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p. 556-570
Received: 7 November 2006 / Accepted: 7 December 2006 / Published: 18 December 2006
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| Download PDF Full-text (1557 KB) Abstract: Quantitative structure-activity relationships (QSARs) for benz[a]anthracene (BA)mutagens using 73 descriptors were searched. The mutagenicity data was obtained fromAmes assays for Mycobacterium vanbaalenii, Mycobacterium gilvum and Mycobacteriumflavescens strains. These data were fitted using a mutagenicity-cytotoxicity competitionmodel which defines the mutagenic potencies of BA metabolites, and include oxides,phenols, quinones, and dihydrodiols. The QSAR equations were derived using the moleculardescriptor set (charged partial surface area, spatial, thermodynamic and electronicdescriptors) and semi-empirical energetic and charge descriptors. Genetic functionapproximation was used to reduce and fit independent variables, including linear- andquadratic-based functions. Multiple QSAR equations were generated and a separate QSARequation was chosen and evaluated for each strain using conventional r2, F-test, and cross-validated r2. Each strain exhibited its own characteristic descriptors.
p. 571-589
Received: 20 November 2006 / Accepted: 14 December 2006 / Published: 18 December 2006
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| Download PDF Full-text (1417 KB) Abstract: The genome of T. caldophilus GK24 was recently sequenced and annotated as 14contigs, equivalent to 2.3 mega basepairs (Mbp) of DNA. In the current study, we identifieda unique 13.7 kbp DNA sequence, which included the endocellulase gene of T. caldophilusGK24, which did not appear to be present in the complete genomic sequence of the closelyrelated species T. thermophilus HB27 and HB8. Congo-red staining revealed a uniquephenotype of cellulose degradation by strain GK24 that was distinct from other closelyrelated Thermus strains. The results showed that strain GK24 is an aerobic, thermophilic,cellulolytic eubacterium which belongs to the group T. thermophilus. In order to understandthe mechanism of production of cellobiose in T. caldophilus GK24, a three-dimensionalmodel of the endocellulase, TcCel5A, was generated based on known crystal structures.Using this model, we carried out a flexible cellotetraose docking study.
p. 590-600
Received: 14 September 2006 / Accepted: 14 November 2006 / Published: 19 December 2006
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| Download PDF Full-text (173 KB) Abstract: Photochemical properties of the ionic liquid (RTIL) 1-butyl-3-methylimidazoliumhexafluorophosphate [bmim][PF6 ] and its binary mixed solutions with organic solvent(DMF and MeCN) were investigated by laser photolysis at an excitation wavelength of 355nm, using anthraquinone (AQ) as a probe molecule. It was indicated that the triplet excitedstate of AQ (3 AQ*) can abstract hydrogen from [bmim][PF6 ]. Moreover, along with thechange of the ratio of RTIL and organic solvent, the reaction rate constant changes regularly.Critical points were observed at volume fraction VRTIL = 0.2 for RTIL/MeCN and VRTIL =0.05 for RTIL/DMF. For both systems, before the critical point, the rate constant increasesrapidly with increasing VRTIL ; however, it decreases obviously with VRTIL after the criticalpoint. We conclude that the concentration dependence is dominant at lower VRTIL , while theviscosity and phase transformation are dominant at higher VRTIL for the effect of ionic liquidon the decay of rate constant.
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