Elucidation of pH-Induced Protein Structural Changes: A Combined 2D IR and Computational Approach.

The acid-base behavior of amino acids plays critical roles in several biochemical processes. Depending on the interactions with the protein environment, the p values of these amino acids shift from their respective solution values. As the side chains interact with the polypeptide backbone, a pH-induced change in the protonation state of aspartic and glutamic acids might significantly influence the structure and stability of a protein.

Association-Dissociation Dynamics of Ionic Electrolytes in Low Dielectric Medium.

Ionic electrolytes are known to form various complexes which exist in dynamic equilibrium in a low dielectric medium. However, structural characterization of these complexes has always posed a great challenge to the scientific community. An additional challenge is the estimation of the dynamic association-dissociation time scales (lifetime of the complexes), which are key to the fundamental understanding of ion transport.

Transition of a Deep Eutectic Solution to Aqueous Solution: A Dynamical Perspective of the Dissolved Solute.

Disruption of the deep eutectic solvent (DES) nanostructure around the dissolved solute upon addition of water is investigated by polarization-selective two-dimensional infrared spectroscopy and molecular dynamics simulations. The heterogeneous DES nanostructure around the solute is partially retained up to 41 wt % of added water, although water molecules are gradually incorporated in the solute's solvation shell even at lower hydration levels. Beyond 41 wt %, the solute is observed to be preferentially solvated by water.

Stabilization of Azapeptides by N···H-N Hydrogen Bonds.

An unusual N···H-N hydrogen bond (HB) was previously proposed to stabilize the azapeptide β-turns. Herein we provide experimental evidence for the N···H-N HB and show that this HB endows a stabilization of 1-3 kcal·mol and enforces the trans-cis-trans (t-c-t) and cis-cis-trans (c-c-t) amide bond conformations in azapeptides and -methyl-azapeptides, respectively. Our results indicate that these N···H-N HBs can have stabilizing contributions even in short azapeptides that cannot fold to form β-turns.

Evidence of an n(amide) → π* Interaction in -Alkyl-,'-diacylhydrazines.

1,2-Dibenzoyl-1--butylhydrazine (RH-5849) and related -alkyl-,'-diacylhydrazines are environmentally benign insect growth regulators. Herein, we show that an unusual n(amide) → π* interaction mediated by a hydrazide amide nitrogen atom plays a crucial role in stabilizing their biologically active trans-cis (t-c) rotameric conformations. We provide NMR and IR spectroscopic evidence for the presence of these interactions, which is also supported by X-ray crystallographic and computational studies.

The Curious Case of Aqueous Warfarin: Structural Isomers or Distinct Excited States?

Warfarin is a potent anti-coagulant drug and is on the World Health Organization's List of Essential Medicines. Additionally, it displays fluorescence enhancement upon binding to human serum albumin, making warfarin a prototype fluorescent probe in biology. Despite its biological significance, the current structural assignment of warfarin in aqueous solution is based on indirect evidence in organic solvents.

Hydrocarbon Chain-Length Dependence of Solvation Dynamics in Alcohol-Based Deep Eutectic Solvents: A Two-Dimensional Infrared Spectroscopic Investigation.

Deep eutectic solvents (DESs) have gained popularity in recent years as an environmentally benign, inexpensive alternative to organic solvents for diverse applications in chemistry and biology. Among them, alcohol-based DESs serve as useful media in various applications due to their significantly low viscosity as compared to other DESs. Despite their importance as media, little is known how their solvation dynamics change as a function of the hydrocarbon chain length of the alcohol constituent.