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221.
Shimin Xu Lawrence S. Bartell 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,31(1):117-123
Molecular dynamics simulations of the behavior of molecules in crystalline clusters of TeF6 were carried out on systems of 100, 150, 250, and 350 molecules. Several diagnostic functions were applied to investigate whether rotational melting occurred before translational melting. These functions included the coefficient of rotational diffusionD θ(T), the “orientational Lindemann index” δθ(T), the “orientational angular distribution function”Q(θ,T), and the “orientational pair-correlation function”g θ(r, T). All indicators implied that rotational melting occurred before translational melting, that it began with the outermost molecules, and that its onset for smaller clusters was at lower temperatures than for larger clusters. Results also showed that the rotational transition coincided with the transition from a lower symmetry phase (monoclinic) to cubic, a phenomenon that had been noted by others to occur with some regularity for systems of globular molecules. 相似文献
222.
Matteo Scampicchio Nathan S. Lawrence Alessandra Arecchi Stella Cosio Saverio Mannino 《Electroanalysis》2007,19(1):85-90
Cyclic voltammetry has been applied to the rapid measurement of free SH‐compounds in food flours samples. The protocol is based on the electrochemical adaptation of the Ellman's test, where the DTNB reacts with SH‐compounds present in food flour extracts, resulting in the equimolar production of the electroactive compound TNBA which, in turns, reacts with phenylendiamine. The reaction is found to provide an analytical signal from which to quantify indirectly free sulfhydryl compounds in flours extracts. 相似文献
223.
Dr. Marcelo M. Pedroso Prof. James A. Larrabee Dr. Fernanda Ely Shuhui E. Gwee Dr. Nataša Mitić Prof. David L. Ollis Prof. Lawrence R. Gahan Prof. Gerhard Schenk 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):999-1009
The diesterase Rv0805 from Mycobacterium tuberculosis is a dinuclear metallohydrolase that plays an important role in signal transduction by controlling the intracellular levels of cyclic nucleotides. As Rv0805 is essential for mycobacterial growth it is a promising new target for the development of chemotherapeutics to treat tuberculosis. The in vivo metal‐ion composition of Rv0805 is subject to debate. Here, we demonstrate that the active site accommodates two divalent transition metal ions with binding affinities ranging from approximately 50 nm for MnII to about 600 nm for ZnII. In contrast, the enzyme GpdQ from Enterobacter aerogenes, despite having a coordination sphere identical to that of Rv0805, binds only one metal ion in the absence of substrate, thus demonstrating the significance of the outer sphere to modulate metal‐ion binding and enzymatic reactivity. CaII also binds tightly to Rv0805 (Kd≈40 nm ), but kinetic, calorimetric, and spectroscopic data indicate that two CaII ions bind at a site different from the dinuclear transition‐metal‐ion binding site. CaII acts as an activator of the enzymatic activity but is able to promote the hydrolysis of substrates even in the absence of transition‐metal ions, thus providing an effective strategy for the regulation of the enzymatic activity. 相似文献
224.
Jasper AW Klippenstein SJ Harding LB Ruscic B 《The journal of physical chemistry. A》2007,111(19):3932-3950
The CH3 + OH bimolecular reaction and the dissociation of methanol are studied theoretically at conditions relevant to combustion chemistry. Kinetics for the CH3 + OH barrierless association reaction and for the H + CH2OH and H + CH3O product channels are determined in the high-pressure limit using variable reaction coordinate transition state theory and multireference electronic structure calculations to evaluate the fragment interaction energies. The CH3 + OH --> 3CH2 + H2O abstraction reaction and the H2 + HCOH and H2 + H2CO product channels feature localized dynamical bottlenecks and are treated using variational transition state theory and QCISD(T) energies extrapolated to the complete basis set limit. The 1CH2 + H2O product channel has two dynamical regimes, featuring both an inner saddle point and an outer barrierless region, and it is shown that a microcanonical two-state model is necessary to properly describe the association rate for this reaction over a broad temperature range. Experimental channel energies for the methanol system are reevaluated using the Active Thermochemical Tables (ATcT) approach. Pressure dependent, phenomenological rate coefficients for the CH3 + OH bimolecular reaction and for methanol decomposition are determined via master equation simulations. The predicted results agree well with experimental results, including those from a companion high-temperature shock tube determination for the decomposition of methanol. 相似文献
225.
Dr. Pavel Zrazhevskiy Dr. Shreeram Akilesh Dr. Wanyi Tai Konstantin Queitsch Prof. Lawrence D. True Prof. Jonathan Fromm Prof. David Wu Prof. Peter Nelson Prof. John A. Stamatoyannopoulos Prof. Xiaohu Gao 《Angewandte Chemie (International ed. in English)》2016,55(31):8975-8978
Integration of imaging data across different molecular target types can provide in‐depth insight into cell physiology and pathology, but remains challenging owing to poor compatibility between target‐type‐specific labeling methods. We show that cross‐platform imaging analysis can be readily achieved through DNA encoding of molecular targets, which translates the molecular identity of various target types into a uniform in situ array of ssDNA tags for subsequent labeling with complementary imaging probes. The concept was demonstrated through multiplexed imaging of mRNAs and their corresponding proteins with multicolor quantum dots. The results reveal heterogeneity of cell transfection with siRNA and outline disparity in RNA interference (RNAi) kinetics at the level of both the mRNA and the encoded protein. 相似文献
226.
The effect of carbon nanotubes on the electrochemical response of the pH sensing, redox-active copolymer poly(vinylanthracene-co-vinylferrocene) has been studied. A clear increase in the linear response of the anthracene moiety with pH is observed in the presence of carbon nanotubes. 相似文献
227.
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229.
Harvey RD Barlow DJ Drake AF Kudsiova L Lawrence MJ Brain AP Heenan RK 《Journal of colloid and interface science》2007,315(2):648-661
Encapsulation efficiencies of vesicles formed by the nonionic surfactant 1,2-dioctadecyl-rac-glycerol-3-omega-methoxydodecylethylene glycol (abbreviated as 2C18E12) and its phospholipid counterpart, distearoylphosphatidylcholine (DSPC) at 298 K, were determined by the entrapment of the water-soluble dye, carboxyfluorescein (CF) to be 0.045+/-0.001 and 0.03+/-0.04 L mol(-1) for 2C18E12 vesicles prepared using low osmolarity (270 m Osm) Krebs-Henseleit (K-H) buffer and a modified 'high salt' (1600 m Osm) variant of K-H buffer, respectively, and 0.64+/-0.01 and 0.31+/-0.04 Lmol(-1) for DSPC vesicles prepared under the same conditions and in the same buffers. Freeze fracture electron microscopy studies confirmed the presence of vesicles when 2C18E12 and DSPC were dispersed in water and both buffer solutions. Small angle neutron scattering (SANS) studies, using D2O in place of H2O, showed that when 2C18E12 vesicles were prepared in the 'high salt' variant of K-H buffer as opposed to K-H buffer or water, a higher proportion of multilamellar vesicles (MLV) were formed. Furthermore when prepared in the 'high salt' variant of K-H buffer, the 2C18E12 bilayers were thinner, and when present in the form of MLV exhibited a smaller layer of water separating the bilayers. However, even in the absence of electrolyte, 2C18E12 formed surprisingly thin bilayers due to the penetration of the polyoxyethylene chains into the hydrophobic chain region of the bilayer. Due to the dehydrating effect of the high concentration of electrolyte present in the 'high salt' variant of K-H, the polyoxyethylene head groups penetrated further into the hydrophobic region of the bilayer making the bilayer even thinner. In the case of the DSPC vesicles, although the SANS study showed an increase in the relative proportion of multilamellar to unilamellar vesicles when samples were prepared in the 'high salt' variant of K-H buffer, no differences were observed in the thickness and the d-spacing of the vesicle bilayers. Variable temperature turbidity measurements of 2C18E12, and DSPC vesicles prepared in water indicated phase changes at 320+/-0.5 and 327+/-0.5 K, respectively, and were unchanged when the 'high salt' variant of K-H buffer was used as hydrating medium. Taken together, these results suggest that a low phase transition temperature was not the reason for the poor entrapment efficiency of 2C18E12 vesicles but rather the very 'thin' hydrophobic barrier formed by the penetration of the polyoxyethylene chains into the hydrophobic region of the bilayer. 相似文献
230.
Jackson T Woo LW Trusselle MN Chander SK Purohit A Reed MJ Potter BV 《Organic & biomolecular chemistry》2007,5(20):2940-2952
The synthesis and biological evaluation of a series of novel Dual Aromatase-Sulfatase Inhibitors (DASIs) are described. It is postulated that dual inhibition of the aromatase and steroid sulfatase enzymes, both responsible for the biosynthesis of oestrogens, will be beneficial in the treatment of hormone-dependent breast cancer. The compounds are based upon the Anastrozole aromatase inhibitor template which, while maintaining the haem ligating triazole moiety crucial for enzyme inhibition, was modified to include a phenol sulfamate ester motif, the pharmacophore for potent irreversible steroid sulfatase inhibition. Adaption of a synthetic route to Anastrozole was accomplished via selective radical bromination and substitution reactions to furnish a series of aromatase inhibitory pharmacophores. Linking these fragments to the phenol sulfamate ester moiety employed SN2, Heck and Mitsunobu reactions with phenolic precursors, from where the completed DASIs were achieved via sulfamoylation. In vitro, the lead compound, 11, had a high degree of potency against aromatase (IC50 3.5 nM), comparable with that of Anastrozole (IC50 1.5 nM) whereas, only moderate activity against steroid sulfatase was found. However, in vivo, 11 surprisingly exhibited potent dual inhibition.Compound 11 was modelled into the active site of a homology model of human aromatase and the X-ray crystal structure of steroid sulfatase. 相似文献