Non-hydrogen-bonded isomers were photogenerated by UV (lambda > 335 nm) irradiation of o-hydroxybenzaldehyde (salicylaldehyde) and o-hydroxyacetophenone monomers isolated in low-temperature Ar matrixes. These photoisomerizations were found to be photoreversible. Upon shorter wavelength (lambda > 235 nm or lambda > 270 nm) UV irradiation, the initial forms of the compounds (with intramolecular h...

abstract statement of problem: bleaching systems with different concentrations and applications are widely used to improve the visual appearance of the teeth, but one of the complications of these materials is reduction of bond strength for immediately bonding to the bleached enamel. objectives: the aim of this study was to evaluate the influence of using different modified hydrogen peroxide bl...

Proton transport across lipid membranes is a fundamental aspect of biological energy transduction (metabolism). This function is mediated by a Grotthuss mechanism involving proton hopping along hydrogen-bonded networks embedded in membrane-spanning proteins. Using molecular simulations, we have explored the structural, dynamic, and thermodynamic properties giving rise to long-range proton trans...

We analyze the correlated motions of hydrogen bonded clusters in liquid hydrogen fluoride, methanol, and water using the Instantaneous Normal Mode approach. In the case of hydrogen fluoride and methanol, which form a topologically linear hydrogen bond network, the relevant cluster is a triplet formed by a molecule and its two neighbors. In the case of water, whose hydrogen bond structure has a ...

Nitrogen 1s (N 1s) core-to-Rydberg excitation spectra of hydrogen-bonded clusters of ammonia (AM) have been studied in the small cluster regime of beam conditions with time-of-flight (TOF) fragment-mass spectroscopy. By monitoring partial-ion-yield spectra of cluster-origin products, "cluster" specific excitation spectra could be recorded. Comparison of the "cluster" band with "monomer" band re...

the relative stability of hydrogen-bonded of molybdate-phosphonic acid (mpa) complex (1:2) ingas phase has been carried out using density functional theory (dft) methods. the methods are usedfor calculations are b3lyp, bp86 and b3pw91 that have been studied in two series of basis sets: d95**and 6-31+g(d,p) for hydrogen and oxygen atoms; lanl2dz for mo and phosphorus. predictedhydrogen-bond geom...

The heme-copper oxygen reductases are redox-driven proton pumps. In the current work, the effects of mutations in a proposed exit pathway for pumped protons are examined in the ba(3)-type oxygen reductase from Thermus thermophilus, leading from the propionates of heme a(3) to the interface between subunits I and II. Recent studies have proposed important roles for His376 and Asp372, both of whi...

Interfacial structures of water at polyvinyl alcohol (PVA) and poly(2-acrylamido-2-methypropane) sulfonic acid sodium salt (PNaAMPS)/quartz interfaces were investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at 3200 and 3400 cm(-1), corresponding to the symmetric OH stretching of tetrahedrally coordinated, i.e., strongly hydrogen bo...

Herein, we report on the folding pattern observed in a synthetic peptide featuring two highly mutually dependent, yet strikingly dissimilar, closed networks of hydrogen-bonded rings that work in a cumulative fashion to stabilize the entire folded architecture of the peptide. Structural studies unequivocally suggest that disruption of any one of these mutually-dependent hydrogen-bonded networks ...