Intermolecular charge flux as the origin of infrared intensity enhancement upon halogen-bond formation of the peptide group

Abstract

The changes in the vibrational properties of the peptide group upon formation of O...X and N...X halogen bonds are studied theoretically. Calculations are carried out for complexes of N-methylacetamide (NMA), a well known model molecule of the peptide group, with halogen-containing molecules. For comparison, calculations are also carried out for some NMA-water hydrogen-bonding complexes. It is shown that the infrared (IR) intensity of the amide I mode of the peptide group is enhanced significantly (up to about 520 km mol(-1) or 2.6 times) upon C=O...X halogen-bond formation, in spite of rather modest magnitudes of the intermolecular electric field and of the changes in the C=O bond length and in the amide I vibrational frequency as compared with the cases of the C=O...H(D) hydrogen bonding. From the analysis of the changes in the dipole derivative and in the electronic structure, it is shown that this IR intensity enhancement arises from the intermolecular charge flux. For the N...X halogen bonding complexes, some characteristic changes in the vibrational properties are seen, among which the IR intensity enhancement of the ND out-of-plane wagging mode is most notable. The reason why such large IR intensity enhancements are seen for these particular vibrational modes is examined.

Amide I Vibrational Properties Affected by Hydrogen Bonding Out-of-Plane of the Peptide Group

“…With regard to the hydration-induced frequency shifts of the amide I mode, a widely accepted understanding is that the effects of individual water molecules are nearly additive, as supported by the results of the previous theoretical calculations on the N-methylacetamide...nH 2 O (n = 1-3) complexes, 38,39 and this forms a basis of all the electrostatic models. [19][20][21][22][23][24][25][26][27] Therefore, it is meaningful to analyze the effect of an individual water molecule on the amide I frequency shift for examining such an additive element, and it is required for any reasonable electrostatic model to reproduce the situation of the hydration of a single water molecule.…”

Infrared intensities and charge mobility in hydrogen bonded complexes

“…3 Many studies focused mainly on the analysis of equilibrium charges while only in recent papers also charge fluxes have been analyzed. 9,10,18,21,22 In a very recent paper, 23 we presented an analytical method to extract the whole set of charge fluxes through the evaluation of second derivatives of the dipole (i.e., APTs derivatives); the method has been applied with success to different planar molecules, shedding light on some peculiar properties of charge flux parameters.…”

Strong N−X⋅⋅⋅O−N Halogen Bonds: A Comprehensive Study on N‐Halosaccharin Pyridine N‐Oxide Complexes

“…However, later, it was shown that correct trends of I⋅⋅⋅Y XB strengths can be predicted if the polarization of donor halogen in the presence of the acceptor is described . The accurate prediction of N−X⋅⋅⋅ − O−N + interaction strengths by Δ E model here, suggest that inclusion of σ‐hole parameters to molecular mechanics (MM) force fields to model the influence the anisotropy of donor atom electrostatic surface potentials have on XBs could result in better descriptions of halogen‐bonded systems by MM …”