We have deposited thin films of SiO2 by remote plasma-enhanced chemical vapor deposition and have identified similar infrared (IR) spectroscopic signatures of Si–OH groups incorporated during either film growth, or the cooling down process in the deposition chamber. These films can also be hygroscopic and, on postdeposition exposure to atmospheric water vapor, they show changes in the IR spectra associated with the incorporation of additional Si–OH groups. These changes are (i) the development of a new symmetric feature, centered at about 3350 cm−1, within the asymmetric O–H stretching band generated during growth and/or cooling down; (ii) the development of a new spectral feature at 925 cm−1; and (iii) a shift in the Si–O bond-stretching band to higher wavenumber. We show that the first two changes in the IR spectra are due to near-neighbor Si–OH bonding groups that result from the reaction between water vapor and the Si–O–Si bonds of the SiO2 host network. These spatially correlated Si–OH groups have different spectral features, due to relatively strong hydrogen bonding interactions, from the randomly distributed Si–OH groups that are incorporated initially during film growth and/or cooling down. The shift in the frequency of the Si–O stretching band derives from a preferential reaction of water with strained and highly reactive Si–O–Si bonding groups, i.e., those with the smallest Si–O–Si bond angles which are attacked by water vapor, resulting in the formation of near–neighbor pairs of Si–OH bonding groups.

Competition between cation-π interactions and intermolecular hydrogen bonds inalkali metal ion-phenol clusters. II. Phenol trimer Structures and rearrangement reactions of 4 -aminophenol ( H 2 O ) 1 + and 3 -aminophenol ( H 2 O ) 1 + clusters J. Chem. Phys. 123, 074320 (2005); 10.1063/1.2008255 The energetics and structural properties of diazomethyl (HCNN) and cyanomidyl (HNCN) radicals and their related cations and anions from ab initio calculations J. Chem. Phys. 122, 064316 (2005); 10.1063/1.1844314 Intermolecular vibrations of the jet-cooled 2-pyridone2-hydroxypyridine mixed dimer, a model for tautomeric nucleic acid base pairsThe phenol•N 2 complex cation has been studied with a combination of two-color resonant zero kinetic energy ͑ZEKE͒ and mass analyzed threshold ionization ͑MATI͒ spectroscopies to probe the interaction of a polar cation with a quadrupolar solvent molecule. Extended vibrational progressions are observed in three modes which are assigned as the in-plane bend ͑35 cm Ϫ1 ͒, the stretch ͑117 cm Ϫ1 ͒, and in-plane wag ͑130 cm Ϫ1 ͒ intermolecular vibrations, and are consistent with a structure where the N 2 forms a directional bond to the phenol OH group in the plane of the aromatic ring. Ab initio calculations at the UMP2/6-31G*, UHF/cc-pVDZ, and UMP2/cc-pVDZ levels of theory support this assignment. The spectra also provide a value for the adiabatic ionization energy (67 423 cm Ϫ1 Ϯ4.5 cm Ϫ1 ) and an estimate of the dissociation energy of the cluster (1650 Ϯ20 cm Ϫ1 ) which illustrate that the quadrupolar nitrogen molecule binds considerably more strongly to the phenol cation than a rare gas atom. These results constitute the first report of an aromatic•N 2 complex where the interaction can be described in terms of weak hydrogen bonding, rather than in terms of a van der Waals bond to the -system of the benzene ring.

Initial-velocity measurements for the phospholysis and synthesis of α,α-trehalose catalysed by trehalose phosphorylase from Schizophyllum commune and product and dead-end inhibitor studies show that this enzyme has an ordered Bi Bi kinetic mechanism, in which phosphate binds before α,α-trehalose, and α--glucose is released before α--glucose 1-phosphate. The freeenergy profile for the enzymic reaction at physiological reactant concentrations displays its largest barriers for steps involved in reverse glucosyl transfer to -glucose, and reveals the direction of phospholysis to be favoured thermodynamically. The pH dependence of kinetic parameters for all substrates and the dissociation constant of -glucal, a competitive dead-end inhibitor against -glucose (K i l 0.3 mM at pH 6.6 and 30 mC), were determined. Maximum velocities and catalytic efficiencies for the forward and reverse reactions decrease at high and low pH, giving apparent pK values of 7.2-7.8 and 5.5-6.0 for two groups whose correct protonation state is required for catalysis. The pH dependences of k cat \K are interpreted in terms of

Initial-velocity measurements for the phospholysis and synthesis of α,α-trehalose catalysed by trehalose phosphorylase from Schizophyllum commune and product and dead-end inhibitor studies show that this enzyme has an ordered Bi Bi kinetic mechanism, in which phosphate binds before α,α-trehalose, and α-d-glucose is released before α-d-glucose 1-phosphate. The free-energy profile for the enzymic reaction at physiological reactant concentrations displays its largest barriers for steps involved in reverse glucosyl transfer to d-glucose, and reveals the direction of phospholysis to be favoured thermodynamically. The pH dependence of kinetic parameters for all substrates and the dissociation constant of d-glucal, a competitive dead-end inhibitor against d-glucose (Ki = 0.3mM at pH6.6 and 30°C), were determined. Maximum velocities and catalytic efficiencies for the forward and reverse reactions decrease at high and low pH, giving apparent pK values of 7.2–7.8 and 5.5–6.0 for two groups whose correct protonation state is required for catalysis. The pH dependences of kcat/K are interpreted in terms of monoanionic phosphate and α-d-glucose 1-phosphate being the substrates, and of the pK value seen at high pH corresponding to the phosphate group in solution or bound to the enzyme. The Ki value for the inhibitor decreases outside the optimum pH range for catalysis, indicating that binding of d-glucal is tighter with incorrectly ionized forms of the complex between the enzyme and α-d-glucose 1-phosphate. Each molecule of trehalose phosphorylase contains one Mg2+ that is non-dissociable in the presence of metal chelators. Measurements of the 26Mg2+/24Mg2+ ratio in the solvent and on the enzyme by using inductively coupled plasma MS show that exchange of metal ion between protein and solution does not occur at measurable rates. Tryptic peptide mass mapping reveals close structural similarity between trehalose phosphorylases from basidiomycete fungi.

We report electronic absorption spectra, recorded using one- and two-color resonance-enhanced multiphoton ionization spectroscopy, of the Au-Kr complex. The transition is localized on the gold atom, and corresponds to a 6p<--6s atomic excitation; we observe transitions to the D (2)Pi(1/2) and D (2)Pi(3/2) spin-orbit states. In addition, we report the results of ab initio calculations, which consider electronic states arising from the 6 (2)S, 5 (2)D, and 6 (2)P atomic energy levels of Au. Further, we also report an accurate value for the dissociation energy of the ground state of Au-Kr, based on basis set extrapolated RCCSD(T) calculations. The experimental results are discussed in the light of the theoretical ones.