Publications (39) View all
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Article: Effect of Solvent Composition on Porosity, Surface Morphology and Thermal Behavior of Metal Alginate Prepared from Algae (Undaria pinnatifida)
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ABSTRACT: Alginates, extracted from algae are linear unbranched polymers containing β-(1→4)-linked d-mannuronic acid (M) and α-(1→4)-linked l-guluronic acid (G) residues. The conversion of alginic acid into the metal alginate is confirmed using FTIR spectroscopy. Asymmetric and symmetric stretching of free carboxyl group present in metal alginate occurs almost at the same position in various solvent compositions. Total intrusion volume of metal alginate prepared in propanol (0.0742mL/g) is greater compared to those in ethanol (0.0648mL/g) and methanol (0.0393mL/g) as solvent. Surface morphology as well as porosity and pore size distribution of metal alginate are greatly influenced by solvent. It can be seen from thermal analysis results that calcium alginate prepared using different solvent compositions started decomposing at 100°C, but rapid degradation started around 200°C. The results showed a stepwise weight loss during thermal sweep, indicating different types of reactions during degradation. First and second step of rapid degradation was situated around 200–300 and 300–550°C, respectively; whereas the final step is situated around 550–650°C. The trend of degradation was similar for all the solvents, although the amount of final residue varied from one solvent to another. At the same time, lower thermal stability was also observed with higher heating rates. Additionally, a kinetic analysis was performed to fit with TGA data, where the entire degradation process has been considered as three consecutive first order reactions. KeywordsMetal alginate-Porosity-Surface morphology-Thermal behavior-Kinetic analysisJournal of Polymers and the Environment 05/2012; 18(1):45-56. · 1.35 Impact Factor -
Article: Antibacterial effects of the urushiol component in the sap of the lacquer tree (Rhus verniciflua Stokes) on Helicobacter pylori.
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ABSTRACT: Urushiol is a major component of the lacquer tree which has been used as a folk remedy for the relief of abdominal discomfort in Korea. The aim of this study was to evaluate the antibacterial effects of the urushiol on Helicobacter pylori. Monomer and 2-4 polymer urushiol were used. In the in vitro study, pH- and concentration-dependent antibacterial activity of the urushiol against H. pylori were investigated. In addition, the serial morphological effects of urushiol on H. pylori were examined by electron microscopy. In vivo animal study was performed for the safety, eradication rate, and the effect on gastritis of urushiol. The expression of pro-inflammatory cytokines was checked. All strains survived within a pH 6.0-9.0. The minimal inhibitory concentrations of the extract against strains ranged 0.064-0.256 mg/mL. Urushiol caused separation of the membrane and lysis of H. pylori within 10 minutes. Urushiol (0.128 mg/mL × 7 days) did not cause complications on mice. The eradication rates were 33% in the urushiol monotherapy, 75% in the triple therapy (omeprazole + clarithromycin + metronidazole), and 100% in the urushiol + triple therapy, respectively. H. pylori-induced gastritis was not changed by urushiol but reduced by eradication. Only the expression of interleukin-1β in the gastric tissue was significantly increased by H. pylori infection and reduced by the urushiol and H. pylori eradication (p = .014). The urushiol has an antibacterial effect against H. pylori infection and can be used safely for H. pylori eradication in a mouse model.Helicobacter 12/2011; 16(6):434-43. · 3.15 Impact Factor -
Article: Tailoring Interfaces for Electrochemical Synthesis of Semiconductor Films: BiVO4, Bi2O3, or Composites
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ABSTRACT: The mechanistic aspects of a two-step method for the electrodeposition of a BiVO4 semiconductor (previously developed in the Rajeshwar/Tacconi laboratory) were elaborated by the combined application of voltammetry and EQCM. The electrosynthesized films were also characterized ex situ using SEM, EDX, XRD, and XPS. Stripping of pre-electrodeposited bismuth films, followed by reaction either with VO43− (formed by hydrolysis from the initially added VO3− species) or with hydroxide ions, produced BiVO4 or Bi2O3 thin films in situ on the Pt electrode. The deposition potential, pH of the electrolyte, and choice of vanadium precursor were shown to be crucial variables in the composition of the electrodeposited film. When a more positive potential than 0.5 V (vs Ag/AgCl reference) was applied to the Bi-modified electrode in VO3−-containing electrolyte, the content of Bi2O3 in the film increased instead of BiVO4. Stripping efficiency of the predeposited bismuth layer was increased at acidic electrolytes and resulted in higher BiVO4 content in electrodeposited films, whereas hydrolytic conversion of VO3− to VO43− was promoted in basic electrolytes. Formation of Bi2O3 was also favored by the use of alkaline electrolytes (e.g., pH 10) for the electrodeposition. Photoelectrochemical experiments showed the electrosynthesized BiVO4 to be an n-type semiconductor, and reproducible photocurrents were obtained using a Na2SO4 supporting electrolyte.03/2011; -
Article: Compositional analysis of electrodeposited bismuth telluride thermoelectric thin films using combined electrochemical quartz crystal microgravimetry--stripping voltammetry.
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ABSTRACT: Bismuth telluride (Bi 2Te 3 ) is a benchmark material for thermoelectric power generation and cooling applications. Electrodeposition is a versatile technique for preparing thin films of this material; however, it affords films of variable composition depending on the preparation history. A simple and rapid assay of electrodeposited films, therefore, has both fundamental and practical importance. In this study, a new protocol for the electroanalysis of Bi 2Te 3 thin films is presented by combining the two powerful and complementary techniques of electrochemical quartz crystal microgravimetry (EQCM) and stripping voltammetry. First, any free (and excess) tellurium in the electrodeposited film was reduced to soluble Te ( 2- ) species by scanning to negative potentials in a 0.1 M Na 2SO 4 electrolyte, and the accompanying frequency increase (mass loss) was used to determine the content of free tellurium. The film was again subjected to cathodic stripping in the same medium (to generate Bi (0) and soluble Te (2-) from the Bi 2 Te 3 film component of interest), and the EQCM frequency change was used to determine the content of chemically bound Te in the Bi 2Te 3 thin film and thereby the compound stoichiometry. Finally, the EQCM frequency change during Bi oxidation to Bi (3+) and the difference between total Bi and Bi in Bi 2Te 3 resulted in the assay of free (excess) Bi in the electrodeposited film. Problems associated with the chemical/electrochemical stability of the free Bi species were circumvented by a flow electroanalysis approach. Data are also presented on the sensitivity of electrodeposited Bi 2Te 3 film composition to the electrodeposition potential. This newly developed method can be used for the compositional analysis of other thermoelectric thin-film material candidates in general.Analytical Chemistry 10/2008; 80(17):6724-30. · 5.86 Impact Factor -
Article: Competitive enzyme-linked immunosorbent assay for the determination of catecholamine, dopamine in serum.
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ABSTRACT: A competitive enzyme-linked immunosorbent assay for dopamine (DA) has been optimized and characterized. DA is sensitive to oxygen and light according to a function of the pH on the DA oxidation process. The phenolic groups in DA are readily oxidisable to a quinoid form and thus, free DA deteriorates in alkaline media. Thus, effect of factors such as pH, enzyme-label with substrate, ionic strength and reaction time was considered on performance of ELISA. Assay was performed with 5 microg mL(-1) of BSA-DA and 1/7500 dilution of anti-DA antibody. A dose-response curve was constructed, and a limit of detection and a dynamic range for DA were accomplished to 1.0x10(-9) M (0.19 microg L(-1)) and five orders (3.2x10(-8) M to 3.2x10(-3) M) of magnitude, respectively. The correlation diagram of the absorbance obtained both in buffer and in serum has shown good agreement with correlation coefficient (R(2) = 0.9947): Abs. (in serum) = 0.6128 x Abs. (in buffer) + 0.2926. The cross-reactivity was examined with the structurally similar compounds. And the results demonstrated that epinephrine and 3-methoxytyramine showed cross-reactivity (18.9% each), whereas 3,4-dihydroxyphenylacetic acid and homovanillic acid showed low cross-reactivity (<1%). And percent recoveries of DA in serum were quite satisfactory. This provides usefulness of the present assay to monitor DA in serum.Analytica chimica acta 07/2008; 619(1):87-93. · 4.31 Impact Factor
