Aerobic and anaerobic microbial degradation of poly-beta-hydroxybutyrate produced by Azotobacter chroococcum

Food industry wastewater served as a carbon source for the synthesis of poly-β-hydroxybutyrate (PHB) by Azotobacter chroococcum. The content of polymer in bacterial cells grown on the raw materials reached 75%. PHB films were degraded under aerobic, microaerobic, and anaerobic conditions in the presence and absence of nitrate by microbial populations of soil, sludges from anaerobic and nitrifying/denitrifying reactors, and sediment from a sludge deposit site. Changes in molecular mass, crystallinity, and mechanical properties of PHB were studied. Anaerobic degradation was accompanied by acetate formation, which was the main intermediate utilized by denitrifying bacteria or methanogenic archaea. On a decrease in temperature from 20 to 5° C in the presence of nitrate, the rate of PHB degradation was 7.3 times lower. Under anaerobic conditions and in the absence of nitrate, no PHB degradation was observed, even at 11°C. The enrichment cultures of denitrifying bacteria obtained from soil and anaerobic sludge degraded PHB films for a short time (3–7 d). The dominant species in the enrichment culture from soil were Pseudomonas fluorescens and Pseudomonas stutzeri. The rate of PHB degradation by the enrichment cultures depended on the polymer molecular weight, which reduced with time during biodegradation.     

Derivatives of condensed pyrimidine,pyrazine, and pyridine systems

Pyrazinothiazines and the corresponding 3-hydroxy-3,4-dihydroquinoxalinothiazines, which are dehydrated to quinoxalinothiazines under the influence of acidic agents, are formed in the reaction of 2-mercapto-3-amino-5,6-dimethylpyrazine and 2-mercapto-3-aminoquinoxalines with - or -chloroacetoacetic esters in the presence of an equimolar amount of alkali. The IR, UV, and PMR spectra are presented.See [1] for communication XXXIV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 695–697, May, 1977.     

Mechanics and surface ultrastructure changes of poly(3-hydroxybutyrate) films during enzymatic degradation in pancreatic lipase solution

A study of in vitro biodegradation of poly(3-hydroxybutyrate) (PHB) in model conditions was performed. The porcine pancreatic lipase solutions at different concentrations in the two buffer systems (phosphate-buffered saline (PBS) and simulating body fluid (SBF)) were chosen as model biodegradation media. At first, optimal concentration of pancreatic lipase (0.25 mg/ml in PBS) was determined: in these media the decomposition of PHB films realized faster according to the data of gravimetric analysis. Differential scanning calorimetry showed an increase in the crystallinity of the samples (from 49% to 59%) after enzymatic degradation. These data are confirmed by method of nanoindentation, where the increase of the Young's modulus during the degradation (from 1.37 GPa to 4.4 GPa) was shown. This is due to the crystallization of the amorphous polymer component, and its decomposition and dissolving. During biodegradation three types of polymer ultrastructure changes were observed on the surfaces of the films: appearance of new lamellae, disappearance of lamellae and disintegration of lamellae into shorter fragments.     

Evaluation of power sums of roots for systems of non-algebraic equations in ℂ n

The goal of this paper is the evaluation of power sums of roots for systems of nonalgebraic equations consisting of entire or meromorphic functions of finite orders of growth. These power sums are connected with some residue integrals different from the Grothendieck residues. As an application we evaluate sums of certain multiple series.     

Modification of Ceria Nanoparticles by Accelerated Electron Irradiation

Physics of the Solid State - The luminescence and optical properties of ceria (CeO2) nanoparticles irradiated by accelerated electrons with an energy of 10 MeV are investigated in this work. CeO2...