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Yongseog Chung,Hoon Cho 대한약학회 2004 Archives of Pharmacal Research Vol.27 No.8
Tacrolimus (FK506), which is isolated from Streptomyces tsukubaensis, is a new potent immunosuppressant. Because of poor solubility in water, the conventional intravenous dosage forms of tacrolimus contain surfactants such as cremophor EL (BASF Wyandotte Co.) or hydrogenated polyoxy 60 castor oil (HCO-60) which may cause adverse effects. This study relates to a polymer-tacrolimus conjugate, which can be dissolved in water, formed by chemically binding the sparingly soluble drug, tacrolimus, with the water soluble polymer, methoxypoly(ethylene glycol) (mPEG). Water soluble tacrolimus-mPEG conjugates have been synthesized and shown to be function in vitro as prodrugs. These conjugates are in the form of an ester wherein the 24-, 32- or 24,32-positions are esterified. The desired 24-, 32- or 24,32-esterified compounds were obtained by initially acylating of tacrolimus with iodoacetic acid at the 24-, 32-, or 24,32-positions and then reacting the resulting acylated tacrolimus with a mPEG in the presence of a base such as sodium bicarbonate. These conjugates were converted again into tacrolimus by the action of enzymes in human liver homogenate, and the half-lives of the conjugates are approximately 10 min in the homogenate, indicating that the esterified tacrolimus derivatives may be practically applicable as a prodrug for the immunosuppressant.
Jikang Yoo,Yongseog Chung,Cheol-Hee Choi,Bok Hee Kim,조훈,Hyun-Suk Choi 대한약학회 2008 Archives of Pharmacal Research Vol.31 No.2
A series of nine new compounds bridged by acyl groups at the 5,8-dihydroxyl group of DHNQ were synthesized and their cytotoxic activity against L1210 and P388 cancer cells was examined. Their antitumor action in mice bearing S-180 cells in the peritoneal cavity was also assessed. Increasing the size of the acyl group (compounds 7-9) up to propyl increased the antitumor activity (T/C value), whereas the cytotoxicity of these compounds was comparable against L1210 (lymphocytic leukemia) and P388 (lymphoid neoplasm) cancer cells. Further increasing in the chain length (compounds 11-15) decreased the potency. Thus, acyl group chains of three carbon atoms is optimal for antitumor activity. The most potent compound of this series was 2-[N-methyl-N-(4-methyl-1,3-benzothiazol-2-yl)aminomethyl]-5,8-dipropylcarbonyloxy- 1,4-naphthoquinone (compound 9) with a T/C (%) value of 354.
Charge Redistribution and Electronic Behavior in Pd-Au Alloys
LEE, Youn-Seoung,JEON, Yongseog,CHUNG, Yong-Duck,LIM, Kwan-Yong,WHANG, Chung-Nam,OH, Se-Jung 대전산업대학교 반도체기술연구소 2000 半導體技術硏究所報 Vol.2 No.-
Au L_3edge X-ray absorption near-edge structure (XANES) spectra have been obtained for arcmelted Pd-An alloys. The results show a significant increase in the Au L_3-edge white-line area relative to pure Au upon alloying, indicating a decrease in the d charge at the Au site. The XANES results are combined with the x-ray photoelectron core-level shifts to derive estimates for the net charge transfer of the Au sites in PD-Au alloy system. By applying the charge compensation model, we find that Au loses d charge and gains almost the same number of sp-like electrons while Pd gains d charge and loses sp charge. This electron redistribution due to hybridization in the alloy leads a small net charge transfer from the Pd site to the Au site, in accordance with electronegativity and electroneutrality arguments.
XPS core-level shifts and XANES studies of Cu-Pt and Co-Pt alloys
Lee, Youn-Seoung,Lim, Kwan-Yong,Chung, Yong-Duck,Whang, Chung-Nam,Jeon, Yongseog 대전산업대학교 반도체기술연구소 2000 半導體技術硏究所報 Vol.2 No.-
The K and L_2.3 absorption edges and core-level binding-energy shifts for pure Co, Cu and Pt and Co-Pt and Cu-Pt alloys are measured to investigate changes in electronic structures of these alloys. Enhancements and depletion of the white lines in the alloys as compared to pure elements were correlated with changes in the unoccupied density of states upon alloying. We find that the Pt atoms lost d_3/2 electrons and gained d_5/2 electrons when alloyed with Cu and Co. However, the total 5d occupancy changes of the Pt were very little in Cu-Pt alloys, and this is consistent with the small shifts of Pt 4f core-level binding energy. From the quantitative analysis of Cu and Co K-edge absorption spectra, it is found tha Cu and Co have significant valence occupation changes due to dehybridization of p-d states. From these results, we suggest that the core-level shifts are affected mainly by the d-valence electron changes in these alloys. Copyright