High resolution 1H NMR structural studies of sucrose octaacetate in supercritical carbon dioxide

High pressure (HP), high resolution (HR), proton nuclear magnetic resonance (1H NMR) spectroscopy has been utilized for the first time to investigate the solution structure of a carbohydrate based system, sucrose octaacetate (SOA), in supercritical CO2. The studies indicate that the average solution state conformation of the alpha-D-Glucopyranosyl ring of SOA in scCO2 medium is consistent with the 4C1 chair form, while the beta-D-fructofuranosyl ring adopts an envelope conformation. The investigations also suggest that scCO2 is a promising medium to study the solution structure and conformation of acetylated sugar systems. Spectral manifestations of a specific interaction between the acetate methyl protons and CO2 molecules are also presented.     

Polyhydroxybutyrate production from carbon dioxide by cyanobacteria

Genetic characterization and enhancement of polyhydroxybutyrate (PHB) accumulation in cyanobacteria were investigated for efficient PHB production from CO₂. The genome DNAs in the PHB-accumulating strains Synechococcus sp. MA19 and Spirulina platensis NIES46 retained the highly homologous region to phaC of Synechocystis PCC6803, whereas low homology was detected in the nonaccumulating strains Synechococcus sp. PCC7942 and Anabaenacylindrica NIES19. Synechococcus sp. MA19, which accumulates PHB up to 30% of dry cell weight from CO₂ as the sole carbon source, was mutated by insertion of transposon Tn5 to enhance the PHB accumulation. Genetic and physiological analysis of the mutant indicated that decreased phosphotransacetylase activity could trigger an increase of acetyl coenzyme A leading to enhancement of PHB accumulation. PHB synthase in Synechococcus sp. MA19 was probably attached to thylakoid membrane since PHB granules were associated with pigments. A genetically engineered cyanobacteria retaining soluble PHB synthase from Ralstonia eutropha accumulated pigment-free PHB granules, which is an advantage for the purification of PHB.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Whole-molecule calculation of log p based on molar volume, hydrogen bonds, and simulated 13C NMR spectra

The prediction of Log P is usually accomplished using either substructure or whole-molecule approaches. However, these methods are complicated, and previous whole-molecule approaches have not been successful for the prediction of Log P in very complex molecules. The observed chemical shifts in nuclear magnetic resonance (NMR) spectroscopy are related to the electrostatics at the nucleus, which are influenced by solute-solvent interactions. The different solvation effects on a molecule by either water or methanol have a strong effect on the NMR chemical shift value. Therefore, the chemical shift values observed in an aqueous and organic solvent should correlate to Log P. This paper develops a rapid, objective model of Log P based on molar volume, hydrogen bonds, and differences in calculated 13C NMR chemical shifts for a diverse set of compounds. A partial least squares (PLS) model of Log P built on the sum of carbon chemical shift differences in water and methanol, molar volume, number of hydrogen bond donors and acceptors in 162 diverse compounds gave an r2 value of 0.88. The average r2 for 10 training models of Log P made from 90% of the data was 0.87+/-0.01. The average q2 for 10 leave-10%-out cross-validation test sets was 0.87+/-0.05.     

Activation of the pre-supplementary motor area but not inferior prefrontal cortex in association with short stop signal reaction time – an intra-subject analysis

Background  

Our previous work described the neural processes of motor response inhibition during a stop signal task (SST). Employing the race model, we computed the stop signal reaction time (SSRT) to index individuals' ability in inhibitory control. The pre-supplementary motor area (preSMA), which shows greater activity in individuals with short as compared to those with long SSRT, plays a role in mediating response inhibition. In contrast, the right inferior prefrontal cortex (rIFC) showed greater activity during stop success as compared to stop error. Here we further pursued this functional differentiation of preSMA and rIFC on the basis of an intra-subject approach.     

Phosphotransacetylase as a key factor in biological production of polyhydroxybutyrate

Phosphotransa cetylase (Pta) catalyzes the reversible conversion of, acetyl-coenzyme A (CoA) to acetyl phosphate. Polyhydroxybutyrate (PHB) synthase and accumulation were compared between a Pta-deficient mutant and the wild-type Escherichia coli, which were transformed with pAE100, coding for 3-ketothiolase, NADPH-dependenta cetoacetyl-CoA reductase, and PHB synthase from Ralstonia eutropha. During the growth period, PHB synthase activity in the Pta-deficient mutant was lower than that in the wild type. PHB accumulation in the Pta-deficient mutant, however, was higher than that in wild-type cells grown in Luria-Bertani (LB) medium containing 1% glucose (high C:N ratio). The Pta-deficient mutant showed PHB accumulation even in LB medium (low C:N ratio), whereas wild-type cells showed no PHB accumulation. These data suggest the activation of PHB synthase by acetyl phosphate that is synthesized by Pta. A decrease in Pta activity probably causes some increase in acetyl-CoA as substrate for the PHB synthesis pathway, resulting in increased PHB accumulation.