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We examined the partition of two amines, procaine and metoprolol, in ionic and charge-neutral forms between organic solvent (O) 1,2-dichloroethane and water (W) phases, each of which contained a common ion, [(C n F 2n+1 SO 2 ) 2 N] − , as tetrabutylammonium and Li + salts, respectively, to control the potential difference at the O|W interface, Δ O W ϕ. The interfacial system would be useful in the study of the partitioning of ionic species, which depends on Δ O W ϕ. With different pH levels, the dependence of the distribution ratio on Δ O W ϕ satisfied the prediction from the theoretical equation, giving the formal potentials for the transfer of the ionic forms at the O|W interface. We also examined the partition of nourseothricin, a mixture of streptothricin antibiotics with different sizes of lysine oligomers. They would exist as di-, tri-, tetra- and pentavalent cations in fully protonated forms. The distribution ratio for each ionic species could be determined simultaneously using an HPLC technique. The dependence of the distribution ratio on Δ O W ϕ for each species also satisfied the prediction, giving their formal potentials. Therefore, the present interfacial system can be applied when both ionic and charge-neutral species are partitioned and when the sample is of low purity or is a mixture. [ABSTRACT FROM AUTHOR]

Ion-transfer reactions at the interface between fluorous solvent 1,1,1,2,3,4,4,5,5,5-decafluoropentane (DFP) and water (W) were investigated voltammetrically. Within the potential window at the DFP | W interface, various non-fluorinated ions, including tetraphenylarsonium and tetraphenylborate, and fluorinated ions, including fluorocomplex and perfluoro- n -alkanoate ions, gave reversible voltammetric waves for their ion transfer across the DFP | W interface. Based on the tetraphenylarsonium-tetraphenylborate assumption, the formal potentials of their ion transfer could be determined in terms of the Galvani potential difference. Also, formal potentials for the transfer of bis(perfluoroalkanesulfonyl)imide ions at the DFP | W interface were determined potentiometrically. The formal Gibbs energies for the transfer of ions from DFP to W, which would provide the criteria necessary for evaluating the fluorophilicity/hydrophilicity of ions were calculated from the formal potentials, and were compared with the transfer energies from 1,2-dichloroethane to W and those from the organic solvent to DFP, as quantitative scales of the ions' lipophilicity/hydrophilicity and fluorophilicity/lipophilicity. [ABSTRACT FROM AUTHOR]

We present the availability of a fluorous solvent, 1,1,1,2,3,4,4,5,5,5-decafluoropentane (C5F10), for the non-aqueous medium in liquid-liquid electrochemistry. The solvent is immiscible, and forms stable interface with water (W). The solvent dissolved a high concentration of a hydrophobic electrolyte, tetrabutylammonium bis(nona fluorobutanesulfonyl)imide (TBABNSI), and the TBABNSI (C5F10) solution gave a high conductivity. The TBABNSI (C5F10)| LiCl (W) interface gave a polarizable potential window. Within the potential window, tetramethylammonium ion gave a reversible voltammetric wave due to its transfer across the C5F10 | W interface. The potential window became wider by replacement of the supporting electrolytes in C5F10- and W-phases. The results indicate that various ion-transfer reactions at the C5F10 | W interface can be studied voltammetrically. [ABSTRACT FROM AUTHOR]

Abstract: The formation of 18-molybdopyrophosphate anion has been studied to develop a simple and rapid assay of the enzymatic reaction involving . By the addition of anion to an acidic acetonitrile–water solution containing anion, the colorless Mo(VI) solution immediately became yellow due to the formation of 18-molybdopyrophosphate anion. The absorbance of the mixture at, for example, 450nm was proportional to the analytical concentration of anion. Although the test Mo(VI) solution remained colorless by the addition of AMP, it gradually turned to yellow by ATP. The undesired color development is attributed to the formation of a yellow molybdophosphate species accompanied by the dissociation of from the unstable ATP molecule. However, the color development became much slower when ethylenediaminetetraacetic acid was added into an assay mixture, where ATP may form a kinetically stable species. Thus, anion can be determined spectrophotometrically in the enzymatic reaction mixture containing ATP. By the addition of ascorbic acid, the yellow mixture turned to blue due to the reduction of the molybdopyrophosphate anion. Thus, anion can be detected colorimetrically by the blueness. The spectrophotometric and colorimetric methods could be applied advantageously to the assay of acetyl-CoA synthetase. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: Theoretical equations of ac-voltammetric current or the equivalent admittance and/or impedance of the electron transfer reaction between a redox couple of A species, ARED and AOX, in organic (O) phase and another redox couple of B species, BOX and BRED, in aqueous or water (W) phase at the O∣W interface: ARED(O)+BOX(W)=AOX(O)+BRED(W) are derived when the electron transfer reaction is dc-voltammetric-reversible. The theoretical equations are discussed with reference to the mechanisms by which the electron transfer reaction may take place at the interface, that is, either by the heterogeneous electron transfer reaction mechanism at the interface or by the mechanism in which the homogeneous electron transfer reaction is associated with the ion transfer across the interface. [Copyright &y& Elsevier]

Abstract: The electron transfer reaction between bis(phthalocyaninato)lutetium(III) ([Lu(pc)2]0) in 1,2-dichloroethane (1,2-DCE) and hexacyanoferrate(II/III) redox couple ([Fe(CN)6]4−/3−) in water (W) at the interface was studied by the use of normal pulse voltammetry and ac-voltammetry. The ac-voltammetric results have reconfirmed that the electron transfer reaction between [Lu(pc)2] in 1,2-DCE and [Fe(CN)6]4−/3− in W takes place by way of the heterogeneous electron transfer at the interface, but not by the homogeneous electron transfer reaction associated with the ion transfer of redox species across the interface. The kinetic parameters of the heterogeneous electron transfer reaction at the interface were determined. [Copyright &y& Elsevier]

The article studies the kinetics of glucoamylase-catalyzed hydrolysis of starch granules from six different botanical sources such as rice, wheat, maize, cassava, sweet potato and potato using an electrochemical glucose sensor. According to the authors, a higher rate of hydrolysis was obtained as a smaller size of starch granules was used. The authors also present a comparison of the catalytic constants of the adsorbed enzyme in relation to the crystalline structure of the starch granules.

Abstract: An amperometric biosensor for the detection of cellobiose has been introduced to study the kinetics of enzymatic hydrolysis of crystalline cellulose by cellobiohydrolase. By use of a sensor in which pyrroloquinoline quinone-dependent glucose dehydrogenase was immobilized on the surface of electrode, direct and continuous observation of the hydrolysis can be achieved even in a thick cellulose suspension. The steady-state rate of the hydrolysis increased with increasing concentrations of the enzyme to approach a saturation value and was proportional to the amount of the substrate. The experimental results can be explained well by the rate equations derived from a three-step mechanism consisting of the adsorption of the free enzyme onto the surface of the substrate, the reaction of the adsorbed enzyme with the substrate, and the liberation of the product. The catalytic constant of the adsorbed enzyme was determined to be 0.044±0.011s−1. [Copyright &y& Elsevier]

Abstract: The electron transfer (ET) reaction between bis(cyclopentadienyl)iron(II) ([FeII(C5H5)2]) in 1,2-dichloroethane (1,2-DCE) and in nitrobenzene (NB) and hexacyanoferrate redox couple ([FeII/III(CN)6]4−/3−) in water (W) at the interface has been studied by use of normal-pulse voltammetry. The voltammetric results indicate that the ET reaction between [FeII(C5H5)2] in O (O=1,2-DCE or NB) and [FeII/III(CN)6]4−/3− in W takes place not by way of the heterogeneous ET at O|W interface but by the mechanism in which a homogeneous ET reaction between [FeII(C5H5)2] (partially distributed from O) and [FeIII(CN)6]3− takes place in W phase and the resultant [FeIII(C5H5)2]+ ion is responsible for the current passage across the interface. From the limiting current, the forward rate constants of the homogeneous ET reaction: [Fe(C5H5)2]+[Fe(CN)6]3− =[Fe(C5H5)2]+ +[Fe(CN)6]4− in W phase, , were determined to be (3.2±2.0)×1010 M−1 s−1 and (2.0±1.3)×1010 M−1 s−1 with the 1,2-DCE|W (1.5M Li2SO4) and NB|W (1.5M Li2SO4) interfaces, respectively. These values are in the order of the rate constant of diffusion-controlled bimolecular reaction in solution. Also, the formal (standard) potentials of the transfer of [Fe(C5H5)2]+ ion at the interface, , were determined to be −0.015±0.014V and −0.087±0.015V with the 1,2-DCE|W (1.5M Li2SO4) and NB|W (1.5M Li2SO4) interfaces, respectively. [Copyright &y& Elsevier]

Abstract: Theory of normal-pulse voltammetric current of electron transfer (ET) reaction at organic solvent(O)/water(W) interface between a redox couple of A species, ARED and AOX, in O phase and another redox couple of B species, BOX and BRED, in W phase has been discussed. ARED is supposed to be a neutral molecule and AOX a cation, whereas both BRED and BOX are supposed to be highly hydrophilic. Then, two kinds of the reaction mechanism, that is, (1) the heterogeneous ET reaction: ARED(O)+BOX(W)=AOX(O)+BRED(W) at the O/W interface producing the voltammetric current, and (2) the transfer of ARED(O) molecule from O to W phase across the interface, then the homogeneous ET reaction: ARED(W)+BOX(W)=AOX(W)+BRED(W) in W phase, followed by the transfer of AOX(W) cation from W to O phase producing the voltammetric current, are considered. Theoretical equations of normal-pulse voltammetric current of the ET reaction at O/W interface are derived under the assumptions (i) that the ET reaction is pseudo-monomolecular with respect to A species, (ii) that the partition of ARED molecule between O and W phases is highly biased to O phase, and (iii) that the rate constants of homogeneous ET reaction in W phase are sufficiently large. Application of the theoretical equations to investigate the mechanism of the ET reaction at O/W interface has been discussed. [Copyright &y& Elsevier]

Abstract: The electron transfer (ET) reaction between bis(butylcyclopentadienyl)iron(II) ([FeII(C5H4Bu)2]) in 1,2-dichloroethane (1,2-DCE) and the hexacyanoferrate redox couple ([FeII/III(CN)6]4−/3−) in water (W) at the 1,2-DCE∣W interface has been studied by use of normal pulse voltammetry and cyclic voltammetry. In normal pulse voltammetry, S-shaped current vs. potential curves with well-defined limiting currents attributable to the interfacial ET reaction were observed. The voltammetric results can be explained well by the theoretical equations [M. Senda, Rev. Polarogr. (Jpn), 49 (2003) 219; 50 (2004) 60] according to a so-called IT-mechanism, that is, the [FeII(C5H4Bu)2] molecule is transferred from the 1,2-DCE to the W phase across the interface, then the ET reaction takes place homogeneously in the W phase between [FeIII(CN)6]3−(W) and [FeII(C5H4Bu)2](W) to produce [FeII(CN)6]4−(W) and [FeIII(C5H4Bu)2]+(W), which is followed by the transfer of the [FeIII(C5H4Bu)2]+ ion from the W to the 1,2-DCE phase across the interface to give the voltammetric current. Experimental results from cyclic voltammetry are also explained well by the IT-mechanism. [Copyright &y& Elsevier]

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 0.1 M tetraoctylammonium tetrakis(4-chlorophenyl)borate (O)|0.05 M Li2SO4 (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. [Copyright &y& Elsevier]

The electron transfer reaction across the 1,6-dichlorohexane (1,6-DCH)|water (W) interface where bis(pentamethylcyclopentadienyl)iron(II/III) ([FeII/III(C5Me5)2]0/+) as the organic redox couple in 1,6-DCH is present in excess has been studied by cyclic voltammetry. The 1,6-DCH|W interface gave a potential window where the transfer of [FeIII(C5Me5)2]+ ion as well as that of [FeII(C5Me5)2]0 across the interface can be neglected. When hexaammineruthenium(III) and cyano complexes of iron protoporphyrin IX and microperoxidase-11, which do not transfer across the 1,6-DCH|W interface in the potential range tested, are present in W as the aqueous reactant, well-defined voltammetric waves due to the heterogeneous electron transfer have been observed within the potential window. The voltammetric waves can be assigned to reversible one-electron transfer controlled by diffusion of the aqueous redox couple in W. The reversible half-wave potentials are consistent with those predicted from simple voltammetric experiments with a Pt electrode. [Copyright &y& Elsevier]

Bacteria produce polycationic homopoly(amino acid)s, which are characterized by isopeptide backbones. Although the biological significance of polycationic homopoly(amino acid)s remains unclear, increasing attention has recently been focused on their potential use to achieve cellular internalization. Here, for the first time, we provide direct evidence that two representative bacterial polycationic isopeptides, ε-poly-l-α-lysine (ε-PαL) and ε-oligo-l-β-lysine (ε-OβL), were internalized into mammalian cells by direct cell-membrane penetration and then diffused throughout the cytosol. In this study, we used clickable ε-PαL and ε-OβL derivatives carrying a C-terminal azide group, which were enzymatically produced and then conjugated with a fluorescent dye to analyze subcellular localization. Interestingly, fluorescent proteins conjugated with the clickable ε-PαL or ε-OβL were also internalized into cells and diffused throughout the cytosol. Notably, a Cre recombinase conjugate with ε-PαL entered cells and mediated the Cre/loxP recombination, and ε-PαL was found to deliver a full-length IgG antibody to the cytosol and nucleus. Bacteria-derived polycationic homopoly(amino acid)s are reported for the first time to directly penetrate cell membrane and deliver proteins of interest into cells, representing a new type of cell penetrating peptides for intracellular delivery. [ABSTRACT FROM AUTHOR]

Seven new bis(μ-oxo)dimanganese complexes with Mn2(III , III) or Mn2(III , IV) oxidation states were prepared using quinoline- and isoquinoline-based tetraamine ligands. The structures of the ligands include ethylenediamine, trans-1,2-cyclohexanediamine and tripodal amine, bearing two or three nitrogen-containing heteroaromatics. Regardless of the skeleton and number of aliphatic nitrogen atoms in the ligands, quinoline complexes stabilize the Mn2(III , III) oxidation state, whereas, isoquinoline ligands afford Mn2(III , IV) complexes. A systematic comparison of the differences in structural parameters and redox potentials of a total of 14 complexes with a (μ-O)2Mn2 diamond core, which includes corresponding pyridine and quinoxaline derivatives as supporting ligands, highlights the distinct deviation of quinoline and tripodal amine motifs in this ligand series. [ABSTRACT FROM AUTHOR]

We describe a new colorimetric assay method using glucose oxidase (GOx) to detect ε-poly- l -lysine (εPL). This method uses εPL's remarkable effect of promoting the enzymatic reaction of GOx with ferricyanide ion. This reaction reduces ferricyanide ion to ferrocyanide ion, accompanied by a color change from yellow to colorless. In this colorimetric assay, the detection limit of εPL was estimated to be approximately 0.5 mg/L when purified εPL samples were used. εPL has usually been produced by a fermentation process using Streptomyces albulus species. The components of the culture broth showed interference effects against the assay method. However, due to the high sensitivity of the assay method for εPL, εPL could be detected in the culture broth without any pretreatment. The detectable concentration of εPL in the culture broth, c PL,ac , was estimated to be approximately 20 mg/L. By combining the Berlin blue reaction with this method, the c PL,ac was reduced to 10 mg/L. In light of the proposed method's simplicity and sensitivity, it could be useful for screening εPL synthetic enzymes and microorganisms. [ABSTRACT FROM AUTHOR]

Iron oxide-based nanoparticles (NP) were covalently modified with sinapic acid (SA) through a condensation reaction to assist the ionization of both large and small molecules. The morphology of SA-modified NPs (SA-NP) was characterized by transmission electron microscopy (TEM), and the modification of the NP surface with SA was confirmed using ultraviolet (UV) and infrared (IR) spectroscopy. The number of SA molecules was estimated to be 6 per NP. SA-NP-assisted laser desorption/ionization was carried out on small molecules, such as pesticides and plant hormones, and large molecules, such as peptides and proteins. A peptide fragment from degraded proteins was detected more efficiently compared with conventional methods. [ABSTRACT FROM AUTHOR]

The transfer of streptothricin antibiotics containing a β-lysine monomer (ST-F), trimer (ST-D), and tetramer (ST-C) at a polarizable nitrobenzene (NB) | water (W) interface was studied by cyclic voltammetry. Under acidic conditions, the streptothricins existed in fully protonated forms, as ST-F 2 + , ST-D 4 + and ST-C 5 + cationic species. Within the potential range tested, ST-D 4 + and ST-C 5 + ions gave reversible voltammograms due to their transfer across the NB | W interface. The formal potentials, Δ O W ϕ 0 S ’ T , of ST-D 4 + and ST-C 5 + ions were determined. In the presence of a neutral ligand (L), dibenzo-18-crown-6, in NB, ST-F 2 + , ST-D 4 + and ST-C 5 + ions gave reversible voltammograms due to their transfer assisted by the formation of ST-FL 2 2 + , ST-DL 4 4 + and ST-CL 5 5 + complexes with the ligand in NB. Using the Δ O W ϕ 0 S ’ T -values, association constants between the NH 3 + -groups of ST-D 4 + and ST-C 5 + ions and the crown ether in NB were determined. The association constants were in agreement with each other. By assuming that the association constant of ST-F 2 + was equal to those of the ST-D 4 + and ST-C 5 + ions, the Δ O W ϕ 0 S ’ T of the ST-F 2 + ion was estimated. Interestingly, the determined Δ O W ϕ 0 S ’ T -value was increasingly negative in the order of ST-F 2 + (~ 0.24 V) > ST-D 4 + (0.199 V) > ST-C 5 + (0.194 V), indicating that the lysine oligomer affected the phase-transfer characteristics of streptothricin. [ABSTRACT FROM AUTHOR]

Abstract: The transfer of a biopolymer, ε-poly-L-lysine (εPL), at a polarized nitrobenzene (NB) | water (W) interface was studied voltammetrically. Despite the polydispersity of sample (n =25–35, n being the degree of polymerization), an S-shaped current-potential curve with a well-defined limiting current was observed in normal pulse voltammogram for the transfer of εPL at the NB | W (pH 3.0) interface. In the W-phase, εPL would exist in the fully protonated form, and the limiting current can be explained by the diffusion of the polycationic εPL species. Also a pair of anodic and cathodic peak currents was observed by cyclic voltammetry. The midpoint potential was in agreement with the half-wave potential in the normal pulse voltammogram. The influence of pH and the supporting electrolyte anions in both phases on the voltammograms has been also studied. By the addition of dibenzo-18-crown-6 (DB18C6) to NB, the half-wave potential shifted to negative potentials. This can be interpreted as being due to the εPL-transfer facilitated by the formation of εPL-DB18C6 complex in NB. The concentration dependence of the half-wave potential can be explained by the formation of 1:n εPL-DB18C6 complex. The results suggest the applicability of the voltammetric technique to compare the phase-transfer characteristics of εPL and the derivatives. [Copyright &y& Elsevier]

The streptothricin (ST) antibiotics, produced by Streptomyces bacteria, contain L-?-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-?-lysine by ORF 5, followed by transfer to the T domain of ORF 18. In contrast, L-?-lysine molecules adenylated by ORF 19 are used to elongate an L-?-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-?-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. [ABSTRACT FROM AUTHOR]