Reaction dynamics of Cl+CH3SH: rotational and vibrational distributions of HCl probed with time-resolved Fourier-transform spectroscopy

Rotationally resolved infrared emission spectra of HCl(v=1-3) in the reaction of Cl+CH3SH, initiated with radiation from a laser at 308 nm, are detected with a step-scan Fourier-transform spectrometer. Observed rotational temperature of HCl(v=1-3) decreases with duration of reaction due to collisional quenching; a short extrapolation to time zero based on data in the range 0.25-4.25 micros yields a nascent rotational temperature of 1150+/-80 K. The rotational energy averaged for HCl(v=1-3) is 8.2+/-0.9 kJ mol(-1), yielding a fraction of available energy going into rotation of HCl, fr=0.10+/-0.01, nearly identical to that of the reaction Cl+H(2)S. Observed temporal profiles of the vibrational population of HCl(v=1-3) are fitted with a kinetic model of formation and quenching of HCl(v=1-3) to yield a branching ratio (68+/-5):(25+/-4):(7+/-1) for formation of HCl(v=1):(v=2):(v=3) from the title reaction and its thermal rate coefficient k(2a)=(2.9+/-0.7)x10(-10) cm(3) molecule(-1) s(-1). Considering possible estimates of the vibrational population of HCl(v=0) based on various surprisal analyses, we report an average vibrational energy 36+/-6 kJ mol(-1) for HCl. The fraction of available energy going into vibration of HCl is f(v)=0.45+/-0.08, significantly greater than a value fv=0.33+/-0.06 determined previously for Cl+H2S. Reaction dynamics of Cl+H(2)S and Cl+CH3SH are compared; the adduct CH3S(Cl)H is likely more transitory than the adduct H(2)SCl.     

Reversible formation of DNA G-quadruplex hairpin dimers from stilbenediether conjugates

Rapid and reversible G-quadruplex hairpin dimer formation is observed for bis(oligonucleotide) conjugates possessing stilbenediether (Sd) linkers connecting two short poly(G) sequences.     

A zwitterion of 1,5‐bis­(2‐hydroxy­benzamido)‐3‐aza­pentane: a two‐dimensional hydrogen‐bonding network involving dimers

The title compound, 2‐{N‐[2‐(2‐hydroxy­benzamido)ethyl­ammonio­ethyl]amino­carbon­yl}phenolate, C₁₈H₂₁N₃O₄, crystallizes in a zwitterionic form as a result of inter­molecular proton transfer and possesses a negatively charged phenolate group and a protonated amino group. The 2‐hydroxy­benzamide and 2‐(amino­carbonyl)­phenolate moieties attached to the two ends of the C—C—N—C—C backbone adopt a cis conformation in relation to this backbone. All N‐ and O‐bound H atoms are involved in hydrogen‐bond formation; the zwitterions are first linked into head‐to‐tail dimers, which are further organized into a two‐dimensional network parallel to the crystallographic bc plane.     

Studies on the reactions of silyl enol ether with perfluoroorganic compounds1 III. Synthesis of perfluoroalkylated α, β-unsaturated aldehydes and their derivatives

Per- and poly-fluoroalkylated α, β-unsaturated alkenals were synthesized by the reaction of silyl enol ether of alkanals with per- and poly-fluoroalkyl iodide initiated by Na₂S₂O₄ conveniently in high yield. Their corresponding alkenol and 2,4-dinitrophenylhydrazone were also synthesized.     

Studies of the electrochemical behavior of epinephrine at a homocysteine self-assembled electrode

The self-assembled electrode with the homocysteine monolayer (Hcy/Au) has been characterized by infrared spectroscopy and ac impedance spectroscopy in electrolyte. The Hcy/Au electrode is demonstrated to promote the electrochemical response of epinephrine (E) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant (k_s) is 2.1×10⁻² cm s⁻¹ at the self-assembled electrode. The reduction peak of E can be used to determine the concentration of E in presence of ascorbic acid (AA) owing to the Hcy/Au also promoting the electrochemical oxidation of AA.     

The formation of a compact polymer film on a copper electrode from benzimidazole solution

The effects of the pretreatment of copper in benzimidazole solutions on the anodic reactions have been observed. The structures of the chemisorbed benzimidazole on copper were studied by using the infrared reflection-absorption technique and X-ray photoelectron spectroscopy. It was found that a compact film of benzimidazolato copper(I) was formed on the copper surface when copper was immersed in a stirred benzimidazole solution and cyclic voltammetry applied. This compact polymer film inhibited anodic oxidation effectively.     

Studies of the g factors and zero-field splitting for the trigonal Ti(2+)(Ga)-S(p) defect center in GaP crystal

The EPR g factors g(parallel), g(perpendicular) and zero-field splitting D suggested to be caused by a donor-acceptor nearest-neighbour pair defect [Ti(Ga)(2+)-Sp] in GaP:Ti(2+) co-doped with sulphur are calculated from the high-order perturbation formulas based on a two spin-orbit coupling parameter model for the EPR parameters of 3d(2) ion in trigonal symmetry. The calculated results are close to the observed values. The suggestion of [Ti(Ga)(2+)-Sp] pair defect in GaP:Ti co-doped with sulphur is also confirmed from this calculation.     

Synthesis of [1,2-3H2]-polystyrene

The synthesis of [1,2-³H₂]-polystyrene consisted of a two step reaction. First catalytic tritium gas addition to phenylacetylene was used to prepare [1,2-³H₂]-styrene and then it was polymerized to [1,2-³H₂]-polystyrene in the present of an initiator.     

Recognition and quantification of binary and ternary mixtures of isomeric peptides by the kinetic method: metal ion and ligand effects on the dissociation of metal-bound complexes

The kinetic method is applied to differentiate and quantify mixtures of isomeric tripeptides based on the competitive dissociations of divalent metal ion-bound clusters in an ion trap mass spectrometer. This methodology is extended further to determine compositions of ternary mixtures of the isomers Gly-Gly-Ala (GGA), Ala-Gly-Gly (AGG), and Gly-Ala-Gly (GAG). This procedure also allows to perform chiral quantification of a ternary mixture of optical isomers. The divalent metal ion Ca(II) is particularly appropriate for isomeric distinction and quantification of the isobaric tripeptides Gly-Gly-Leu/Gly-Gly-Ile (GGL/GGI). Among the first-row transition metal ions, Cu(II) yields remarkably effective isomeric differentiation for both the isobaric tripeptides, GGI/GGL using GAG as the reference ligand, and the positional isomers GAG/GGA using GGI as the reference ligand. This is probably due to agostic bonding: alpha-agostic bonding occurs between Cu(II) and GAG and beta-agostic bonding between Cu(II) and GGI, each produces large but different steric effects on the stability of the Cu(II)-bound dimeric clusters. These data form the basis for possible future quantitative analyses of mixtures of larger peptides such as are generated, for example, in combinatorial synthesis of peptides and peptide mimics.     

A small molecule with osteogenesis-inducing activity in multipotent mesenchymal progenitor cells

Purmorphamine, which is a 2,6,9-trisubstituted purine compound, was discovered through cell-based high-throughput screening from a heterocycle combinatorial library. It differentiates multipotent mesenchymal progenitor cells into an osteoblast lineage. It will serve as a unique chemical tool to study the molecular mechanisms of osteogenesis of stem cells and bone development.