Effect of the carbon filler on the curing kinetics of epoxycyanate cooligomer

The influence of carbon fibre on the curing kinetics of the prepolymer based on bisphenol A cyanurate and epoxy resin has been studied using infra‐red spectroscopy. It was found that curing process of prepolymer is very complicated. It is shown that in curing the prepolymer a number of the sequential transformations of ones cycle structure into others occurs. An introduction of the carbon fiber (CF) of two types, original CF and modified CF (MCF) containing phosphate groups, affect strongly the prepolymer curing. Both CF and MCF accelerate the conversion rate of epoxy groups. In the case of cyanate groups, the former does not practically affect their conversion whereas the latter decelerates strongly this process. In the paper the influence mechanism of CF is considered.     

Solvent Effect on the Enthalpy of Solution and Partial Molar Volume of the Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate

Enthalpies of solution and partial molar volumes of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate were determined in 15 solvents of different polarity. Very large differences of the enthalpies of solution (????_sol H _IL=38.9?kJ?mol^?1) and partial molar volumes (??V _IL=43 cm³?mol^?1) are nearly the same as observed for lithium perchlorate solutions. These results clearly indicate that the low values of the macroscopic polarity parameters of [bmim]BF₄ do not correspond with the large differences of the intermolecular interactions in IL solutions. The values of the partial molar volume of the cation, $V_{[\mathrm{bmim}]^{+}}$ , were estimated for the first time. The changes of the partial molar volumes, V _IL, reflect mainly the changes of anion volume, $V_{\mathrm{BF}_{4}^{-}}$ . The rate of the Diels?CAlder reaction of 9,10-dimethylanthracene with maleic anhydride in the [bmim]BF₄ medium was nearly the same as in common molecular solvents.     

Reaction of Polynitrotoluenes with Phthalic Anhydride

2,4-Dinitro- and 2,4,6-trinitrotoluenes react with phthalic anhydride in boiling N,N-dimethylaniline to give nitro group reduction products.     

Measurement of the parity-violating longitudinal single-spin asymmetry for W± boson production in polarized proton-proton collisions at sqrt[s] = 500 GeV

We report the first measurement of the parity-violating single-spin asymmetries for midrapidity decay positrons and electrons from W+ and W- boson production in longitudinally polarized proton-proton collisions at sqrt[s] = 500 GeV by the STAR experiment at RHIC. The measured asymmetries, A(L)(W+) = -0.27 ± 0.10(stat.) ± 0.02(syst.) ± 0.03(norm.) and A(L)(W-) = 0.14 ± 0.19(stat.) ± 0.02(syst.) ± 0.01(norm.), are consistent with theory predictions, which are large and of opposite sign. These predictions are based on polarized quark and antiquark distribution functions constrained by polarized deep-inelastic scattering measurements.     

Theoretical study of the amazing firefly bioluminescence: the formation and structures of the light emitters

Reaction mechanisms for the formation of the keto-form of oxyluciferin (OxyLH(2)) from the luciferin of fireflies via a dioxetanone intermediate are predicted using the B3LYP/6-31G theoretical method. The ring opening of a model dioxetanone and the decarboxylation proceed in one step via a singlet diradical transition structure with an activation barrier of 18.1 and an exothermicity of 90.8 kcal/mol. The S(0) --> S(1) vertical excitation energies predicted with time dependent density functional theory, TDDFT B3LYP/6-31+G, for the anionic and neutral forms of OxyLH(2) are in the range of 60 to 80 kcal/mol. These energetic results support the generally accepted theory of chemically initiated electron exchange luminescence (CIEEL). The chemical origin of the multicolor bioluminescence from OxyLH(2) is examined theoretically using the TDDFT B3LYP/6-31+G, ZINDO//B3LYP/6-31+G, and CIS/6-31G methods. A change in color of the light emission upon rotation of the two rings in the S(1) excited state of OxyLH(2) is unlikely because both possible emitters, the planar keto- and enol-forms, are minima on the S(1) potential energy surface. The participation of the enol-forms of OxyLH(2) in bioluminescence is plausible but not required to explain the multicolor emission. According to predictions at the TDDFT B3LYP level, the color of the bioluminescence depends on the polarization of the OxyLH(2) in the microenvironment of the enzyme-OxyLH(2) complex.     

Aminoborohydrides 15. The first mild and efficient method for generating 2-(dialkylamino)-pyridines from 2-fluoropyridine

[reaction: see text] Lithium aminoborohydride (LAB) reagents promote the amination of 2-fluoropyridine under mild reaction conditions, providing 2-(dialkylamino)pyridines in excellent yield and purity. Treatment of 2-fluoropyridine with 1.1 equiv of lithium aminoborohydride at room temperature affords complete conversion after 1 h. This is the first general way by which 2-(dialkylamino)pyridines may be directly obtained from fluoropyridines under ambient reaction conditions. 2-Chloropyridine can also be converted to 2-(dialkylamino)pyridine by simply increasing the number of LAB equivalents and the reaction temperature.     

Relationship between the structure of the protein globule and bioluminescence spectra of firefly luciferase

Bioluminescence spectra for various native and mutant luciferases from fireflies and beetles were analyzed in the light of the known theoretical concepts on the influence of the microenvironment of the emitter on its emission spectra. The mechanism for the explanation of the nature of changing bioluminescence spectra for natural and artificial mutations of the amino acid residues in the protein globule of luciferases was proposed.