Simultaneous determination of cefazolin in rat blood and brain by microdialysis and microbore liquid chromatography

A sensitive microbore liquid chromatographic method combined with the minimally invasive technique of microdialysis was devised for simultaneously and continuously monitoring the levels of unbound blood and brain cefazolin in rats. Microdialysis probes were inserted into the jugular vein and brain striatum for blood and brain sampling, respectively. Chromatographic conditions consisted of a mobile phase of methanol-acetonitrile-100 mM monosodium phosphoric acid (20:10:70, v/v, pH 4.5) pumped through a microbore reversed-phase column at a flow rate of 0.05 mL/min. The ultraviolet detection wavelength was set at 270 nm. An on-line design allowed direct and continuous analysis of protein-free samples in the dialysate. Microdialysis probes, being home-made, were screened for acceptable in vivo recovery. Chromatographic resolution and detection were validated for response linearity as well as intra-day and inter-day variabilities. This method was then applied to pharmacokinetic profiling of protein unbound cefazolin in both the blood and brain following intravenous administration (10 mg/kg, i.v., n = 6). Rapid appearance of cefazolin in the rat brain striatal dialysate following drug injection suggested good blood-brain barrier penetration. According to a non-compartmental pharmacokinetics model, the area under the concentration (AUC) vs time ratio of cefazolin in rat brain and blood was 6%.     

The magnetic susceptibilities of cobaltocene and chromocene

The magnetic susceptibilities of cobaltocene and chromocene have been measured between 83 and 293 K; for cobaltocene the results suggest an appreciable orthorhombic splitting of the ²∏(σ²πδ⁴ ground state, whilst for chromocene the data provide further support for the ³Δ(σδ³) ground state previously deduced.     

State of the art and limitations of quantitative polymerase chain reaction

Consequential to the implementation of European Commission (EC) Regulation 1139/98, EC Regulation 49/2000, and EC Regulation 50/2000 has been the need to measure accurately the levels of the genetically modified (GM) species Roundup Ready Soya and Bt 176 Maize that are present in food. Analytical methods to detect and quantitate these transgenic species have received much attention particularly with respect to the deminimus threshold of 1% for their presence in materials derived from non-GM identity-preserved (IP) supplies. The relative advantages and limitations of threshold analysis by double-competitive polymerase chain reaction (PCR) and quantitative real-time PCR are discussed in their application to the quantitative analysis of processed foods. Consideration is also given to other factors involved in the analyses that affect the performance of quantitative procedures, and to the many uncertainties involved in the precision of a reported analytical result.     

Time-weighted average sampling of airborne n-valeraldehyde by a solid-phase microextration device

A solid-phase microextraction (SPME) device was used as a time-weighted average sampler for n-valeraldehyde. The SPME device was first modified to improve the wearer's acceptance as a passive sampler. Then a poly(dimethylsiloxane)-divinylbenzene fiber was used and O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was loaded onto the fiber. Vapors of known concentrations around the threshold limit values time-weighted average of n-valeraldehyde and specific relative humidities (RHs) were generated by syringe pumps in a dynamic generation system. n-Valeraldehyde vapors in gas bags were also generated. An exposure chamber was designed to allow measurement of face velocities, temperatures, exposing vapor concentrations, and RHs. Gas chromatography with flame ionization detection was used for sample analysis. The appropriate adsorption time for SPME coating PFBHA was determined to be 2 min and the desorption time for oxime formed after sampling was optimized to be 2 min. The experimental sampling constant was found to be (3.86+/-0.13) x 10(-2) cm3/min and face velocity was not expect to have effect on the sampler.     

Searching of chemical structure data bases with parallel computer hardware

The use of two types of parallel computer hardware for increasing the efficiency of processing in chemical structure data bases is discussed. The distributed array processor can be used for the clustering of 2-D chemical structure data bases by using the Jarvis—Patrick clustering method and for the ranking of output in an experimental system for substructure searching in the 3-D macromolecules in the Protein Data Bank. The Inmos transputer can be used in the construction of PC-based systems for 2-D substructure searching and in the identification of the maximal substructures common to pairs of 3-D molecules.     

Asymmetric induction in mixed [2 + 2] photoadditions employing a chiral auxiliary in the alkene component

Asymmetric induction was achieved in the photoaddition of 3-methyl-2-cyclohexenone to optically active enoates 1a–c and the absolute configuration of the major adduct was determined.     

Splicing I: Using mixed basis sets in ab initio calculations

The effect of mixing (or “splicing”) extended and minimal basis sets on molecular properties such as geometries, Mulliken charges, dipoles, and internal rotation barriers was studied for several test molecules. The effect is gauged by comparison with full extended basis set calculations. It is found that splicing improves most properties relative to full minimal basis set calculations, and little accuracy is lost if the splicing is done in a judicious manner.     

CHLOROPHYLL ONE-ELECTRON PHOTOCHEMISTRY-II. PHOTOSENSITIZATION BY CHLOROPHYLL,PHEOPHYTIN AND BACTERIOCHLOROPHYLL OF A ONE-ELECTRON TRANSFER REACTION BETWEEN ETHANOL AND QUINONE*

Abstract— Chlorophyll, pheophytin and bacteriochlorophyll sensitize a one-electron transfer in the presence of quinones in ethanol, to produce a ternary complex of ground state porphyrin analog, alcohol cation radical and semiquinone anion radical as the primary photo-product at low temperature. A similar photo-oxidation of alcohol to produce a binary complex is caused by direct excitation of quin-one in the absence of chlorophyll. The mechanisms of these reactions and their implications for photosynthesis are discussed.     

Regioselective ortho lithiation of halopyridines

Regioselective ortho lithiation of 2-, 3-, and 4-halopyridines is achieved with lithium diisopropylamide (?78°, tetrahydrofuran) to afford, upon quenching with electrophilic reagents, 2,3- and 3,4-disubstituted pyridines in good to excellent yield.