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961.
Dong M Si YQ Sun SY Pu XP Yang ZJ Zhang LR Zhang LH Leung FP Lam CM Kwong AK Yue J Zhou Y Kriksunov IA Hao Q Lee HC 《Organic & biomolecular chemistry》2011,9(9):3246-3257
Human CD38 is a novel multi-functional protein that acts not only as an antigen for B-lymphocyte activation, but also as an enzyme catalyzing the synthesis of a Ca(2+) messenger molecule, cyclic ADP-ribose, from NAD(+). It is well established that this novel Ca(2+) signaling enzyme is responsible for regulating a wide range of physiological functions. Based on the crystal structure of the CD38/NAD(+) complex, we synthesized a series of simplified N-substituted nicotinamide derivatives (Compound 1-14). A number of these compounds exhibited moderate inhibition of the NAD(+) utilizing activity of CD38, with Compound 4 showing the highest potency. The crystal structure of CD38/Compound 4 complex and computer simulation of Compound 7 docking to CD38 show a significant role of the nicotinamide moiety and the distal aromatic group of the compounds for substrate recognition by the active site of CD38. Biologically, we showed that both Compounds 4 and 7 effectively relaxed the agonist-induced contraction of muscle preparations from rats and guinea pigs. This study is a rational design of inhibitors for CD38 that exhibit important physiological effects, and can serve as a model for future drug development. 相似文献
962.
Qian DB Ma X Chen Z Zhang DC Zhang SF Li B Zhu XL Liu HP Wen WQ 《Physical chemistry chemical physics : PCCP》2011,13(8):3328-3333
Hot C(60) molecules under nanosecond laser excitation decay by a variety of fragmentation channels. An experimental search has been made to determine the excitation temperature of fragmented C(60)via analyzing the momentum distributions of the prompt ionic fragments C(n)(+) (n ≤ 58). It was found that all the C(60) precursors appearing as these ionic fragments have almost the same temperature and the temperature shows little variation with the laser fluences in our limited range. The results provide a clear evidence that a first-order phase transition in the fragmented C(60) is occurring at this temperature. The value of phase transition temperature is found to be about 6050 ± 250 K, which is in a good agreement with the most recent estimations based on the molecular dynamics simulation. This approach offers an experimental opportunity for studying the fragmentation thermodynamics of more complex polyatomic molecules under excitation temperature determined conditions. 相似文献
963.
Five new sesquiterpenoids, namely, 8β‐(angeloyloxy)‐4β,6α,15‐trihydroxy‐14‐oxoguaia‐9,11(13)‐dien‐12‐oic acid 12,6‐lactone ( 1 ), 4β,6α,15‐trihydroxy‐8β‐(isobutyryloxy)‐14‐oxoguaia‐9,11(13)‐dien‐12‐oic acid 12,6‐lactone ( 2 ), 11,12,13‐trinorguai‐6‐ene‐4β,10β‐diol ( 3 ), (1(10)E,4E,8Z)‐8‐(angeloyloxy)‐6α,15‐dihydroxy‐14‐oxogermacra‐(1(10),4,8,11(13)‐tetraen‐12‐oic acid 12,6‐lactone ( 9 ), and (1(10)E,4β)‐8β‐(angeloyloxy)‐6α,14,15‐trihydroxygermacra‐1(10),11(13)‐dien‐12‐oic acid 12,6‐lactone ( 11 ), and three new artifacts, (1(10)E,4Z)‐8β‐(angeloyloxy)‐9α‐ethoxy‐6α,15‐dihydroxy‐14‐oxogermacra‐1(10),4,11(13)‐trien‐12‐oic acid 12,6‐lactone ( 6 ), (1(10)E,4Z)‐8β‐(angeloyloxy)‐9α,13‐diethoxy‐6α,15‐dihydroxy‐14‐oxogermacra‐1(10),4‐dien‐12‐oic acid 12,6‐lactone ( 7 ), and (1(10)E,4Z)‐8β‐(angeloyloxy)‐9α‐ethoxy‐6α,15‐dihydroxy‐13‐methoxy‐14‐oxogermacra‐1(10),4‐dien‐12‐oic acid 12,6‐lactone ( 8 ), together with the three known sesquiterpenoids 4, 5 , and 10 , were isolated from the aerial parts of Siegesbeckia orientalis L. Their structures were established by spectral methods, especially 1D‐ and 2D‐NMR spectral methods. 相似文献
964.
965.
966.
P. G. Royall D. Q. M. Craig M. Reading T. J. Lever 《Journal of Thermal Analysis and Calorimetry》2000,60(3):795-805
The purpose of this study was to investigate the feasibility of modulating the temperature programme of a conventional DSC
by use of an alternating gas-flow system. Modulated temperature differential scanning calorimetry (MTDSC) is an important
thermal analysis technique but suffers from a limited applicable frequency range due to the mass of the sample and DSC cell
leading to the impingement of thermal conductivity effects. We suggest that the frequency limit can be increased by replacing
the cell as the source of temperature modulation with an external gaseous source, directed towards the sample and reference
pans. In this evaluation, an alternating gas-flow was passed through a line to a forced gas-flow accessory (FGFA). The FGFA
consisted of two matched cylinders containing chambers that allowed pre-temperature-equilibration of the stream of gas before
it was passed over the sample and reference pans. The development of this device revealed the essential practical requirements
of gas-flow modulation for high-frequency temperature modulation. These include the following: an appropriately sealed tunable
gas supply to both sample and reference pans, an effective method for high-frequency cycling of the gas-flow rate, a small
aperture to deliver the flowing gas directly over the pan and a temperature equilibration chamber. The results from samples
of quenched PET and amorphous Saquinavir indicate that gas-flow modulation is indeed feasible, with the FGFA able to raise
the attainable temperature modulation frequency by an order of magnitude compared to conventional MTDSC.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
967.
W. Y. Feng Q. F. Qian W. J. Ding Z. F. Chai 《Journal of Radioanalytical and Nuclear Chemistry》2000,244(2):321-325
Chromium speciation was investigated in the liver cytosol, serum and urine of normal and diabetic rats after a single intravenous injection of enriched stable isotope 50Cr tracer solution. Sephadex G-25 gel chromatography combined with instrumental neutron activation analysis was used to isolate and characterize protein-bound chromium in the above materials. The results indicate that Cr is mainly combined with a high-molecular-weight protein either in liver cytosol or serum. A low-molecular-weight, Cr-containing compound (LMWCr) was found in all the observed liver, serum and urine samples of both normal and diabetic rats. Chromium is excreted chiefly as LMWCr in urine. 相似文献
968.
Cationic cyanine as a near-infrared fluorescent probe for the determination of nucleic acids 总被引:3,自引:0,他引:3
A new method with a cationic near-IR cyanine as fluorescent probe was developed for the determination of nucleic acids. The near-IR cyanine shows maximum excitation and emission wavelengths at 765 and 790 nm, respectively, in aqueous solution. The method is based on the fluorescence decrease of near-IR cyanine in the presence of nucleic acids. Under optimal conditions, the ratio of fluorescence intensity in the absence and presence of nucleic acids was proportional to the concentration of nucleic acids over the range 0.10-1.2 microg/mL for CT (calf thymus) DNA or SM (salmon sperm) DNA, and 0.10-1.6 microg/mL for yeast RNA. The detection limits were 30 ng/mL for CT DNA, 25 ng/mL for SM DNA and 70 ng/mL for yeast RNA. The relative standard deviation (n = 6) was 2.1% for 500 ng/mL CT DNA, 2.4% for 500 ng/mL SM DNA and 2.7% for 500 ng/mL yeast RNA, respectively. 相似文献
969.
Tucker Melvin P. Mitri Ragheed K. Eddy Fannie P. Nguyen Q. A. Gedvilas Lynn M. Webb John D. 《Applied biochemistry and biotechnology》2000,84(1-9):39-50
The process of converting renewable lignocellulosic biomass to ethanol requires a number of steps, and pretreatment is one
of the most important. Pretreatment usually in volves a hydrolysis of the easily hydrolyzed hemicellulosic component of biomass
using some form of thermal/chemical/mechanical action that results in a product that can be further hydrolyzed by cellulase
enzymes (the cellulosic portion). The sugars produced can then befermented to ethanol by fermentative microorganisms. If the
pretreatment step is not severe enough, the resultant residue is not as easily hydrolyzed by the cellulase enzyme. More severe
pretreatment conditions result in the production of degradation products that are toxic to the fermentative microorgan ism.
In this article, wereport the quantitative analysis of glucose, mannose, xylose, and acetic acid using Fourier transform infrared
(FTIR) spectroscopy on liquors from dilute-acid-pretreated softwood and hard wood slurries. Comparison of FTIR and high-performance
liquid chromatography quantitative analyses of these liquorsare reported. Recent developments in infrared probe technology
has enabled the rapid quantification of these sugars by FTIR spectroscopy in the batch reactor during optimization of the
pretreatment conditions, or interfaced to the computer controlling a continuous reactor for on-line monitoring and control. 相似文献
970.
Application of magdala red as a fluorescence probe in the determination of nucleic acids 总被引:3,自引:0,他引:3
A fluorescence quenching method was developed for the rapid determination of DNA and RNA using magdala red as fluorescence probe. In weakly acidic medium, the fluorescence of magdala red (lambdaex/lambdaem = 540/555 nm) can be largely quenched by DNA or RNA. The calibration graphs are linear over the range 0.01-1.2 microg/mL for both calf thymus DNA (CT DNA) and salmon DNA (SM DNA), and 0.015-1.0 microg/mL for yeast RNA, respectively. The corresponding detection limits are 6.0 ng/mL for CT DNA, 7.0 ng/mL for SM DNA and 15.0 ng/mL for yeast RNA, respectively. CT DNA could be determined in the presence of 20% (w/w) yeast RNA, and the relative standard deviation of six replicate measurements is 3.18% for 400 ng/mL of CT DNA. Interference from coexisting substances in the determination of DNA was also examined. Real samples were determined with satisfactory results. 相似文献