Synthesis and electrospray ionization mass spectra of AZT/d4T boranophosphates

New anti-HIV prodrugs, conjugates of AZT and d4T with boranophosphates, were prepared by the H-phosphonate method. Their structures were determined by negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated, and most of the fragment ions contained the boranophosphate or phosphinate group.     

Determination of some reactive oxygen species scavengers based on the peroxidase-oxidase oscillator

This paper reports a new method for detection of ROS scavengers including superoxide dismutase, ascorbic acid and glutathione based on a 'probe' of peroxidase-oxidase biochemical oscillator. The oscillation period and amplitude change with different concentrations of scavengers. The linear ranges of superoxide dismutase, ascorbic acid and glutathione are respectively 1.56 x 10(-4)-1.56 x 10(-3) mg mL(-1), 1.75 x 10(-7)-1.75 x 10(-5) mol L(-1) and 9.38 x 10(-7)-7.5 x 10(-5) mol L(-1). The selectivity, linearity and precision for superoxide dismutase, ascorbic acid, and glutathione are presented and discussed. The results compared well with other standard methods for determination of superoxide dismutase, ascorbic acid and glutathione. Some possible steps in the overall reaction mechanisms are discussed.     

Separation and quantitation of components in FD&C Red No. 3 using capillary electrophoresis

The use of capillary electrophoresis as a technique to separate and quantitate components of FD&C Red No. 3 (erythrosine, color index No. 45430) is described. The fluorescein isomers, 2',4',5'-triiodofluorescein (2,4,5-I3F) and 2',4',7'-triiodofluorescein (2,4,7-I3F), the most abundant by-products formed during the preparation of the dye, were selected for quantitation studies. The separation of other lower halogenated impurities was also demonstrated. Electrophoretic mobility of the compounds was achieved in a 50 mM borate, 25 mM sodium dodecyl sulfate buffer at pH 9.3. The limits of quantitation were found to be 0.15% (w/w) (2,4,5-I3F) and 0.14% (w/w) (2,4,7-I3F) (relative to the mass of FD&C Red No. 3). The method is linear from 0.08 to 20.0% (w/w) for 2,4,5-I3F and between 0.06 and 17.0% (w/w) for 2,4,7-13F. In addition, relative standard deviations of 2.03 and 5.11% were determined from precision studies in the repeat analysis of FD&C Red No. 3 for 2,4,5-I3F and 2,4,7-I3F, respectively. Overall, the CE method produced data in excellent agreement with the reference HPLC method, used considerably less solvent and sample, generated less waste and was found to be considerably more cost efficient.     

三异丙氧钐催化下醇的选择性乙酰化反应

本文报道了三异丙氧钐(5%)催化下，以乙酸乙酯为乙酰化试剂醇的选择性乙酰化反应。此法操作简便，产率良好。     

LaCO几何、电子结构和化学键的研究

长期以来 ,人们对希土羰基化合物的存在一直持怀疑态度[1 ] ,尽管 Slater[2 ] 等用基质隔离法合成部分希土羰基化合物的成功消除了这种疑问 ,但由于此类化合物高度的不稳定性 ,其几何结构至今尚未确定 ,希土羰基化合物的电子结构和化学键更是困扰人们的重要课题。希土羰基化合物是具有 L n- C键的最简单希土有机金属化合物 ,其结构和性能具有一定的代表性 ,探讨其化学键合本质及其不稳定的原因对深入了解希土金属有机化合物结构和性能的关系具有十分重要的意义。一 .研究方法本文采用洪功义、黎乐民等[3 ] 改进的高精度求解密度泛函理论方…     

Enantioselective Addition of Iodine Azide to α,β-Unsaturated Carboxylic Acid Derivatives

The addition of iodine azide to chiral conjugated N-enoyl-sultam or α,β-unsaturated N-acyloxazolidinones generated two asymmetric centers at C(α) and C(β) with high π-face differentiation and regioselectivity. The diastereomerically pure product was easily obtained by crystallization with purity up to 94% de. The structure of 2a was determined by X-ray diffraction analysis which also indicated that B and 4 are reactive conformations.     

PVA固定化脲酶电极的制作及电极特性的研究

利用PVA低温下的物理交联固定酶,制成酶电极并在不同尿素浓度、pH值、温度等条件下进一步研究这种酶电极的响应特性.     

Analysis of urban dust (PM<Subscript>2</Subscript>/PM<Subscript>10-2</Subscript>) in Daejeon city by instrumental neutron activation analysis

Summary As part of an air pollution monitoring study, airborne particulate matter (PM₂/PM_10-2) samples were collected from 2000 to 2003 at two sampling sites in an urban region, Daejeon, the middle of Korea. Mass concentrations of both fine and coarse fractions and that of the black carbon in the fine particles were measured using the Gent stacked filter unit sampler and the smoke stain reflectometer, respectively. In the collected samples the concentrations of 24 elements were analyzed using instrumental neutron activation analysis. Monitored data were investigated for their temporal trends under different environmental conditions and their seasonal correlation patterns. Crustal enrichment factors were also estimated to establish the contribution between anthropogenic and crustal origin. Patterns for airborne particle matter (APM) and elemental concentrations, seasonal variation of some marker elements were investigated. The results can be applied for the investigation of further air pollution sources and for the evaluation of air quality.     

Sedimentation of a composite particle in a spherical cavity

The boundary effect on the sedimentation of a colloidal particle is investigated theoretically by considering a composite sphere, which comprises a rigid core and an ion-penetrable membrane layer, in a spherical cavity. A pseudo-spectral method is adopted to solve the governing electrokinetic equations, and the influences of the key parameters on the sedimentation behavior of a particle are discussed. We show that both the qualitative and quantitative behaviors of a particle are influenced significantly by the presence of the membrane layer. For example, if the membrane layer is either free of fixed charge or positively charged and the surface potential of the rigid core is sufficiently high, the sedimentation velocity has a local minimum and the sedimentation potential has a local maximum as the thickness of the double layer varies. These local extrema are not observed when the membrane layer is negatively charged. If the double layer is thin, the influence of the fixed charge in the membrane layer on the sedimentation potential is inappreciable.     

Simultaneous determination of nicotine and its metabolite, cotinine, in rat blood and brain tissue using microdialysis coupled with liquid chromatography: pharmacokinetic application

To elucidate the disposition of nicotine in the brain is important because the neuropharmacological effects from nicotine exposure are centrally predominated. The aim of the present study was to develop a rapid and simple method for the simultaneous determination of unbound nicotine and its main metabolite, cotinine, in rat blood and brain tissue. We coupled a multiple sites microdialysis sampling technique with HPLC-UV system to characterize the pharmacokinetics of both nicotine and cotinine. Microdialysis probes were inserted into the jugular vein/right atrium and brain striatum of Sprague-Dawley rats, and nicotine (2 mg/kg, i.v.) was administered via the femoral vein. Dialysates were collected every 10 min and injected directly into a HPLC system. Both nicotine and cotinine were separated by a phenyl-hexyl column (150 mm x 4.6 mm) from dialysates within 12 min. The mobile phase consisted of an acetonitrile-methanol-20 mM monosodium phosphate buffer (55:45:900, v/v/v, pH adjusted to 5.1) with a flow-rate of 1 ml/min. The wavelength of the UV detector was set at 260 nm. The limit of quantification for nicotine and cotinine were 0.25 microg/ml and 0.05 microg/ml, respectively. Intra- and inter-day precision and accuracy of both measurements fell well within the predefined limits of acceptability. The blood and brain concentration-time profile of nicotine and cotinine suggests that nicotine is easily to get into the central nervous system and cotinine exhibits a long retention time and accumulates in blood.