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排序方式: 共有138条查询结果,搜索用时 31 毫秒
31.
A keypad emulation method for controlling microprocessor-based instruments by laboratory microcomputers is presented. It is applicable to instruments that use "polled" keypad arrays; the instrument can be controlled by the laboratory computer or operated independently by manual keypad entry. To illustrate the approach, a microprocessor-based HPLC solvent-delivery system was controlled by a laboratory microcomputer which synchronized and sequenced the entire HPLC experiment, including solvent delivery, valve control for column switching and back-flushing, data-acquisition, and dataprocessing. 相似文献
32.
The retinal analogues 3-methyl-5-(1-pyryl)-2E,4E-pentadienal (1) and 3,7-dimethyl-9-(1-pyryl)-2E,4E,6E,8E-nonatetr aenal (2), which contain the tetra aromatic pyryl system, have been synthesized and characterized in order to examine the effect of the extended ring system on the binding capabilities and the function of bacteriorhodopsin (bR). The two bR mutants, E194Q and E204Q, known to have distinct proton-pumping patterns, were also examined so that the effect of the bulky ring system on the proton-pumping mechanism could be studied. Both retinals formed pigments with all three bacterioopsins, and these pigments were found to have absorption maxima in the range 498-516 nm. All the analogue pigments showed activity as proton pumps. The pigment formed from wild-type apoprotein bR with 1 (with the shortened polyene side chain) showed an M intermediate at 400 nm and exhibited fast proton release followed by proton uptake. Extending the polyene side chain to the length identical with retinal, analogue 2 with wild-type apoprotein gave a pigment that shows M and O intermediates at 435 nm and 650 nm, respectively. This pigment shows both fast and slow proton release at pH 7, suggesting that the pKa of the proton release group (in the M-state) is higher in this pigment compared to native bR. Hydrogen azide ions were found to accelerate the rise and decay of the O intermediate at neutral pH in pyryl 2 pigment. The pigments formed between 2 and E194Q and E204Q showed proton-pumping behavior similar to pigments formed with the native retinal, suggesting that the size of the chromophore ring does not alter the protein conformation at these sites. 相似文献
33.
Timothy D. Spitzer Ronald C. Crouch Gary E. Martin Maged H. M. Sharaf Paul L. Schiff Albert N. Tackie Gilbert L. Boye 《Journal of heterocyclic chemistry》1991,28(8):2065-2070
The reisolation of the indoloquinoline alkaloid quindoline (also known as norcryptolepine) from Cryptolepis sanguinolenta is reported. The structure was unequivocally confirmed by two-dimensional nmr methods; the proton and carbon spectra were assigned for the first time. Because of congestion in the proton spectrum HMQC-TOCSY was used as an alternative to the more familiar COSY experiment. In addition to establishing proton-proton connectivities, HMQC-TOCSY affords the added benefit of providing, in an indirect sense, connectivity information between protonated carbons. 相似文献
34.
Crouch DJ O'Brien P Malik MA Skabara PJ Wright SP 《Chemical communications (Cambridge, England)》2003,(12):1454-1455
A new approach to the one-step synthesis of cadmium selenide (CdSe) quantum dots is reported using the air stable complex cadmium imino-bis(diisopropylphosphine selenide); the ligand is readily prepared from elemental selenium and the precursor, quantum dots of comparable quality to those prepared by conventional methods are obtained. 相似文献
35.
E. Starr Hazard III Rajni Govindjee Thomas G. Ebrey Rosalie K. Crouch 《Photochemistry and photobiology》1992,56(6):929-934
Halobacterium halobium, grown in a defined medium where tyrosine had been largely replaced with m-fluorotyrosine, biosynthetically produced purple membrane. Analysis of this membrane by high pressure liquid chromatography of phenylthiocarbamyl derivatized amino acids of membrane acid hydrolysates revealed that up to 50% of the tyrosine was present as the m-fluorotyrosine form. Yields of the purple membrane decreased as the level of incorporation increased. The experimental purple membrane showed a single 19F NMR resonance at -61.983 ppm (relative to trifluoroacetic acid). The bacteriorhodopsin (bR) in the purple membrane was normal as assayed by gel electrophoresis, isoelectric focusing, circular dichroic spectra, and UV-visible spectra. However, the fluorinated tyrosine bacteriorhodopsins at near neutral pH exhibited slightly slower rates of proton uptake and a slower M-state decay with biphasic kinetics reminiscent of alkaline solutions of bR (pH > 9). These results imply that the tyrosines in bacteriorhodopsin may play a role in the photoactivated proton translocation process of this pigment. 相似文献
36.
Observation of a neutrino burst in coincidence with supernova 1987A in the Large Magellanic Cloud 总被引:1,自引:0,他引:1
Bionta RM Blewitt G Bratton CB Casper D Ciocio A Claus R Cortez B Crouch M Dye ST Errede S Foster GW Gajewski W Ganezer KS Goldhaber M Haines TJ Jones TW Kielczewska D Kropp WR Learned JG LoSecco JM Matthews J Miller R Mudan MS Park HS Price LR Reines F Schultz J Seidel S Shumard E Sinclair D Sobel HW Stone JL Sulak LR Svoboda R Thornton G van der Velde JC Wuest C 《Physical review letters》1987,58(14):1494-1496
37.
Lydia Dewis Ron Crouch Dave Russell Craig Butts 《Magnetic resonance in chemistry : MRC》2019,57(12):1143-1149
With the rise in fluorinated pharmaceuticals, it is becoming increasingly important to develop new 19F NMR-based methods to assist in their analysis. Crucially, obtaining information regarding the conformational dynamics of a molecule in solution can aid the design of strongly binding therapeutics. Herein, we report the development of a 2D 1H–19F Heteronuclear Overhauser Spectroscopy (HOESY) experiment to measure 1H–19F internuclear distances, with accuracies of ~5% when compared with 1H–19F internuclear distances calculated by quantum chemical methods. We demonstrate that correcting for cross-relaxation of 1H, using the diagonal peaks from the 2D 1H–1H Nuclear Overhauser Enhancement Spectroscopy (NOESY), is critical in obtaining accurate values for 1H–19F internuclear distances. Finally, we show that by using the proposed method to measure 1H–19F internuclear distances, we are able to determine the relative stereochemistry of two fluorinated pharmaceuticals. 相似文献
38.
Fan J Wu BX Sarna T Rohrer B Redmond TM Crouch RK 《Photochemistry and photobiology》2006,82(6):1461-1467
The protein RPE65 is essential for the generation of the native chromophore, 11-cis retinal, of visual pigments. However, the Rpe65 knockout (Rpe65-/-) mouse shows a minimal visual response due to the presence of a pigment, isorhodopsin, formed with 9-cis retinal. Isorhodopsin accumulates linearly with prolonged dark-rearing of the animals. The majority of Rpe65-/- mice have an agouti coat color. A tan coat color subset of Rpe65-/- mice was found to have an enhanced visual response as measured by electroretinograms. The enhanced response was found to be due to increased levels of 9-cis retinal and isorhodopsin pigment levels. Animals of both coat colors reared in cyclic light have minimal levels of regenerated pigment and show photoreceptor degeneration. On dark-rearing, pigment accumulates and photoreceptor degeneration is decreased. In the tan Rpe65-/- mice, the level of photoreceptor degeneration is less than in the agouti animals, which have an increased pigment and decreased free opsin level. Therefore, photoreceptor damage correlates with the amount of the apoprotein present, supporting findings that the activity from unregenerated opsin can lead to photoreceptor degeneration. 相似文献
39.
Ablonczy Z Darrow RM Knapp DR Organisciak DT Crouch RK 《Photochemistry and photobiology》2005,81(3):541-547
The damaging effects of intense light on the rat retina are known to vary depending on the time of day of exposure. The purpose of this study was to determine if rhodopsin phosphorylation patterns, a measure of the activity of the pigment, varied in a similar manner. After 10 min in strong light (1400 lux), all six threonine and serine sites in the rat rhodopsin C-terminus were phosphorylated, with mono- to tetraphosphorylation being substantially more prominent than penta- to hexaphosphorylation. The level and multiplicity of rhodopsin phosphorylations were reduced both with the duration of light exposure and the duration of subsequent darkness. Although showing vast differences in susceptibility to light damage, rats exposed at 5 P.M. or 1 A.M. showed similar rhodopsin phosphorylation levels and patterns. These data indicate that a process controlled by circadian rhythm other than rhodopsin phosphorylation is involved either in damaging or mediating the damage evoked by intense light exposure. 相似文献
40.
Ronald C. Crouch Ashok V. Bhatia O. William Lever 《Journal of heterocyclic chemistry》1990,27(2):385-389
High field 1H nmr studies have shown that the nature of the C -14 substituents has a remarkable influence on ring C conformation of epoxymorphinan opioids which have a 6α-hydroxyl group. In sharp contrast to the ring C twist-boat conformation observed in those 6α-hydroxy compounds which also have a 14-hydroxyl group (α-naltrexol; α-oxymorphol), ring C exists predominantly as a chair conformer in 6α-hydroxy compounds which have a proton bound to C -14 (dihydromorphine; dihydrocodeine). The 6β-hydroxy compounds (β-naltrexol; β-oxymorphol) have a ring C chair conformation in agreement with earlier studies. 相似文献