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101.
Oleinikova A Smolin N Brovchenko I Geiger A Winter R 《The journal of physical chemistry. B》2005,109(5):1988-1998
The formation of spanning hydrogen-bonded water networks on protein surfaces by a percolation transition is closely connected with the onset of their biological activity. To analyze the structure of the hydration water at this important threshold, we performed the first computer simulation study of the percolation transition of water in a model protein powder and on the surface of a single protein molecule. The formation of an infinite water network in the protein powder occurs as a 2D percolation transition at a critical hydration level, which is close to the values observed experimentally. The formation of a spanning 2D water network on a single rigid protein molecule can be described by adapting the cluster analysis of conventional percolation studies to the characterization of the connectivity of the hydration water on the surface of finite objects. Strong fluctuations of the surface water network are observed close to the percolation threshold. Our simulations also furnish a microscopic picture for understanding the specific values of the experimentally observed hydration levels, where different steps of increasing mobility in the hydrated powder are observed. 相似文献
102.
Haisch C Niessner R Matveev OI Panne U Omenetto N 《Analytical and bioanalytical chemistry》1996,356(1):21-26
An experimental set-up for the detection of elemental chlorine in chlorinated hydrocarbons (CHCs) is described based on a miniaturized system, which could be used for on-line monitoring of chlorinated compounds. With an optimized time-resolved detection chlorine from CHCs like CCl4 can be determined by Laser-Induced-Breakdown-Spectroscopy (LIBS) with g/g-detection limits in the gas phase. The application of a miniaturized Nd : YAG laser resulted only in a minor loss in performance, hence it could be used for designing a rugged and small on-line sensor. In addition, preliminary results for the detection of chlorine via the formation of CuCl in the plasma formed by focussing the laser on a copper surface are reported. Utilizing the luminescence of the CuCl D-system at 440 nm, a tenfold improvement in the detection limits was obtained. It appears that the formation of ad hoc selected, small molecules in a laser plasma could be a promising alternative for the selective and sensitive analysis of gaseous chlorinated and other species. 相似文献
103.
Arikainen EO Boden N Bushby RJ Lozman OR Vinter JG Wood A 《Angewandte Chemie (International ed. in English)》2000,39(13):2333-2336
104.
Yamamoto A Akiba N Kodama S Matsunaga A Kato K Nakazawa H 《Journal of chromatography. A》2001,928(2):139-144
A multi-beam circular dichroism (CD) detector which is easily constructed by inserting inexpensive optics into a conventional photo-diode array detector has an advantage of simultaneous detection of the absorbance and CD. The enantiomeric purity determination of malic acid in beverages was performed by this detection system. Malic acid when complexed with Cu(II) was found to have an absorbance maximum at around 750 nm. The L-malic acid-Cu(II) complex showed a positive Cotton effect in its absorbance band and its anisotropy factor (delta epsilon/epsilon) was relatively large at about 1/170. This complex was retained on a reversed-phase column with the addition of racemic 2-hydroxy-3-methylbutyric acid to the mobile phase as the ligand. A plot of the relative peak areas between the CD and the absorption (delta abs/abs) versus optical purity showed good linearity with a correlation coefficient of 0.999, and the precision expressed as the relative standard deviation of the errors from the regression line was +/-2.7% (2sigma). The accuracy of the proposed method was assessed by capillary electrophoresis. Eight commercially available juice products were analyzed using this method. Five of them were thought to be adulterated with synthetic malic acid. 相似文献
105.
The one-pot cyclocondensation of 2,6-diaminopyrimidin-4-one, an aromatic or aliphatic aldehyde and a beta-ketoester in acetic acid, or dimethyl sulfoxide in the presence of zinc(II) bromide, under thermal conditions provided dihydropyrido[2,3-d]pyrimidin-4(3H)-ones in good yield and with total regiocontrol. 相似文献
106.
Minamide T Mitsubayashi K Jaffrezic-Renault N Hibi K Endo H Saito H 《The Analyst》2005,130(11):1490-1494
Methyl mercaptan (MM) is known as one of the major chemicals of halitosis (bad breath). In this study, a bioelectronic gas sensor (bio-detector) for gaseous MM was developed and was applied to measure halitosis in breath. The bio-detector consisted of a Clark-type dissolved oxygen electrode, a monoamine oxidase type-A (MAO-A) immobilized membrane and a reaction unit that had liquid and gaseous compartments separated by a hydrophobic porous polytetrafluoroethylene (PTFE) diaphragm membrane. The tip of the electrode covered with MAO-A membrane was placed into the liquid compartment as touching to the PTFE diaphragm membrane. In order to amplify the bio-detector output, a substrate regeneration cycle caused by coupling the monooxygenase with l-ascorbic acid as reducing reaction with reagent system, was applied. The results of MM vapor measurements showed the calibration range of the bio-detector for MM vapor was from 0.087 to 11.5 ppm (correlation coefficient: 0.993) and included the human sense of smell level 5 (0.2 ppm). The bio-detector had good selectivity being attributed to enzyme specificity was obtained for several substances (trimethyl amine, ammonia, dimethyl sulfide, etc.). The bio-detector was applied for halitosis measurement. Expired gases in five subjects were sampled every hour and the concentrations of MM in the expired gases were monitored. The output of bio-detector showed behaviour of halitosis level changes in a day such as increasing with passage of time and decreasing after eating. 相似文献
107.
Simultaneous determination of copper, zinc, cadmium and mercury with high sensitivity is possible by neutron activation analysis. After irradiation, the samples are digested and an initial separation of the four elements made by means of an ion-exchange resin. The elements in the separated fractions are then treated to give radio-chemical purity, precipitated, and their activities measured. A purely instrumental technique for the analysis of zinc in samples of biological material is also described. The samples are irradiated for a week and after the activity has decayed for about three months it is measured on a gamma-spectrometer. 相似文献
108.
The [3,3]-sigmatropic rearrangement took place smoothly during the course of trifluoroacetylation of O-phenyloxime at below room temperature to give the dihydrobenzofuran or benzofuran as a result of concomitant cyclization. 相似文献
109.
Henriques ES Floriano WB Reuter N Melo A Brown D Gomes JA Maigret B Nascimento MA Ramos MJ 《Journal of computer-aided molecular design》2001,15(4):309-322
We present the search for a new model of -factor XIIa, a blood coagulation enzyme, with an unknown experimental 3D-structure. We decided to build not one but three different models using different homologous proteins as well as different techniques and different modellers. Additional studies, including extensive molecular dynamics simulations on the solvated state, allowed us to draw several conclusions concerning homology modelling, in general, and -factor XIIa, in particular. 相似文献
110.
This paper concerns with three series of experiments about dimethylsulfide gas phase oxidation, carried out at increasing NOx level (< 20 ppb, 1 ppm, 10 ppm) to show the relation between the amounts of nitrogen oxides and the molar yields of sulfur containing products. DMSO, DMSO2, HCHO, HCOOH and SO2 were found as main reaction products. From these experiments and from preceding studies, a sensitive decrease in the quantity of total sulfur products in aerosol phase is underlined. This result derives from the reaction of NOx with CH3S(O)O2 and CH3S(O)OO radicals, which leads to stable intermediates as methylsulphonylperoxynitrate, MSPN, with a characteristic PAN-like structure. 相似文献