Total synthesis of (+)-xyloketal D, a secondary metabolite from the mangrove fungus Xylaria sp.

(+)-Xyloketal D was prepared in a one-pot multistep domino reaction by heating optically active 5-hydroxy-4-methyl-3-methylenepentan-2-one (R) in toluene with 2,4-dihydroxyacetophenone. The absolute configuration of the natural product was confirmed by preparation of the starting enone from a lactone of established absolute configuration.     

Preliminary Study on the Effect of pH on Thermal Transformation of Some Diphasic Al2O3-SiO2 Gels

Diphasic Al₂O₃-SiO₂ gels have been synthesized by hydrolyzing ethyl orthosilicate at three different pH ranges in presence of colloidal boehmite. Result shows that dominant mullitization process are sensitive to pH of the gelation process. At highly acidic pH range, solid state reaction between corundum and cristobalite occurs, and develops liquid phase for mullite nucleation. At moderately acidic pH, nucleation and crystallization are most operative for nucleation in aluminosilicate matrix. In highly basic pH region, Al-Si spinel phase develops by incorporation of Si in aluminous phase as intermediary phase. Polymorphic transformation of it may be the cause of sudden mullitization. The changes in crystallization sequence in three distinct processes may be due to variation in the nature and size of silicic acid particle formed by hydrolysis and condensation of TEOS at different pH.     

A comparative study of solvent extraction of total petroleum hydrocarbons in soil

Three non-specific methods for the extraction of total petroleum hydrocarbons (TPH) from soil into organic solvent were compared. The techniques used for sample preparation were Soxhlet extraction, closed-vessel microwave-assisted extraction, and CEN shake extraction. The total concentrations of extracted compounds in the boiling point range of C10–C40 were determined by gas chromatography with flame ionization detection. The best recovery (99%) and repeatability (±3%) from standard oil mixtures were obtained with microwave-assisted extraction. However, the different extraction methods exhibited different behaviour when spiked soil samples were extracted. The best repeatability was obtained with CEN shake extraction (±6%) but the repeatability values for Soxhlet and microwave-assisted methods were quite high (>20%). However, the larger uncertainties of the latter extraction methods does not necessarily limit the applicability of these methods to the determination of petroleum hydrocarbons in soil, as in the assessment of soil contamination the expanded uncertainty of the result is usually not limited by analytical uncertainty, but rather by the uncertainty of the primary sampling stage. However, distinctive variation found in the chromatographic profiles illustrates that discretion should be obeyed when chromatograms obtained after application of different extraction methods on petroleum contaminated samples are to be used in the fingerprinting or age dating studies. Otherwise, misleading conclusions concerning the age of spillage could be drawn.     

Synthesis of (+)-zeylenone from shikimic acid

Starting from shikimic acid, the total synthesis of zeylenone was studied. The product was proved to be the (+)antipode of zeylenone through analysis and comparison of their respective spectra (including NMR, MS, IR and CD) and optical data. The absolute configuration of the natural product was thus determined to be (1S,2S,3R).     

Topological effect on MO energies,IV. The total π-electron energy ofS- andT-isomers

A novel general property of theS- andT-isomers (a concept which has been introduced and elaborated elsewhere^{1, 2}) of alternant hydrocarbons is demonstrated, namely that due to the HMO total -electron energy theS-isomer should always be more stable than theT-isomer. Some other classes of conjugated isomers are also constructed, for which similar inequalities are derived.

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Topologischer Effekt bei MO-Energien, 4. Mitt.: Die -Elektronen-Gesamtenergie vonS- undT-Isomeren

Zusammenfassung Es wird allgemein gezeigt, daß bei einemS-T-Isomerenpaar (beschrieben in^{1, 2}) eines alternierenden Kohlenwasserstoffes infolge der HMO -Elektronen-Gesamtenergie dasS-Isomere stets stabiler sein sollte als dasT-Isomere. Weitere Klassen konjugierter Isomere werden konstruiert und ähnliche Ungleichungen angegeben.

     

Quo Vadis total reflection X-ray fluorescence?

The multielement trace analytical method ‘total reflection X-ray fluorescence’ (TXRF) has become a successfully established method in the semiconductor industry, particularly, in the ultra trace element analysis of silicon wafer surfaces. TXRF applications can fulfill general industrial requirements on daily routine of monitoring wafer cleanliness up to 300 mm diameter under cleanroom conditions. Nowadays, TXRF and hyphenated TXRF methods such as ‘vapor phase decomposition (VPD)-TXRF’, i.e. TXRF with a preceding surface and acid digestion and preconcentration procedure, are automated routine techniques (‘wafer surface preparation system’, WSPS). A linear range from 10⁸ to 10¹⁴ [atoms/cm²] for some elements is regularly controlled. Instrument uptime is higher than 90%. The method is not tedious and can automatically be operated for 24 h/7 days. Elements such as S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, Sn, Sb, Ba and Pb are included in the software for standard peak search. The detection limits of recovered elements are between 1×10¹¹ and 1×10⁷ [atoms/cm²] depending upon X-ray excitation energy and the element of interest. For the determination of low Z elements, i.e. Na, Al and Mg, TXRF has also been extended but its implementation for routine analysis needs further research. At present, VPD-TXRF determination of light elements is viable in a range of 10⁹ [atoms/cm²]. Novel detectors such as silicon drift detectors (SDD) with an active area of 5 mm², 10 mm² or 20 mm², respectively, and multi-array detectors forming up to 70 mm² are commercially available. The first SDD with 100 mm² (!) area and integrated backside FET is working under laboratory conditions. Applications of and comparison with ICP-MS, HR-ICP-MS and SR-TXRF, an extension of TXRF capabilities with an extremely powerful energy source, are also reported.     

The American (USA) perspective six years after implementation of CLIA'88 (Federal) regulations

 On September 1, 1992 all testing sites in the United States were required to comply with the Clinical Laboratory Improvement Amendments of 1988 (CLIA'88). These regulations, based on both total quality management (TQM) and continuous quality improvement (CQI) principles, reshaped the environment for more than 90% of laboratories. CLIA'88 represented a revolutionary change by imposing universal, uniform regulations based on test complexity for all sites examining materials derived from the human body for the purpose of providing information for the diagnosis, prevention, or treatment of disease. CLIA'88 specifies minimum requirements for personnel, quality control, and proficiency testing (PT). In addition, laboratories are required to follow manufacturers' directions and comply with other specified good laboratory practices. PT is mandated for most of the frequently run analyses and quality assurance requirements integrate the principles of CQI as well as TQM into the regulatory process. Biannual inspection is integral to CLIA'88, however, laboratories can choose other federally approved ("deemed") professional organizations, such as the Commission on Office Laboratory Accreditation, the College of American Pathologists, or the Joint Commission on Accreditation of Healthcare Organization, having standards that meet or exceed those of CLIA'88. CLIA'88 has still not been finalized. This article discusses the impact and changes since CLIA's implementation in 1992. Received: 5 October 1998 · Accepted: 20 October 1998     

An iterative acetylene-epoxide coupling strategy for the total synthesis of longimicin C

Longimicin C, a naturally occurring annonaceous acetogenin possessing a C₂-symmetrical bis-THF moiety and a short hydrocarbon chain between its THF-containing region and a terminal γ-lactone, was synthesized for the first time. The total synthesis was successfully achieved by an iterative acetylene-epoxide coupling strategy. d-Mannitol was used to establish the bis-THF-containing segment, in which the additional stereochemistries were introduced by Sharpless dihydroxylations and intramolecular Williamson etherifications. Regioselective epoxide-openings by the appropriate terminal acetylenes allowed coupling and elaboration of all four fragments including the introduction of three essential hydroxyls into the proper sites of the target skeleton.     

细胞呼吸爆发的微量量热学研究

The heat production of Wistar rat polymorphonuclear leukocytes (PMN) was measured by an LKB 2277 Thermal Activity Monitor. When PMN were activited with phorbol-12-myristate13-acetate (PMA), the respiratory burst was recorded by greatly incr eased heat production. Experiment was also carred out in the present of the inhibitor, Total Flavonoids of Lycium Barbarum L. (TFL). The respiratory burst heat production peak was disappeared, but the heat production curve was higher than that of PMA because TFL increased the metabolic activities of PMN.     

Comparative evaluation of Fe(III) reducing power-based antioxidant capacity assays in the presence of phenanthroline, batho-phenanthroline, tripyridyltriazine (FRAP), and ferricyanide reagents

The chemical diversity of antioxidants in complex matrices such as plant extracts makes it difficult to separate and quantify antioxidants from these solutions. Therefore it is desirable to establish methods that can measure the total antioxidant capacity (TAC) levels directly from plant extracts. Iron(III)-based TAC assays, especially the most widely used FRAP (ferric-reducing antioxidant power), play an important role in this regard. However, many problems have been reported in the application of the FRAP assay, the most serious one being the incomplete oxidation of a number of antioxidants during the time protocol of the assay. Thus, six different ferric ion-based total antioxidant capacity (TAC) assays have been comparatively tested, modified, and improved so as to obtain more sensitive and precise results for complex mixtures, namely: 1,10-phenanthroline (o-phen) method (with incubation), batho-phenanthroline method (with incubation), original FRAP method, modified FRAP method (with incubation), original ferricyanide method, and modified ferricyanide method (with incubation). Two new assays in this regard (i.e., o-phen and batho-phen) have been established, and the existing assays (FRAP and ferricyanide) have been modified so as to let the oxidation reactions of antioxidants reach completion. The molar absorptivity for a variety of antioxidants was highest for modified FRAP, batho-phen, and original FRAP methods. The absorption maximum wavelength shifted batochromically to a higher extent for modified ferricyanide, FRAP, and batho-phen procedures, decreasing the possibility of interferences due to organics absorbing in the near-UV range of the visible spectrum where most antioxidant assays are performed. The linear concentration ranges were shown to be further extended and linear correlation coefficients improved with respect to the most widely used ferric-based assay, FRAP. Of the six assays tested and developed, only the modified ferricyanide procedure gave high intercept values and low addivitity of TAC values of constituents in complex mixtures, requiring further attention of method optimization. Thus, it was shown that the most widely used FRAP could be effectively modified, and o-phen, batho-phen, and ferricyanide methods constitute cheaper alternatives to FRAP under certain conditions, with partly improved molar absorptivity (and thus sensitivity) for antioxidants, lower intercept values (and higher precision), broader linear range (and higher flexibility), and better additivity of TAC values of antioxidant constituents in mixtures.