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91.
The dissociative adsorption of methane on the Pt(111) surface has been investigated and characterized over the 1-10 Torr pressure and 300-500 K temperature ranges using sum frequency generation (SFG) vibrational spectroscopy and Auger electron spectroscopy (AES). At a reaction temperature of 300 K and a pressure of 1 Torr, C-H bond dissociation occurs in methane on the Pt(111) surface to produce adsorbed methyl (CH(3)) groups, carbon, and hydrogen. SFG results suggest that C-C coupling occurs at higher reaction temperatures and pressures. At 400 K, methyl groups react with adsorbed C to form ethylidyne (C(2)H(3)), which dehydrogenates at 500 K to form ethynyl (C(2)H) and methylidyne (CH) species, as shown by SFG. By 600 K, all of the ethylidyne has reacted to form the dissociation products ethynyl and methylidyne. Calculated C-H bond dissociation probabilities for methane, determined by carbon deposition measured by AES, are in the 10(-8) range and increase with increasing reaction temperature. A mechanism has been developed and is compared with conclusions from other experimental and theoretical studies using single crystals. 相似文献
92.
Infrared-visible sum frequency generation (SFG) vibrational spectroscopy, in combination with fluorescence microscopy, was employed to investigate the surface structure of lysozyme, fibrinogen, and bovine serum albumin (BSA) adsorbed on hydrophilic silica and hydrophobic polystyrene as a function of protein concentration. Fluorescence microscopy shows that the relative amounts of protein adsorbed on hydrophilic and hydrophobic surfaces increase in proportion with the concentration of protein solutions. For a given bulk protein concentration, a larger amount of protein is adsorbed on hydrophobic polystyrene surfaces compared to hydrophilic silica surfaces. While lysozyme molecules adsorbed on silica surfaces yield relatively similar SFG spectra, regardless of the surface concentration, SFG spectra of fibrinogen and BSA adsorbed on silica surfaces exhibit concentration-dependent signal intensities and peak shapes. Quantitative SFG data analysis reveals that methyl groups in lysozyme adsorbed on hydrophilic surfaces show a concentration-independent orientation. However, methyl groups in BSA and fibrinogen become less tilted with respect to the surface normal with increasing protein concentration at the surface. On hydrophobic polystyrene surfaces, all proteins yield similar SFG spectra, which are different from those on hydrophilic surfaces. Although more protein molecules are present on hydrophobic surfaces, lower SFG signal intensity is observed, indicating that methyl groups in adsorbed proteins are more randomly oriented as compared to those on hydrophilic surfaces. SFG data also shows that the orientation and ordering of phenyl rings in the polystyrene surface is affected by protein adsorption, depending on the amount and type of proteins. 相似文献
93.
The equilibrium between [Ce(H2O)9]3+ and [Ce(H2O)8]3+ has been followed in aqueous solution at 298 K by variable-pressure UV spectroscopy at 295 nm. The dervied volume of reaction for the dissociation of this enneaaqua ion is ΔV0 = +10.9 cm3. mol?1. This value, together with the previously determined activation volume, ΔV≠ = ?6 cm3. mol?1, for H2O exchange on [Ln(H2O)8]3+ (Ln = Tb to Tm), allows the assignment of an associative interchange Ia mechanism on these octaaqua ions. 相似文献
94.
Gabor Patonay Isiah M. Warner 《Journal of inclusion phenomena and macrocyclic chemistry》1991,11(4):313-322
This study focuses on the inclusion complexes of -,- and-cyclodextrins with benzo (a) pyrene, as indicated by induced circular dichroism data. The benzo(a)pyrene complex exhibits a significant induced ellipticity in the presence of-cyclodextrin, while the other two cyclodextrins did not produce a significant induced circular dichroism signal. In the presence of deuterium oxide, which is larger than the water molecule, the ellipticity is larger. The changes in ellipticity with increasing cyclodextrin concentration are observed to follow the changes in equilibrium of the pyrene--cyclodextrin system. The study of these systems using circular dichroism measurements yields a method of estimating the possible stoichiometry of this complex. 相似文献
95.
We investigate the structure of a collineation group G leaving invariant a hyperoval (n+2 — arc) of a finite projective plane of even order n. The main result is that n=2, 4 or 16 when G acts transitively on and 4¦|G|. The case n=16 is investigated in some details. 相似文献
96.
Contamination of the structural materials of nuclear reactors is a crucial question in view of radiation protection, especially,
if due to some leakage, uranium and its fission products appear in the cooling water. Since it is rather difficult to obtain
in situ experimental data on the actual amount of adsorbed radioactive species, the surface contamination may be quantified
by measuring bulk activity concentrations of the cooling water and by calculating the amount of adsorbed material on the surfaces
by using a partition coefficient. To do this, the knowledge of an appropriate adsorption isotherm is needed. Thus, our paper
presents results, based on electrochemical measurements, about the extent and effect of the adsorption of certain fission
products—caesium and iodide—in their ionic forms on the surface of some alloys used in the nuclear industry. Our findings
allow the conclusion that the adsorption of these ions can be described by a Langmuir-type isotherm, where the saturation
values correspond to surface monolayers. 相似文献
97.
98.
99.
Preparation of fluorescein isothiocyanate (FITC)-encapsulated silica nanoparticles (F-SiNPs) via seven different approaches to be used as developing agents for fingerprints detection is presented in this report. In this study, the suitability of each synthesis route toward incorporation of the selected fluorophore into silica matrix and its efficiency in fingerprints detection were systematically studied. The composition of the particles was designed to examine the hydrophobic and dipole-dipole interactions between the silicate backbone and both of the fluorescent reporter molecules and the fingerprint residues. F-SiNPs were prepared with two conventional sol-gel approaches; the Stöber method and the water in oil reverse microemulsion (WORM) method. The alkoxysilane precursor, tetraethoxyorthosilicate (TEOS) and its binary mixtures with phenyltriethoxysilane (PTEOS) or 3-aminopropyl triethoxysilane (APTES) have been used in preparing the F-SiNPs to study the effect of nanoparticles composition on fingerprints development. In addition, FITC was conjugated with APTES so it can be covalently bonded to the silica matrix and to be compared with non-covalently FITC-doped SiNPs. Moreover, the enhancement effect of introducing polyvinylpyrrolidone (PVP) onto the surface of the less hydrophobic F-SiNP on fingerprints detection on different non-porous surfaces was also investigated. The mean diameters of the F-SiNPs were between 4.1?±?0.6 and 110.4?±?31.1 nm as obtained from the TEM size measurement for the nanoparticles prepared by the WORM and Stöber methods, respectively. The obtained results clearly highlight the advantages of using a mixture of TEOS and PTEOS alkoxysilane precursors in preparing F-SiNPs with remarkable encapsulation efficiency and clear detection of fingerprints due to efficient embedding of the fluorophore inside the silica network even without conjugation. It was also observed that both the Stöber and WORM methods can be used in preparing the F-SiNPs developing agents and that PVP coated particles did not show any significant enhancement in fingerprints visualization. 相似文献
100.