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31.
Solution‐State 17O Quadrupole Central‐Transition NMR Spectroscopy in the Active Site of Tryptophan Synthase
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Robert P. Young Bethany G. Caulkins Dr. Dan Borchardt Dr. Daryl N. Bulloch Dr. Cynthia K. Larive Dr. Michael F. Dunn Dr. Leonard J. Mueller 《Angewandte Chemie (International ed. in English)》2016,55(4):1350-1354
Oxygen is an essential participant in the acid–base chemistry that takes place within many enzyme active sites, yet has remained virtually silent as a probe in NMR spectroscopy. Here, we demonstrate the first use of solution‐state 17O quadrupole central‐transition NMR spectroscopy to characterize enzymatic intermediates under conditions of active catalysis. In the 143 kDa pyridoxal‐5′‐phosphate‐dependent enzyme tryptophan synthase, reactions of the α‐aminoacrylate intermediate with the nucleophiles indoline and 2‐aminophenol correlate with an upfield shift of the substrate carboxylate oxygen resonances. First principles calculations suggest that the increased shieldings for these quinonoid intermediates result from the net increase in the charge density of the substrate–cofactor π‐bonding network, particularly at the adjacent α‐carbon site. 相似文献
32.
Lesnyak V Wolf A Dubavik A Borchardt L Voitekhovich SV Gaponik N Kaskel S Eychmüller A 《Journal of the American Chemical Society》2011,133(34):13413-13420
A 3D metal ion assisted assembly of nanoparticles has been developed. The approach relies on the efficient complexation of cadmium ions and 5-mercaptomethyltetrazole employed as the stabilizer of both colloidal CdTe and Au nanoparticles. It enables in a facile way the formation of hybrid metal-semiconductor 3D structures with controllable and tunable composition in aqueous media. By means of critical point drying, these assemblies form highly porous aerogels. The hybrid architectures obtained are characterized by electron microscopy, nitrogen adsorption, and optical spectroscopy methods. 相似文献
33.
The distribution of oxygen and other elements within the leached layer of a soda-lime glass after a short-time treatment (15–60 min) in pure H2
18O and D2
18O was investigated by means of neutral primary beam secondary ion mass spectrometry (NPB-SIMS). The18O– profiles resulting from the penetration of an oxygen containing species are not disturbed by interference of the species H2
16O–, originating from the residual gas in the vacuum chamber. In agreement with previous results, no isotope effect could be detected. Hydration of the glass leads to a pronounced matrix effect which impedes oxygen analysis in the negative secondary ion mode. The ratio of the maximum18O– intensity in the leached layer to the16O– intensity in the bulk was recorded as a function of time for one series of experiments. The result is in accordance with the time-dependence of the Na2O concentration in the leached layer. 相似文献
34.
Bucar DK Henry RF Lou X Borchardt TB Zhang GG 《Chemical communications (Cambridge, England)》2007,(5):525-527
Co-crystal formation between caffeine and adipic acid has been explored over the years without success; utilizing the newly developed co-crystal screening method, we have finally discovered this "hidden" caffeine and adipic acid co-crystal. 相似文献
35.
36.
Kirsten Moritz Reinhard Herbig Tanja Damjanovi Christos Argirusis Günter Borchardt 《Colloids and surfaces. A, Physicochemical and engineering aspects》2009,350(1-3):13-21
Mullite and mullite/Al2O3 precursor sols have been developed for the deposition of oxidation barrier coatings on carbon fibre reinforced composites using a combination of sol–gel synthesis and electrophoresis.The sols were synthesised by controlled hydrolysis and condensation of TEOS (tetraethoxysilane) and Al(OBus)3 (aluminium tri-sec-butylate). The main objective was the definition of synthesis conditions which yield sols suitable for the electrophoretic deposition (EPD). Measurements of the Electrokinetic Sonic Amplitude were used to investigate the electrokinetic properties of the sols in the as-prepared state and depending on the later addition of H2O. 29Si CP/MAS NMR spectra of dried precursor samples were recorded to study the homogeneity of Al/Si mixture. The progress of crystallisation with increasing temperature of heat treatment was examined by XRD. Oxidation protection coatings on C/C–SiC composites were prepared by EPD.Whereas a low H2O to TEOS ratio during the sol synthesis was advantageous for a low mullite formation temperature, a high H2O to TEOS ratio was necessary to enable the EPD. The synthesis of a sol with a low H2O to TEOS ratio in the first step and the later modification of this sol by the addition of water was a successful method to combine the required electrokinetic properties and mullitisation temperatures below 1200 °C. 相似文献
37.
38.
Jerry C. Yeh Ronald T. Borchardt Angelo Vedani 《Journal of computer-aided molecular design》1991,5(3):213-234
Summary
S-adenosyl-l-homocysteine hydrolase (AdoHcy hydrolase, EC 3.3.1.1.), a specific target for antiviral drug design, catalyzes the hydrolysis of AdoHcy to adenosine (Ado) and homocysteine (Hcy) as well as the synthesis of AdoHcy from Ado and Hcy. The enzyme isolated from different sources has been shown to contain tightly bound NAD+.Based on the 2.0 Å-resolution X-ray crystal structure of dogfish lactate dehydrogenase (LDH), which is functionally homologous to AdoHcy hydrolase, and the primary sequence of rat liver AdoHcy hydrolase, we have derived a molecular model of an extended active site for AdoHcy hydrolase. The computational mutation was performed using the software MUTAR (Yeh et al., University of Kansas, Lawrence), followed by molecular mechanics optimizations using the programs AMBER (Singh et al., University of California, San Francisco) and YETI (Vedani, University of Kansas). Solvation of the model structure was achieved by use of the program SOLVGEN (Jacober, University of Kansas); 56 water molecules were explicitly included in all refinements. Some of these may be involved in the catalytic reaction.We also studied a model of the complex of AdoHcy hydrolase with NAD+, as well as the ternary complexes of the redox reaction catalyzed by AdoHcy hydrolase and has been used to differentiate the relative binding strength of inhibitors. 相似文献
39.
John K. Borchardt E. Dwyann Dalrymple 《Journal of polymer science. Part A, Polymer chemistry》1982,20(7):1745-1764
A multiple-correlation analysis program was used to generate equations relating the Alfrey–Price Q and e values of vinyl monomers to the 13C-NMR absorption frequencies of the α- and β-carbon atoms of the monomers. Separate equations for the calculation of Q and e values of styrenes, chlorinated olefins, acrylates, methacrylates, vinyl ethers, and esters, nitrogen containing monomers, allyl compounds, and miscellaneous olefins were developed. The correlation coefficients of most of these equations were greater than 0.99 and permit accurate calculation of the Q and e values. The Q and e values so calculated may then be used to obtain estimates of the reactivity ratios in copolymerizations prior to actually performing the experiments. Attempts to develop a single Q value equation and a single e value equation for 63 vinyl monomers of the above classes resulted in relations having correlation coefficients of 0.63 and 0.81, respectively, too low to permit sufficiently accurate calculation of the Q and e values. 相似文献
40.