Crowding and conformation interplay on human DNA G-quadruplex by ultraviolet resonant Raman scattering.

The G-quadruplex-forming telomeric sequence (TTAGGG)4TT was investigated by polarized Ultraviolet Resonance Raman Scattering (UVRR) at 266 nm. The presence of 40% poly(ethylene glycol) and the so-called "self-crowding" condition were used to induce the hybrid-to-parallel topology transition. Analysis of frequency shifts with temperature showed the role of several functional groups in the topological transitions and provides structural dynamical information. Circular dichroism under similar conditions was used as a reference. UVRR shed light on the effect of intramolecular interactions and of local and environmental dynamics in promoting different G-quadruplex topologies, induced by solution conditions or by temperature changes. Overall, these findings showed the enormous potential of this spectroscopy for G-quadruplex conformational studies.

Interfacial Water and Microheterogeneity in Aqueous Solutions of Ionic Liquids.

In this work, aqueous solutions of two prototypical ionic liquids (ILs), [BMIM][BF4] and [BMIM][TfO], were investigated by UV Raman spectroscopy and small-angle neutron scattering (SANS) in the water-rich domain, where strong heterogeneities at mesoscopic length scales (microheterogeneity) were expected. Analyzing Raman data by a differential method, the solute-correlated (SC) spectrum was extracted from the OH stretching profiles, emphasizing specific hydration features of the anions. SC-UV Raman spectra pointed out the molecular structuring of the interfacial water in these microheterogeneous IL/water mixtures, in which IL aggregates coexist with bulk water domains. The organization of the interfacial water differs for the [BMIM][BF4] and [BMIM][TfO] solutions, being affected by specific anion-water interactions. In particular, in the case of [BMIM][BF4], which forms weaker H-bonds with water, the aggregation properties clearly depend on concentration, as reflected by local changes in the interfacial water. On the other hand, stronger water-anion hydrogen bonds and more persistent hydration layers were observed for [BMIM][TfO], which likely prevent changes in IL aggregates. The modeling of SANS profiles, extended to [BPy][BF4] and [BPy][TfO], evidences the occurrence of significant concentration fluctuations for all of the systems: this appears as a rather general phenomenon that can be ascribed to the presence of IL aggregation, mainly induced by (cation-driven) hydrophobic interactions. Nevertheless, larger concentration fluctuations were observed for [BMIM][BF4], suggesting that anion-water interactions are relevant in modulating the microheterogeneity of the mixture.

Amide Spectral Fingerprints are Hydrogen Bonding-Mediated.

The origin of the peculiar amide spectral features of proteins in aqueous solution is investigated, by exploiting a combined theoretical and experimental approach to study UV Resonance Raman (RR) spectra of peptide molecular models, namely N-acetylglycine-N-methylamide (NAGMA) and N-acetylalanine-N-methylamide (NALMA). UVRR spectra are recorded by tuning Synchrotron Radiation at several excitation wavelengths and modeled by using a recently developed multiscale protocol based on a polarizable QM/MM approach. Thanks to the unparalleled agreement between theory and experiment, we demonstrate that specific hydrogen bond interactions, which dominate hydration dynamics around these solutes, play a crucial role in the selective enhancement of amide signals. These results further argue the capability of vibrational spectroscopy methods as valuable tools for refined structural analysis of peptides and proteins in aqueous solution.