1. Angelo Perera, Javix Thomas, Christian Merten,a and Yunjie Xu
IR and VCD spectra of methyl glycidate in CCl4 and H2O: The clusters-in-a-liquid solvation model
Angelo Perera, Javix Thomas, Christian Merten,a and Yunjie Xu
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
a Present address: Physikalische Chemie II, Ruhr University Bochum, Bochum, Germany
ICAVS9, Victoria, BC, Canada, June 11-17, 2017 1

2. Complex nature of (chiral) biomolecules in water
Interactions between chiral biomolecules and water play a crucial role in life sciences.
Modelling such interactions adequately are challenging for a number of reasons:
1) A large number of intermolecular hydrogen bonding interactions.
2) Conformational flexibility of the chiral biomolecules.
3) The variation of intermolecular hydrogen bonding topologies with respect to time. 2

3. The experimental techniques
FTIR and vibrational circular dichroism (VCD) spectroscopy
Rotational strength =
 cos
positive zero negative
∆A = AL - AR
VCD is sensitive to
absolute configuration;
Conformation;
solvation effects.
G. Yang, and Y. Xu, Top. Curr. Chem. 2011, 298, 189.
L. A. Nafie, Vibrational Optical Activity: Principles and Applications, John Wily & Sons, Ltd., Chichester, 3

4. The clusters-in-a-liquid solvation model Solvent molecules in the bulk
Three key aspects:
Chiroptical spectral signatures are not from chiral solute but its complexes with water.
These important hydration clusters are long-lived species in solution.
It is important to include the implicit solvent effects generated by the bulk water environment using for example polarizable continuum model (PCM).
The selection of the long-lived hydrates of chiral solute with PCM is based on their capability to predict the observed chiroptical spectral features in solution.
A. Perera, J. Thomas, M. R. Poopari , Y. Xu, Front. Chem. 2016, 4, 1.
Solute-(water)n
cluster
It is of great advantage to have an experimental technique which clearly separate effects due to the explicit chiral solute – solvent interactions and the implicit bulk solvent.
Solvent molecules in the bulk
chem.yu.edu.jo/rawash/chem20495/Solvation/Models.ppt 4

5. The molecule: methyl glycidate (MG)
MG has several H-bonding sites and is also small enough for ab initio cal.
Conformations of MG was studied using rotational spectroscopy.
J. Thomas, J. Yiu, J. Rebling, W. Jäger, Y. Xu, J. Phys. Chem. A, 2013, 117,
experimental ratio of about 60%: 40%. deltaG=0.8 kJ/mol
Emphasize this level of theory is used through out.
Two major conformations of R-MG
Epoxy oxygen
Ester oxygen
anti-R-MG (most stable) syn-R-MG (~0.32 kJ/mol less stable)
B3LYP-D3BJ/ G(2d,p) the gas phase. 5

6. Comparison of experimental IR and VCD spectra of R-MG in water and CCl4
In CCl4 : [MG] = 0.05 M and path length = 25 μm
In H2O : [MG] = 6 M and path length = 3 μm 6

7. Comparison of the experimental and theoretical IR and VCD spectra in CCl4
Using PCM of CCl4 at 298K
anti-R-MG = 55%; syn-R-MG = 45%
Pop. weigh. VCD-R-MG-Gas
syn-R-MG -Gas
Pop. weigh. IR-R-MG-Gas
syn-R-MG-Gas
anti-R-MG-Gas
anti-R-MG-Gas
Pop. weigh. VCD-R-MG-PCM-CCl4
Pop. weigh. IR-R-MG-PCM-CCl4
With the PCM of CCl4
anti-R-MG:
55% at 298K;
∆G=0.00 kJ/mol.
syn-R-MG:
45% at 298 K;
∆G= 0.46 kJ/mol
Exp. IR: R-MG in CCl4
In Gas phase at 298K
anti-R-MG = 53%; syn-R-MG = 47%
Exp. VCD: R-MG in CCl4 7

8. The clusters-in-a-liquid solvation model
Comparison of the experimental and simulated IR and VCD spectra of R-MG in H2O
Pop. weigh. IR-R-MG-PCM-H2O
Pop. weigh. VCD-R-MG-PCM-H2O
Exp. VCD: R-MG in H2O
Using PCM of H2O at 298K
anti-R-MG = 70%; syn-R-MG = 30%
Specific hydrates rather than the chiral solute itself are the main species in water and contribute mainly to the observed VCD spectrum.
Chirality transfer features observed in the water bending region provide direct spectral evidence for the existence of the long-lived chiral hydrates.
The clusters-in-a-liquid solvation model
Exp. IR: R-MG in H2O
Calculated at the B3LYP-D3BJ/ G(2d,p) level of theory with D3BJ empirical dispersion correction
The failure of modelling experimental chirality transfer VCD feature at 1650 cm-1 is related to the absence explicit R-MG–water interactions. 8

9. Monohydrated complexes of R-MG
(1.49 kJ/mol)
(0.48 kJ/mol)
(0.97 kJ/mol)
(1.79 kJ/mol)
(10.2 kJ/mol)
(3.46 kJ/mol)
B3LYP-D3BJ / G(2d,p) with PCM of water
(0.00 kJ/mol)
(2.18 kJ/mol) 9

10. Simulated IR and VCD spectra of the R-MG-H2O complexes with PCM of water
10%
24% 6%
0.4%
12%
16%
20%
13% 10

11. Dihydrated complexes of R-MG
(0.00 kJ/mol)
(0.47 kJ/mol)
(2.84 kJ/mol)
(0.85 kJ/mol)
(3.38 kJ/mol)
(3.37 kJ/mol)
(3.44 kJ/mol)
(3.85 kJ/mol)
B3LYP-D3BJ/ G(2d,p) with PCM of water
(3.92 kJ/mol)
(3.96 kJ/mol) 11

12. Simulated IR and VCD spectra of the R-MG-(H2O)2 complexes with PCM of water5%
5.2%
4.3%
4.2%
20%
17%
6.5%
5.2%
14%
4.1% 12

13. Comparison of the experimental and simulated IR and VCD spectra of R-MG in water
The following empirical Boltzmann factors are used:
anti-R-MG-2H2O-4 = 0.65, syn-R-MG-H2O-6 = 0.25, syn-R-MG-H2O-1 = 0.05, syn-R-MG-2H2O-3 = 0.05. 13

14. Conclusions
The simulation of IR and VCD features of R-MG in CCl4 and water allows one to differentiate the impact of explicit and implicit solvent effects in water and CCl4.
The comparison between the simulation and experimental IR and VCD features of R-MG in water emphasises the existence of the long-lived hydrated complexes of R-MG in water.
The success of the clusters-in-a-liquid approach in this example and others demonstrates the connection between the properties of small hydrated clusters and those of solution. 14

15. Thank you! Acknowledgements Funding $$$:
International Mercator Fellowship, DFG.
Thank you!