Hajime Katano

Ion-transfer voltammetry at 1,6-dichlorohexane|water and 1,4-dichlorobutane|water interfaces.

The usefulness of 1,6-dichlorohexane (1,6-DCH) and 1,4-dichlorobutane (1,4-DCB) as organic solvent (O) for ion-transfer voltammetry at O|water (W) interface has been examined, and the results are compared with those with 1,2-dichloroethane (1,2-DCE). The width of potential window of the 0.1M tetraoctylammonium tetrakis(4-chlorophenyl)borate (O)|0.05M Li(2)SO(4) (W) interface increased in the sequence: O = 1,6-DCH > 1,4-DCB > 1,2-DCE. The voltammetric behavior of the transfer of various cations and anions at the 1,6-DCH|W and 1,4-DCB|W interfaces has been shown to be of reversible nature, and the midpoint potentials or the reversible half-wave potentials have been determined. The midpoint potentials of hydrophilic ions have also been determined by the analysis of anodic final rise or cathodic final decent of the voltammograms with the O|W interfaces, where the W contains a salt of the hydrophilic ion. Also, the effect of ion-pair formation in O on the midpoint potentials has also been discussed.

A stand-alone adenylation domain forms amide bonds in streptothricin biosynthesis

The streptothricin (ST) antibiotics, produced by Streptomyces bacteria, contain L-β-lysine ((3S)-3,6-diaminohexanoic acid) oligopeptides as pendant chains. Here we describe three unusual nonribosomal peptide synthetases (NRPSs) involved in ST biosynthesis: ORF 5 (a stand-alone adenylation (A) domain), ORF 18 (containing thiolation (T) and condensation (C) domains) and ORF 19 (a stand-alone A domain). We demonstrate that ST biosynthesis begins with adenylation of L-β-lysine by ORF 5, followed by transfer to the T domain of ORF 18. In contrast, L-β-lysine molecules adenylated by ORF 19 are used to elongate an L-β-lysine peptide chain on ORF 18, a reaction unexpectedly catalyzed by ORF 19 itself. Finally, the C domain of ORF 18 catalyzes the condensation of L-β-lysine oligopeptides covalently bound to ORF 18 with a freely diffusible intermediate to release the ST products. These results highlight an unusual activity for an A domain and unique mechanisms of crosstalk within NRPS machinery.

Charge dependence of one-electron redox potentials of Keggin-type heteropolyoxometalate anions

Abstract The two-step one-electron reduction processes of Keggin-type heteropolymolybdate and heteropolytungstate anions were investigated in several solvents using cyclic voltammetry. The slope of a plot of standard redox potentials E° against the ionic charge ΔE° was evaluated. It was found by theoretical considerations that ΔE° consists of a constant term independent of the solvent and another term comprising the charge-dependent component of the solvation energy. The difference between ΔE° for water and for 1,2-dichloroethane (1,2-DCE) was in good agreement with the value estimated from the transfer energies across the 1,2-DCE|water interface which were measured by ion transfer voltammetry. The values of ΔE° in various solvents cannot be explained by the Born-type electrostatic solvation energy, suggesting that the short-range interaction is important for the interaction of a Keggin anion with solvent molecules.

Voltammetric study of the transfer of heavy metal ions at the nitrobenzene | water interface assisted by 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine ☆

The transfer of heavy metal ions across the polarized nitrobenzene water interface assisted by 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (DPT) present in the nitrobenzene phase has been studied by normal pulse voltammetry and cyclic voltammetry. Voltammetric waves of Pb 2 + and Cd 2 + ions were reversible, whereas that of Zn 2 + ion was quasi-reversible. Voltammetric waves of Hg 2+ , Fe 2+ , and Co 2 + ions were more or less irreversible. The voltammogram of Cu 2 + ion showed a two-step wave. The dependence of the reversible half-wave potentials of Pb 2 + , Cd 2+ , and Zn 2 + ions on the concentration of DPT in the nitrobenzene phase reveals that their ion-transfer is assisted by the formation of 1:n metal-DPT complex(es) in nitrobenzene; Pb 2+ : n = 3 and 4 with the formal formation constants (log β n O ) of log β 3 O = 18.2 ± 0.1 and log β 4 O = 20.4 ± 0.1; Cd 2+ : n = 3 with log β 3 O = 27.1 ± 0.1; and Zn 2+ : n = 3 with log β 3 O = 36.0 ± 0.1, respectively.

Voltammetric study of the partition of amines between water and an organic solvent

Ion-transfer voltammetry of organic amines at an organic solvent/water (O/W) interface is studied. A theoretical equation of the current vs. potential curve of amines at a dropping electrolyte electrode is derived. The partition processes of both protonated and neutral forms of amine at O/W interface are taken into account. Kinetics of the protonation reaction between the neutral and protonated forms in W phase is also taken into account using the reaction layer theory. The theoretical prediction is in good agreement with the experimental results obtained with procaine at nitrobenzene/water interface using a dropping electrolyte electrode. Ion-transfer voltammetry and polarography is useful for studying the partition of amines between O and W phases in both neutral and protonated forms and the protonation reaction of amines in W phase as well.

Kinetic Analysis of Glucoamylase-Catalyzed Hydrolysis of Starch Granules from Various Botanical Sources

The kinetics of glucoamylase-catalyzed hydrolysis of starch granules from six different botanical sources (rice, wheat, maize, cassava, sweet potato, and potato) was studied by the use of an electrochemical glucose sensor. A higher rate of hydrolysis was obtained as a smaller size of starch granules was used. The adsorbed amount of glucoamylase on the granule surface per unit area did not vary very much with the type of starch granules examined, while the catalytic constants of the adsorbed enzyme (k 0) were determined to be 23.3±4.4, 14.8±6.0, 6.2±1.8, 7.1±4.1, 4.6±3.0, and 1.6±0.6 s−1 for rice, wheat, maize, cassava, sweet potato, and potato respectively, showing that k 0 was largely influenced by the type of starch granules. A comparison of the k 0-values in relation to the crystalline structure of the starch granules suggested that k 0 increases as the crystalline structure becomes dense.

Mass Spectrometry Imaging Analysis of Location of Procymidone in Cucumber Samples.

The localization of procymidone fungicide residue in cucumbers was investigated by mass spectrometry imaging (MSI). Cucumbers were grown, harvested, and then divided into two groups that were either sprayed or not sprayed with procymidone. The content of procymidone in the cucumbers was quantitatively determined by chromatographic techniques. Subsequently, the spatial distribution of procymidone was imaged by MSI. Procymidone reached the central part of the cucumbers following spraying compared with the control.

ε-Poly-l-Lysine Peptide Chain Length Regulated by the Linkers Connecting the Transmembrane Domains of ε-Poly-l-Lysine Synthetase

ABSTRACT ε-Poly-l-lysine (ε-PL), consisting of 25 to 35 l-lysine residues with linkages between the α-carboxyl groups and ε-amino groups, is produced by Streptomyces albulus NBRC14147. ε-PL synthetase (Pls) is a membrane protein with six transmembrane domains (TM1 to TM6) as well as both an adenylation domain and a thiolation domain, characteristic of the nonribosomal peptide synthetases. Pls directly generates ε-PL chain length diversity (25- to 35-mer), but the processes that control the chain length of ε-PL during the polymerization reaction are still not fully understood. Here, we report on the identification of Pls amino acid residues involved in the regulation of the ε-PL chain length. From approximately 12,000 variants generated by random mutagenesis, we found 8 Pls variants that produced shorter chains of ε-PL. These variants have one or more mutations in two linker regions connecting the TM1 and TM2 domains and the TM3 and TM4 domains. In the Pls catalytic mechanism, the growing chain of ε-PL is not tethered to the enzyme, implying that the enzyme must hold the growing chain until the polymerization reaction is complete. Our findings reveal that the linker regions are important contributors to grasp the growing chain of ε-PL.

Detection of Biopolymer ϵ-poly-L-lysine with Molybdosilicate Anion for Screening of Synthetic Enzymes

ϵ-Poly-L-lysine (ϵ-PL) exists as a cationic polymer in acidic solution. Yellow tetravalent 12-molybdosilicate ([SiMo12O40]4−) anion is formed in acidic solution containing and anions. By mixing the test ϵ-PL solution with the acidic − solution, the [SiMo12O40]4− anion associates with the cationic ϵ-PL to form yellow precipitate. The yellowness of the supernatant decreased with the initial concentration of ϵ-PL in the test solution due to the residual [SiMo12O40]4− anion. By addition of ascorbic acid to the supernatant, the residual [SiMo12O40]4− anion was reduced to blue molybdosilicate species. Thus the concentration of ϵ-PL in sample media can also be estimated by the blueness of the reaction mixture. The present method can be applied successfully to the screening of ϵ-PL-synthetase in culture media.

Effect of diffuse layer on the rate of electron transfer across an electrolyte vb electrolyte solution interface

Abstract The basic equations of the kinetics of electron transfer across an electrolyte vb electrolyte solution interface, in which the effect of diffuse layers on both sides is taken into account on a simplified model of electric double layer, are presented. Two ideal processes, an inner-layer rate-determining process and a diffuse-layer rate-determining process, are discussed. Theoretical predictions derived from the basic equations are discussed. Some abnormal transfer coefficients can be explained by the theory.