing steric demand and electronic influence of the mesosubstitutents, the reactivity difference between the two NH-tautomers decreases. Finally, our results highlight the need to consider the difference in reactivity of the NH-tautomers of corroles when studying their chemical behavior and applications.

Acknowledgements This work has been carried out with financial support from FP-7 project DphotoD-PEOPLEIRSES-GA-2009-247260. M. Presselt gratefully acknowledges financial support by the Carl- 15 -



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 20

Zeiss-Foundation. W. Maes thanks the FWO (Fund for Scientific Research – Flanders), Hasselt University and the Ministerie voor Wetenschapsbeleid for continuing financial support. M. Kruk thanks the State Program of Scientific Research of the Republic of Belarus “Convergence” (project 3.2.02). The authors are also grateful to H. Schwanbeck from the Ilmenau University Computer Center for technical assistance. Furthermore, we like to thank Prof. Andreas Klamt for fruitful discussions and hints.

References 1. Johnson, A. W.; Kay, I. T. Corroles I. Synthesis. J. Chem. Soc. 1965, 1620. 2. Gryko, D. T. Recent Advances in the Synthesis of Corroles and Core-Modified Corroles. Eur. J. Org. Chem. 2002, 1735-1743. 3. Ghosh, A. A Perspective of One-Pot Pyrrole-Aldehyde Condensations as Versatile SelfAssembly Processes. Angew. Chem. Int. Ed. 2004, 43, 1918-1931. 4. Simkhovich, L.; Mahammed, A.; Goldberg, I.; Gross, Z. Synthesis and Characterization of Germanium, Tin, Phosphorus, Iron, and Rhodium Complexes of Tris(pentafluorophenyl)corrole, and the Utilization of the Iron and Rhodium Corroles as Cyclopropanation Catalysts. Chem. Eur. J. 2001, 7, 1041-1055. 5. Mahammed, A.; Gross, Z. Albumin-Conjugated Corrole Metal Complexes: Extremely Simple yet very Efficient Biomimetic Oxidation Systems. J. Am. Chem. Soc. 2005, 127, 28832887. 6. Aviv, I.; Gross, Z. Corrole-Based Applications. Chem. Commun. 2007, 1987-1999. 7. Barbe, J. M.; Canard, G.; Brandes, S.; Guilard, R. Selective Chemisorption of Carbon Monoxide by Organic-Inorganic Hybrid Materials Incorporating Cobalt(III) Corroles as Sensing Components. Chem. Eur. J. 2007, 13, 2118-2129. 8. Rebane, A.; Drobizhev, M.; Makarov, N. S.; Koszarna, B.; Tasior, M.; Gryko, D. T. TwoPhoton Absorption Properties of Meso-Substituted A3-Corroles. Chem. Phys. Lett. 2008, 462, 246-250. 9. Flamigni, L.; Gryko, D. T. Photoactive Corrole-Based Arrays. Chem. Soc. Rev. 2009, 38, 1635-1646. 10. Aviv-Harel, I.; Gross, Z. Aura of Corroles. Chem. Eur. J. 2009, 15, 8382-8394. 11. Lee, C. H.; Dogutan, D. K.; Nocera, D. G. Hydrogen Generation by Hangman Metalloporphyrins. J. Am. Chem. Soc. 2011, 133, 8775-8777. 12. Aviv-Harel, I.; Gross, Z. Coordination Chemistry of Corroles with Focus on Main Group Elements. Coord. Chem. Rev. 2011, 255, 717-736. 13. Ghosh, A.; Ravikanth, M. Synthesis, Structure, Spectroscopic, and Electrochemical Properties of Highly Fluorescent Phosphorus(V)-Meso-Triarylcorroles. Chem. Eur. J. 2012, 18, 6386-6396. 14. Walker, D.; Chappel, S.; Mahammed, A.; Brunschwig, B. S.; Winkler, J. R.; Gray, H. B.; Zaban, A.; Gross, Z. Corrole-Sensitized TiO2 Solar Cells. J. Porphyrins Phthalocyanines 2006, 10, 1259-1262. 15. Thomas, K. E.; Alemayehu, A. B.; Conradie, J.; Beavers, C. M.; Ghosh, A. The Structural Chemistry of Metallocorroles: Combined X-ray Crystallography and Quantum Chemistry Studies Afford Unique Insights. Acc. Chem. Res. 2012, 45, 1203-1214. 16. Huang, H. C.; Shown, I.; Chang, S. T.; Hsu, H. C.; Du, H. Y.; Kuo, M. C.; Wong, K. T.; Wang, S. F.; Wang, C. H.; Chen, L. C., et al. Pyrolyzed Cobalt Corrole as a Potential NonPrecious Catalyst for Fuel Cells. Adv. Funct. Mater. 2012, 22, 3500-3508. - 16 -


Page 17 of 20

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


17. Stergiannakos, T.; Tylianakis, E.; Klontzas, E.; Trikalitis, P. N.; Froudakis, G. E. Hydrogen Storage in Novel Li-Doped Corrole Metal-Organic Frameworks. J. Phys. Chem. C 2012, 116, 8359-8363. 18. Santos, C. I. M.; Oliveira, E.; Fernandez-Lodeiro, J.; Barata, J. F. B.; Santos, S. M.; Faustino, M. A. F.; Cavaleiro, J. A. S.; Neves, M.; Lodeiro, C. Corrole and Corrole Functionalized Silica Nanoparticles as New Metal Ion Chemosensors: A Case of Silver Satellite Nanoparticles Formation. Inorg. Chem. 2013, 52, 8564-8572. 19. D'Urso, A.; Nardis, S.; Pomarico, G.; Fragala, M. E.; Paolesse, R.; Purrello, R. Interaction of Tricationic Corroles with Single/Double Helix of Homopolymeric Nucleic Acids and DNA. J. Am. Chem. Soc. 2013, 135, 8632-8638. 20. Tortora, L.; Pomarico, G.; Nardis, S.; Martinelli, E.; Catini, A.; D'Amico, A.; Di Natale, C.; Paolesse, R. Supramolecular Sensing Mechanism of Corrole Thin Films. Sens. Actuators B-Chem. 2013, 187, 72-77. 21. Ciuciu, A. I.; Flamigni, L.; Voloshchuk, R.; Gryko, D. T. Light Energy Collection in a Porphyrin-Imide-Corrole Ensemble. Chem. Asian J. 2013, 8, 1004-1014. 22. Ivanova, Y. B.; Savva, V. A.; Mamardashvili, N. Z.; Starukhin, A. S.; Ngo, T. H.; Dehaen, W.; Maes, W.; Kruk, M. M. Corrole NH Tautomers: Spectral Features and Individual Protonation. J. Phys. Chem. A 2012, 116, 10683-10694. 23. Kruk, M.; Ngo, T. H.; Verstappen, P.; Starukhin, A.; Hofkens, J.; Dehaen, W.; Maes, W. Unraveling the Fluorescence Features of Individual Corrole NH Tautomers. J. Phys. Chem. A 2012, 116, 10695-10703. 24. Ziegler, C. J.; Sabin, J. R.; Geier, G. R.; Nemykin, V. N. The First TDDFT and MCD Studies of Free Base Triarylcorroles: A Closer Look into Solvent-Dependent UV-Visible Absorption. Chem. Commun. 2012, 48, 4743-4745. 25. Kruk, M.; Ngo, T. H.; Savva, V.; Starukhin, A.; Dehaen, W.; Maes, W. SolventDependent Deprotonation of Meso-Pyrimidinylcorroles: Absorption and Fluorescence Studies. J. Phys. Chem. A 2012, 116, 10704-10711. 26. Beenken, W.; Presselt, M.; Ngo, T. H.; Dehaen, W.; Maes, W.; Kruk, M. Molecular Structures and Absorption Spectra Assignment of Corrole NH Tautomers. J. Phys. Chem. A 2014, 118, 862-871. 27. Maes, W.; Ngo, T. H.; Vanderhaeghen, J.; Dehaen, W. Meso-Pyrimidinyl-Substituted A2B-Corroles. Org. Lett. 2007, 9, 3165-3168. 28. Ngo, T. H.; Nastasi, F.; Puntoriero, F.; Campagna, S.; Dehaen, W.; Maes, W. MesoPyrimidinyl-Substituted A2B- and A3-Corroles. J. Org. Chem. 2010, 75, 2127-2130. 29. Ngo, T. H.; Puntoriero, F.; Nastasi, F.; Robeyns, K.; Van Meervelt, L.; Campagna, S.; Dehaen, W.; Maes, W. Synthetic, Structural, and Photophysical Exploration of MesoPyrimidinyl-Substituted AB2-Corroles. Chem. Eur. J. 2010, 16, 5691-5705. 30. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Revision A.02; Gaussian Inc.: Wallingford CT, 2009. 31. Presselt, M.; Dietzek, B.; Schmitt, M.; Rau, S.; Winter, A.; Jäger, M.; Schubert, U. S.; Popp, J. A Concept to Tailor Electron Delocalization: Applying QTAIM Analysis to PhenylTerpyridine Compounds. J. Phys. Chem. A 2010, 114, 13163-13174. 32. Presselt, M.; Schnedermann, C.; Müller, M.; Schmitt, M.; Popp, J. Derivation of Correlation Functions to Predict Bond Properties of Phenyl-CH Bonds Based on Vibrational and H-1 NMR Spectroscopic Quantities. J. Phys. Chem. A 2010, 114, 10287-10296. 33. Presselt, M.; Schnedermann, C.; Schmitt, M.; Popp, J. Prediction of Electron Densities, the Respective Laplacians and Ellipticities in Bond-Critical Points of Phenyl-CH-Bonds via Linear Relations to Parameters of Inherently Localized CD Stretching Vibrations and 1HNMR-Shifts. J. Phys. Chem. A 2009, 113, 3210-3222.

- 17 -



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 20

34. Presselt, M.; Dietzek, B.; Schmitt, M.; Winter, A.; Chiper, M.; Friebe, C.; Schubert, U. S.; Popp, J. The Influence of Zinc(II) in a bis-Terpyridine-Phenylene Complex on the piConjugation between the Terpyridine and the Phenylene Moiety. J. Phys. Chem. C 2008, 112, 18651-18660. 35. Winter, A.; Friebe, C.; Chiper, M.; Schubert, U. S.; Presselt, M.; Dietzek, B.; Schmitt, M.; Popp, J. Synthesis, Characterization and Electrooptical Properties of Zn(II) Complexes with pi-Conjugated Terpyridines as Ligands. ChemPhysChem 2009, 10, 787-798. 36. Eger, W.; Presselt, M.; Jahn, B.; Schmitt, M.; Popp, J.; Anders, E. Metal Mediated Reaction Modeled on Nature: The Activation of Isothiocyanates Initiated by Zinc Thiolate Complexes. Inorg. Chem. 2011, 50, 3223-3233. 37. Beenken, W. J. D.; Herrmann, F.; Presselt, M.; Hoppe, H.; Shokhovets, S.; Gobsch, G.; Runge, E. Sub-Bandgap Absorption in Organic Solar Cells: Experiment and Theory. Phys. Chem. Chem. Phys. 2013, 15, 16494-16502. 38. Preiß, J.; Jäger, M.; Rau, S.; Dietzek, B.; Popp, J.; Martínez, T.; Presselt, M. How Does Peripheral Functionalization of Ruthenium(II)-Terpyridine Complexes Affect Spatial Charge Redistribution after Photoexcitation at the Franck-Condon Point? ChemPhysChem 2015, 16, 1395-1404. 39. Ufimtsev, I. S.; Martínez, T. J. TeraChem, v1.5-dev; PetaChem, LLC: Los Altos Hills, CA, 2012. 40. Ufimtsev, I. S.; Martínez, T. J. Quantum Chemistry on Graphical Processing Units. 3. Analytical Energy Gradients, Geometry Optimization, and First Principles Molecular Dynamics. J. Chem. Theory Comput. 2009, 5, 2619-2628. 41. Wolfram-Research, I. Mathematica Edition: Version 8.0, 8.0; Wolfram Research, Inc.: Champaign, Illinois, 2010. 42. Schaftenaar, G.; Noordik, J. H. Molden: A Pre- and Post-Processing Program for Molecular and Electronic Structures. J. Comput.-Aided Mol. Des. 2000, 14, 123-134. 43. Bergman, D. L.; Laaksonen, L.; Laaksonen, A. Visualization of Solvation Structures in Liquid Mixtures. J. Mol. Graphics Modell. 1997, 15, 301-306. 44. Laaksonen, L. A Graphics Program for the Analysis and Display of Molecular-Dynamics Trajectories. J. Mol. Graphics 1992, 10, 33-34. 45. Klamt, A.; Schüürmann, 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. 46. Klamt, A.; Eckert, F.; Diedenhofen, M.; Beck, M. E. First Principles Calculations of Aqueous pK(a) Values for Organic and Inorganic Acids using COSMO-RS Reveal an Inconsistency in the Slope of the pK(a) Scale. J. Phys. Chem. A 2003, 107, 9380-9386. 47. Eckert, F.; Klamt, A. Accurate Prediction of Basicity in Aqueous Solution with COSMORS. J. Comput. Chem. 2006, 27, 11-19. 48. Ahlrichs, R.; Bär, M.; Häser, M.; Horn, H.; Kölmel, C. Electronic Structure Calculations on Workstation Computers: the Program System TURBOMOLE. Chem. Phys. Lett. 1989, 162, 165-169. 49. Von Arnim, M.; Ahlrichs, R. Performance of Parallel TURBOMOLE for Density Functional Calculations. J. Comput. Chem. 1998, 19, 1746-1757. 50. Schäfer, A.; Huber, C.; Ahlrichs, R. Fully Optimized Contracted Gaussian Basis Sets of Triple Zeta Valence Quality for Atoms Li to Kr. J. Chem. Phys. 1994, 100, 5829-5835. 51. Eichkorn, K.; Treutler, O.; Öhm, H.; Häser, M.; Ahlrichs, R. Auxiliary Basis Sets to Approximate Coulomb Potentials. Chem. Phys. Lett. 1995, 240, 283-289. 52. Sierka, M.; Hogekamp, A.; Ahlrichs, R. Fast Evaluation of the Coulomb Potential for Electron Densities using Multipole Accelerated Resolution of Identity Approximation. J. Chem. Phys. 2003, 118, 9136-9148.

- 18 -


Page 19 of 20

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


53. 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. 54. Ghosh, A.; Jynge, K. Molecular Structures and Energetics of Corrole Isomers: A Comprehensive Local Density Functional Theoretical Study. Chem. Eur. J. 1997, 3, 823-833. 55. Zhang, S. M. A Reliable and Efficient First Principles-Based Method for Predicting pKa Values. 4. Organic Bases. J. Comput. Chem. 2012, 33, 2469-2482. 56. Klamt, A.; Jonas, V. Treatment of the Outlying Charge in Continuum Solvation Models. J. Chem. Phys. 1996, 105, 9972-9981. 57. Eckert, F.; Diedenhofen, M.; Klamt, A. Towards a First Principles Prediction of pK(a): COSMO-RS and the Cluster-Continuum Approach. Mol. Phys. 2010, 108, 229-241. 58. Klamt, A.; Reinisch, J.; Eckert, F.; Hellweg, A.; Diedenhofen, M. Polarization Charge Densities provide a Predictive Quantification of Hydrogen Bond Energies. Phys. Chem. Chem. Phys. 2012, 14, 955-963. 59. Klamt, A.; Reinisch, J.; Eckert, F.; Graton, J.; Le Questel, J. Y. Interpretation of Experimental Hydrogen-Bond Enthalpies and Entropies from COSMO Polarisation Charge Densities. Phys. Chem. Chem. Phys. 2013, 15, 7147-7154. 60. Rosa, A.; Ricciardi, G.; Baerends, E. J. Synergism of Porphyrin-Core Saddling and Twisting of Meso-Aryl Substituents. J. Phys. Chem. A 2006, 110, 5180-5190. 61. Medforth, C. J.; Senge, M. O.; Smith, K. M.; Sparks, L. D.; Shelnutt, J. A. Nonplanar Distortion Modes for Highly Substituted Porphyrins. J. Am. Chem. Soc. 1992, 114, 98599869. 62. Stone, A.; Fleisher, E. B. The Molecular and Crystal Structure of Porphyrin Diacids. J. Am. Chem. Soc. 1968, 90, 2735. 63. Kruk, M. M.; Starukhin, A. S.; Maes, W. Influence of Macrocycle Protonation on the Photophysical Properties of Porphyrins. Macroheterocycles 2011, 4, 69-79. 64. Senge, M. O. The Conformational Flexibility of Tetrapyrroles - Current Model Studies and Photobiological Relevance. J. Photochem. Photobiol. B-Biol. 1992, 16, 3-36. 65. Shelnutt, J. A.; Song, X. Z.; Ma, J. G.; Jia, S. L.; Jentzen, W.; Medforth, C. J. Nonplanar Porphyrins and their Significance in Proteins. Chem. Soc. Rev. 1998, 27, 31-41. 66. Presselt, M.; Wojdyr, M.; Beenken, W. J. D.; Kruk, M.; Martínez, T. J. Steric and Electronic Contributions to the Core Reactivity of Monoprotonated 5-Phenylporphyrin: A DFT Study. Chem. Phys. Lett. 2014, 603, 21-27. 67. Presselt, M.; Dehaen, W.; Maes, W.; Klamt, A.; Martínez, T.; Beenken, W. J. D.; Kruk, M. Quantum Chemical Insights into the Dependence of Porphyrin Basicity on the Meso-Aryl Substituents: Thermodynamics, Buckling, Reaction Sites and Molecular Flexibility. PCCP 2015, 17, 14096-14106.

- 19 -



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

Graphical Abstract

- 20 -


Page 20 of 20

Origin of the Individual Basicity of Corrole NH-Tautomers - American

Recommend Documents