Selective quenching of tryptophanyl fluorescence in bovine serum albumin by the iodide ion

Modified Stern-Volmer equation is obeyed by bovine serum albumin (BSA)-iodide system showing selective quenching of tryptophanyl fluorescence of BSA. The fraction of accessible protein fluorescence is 0.56 and the effective Stern-Volmer constant is 290 M^-1 at pH 7.4 in 0.005 M phosphate buffer at 25°C. Collisional quenching is operative both in the BSA -I⁻¹ system and the model system, tryptophan-I⁻¹. It is supported by the observed relationship between the ratio of quenching rate constants (k _q ) and diffusion coefficients and alsok _q with bulk viscosity.     

Tobacco protein separation by aqueous two-phase extraction

Tobacco has long been considered as a host to produce large quantity of high-valued recombinant proteins. However, dealing with large quantities of biomass is a challenge for downstream processing. Aqueous two-phase extraction (ATPE) has been widely used in purifying proteins from various sources. It is a protein-friendly process and can be scaled up easily. In this paper, ATPE was studied for its applicability to recombinant protein purification from tobacco with egg white lysozyme as the model protein. Separate experiments with poly(ethylene glycol) (PEG)-salt-tobacco extract and PEG-salt-lysozyme were carried out to determine the partition behavior of tobacco protein and lysozyme, respectively. Two-level fractional factorial designs were used to study the effects of factors such as, PEG molecular mass, PEG concentration, the concentration of phase forming salt, sodium chloride concentration and pH, on protein partitioning. The results showed that, among the studied systems, PEG-sodium sulfate system was most suitable for lysozyme purification. Detailed experiments were conducted by spiking lysozyme into the tobacco extract. The conditions with highest selectivity of lysozyme over native tobacco protein were determined using a response surface design. The purification factor was further improved by decreasing the phase ratio along the tie line corresponding to the phase compositions with the highest selectivity. Under selected conditions the lysozyme yield was predicted to be 87% with a purification factor of 4 and concentration factor of 14. From this study, ATPE was shown to be suitable for initial protein recovery and partial purification from transgenic tobacco.     

Asymptotic null controllability of nonlinear perturbed systems

In this paper, sufficient conditions are obtained for the asymptotic null controllability of the system $$\dot x(t) = g(t,x(t)) + B(t,x(t))u(t) + f(t,x(t),u(t)).$$ The results are obtained by using the Leray-Schauder fixed-point theorem.     

Aqueous polymerization of ethyl acrylate initiated by ceric ion-reducing agent system in sulphuric acid medium

Kinetic study of aqueous polymerization of ethyl acrylate (EA) is carried out at 30 °C in dilute sulphuric acid medium by employing ammonium ceric sulphate–methyl ethyl ketone (MEK) as redox initiator system. The ceric ion consumption is found to be first order with respect to ceric ion and half order with respect to reducing agent concentrations. No complex formation between ceric ion and reducing agent is observed. The orders with respect to ceric ion, reducing agent and monomer concentrations are evaluated for the aqueous polymerization of EA by Ce(IV)–MEK redox initiator system, and are found to be 0.5, 0.5 and 1.4, respectively . The overall activation energy, E _overall, for aqueous polymerization of EA in the temperature region of 27–40°C is found to be 20.27 kJ/mol. A kinetic scheme for the aqueous polymerization of EA initiated by Ce(IV)–MEK redox initiator system is presented.This revised version was published online in June 2005 with corrections to figure legends as well as small corrections within text.     

Stereochemical preference of Candida parapsilosis ATCC 7330 mediated deracemization: E- versus Z-aryl secondary alcohols

The stereochemical preference of the biocatalyst, Candida parapsilosis ATCC 7330, was investigated with respect to the E/Z configuration in the deracemization and the asymmetric reduction of aryl secondary alcohols and prochiral ketones, respectively. The biocatalyst preferred the E-isomers over Z-isomers as substrates as evidenced from the experimental results of >99% ee and up to 86% isolated yield for E-secondary alcohols. The synthesis of enantiomerically pure E-4-phenylbut-3-ene-1,2-diol (ee >99%, isolated yield 86%) by whole cell mediated deracemization is reported here for the first time. The geometric preference of the enzymes was confirmed by using the cell free extract of this biocatalyst. Mechanistic insights using in silico studies showed that the E-isomers when located in the active site are favourably placed with respect to the catalytic triad (Ser-Tyr-Lys) for hydride transfer from NADPH.     

Delay-probability-distribution-dependent stability of uncertain stochastic genetic regulatory networks with mixed time-varying delays: An LMI approach

This paper investigates the delay-probability-distribution-dependent stability problem of uncertain stochastic genetic regulatory networks (SGRNs) with mixed time-varying delays. The information of the probability distribution of the time-delay is considered and transformed into parameter matrices of the transferred SGRNs model. Based on the Lyapunov–Krasovskii functional and stochastic analysis approach, a delay-probability-distribution-dependent sufficient condition is obtained in the linear matrix inequality (LMI) form such that delayed SGRNs are robustly globally asymptotically stable in the mean square for all admissible uncertainties. Finally a numerical example is given to illustrate the effectiveness of our theoretical results.     

Green synthesis of naphtho[2,3-f]quinolin-13-one and naphtho[2,3-a]acridin-1(2H)-one derivatives catalyzed by heteropoly acid supported montmorillonite K-10 clay

Herein, synthesis of a series of naphtho[2,3-f]quinolin-13-one and naphtho[2,3-a]acridin-1(2H)-one derivatives directly by one-pot multi-component reaction of 1,3-dicarbonyl compounds (1,3-indanedione/1,3-cyclohexanedione), 2-aminoantharacene/2-naphthylamine and various substituted aldehydes under solvent-free conditions using heteropoly-11-molybdo-1-vanadophosphoric acid supported on montmorillonite K-10 clay catalyst (10% PVMoK-10) is reported. The successful formation of naphtho[2,3-f]quinolin-13-one and naphtho[2,3-a]acridin-1(2H)-one derivatives was confirmed by various spectroscopic techniques. This study offers a green approach for the synthesis of novel quinolinone derivatives.     

Metal‐Free CH Bond Activation of Branched Aldehydes with a Hypervalent Iodine(III) Catalyst under Visible‐Light Photolysis: Successful Trapping with Electron‐Deficient Olefins

Direct acyl radical formation of linear aldehydes (RCH₂‐CHO) and subsequent hydroacylation with electron‐deficient olefins can be effected with various types of metal and nonmetal catalysts/reagents. In marked contrast, however, no successful reports on the use of branched aldehydes have been made thus far because of their strong tendency of generating alkyl radicals through the facile decarbonylation of acyl radicals. Here, use of a hypervalent iodine(III) catalyst under visible light photolysis allows a mild way of generating acyl radicals from various branched aldehydes, thereby giving the corresponding hydroacylated products almost exclusively. Another characteristic feature of this approach is the catalytic use of hypervalent iodine(III) reagent, which is a rare example on the generation of radicals in hypervalent iodine chemistry.     

Phytochemicals as Inhibitors of Bacterial Cell Division Protein FtsZ: Coumarins Are Promising Candidates

Naturally occurring phytochemicals with reported antibacterial activity were screened for their ability to inhibit the bacterial cell division protein Escherichia coli FtsZ. Among the representative compounds, coumarins inhibit the GTPase and polymerization activities of this protein effectively. Further screening with ten coumarin analogs we identified two promising candidates, scopoletin and daphnetin. The former is found to inhibit the GTPase activity of the protein in a noncompetitive manner. Docking of these coumarins with the modeled protein indicate that they bind to T7 loop, which is different from the GTP-binding site (active site), thereby supporting the experimental data. Lowest binding energy is obtained with scopoletin. 3D QSAR indicates the need for groups such as hydroxyl, diethyl, or dimethyl amino in the 7th carbon for enhanced activity. None of the coumarins exhibited cytotoxicity against NIH/3T3 and human embryonic kidney cell lines. The length of Bacillus subtilis increases in the presence of these compounds probably due to the lack of septum formation. Results of this study indicate the role of coumarins in halting the first step of bacterial cell division process.