Biomedical subjects

Toshiyuki Osakai

Publications and source records attributed to Toshiyuki Osakai.

14 recordsLinked to original sources

PubMed2006

Electrochemical extraction of proteins by reverse micelle formation.

The transfer of proteins by the anionic surfactant bis(2-ethylhexyl) sulfosuccinate (AOT) at a polarized 1,2-dichloroethane/water (DCE/W) interface was investigated by means of ion-transfer voltammetry. When the tetrapentylammonium salt of AOT was added to the DCE phase, the facilitated transfer of certain proteins, including cytochrome c (Cyt c), ribonuclease A, and protamine, could be controlled electrochemically, and a well-defined anodic wave for the transfer was obtained. At low pH values (e.g., pH 3.4), the anodic wave was usually well-separated from the wave for the formation of protein-free (i.e., unfilled) reverse micelles. The anodic wave for the protein transfer was analyzed by applying the theory for facilitated transfer of ions by charged ligands and then supplying information regarding the number of AOT anions reacting with one protein molecule and the total charge carried by the protein transfer. However, controlled-potential electrolyses performed for the transfer of Cyt c, which is red, revealed that the protein-AOT complexes were unstable in DCE and liable to aggregate at the interface when the pH of the W phase was 3.4. At pH 7.0, when formation of unfilled reverse micelles occurred simultaneously, the protein-AOT complexes appeared to be stabilized, probably via fusion with unfilled reverse micelles.

Animals↗

PubMed2006

Quantitative analysis of the structure-hydrophobicity relationship for di- and tripeptides based on voltammetric measurements with an oil/water interface.

The transfer of 18 di- and 27 tripeptides with un-ionizable amino acid side chains at a nitrobenzene/water (NB/W) interface was studied by cyclic voltammetry. The reversible half-wave potential (E(r)(1/2)), i.e., the midpoint potential could be accurately determined at pH 2 for both the facilitated and non-facilitated transfers, respectively, in the presence and absence of dibenzo-18-crown-6 (DB18C6) in NB. A multiple linear regression analysis was then performed for the E(r)(1/2) using the 'corrected' Dubois steric parameter for amino acid side chain substitutents. The result shows that the hydrophobicity of the peptides is governed not only by the intrinsic hydrophobicity of the peptide backbone and side chains, but also by the steric effects of side chain substituents. For the non-facilitated transfer of peptides, the steric effect of a bulky side chain is more significant at the N-terminus than at the C-terminus (and central for tripeptides). The more bulky the side chain at the N-terminus, the less hydrophobic the peptide becomes due to inhibition of the solvation of a terminal -NH(3)(+) group by organic solvents. For the facilitated transfer by DB18C6, however, the steric effect of a bulky side chain is the most significant at the central position of a tripeptide. A MOPAC calculation of optimized structures of DB18C6-peptide complexes has also shown that there is a notable steric hindrance between the central side chain and the benzene rings of DB18C6, which would reduce the 'apparent' hydrophobicity or transferability of the tripeptide.

Amino Acids, Branched-Chain↗

PubMed2005

Correlation between reduction potentials and inhibitory effects on Epstein-Barr virus activation by emodin derivatives.

As a continuation of studies using natural and synthetic products as cancer chemopreventive agents, we examined the reduction-oxidation potentials of hydroxylated emodin derivatives prepared from emodin in phosphate buffer at pH 7.2 using cyclic voltammetry. A significant correlation was found between the reduction potentials and number of the hydroxyl groups and the inhibitory effects of the hydroxylated emodin derivatives on Epstein-Barr virus early antigen activation. The electronic properties, i.e. LUMO energy and atomic charges of carbon at the 9-position (C(9)) and oxygen at the 11-position (O(11)), may also be useful for estimating the inhibitory effect on EBV-EA activation.

Antigens, Viral↗

PubMed2005

Structure-activity relations of azafluorenone and azaanthraquinone as antimicrobial compounds.

Antimicrobial activities of two azafluorenones, four 1-azaanthraquinones, five 2-azaanthraquinones, and one 2-azaquinone were tested. Several azaanthraquinones possessed broad, potent activity, while the azafluorenones demonstrated weak activity. The following structure-activity relationship was postulated: (1) activity decreased in the order 2-azaanthraquinones>1-azaanthraquinones>azafluorenones; and (2) a hydroxyl group at the peri-carbonyl group enhanced activity. In addition, correlations among reduction potential, hydrophobic parameter, and antimicrobial activity were discussed.

Anthraquinones↗

PubMed2004

Correlation between reduction potentials and inhibitory effects on Epstein-Barr virus activation of poly-substituted anthraquinones.

As a continuation of our studies using natural and synthetic products as cancer chemopreventive agents, we examined the reduction potentials of some poly-substituted anthraquinones in phosphate buffer at pH 7.2 by means of cyclic voltammetry. A definite correlation has been found between the reduction potentials and the inhibitory effects of the poly-substituted anthraquinones on Epstein-Barr virus early antigen activation. It has been further shown that the correlation can be enhanced by introducing log P as an additional parameter.

Anthraquinones↗

PubMed2004

Correlation of redox potentials and inhibitory effects on Epstein-Barr virus activation of 2-azaanthraquinones.

As a continuation of our studies using natural and synthetic products as cancer chemopreventive agents, we examined the standard redox potentials of some 2-azaanthraquinones in phosphate buffer at pH 7.2 by means of cyclic voltammetry. A definite correlation has been found between the redox potentials and the inhibitory effects of the 2-azaanthraquinones on Epstein-Barr virus early antigen (EBV-EA) activation. It has been further shown that the correlation can be enhanced by introducing an electronic properties, i.e. the atomic charges at the C5 and O12 atoms in the quinone skeleton ring and the HOMO energy as additional parameters.

Anthraquinones↗

PubMed2004

Product analysis of caffeic acid oxidation by on-line electrochemistry/electrospray ionization mass spectrometry.

On-line electrochemistry/electrospray ionization mass spectrometry (EC/ESI-MS) was developed using a microflow electrolytic cell. This technique was applied to electrochemical oxidation of caffeic acid (CAF) which is known to be a highly antioxidative agent. Effects of electrolytic potentials on ion intensities of product ions and on electrolytic currents were examined at different pHs. Dimer products were detected at electrolytic potentials of E = 0.7 V (vs. Ag/AgCl) and trimer products at 1.0 V at pH 9. Dimer products were distinguished from hydrogen-bonded complexes by MS/MS experiments. Hydrogen/deuterium exchange experiments determined the number of hydroxyl and carboxyl groups in the Dimers formed by electrolysis. The mechanism of oxidative polymerization of CAF is discussed with speculation as to the structure of the dimer product.

Antioxidants↗

PubMed2004

A true electron-transfer reaction between 5,10,15,20-tetraphenylporphyrinato cadmium(II) and the hexacyanoferrate couple at the nitrobenzene/water interface.

The ability of some metal complexes of 5,10,15,20-tetraphenylporphyrin (TPP) to give a voltammetric wave due to the heterogeneous electron transfer (ET) at a nitrobenzene (NB)/water (W) interface has been examined. The previously-proposed, electron-conductor separating oil-water (ECSOW) system has been successfully employed to find that the TPP complex with cadmium(II) added to NB gives a well-defined, reversible wave for the heterogeneous (i.e., "true") ET with the hexacyanoferrate couple in W. A digital simulation analysis has entirely excluded the possibility of the ion-transfer mechanism due to the homogeneous ET in W. The a.c. impedance method has then been used to determine the kinetic parameters including the standard rate constant k0 (= 0.10 cm M(-1) s(-1)) and the transfer coefficient alpha (= 0.53 at the half-wave potential). These values are in good agreement with those predicted from the Marcus theory with the assumption that the heterogeneous ET due to molecular collision occurs at the "sharp" NB/W interface.

Journal Article↗

PubMed2004

Photoinduced electron transfer of 5,10,15,20-tetraphenylporphyrinato zinc(II) at the polarized water/1,2-dichloroethane interface.

The photocurrent at the polarized water/1,2-dichloroethane (DCE) interface was successfully observed in the presence of a lipophilic sensitizer, 5,10,15,20-tetraphenylporphyrinato zinc (ZnTPP), in the organic phase. The photocurrent transient responses were apparently affected by the employed organic supporting electrolyte: tetrapenthylammonium tetraphenylborate (TPnATPB) or tris(tetraoctylammonium)tungstophosphate ((TOcA)3PW12O40). The photocurrent measured in the TPnATPB system exhibited rather slow responses associated with the ion transfer of photoproducts. On the other hand, the photoinduced heterogeneous electron transfer could be observed in the use of (TOcA)3PW12O40. The photocurrent intensity in the (TOcA)3PW12O40 system exhibited an apparent pH dependence and the photoreduction of hydrogen ions probably took place at the water/DCE interface. By analyzing the real and imaginary components of the photocurrent depending on the photoexcitation frequency, we roughly estimated the phenomenological rate constants of the product separation (k(ps)) and recombination (k(rec)) processes as log(k(ps)/s(-1)) = 1.5 +/- 0.2 and log(k(rec)/s(-1)) = 1.8 +/- 0.1, respectively.

Journal Article↗

PubMed2003

Correlation of redox potentials and inhibitory effects on Epstein-Barr virus activation of naphthoquinones.

As a continuation of our studies using natural and synthetic products as cancer chemopreventive agents, we examined the standard redox potentials of some naphthoquinones in phosphate buffer at pH 7.2 by means of cyclic voltammetry. A definite correlation has been found between the redox potentials and the inhibitory effects of the naphthoquinones on Epstein-Barr virus early antigen activation. It has been further shown that the correlation can be enhanced by introducing an electronic property, i.e. the atomic charges at the C(4) and O(10) atoms in the quinone skeleton ring as additional parameters.

Animals↗

PubMed2003

Temperature effect on the selective hydration of sodium ion in nitrobenzene.

The effect of the temperature on the co-extraction of water molecules with Na+ from water to nitrobenzene (NB) in the presence of dipicrylaminate ion has been studied. The number (n) of water molecules co-extracted with a Na+ ion, as measured by the Karl Fischer method, increased from 3.1 to 5.2 with increasing temperature (6-65 degrees C). This observation is in apparent contradiction to the expectation from simple thermodynamics because hydration is generally an entropically unfavorable process. Additional 1H NMR experiments for the selective hydration of Na+ in deuterated NB have confirmed that the association constants of water with Na+ indeed decrease with increasing temperature. On the other hand, however, it has been shown that water solubility into NB substantially increases with temperature. We conclude that the latter effect overwhelms the former unfavorable entropy effect, which results in a net increase of the n-value, as observed.

Journal Article↗

PubMed2002

Higher radical scavenging activities of polyphenolic antioxidants can be ascribed to chemical reactions following their oxidation.

Radical scavenging activities of 34 natural antioxidants were investigated from an electrochemical viewpoint. While the correlation of the oxidation potentials with their DPPH radical scavenging activities (represented by EC(50)) was not high (the correlation coefficient, r=0.73), the number of electrons n required for oxidation of an antioxidant, being obtained by continuous flow-column electrolysis with a slower flow rate (0.05 ml min(-1)), did show a good correlation with EC(50) (1/EC(50)=1.67n+0.50 with r=0.94). The n values of most polyphenols were increased with a decrease in the flow rate, while those of nonpolyphenols were invariant. This suggests that a slower subsequent chemical reaction(s) should be involved in the oxidation of polyphenols, whose higher radical scavenging activities seem to be ascribed to the chemical reactions. In this study, we have proposed a possible mechanism for the oxidation of polyphenols, in which the oxidizable -OH moieties are reproduced through an oxidative dimerization (or more highly polymerization).

Antioxidants↗

PubMed2002

Mechanistic study of the oxidation of caffeic acid by digital simulation of cyclic voltammograms.

The oxidation mechanism of caffeic acid (CAF) has been studied by means of cyclic voltammetry with the plastic formed carbon or glassy carbon electrode. CAF gives a well-developed two-electron reversible wave in acidic media, whereas it shows an irreversible behavior, i.e., a decrease of the rereduction peak, in less acidic media, suggesting that the oxidation of CAF follows an irreversible chemical reaction(s). Digital simulation analyses based on different oxidation mechanisms have been performed for the voltammograms obtained with the GC electrode in 1:1 (v/v) water:ethanol solutions. The results clearly show that the seeming two-electron oxidation of CAF occurs stepwise via one-electron processes, each of which follows an irreversible chemical reaction. It has also been suggested that the semiquinone radical as an intermediate of the one-electron oxidation should play an important role in the oxidation reaction. Evaluations of the rate constants for the chemical reactions have further suggested that the chemical reactions are dimerization reactions.

Caffeic Acids↗

PubMed2002

Complete electrolysis using a microflow cell with an oil/water interface.

A novel microflow cell with a nitrobenzene (NB)/water (W) interface was developed. A poly(tetrafluoroethylene) membrane filter was employed to prepare the NB/W interface which was formed over a thin channel (0.1 mm thick, 48 cm long) on a silver plate. The silver plate was electrolyzed in advance and served as an Ag/AgCl electrode for controlling the Galvani potential difference across the NB/W interface as well as detecting the current flowing through the interface. Using the microflow cell, complete electrolysis was accomplished for the interfacial transfer of a representative ion (i.e., tetramethylammonium ion). Thus, the present microflow cell was shown to be promising for coulometric (i.e., absolute quantitative) analysis of ions. Also, the microflow cell was shown to be useful for determination of the number of electrons for complicated charge-transfer processes at the oil/water interface.

Journal Article↗