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1.
C. D. Kalkar V. M. Raut M. Getahun 《Journal of Radioanalytical and Nuclear Chemistry》1991,155(2):79-90
It is well known that paramagnetic centers are formed when Na2SO4 crystals are exposed to -radiation. The dissolution of such crystals in aqueous ammonium nitrate results in reduction of nitrate to nitrite. Various factors which influence the yield of nitrite are investigated. The yield of nitrite is found to vary with the amount of irradiated Na2SO4 added, the dose absorbed by Na2SO4 crystals, the storing period of the irradiated salt, photoannealing time, concentration of aqueous ammonium nitrate and particle size of the Na2SO4 crystals. The G(NO
2
–
) value under optimum conditions of the conversion of nitrate to nitrite by irradiated Na2SO4 in aqueous ammonium nitrate is 0.009. The efficiency of energy transfer is 1.5%. The mechanism of reduction is based on the reactions of paramagnetic centers with nitrate ions. 相似文献
2.
Getahun Z Huang CY Wang T De León B DeGrado WF Gai F 《Journal of the American Chemical Society》2003,125(2):405-411
It is well-known that the C=N stretching vibration in acetonitrile is sensitive to solvent. Therefore, we proposed in this contribution to use this vibrational mode to report local environment of a particular amino acid in proteins or local environmental changes upon binding or folding. We have studied the solvent-induced frequency shift of two nitrile-derivatized amino acids, which are, AlaCN and PheCN, in H(2)O and tetrahydrofuran (THF), respectively. Here, THF was used to approximate a protein's hydrophobic interior because of its low dielectric constant. As expected, the C=N stretching vibrations of both AlaCN and PheCN shift as much as approximately 10 cm(-1) toward higher frequency when THF was replaced with H2O, indicative of the sensitivity of this vibration to solvation. To further test the utility of nitrile-derivatized amino acids as probes of the environment within a peptide, we have studied the binding between calmodulin (CaM) and a peptide from the CaM binding domain of skeletal muscle myosin light chain kinase (MLCK(579-595)), which contains a single PheCN. MLCK(579-595) binds to CaM in a helical conformation. When the PheCN was substituted on the polar side of the helix, which was partially exposed to water, the C=N stretching vibration is similar to that of PheCN in water. In constrast, when PheCN is introduced at a site that becomes buried in the interior of the protein, the C=N stretch is similar to that of PheCN in THF. Together, these results suggest that the C=N stretching vibration of nitrile-derivatized amino acids can indeed be used as local internal environmental markers, especially for protein conformational studies. 相似文献
3.
Nanda V Rosenblatt MM Osyczka A Kono H Getahun Z Dutton PL Saven JG Degrado WF 《Journal of the American Chemical Society》2005,127(16):5804-5805
Metal-binding sites in metalloproteins frequently occur at the interfaces of elements of secondary structure, which has enabled the retrostructural analysis of natural proteins and the de novo design of helical bundles that bind metal ion cofactors. However, the design of metalloproteins containing beta-structure is less well developed, despite the frequent occurrence of beta-conformations in natural metalloproteins. Here, we describe the design and construction of a beta-protein, RM1, that forms a stable, redox-active 4-Cys thiolate Fe(II/III) site analogous to the active site of rubredoxin. The protein folds into a beta-structure in the presence and absence of metal ions and binds Fe(II/III) to form a redox-active site that is stable to repeated cycles of oxidation and reduction, even in an aerobic environment. 相似文献
4.
Tucker MJ Getahun Z Nanda V DeGrado WF Gai F 《Journal of the American Chemical Society》2004,126(16):5078-5079
We studied here the binding of the mastoparan X peptide to a zwitterionic lipid bilayer (POPC) and demonstrated that nitrile-derivatized amino acids can be used to determine the hydration state (or change in hydration state) of specific sites of membrane-interactive peptides (upon binding). We have also shown that polarized ATR-FTIR measurements can further be used to uncover information regarding the spatial orientation of individual side chains as well as their conformational preference within the lipid bilayer. 相似文献
5.
Gurmessa Getahun Tadesse Singh Girija Shankar 《Research on Chemical Intermediates》2017,43(11):6447-6504
Research on Chemical Intermediates - Metal–carbenoids from α-diazocarbonyl compounds are well-known reactive intermediates with a long history of useful applications in synthetic organic... 相似文献
6.
Huang CY Klemke JW Getahun Z DeGrado WF Gai F 《Journal of the American Chemical Society》2001,123(38):9235-9238
The helix-coil transition of a synthetic alpha-helical peptide (the D-Arg peptide), Ac-YGG(KAAAA)(3)-CO-D-Arg-CONH(2), was studied by static far-UV circular dichroism (CD) and time-resolved infrared spectroscopy coupled with the laser-induced temperature-jump technique for rapid relaxation initiation. Equilibrium thermal unfolding measurements of the D-Arg peptide monitored by CD spectroscopy reveal an apparent two-state helix-coil transition, with a thermal melting temperature around 10 degrees C. Time-resolved infrared (IR) measurements following a laser-induced temperature jump, however, reveal biphasic (or multiphasic) relaxation kinetics. The fast phase rises within the 20 ns response time of the detection system. The slow phase has a decay lifetime of approximately 140 ns at 300 K and exhibits monotonic temperature dependence with an apparent activation energy around 15.5 kcal/mol. 相似文献
7.
Two convenient synthetic routes to 1,4-difluoroanthracene-9,10-dione are described. 相似文献
8.
Balakrishnan G Hu Y Bender GM Getahun Z DeGrado WF Spiro TG 《Journal of the American Chemical Society》2007,129(42):12801-12808
The alpha-helix is a ubiquitous structural element in proteins, and a number of studies have addressed the mechanism of helix formation and melting in simple peptides. However, fundamental issues remain to be resolved, particularly the temperature (T) dependence of the rate. In this work, we report application of a novel kHz repetition rate solid-state tunable NIR (pump) and deep UV Raman (probe) laser system to study the dynamics of helix unfolding in Ac-GSPEA3KA4KA4-CO-D-Arg-CONH2, a peptide designed for helix stabilization in aqueous solution. Its T-dependent UV resonance Raman (UVRR) spectra, excited at 197 nm for optimal enhancement of amide vibrations, were decomposed into variable contributions from helix and coil spectra. The helix fractions derived from the UVRR spectra and from far UV CD spectra were coincident at low T but deviated increasingly at high T, the UVRR curve giving higher helix content. This difference is consistent with the greater sensitivity of UVRR spectra to local conformation than CD. After a laser-induced T-jump, the UVRR-determined helix fractions defined monoexponential decays, with time-constants of approximately 120 ns, independent of the final T (Tf = 18-61 degrees C), provided the initial T (Ti) was held constant (6 degrees C). However, there was also a prompt loss of helicity, whose amplitude increased with increasing Tf, thereby defining an initial enthalpic phase, distinct from the subsequent entropic phase. These phases are attributed to disruption of H-bonds followed by reorientation of peptide links, as the chain is extended. When Ti was raised in parallel with Tf (10 degrees C T-jumps), the prompt phase merged into an accelerating slow phase, an effect attributable to the shifting distribution of initial helix lengths. Even greater acceleration with rising Ti has been reported in T-jump experiments monitored by IR and fluorescence spectroscopies. This difference is attributable to the longer range character of these probes, whose responses are therefore more strongly weighted toward the H-bond-breaking enthalpic process. 相似文献
9.
Time-resolved infrared study of the helix-coil transition using (13)C-labeled helical peptides. 总被引:2,自引:0,他引:2
C Y Huang Z Getahun T Wang W F DeGrado F Gai 《Journal of the American Chemical Society》2001,123(48):12111-12112
10.
H. Getahun L. F. Errea C. Illescas L. Méndez I. Rabadán 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,60(1):45-49
Single electron capture and single ionization total cross sections in collisions of proton with ethylene are calculated for
an
energy range 25 keV ≤
E
≤ 150 keV, using the classical trajectory Monte Carlo method. Multi-center model potentials are employed to represent
the interaction of the active electron on each molecular orbital with the C2H4+_{4}^{+} core. The results are compared with experimental results for single electron capture. 相似文献