Biomedical subjects

Kyohei Yamaguchi

Publications and source records attributed to Kyohei Yamaguchi.

4 recordsLinked to original sources

PubMed2005

Dynamic interaction between alkylammonium ions and beta-cyclodextrin by means of ultrasonic relaxation.

Ultrasonic absorption measurements in the frequency range from 0.8 to 220 MHz were carried out in aqueous solutions of pentylammonium chloride (PEACL) and hexylammonium chloride (HEACL) with beta-cyclodextrin (beta-CD) at pH approximately 7.2 and 25 degrees C. A single relaxational absorption was attributed to a perturbation of a chemical relaxation associated with the formation of a complex between beta-CD and the alkylammonium chlorides. The rate and equilibrium constants for the complexation reaction were determined from the concentration dependence of the relaxation frequency. Increasing the chain length of the alkylammonium ion led to an increase in the stability of the complex and slowed the exit rate of the ion from the beta-CD cavity. The standard volume change of the reaction was obtained from a maximum absorption per wavelength and was attributed to water molecules being expelled from the cavity with concomitant alkylammonium ion insertion.

Alkylation↗

PubMed2004

Ultrasonic relaxation due to inclusion complex of amino acid by beta-cyclodextrin in aqueous solution.

Ultrasonic absorption coefficients in the frequency range of 0.8-95 MHz were measured in aqueous solutions of L-methionine or L-norleucine (guest) in the presence and absence of beta-cyclodextrin (beta-CD, host) at 25 degrees C. A single relaxational absorption was observed only in the solutions containing the guest and host. The ultrasonic relaxation was attributed to a perturbation of a chemical equilibrium associated with an interaction between beta-CD and the amino acid to form the host-guest complex. The kinetic and thermodynamic parameters in the system of L-norleucine with beta-CD were determined from the concentration dependence of the relaxation frequency and the maximum absorption per wavelength. Because of the concentration independence of the relaxation frequency in L-methionine system with beta-CD, the equilibrium constant and the standard volume change of the complexation reaction were estimated first from the concentration dependence of maximum absorption per wavelength, and subsequently the rate constants were calculated with the help of the estimated equilibrium constant and the observed relaxation frequency. The results obtained in this study were compared with those for systems of beta-CD with other amino acids or alcohols having comparable hydrophobicity.

Absorption↗

PubMed2002

A cross-sectional survey of 32 workers exposed to hexahydrophthalic and methylhexahydrophthalic anhydrides.

The relation between exposure and sensitization or the appearance of symptoms of the eyes and airways was investigated in a cross-sectional study on 32 workers from a plant using epoxy resin with a mixture of hexahydrophthalic anhydride (HHPA) and methylhexahydrophthalic anhydride (MHHPA) as a hardener. The main component in the hardener was HHPA, and the geometric mean concentrations of HHPA in the workplaces were extremely low (<40 microg/m3) in recent years, compared to the Occupational Exposure Limit-Ceiling for phthalic anhydride (2 mg/m3). However, specific IgE antibody to HHPA was detected in serum from 8 (25%) out of the workers: of those, 5 workers experienced symptoms of the eyes and nose during work (group sensitized symptomatic (SS)) and 3 workers did not (group sensitized nonsymptomatic (SN)). The other 24 workers had no signs of sensitization and did not complain of work-related symptoms. Based on occupational history and anamnestic data, it was concluded that one subject in the SS group and all the subjects in the SN group had been sensitized by higher exposures in the past. The symptoms of 4 subjects in the SS group occurred only when carrying out short-time, particular tasks (15-30 min) a few times a day, such as the resin mixing procedures, manual application of the resin, or opening of ovens. High peak exposures were estimated to have occurred during the particular tasks. Our results suggest that short-time peak exposures may have a great impact on the development of specific IgE or work-related symptoms. Therefore, to minimize the risk of sensitization and work-related symptoms, a reduction of exposure during particular tasks with high peak exposures, along with a decrease in mean 8-h time-weighted average exposure, should be achieved.

Adult↗

PubMed2002

Occupational dermatitis from a one-component naphthalene type epoxy adhesive.

In an electronics plant, a new one-component naphthalene type epoxy resin was used as an adhesive for reinforcing a circuit board. The resinous part of the adhesive consisted of diglycidyl ether of bisphenol A (DGEBA) and 1,6-bis(2,3-epoxypropoxy)naphthalene type epoxy resins. The hardener was methylhexahydrophthalic anhydride (MHHPA). Of 54 workers, 15 (27.8%) were diagnosed to have work-related dermatitis but were not patch tested. Therefore, it was impossible to determine the specific agent responsible for the worker's symptoms or to distinguish between allergic and irritant contact dermatitis. They worked without protective gloves until they started to develop skin symptoms. The hands were the commonly affected region (13 out of 15 cases). The latent period of dermatitis was very short (mean 2.2 weeks). Of these, 10 cases (66.7%) received medication for dermatitis, and 9 cases (60%) were transferred to other work. The work-related skin symptoms were closely related to the specific tasks, i.e., filling dispensers with the adhesive and manual application of the adhesive to a portion of a circuit board using a dispenser. For occupational hygiene reasons, contact with epoxy resins should be minimized by taking all possible measures into use, including protective gloves. Further studies are required to clarify the allergenicity of 1,6-bis(2,3-epoxypropoxy)naphthalene, since very little is known about the mechanism through which it leads to the symptoms of dermatitis.

Adhesives↗