The role of triplet states in dye sensitization of ZnO electrodes

The quantum efficiency of photooxidation of a number of xanthene dyes at ZnO single crystal electrodes has been found to depend on the solution concentration of a triplet quenching agent, FeCN^4?₆, providing evidence for triplet state participation in the oxidation reaction.     

Über Pterinchemie. 49. Mitteilung. Eine neue Synthese von 5-Formyl-6, 7-dimethyl-5,6,7,8-tetrahydropterin und 5,6,7-Trimethyl-5,6,7,8-tetrahydropterin

Starting with 5-formyl-6,7-dimethyl-5,6,7,8-tetrahydropterine (II), a new synthesis of 5,6,7-trimethyl-5,6,7,8-tetrahydropterine (III) is described. Thereby the chemical behaviour of the 5-formyl group in II is investigated, in order to enable the unequivocal differentiation between formylation at position 5 and at position 10 in folic and tetrahydrofolic acid derivatives. ¹³C-NMR. spectra of II and III are discussed.     

Determination of lithium in human serum by electrothermal atomic absorption spectrometry

An efficient method was developed for the determination of nanogram levels of lithium in biological samples. Serum samples from human subjects from southeastern Spain, treated or not treated with lithium carbonate, were analyzed by electrothermal atomic absorption spectrometry. The samples were previously treated with a matrix modifier consisting of 0.1% Triton X-100 and injected through a graphite tube with L'vov platform. The Li concentrations measured by the procedure described for the 3 certified reference samples used were not significantly different (p > 0.05) than certified levels. Sample recoveries and variability during several days, with coefficients of variation from 4.00 to 14.8%, demonstrated the reliability and accuracy of this technique. Mean Li concentration determined in the serum of individuals with psychiatric disorders treated with Li (n = 117, 5.077 +/- 1.795 microg Li/mL) was significantly higher (p < 0.001) than that in individuals not treated with Li (n = 24, 1.902 +/- 2.054 ng Li/mL).     

Rapid flow-injection sandwich-type immunoassays of proteins using an immobilized antibody reactor and adenosine deaminase-antibody conjugates

A rapid flow-injection sandwich enzyme immunoassay suitable for the direct determination of proteins in biological samples is described. The proposed system utilizes highly active adenosine deaminase—antibody conjugates in conjunction with a flow-through immunoreactor and an ammonium ion-selective potentiometric detector. After appropriate sample/reagent injection steps, the enzyme activity bound to the reactor is measured by diverting a coninuously flowing stream of substrate (adenosine) through the packed immunocolumn and detecting liberated ammonium ions downstream with a tubular ammonium ion-selective electrode. The bound enzyme activity is directly proportional to the concentration of analyte in the original sample. By using non-equilibrium flow-rates of sample and reagent slugs, a single protein assay takes less than 12 min, including regeneration of the reactor. The proposed method is shown to be selective, reproducible and capable of determining accurately the model protein (human IgC) at sub-μg ml^?1 concentrations.     

Use of diode-array detectors for the simultaneous spectrophotometric determination of calcium and magnesium by flow injection

A method for the simultaneous flow injection spectrophotometric determination of calcium and magnesium with Arsenazo III based on the use of diode-array detector and merging zones is described. The method is applicable to the resolution of mixtures in which the chromogenic reagent has a high absorbance and its spectrum strongly overlaps those of its complexes. In resolving the mixtures, the excess reagent is considered as another component. Quantitation is based on the normal absorbance and first-derivative absorbance spectra. The method is applied to 0.2–1.5 μg ml^?1 Ca and 0.1–1.0 μg ml^?1 Mg. The analysis rate is 50 h^?1.     

Syntheses of a Cp'Re=S derivative and more complex products

The reaction of Cp'ReCl(2)S(3) (Cp' = Me(4)EtC(5)) with slightly less than 2 equiv of a phosphine reagent results in the formation of [Cp'Re(Cl)(2)(mu-S)](2), 2, which has been characterized by an X-ray diffraction study. Reactions of 2 with nucleophiles did not lead to monomeric derivatives of the type Cp'ReS(Cl)(2)(Nuc). The reaction of Cp'ReCl(2)(SC(2)H(4)S) with (Me(3)Si)(2)S resulted in the formation of three new products: Cp'ReS(SC(2)H(4)S), 4; Cp'Re(S(3))(SC(2)H(4)S), 5; and a tetranuclear derivative, [(Cp'Re)(2)(mu-S)(mu,eta(2)-SC(2)H(4)S)(mu,eta(1)-SC(2)H(4)S](2)Cl(2), 6. Complexes 4 and 6 have been characterized by X-ray diffraction studies. The electrochemical properties of the mononuclear Re=S derivative, 4, are compared with those of Re=O and Re=NR analogues.     

Automated carbohydrate synthesis to drive chemical glycomics

This feature article describes the development of the first automated solid-phase oligosaccharide synthesizer. A series of chemical challenges had to be addressed to accomplish this breakthrough and provide rapid access to oligosaccharides of biological significance. Accelerated synthesis of glycoconjugates promises to greatly impact the emerging field of glycobiology. Chemical glycomics uses synthetic carbohydrates and analogs to study their role in recognition, signal transduction pathways and other events of fundamental biomedical significance and shapes up to become the next major wave in biomedical research. The automated synthesis of a novel malaria vaccine candidate is discussed to illustrate the medical potential of chemical glycomics.     

A mathematical evaluation of dose-dependent PpIX fluorescence kinetics in vivo

The in vivo pharmacokinetics of protoporphyrin IX (PpIX) after administration of 5-aminolevulinic acid (ALA) cannot be described accurately by mathematical models using first-order rate processes. We have replaced first-order reaction rates by dose-dependent (Michaelis-Menten [MM]) reaction rates in a mathematical compartment model. Different combinations of first-order and dose-dependent reaction rates were evaluated to see which one would improve the goodness-of-fit to experimentally determined in vivo PpIX fluorescence kinetics as a function of concentration. The mathematical models that were evaluated are all based on a three-compartment model for drug distribution, conversion to PpIX and subsequent conversion to heme. Implementation of dose-dependent reaction rates improved the goodness-of-fit and enabled interpolation to other drug doses. For most data sets the time constant for delivery to the target cells turned out to be dose dependent. For all data sets the use of MM rates for the conversion of ALA to PpIX yielded better fits. The clearance of PpIX turned out to be a first-order process for all doses and types of administration. Fluorescence curves measured on a specific tissue type but obtained in different studies with different measurement techniques could be described with a single set of parameters.     

Benzolactams. 4. Reaction of 3',4'- or 4',5'-dialkoxy-substituted 1-(2'-Bromobenzyl)-2-ethoxycarbonyl-1,2,3,4-tetrahydroisoquinolines with alkyllithium. 1,2 and 1,4 additions of alkyllithium to benzolactams

Treatment of 1-(2'-bromo-3',4'-dialkoxybenzyl)-1,2,3, 4-tetrahydroisoquinoline carbamates, 1a,c, with excess alkyllithium gave 8-oxoberbines, 2a,c, which were successively attacked in situ with another molecule of alkyllithium to give 1,2 and/or 1,4 addition products. A primary alkyllithium, such as MeLi or BuLi, gave a 1,2 addition product, 8-methyleneberbine 9a or 8-butylideneberbine 3a. t-BuLi preferred 1,4 addition, followed by elimination of the alkoxy group, to give 9-tert-butyl-8-oxoberbine 6a or 7c. s-BuLi gave a mixture of 1,2 and 1,4 addition products, 1-[2'-(2' '-methylbutyryl)benzyl]-1,2,3,4-tetrahydroisoquinoline 4a and 9-s-butyl-8-oxoberbine 5a. Similar treatments of carbamate 1b having no alkoxy group at its 3' position gave 1,2 addition products, 8-butylideneberbine 3b, 1-[2'-(2' '-methylbutyryl)benzyl]-1,2,3, 4-tetrahydroisoquinoline 4b, and 1-(2'-pivaloylbenzyl)-1,2,3, 4-tetrahydroisoquinoline 6b, in all cases. Reactions of 1a with s-BuMgCl and isoPrMgCl also gave the 1,4 adduct, 5a, and its 9-isoPr analogue, 12a. Treatment of 9a with excess NaBH(4) in AcOH gave (+/-)-coralydine (10b).