Drying agents for water-free introduction of desorption solvent into a GC after on-line SPE of aqueous samples

Summary A small cartridge containing a drying agent is inserted between a solid phase extraction (SPE) column and a gas chromatograph (GC) to enable the introduction of water-free desorption solvent into the GC in on-line liquid chromatography (LC)-type enrichment of trace-level analytes from water samples. Some characteristics of the drying agents, such as their capacity to retain water and their re-usability after heating, have been tested. Possible interactions of the drying agent with the analytes, e.g., irreversible adsorption or catalyzed degradation, have been checked for a wide range of alkanes, alkylbenzenes chlorobenzenes, chlorophenols and phthalate esters. Using the on-line SPE-GC system with flame ionization detection (FID) and spiked samples containing different levels of the test compounds, the repeatability was shown to be satisfactory (6–17%). For 10 mL samples, the detection limits were lower than 0.1 g/L. The on-line SPE-GC-FID system here presented can be used for the repeated analysis of water samples without exchange of the dyring cartridge. The technique is applied to the analysis of tap water.     

Direct determination of sulfite in food samples by a biosensor based on plant tissue homogenate

In the work described here, a biosensor was developed for the determination of sulfite in food. Malva vulgaris tissue homogenate containing sulfite oxidase enzyme was used as the biological material. M. vulgaris tissue homogenate was crosslinked with gelatin using glutaraldehyde and fixed on a pretreated Teflon membrane. Sulfite was enzymatically converted to sulfate in the presence of the dissolved oxygen, which was monitored amperometrically. Sulfite determination was carried out by standard curves, which were obtained by the measurement of consumed oxygen level related to sulfite concentration. Several operational parameters had been investigated: the amounts of plant tissue homogenate and gelatin, percentage of glutaraldehyde, optimum pH and temperature. Also, some characterization studies were done. There was linearity in the range between 0.2 and 1.8 mM at 35 °C and pH 7.5. The results of real sample analysis obtained with the biosensor agreed well with the enzymatic reference method using spectrophotometric detection.     

A simple and simultaneous determination of acyclovir and ganciclovir in human plasma by high-performance liquid chromatography

A simple high-performance liquid chromatographic method was developed for the simultaneous determination of the therapeutic levels of acyclovir and ganciclovir in human plasma. After precipitation of plasma proteins with 6% perchloric acid, acyclovir and ganciclovir were simultaneously determined by reversed-phase chromatography with spectophotometric detection at 254 nm. The peak heights for acyclovir and ganciclovir were linearly related to their concentrations ranging from 0.063 to 2.080 micro g/mL. The recovery was 100.48-102.84% for acyclovir and 99.26-103.07% for ganciclovir. The intra- and inter-day relative standard deviation values were in the range 0.186-8.703% for acyclovir and 0.137-6.424% for ganciclovir. The detection limits for both compounds were 0.01 micro g/mL determined as the signal-to-noise ratio of 3. The present method is applicable to therapeutic monitoring during antiviral medication.     

合成2—芳氧基—5—氟—3H—4—嘧啶酮的新方法

由２－氰－５－氟－３Ｈ－４－嘧啶酮和取代苯酚钠在常压下反应，合成了７个未见文献报道的２－芳氧基－５－氟－３Ｈ－４－嘧啶酮化合物，产率７０￣８７％，结构经ＩＲ、＾１Ｈ ＮＭＲ和ＭＳ证实。     

Kinetics of radical telomerization of vinylidene fluoride in the presence of CCl3Z chain transfer agents

The kinetics of radical telomerization of VDF at 141 °C, initiated by ditertbutylperoxide, in the presence of three chain transfer agents (CTAs), HCCl₃, CCl₄ and CCl₃Br, are presented. The values of the chain transfer constants were assessed as 35, 0.25 and 0.06 at 141 °C for CCl₃Br, CCl₄ and HCCl₃, respectively. The values of the degree of polymerization (DP_n) were obtained for each CTA and were compared for the same CTA concentration. Hence, CCl₃Br behaved as an efficient CTA towards VDF and usually afforded the monoadduct selectively, but in certain conditions the VDF diadduct can also be produced. In contrast, HCCl₃ was not so efficient since a polymeric structure was identified as the major product.     

Multiple binding modes of the camptothecin family to DNA oligomers

The binding constants of camptothecin, topotecan and its lactone ring-opened carboxylate derivative to DNA octamers were measured by UV and NMR spectroscopy. The self-association of topotecan (TPT) was also measured. The carboxylate form of TPT binds in the same way as the lactone, but more weakly. Titration of TPT into d(GCGATCGC)2 shows a preferred location stacked onto the terminal G1 base. However, the intermolecular NOEs cannot be reconciled with a single conformation of the complex, and suggest a model of a limited number of conformations in fast exchange. MD calculations on four pairs of starting structures with TPT stacked onto the G1-C8 base pair in different orientations were therefore performed. The use of selected experimental "docking" restraints yielded ten MD trajectories covering a wide conformational space. From a combination of calculated free energies, NOEs and chemical shifts, some of the structures produced could be eliminated, and it is concluded that the data are consistent with two major families of conformations in fast exchange. One of these is the conformation found in a crystal of a TPT/DNA/topoisomerase I ternary complex [Proc. Natl. Acad. Sci. USA 2002, 99, 15 387-15 392].     

Relative Abundance of Alpha-Amylase/Trypsin Inhibitors in Selected Sorghum Cultivars

Sorghum is of growing interest and considered as a safe food for wheat related disorders. Besides the gluten, α-amylase/trypsin-inhibitors (ATIs) have been identified as probable candidates for these disorders. Several studies focused on wheat-ATIs although there is still a lack of data referring to the relative abundance of sorghum-ATIs. The objective of this work was therefore to contribute to the characterization of sorghum ATI profiles by targeted proteomics tools. Fifteen sorghum cultivars from different regions were investigated with raw proteins ranging from 7.9 to 17.0 g/100 g. Ammonium bicarbonate buffer in combination with urea was applied for protein extraction, with concentration from 0.588 ± 0.047 to 4.140 ± 0.066 mg/mL. Corresponding electrophoresis data showed different protein profiles. UniProtKB data base research reveals two sorghum ATIs, {"type":"entrez-protein","attrs":{"text":"P81367","term_id":"3913899","term_text":"P81367"}}P81367 and {"type":"entrez-protein","attrs":{"text":"P81368","term_id":"3913900","term_text":"P81368"}}P81368; both reviewed and a targeted LC–MS/MS method was developed to analyze these. Quantifier peptides ELAAVPSR ({"type":"entrez-protein","attrs":{"text":"P81367","term_id":"3913899","term_text":"P81367"}}P81367) and TYMVR ({"type":"entrez-protein","attrs":{"text":"P81368","term_id":"3913900","term_text":"P81368"}}P81368) were identified and retained as biomarkers for relative quantification. Different reducing and alkylating agents were assessed and combination of tris (2 carboxyethyl) phosphine/iodoacetamide gave the best response. Linearity was demonstrated for the quantifier peptides with standard recovery between 92.2 and 107.6%. Nine sorghum cultivars presented up to 60 times lower ATI contents as compared to wheat samples. This data suggests that sorghum can effectively be considered as a good alternative to wheat.     

Actin-binding marine macrolides: total synthesis and biological importance

Marine organisms produce a fascinating range of structurally diverse secondary metabolites, which often possess unusual and sometimes unexpected biological activities. This structural diversity makes these marine natural products excellent molecular probes for the investigation of biochemical pathways. Recently, a number of novel and stereochemically complex macrolides, having a large macrolactone (22- to 44-membered) ring, that interact with the actin cycloskeleton have been isolated from different marine sources. Actin, like tubulin, is a major component of the cytoskeleton and has important cellular functions. Although the details of these interactions are still under investigation, these marine macrolides are becoming increasingly important as novel molecular probes to help elucidate the cellular functions of actin. Owing to their potent antitumor activities, these compounds, for example the aplyronines, also have potential for preclinical development in cancer chemotherapy. Their appealing molecular structures, with an abundance of stereochemistry, and biological significance, coupled with the extremely limited availability from the marine sources, have stimulated enormous interest in the synthesis of these compounds. This review summarizes the biological properties of these unusual marine natural products and features the recently completed total syntheses of swinholide A, scytophycin C, aplyronine A, mycalolide A--all of these being potent cytotoxic agents that target actin--and a diastereoisomer of ulapualide A. Rather than detailing each individual step of these multistep total syntheses, the different synthetic strategies, key reactions, and methods adopted for controlling the stereochemistry are compared.     

An experimental and theoretical study of the Cp2VO2CO: use of 13CO3(2-) for structure investigation of d1-metallocene complexes

EPR study has shown that the anticancer agent vanadocene dichloride (Cp2VCl2) interacts with carbonate contained in physiological solutions. Chelate complex Cp2VO2CO (|A(iso)(51V)| = 175.1 MHz, g(iso) = 1.9861) is the only paramagnetic species formed in the range about the physiological pH (5.5-11.0). The super-hyperfine coupling (|a(iso)(13C)| = 24.1 MHz) was evidenced at measurements using 13C labelled carbonate. The structure of carbonate complex was validated by comparison of observed and theoretical calculated HFC tensors (at the density functional level of theory).