High‐Pressure and Concentration‐Dependent Studies on C‐H—O Interactions of Binary Aqueous Mixtures: Formic Acid/D₂O and Acetone/D₂O

Abstract

The C‐H—O interactions of formic acid and acetone aqueous solutions were studied under various concentrations. The infrared spectra of acetone/D2O were also measured as a function of pressure. The C‐H stretching frequency of formic acid reveals a red‐shift with dilution. On the other hand, upon diluting acetone with D2O, the blue‐shift with dilution in C‐H stretching frequency was observed. Further high‐pressure study provides the experimental evidence for the enhancement of hydrophobic hydration as the sample was compressed to high‐pressure ices, while C‐H vibration of acetone, being trans formed from liquid to high‐pressure ice VII, are altered into a band located at ∼2950 cm−1. The C‐H—O inter action may be a distinct possibility to understand the band‐shape and frequency‐shift of the C‐H stretching modes of formic acid/D2O and acetone/D2O.

Intermolecular Interactions in Aqueous Dimethyl Sulphoxide and Acetic Acid Probed by High‐Pressure FTIR

“…The or igin of the C-H bond-shortening upon form ing a weak hy drogen bond has been the sub ject of nu mer ous dis cus sions. 2,[20][21][22] The blueshift in fre quency may be at trib uted to the strengthen ing of elec tro static/dis per sion C-H---O con tacts or re pulsive con tri bu tion due to com pres sion. 20 Thus, elec tron density from the hy dro gen, be ing elec tron rich with re spect to the car bon, may move into the C-H bond as the pres sure increased as a re sult of the short en ing of the C-H bond.…”

“…Re cently the com bi na tion of high pres sure and spec tro scopic meth ods is be gin ning to map the conformational land scapes of small bi o log i cal re lated mo lecu lar com plexes. [19][20][21] In or der to as sess the in di vid ual ef fects of the aliphatic res i dues on the wa ter struc tures, the pres ent ar ti cle de scribes the ap pli ca tion of the high-pressure method to aque ous DMSO and aque ous ace tic acid, as a pre lude to the in ves ti ga tion of their hy drated mo lec u lar con for ma tions. Liq uid DMSO was char ac ter ized by pres sure in di cat ing sig nif i cant struc tural lo cal or der, 12 while short-range or der in liq uid DMSO is strongly in creased at higher den si ties due to a re ar range ment of neigh bor ing mol e cules to form strongly as so ci ated clus ters.…”

Thermodynamic Studies on Amino Acid Solvation in some Aqueous Alcohols

“…Much attention has been paid [1][2][3][4] to determine the various thermodynamic properties of an aqueous solution of amino acids at different aqueous organic media. The purpose of such studies is to gain the various aspects of protein folding and unfolding processes and protein hydration.…”