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991.
Santosh Kumar Verma 《Talanta》2007,71(4):1546-1552
The feasibility of employing diffuse reflectance Fourier transform infrared spectroscopy (DRS-FTIR) as a sensitive tool in the submicrogram level determination of sulphate (SO42−) was checked in this work. This paper presents the development of a new, rapid and precise analytical method for ppb levels of sulphate (SO42−) in environmental samples like coarse and fine aerosol particles, dry deposits and soil. The determination of submicrogram levels of sulphate is based on the selection of a quantitative analytical peak at 617 cm−1 among the three observed vibrational peaks and preparing calibration curve using different known concentrations of sulphate by diffuse reflectance-Fourier transform infra red spectrometric (DRS-FTIR) technique. Pre-weighed and ground IR grade KBr was used as substrate over which remarkably wide range of known concentration of sulphate was sprayed and dried. The dried sample was analysed by DRS-FTIR. Three calibration curves for three different concentration ranges of sulphate were prepared for samples containing low and relatively higher sulphate contents. The relative standard deviation (n = 8) for the sulphate concentration ranges, 2.5-35.5, 25.5-165, 55-1000 μg/0.5 g KBr, as used to prepare calibration curves, were 2.4%, 2.1% and 1.5%, respectively. The relative standard deviation for the sulphate concentration in real samples were found to be in the range, 3.11-5.76% (n = 16), 4.05-7.75% (n = 16) and 1.48-3.52% (n = 10) for aerosol, dry deposits and soil, respectively. The LOD of the method is 0.20 μg/g SO42−. The F- and t-tests were performed to check the analytical quality assurance test. The noteworthy feature of the reported method is the non-interference of any of the associated anions and cations. The results were compared with that of ion-chromatographic method with high degree of acceptability. The method can be applied in wide concentration ranges. A method for sulphate determination was introduced that did not require pretreatment of samples. This method employed the direct determination of the sulphate. The method is reagent less, nondestructive, very fast, repeatable, and accurate and has high sample throughput value. 相似文献
992.
Shaojing Bu Chunxiang Cui Xiaoxin Liu Ling Bai 《Journal of Sol-Gel Science and Technology》2007,43(2):151-159
Porous nanocrystalline TiO2 films have been prepared on cp-Ti substrates for biomedical usage by a sol–gel process from the solutions containing polyethylene
glycol (PEG) as a template. Variations of the crystal structure with heat-treatment temperature determined by XRD are different
for TiO2 films and powders, due to the effect of titanium substrate. The surface texture of porous TiO2 films is analyzed by means of SEM and found to greatly depend on the concentration and molecular weight of PEG. The pore
formation mechanism is discussed in relation to the self-assembly of PEG and phase separation between PEG adsorbed on TiO2 oligomers and ethanol. 相似文献
993.
Miles EW 《Chemical record (New York, N.Y.)》2001,1(2):140-151
Tryptophan synthase is a classic enzyme that channels a metabolic intermediate, indole. The crystal structure of the tryptophan synthase alpha2beta2 complex from Salmonella typhimurium revealed for the first time the architecture of a multienzyme complex and the presence of an intramolecular tunnel. This remarkable hydrophobic tunnel provides a likely passageway for indole from the active site of the alpha subunit, where it is produced, to the active site of the beta subunit, where it reacts with L-serine to form L-tryptophan in a pyridoxal phosphate-dependent reaction. Rapid kinetic studies of the wild type enzyme and of channel-impaired mutant enzymes provide strong evidence for the proposed channeling mechanism. Structures of a series of enzyme-substrate intermediates at the alpha and beta active sites are elucidating enzyme mechanisms and dynamics. These structural results are providing a fascinating picture of loops opening and closing, of domain movements, and of conformational changes in the indole tunnel. Solution studies provide further evidence for ligand-induced conformational changes that send signals between the alpha and beta subunits. The combined results show that the switching of the enzyme between open and closed conformations couples the catalytic reactions at the alpha and beta active sites and prevents the escape of indole. 相似文献
994.
Paier J Stockner T Steinreiber A Faber K Fabian WM 《Journal of computer-aided molecular design》2003,17(1):1-11
A 3D QSAR analysis (quantitative structure activity relationships) of a set of 2,2-disubstituted epoxides, substrates for epoxide hydrolases originating from four different organisms, was conducted by CoMFA (comparative molecular field analysis) and CoMSIA (comparative molecular similarity indices analysis), with respect to the enantioselective ring opening to the corresponding vicinal diol. Structural variations of the substrates include alkyl chains of different lengths, unsaturated moieties ((E)- and (Z)-alkenyl, alkinyl, aryl) and electronegative groups (ether oxygens, halogen atoms) at different locations within the 2-substituent group. Generally, all four organisms, namely Rhodococcus ruber NCIMB 11216, Rhodococcus ruber DSM 43338, Rhodococcus ruber DSM 44540 and Rhodococcus ruber DSM 44539, preferentially react with the (S)-enantiomer of the epoxide. Enantioselectivities (enantiomeric ratio, lnE values) show a rather large variation, ranging from almost no (lnE<1) to nearly complete selectivity (lnE>5.3). In addition, the response of the epoxide hydrolases stemming from the four organisms towards structural modifications of the substrate is different. Models for the enantioselectivity (enantiomeric ratio, ln E values) obtained by CoMFA and CoMSIA are of different but reasonable predictive power, e.g., q2
CV=0.701 and r2=0.937 for the CoMFA model of Rhodococcus ruber DSM 43338. Enantiomeric ratios for the test molecules can be well predicted. Plots of steric and electrostatic CoMFA (CoMSIA) fields allow conclusions to be drawn for the choice of the most suitable organism for a specific type of substrate. 相似文献
995.
《Surface and interface analysis : SIA》2018,50(2):180-187
The solvent‐provoked formation and evolution of thin film buckling‐delamination on a compliant substrate have been studied. The film surface is observed by an optical microscope showing a remarkable dynamic buckling‐delamination development and a subsequent stable branched‐straight state. It is revealed that the initiation, propagation, and the resulting patterns of film buckles are strongly dependent on the solvent type, film stress, interfacial adhesion, and film thickness. The buckling could be controlled further by a reasonable chemical solvent configuration and used to provide useful information for the pattern creation on polymer systems in diverse fields, such as micro/nanofabrication and optics. 相似文献
996.
《Surface and interface analysis : SIA》2018,50(9):879-888
This paper reports on deposition of acrylic acid films polymerized by an efficient and cost‐effective technique of dielectric barrier corona discharge at atmospheric pressure. The liquid acrylic acid was vaporized and carried by argon gas into plasma to deposit polyacrylic acid films on polydimethylsiloxane substrate. A nonthermal corona discharge was generated in a pyrex flask using a steel tube‐to‐plate asymmetric electrode configuration. The plasma was excited using an in‐house developed power supply operating with continuous wave signals of 10‐kHz frequency. The emission spectra of plasma species were recorded to know their contribution during deposition process. The deposited surfaces were characterized using contact angle measurements, atomic force microscopy, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy and film thickness measurements. A maximum film growth rate of 363 nm/min was achieved under optimal condition of discharge. The results suggest that this plasma technique is capable of depositing organic coatings with a high concentration of carboxylic functional groups that could be potentially used for biomedical and microfluidic applications. 相似文献
997.
《Macromolecular bioscience》2018,18(2)
Stem cells are a promising cell source for regenerative medicine due to their differentiation and self‐renewal capacities. In the field of regenerative medicine and tissue engineering, a variety of biomedical technologies have been tested to improve proangiogenic activities of stem cells. However, their therapeutic effect is found to be limited in the clinic because of cell loss, senescence, and insufficient therapeutic activities. To address this type of issue, advanced techniques for biomaterial synthesis and fabrication have been approached to mimic proangiogenic microenvironment and to direct proangiogenic activities. This review highlights the types of polymers and design strategies that have been studied to promote proangiogenic activities of stem cells. In particular, scaffolds, hydrogels, and surface topographies, as well as insight into their underlying mechanisms to improve proangiogenic activities are the focuses. The strategy to promote angiogenic activities of hMSCs by controlling substrate repellency is introduced, and the future direction is proposed. 相似文献
998.
A new model for the ionization depth distribution function has been proposed. Within the framework of this model full electron flux is considered to be divided into two fluxes propagating in forward and backward directions through a sample. The intensities of these fluxes can be derived on the basis of simple assumptions of electron-solid interactions. The approach can be effectively applied to a system with an arbitrary form of depth concentration profile. The obtained results are in reasonable agreement with Monte Carlo simulations and experimental results. Some mathematical techniques have been presented for quantitative analysis of thin films on substrates and element depth distribution. 相似文献
999.
Maurizio Toselli Michele Marini Paola Fabbri Massimo Messori Francesco Pilati 《Journal of Sol-Gel Science and Technology》2007,43(1):73-83
Organic–inorganic hybrid materials were prepared through the sol–gel approach starting from tetraethoxysilane (TEOS), as silica
precursor, and triethoxysilane terminated polymers; before gelling the solutions were applied to polyethylene (PE) films and
slabs by spin-coating, without any previous surface pre-treatment of the substrate, and finally the coatings were thermally
cured at 60 °C for 24 h. Among the various polymers used to prepare the coatings, only polyethylene-b-poly(ethylene glycol) copolymers gave good results in terms of adhesion to the PE substrates, and hybrid coatings with different
organic–inorganic ratios were prepared. As suggested by visual inspection and SEM investigation, and confirmed by the critical
loads derived from scratch tests, a good adhesion of the coating to the PE substrates was obtained, probably due to the presence
of PE segments in the organic phase of the coating. Transparency as well as SEM and DSC data were in agreement with the formation
of a nanostructured hybrid coating, with a high level of interpenetration between organic and inorganic domains. It was also
observed that these hybrid coatings are able to improve significantly the scratch resistance and slightly increase the wettability
with respect to uncoated PE. This approach to the surface-properties modification of PE appears as a simple and convenient
method for the functionalization of PE substrates. 相似文献
1000.