o-hydroxylmethylphenylchalcogens: synthesis, intramolecular nonbonded chalcogen...OH interactions, and glutathione peroxidase-like activity

[Structure: see text]. The synthesis and characterization of a series of organochalcogen (Se, Te) compounds derived from benzyl alcohol 13 are described. The synthesis of the key precursor dichalcogenides 15, 22, and 29 was achieved by the ortho-lithiation route. Selenide 18 was obtained by the reaction of the dilithiated derivative 14 with Se(dtc)2. Oxidation of 15 and 22 with H2O2 afforded the corresponding cyclic ester derivatives 17 and 24, respectively. Oxidation of selenide 18 with H2O2 affords the spirocyclic compound 19. The presence of intramolecular interactions in dichalcogenides 15 and 22 has been proven by single-crystal X-ray studies. The cyclic compounds 17 and 19 have also been characterized by single-crystal X-ray studies. GP(X)-like antioxidant activity of selenium compounds has been evaluated by the coupled bioassay method. Density functional theory calculations at the mPW1PW91 level on ditelluride 22 have identified a fairly strong nonbonding interaction between the hydroxy oxygen and tellurium atom. The second-order perturbation energy obtained through NBO analysis conveys the involvement of n(O) --> sigma(Te-Te) orbital overlap in nonbonding interaction. Post wave function analysis with the Atoms in Molecules (AIM) method identified distinct bond critical point in 15 and 22 and also indicated that the nonbonding interaction is predominantly covalent. Comparison between diselenide 15 and ditelluride 22 using the extent of orbital interaction as well as the value of electron density at the bond critical points unequivocally established that a ditelluride could be a better acceptor in nonbonding interaction, when the hydroxy group acts as the donor.     

Dynamics of solvation and rotational relaxation of Coumarin 153 in ionic liquid confined nanometer-sized microemulsions

The effects of confinement of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate on solvation dynamics and rotational relaxation of Coumarin 153 (C-153) in Triton X-100/cyclohexane microemulsions have been explored using steady-state and picosecond time-resolved emission spectroscopy. The steady-state and rotational relaxation data indicate that C-153 molecules are incorporated in the core of the microemulsions. The average rotational relaxation time increases with increase in w ([bmim][BF(4)]/[TX-100]) values. The solvent relaxation in the core of the microemulsion occurs on two different time scales and is almost insensitive to the increase in w values. The solvent relaxation is retarded in the pool of the microemulsions compared to the neat solvent. Though, the retardation is very small compared to several-fold retardation of the solvation time of the conventional solvent inside the pool of the microemulsions.     

Optimal control of ultrafast cis-trans photoisomerization of retinal in rhodopsin via a conical intersection

Optimal control simulation is applied to the cis-trans photoisomerization of retinal in rhodopsin within a two-dimensional, two-electronic-state model with a conical intersection [S. Hahn and G. Stock, J. Phys. Chem. B 104, 1146 (2000)]. For this case study, we investigate coherent control mechanisms, in which laser pulses work cooperatively with a conical intersection that acts as a "wave-packet cannon." Optimally designed pulses largely consist of shaping subpulses that prepare a wave packet, which is localized along a reaction coordinate and has little energy in the coupling mode, through multiple electronic transitions. This shaping process is shown to be essential for achieving a high target yield although the envelopes of the calculated pulses depend on the local topography of the potential-energy surfaces around the conical intersection and the choice of target. The control mechanisms are analyzed by considering the motion of reduced wave packets in a nuclear configuration space as well as by snapshots of probability current-density maps.     

Vibrational overtone spectroscopy of jet-cooled methanol from 5000 to 14 000 cm(-1)

Spectra of jet-cooled methanol in the overtone and combination region from 5000 to 14 000 cm(-1) have been obtained by means of infrared laser-assisted photofragment spectroscopy. Many of the observed features are assigned to combination bands of the type nnu(1)+nu(6), nnu(1)+nu(8), and nnu(1)+nu(6)+nu(8) (n=1,2,3), where nu(1) is the OH stretch, nu(6) is the OH bend, and nu(8) is the CO stretch. These bands show sharp torsion-rotation structure with features as narrow as 0.1 cm(-1). We also observe CH stretch overtones that are weaker than the OH containing combination bands and lack distinct torsion-rotation structure above v(CH)=2. The extent of observed structure on these bands allows us to place limits on the intramolecular vibrational energy redistribution decay rates in the upper vibrational states. We report a global fit of the observed band centers to a simple expression involving low-order anharmonicity constants.     

Efficient trapping of HNO by deoxymyoglobin

Nitrosyl hydride, HNO, also commonly termed nitroxyl, is a transient species that has been implicated in the biological activity of nitric oxide, NO. Herein, we report the first generation of a stable HNO-metal complex by direct trapping of free HNO. Deoxymyoglobin (Mb-Fe(II)) rapidly reacts with HNO produced from the decomposition of methylsulfonylhydroxylamine (MSHA) or Angeli's salt (AS) in aqueous solutions from pH 7 to pH 10, forming an adduct, Mb-HNO. The unique 1H NMR signal of the Fe-bound HNO at 14.8 ppm allows definitive proof of its formation. The generation of Mb-HNO and quantification of various myoglobin byproducts were accomplished by correlation of 1H NMR, UV-vis, and EPR spectroscopies. Typically, the maximum Mb-HNO yield obtained is 60-80%; competitive side reactions with byproducts as well as the further reactivity of the Mb-HNO decrease the overall yield. At pH 10, the observed rate of Mb-HNO generation by trapping HNO from MSHA is close to that for MSHA decomposition; kinetic simulations give a lower limit to the bimolecular rate of trapping as 1.4 x 10(4) M(-1) s(-1). The binding of HNO to deoxymyoglobin is rapid and essentially irreversible, which suggests that the biological activity of nitroxyl may be mediated by its reactivity with ferrous heme proteins such as myoglobin and hemoglobin.     

Ion-exclusion chromatography with conductimetric detection of aliphatic carboxylic acids on a weakly acidic cation-exchange resin by elution with benzoic acid-beta-cyclodextrin

In this study, an aqueous solution consisting of benzoic acid with low background conductivity and beta-cyclodextrin (beta-CD) of hydrophilic nature and the inclusion effect to benzoic acid were used as eluent for the ion-exclusion chromatographic separation of aliphatic carboxylic acids with different pKa values and hydrophobicity on a polymethacrylate-based weakly acidic cation-exchange resin in the H+ form. With increasing concentration of beta-cyclodextrin in the eluent, the retention times of the carboxylic acids decreased due to the increased hydrophilicity of the polymethacrylate-based cation-exchange resin surface from the adsorption of OH groups of beta-cyclodextrin. Moreover, the eluent background conductivity decreased with increasing concentration of beta-cyclodextrin in 1 mM benzoic acid, which could result in higher sensitivity for conductimetric detection. The ion-exclusion chromatographic separation of carboxylic acids with high resolution and sensitivity was accomplished successfully by elution with a 1 mM benzoic acid-10 mM cyclodextrin solution without chemical suppression.     

Gas chromatography/negative-ion chemical ionisation mass spectrometry for the quantitative analysis of morphine in human plasma using pentafluorobenzyl carbonate derivatives

A sensitive and specific method for the quantitative determination of morphine in human plasma is presented. Morphine was extracted from plasma by solid phase extraction on C18 and converted to its pentafluorobenzyl carbonate trimethylsilyl derivative. The derivatives were analysed without further purification. Using gas chromatography/negative ion chemical ionisation mass spectrometry, a useful diagnostic fragment ion at m/z 356 is obtained at high relative abundance. Deuterated morphine was used as internal standard. Calibration graphs were linear within the range 1.25 to 320 nmol/L. Intra-day precision was 3.82% (15 nmol/L), 2.85% (75 nmol/L) and 4.13% (225 nmol/L), inter-day variability was found to be 1.77% (15 nmol/L), 4.95% (75 nmol/L) and 9.88% (225 nmol/L). Inter-day accuracy showed deviations of 2.18% (15 nmol/L), -0.72% (75 nmol/L) and -0.13% (225 nmol/L). The method is rugged and robust and has been applied to the batch analysis of morphine during pharmacokinetic profiling of the drug.     

UV index experimental values during the years 2000 and 2001 from the Spanish broadband UV-B radiometric network

An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson-Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.     

不同温度下氨基酸在α-咖啡碱水溶液中的体积、粘度及折光率特性

Measurements of density(ρ), viscosity(η), and refractive index(n), were carried out on α-amino acids, DL-solution at 298.15, 303.15, 308.15, and 313.15 K. These measurements have been carried out to evaluate some important parameters, viz., apparent molar volume (φv), partial molar volume (φv0), transfer volume (φ0v (tr)), viscosity A and B coefficients of Jones-Dole equation, free energies of activation per mole of solvent (△μ0#1) and solute (△μ0#2),enthalpies (△H*) and entropies (△S*) of activation of viscous flow, variation of B with temperature ((a)B/(a)T)P, and molar refractive index (RD). These parameters have been interpreted in terms of solute-solute and solute-solvent interactions and structure making/breaking ability of solutes in the given solution.     

Chemical Reduction of CO2 to Different Products during Photo Catalytic Reaction on TiO2 under Diverse Conditions： an Overview

The chemical reduction of CO_2 remains a challenge with respect to the reversal of the oxidative degradation of any organic materials.The conversion of CO_2 into useful substances is essential in developing al- ternative fuels and various raw materials for different in- dustries.This also aids in preventing the continuous rise in tropospheric temperature due to the green house effect of CO_2.In this article an overview of the growth taken place so far in the field of CO_2 chemical reduction is pre- sented.The discussion comprises of photochemical meth- ods for the development of different products,viz.CO, CH_3O_H and CH_4,through chemical reduction of CO_2. This includes the use of photo catalysts,mainly TiO_2, and the role of a hole scavenger(such as 2-propanol)for this purpose.