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61.
Hua Jin Avvaru Praveen Kumar Do-Hyeon Paik Kwon-Chul Ha Young-Jae Yoo Yong-Ill Lee 《Microchemical Journal》2010,94(2):139-147
A rapid, sensitive and specific ultra-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UPLC–QToF-MS) method has been developed and validated for simultaneous determination of three tetracyclines (TCs) including oxytetracycline, tetracycline, and chlortetracycline in human urine. Human urine sample preparation involves pH adjustment to 4 with hydrochloric acid, pre-concentration, and cleanup by solid phase extraction (SPE) process. The chromatographic separation of all TCs was achieved in less than 5 min using UPLC and ESI-QToF-MS was successfully employed for the identification and quantification. The accurate masses of the product ions were calculated using lock mass correction, and were deviated from the theoretical masses by 0.5–1.9 mDa and 1.1–4.5 ppm, respectively. The developed method was validated in terms of linearity, sensitivity, selectivity, decision limit, detection capability, accuracy, and precision. Limit of detection and limit of quantitation for all TCs were estimated in the range of 0.089–0.138 ng mL− 1 and 0.294–0.455 ng mL− 1, respectively. High overall recoveries of greater than 90% were achieved with linear responses over the 0.5–2 ng mL− 1 range for all TCs in urine samples. 相似文献
62.
Paik Dong Soo Rao A.V. Prasada Komarneni S. 《Journal of Sol-Gel Science and Technology》1997,10(2):213-220
Randomly oriented ferroelectric BaTiO3 and (Ba0.6Sr0.4) TiO3 thin films on platinum coated Si (100) were prepared by a sol-gel method. The precursor solutions were derived from barium hydroxide or a mixture of barium/strontium hydroxides dissolved in acetic acid and titanium butoxide. Polarization versus applied voltage hysteresis studies indicated a remanent polarization of 3 µC/cm2 and a coercive field of 43.4 kV/cm for BaTiO3 films annealed at 800°C for 1 h. Corresponding parameters for (Ba0.6Sr0.4)TiO3 films annealed at 800°C were found to be 7.2 µC/cm2 and 102.7 kV/cm, respectively. Microstructural study of the surface morphology of these films indicated grains of less than 0.1 µm in size. The leakage current for (Ba0.6Sr0.4)TiO3 films was found to be two orders of magnitude lower than that for BaTiO3 films. 相似文献
63.
Methyl diazoacetate reacted with the ketene acetal I in the presence of dirhodium tetraacetate yielding the metastable cyclopropanone ketal ester II, which was converted to the primary and tertiary cyclopropyl carbinols III and IV by treatment with lithium aluminum hydride and methyl lithium, respectively. Diazoacetonitrile yielded a stable crystalline cyclopropanone ketal nitrile X following reaction with the ketene acetal I. 相似文献
64.
Synthesis,plasma clearance,and in vitro stability of protein containing a conjugated indium-111 chelate 总被引:1,自引:0,他引:1
C. H. Paik D. E. Herman W. C. Eckelman R. C. Reba 《Journal of Radioanalytical and Nuclear Chemistry》1980,57(2):553-564
A new bifunctional chelating agent, N′-(p-diazoniumbenzyl)-N,N N″,N″-diethylenetri-aminetetraacetic acid (DTTA) was synthesized.
The compound as coupled to methyl p-hydroxybenzimidate and the resulting azoimidate was attached to lysine residues of monomeric
human serum albumin (HSA) via the amidination reaction. Blood clearnace of111In-labelled DTTA conjugated to HSA (AAHSA) in rabbits was biphasic. The first phase has a clearance indistinguishable from
that of125I-labeled HSA. During the second phase, the111In-labeled AAHSA was cleared more rapidly so that between 24 hours and 48 hours the percent of the injected dose of111In-labeled AAHSA in the blood was significantly lower than that of125I-labeled HSA. Highly conjugated111In-labeled AAHSA (0.9 DTTA/HSA) showed accelerated clearance at 24 and 48 hours compared to lightly conjugated protein (<0.9
DTTA/HSA). As a result we postulate that the level of conjugation is the critical parameter controlling the blood clearance. 相似文献
65.
C. H. Paik F. Vieras W. C. Eckelman R. C. Reba 《Journal of Radioanalytical and Nuclear Chemistry》1980,60(1):281-289
99mTc-labeled transferrin was prepared by reduction of99mTcO
4
−
; with stannous DTPA or stannous citrate followed by equilibration of the technetium chelate with human transferrin. The rate
of transfer of99mTc to transferrin in the presence of 0.015M citrate buffer was dependent on pH in the order pH 2.1> pH 7.2> pH 4.1> pH 5.9.
The incorporation rate was inversely proportional to the concentration of DTPA and citrate buffer. The replacement of citrate
buffer by acetate buffer or oxalate buffer reduced drastically the formation of99mTc-labeled transferrin at pH 4.1. The formation of99mTc-labeled transferrin prepared from the reduction of99mTcO
4
−
with stannous citrate was faster than that from the reduction with stannous DTPA in the presence of 0.015M citrate buffer
and pH 2.5. Equilibration of transferrin with99mTc-labeled pyrophosphate did not produce99mTc-labeled transferrin at pH 4.5. The ligand exchange labeling of99mTc to transferrin in 0.015M citrate did not cause appreciable denaturation of the protein at all pH values. This method also
enabled labeling of the protein in a low concentration (2.6·10−4 M) via tin reduction. Sequential external imaging of the99mTc-labeled transferrin in Sprague-Dawley rats bearing Walker-256 carcinosarcoma showed optimal tumor localization occurred
at 3 hr after injection. In spite of this,99mTc-labeled transferrin does not appear to be a suitable imaging agent because of the low tumor to blood ratio of99mTc (0.50±0.17) at 3 hr post injection. This is similar to that of6 7Ga-citrate (0.43±0.15%). 相似文献
66.
Kwanpyo Lee Myunghyun Paik Suh Junghun Suh 《Journal of polymer science. Part A, Polymer chemistry》1997,35(9):1825-1830
Equilibrium constant (KCP) for coordinative polymerization is measured for the first time. Constant KCP is defined as [L]cp/[M][L], where [L]cp represents the concentration of the ligand present in the coordination polymer. Plot of absorbance changes measured for 3, a water-soluble derivative of o,o′-dihydroxyazobenzene, against the concentration of Ni(II) ion indicates formation of a 1 : 1-type complex in water at pH 7.74 and 25°C when Ni (II) is added in excess of 3. The 1 : 1-type complex can be either Ni 3, the monomeric complex, or (Ni 3 )n, the coordination polymer. The equilibrium constant for formation of the 1 : 1-type complex is estimated as 1013.10 by using UO22+ ion as the competing metal ion. For the Ni(II) complex of an o,o′-dihydroxyazobenzene derivative attached to poly(ethylenimine), the formation constant is estimated as 105.36. Due to the structure of the polymer, possibility of coordinative polymerization is excluded for the polymer-based ligand. The much greater equilibrium constant for formation of the Ni(II) complex of 3, therefore, indicates formation of (Ni 3 )n instead of Ni 3. The value of KCP for (Ni 3 )n shows that only 10−7% of the initially added 3 is left unpolymerized when Ni(II) is added in excess of 3 by 10−4 M. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1825–1830, 1997 相似文献
67.
Hong YS Lee D Kim W Jeong JK Kim CG Sohng JK Lee JH Paik SG Lee JJ 《Journal of the American Chemical Society》2004,126(36):11142-11143
The post-polyketide synthase modification of geldanamycin (1) biosynthesis is of interest as a means of introducing structural diversity into the compound. From the inactivation of a gene encoding carbamoyltransferase, we demonstrated that the C-17 hydroxylation and the C-21 oxidation precede O-carbamoylation and that the hypothetical progeldanamycin does not possess a double bond at C-4 and C-5. More importantly, our result revealed new intermediates 4,5-dihydro-7-O-descarbamoyl-7-hydroxygeldanamycin (3) and 4,5-dihydrogeldanamycin (5), indicating that O-carbamoylation occurs prior to the C-4,5 cis double bond formation in geldanamycin biosynthesis. 相似文献
68.
69.
This paper presents a mathematical model and simulated annealing based solution approach for finding optimal location updates and paging area configuration for mobile communication networks. We use a two-layered zone-based location registration and paging scheme in which the costs of location updates and paging signaling traffic are reduced by introducing a two-step paging process. The location updates and paging procedures in a two-layered scheme are first described, and an approximation of the measure required for calculating the paging-related signaling volume is provided based on assumptions of cell shapes and mobile stations’ movement patterns. A simulated annealing (SA)-based solution method is devised along with a greedy heuristic, and computational experiments are conducted to illustrate the superiority of the proposed SA-based method over other solution methods. 相似文献
70.
The inflow ahead of a rotating propeller attached to a container ship model was visualized using a two-frame particle image
velocimetry (PIV) technique. For illuminating the inflow region, a transparent window was installed at the stern of the ship
model. Ensemble-averaged mean velocity fields were measured at four different blade phases under the design loading condition.
The characteristics of the inflow in the upper plane above the propeller axis are quite different from those below the propeller
axis. In the far upstream region above the propeller axis, most of the inflow comes from the hull wake and the axial velocity
is very small. As the inflow moves toward the propeller plane, its axial velocity component increases rapidly. In addition,
the variation of the inflow characteristics with respect to phase angle becomes apparent. The thick hull boundary layer and
out-of-plane motion resulting from the propeller rotation produce a large turbulent kinetic energy around the tip of the propeller
blade in the upper inflow region. The axial velocity distribution of the propeller inflow is asymmetric with respect to the
vertical center axis, exhibiting different axial velocities on the port and starboard sides. 相似文献