Li-Chin Chuang

Determination of three-dimensional solution structure of waglerin I, a toxin from Trimeresurus wagleri, using 2D-NMR and molecular dynamics simulation

The solution conformation of a synthetic snake venom toxin waglerin I, has been determined by using proton nuclear magnetic resonance spectroscopy. By a combination of various two-dimensional NMR techniques, the 1H-NMR spectrum of waglerin I was completely assigned. A set of 247 interproton distance restraints was derived from nuclear Overhauser enhancement (NOE) measurements. These NOE constraints, in addition to the 2 dihedral angle restraints (from coupling constant measurements) and 7 omega torsion angel restraints for prolines, formed the basis of three-dimensional structure determined by molecular dynamics techniques. The 19 structures that were obtained satisfy the experimental restraints, and display small deviation from idealized covalent geometry. Analysis of converged structures indicates that the toxin has no special secondary structure. In the solution structure of waglerin I, the central ring region is well defined but the N- and C-termini possesses more disorder.

Photocatalytic Degradation Mechanism and Kinetics of Caffeine in Aqueous Suspension of Nano-TiO2

This study investigated TiO2 photocatalytic degradation of caffeine, a stimulating drug, in aqueous suspensions of titanium dioxide under a variety of conditions. Pure TiO2 powders were prepared using a modified homogeneous-precipitation process at low temperature (HPPLT) method. The degradation was studied by monitoring the intermediates employing high performance liquid chromatography (HPLC) separation coupled to an atmospheric pressure ionization mass spectrometry (API-MS) system operated under selected ion monitoring (SIM). These results indicate the original concentration of caffeine almost completely degraded within 360 min, and a degradation ratio of more than 50 % appearing within 120 min of irradiation in a pH range of 3—10. The reaction rates for the decomposition of caffeine in water are higher for runs at pH 3 (k = 0.013 min-1) and pH 11 (k = 0.012 min-1). The proposed conversion mechanism of caffeine was used. The caffeine was first oxidized to become dimethyl parabanic acid and further degraded to di(hydroxymethyl) parabanic acid. This study also detected the product from N-demthylation, theophyline.

Photocatalytic degradation of parabens in aquatic environment: Kinetics and degradation pathway

Parabens are p-hydroxybenzoic acid ester compounds widely used as preservatives in foods, cosmetics, toiletries and pharmaceuticals. These compounds exert a weak estrogenic activity as determined by in vitro estrogen receptor assay and in vivo uterotrophic assay. The photocatalytic degradation of parabens (butylparaben and ethylparaben), as a function of pH and initial concentration of parabens, was investigated in the presence of TiO2 photocatalyst (P-25, “Degussa”). Experiments conducted at pH 4 with O2-sparged concentration of 15 mg/L showed that in terms of the photocatalytic efficiency the catalysts were slightly superior to those tested at pH 6-11. The intrinsic reaction rates of 2.08 × 102 and 1.81 × 102 μmol L−1min−1 were estimated, and Langmuir-Hinshelwood model adsorption constants K were calculated as 0.05 and 0.06 L/μmol for butylparaben and ethylparaben, respectively. Ten organic intermediates appeared during the photocatalytic degradation of parabens, and were identified by LC/MS/MS. In addition, a tentative reaction pathway was proposed.

Nanomechanical Properties of Prepared-TiO2 Films Using Nanoindentation Technique

Nanoindentation was used to measure the hardness and Young’s modulus of prepared-TiO2 films. The thickness and refractive index of the TiO2 films were measured using ellipsometry with a monochromator. Scanning electron microscopy was used to determine the micrography of the TiO2 films. Pure TiO2 films were prepared from sols made by 3 % (w/w) of prepared-TiO2 suspension solution coated onto silicon wafers. After the dip-coating was completed, the coatings were further treated by various procedures, natural air-drying, water-vapor exposure, and calcinations. The prepared-TiO2 films were smooth and free of macro cracking. The grain sizes of these films were uniform and in the range of 50–100 nm and the films were of rutile structure. The prepared-TiO2 coatings exhibited more favorable porosity in water-vapor exposure than those under other conditions. The T-H2SO4 coatings exhibited higher hardness and modulus than those with T-H2O and T-NH4OH coatings after high temperature calcination. The values of hardness and modulus for T-H2SO4 coatings were 11.93 GPa and 226.25 GPa, respectively. Curves of hardness and modulus as a function of depth (0–2200 nm) of the coatings under calcination conditions show a peak at shallow contact depth within 100 nm and then demonstrate being rather constant. The hardness and modulus curve obtained from T-H2SO4 coatings in water-vapor exposure are rather constant.

Degradation of Butylparaben by Ozonation and UV/TiO2 Processes

Butylparaben is widely used as a bactericide and as an antimicrobial agent in the formation of personal care products (PCPs). Owing to a certain estrogenic activity, a possible relationship with breast cancer has been proved by many researchers. The removal efficiency of butylparaben in aqueous solutions was studied using advanced oxidation processes (AOPs). These results indicate that the reaction rates for the ozonation of butylparaben in water are higher under the concentration of ozone 5 mg/L in alkaline condition. The original concentration of butylparaben almost degraded within 50, 30, and 20 min at ozone concentrations of 1, 3, and 5 mg/L, respectively at pH 11 runs. The ozonation imposed butylparaben with a time dependence that appeared to follow pseudo first-order kinetics. The original butylparaben was degraded 50 %, 40%, 35%, and 32% within 24 hr at pH 3, 6, 9, and 11 respectively by UV/TiO2 process in the O2-sparged concentration of 30 mg/L. The rate constants are 0.045, 0.043, 0.025, and 0.020 hr-1 at the butylparaben concentrations of 10.30, 20.60, 30.90, and 41.20 μM, respectively.

Conformation of a cyclic opioid peptide analog by NMR and molecular dynamics simulation

The conformation of a new Ty-c[Lys-Phe-Asp]-NH2 cyclic opioid peptide synthesized by solid phase method, has been determined from two-dimensional NMR and distance geometry followed by restrained molecular dynamics simulation. The conformation of the ring is well-defined, but the exocylic Tyr-1 and Phe-3 side-chain moiety possesses significant orientational freedom.

Degradation of Sulfa Pharmaceuticals in Aquatic Environment by O3 and UV/TiO2 Processes

The removal efficiencies of sulfamerazine (SMR) and sulfamethoxypyridazine (SMP) in aqueous solutions were studied using advanced oxidation technologies. The results show similar removal kinetics for two sulfa pharmaceuticals and that complete removal of all is achieved within 90 min of ozonation at the concentration of O3 (1 mgL-1) without controlling the pH. The rate constants were calculated as 0.0143 and 0.0113 min-1 for SMR and SMP, respectively. The catalysts exhibited a superior removal efficiency of SMP to those of SMR with a TiO2 concentration of 2.0 gL-1. The disappearance of these two sulfa pharmaceuticals follows a pseudo-first-order kinetics according to the Langmuir-Hinshelwood (L-H) model. The rate constants were calculated as 5 × 10-3 and 6 × 10-4 min-1 for SMR and SMP, respectively. Advanced oxidation processes (AOPs), such as O3 and UV/TiO2 processes should be an effective treatment for removing these sulfa pharmaceuticals.

Degradation Mechanism of Aqueous Sulfamerazine by AOPs of O3 and UV/TiO2

Advanced Oxidation Processes (AOPs) is a promising treatment technology for eliminating trace micropollutants, in the treatment of wastewaters containing sulfamerazine (one of pharmaceuticals) using O3 and UV/TiO2 process, respectively. The degradation was studied by monitoring the intermediates employing high performance liquid chromatography (HPLC) separation coupled with an atmospheric pressure ionization mass spectrometry (API-MS) system operated under selected ion monitoring (SIM). The results indicate that the original sulfamerazine almost was degraded within 90 min under the concentration of ozone 3 mg/L at different pH runs. The ozonation of sulfamerazine demonstrated the best degradation efficiency for runs at pH 8 than for runs at pH 6 and pH 11, respectively, under the concentration of ozone 1 or 3 mg/L. The original sulfamerazine was completely degraded within irradiation time of 5 hr at pH 6 runs in the concentration of O2-sparged 30 mg/L during the photocatalytic process. The rate constants are 0.086, 0.08, 0.04, and 0.027 hr-1 at the concentration of sulfamerazine 14.22, 21.33, 35.55, and 42.66 μM, respectively. Two intermediates were observed during the photocatalytic degradation of sulfamerazine.