Theoretical Modeling of the Chirality Discrimination of Enantiomers by

Article pubs.acs.org/JPCA

Theoretical Modeling of the Chirality Discrimination of Enantiomers by Nanotubular Cyclic Peptides using Gas-Phase Photoelectron Spectroscopy: An ONIOM Spectroscopic Calculations H. Farrokhpour,* S. Karachi, and A. Najafi Chermahini Department of Chemistry, Isfahan University of Technology, Isfahan, Iran, 84156-83111 ABSTRACT: In the present work, the chirality recognition of the enantiomers of a chiral molecule (1phenyl-1-propanol) interacting with a nanotubular cyclic peptide (E-type cyclic decapeptide) was investigated by their ionization in the gas phase, theoretically. The absolute energy difference between the interaction of the S- and R-enantiomer with the cyclic peptide, calculated at the M06-2X/6-311+ +G(d, p) level of theory, was 4.70 kcal·mol−1. Two different schemes of “Our own N-layered Integrated molecular Orbital and molecular Mechanics (ONIOM)” method such as (quantum mechanics (QM):molecular mechanics (MM)) and (QM:QM) were employed to study the effect of the interaction on the gas-phase ionization energies of the enantiomers and cyclic peptide, separately. The symmetry-adapted cluster/configuration interaction (SAC-CI) methodology was used for the calculation of the ionization energies. It was found that the difference between the interactions of Rand S-enantiomer with the cyclic peptide caused different changes in the photoelectron spectrum of each enantiomer so that these changes could be used for the chirality discrimination of the enantiomers in the gas phase. Similarly, the photoelectron spectrum of the cyclic peptide interacting with the R and S-enantiomer were calculated, separately, and it was observed that the difference in the interaction with the R- and S-enantiomer created different changes in the spectrum of cyclic peptide. Finally, it was shown that the difference in the interaction of cyclic peptide with the enantiomers of a chiral molecule in the gas phase can be used for the identification of enantiomers in the gas phase by the direct ionization. is also very important in biochemistry5 and organic synthesis.6 Most of the processes related to the interaction of a chiral ligand, such as a drug, with enzymes or protein receptors are characterized by marked enantioselectivity.7 One of the most important focuses of the host−guest chemistry and supramolecular chemistry is the inclusion complex.8−12 In this case, some macrocyclic molecules such as crown ethers, cyclodextrins (CDs), calixarenes, macrocyclic antibiotics, proteins, and recently cyclic peptides have been studied as host candidates for their interesting and useful properties in molecular recognition and chiral separations.13−16 Understanding the forces at play in chirality recognition and the effect of these forces on the electronic properties of the enantiomers interacting with chiral discriminating agent requires theoretical along with experimental study at the molecular level in the gas phase. The complex of the chiral molecules with the agent molecule is formed by supersonic expansion techniques which rely on adiabatic expansion of a gas mixture through a small-diameter nozzle.17 Different spectroscopic methods such as laser-induced fluorescence (LIF),18 resonance-enhanced twoor multiphoton ionization (REMPI),19 and IR spectroscopy20−22 are three popular techniques for chirality discrimination of jetcooled complexes. For example, Al Rabaa et al.23 used the LIF method to measure the shift in the energy of S0−S1 transition of

1. INTRODUCTION Molecular chirality is one of the most important phenomena in nature. Homochirality is one of the interesting aspects of life so that the large biomolecules tend to be constructed from the units of the same chirality. For example, the proteinogenic amino acids all have the L configuration in human beings, while their D enantiomer is required for forming bacterial cell walls. The reason for this selection is related to the subtle difference in the energy between two enantiomers due to the parity violation effect.1,2 As known, the enantiomeric forms of a chiral molecular species exist as two nonsuper imposable mirror images and thus have a distinct handedness. Such mirror-image molecular species would be expected to have identical physical and chemical properties in general (neglecting the minute parity-violating weak interaction), but they can exhibit markedly different properties when they are themselves embedded into a nonisotropic physical or chemical environment. Chirality recognition is defined as the ability of a chiral probe to differentiate between the two enantiomers of a chiral molecule, and it happens through the interaction of enantiomers and diastereomers of a molecule with another molecule. Noncovalent interactions are particularly intriguing when they involve chiral molecules, because the interactions change in a subtle way upon replacing one of the partners by its mirror image. In this case, the specific interaction (especially, hydrogen bonding) of one enantiomer is different from the other one. These interactions play a major role in supramolecular chirality3 or chirality effects in molecular imprinting.4 Chirality recognition © XXXX American Chemical Society

Received: July 24, 2016 Revised: August 8, 2016

A

DOI: 10.1021/acs.jpca.6b07403 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A

are currently in common use, such as B3LYP.31 M06-2X and M05-2X can capture the electron correlation in the medium range (≤5 Å). The length of the hydrogen bond in most of the hydrogen bonded complexes is below 3.5 Å. It has also been shown that the M06-2X and M05-2X functionals are appropriate for the optimization of the complexes with hydrogen bonding in biomolecules.32 Thanthiriwatte et al. have confirmed that the M06-2X functional can predict the length of the hydrogen bond in excellent agreement with that predicted by the CCSD(T) level of theory with the same basis set. In addition, they have shown that the M06-2X functional is one of the best DFT functional for the prediction of the hydrogen bond energy with the mean average error of 0.5 kcal/mol.33 To see the effect of interaction on the ionization of enantiomers, ONIOM method34 was selected for the description of the guest−host system. ONIOM method can use a molecular mechanics method for the system as a whole and an ab initio one for the site of interest; such calculations are referred to as (QM:MM). Alternatively, two ab initio methods can be combined; in this case, the calculation type is called (QM:QM). Two different two-layer ONIOM schemes including (QM:MM) and (QM:QM) were selected for the calculation of the ionization energies and photoelectron spectra of two enantiomers of 1-phenyl-1-propanol and cyclic peptide, separately. The SAC-CI methodology35−41 along with the 631+G(d, p) basis set was selected for the high layer part of the system and the DFT method employing M06-2X functional and 6-311++G(d, p) basis set was used for the low layer part of system in the ONIOM (QM:QM) scheme. For the ONIOM(QM:MM) calculations, the SAC-CI method with the 631+G(d, p) basis set and the universal force field (UFF) was used for the high and low layer part of system, respectively. In ONIOM calculations, the intermolecular interaction between the high and low layer part is accounted for the computational method selected for the low layer part of the system. To see the effect of 1-phenyl-1-propanol on the ionization of cyclic peptide, only ONIOM (QM:MM) calculations at the same level of theory were performed, and the cyclic peptide was considered as the high layer and 1-phenyl-1-propanol as the low layer part of system. The ionization energies of the cyclic peptide were calculated at the SAC-CI level of theory using 6-31+G(d, p) basis set. The SAC-CI method is one of the accurate correlative methods for calculating the ionization and excitation energies of the molecules. The mean average error of this method is below 0.3 eV based on the comparison of the calculated ionization energies of many compounds with the corresponding experimental values.42

naphthalene ring when complexed with chiral molecule in the gas phase as enantioselective shift. Recently, a new form of circular dichroism, called photoelectron circular dichroism (PECD) has received attention from both experimentalists and theoreticians. PECD is observed as a dissymmetry in the angle-resolved photoemission from randomly oriented pure enantiomers when ionized by left and right circularly polarized light.24 Mons et al. measured the relative gas-phase binding energy of the two diastereoisomeric complexes of (R)-1-phenylethanol with (R)and (S)-butan-2-ol formed in a supersonic expansion from fragmentation measurements following two-color resonance two-photon ionization of the complex.25 There are two complete reviews by Zehnacker et al. on the chirality recognition between neutral molecules in the gas phase which mainly focus on the experimental aspects of chirality recognition.26,27 In this work, the feasibility of using photoelectron spectroscopy for chirality recognition in the gas phase was studied, theoretically, on a selected host−guest species. For this purpose, the photoelectron spectra of the complexes of enantiomers of 1phenyl-1-propanol interacting with E-type cyclic decapeptide were calculated and compared to each other. This comparison enabled us to investigate the effect of the difference in the interaction of enantiomers with the host molecule on their ionization potentials and show the possibility of using their valence photoelectron spectra for their chirality discrimination in the gas phase. In addition, the calculated photoelectron spectra of two enantiomers were assigned, and the effect of their interaction with the host molecule on the assignment of their ionization bands was investigated. Similarly, the effect of interaction on the photoelectron spectrum of cyclic peptide as the host molecule was also studied. The theoretical study performed in this work opens up the intriguing possibility of using direct photoelectron spectroscopy for the chirality discrimination of the enantiomers of a molecule interacting with the nanotubular cyclic peptide for the experimentalist.

2. COMPUTATIONAL DETAILS The structures of the complexes of two enantiomers of 1-phenyl1-propanol interacting with E-type cyclic decapeptide, taken from the work of Zhao et al.,28 were reoptimized further at the density functional theory (DFT) employing a DFT functional which can account the dispersion and long-range interaction in noncovalent complexes. The functional of M06-2X29 and 6-311+ +G(d, p) basis set were used for the further optimization of complexes considering the flexible geometry for both the cyclic peptide and enantiomers. It should be mentioned that the final optimization of the enantiomers interacting with the cyclic peptide had been performed at the B3LYP/6-31+G(d) level of theory in the work of Zhao et al. without considering the dispersion and long-range interactions. The interaction energy between the enantiomers and cyclic peptides was calculated at the M06-2X/6-311++G(d, p) level of theory considering the basis set superposition error (BSSE).30 The optimized structures were used for calculating the ionization energies and photoelectron spectra of enantiomers and cyclic peptide. M06-2X functional along with a moderate basis set is appropriate for studying the weakly interacting system such as van der Waals (vdW) and hydrogen-bonded complexes. There are several detailed studies in the literature on the evaluation of the different DFT functionals for studying the weak interactions.31−33 Hohenstein et al. have shown that the M062X and M05-2X functionals can describe the noncovalent interactions considerably better than density functionals which

3. RESULTS AND DISCUSSION 3.1. Interaction Energy. The initial structures of the complex between enantiomers and cyclic decapeptide were taken from ref 28. The glycine amino acid, as the simplest amino acid, was the structural unit of the selected cyclic peptide and ten glycine amino acids formed the structure of the cyclic peptide. The full story of the optimization of the initial structures, used in this work, has been explained in ref 28 in detail and is not explained here. It should be mentioned that a step-by-step optimization procedure had been used in the work of Zhao et al.,28 and the last step of reoptimization had been performed at the B3LYP/6-31+G(d, p) level of theory in their work with considering the flexible geometry for both cyclic peptide and the enantiomers. The optimization improved in our work by changing the DFT functional from B3LYP to M06-2X and the B


Article


Figure 1. (a) Optimized structure of the complex of (S)-1-phenyl-1-propanol interacting with E-cyclic decapeptide (b) Optimized structure of (R)-1phenyl-1-propanol interacting with E-cyclic decapeptide. The optimized structures have been calculated at the M06-2X/6-311++G(d,p) level of theory. Side view (left) and top view (right) has been shown. The dashed red lines are the candidates of the hydrogen bonds.

phenyl-1-propanol with the cyclic peptide, reported by Zhao et al.28 at the B3LYP/6-31+G(d, p) level of theory, are −2.52 and −4.77 kcal·mol−1, respectively. It can be seen that the M06-2X functional, due to considering the dispersion forces, predicts more interaction energy for the enantiomers compared to B3LYP method. In addition, the absolute difference between the interaction energy of R and S-enantiomer with the cyclic peptide, at the B3LYP/6-31+G(d) level of theory, is about 2.25 kcal· mol−1 which is lower than the value obtained using M06-2X functional. This comparison shows the importance of the dispersion interactions in the guest−host chemistry. The M062X functional considers the effects of dispersion correlations at the intermediate range, and in this respect, it is among the best of its kind. Indeed, the M06-2X functional often gives reasonably good interaction energies for van der Waals complexes near equilibrium geometries,43 where the monomer densities overlap substantially contains no long-range dispersion terms of any kind but has been parametrized to mimic short- and intermediaterange dispersion effects.44 Figure 1 also shows that there is one hydrogen bond between each enantiomer and cyclic peptide (see red dashed lines in Figure 1). The natural population analysis (NPA) including calculation of natural atomic charges and second-order

basis set from 6 to 31+G(d) to 6-311++G(d, p) considering the flexible geometry for the cyclic peptide and enantiomers. As mentioned before, the M06-2X functional considers the electronic correlation and the long-range interactions considerably better than B3LYP functional. Therefore, the optimized structures obtained using M06-2X functional and the difference between the interactions of two enantiomers with the cyclic peptide are more reasonable than those obtained using the B3LYP functional. Figure 1 shows the optimized structures of the complexes of two enantiomers of 1-phenyl-1-propanol with the cyclic decapeptide. The calculated interaction energy between the cyclic peptide with (R-) and (S)-1-phenyl-1-propanol is −23.038 and −27.700 kcal·mol−1, respectively. It is seen that the attractive interaction energy for the S-enantiomer is more than Renantiomer. Figure 1 shows that both the cyclic peptide and 1phenyl-1-propanol undergo changes in their conformation upon complexation. Comparison of Figure 1a with 1b shows that the difference between the interaction of R- and S-enantiomer with the cyclic peptide results to the different deformation in the structure of cyclic peptide and also conformation of enantiomers. The absolute value of the difference between the interaction energies of two enantiomers, obtained in this work, is about 4.70 kcal·mol−1. The calculated interaction energy of (R)- and (S)-1C


Article


Figure 2. Molecular orbitals of (a) isolated (R)-1-phenyl-1-propanol in the gas phase (b) The complex of (R)-1-phenyl-1-propanol with the cyclic peptide. The molecular orbitals have been calculated at the M06-2X/6-31+G(d, p) level of theory. The numbers show the Kohn−Sham energies of the molecular orbitals relative to the energy of HOMO of isolated (R)-1-phenyl-1-propanol in the gas phase (8.00 eV). The arrows show the correlation between the orbitals. The asterisks show the new molecular orbitals which have been created due to the interaction between the (R)-1-phenyl-1propanol with cyclic peptide.

are +0.491 and −0.705. It can be seen that H atom is more positive in (S)-1-phenyl-1-propanol and O atom is more negative in (R)-1-phenyl-1-propanol. Therefore, it can be concluded that the difference between the two hydrogen bonds is mainly related to the difference in their length. The hydrogen bond between the (S)-1-phenyl-1-propanol and cyclic peptide is slightly shorter than that for the (R)-1-phenyl-1-propanol. Therefore, the strength of the hydrogen bond in Figure 1a is more than that in Figure 1b. To confirm this, the calculated values of E(2) for the hydrogen bond of Figure 1a and 1b are 3.82 and 0.74 kcal/mol, respectively. It can be seen that the hydrogen bond between the S-enantiomer and the cyclic peptide is more stronger than that for the R-enantiomer. 3.2. Effect of Interaction on the Shape and Energies of Molecular Orbitals of Enantiomers. Figure 2 and 3 compare the calculated molecular orbitals of isolated (R)- and (S)-1-

perturbation analysis of Fock matrix in natural bond orbital (NBO) basis was carried out at the M06-2X/6-311++G(d, p) level of theory using NBO version 5.45 The stabilization energy E(2) associated with the delocalization i → j (for each donor NBO (i) and acceptor NBO(j) was estimated as E(2) = ΔEij = qi(F(i , j)2 )/(εj − εi)

where qi is the donor orbital occupancy, εj and εi are diagonal elements (orbital energies) and F(i, j) is the off-diagonal NBO Fock matrix elements. The length of the hydrogen bond in Figure 1a and 1b are 1.96 and 2.03 Å, respectively, which shows that the length of the hydrogen bond for (S)-1-phenyl-1propanol is shorter than that for (R)-1-phenyl-1-propanol. The calculated natural charges of H and O atom, contributing in the hydrogen bond, in Figure 1a is +0.508 and −0.689, respectively. Similarly, the corresponding values for the structure of Figure 1b D


Article


Figure 3. Molecular orbitals of (a) isolated (S)-1-phenyl-1-propanol in the gas phase (b) The complex of (R)-1-phenyl-1-propanol with the cyclic peptide. The molecular orbitals have been calculated at the M06-2X/6-31+G(d, p) level of theory. The numbers show the energies of the molecular orbitals relative to the energy of HOMO of isolated (R)-1-phenyl-1-propanol in the gas phase (8.15 eV). The arrows show the correlation between the orbitals. The asterisks show the new molecular orbitals which have been created due to the interaction between the (S)-1-phenyl-1-propanol with cyclic peptide.

phenyl-1-propanol with the molecular orbitals of the complexes of (R)- and (S)-1-phenyl-1-propanol interacting with the cyclic peptide (see Figure 1) in order of increasing energy, respectively. It should be mentioned that those of the molecular orbitals of the complexes which have contribution on the enantiomers have only been shown in the figures. The molecular orbitals of the isolated forms of enantiomers and their complexes with the cyclic peptide have been calculated at the M06-2X level of theory employing 6-31+G(d, p) basis set. In addition, the calculated Kohn−Sham energies of the molecular orbitals relative to the energy of highest occupied molecular orbital (HOMO) of isolated enantiomers have also been reported in the figures. Figure 2 shows that the HOMO of the complex of Renantiomer with the cyclic peptide has been completely localized on the guest molecule and its shape is similar to the shape of the HOMO of isolated R-enantiomer. Therefore, it can be concluded that HOMO of the complex is only related to the enantiomer. As

seen, the relative energy of the HOMO of complex is equal to the relative energy of the HOMO of the isolated R-enantiomer (8.00 eV). It can be concluded that the interaction of the R-enantiomer with the cyclic peptide has no effect on the energy and shape of the HOMO of R-enantiomer. Similarly, the HOMO of the complex of S-enantiomer with the cyclic peptide has been completely localized on the enantiomer, but this orbital has been unstabilized as +0.19 eV relative to the HOMO of the isolated Senantiomer due to the interaction. The HOMO-1 of the complex of R and S-enantiomers with the cyclic peptide are mostly localized on the enantiomers. The relative energy of the HOMO1 of the R-enantiomer interacting with the cyclic peptide is nearly equal to that of the isolated R-enantiomer while the HOMO-1 of the S-enantiomer is unstabilized due to the interaction with the cyclic peptide. It can be concluded that the HOMO and HOMO1 of the S-enantiomer are unstabilized compared to the Renatiomer due to the interaction with the cyclic peptide. E


Article

The Journal of Physical Chemistry A The next molecular orbital of the complexes which has contribution from the enantiomers is HOMO-11 (assigned with the asterisk in Figure 2 and 3). This molecular orbital has contributions from both enantiomers and cyclic peptide. The shape of a part of HOMO-11, localized on the enantiomer, is not similar to the molecular orbitals of the isolated enantiomers in the gas phase. Therefore, it can be concluded that HOMO-11 is a new molecular orbital which has been created due to the interaction between the enantiomers and cyclic peptide. Comparison of Figure 2 with Figure 3 shows that the contribution of the cyclic peptide in HOMO-11 for the Renantiomer is higher than that for the S-enantiomer. The shape of the HOMO-2 of the isolated R- and S-enantiomer is similar to the shape of a part of HOMO-15 and HOMO-12 of the complex of R- and S-enantiomers with the cyclic peptide, respectively. The energy of HOMO-15 of the complex of R-enantiomer with cyclic peptide is nearly equal to the energy of HOMO-2 of its isolated enantiomer, whereas the HOMO-12 of the complex of S-enantiomer with cyclic peptide has been unstabilized relative to the HOMO-2 of isolated S-enantiomer due to the interaction. The HOMO-3, HOMO-4, HOMO-5, HOMO-6, and HOMO-7 of the isolated R-enantiomer correspond to the HOMO-23, HOMO-24, HOMO-25, HOMO-27, and HOMO-28 of the complex of R-enantiomer with the cyclic peptide, respectively. Similarly, the HOMO-3, HOMO-4, HOMO-5, HOMO-6, and HOMO-7 of the isolated S-enantiomer correspond to the HOMO-22, HOMO-24, HOMO-25, HOMO-26, and HOMO27 of the complex of S-enantiomer with the cyclic peptide. Similar to HOMO-11, the HOMO-26, and HOMO-23 of the complexes, assigned with the asterisks in Figure 2 and 3, respectively, have been created due to the interaction between the enantiomers with the cyclic peptide. It is interesting to notice that HOMO-26 in Figure 2 is completely related to the Renantiomer. The final conclusion of this part is that the interaction of the enantiomers with the cyclic peptide and the deformation of both cyclic peptide and enantiomers due to the interaction, mostly unstabilized the molecular orbitals of the enantiomers and this is more evident for the S-enantiomer compared to R-enantiomer. This conclusion shows that the interaction of the S-enantiomer with the cyclic peptide should be more than that of the Renantiomer with the cyclic peptide. 3.3. Effect of Interaction on the Ionization of Enantiomers of 1-Phenyl-1-propanol. In this part, the photoelectron spectra of the enantiomers of 1-phenyl-1propanol, interacting with the cyclic peptide, are calculated in the gas phase and compared with corresponding photoelectron spectra of the optimized isolated enantiomers in the gas phase (see Figure 4). This comparison shows the effect of the interaction on the ionization energies of enantiomers and their electronic structures. The photoelectron spectra were produced by convoluting the calculated discrete ionization bands with the Gaussian distribution function. The Gaussian width (200 meV; full width at half-maximum) was considered for all the photoelectron bands. The ionization energies of the enantiomers interacting with the cyclic peptide were calculated using ONIOM(SAC-CI/631+G(d, p):UFF) level of theory considering the electrostatic interaction between the enantiomer and cyclic peptide. In addition, the polarization of the wave function of the enantiomers in the electrostatic field of cyclic peptide was also considered. Table 1 tabulated the calculated ionization energies

Figure 4. Calculated photoelectron spectra of the enantiomers of 1phenyl-1-propanol. (a) (R)-1-phenyl-1-propanol interacting with the cyclic peptide calculated at the ONIOM(SAC-CI/6-31+G(d, p):UFF) level of theory; (b) (S)-1-phenyl-1-propanol interacting with cyclic peptide calculated at the ONIOM(SAC-CI/6-31+G(d, p):UFF) level of theory; and (c) isolated 1-phenyl-1-propanol in the gas phase calculated at the SAC-CI/6-31+G(d, p) level of theory. The vertical lines show the position and intensities of the calculated ionization bands.

and the main electronic configuration of the calculated ionic states for the enantiomers interacting with the cyclic peptide and isolated 1-phenyl-1-propanol in the gas phase obtained at the SAC-CI/6-31+G(d, p) level of theory. Comparison of spectra a and b with c in Figure 4 shows that the interaction of enantiomers with the cyclic peptide shifts the ionization bands of enantiomers, located in the range of 8 to 12 eV, to the lower binding energy. For example, there is a decrease of 0.5 eV in the value of the first ionization energy of two enantiomers due to the interaction with the cyclic peptide. The other important point is that the energy separation among the ionization bands in the region of 11 to 15 eV in the spectra a and b is more than that in spectrum c. This shows that the interaction with cyclic peptide decreases the density of the ionic states of the enantiomers compared to their isolated forms in this energy region. A part of the spectrum a, below 11 eV and containing four ionization bands ,is similar to spectrum b (see Figure 4). Also, a part of the spectrum of isolated 1-phenyl-1-propanol (spectrum c), below 14 eV, is very similar to the calculated spectrum of (S)1-phenyl-1-propanol interacting with the cyclic peptide. Comparison of the spectrum a with b in Figure 4 shows the change in the relative position of the ionization bands due to the difference in the intermolecular interaction of enantiomers with the cyclic peptide. Figure 4 shows that the main change in the relative position of ionization bands of enantiomers due to the interaction is related to the energy region above 11 eV. The region showing the difference between the spectra of enantiomers have been identified by a purple box in Figure 4. The peak assigned with the asterisk in the spectrum of (R)-1phenyl-1-propanol (spectrum a) has been centered in an energy F


Article


Table 1. Calculated Ionization Energies and the Main Electronic Configuration of the Ionic States of the (R)-1-Phenyl-1-propanol and (S)-1-Phenyl-1-Propanol Interacting with the Cyclic Decapeptide Calculated at the ONIOM(SAC-CI/6-31+G(d, p):UFF) Level of Theory and Isolated 1-Phenyl-1-propanol Calculated at the SAC-CI/6-31+G(d, p) Level of theory (R)-1-phenyl-1-propanol

(S)-1-phenyl-1-propanol

isolated 1-phenyl-1-propanol

IE (eV)

main configuration

IE (eV)

main configuration

IE (eV)

main configuration

7.815 8.191 9.548 10.299 10.891 11.172

0.97(HOMO) 0.97HOMO-1 0.94HOMO-2 0.95HOMO-3 0.96HOMO-4 0.87HOMO-5 + 0.31HOMO-6

7.841 8.210 9.334 10.451 10.963 11.146

0.97 HOMO 0.97HOMO-1 0.94HOMO-2 0.94HOMO-3 0.90HOMO-4 0.56HOMO-7 + 0.52HOMO-6

8.218 8.586 9.686 10.529 11.380 11.598

11.500

0.72HOMO-6 − 0.50HOMO-7

11.219

0.69HOMO-5 + 0.60HOMO-7

11.651

11.740

0.73HOMO-6 + 0.52HOMO-7

11.711

11.759

11.966 12.702 13.387

0.34HOMO-7 + 0.86HOMO-8 0.90HOMO-9 0.64HOMO-11 + 0.63HOMO-10

12.183 12.941 13.265

0.73HOMO-6 + 0.45HOMO-5 − 0.42HOMO-7 0.94HOMO-8 0.9HOMO-9 0.88HOMO-10 + 0.29HOMO-13

0.97HOMO 0.97HOMO-1 0.94HOMO-2 0.94HOMO-3 −0.56HOMO-4 + 0.72HOMO-5 0.52HOMO-7 + 0.51HOMO-5 + 0.47HOMO-6 −0.75HOMO−7 + 0.38HOMO-6 + 0.33HOMO-4 −0.67HOMO-6 + 0.63HOMO-4

13.490

0.59HOMO-11 − 0.72HOMO-10

13.523

0.93HOMO-11

13.914

13.875 14.133

−0.42HOMO-12 + 0.84HOMO-13 −0.77HOMO-12 + 0.39HOMO-11 − 0.38HOMO-13 0.95HOMO-14

13.888 14.176

0.91HOMO-12 −0.87HOMO-13 + 0.28HOMO-10

14.023 14.372

0.89HOMO-8 − 0.30HOMO-9 −0.85HOMO-9 − 0.34HOMO-8 0.66HOMO-11 + 0.47HOMO-12 + 0.39HOMO-10 0.64HOMO-11 − 0.61HOMO-12 − 0.33HOMO-13 −0.74HOMO-10 + 0.46HOMO-12 0.81HOMO-13 − 0.38HOMO-10

14.879

0.94HOMO-14

14.551

0.90HOMO-14

14.788

region which has no overlap with the peaks of the spectrum of (S)-1-phenyl-1-propanol (spectrum b). Similarly, two peaks, assigned with an asterisk, in the spectrum of (S)-1-phenyl-1propanol have no overlap with the peaks of the spectrum of (R)1-phenyl-1-propanol. These peaks can be selected for the recognition of the enantiomers of 1-phenyl-1-propanol in the gas phase if the spectrum of cyclic peptide has no peak in this region. Figure 5 shows the calculated spectra of the enantiomers interacting with the cyclic peptide obtained at the ONIOM(SAC-CI/6-31+G(d, p):M06-2X/6-31+G(d, p)) level of theory. In this case, the interaction between the enantiomers and the cyclic peptide is considered quantum mechanically at the M062X/6-31+G(d, p) level of theory. It can be seen that the shape of the calculated spectra of enantiomers are similar to those calculated using ONIOM(SAC-CI/6-31+G(d, p):UFF) method. Similarly, the interaction causes that the first ionization energy of the enantiomers decreases, whereas this decrease is lower than the value obtained using ONIOM(SAC-CI/631+G(d, p):UFF) method. Similarly, Table 2 tabulated the ionization energies and the main electronic configuration of the calculated ionic states of the enantiomers interacting with the cyclic peptide at the ONIOM(SAC-CI/6-31+G(d, p):M06-2X/ 6-31+G(d, p)) level of theory and those of isolated 1-phenyl-1propanol in the gas phase obtained at the SAC-CI/6-31+G(d, p) level of theory. 3.4. Assignment of the Ionization Bands of the Enantiomers. Table 1 shows that the first, second, third, fourth, and fifth ionization bands of enantiomers, interacting with the cyclic peptide, and isolated 1-phenyl-1-propanol in the gas phase are related to remove one electron from the HOMO, HOMO-1, HOMO-2, HOMO-3, and HOMO-4 of the molecules, respectively. It should be mentioned that only the interaction of the cyclic peptide on the electronic structure of the enantiomers, at the MM level of theory, is considered in the ONIOM(SAC-CI/6-31+G(d, p):UFF) level of theory, and no

12.291 12.709 13.754

Figure 5. Calculated photoelectron spectra of the enantiomers of 1phenyl-1-propanol. (a) (R)-1-phenyl-1-propanol interacting with the cyclic peptide calculated at the ONIOM(SAC-CI/6-31+G(d, p):M062X/6-31+G(d, p)) level of theory; (b) (S)-1-phenyl-1-propanol interacting with the cyclic peptide calculated at the ONIOM(SACCI/6-31+G(d, p): M06-2X/6-31+G(d, p)) level of theory; and (c) isolated 1-phenyl-1-propanol in the gas phase calculated at the SAC-CI/ 6-31+G(d, p) level of theory. The vertical lines show the positions and intensities of the calculated ionization bands.

electron is considered for the cyclic peptide in the calculations. Therefore, the molecular orbitals of enantiomer+cyclic peptide G


Article


Table 2. Calculated Ionization Energies and the Main Electronic Configuration of the Ionic States of the (R)-1-Phenyl-1-propanol and (S)-1-Phenyl-1-Propanol Interacting with the the Cyclic Peptide Calculated at the ONIOM(SAC-CI/6-31+G(d, p): M06-2X/ 6-31+G(d, p)) Level of Theory and Isolated 1-Phenyl-1-Propanol at the SAC-CI/6-31+G(d, p) Level of theory (R)-1-phenyl-1-propanol

(S)-1-phenyl-1-propanol

isolated 1-phenyl-1-propanol

IE (eV)

main configuration

IE (eV)

main configuration

IE (eV)

main configuration

8.00 8.363 9.762 10.558 11.171 11.394

0.97HOMO 0.97HOMO-1 0.94HOMO-2 0.95HOMO-3 0.95HOMO-4 0.91HOMO-5

8.104 8.474 9.646 10.739 11.240 11.459

8.218 8.586 9.686 10.529 11.380 11.598

11.789

−0.67HOMO-6 + 0.65HOMO-7

11.527

0.97HOMO 0.97HOMO-1 0.95HOMO-2 0.93HOMO-3 0.90HOMO-4 0.70HOMO-5 − 0.34HOMO-6 + 0.41HOMO-7 0.50HOMO-5 − 0.76HOMO-7

11.651

12.071 12.284 12.990 13.671

12.049 12.485 13.244 13.574

0.85HOMO-6 + 0.32HOMO-7 0.94HOMO-8 0.90HOMO-9 0.87HOMO-10

11.759 12.291 12.709 13.754

13.778

−0.65HOMO-6 − 0.66HOMO-7 0.93HOMO-8 0.92HOMO-9 −041HOMO-10 − 0.77HOMO-11 − 0.32HOMO-12 0.86HOMO-10 − 0.38HOMO-11

13.817

0.93HOMO-11

13.914

14.169 14.415 15.082

0.47HOMO-12 + 0.82HOMO-13 −0.44HOMO-13 + 0.73HOMO-12 0.94HOMO-13

14.198 14.473 15.217

0.90HOMO-12 0.85HOMO-13 0.94HOMO-14

14.023 14.372 14.551

0.97HOMO 0.97HOMO-1 0.94HOMO-2 0.94HOMO-3 −0.56HOMO-4 + 0.72HOMO-5 0.52HOMO-7 + 0.51HOMO-5 + 0.47HOMO-6 −0.75HOMO-7 + 0.38HOMO-6 + 0.33HOMO-4 −0.67HOMO-6 + 0.63HOMO-4 0.89HOMO-8 − 0.30HOMO-9 −0.85HOMO-9 − 0.34HOMO-8 0.66HOMO-11 + 0.47HOMO-12 + 0.39HOMO-10 0.64HOMO-11−0.61HOMO-12−0.33 HOMO-13 −0.74HOMO-10 + 0.46HOMO-12 0.81HOMO-13 − 0.38HOMO-10 0.90HOMO-14

system are only related to the enantiomer. It is seen that the main configuration of the first to fifth ionization bands of enantiomers interacting with the cyclic peptide are composed of only one single ionized Hartree−Fock (HF) determinants and the Koopmanns theorem46 is valid for them. The main electronic configuration of the fifth ionization band of the isolated 1-phenyl1-propanol in the gas phase is −0.56HOMO-4 + 0.72HOMO-5, whereas the main electronic configuration of the fifth ionic state of the enantiomers interacting with cyclic peptide is only composed from one single ionized determinant related to the ionization from HOMO-4. Therefore, the interaction with the cyclic peptide decreases the electron correlation in the fifth ionic state of the enantiomers because the wave function of this state is not a linear combination of two or more single ionized HF determinants. The other important point is that the fifth ionization band of the isolated 1-phenyl-1-propanol mostly takes place from HOMO-5 because of its higher coefficient in the linear combination of the determinants in the wave function while, the fifth ionization of the enantiomers interacting with the cyclic peptide takes place form HOMO-4. As another example, the main configuration of the twelfth ionic state of the isolated 1phenyl-1-propanol is 0.64(HOMO-11) − 0.61(HOMO-12) − 0.33(HOMO-13). In fact, the wave function of this ionic state is a linear combination of three single ionized HF deteminants related to the ionization from HOMO-11, HOMO-12, and HOMO-13. The wave function of this ionic state changes to 0.59(HOMO-11) − 0.72(HOMO-10) and 0.93(HOMO-11) for the R and S-enantiomer interacting with the cyclic peptide, respectively. The change in the wave function of the ionic states of the enantiomers due to the interaction is seen for the other ionic states which are not explained here more. Lastly, it can be concluded that the difference between the interaction of enantiomers with the cyclic peptide has considerable effect on the wave function of the ionic states of enantiomers so that the place of the ionization on the molecule changes due to the difference in the interaction. 3.5. Effect of Interaction on the Ionization of Cyclic Peptide. The effect of interaction on the electronic structure of

cyclic peptide when it interacts with enantiomers is studied in this part. For this purpose, the ONIOM calculations were performed so that the enantiomer and cyclic peptide were considered at the low and high layer of the system, respectively. The calculations were performed at the ONIOM (SAC-CI/631+G(d, p):UFF) level of theory. In this case, the SAC-CI/631+G(d, p) level of theory was used for the cyclic peptide. Figure 6 displays the calculated photoelectron spectrum of cyclic

Figure 6. Calculated photoelectron spectrum of the cyclic decapeptide (a) interacting with (R)-1-phenyl-1-propanol (red spectrum) and (b) interacting with (S)-1-phenyl-1-propanol (blue spectrum) obtained at the ONIOM(SAC-CI/6-31+G(d, p):UFF) level of theory. The asterisks show the peaks of the cyclic peptide interacting with S-enantiomer which are absent in its spectrum when interacting with R-enantiomer.

peptide interacting with R and (S)-1-phenyl-1-propanol. The calculated spectrum of cyclic peptide in this region contains 40 ionization bands. It can be seen that the difference between the interaction of R- and S-enantiomer with the cyclic peptide causes some differences in the photoelectron spectrum of cyclic peptide when it interacts with R- or S-enantiomer. The peaks assigned with the asterisk in the spectrum of the cyclic peptide interacting with the S-enantiomers are absent in the spectrum of cyclic H


Article


3.6. Photoelectron Spectrum of (Cyclic Peptide+1Phenyl-1-propanol) System. Figure 8 demonstrates the

peptide interacting with the R-enantiomer. These peaks can also be used for the chirality recognition of the S-enantiomer if the overlapping with the spectra of enantiomers does not disappear these resolved peaks. The difference between the two spectra shown in Figure 6 can be attributed to the different interaction with the enantiomers and different structural deformation of the cyclic peptide when interacts with the enantiomers. Figure 7

Figure 8. (a) Calculated photoelectron spectrum of ((S)-1-phenyl-1propanol + cyclic peptide; purple spectrum). Additionally, the calculated spectrum of cyclic peptide (Cyc-S) shown in Figure 6 has been superimposed on it (red spectrum). (b) Calculated photoelectron spectrum of ((R)-1-phenyl-1-propanol + cyclic peptide; black spectrum). In addition, the calculated spectrum of cyclic peptide (Cyc-R) shown in Figure 6 has been superimposed on it (blue spectrum). (c) The sum of the spectrum of ((S)-1-phenyl-1-propanol + cyclic peptide) and ((R)-1-phenyl-1-propanol + cyclic peptide) assigned with “total” in the figure. The explanation about the asterisks and arrows are in section 3.6.

calculated photoelectron spectrum of the (cyclic peptide+(R)1-phenyl-1-propanol) (black trace) and (cyclic peptide+(S)-1phenyl-1-propanol) (purple trace). To obtain these spectra, the spectra of the enantiomers interacting with the cyclic peptide (spectrum a and b in Figure 4) were summed up with the corresponding spectra of the cyclic peptides interacting with the enantiomers shown in Figure 6. The calculated spectrum of the cyclic peptide interacting with the R- and S-enantiomer, shown in Figure 6, has also been included in this figure. Comparison of the spectrum of each (enantiomer+cyclic peptide) with its corresponding cyclic peptide spectrum helps to find the resolved peaks of the enantiomer in the spectrum of (enantiomer+cyclic peptide). The peaks assigned with the black asterisks in Figure 8 show the resolved peaks of the S-enantiomer in the total photoelectron spectrum of the cyclic peptide+(S)-1-phenyl-1propanol. Similarly, the peaks assigned with the green asterisks show the resolved peaks of the R-enantiomer in the total photoelectron spectrum of the cyclic peptide+(R)-1-phenyl-1propanol. The spectrum assigned with ”total” in Figure 8 shows the sum of the spectrum of cyclic peptide+(S)-1-phenyl-1-

Figure 7. Adjustment of the gas-phase optimized structure of isolated cyclic peptide optimized in the gas phase on (a) the structure of cyclic peptide interacting with (R)-1-phenyl-1-propanol taken from Figure 1b and (b) the structure of cyclic peptide interacting with (S)-1-phenyl-1propanol taken from Figure 1a.

shows the adjustment of the structure of the cyclic peptide interacting with the R and S-enantiomer (yellow color molecule) on the optimized structure of the isolated cyclic peptide to see the difference between the deformation of cyclic peptide due to the difference in the interaction with the enantiomers. It can be seen that the amount of deformation in the structure of cyclic peptide interacting with the S-enantiomers is considerably higher than that interacting with the R-enantiomer. This comparison again confirms that the interaction of the cyclic peptide with the S-enantiomer is higher than that with the R-enantiomer. I


Article


shown in Figure 9 with the corresponding spectra in Figure 8 shows the electronic effect of the cyclic peptide on the ionization of enantiomers and vica verse. It can be seen that the spectra shown in Figure 9 shifted to the higher binding energy. The peaks assigned with the asterisks in Figure 8 are also visible and assigned with the black asterisks in Figure 9. Therefore, it can be concluded that the chirality discrimination of the enantiomers in the gas phase interacting with cyclic peptide through the ionization spectroscopy could be possible.

propanol and cyclic peptide+(R)-1-phenyl-1-propanol (black trace and purple spectra in Figure 8). The resolved peaks of this spectrum, located in the range of 11.40 to 12.50 eV, are completely related to the enantiomers and can be used for the chirality recognition. The peaks assigned with the black arrows are completely related to the (S)-1-phenyl-1-propanol and the peak assigned with the green arrow is the candidate of the (R)-1phenyl-1-propanol. The peaks assigned with the blue asterisk on this spectrum are also used for the discrimination of Senantiomer, which are related to the cyclic peptide interacting with S-enantiomer. 3.7. Photoelectron Spectrum of (Cyclic Peptide+1Phenyl-1-propanol) Considering the Electronic Effects of Cyclic Peptide. In the previous sections, only the effect of the interaction of the cyclic peptide on the ionization energies of the enantiomers was considered. For this purpose, the interaction between the guest and host molecule was considered at the MM level of theory and also at QM level of theory, separately. Now turn to examine the electronic effects of the cyclic peptide on the photoelectron spectra of enantiomers. In this case, the photoelectron spectra of the inclusion complexes shown in Figure 1 were calculated at the SAC-CI/6-31+G(d, p) level of theory. In this case, the interaction between the cyclic peptide and the enantiomers is considered at the SAC-CI/6-31+G(d, p) level of theory, and most importantly, the electronic correlation related to the interaction between the enantiomer and cyclic peptide, which was absent in previous calculations, is considered in the calculation of the ionization energies. The main limitations in this part is related to the cost of the calculations on the big systems at the SAC-CI level of theory. For this purpose, only 30 ionization band was calculated for each complex shown in Figure 1. Figure 9 shows the calculated photoelectron spectra of

4. CONCLUSION The chirality discrimination of the enantiomers of 1-phenyl-1propanol was studied on the basis of their interactions with a host molecule which is a cyclic peptide in this work. It was observed that the difference between the interaction of (R)-1-phenyl-1propanol and (S)-1-phenyl-1-propanol with the cyclic peptide is enough to make the difference in the electronic structures of two enantiomers. To see the difference in the electronic structure of two enantiomers due to the interaction, the ionization potential of the enantiomers was calculated. It was concluded that the interaction causes the different shift in the position of the ionization bands of two enantiomers so that some peaks of them can be used for the chirality discrimination. In addition, the effect of interaction on the ionization of cyclic peptide was studied, and it was found that some peaks in the spectrum of cyclic peptide interacting with the (S)-1-phenyl-1-propanol is useful for the discrimination of S-enantiomer. The interaction between the cyclic peptide and enantiomers were considered at the MM and QM level of theory, separately. The molecular orbitals of the enantiomers in the gas phase were compared with the corresponding molecular orbitals of enantiomers interacting with the cyclic peptide. It was observed that the molecular orbitals of (S)-1-phenyl-1-propanol are unstabilized due to the interaction relative to its isolated form. Therefore, it can be concluded that the chirality discrimination of the enantiomers interacting with cyclic peptide in the gas phase through the ionization spectroscopy could be possible. Although the discrimination of the enantiomers with the cyclic peptide by photoelectron spectroscopy has been explained theoretically in this work, the presented results show a new method for recognition of the enantiomers, which is useful for a successful experiment, apart from the difficulties in the experiments. The complex of enantiomers with the cyclic peptide can be produced in the supersonic expansion. The ionization of the produced complexes in the gas phase and recording of their photoelectron spectra with high resolution enables us to discriminate the enantiomers with the aid of theoretical calculations.

■

AUTHOR INFORMATION

Corresponding Author

Figure 9. (a) Calculated spectrum of the complex of (S)-1-phenyl-1propanol with cyclic peptide obtained using SAC-CI/6-31+G(d, p) level of theory. (b) Calculated spectrum of the complex of (R)-1-phenyl-1propanol with cyclic peptide obtained using SAC-CI/6-31+G(d, p) level of theory (c) The sum of the spectrum a and b. The explanation about the asterisks and arrows are in section 3.7.

*E-mail: [email protected]; [email protected]. Tel: +98 31 33913243. Fax: +98 31 33912350. Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS The authors thank the Isfahan University of Technology (IUT) for its financial support.

complexes a and b shown in Figure 1 (spectrum a and b in Figure 9, respectively). The spectrum c in Figure 9 shows the sum of the spectrum a and b. The green arrows shows some of the peaks of the photoelectron spectrum of complex b in Figure 1, which are resolved in the total spectra. Similarly, the orange arrows shows the distinguished peaks of the photoelectron spectrum of complex a in the total spectrum. Comparison the spectra

REFERENCES

(1) Lee, T. D.; Yang, C. N. Question of Parity Conservation in Weak Interactions. Phys. Rev. 1956, 104, 254−258.

J


Article


Pure Glycidol Enantiomers. Phys. Chem. Chem. Phys. 2008, 10, 1628− 1639. (25) Mons, M.; Piuzzi, F.; Dimicoli, I.; Zehnacker, A.; Lahmani, F. Binding Energy of Hydrogen-Bonded Complexes of the Chiral Molecule 1-Phenylethanol, as Studied by 2C-R2PI: Comparison between Diastereoisomeric Complexes with Butan-2-ol and the Singly Hydrated Complex. Phys. Chem. Chem. Phys. 2000, 2, 5065−5070. (26) Zehnacker, A.; Suhm, M. A. Chirality Recognition Between Neutral Molecules in the Gas Phase. Angew. Chem., Int. Ed. 2008, 47, 6970−6992. (27) Zehnacker, A. Chirality Effects in Gas-Phase Spectroscopy and Photophysics of Molecular and Ionic Complexes: Contribution of Low and Room Temperature Studies. Int. Rev. Phys. Chem. 2014, 33, 151− 207. (28) Zhao, H.; Zhu, Y.; Tong, M.; He, J.; Liu, C.; Tang, M. Density Functional Theory Studies on the Inclusion Complexes of Cyclic Decapeptide with 1-Phenyl-1-Propanol Enantiomers. J. Mol. Model. 2012, 18, 851−858. (29) Zhao, Y.; Truhlar, D. G. Comparative DFT Study of van der Waals Complexes: Rare-Gas Dimers, Alkaline-Earth Dimers, Zinc Dimer, and Zinc-Rare-Gas Dimers. J. Phys. Chem. A 2006, 110, 5121−5129. (30) Boys, S. F.; Bernardi, F. The Calculation of Small Molecular Interactions by the Differences of Separate Total Energies. Some Procedures with Reduced Errors. Mol. Phys. 1970, 19, 553−566. (31) Hohenstein, E. G.; Chill, S. T.; Sherrill, C. D. Assessment of the Performance of the M05-2X and M06-2X Exchange-Correlation Functionals for Noncovalent Interactions in Biomolecules. J. Chem. Theory Comput. 2008, 4, 1996−2000. (32) Burns, L. A.; Vázquez- Mayagoitia, Á .; Sumpter, B. G.; Sherrill, C. D. Density-Functional Approaches to Noncovalent Interactions: A Comparison of Dispersion Corrections (DFT-D), Exchange-Hole Dipole Moment (XDM) Theory, and Specialized Functionals. J. Chem. Phys. 2011, 134, 084107. (33) Thanthiriwatte, K. S.; Hohenstein, E. G.; Burns, L. A.; Sherrill, C. D. Assessment of the Performance of DFT and DFT-D Methods for Describing Distance Dependence of Hydrogen-Bonded Interactions. J. Chem. Theory Comput. 2011, 7, 88−96. (34) Dapprich, S.; Komáromi, I.; Byun, K. S.; Morokuma, K.; Frisch, M. J. A New ONIOM Implementation in Gaussian98. Part I. The Calculation of Energies, Gradients, Vibrational Frequencies and Electric Field Derivatives. J. Mol. Struct.: THEOCHEM 1999, 461-462, 1−21. (35) Nakatsuji, H.; Kitao, O.; Yonezawa, T. Cluster expansion of the wave function. Valence and Rydberg Excitations and Ionizations of Pyrrole, Furan, and Cyclopentadiene. J. Chem. Phys. 1985, 83, 723−734. (36) Ehara, M.; Nakatsuji, H. Outer- and Inner-Valence Ionization Spectra of N2 and CO: SAC-CI (general-R) Compared with Full-CI Spectra. Chem. Phys. Lett. 1998, 282, 347−354. (37) Nakatsuji, H.; Ehara, M.; Palmer, M. H.; Guest, M. F. Theoretical Study on the Excited and Ionized States of Titanium tetrachloride. J. Chem. Phys. 1992, 97, 2561−2570. (38) Nakatsuji, H.; Ehara, M. Symmetry Adapted Cluster-Configuration Interaction Study on the Excited and Ionized States of TiBr4 and TiI4. J. Chem. Phys. 1994, 101, 7658−7671. (39) Nakatsuji, H.; Hasegawa, J.; Hada, M. Excited and Ionized States of Free Base Porphin Studied by the Symmetry Adapted ClusterConfiguration Interaction (SAC-CI) Method. J. Chem. Phys. 1996, 104, 2321−2330. (40) Ehara, M.; Ohtsuka, Y.; Nakatsuji, H. Ionization Spectra of XONO2 (X = F, Cl, Br, I) Studied by the SAC-CI Method. Chem. Phys. 1998, 226, 113−123. (41) Nakatsuji, H.; Izawa, M. Calculation of Hyperfine Splitting Constants with Slater-type Cusp Basis by the Symmetry Adapted Cluster-configuration Interaction Theory. J. Chem. Phys. 1989, 91, 6205−6214. (42) SAC-CI Home Page. Quantum Chemistry Research Institute (QCRI). http://www.qcri.or.jp/sacci/. (43) Vydrov, O. A.; Van Voorhis, T. V. Benchmark Assessment of the Accuracy of Several van der Waals Density Functionals. J. Chem. Theory Comput. 2012, 8, 1929−1934.

(2) Wu, C. S.; Ambler, E.; Hayward, R. W.; Hoppes, D. D.; Hudson, R. P. Experimental Test of Parity Conservation in Beta Decay. Phys. Rev. 1957, 105, 1413−1415. (3) Prins, L. J.; Huskens, J.; de Jong, F.; Timmerman, P.; Reinhoudt, D. N. Complete Asymmetric Induction of Supramolecular Chirality in a Hydrogen-Bonded Assembly. Nature 1999, 398, 498−502. (4) Kempe, M.; Mosbach, K. Molecular Imprinting used for Chiral Separations. J. Chromatogr.A 1995, 694, 3−13. (5) Webb, T. H.; Wilcox, C. S. Enantioselective and Diastereoselective Molecular Recognition of Neutral Molecule. Chem. Soc. Rev. 1993, 22, 383−395. (6) Tsukamoto, M.; Kagan, H. B. Recent Advances in the Measurement of Enantiomeric Excesses. Adv. Synth. Catal. 2002, 344, 453−463. (7) Mehvar, R.; Brocks, D. R. Stereospecific Pharmacokinetics and Pharmacodynamics of Beta-Adrenergic Blockers in Humans. J. Pharm. Pharm. Sci. 2001, 4, 185−200. (8) Gellman, S. H. Introduction: Molecular Recognition. Chem. Rev. 1997, 97, 1231−1232. (9) Breslow, R.; Dong, S. D. Biomimetic Reactions Catalyzed by Cyclodextrins and Their Derivatives. Chem. Rev. 1998, 98, 1997−2012. (10) Lee, W. Y.; Park, C. H.; Kim, S. A Novel Star-Shaped Crown Ether: Spontaneous Isomerization of a Macrocyclic Polyketone to a Spirobicyclic Polyketal. J. Am. Chem. Soc. 1993, 115, 1184−1185. (11) Song, L. X.; Wang, H. M.; Yang, Y. Experimental and Theoretical Study on the Inclusion Phenomena of o-Methoxyphenol with α- and βCyclodextrin. Acta. Chim. Sinica 2007, 65, 1593−1599. (12) De Sousa, F. B.; Denadai, A. M. L.; Lula, I. S.; Lopes, J. F.; Dos Santos, H. F.; De Almeida, W. B.; Sinisterra, R. D. Supramolecular Complex of Fluoxetine With β-Cyclodextrin: An Experimental and Theoretical Study. Int. J. Pharm. 2008, 353, 160−169. (13) Ward, T. J. Chiral Separations. Anal. Chem. 2002, 74, 2863−2872. (14) Shahangi, F.; Najafi Chermahini, A.; Farrokhpour, H.; Teimouri, A. Selective Complexation of Alkaline Earth Metal Ions with Nanotubular Cyclopeptides: DFT Theoretical Study. RSC Adv. 2015, 5, 2305−2317. (15) Jafari Chermahini, Z.; Najafi Chermahini, A.; Dabbagh, H. A.; Teimouri, A. Complexation of All-cis Cyclo (L-Pro) 3 and Alkali Metal Cations: A DFT Study. J. Inclusion Phenom. Macrocyclic Chem. 2015, 81, 465−473. (16) Jafari Chermahini, Z.; Najafi Chermahini, A.; Dabbagh, H. A.; Teimouri, A. Metal Ion Binding of S-block Cations and Nanotubular Cyclic (Proline) 4: A Theoretical Study. Struct. Chem. 2015, 26, 675− 684. (17) Smalley, R. E.; Levy, D. H.; Wharton, L. The Fluorescence Excitation Spectrum of the HeI2 van der Waals Complex. J. Chem. Phys. 1976, 64, 3266−3276. (18) Al-Rabaa, A. R.; Bréhéret, E.; Lahmani, F.; Zehnacker, A. Enantiodifferentiation in Jet-Cooled van der Waals Complexes of Chiral Molecules. Chem. Phys. Lett. 1995, 237, 480−484. (19) Lehmann, C. S.; Ram, N. B.; Powis, I.; Janssen, M. H. Imaging Photoelectron Circular Dichroism of Chiral Molecules by Femtosecond Multiphoton Coincidence Detection. J. Chem. Phys. 2013, 139, 234307. (20) Haber, T.; Schmitt, U.; Suhm, M. A. FTIR-Spectroscopy of Molecular Clusters in Pulsed Supersonic Slit-Jet Expansion. Phys. Chem. Chem. Phys. 1999, 1, 5573−5582. (21) Zimmermann, D.; Haber, T.; Schaal, H.; Suhm, M. A. Hydrogen Bonded rings, Chains and Lassos: the Case of T-butyl Alcohol Clusters. Mol. Phys. 2001, 99, 413−425. (22) Farnik, M.; Steinbach, C.; Weimann, M.; Buck, U.; Borho, N.; Suhm, M. A. Size-Selective Vibrational Spectroscopy of Methyl Glycolate Clusters: Comparison with Ragout-jet FTIR Spectroscopy. Phys. Chem. Chem. Phys. 2004, 6, 4614−4620. (23) Al-Rabaa, A.; Le Barbu, K.; Lahmani, F.; Zehnacker-Rentien, A. van der Waals Complexes between Chiral Molecules in a Supersonic Jet: A New Spectroscopic Method for Enantiomeric Discrimination. J. Phys. Chem. A 1997, 101, 3273−3278. (24) Garcia, G. A.; Nahon, L.; Harding, C. J.; Powis, I. Chiral Signatures in Angle-Resolved Valence Photoelectron Spectroscopy of K


Article

The Journal of Physical Chemistry A (44) Zhao, Y.; Truhlar, D. G. The M06 Suite of Density Functionals for Main Group Thermochemistry, Thermochemical Kinetics, Noncovalent Interactions, Excited States, and Transition Elements: Two New Functionals and Systematic Testing of four M06-Class Functionals and 12 other Functionals. Theor. Chem. Acc. 2008, 120, 215−241. (45) Theoretical Chemistry Institute. Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.; Bohmann, J. A.; Morales, C. M.; Weinhold, F. NBO 5.0; University of Wisconsin: Madison, WI, 2001. (46) Koopmans, T. Ü ber die Zuordnung von Wellenfunktionen und Eigenwerten zu den Einzelnen Elektronen Eines Atoms. Physica 1934, 1, 104−113.

L


Theoretical Modeling of the Chirality Discrimination of Enantiomers by

Recommend Documents