高能核碰撞中带电多重数快度与能量和中心度的关系

用强子–弦级联模型JPCIAE及相应的Monte Carlo事例产生器研究相对论性核–核碰撞中带电粒子多重数的赝快度密度对能量和中心度的依赖关系.无需另调任何模型参数的条件下,此模型可以同时较好地描述相对论性pp实验数据及PHOBOS和PHENIX实验组的Au+Au实验数据.本文指出:因〈N_part〉并非严格定义的物理量,致使实验上和理论上确定〈N_part〉有一定任意性,从而使得每参加者核子对的带电粒子赝快度密度随着〈N_part〉的增加可能逐渐增大,也可能逐渐减小,因此用它来区分粒子产生机制是欠妥的.     

Synthesis and structural, spectroscopic and magnetic studies of two new polymorphs of Mn(SeO3)·H2O

Two new manganese(II) selenite polymorphs with formula Mn(SeO₃)·H₂O have been synthesized by slow evaporation from an aqueous solution. The crystal structure of both compounds (1) and (2) have been solved from X-ray diffraction data. The structure of (1) was determined from single-crystal X-ray diffraction techniques. The compound crystallizes in the Ama2 space group, with a=5.817(1), b=13.449(3), and Z=4. The structure of (2) has been solved from X-ray powder diffraction data. This phase crystallizes in the P2₁/n space group with unit-cell parameters of a=4.921(3), b=13.121(7), , β=90.03(2)° and Z=4. Both polymorphs exhibit a layered structure formed by isolated sheets of MnO₆ octahedra and (SeO₃)²⁻ trigonal pyramids in the (010) plane. These layers, which contain one manganese and selenium atom crystallographically independent, are formed by octahedra linked between them through the selenite oxoanions. The difference of both compounds consists in the stacking of the layers along the b-axis. The IR spectra show the characteristic bands of the selenite anion. Studies of luminescence performed at 6 K and diffuse reflectance spectroscopy have been carried out for both phases. The Dq and Racah (B and C) parameters, from luminescence and diffuse reflectance spectroscopy, are Dq=705, B=750, for (1) and Dq=720, B=745, for (2). The ESR spectra of both compounds are isotropic with g-values of 1.99(1). Magnetic measurements indicate the presence of antiferromagnetic couplings in both phases. The J-exchange parameters have been estimated by fitting the experimental magnetic data to a model for square-planar lattice. The values obtained are J/k=-0.83, −0.91 K and J^′/k=-0.97, −1.20 K, for polymorphs (1) and (2), respectively.     

Stereochemical analysis of 3,4-methylenedioxymethamphetamine and its main metabolites by gas chromatography/mass spectrometry

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is consumed as the racemate but some metabolic steps are enantioselective. In addition, chiral properties are preserved during MDMA biotransformation. A quantitative analytical methodology using gas chromatography/mass spectrometry (GC/MS) to determine enantioselective disposition in the body of MDMA and its main metabolites including 3,4-methylenedioxyamphetamine (MDA), 4-hydroxy-3-methoxymethamphetamine (HMMA), and 4-hydroxy-3-methoxyamphetamine (HMA) was developed. Plasma and urine samples were collected from a male volunteer. The analysis of MDMA, MDA, and 4-hydroxy-3-methoxy metabolites by GC/MS required a two-step derivatization procedure. The first step consisted of derivatization of the amine with enantiomerically pure Mosher's reagent ((R)-MTPCl). Triethylamine was used as a base to neutralize hydrochloric acid formed during the reaction allowing quantitative derivatization, which resulted in a substantial improvement in the sensitivity of the method compared with other previously described techniques. Further treatment with ammonium hydroxide was required since both amine and hydroxyl groups underwent derivatization in the reaction. Ammonium hydroxide breaks bonds formed with hydroxyl groups without affecting amine derivatives. The second derivatization step using hexamethyldisilazane was needed for metabolites containing phenol residues. This derivatization method permitted the stereochemically specific study of MDMA and its main monohydroxylated metabolites by GC/MS. A detailed study of the chemical reactions involved in the derivatization steps was indispensable to develop a straightforward, sensitive, and reproducible method for the analysis of the parent drug compound and its metabolites.     

Kinetics and Mechanism of the Photosensitized Oxidation of Furosemide*

Detection of O2(1δg) phosphorescence emission, γmax = 1270 nm, following laser excitation and steady-state competitive methods was employed to measure total rate constants, kT, for the reactions of the diuretic furosemide, 2-methylfurane and furfurylamine with singlet oxygen in several solvents. Correlation of kT values with solvent parameters and product identification shows that the reaction mechanism is strongly solvent dependent. In aliphatic alcohols, the dependence of kT on solvent parameters is similar to the one observed for triethylamine, suggesting a reaction mechanism involving partial charge transfer from the amino group to the singlet oxygen. In nonprotic solvents, the dependence of kT on solvent parameters resembles the behavior found for 2-methylfur-ane and furfurylamine, implying that mostly a 2 + 4 cy-cloaddition mechanism of singlet oxygen to furane ring of furosemide occurs in these solvents. These mechanistic differences are explained in terms of hydrogen-bonding interactions between the carboxylic group in the aromatic ring and the amino group of furosemide. Furthermore, direct generation of C2(1δg) by furosemide was detected. Quantum yields of 0.047 ± 0.003 and 0.078 ± 0.004 were determined in acetonitrile and benzene, respectively. This last result may be related, at least partially, to the photodynamic effects of this diuretic drug.     

A comparative investigation of the fatty acid compositions of the seeds of a number of lines of a genetic collection of Gossypium hirsutum

A comparative analysis has been made of the amounts of lipids and their fatty-acid compositions in the seeds of the lines of agenetic collection of cotton plants of the speciesGossypium hirsutum and their hybrids and the variety Tashkent-1. The results obtained on the fatty-acid compositions of some hybrids make it possible to recommend the use of individual lines of cotton plants as donors for improving the food-value indices of cottonseed oil.Institute of Chemsitry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 173–176, March–April, 1991.     

Spectroscopic study of the light-harvesting protein C-phycocyanin associated with colorless linker peptides

C-Phycocyanin (PC) trimers associated with linker polypeptides were isolated from the phycobilisome (PBS) rods of Synechococcus sp. PCC 7002. LXY refers to a linker polypeptide (L) having an apparent mass of Y kDa, located at position X in the phycobilisome where X can be R (rod), C (core) or RC (rod-core junction). Measurements of the absorption, fluorescence and excitation anisotropy of PC trimer, PC.LR32.3 and PC.LRC28.5 complexes document the spectroscopic modulation of each linker polypeptide on the PC chromophores. The difference spectra between the PC trimer and the PC-linker complexes show that although the effect induced by the linker polypeptides is qualitatively similar in behavior, the extent of the modulation is greater in PC.LRC28.5. Measurements taken at 77 K show that a red-wavelength component of the PC trimer absorption-fluorescence spectra is the target of the linker's influence and that this component is altered to a greater extent by LRC28.5. In addition the 77 K absorbance of the PC trimer resolves band features that are consistent with an excitonic coupling interaction between neighboring alpha 84 and beta 84 chromophores. These band features are also evident in the absorbance of PC.LR32.3 but are absent in PC.LRC28.5 indicating that LRC28.5 may be perturbing the coupling interaction established in the PC trimer alpha 84-beta 84 chromophore pairs. Structurally, the linker polypeptide should disrupt the C3 symmetry in the central cavity of the associated phycobiliprotein and this asymmetric interaction should serve to guide the transfer of excitation energy along PBS rods toward the core elements.     

Diffusion coefficients of 2-fluoroanisole, 2-bromoanisole, allylbenzene and 1,3-divinylbenzene at infinite dilution in supercritical carbon dioxide

The Taylor–Aris chromatographic technique was employed for the determination of diffusion coefficients of 2-fluoroanisole, 2-bromoanisole, allylbenzene and 1,3-divinylbenzene at infinite dilution in supercritical carbon dioxide from 313.16 to 333.16 K and pressures between 15 and 35 MPa. As expected, the diffusivities rise when temperature increases and pressure decreases. Numerous predictive equations are compared with experimental data: Lai–Tan, Liu–Ruckenstein cluster formula, Woerlee, Hippler–Schubert–Troe, Catchpole–King, Eaton–Akgerman, He, He–Yu, Liu–Silva–Macedo, Funazukuri and coworkers, Dariva–Coelho–Oliveira, Zhu–Lu–Zhou–Wang–Shi and the Liu–Ruckenstein RHS formula. The equations of He, He–Yu and Catchpole–King are the best of all, but cannot be used in the whole range of temperatures and solvent densities.     

Distribution of arsenic species in environmental samples collected in Northern Chile

Gradient ion chromatographic separation coupled with ICP-MS was used to resolve and determine the most common arsenic species in environmental and biological samples of carrots, trout, soil, sediment and river water from Region II of Chile. The carrot and trout samples showed a concentration of 49 and 168 µg g^?1, respectively, of total As. Both concentrations are high considering the basal level. In the carrots, percentage of 45 and 31% of total As were found for As(III) and As(V) species, respectively. In the trout, the higher concentration related to AsB at 39% of the total As. As(III) and DMA were also present in relatively high concentrations. The River Loa and the soil in which the carrots are growing also present very high As(V) concentrations of 100 and 17 µg g^?1, respectively. The ratio between the concentration for the same As species found in the living organisms (carrots and trout) and the environment in which they grow (soil and water) can provide important information about the possible absorption or biotransformation of As species in living beings. As(III) and DMA are the species in which the greatest accumulation occurs with respect to the medium in which they are present, and biotransformation also appears to take place.     

Macrocyclic ZnII and CuII complexes as guests of the hybrid composites based on the layered MnPS3 phase. Comparison of spectroscopic properties

A family of macrocyclic complexes [M₂LⁿCl₂] have been synthesized and characterized (M: Cu^II or Zn^II; Lⁿ: macrocyclic ligand derived from 2-hydroxy-5-methyl-1,3-benzenedicarbaldehyde and different aliphatic diamines and o-phenylenediamine). The influence of the aromaticity of the ligand and the metal center on the spectroscopic properties of the complexes (absorption and emission) has been studied. Making use of the weak interactions between hydrated potassium ions and the layers of the K_0.4Mn_0.8PS₃ precursor, the obtained macrocyclic complexes have been intercalated in the interlamellar space by a microwave assisted cationic exchange reaction. The optical properties of the obtained hybrid materials are reported. The absorption edge, recorded by solid state reflectance spectroscopy for Cu^II and the Zn^II macrocycle-based composites, is 1.67–1.76 eV, both shifted to lower energy compared with that of the pristine MnPS₃.