Ab initio mo study on base stacking: Adenine-adenine interaction in single-stranded polyadenylic acid (Poly A)

The interaction energy for base stacking in single-stranded poly A is calculated by an ab initio MO method. The calculated value agrees well with the observed stacking enthalpy. Dispersion and charge transfer interactions are the main factors stabilizing the polynucleotide; the contribution of the former is dominant.     

Liquid-liquid equilibria for four ternary systems containing methanol and cyclohexane

Nagata, I., 1984. Liquid-liquid equilibria for four ternary systems containing methanol and cyclohexane. Fluid Phase Equilibria, 18: 83–92.Liquid-liquid equilibria have been obtained experimentally for the systems methanol-benzene-cyclohexane, methanol-toluene-cyclohexane, methanol-acetone-cyclohexane and methanol-2-propanol-cyclohexane at 298.15 K. The experimental results are compared with predicted values obtained from the UNIQUAC and extended UNIQUAC equations.     

Vapor—liquid equilibria for the ternary Ethanol—2-butanone—benzene system at 298.15 K

Vapor—liquid equilibrium data for the ternary ethanol—2-butanone—benzene system and its constituent binary systems at 298.15 K are presented. The results are correlated with the Wilson, original and modified UNIQUAC equations and the UNIFAC group contribution method.     

Biodegradable network elastomeric polyesters from multifunctional aliphatic carboxylic acids and poly(epsilon-caprolactone) diols

Biodegradable elastomeric network polyesters were prepared from multifunctional aliphatic carboxylic acids such as tricarballylic acid (Yt) or meso-1,2,3,4-butanetetracarboxylic acid (Xb) and poly(epsilon-caprolactone) (PCL) diols with molecular weights of 530, 1,250 and 2,000 g.mol-1. Prepolymers prepared by a melt polycondensation were cast from DMF solution and postpolymerized at 280 degrees C for various periods of times to form a network. The resultant films were transparent, flexible and insoluble in organic solvents. The network polyesters obtained were characterized by IR absorption spectra, WAXS, density measurement, DSC, and tensile test. YtPCL1250, and XbPCL1250 network polyester films showed good elastomeric properties with high ultimate elongation (540-590%), and low Young's modulus (2.5-3.3 MPa). The enzymatic degradation was estimated by the weight loss of network films in a buffer solution with Rhizopus delemar lipase at 37 degrees C. The degree and rate of degradation were significantly affected by the molecular weight of PCL diol, chemical structures of multifunctional aliphatic carboxylic acids and the morphology of network films. The changes in the solid states of network films during the degradation were also estimated by the results of DSC and WAXS. [see text]     

A complete calculation for direct detection of Wino dark matter

In the anomaly-mediated supersymmetry (SUSY) breaking scenario, neutral gaugino of SUL₍₂₎$\mathit{SU}{(2)}_L$ multiplet, Wino, can be the lightest SUSY particle and become a candidate for dark matter. We calculated scattering cross section of Wino dark matter with nucleon, which is responsible for direct detection of the dark matter, on the assumption that the SUSY particles and the heavier Higgs bosons have masses of the order of the gravitino mass in the SUSY standard model. In such a case, the Wino–nucleon coupling is generated by loop processes. We have included two-loop contribution to Wino–gluon interaction in the calculation, since it is one of the leading contributions to the Wino–nucleon coupling. It was found that the spin-independent scattering cross section with proton is ^{10−(46–48)} cm²${10}^{-(46\text{–}48)}{\text{cm}}^2$. While it is almost independent of the Wino mass, the result is quite sensitive to the Higgs boson mass due to the accidental cancellation.     

Photoluminescence of SrGa2S4:Sn,Re(=Ce, Gd) phosphors

The photoluminescence (PL) spectra, PL excitation spectra, color coordinates, and X-ray diffraction spectra are reported for SrGa₂S₄:Sn,Re(=Ce and Gd, respectively) phosphors. By mixing SrGa₂S₄:Sn,Ce phosphors with different Ce³⁺ concentrations, white emissions can be obtained under the excitation of a 340-nm UV LED. Emissions in the green to yellow color range can be obtained from SrGa₂S₄:Sn,Gd phosphors. The rare earth ions enhance the green emission band, which peaks at 534 nm, instead of the yellow one. The origin of this enhancement is discussed. The resonant energy transfer rates are estimated in the cases from Ce³⁺ to the green and yellow centers of Sn²⁺ and between the yellow centers and the green centers.     

Thermal behavior and structure of liquid-crystalline aromatic-aliphatic polyester/poly(tetramethylene oxide) block copolymers

The thermal behavior and structure of poly(hexamethylene p,p′-biben-zoate) (BB-6)/poly(tetramethyleneoxide) (PTMO) block copolymers (BB-6/PTMO) were studied using differential scanning calorimetry, polarizing optical microscopy, and wide-angle and small-angle x-ray diffractometry. As the PTMO fraction increases, BB-6 liquid crystallinity decreased and two transition temperatures [Tc→M (crystal-mesophase) and Tm→i (mesophase-isotropic melt)] move to lower temperatures. BB-6/PTMO containing less than 20 mol% of PTMO retains liquid crystallinity. The isotropic melt-mesophase transition exotherm of BB-6/PTMO in the cooling process moves to lower temperature with increasing PTMO. Contrary to the isotropic melt-mesophase transition, the mesophase-crystal transition exotherm moves to higher temperature, indicating that PTMO segments favor the molecular mobility of BB-6 segments. As the mole fraction of BB-6 increases, the texture indicative of the smectic liquid crystal is gradually disorganized. BB-6/PTMO containing more than 30 mol% of PTMO no longer forms the texture indicative of smectic liquid crystals.     

Sonochemical degradation of chlorophenols in water

Sonochemical degradation of dilute aqueous solutions of 2-, 3- and 4-chlorophenol and pentachlorophenol has been investigated under air or argon atmosphere. The degradation follows first-order kinetics in the initial state with rates in the range 4.5-6.6 microM min-1 under air and 6.0-7.2 microM min-1 under argon at a concentration of 100 microM of chlorophenols. The rate of OH radical formation from water is 19.8 microM min-1 under argon and 14.7 microM min-1 under air in the same sonolysis conditions. The sonolysis of chlorophenols is effectively inhibited, but not completely, by the addition of t-BuOH, which is known to be an efficient OH radical scavenger in aqueous sonolysis. This suggests that the main degradation of chlorophenols proceeds via reaction with OH radicals; a thermal reaction also occurs, although its contribution is small. The addition of appropriate amounts of Fe(II) ions accelerates the degradation. This is probably due to the regeneration of OH radicals from hydrogen peroxide, which would be formed from recombination of OH radicals and which may contribute a little to the degradation. The ability to inhibit bacterial multiplication of pentachlorophenol decreases with ultrasonic irradiation.