Cheong-Soo Hwang

Development of an automated protein-tyrosine phosphatase 1B inhibition assay and the screening of putative insulin-enhancing vanadium(IV) and zinc(II) complexes.

The inhibition of protein-tyrosine phosphatase 1B (PTP1B) is a potential target for treatment of type 2 diabetes. Vanadium and zinc metal coordinated complexes have insulin-enhancing activities, and while vanadium compounds inhibit PTP1B, little is known on the mode of action of zinc compounds. In this study we developed an automated PTP1B inhibition assay that allows for a rapid assessment of the PTP1B inhibition strength of candidate compounds. Synthetic vanadium(IV) and zinc(II) complexes were evaluated: IC50 values for vanadium complexes ranged from 0.06 to 0.8 μm whereas for zinc compounds, values were above 10 μm. Vanadium sulfate, a non-conjugated inorganic salt, had stronger inhibition activity than any of the conjugated metal complexes.

Photosensor and Photocatalytic Activities of the L-Glycine Capped ZnS:Mn Nanocrystals in Aqueous Solution

In this study, water-dispersible manganese (II) ion-doped ZnS nanocrystals (ZnS:Mn NCs) were synthesized by capping the surface with L-glycine molecules at various pH conditions. The UV-Visible and solution photoluminescence (PL) spectra showed broad peaks approximately at 330 and 590 nm, respectively. The calculated relative quantum efficiencies were in the range of 4.9∼5.8%, and the average particle sizes measured from the HR-TEM images were about 8 nm. Moreover, the surface charges of the corresponding ZnS:Mn-Gly NCs were determined by the electrophoretic method as: (-)14.8 mV (pH 2), (-)9.5 mV (pH 5), and (-)6.4 mV (pH 10) respectively. The most negatively charged ZnS:Mn-Gly-pH 2 NCs were applied as a fluorescence sensor to detect copper (II) ions in water by an exclusive luminescence quenching effect. In addition, photocatalytic activity of the ZnS:Mn-Gly-pH 2 NCs was also evaluated by measuring the degradation rate of an organic dye (methylene blue, MB) molecule under the UV light irradiation. The ZnS:Mn-Gly-pH 2 NCs showed the photodegradation efficiency of the MB molecule with a pseudo-first-order reaction constant (kobs) of 4.3 × 10-4 min-1, which is higher than those of other amino acids-capped ZnS:Mn NCs at the same conditions.