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101.
An engineered form of iso-1-cytochrome c with lysine 73 mutated to histidine is shown to increase by nearly 500-fold the rate of a conformational gate that modulates the rate of electron transfer into this protein. This result demonstrates the potential of protein engineering to provide electron transfer gates with tailored properties. The pH dependence of the rate of the conformational electron transfer gate correlates well with the pH dependence of the conformational change from a His 73-ligated heme to a Met 80-ligated heme, determined independently by pH jump methods, allowing unambiguous assignment of the conformational electron transfer gating step. The rate of the electron transfer gate is also modulated by a cis to trans proline isomerization, indicating that both amino acid sequence and the nature of the heme ligand provide avenues for rational design of electron transfer gates which open at different rates. 相似文献
102.
The stereochemical course of cycloalkanone imine reductions by a variety of boron hydride reagents is described; very high stereoselectivity with substituted alkali metal borohydrides is reported. 相似文献
103.
Martyn A. Brown Bruce R. McGarvey Andrzej Ozarowski Dennis G. Tuck 《Journal of organometallic chemistry》1998,550(1-2)
The primary process in the reaction of hexaphenylditin with various substituted orthoquinones (Q) is shown to involve attack by the quinone at a phenyl ligand. The intermediate thus formed decomposes to yield Ph3Sn(SQ·), where S(Q·−) is the corresponding semiquinonate. Rearrangement of these species in solution gives rise to biradicals, while intramolecular electron transfer may lead to the formation and precipitation of Ph2Sn(CAT), where CAT2− is the corresponding substituted catecholate. The identification of these processes depends in part on electron paramagnetic resonance spectroscopy. The reaction of Ph3SnCl or Ph2SnCl2 with Na(TBSQ·) (TBSQ·−=3,5-di-tert-butyl-orthobenzosemiquinonate) results in the formation of Ph2Sn(TBSQ·), which can undergo redistribution and intramolecular electron transfer, so that the solution chemistry of these latter systems is similar to that of the products of the Sn2Ph6+Q reaction. 相似文献
104.
Abstract— The percentage of pigmented to total bacteria in the outdoor atmospheric population was studied in the field and in controlled laboratory experiments to evaluate the effects of solar radiation (SR) on bacterial survival. The field experiments showed that the percentage of pigmented bacteria positively correlated with SR activity during clear summer days. The percentage was lowest during darkness before dawn and around midnight ( ca 33%) and as the SR increased during the day, gradually increased to a maximum of ca 50–60% at noontime to early afternoon and decreased thereafter. In the laboratory the ambient outdoor atmospheric bacteria impacted on culture plates were exposed to simulated SR and a germicidal light. With increased exposure, more nonpig-mented bacteria were killed and the percentage of pigmented bacteria gradually increased. These observations suggest an inverse relationship between the atmospheric bacterial survival and the percentage of pigmented bacteria contained therein, thus supporting the notion that pigmentation might provide protection for outdoor atmospheric bacteria from sunlight damage. As a consequence, viable pigmented bacteria (and other UV-resistant forms) in the atmosphere could be enriched under areas of stratospheric ozone depletion. 相似文献
105.
Physical and chemical strategies that place designed molecules in spatially separated regions of surfactant-templated mesostructured silicate thin films are used to prepare films containing rhodamine 6G (R6G), lanthanide complexes, and both simultaneously. Fluorescence and photoexcitation spectra of R6G in amorphous and structured thin films show that it is located inside the surfactant micelles of structured thin films. A silylated ligand that binds lanthanides condenses to form part of the silica framework and causes the lanthanide to localize in the silica. Luminescence and photoexcitation spectra show that energy transfer from the metal complex to R6G occurs in the films. R6G quenches Tb emission in a concentration-dependent manner. Energy transfer efficiency is calculated using the Tb luminescence lifetime, and this quantity is used to calculate the distance between Tb and R6G with the aid of Forster theory. 相似文献
106.
Hu C Noll BC Schulz CE Scheidt WR 《Journal of the American Chemical Society》2005,127(43):15018-15019
The synthesis, molecular structure, and electronic structure characterization of two five-coordinate high-spin imidazolate-ligated iron(II) porphyrinates are reported. Their electronic structure, as deduced from M?ssbauer spectra obtained in strong magnetic fields, is distinctly different from that of the analogous imidazole-ligated species. The resulting electronic structure models are consistent with all observed differing features in the two classes. 相似文献
107.
John J. Lenhart Linda A. Figueroa Bruce D. Honeyman David Kaneko 《Colloids and surfaces. A, Physicochemical and engineering aspects》1997,120(1-3):243-254
This paper reports the development of a treatment system, using animal chitin as a passive biosorbent, for removing U(VI) from aqueous waste streams. An integral part of this system is a model that provides for the optimization of the treatment system through simulation of U(VI) removal efficiency based on the characteristics of the influent waste stream. The model accounts for changing solution matrix conditions through the coupling of surface complexation and mass transfer models. Complexation of U(VI) by chitin surface sites was modeled using FITEQL. Application of FITEQL in the “forward” mode provided the sorbed and aqueous phase concentrations needed for the mass transfer model. The mass transfer model was derived for both batch and continuously stirred tank reactor (CSTR) configurations using Fick's Law, reactor mass balances and rate law expressions. The coupled model was successfully validated using CSTR data at pH 6.5 and rate constants determined from batch sorption experiments. The CSTR configuration yields a steady-state, eighty percent U(VI) removal for 1 μM influent U(VI) with a solution-phase pH of 6.5 and 3.9 g l−1 chitin. 相似文献
108.
The potassium enolate of 4-methoxy-3-buten-2-one reacts with acid chlorides anhydrides and acylimidazoles by C-acylation and cyclization to afford 2-substituted γ-pyrones directly. 相似文献
109.
Bruce M. Monroe 《Journal of heterocyclic chemistry》1969,6(6):917-919
Reaction of an α,β-unsaturated acid chloride with the anion of 5,5-dimethyl-1,3-cyclohexane-dione ( 2 ) gives either the enol ester ( 4 ) or a cyclized product ( 5 ), depending upon the reaction conditions. When the acid chloride is in excess, the ester is obtained. When the anion is in excess and the acid chloride is acryloyl or crotonyl, the cyclized product is obtained. A similar cyclized product ( 9 ) was formed from acryloyl chloride and an excess of the anion of 4-hydroxy-6-methyl-2-pyrone ( 8 ). 相似文献
110.
Doug Bruce John Biggins Tom Steiner Mike Thewalt 《Photochemistry and photobiology》1986,44(4):519-525
Excitation spectra of chlorophyll- a (Chl- a ) fluorescence in intact cells of Cryptomonas ovata, Chroomonas pauciplastida and Chroomonas salina were determined at 77 K. For all species the excitation spectra for emission from Chl- a associated with photosystem II (PSII) showed increased contributions by a carotenoid (493 nm) and phycobiliproteins, and decreased contributions by carotenoid (417 nm, 505 nm) and Chl- a (445 nm) as compared to excitation spectra for emission from Chl- a associated with photosystem I (PSI). Excitation spectra of C. salina and C. ovata showed an increased contribution by Chl- c 2 to PSII Chl- a fluorescence emission. In all three species the absorbance band positions of Chl- a , as determined from the excitation spectra, were similar to those previously described in green plants. green algae and phycobilisome-containing organisms. Time-resolved 77 K fluorescence emission spectra of C. ovata and C. salina showed successive emission from both phycoerythrin and Chl- c 2 , PSII Chl- a , and PSI Chl- a. C. pauciplastida showed successive emission from phycocyanin, PSII Chl- a , and PSI Chl- a. Spectral red-shifts with time were observed for the phycobiliprotein peaks in all three species. The fluorescence decay of phycoerythrin in C. ovata and C. salina was faster than that of phycocyanin in C. pauciplastida. The results are discussed in relation to the organization of the antenna pigments of PSII and PSI in the cryptophyte algae. 相似文献