Vibrational solvatochromism: Towards systematic approach to modeling solvation phenomena

Abstract

Vibrational solvatochromic frequency shift of IR probe is an effect of interaction between local electric field and IR probe in condensed phases. Despite prolonged efforts to develop empirical maps for vibrational frequency shifts and transition dipoles of IR probes, a systematic approach to ab initio calculation of vibrational solvatochromic charges and multipoles has not been developed. Here, we report on density functional theory (DFT) calculations of N-methylacetamide (NMA) frequency shifts using implicit and coarse-grained models. The solvatochromic infrared spectral shifts are estimated based on the distributed multipole analysis of electronic densities calculated for gas-phase equilibrium structure of NMA. Thus obtained distributed solvatochromic multipole parameters are used to calculate the amide I vibrational frequency shifts of NMA in water clusters that mimic the instantaneous configurations of the liquid water. Our results indicate that the spectral shifts are primarily electrostatic in nature and can be quantitatively reproduced using the proposed model with semi-quantitative accuracy when compared to the corresponding DFT results.

Vibrational solvatochromism. II. A first-principle theory of solvation-induced vibrational frequency shift based on effective fragment potential method

“…However, it should also be noted that such partitioning of the interaction potential and the frequency shift are approximate in nature, not only because the EFP description of the intermolecular interaction potential is an approximation but also because there could be artifacts introduced when thus obtained solvatochromic parameters are used for structurally distorted solute molecules in solutionsnote that, even though the original EFP method itself is based on rigid monomers, the vibrational solvatochromic calculation needs to consider structurally distorted molecules sampled from molecular dynamics simulation. The coarsegrained approach 9,33,34,42 has in this regard an important advantage because it already includes such structural distortion effects (see Refs. 33 and 34).…”

“…In the previous works 2, 9,10,34,42 only the first summation terms in Eqs. (11) and (12) were taken into account because they were believed to be the dominant contributions.…”

“…[50][51][52] Neverthe-less, to our knowledge, no first-principles study of the nonelectrostatic vibrational solvatochromism was undertaken up to date. In particular, it is not clear under what circumstances the electrostatic interaction is the dominant contribution 9,42 to experimentally observed vibrational frequency shift. Note that, in the cases of typical H-bonded complexes, while the charge-transfer energy is usually a minor component in the total binding energy, 53 the contributions from exchangerepulsion, charge-delocalization, and dispersion are known to be large.…”

“…41 Recently, we showed that such electrostatic coarse-grained theory based on solvatochromic cumulative atomic multipole moments (SolCAMM) reproduces the amide I frequency shifts of NMA (and slightly worse of NMA-d) in water clusters, which are comparable to the full density functional theory (DFT) calculation results. 42 Despite the success of previous theoretical approaches, taking into consideration the solute-solvent electrostatic interaction only, the importance and role of other interactions like exchange-repulsion, polarization, dispersion, and chargetransfer terms in vibrational solvatochromism have not been thoroughly studied. Just a few attempts to empirically model frequency shift decomposition have been reported so far.…”

Application of two-dimensional infrared spectroscopy to benchmark models for the amide I band of proteins

“…However, recent studies have suggested important contributions from dispersion, charge transfer, and polarisation effects. 64,66,67,[70][71][72][73] The electrostatic frequency mappings have been tested against ab initio calculations, 50,51,69,74 solvent experiments of single amide units, 52,60,73,75 gas phase experiments 76,77 of small peptides, and linear absorption of proteins. 62,64 So far, only one mapping for the amide unit preceding proline has been presented.…”