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151.
We have developed a process that significantly reduces the number of rotamers in computational protein design calculations. This process, which we call Vegas, results in dramatic computational performance increases when used with algorithms based on the dead-end elimination (DEE) theorem. Vegas estimates the energy of each rotamer at each position by fixing each rotamer in turn and utilizing various search algorithms to optimize the remaining positions. Algorithms used for this context specific optimization can include Monte Carlo, self-consistent mean field, and the evaluation of an expression that generates a lower bound energy for the fixed rotamer. Rotamers with energies above a user-defined cutoff value are eliminated. We found that using Vegas to preprocess rotamers significantly reduced the calculation time of subsequent DEE-based algorithms while retaining the global minimum energy conformation. For a full boundary design of a 51 amino acid fragment of engrailed homeodomain, the total calculation time was reduced by 12-fold. 相似文献
152.
The separation of chlorthalidone enantiomers in capillary electrochromatography on an achiral stationary phase when adding a chiral selector, hydroxypropyl-β-cyclodextrin, to the mobile phase, was optimised. The goal was to investigate the feasibility of modelling retention times and resolution when during the optimisation procedure regular replacement of columns is required due to their fragility. Therefore, it is essential that the packing procedure delivers reproducible columns. The optimisation of an existing chlorthalidone separation was chosen as case study. The influence of two factors, chiral selector concentration and organic modifier content, on the responses was modelled. The experiments performed prior to modelling were defined by a central composite design. Results on different columns, obtained under identical experimental conditions, were found comparable and thus modelling was possible in situations where several columns were required to complete a design. A second-order polynomial model was built for both responses. Optimal separations were also predicted using Derringer’s desirability functions. The optimum was found at 33 mM cyclodextrin and 16% (v/v) acetonitrile on two types of columns (with different packing times) leading to a strong reduction in analysis time for an equally good separation compared to the initial conditions. Measured and predicted responses were found comparable, indicating that acceptable models were obtained. 相似文献
153.
5-(2-Oxazolynyl)cyclopentadiene was designed on the basis of the orbital mixing rule to react with dienophiles with highly contrasteric manner in Diels-Alder reactions. The design was validated by the synthesis and reactions of the corresponding pentamethyl derivative, 5-(2-oxazolynyl)-1,2,3,4,5-pentamethylcyclopentadiene, to afford the products with the ratios of syn/anti=89-93/11-7. 相似文献
154.
Summary A strategy for the optimisation of direct chiral separation of omeprazole and a metabolite, hydroxi-omeprazole, in reversed
phase liquid chromatography is described.
A factorial design was used, where mobile phase pH, concentration of a mobile phase modifier, ionic strength and column temperature
were tested as the variables and enantioselective retention, column efficiency and asymmetry factor as the responses.
The experimental results were evaluated with multivariate analyses, which demonstrated that the column temperature and content
of mobile phase acetonitrile were by far the most important variables. The enantiomers of omeprazole and one of its metabolites
were baseline resolved within 15 minutes. The optimised chromatographic system was used for a separation of the enantiomers
of omeprazole and its main metabolite in a patient plasma sample. 相似文献
155.
Exact rotamer optimization for protein design 总被引:1,自引:0,他引:1
Computational methods play a central role in the rational design of novel proteins. The present work describes a new hybrid exact rotamer optimization (HERO) method that builds on previous dead-end elimination algorithms to yield dramatic performance enhancements. Measured on experimentally validated physical models, these improvements make it possible to perform previously intractable designs of entire protein core, surface, or boundary regions. Computational demonstrations include a full core design of the variable domains of the light and heavy chains of catalytic antibody 48G7 FAB with 74 residues and 10(128) conformations, a full core/boundary design of the beta1 domain of protein G with 25 residues and 10(53) conformations, and a full surface design of the beta1 domain of protein G with 27 residues and 10(60) conformations. In addition, a full sequence design of the beta1 domain of protein G is used to demonstrate the strong dependence of algorithm performance on the exact form of the potential function and the fidelity of the rotamer library. These results emphasize that search algorithm performance for protein design can only be meaningfully evaluated on physical models that have been subjected to experimental scrutiny. The new algorithm greatly facilitates ongoing efforts to engineer increasingly complex protein features. 相似文献
156.
《Electroanalysis》2005,17(4):305-311
Boron‐doped diamond thin‐film electrodes display negligible fouling effects in the presence of high levels of surface‐active materials, including proteins. Dramatic improvements in the stability of the analyte response (compared to common glassy carbon and carbon paste electrodes) are illustrated using bovine serum albumin (BSA), gelatin, and Triton X‐100 in connection with repetitive square‐wave voltammetric (SWV) measurements. The voltammetric response of ascorbic acid at the diamond electrode exhibits negligible shifts in peak potentials and minimal depressions of current signals over a wide range of surfactant concentrations (0–750 ppm). For example, the diamond electrode exhibited 70, 50 and 60 mV potential shifts for 10 repetitive voltammetric scans in the presence of 100 ppm BSA, gelatin and Triton X‐100, respectively, compared to 120, 190, and 280 mV shifts observed at the glassy carbon electrode. Furthermore, only 4.3 and 6.2% of the initial current decays were observed in the presence of 100 ppm Triton X‐100 and gelatin, respectively (compared to 45.2 and 34.4% diminutions at the glassy carbon electrode). Such improved performance was also confirmed from the SWV measurements of uric acid, dihydroxyphenylacetic acid, and catechol. The greatly improved resistance to surfactant interference reflects the fact that the as‐grown diamond thin film, composed of oxide‐free and hydrogen‐terminated surface, has a relatively lower surface energy and minimal electrostatic attributes, either specific or general, so that little adsorption of surface‐active agents occurs. The topographic AFM images of the diamond electrode surface confirm a negligible BSA fouling effect after repetitive SWV measurements. Such enhanced antifouling features make diamond electrodes very attractive for numerous real‐life electroanalytical applications. 相似文献
157.
Differential
scanning calorimetry (DSC) is a thermal analytical tool for preformulation
studies. Extrapolated melting temperature (TP)
and heat of fusion (ΔHf)
can be used as parameters for optimizing the DSC performance. Two model pharmaceuticals
acetaminophen and nicotinamide are used in this study. Using a factorial design
for the experimental model and matrix analysis the results, the effect of
sample mass, heating rate and the nitrogen flow rate were evaluated on the
ΔHf values
and TP values. Two
levels for each of the procedural variables were used as a balanced experimental
design with two sample sizes, two heating rates and two nitrogen flow rates.
It was found that the change in the heating rate caused significant changes
in the ΔHf
values but not the Tp
values for acetaminophen. However, no significant effect was found for the Tp value but ΔHf value was affected to a
certain extent for nicotinamide. 相似文献
158.
Transition metal oxide doped lanthanum gallates, La0.9Sr0.1Ga0.8M0.2O3 (where M=Co, Mn, Cr, Fe, or V), are studied as mixed ionic-electronic conductors (MIECs) for electrode applications. The
electrochemical properties of these materials in air and in H2 are characterized using impedance spectroscopy, open cell voltage measurement, and gas permeation measurement. Three single
cells based on La0.9Sr0.1Ga0.8 Mg0.2O3 (LSGM) electrolyte (1.13 to 1.65 mm thick) but with different electrode materials are studied under identical conditions
to characterize the effectiveness of the lanthanum gallate-based MIECs for electrode applications. At 800 °C, a single cell
using La0.9Sr0.1- Ga0.8Co0.2O3 as the cathode and La0.9Sr0.1Ga0.8Mn0.2O3 as the anode shows a maximum power density of 88 mW/cm2, which is better than that of a cell using Pt as both electrodes (20 mW/cm2) and that of a cell using La0.6Sr0.4CoO3 (LSC) as the cathode and CeO2-Ni as the anode (61 mW/cm2) under identical conditions. The performance of LSGM-based fuel cells with MIEC electrodes may be further improved by reducing
the electrolyte thickness and by optimizing the microstructures of the electrodes through processing.
Received: 9 January 1998 / Accepted: 1 May 1998 相似文献
159.
160.
Predicting the performance of molecularly imprinted polymers: Selective extraction of caffeine by molecularly imprinted solid phase extraction 总被引:2,自引:0,他引:2
A rational design approach was taken to the planning and synthesis of a molecularly imprinted polymer capable of extracting caffeine (the template molecule) from a standard solution of caffeine and further from a food sample containing caffeine. Data from NMR titration experiments in conjunction with a molecular modelling approach was used in predicting the relative ratios of template to functional monomer and furthermore determined both the choice of solvent (porogen) and the amount used for the study. In addition the molecular modelling program yielded information regarding the thermodynamic stability of the pre-polymerisation complex. Post-polymerisation analysis of the polymer itself by analysis of the pore size distribution by BET yielded significant information regarding the nature of the size and distribution of the pores within the polymer matrix. Here is proposed a stepwise procedure for the development and testing of a molecularly imprinted polymer using a well-studied compound—caffeine as a model system. It is shown that both the physical characteristics of a molecularly imprinted polymer (MIP) and the analysis of the pre-polymerisation complex can yield vital information, which can predict how well a given MIP will perform. 相似文献