Critical impeller speed for solid suspension in turbine agitated contactors

The present study in solid-liquid contactors, an attempt has been made to calculate the minimum/critical impeller speed required for complete suspension of solids. A new correlation, involving Reynolds number, modified Froude number, along with the agitation characteristics is proposed. The effect of impeller geometry as well as impeller clearance are clearly established for 6-blade (flat) turbine agitated contactors.List of Symbols B Solid weight fraction (%) - c Clearance of the impeller from the tank bottom (m) - d _P Average particle size(m) - d _R Impeller diameter (m) - d _T Vessel diameter (m) - g Acceleration due to gravity m/sec₂ - N _cs Critical impeller speed (S^–1) Greek Letters Kinematic viscosity m²/sec - _L Density of liquid kg/m³ - _S Density of solid kg/m³ - Density difference between solid and liquid kg/m³     

Intragenic duplication and divergence in the spectrin superfamily of proteins

Many structural, signaling, and adhesion molecules contain tandemly repeated amino acid motifs. The alpha-actinin/spectrin/dystrophin superfamily of F-actin-crosslinking proteins contains an array of triple alpha-helical motifs (spectrin repeats). We present here the complete sequence of the novel beta-spectrin isoform beta(Heavy)- spectrin (beta H). The sequence of beta H supports the origin of alpha- and beta-spectrins from a common ancestor, and we present a novel model for the origin of the spectrins from a homodimeric actin-crosslinking precursor. The pattern of similarity between the spectrin repeat units indicates that they have evolved by a series of nested, nonuniform duplications. Furthermore, the spectrins and dystrophins clearly have common ancestry, yet the repeat unit is of a different length in each family. Together, these observations suggest a dynamic period of increase in repeat number accompanied by homogenization within each array by concerted evolution. However, today, there is greater similarity of homologous repeats between species than there is across repeats within species, suggesting that concerted evolution ceased some time before the arthropod/vertebrate split. We propose a two-phase model for the evolution of the spectrin repeat arrays in which an initial phase of concerted evolution is subsequently retarded as each new protein becomes constrained to a specific length and the repeats diverge at the DNA level. This evolutionary model has general applicability to the origins of the many other proteins that have tandemly repeated motifs.      

Comparisons of the molecular evolutionary process at rbcL and ndhF in the grass family (Poaceae)

We examine rate heterogeneity among evolutionary lineages of the grass family at two plasmid loci, ndhF and rbcL, and we introduce a method to determine whether patterns of rate heterogeneity are correlated between loci. We show both that rates of synonymous evolution are heterogeneous among grass lineages and that are heterogeneity is correlated between loci at synonymous sites. At nonsynonymous sites, the pattern of rate heterogeneity is not correlated between loci, primarily due to an aberrant pattern of rate heterogeneity at nonsynonymous sites of rbcL. We compare patterns of synonymous rate heterogeneity to predictors based on the generation time effect and the speciation rate hypotheses. Although there is some evidence for generation time effects, neither generation time effects nor speciation rates appear to be sufficient to explain patterns of rate heterogeneity in the grass plastid sequences.      

Steroid production in vitro by granulosa, theca, and luteal cells from goat ovaries

Basal progesterone (P4) production by isolated goat ovarian cells in vitro was in the order corpus luteum (CL) greater than granulosa (G) greater than theca (TH), while estradiol (E2) production was in the order TH greater than G greater than CL. In G cells, various concentrations (0.01 to 100 micrograms/ml) of luteinizing hormone (LH), human chorionic gonadotropin (hCG) and follicle-stimulating hormone (FSH) increased P4 and E2 secretion. Testosterone (T, 10(-9) to 10(-5) M) produced dose-dependent increases in P4 and E2 secretion. Testosterone and LH together had an additive effect on E2 secretion. The combined effect of the lower (less than 10(-6) M) concentrations of T and LH on P4 production was marginally higher than either agent alone, but the increase was statistically insignificant; at higher concentrations of T (10(-6) and 10(-5) M) in combination with LH, P4 secretion was similar to that with LH alone, but was significantly (p less than 0.01 and less than 0.001, respectively) less compared to that with T alone. Follicle-stimulating hormone and T together produced a synergistic effect on E2 and an additive effect on P4 production. In TH cells, a dose-dependent increase in P4 and E2 production was observed with LH and hCG, but the effect of FSH was not significant. Testosterone produced a dose-dependent increase in P4 and E2 secretion. Testosterone and LH together induced higher steroid production than either agent alone. However, the increase was not statistically significant compared to T alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chemistry of the alkali-labile lesion formed from iron(II) bleomycin and d(CGCTTTAAAGCG)

Two sets of products are formed from DNA upon treatment with Fe(II).bleomycin + O2. One set, which is believed to derive from a C-4' hydroperoxy derivative of the DNA deoxyribose moiety, includes the four possible base propenals, as well as DNA oligomers having deoxynucleoside 3'-(phosphoro-2"-O-glycolates) at their 3'-termini. The other set of products consists of free bases and alkali-labile lesions, the latter of which had not previously been characterized structurally. By use of the self-complementary dodecanucleotide d(CGCTTTAAAGCG) having a site modified by Fe-bleomycin three nucleotides from the 5'-end, it has been possible to characterize the alkali-labile product as a C-4' hydroxyapurinic acid. When the bleomycin-treated dodecanucleotide was treated with agents that effected decomposition of the alkali-labile lesion, products of the form CpGpx were obtained, and these proved useful for structural characterization of the alkali-labile lesion. Treatment with alkali produced CpGpx, where x was 2,4-dihydroxycyclopentenone. Alternatively, treatment with hydrazine provided a pyridazine derivative, and aqueous alkylamines led to formation of CpGp itself. The structures of all dinucleotides produced from the alkali-labile lesion were verified by direct comparison with authentic synthetic samples.     

Synthesis, characterization, and anti-bacterial efficacy of some novel cyclophane amide

Synthesis of macrocyclic di, tetra- and hexaamides with aza and oxy linkages has been achieved and the inhibitory activity of cyclophane amides against human pathogenic bacteria well documented.     

Cytotoxicity, redox cycling and photodynamic action of two naturally occurring quinones

Two naturally occurring anthraquinones, barleriaquinone-I (BQ-I) and barleriaquinone-II (BQ-II), extracted from Barleria buxifolia, are tested for their cytotoxic action by aerobic incubation with human breast adenocarcinoma cells (MCF7). Cytotoxicities, measured as LD(50) (50% inhibition of colony formation) values, show BQ-II to be more active than BQ-I. Electron paramagnetic resonance studies confirm that BQ-II is reductively activated by NADH:cytochrome c reductase to superoxide anion radical. Cyclic voltammetric studies show one quasi-reversible redox couple for both BQ-I and BQ-II. Also, aerobic solutions of both BQ-I and BQ-II on visible illumination generate reactive oxygen species. Formation of O*-2 is studied by both EPR spin trapping and SOD-inhibitable cytochrome c reduction techniques. BQ-I generates more singlet oxygen as evidenced from the photobleaching of N,N-dimethyl-4-nitrosoaniline.