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11.
Winter R Nixon PG Gard GL Graham DJ Castner DG Holcomb NR Grainger DW 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5776-5781
Recently synthesized (Winter, R.; Nixon, P. G.; Gard, G. L.; Radford, D. H.; Holcomb, N. R.; Grainger, D. W. J. Fluorine Chem. 2001, 107, 23-30) SF5-terminated perfluoroalkyl thiols (SF5(CF2)nCH2CH2SH, where n = 2, 4, and 6) and a symmetric SF5-terminated dialkyl disulfide ([SF5-CH=CH-(CH2)8-S-]2) were assembled as thin films chemisorbed onto gold surfaces. The adsorbed monolayer films of these SF5-containing molecules on polycrystalline gold were compared using ellipsometry, contact angle, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and infrared spectroscopy (FTIR) surface analytical methods. The resulting SF5-dialkyl disulfide monolayer film shows moderate angle dependence in depth-dependent XPS analysis, suggesting a preferentially oriented film. The SF5-terminated perfluoroalkyl thiols exhibit angular-dependent XPS compositional variance depending on perfluoroalkyl chain length, consistent with improved film assembly (increasingly hydrophobic, fewer defects, and more vertical chain orientation increasing film thickness) with increasing chain length. Tof-SIMS measurements indicate that both full parent ions for these film-forming molecules and the unique SF5 terminal group are readily detectable from the thin films without substantial contamination from other adsorbates. 相似文献
12.
W. C. Nixon 《Contemporary Physics》2013,54(3):183-197
The wavelength limitation on resolution indicates that an x-ray microscope may surpass the optical microscope but will not compete with the electron microscope even if all the technical difficulties could be overcome. However, there are other advantages besides resolution that make x-rays an attractive medium for microscopy. The penetration of x-rays allows the examination of the internal detail of a specimen on the micro scale without the need for sectioning and reconstruction. The large depth of focus permits the viewing of this internal detail with equal sharpness and stereographically if necessary. The specimen may be in air at atmospheric pressure, while the electron microscope demands high vacuum, and yet the resolution may be better than that of the optical microscope. Most important, the simple absorption and emission spectra of x-rays leads to the extraction of quantitative information from the image in terms of mass and elements present that in many cases cannot be obtained in any other way. These and other reasons have led to the search for a usable x-ray microscope and the three more successful methods of reflection, contact and projection are discussed here. In addition, recent results on microanalysis show where the bulk of the future work will lie. 相似文献
13.
14.
Mannan Mehta Satheesh Krishnamurthy Suddhasatwa Basu Tony P. Nixon Aadesh P. Singh 《Materials Today Chemistry》2020
In the present study, pristine BiVO4, TiO2 and BiVO4/TiO2 core-shell heterostructured nanoparticles are prepared by hydrothermal methods and studied for structural, morphological, optical, photoelectrochemical water splitting and photocatalytic degradation of methylene blue as an organic pollutant. Both pristine BiVO4 and TiO2 exhibit poor PEC and PC performance under visible light illumination. However, an enhanced PEC and PC activity in BiVO4/TiO2 core-shell heterostructure is observed due to high solar energy absorption and superior charge separation properties in core-shell nanoparticles. The photoelectrode prepared using BiVO4/TiO2 core-shell nanoparticles exhibit a photocathode behavior and produced cathodic photocurrent, however, the pristine BiVO4 and TiO2 photoelectrodes act as photoanode and produced anodic photocurrent. This behavior of change in current direction is also observe in the Mott-Schottky analysis where the BiVO4/TiO2 core-shell nanoparticles photoelectrode exhibits the positive slow showing p-type semiconducting behavior. The change in cathodic photoresponse in core-shell nanoparticles in comparison to anodic photoresponse of BiVO4 and TiO2 nanoparticles is explained in terms of the variations in the work function values. These results highlight the advantages of core-shell nanoparticle of suitable materials for photocatalytic and photoelectrochemical applications. 相似文献
15.
A protein''s adaptive response to its substrates is one of the key questions driving molecular physics and physical chemistry. This work employs the recently developed structure-mechanics statistical learning method to establish a mechanical perspective. Specifically, by mapping all-atom molecular dynamics simulations onto the spring parameters of a backbone-side-chain elastic network model, the chemical moiety specific force constants (or mechanical rigidity) are used to assemble the rigidity graph, which is the matrix of inter-residue coupling strength. Using the S1A protease and the PDZ3 signaling domain as examples, chains of spatially contiguous residues are found to exhibit prominent changes in their mechanical rigidity upon substrate binding or dissociation. Such a mechanical-relay picture thus provides a mechanistic underpinning for conformational changes, long-range communication, and inter-domain allostery in both proteins, where the responsive mechanical hotspots are mostly residues having important biological functions or significant mutation sensitivity.Protein residues exhibit specific routes of mechanical relay as the adaptive responses to substrate binding or dissociation. On such physically contiguous connections, residues experience prominent changes in their coupling strengths. 相似文献
16.
A detailed rotational analysis of the microwave spectrum between 26.5 and 40 GHz of phosphaethene, CH2PH, has been carried out. This molecule is the simplest member of a new class of unstable molecules—the phosphaalkenes. The species can be produced by pyrolysis of (CH3)2PH, CH3PH2 and also somewhat more efficiently from Si(CH3)3CH2PH2. Full first-order centrifugal distortion analyses have been carried out for both 12CH231PH and 12CH231PD yielding: A0 = 138 503.20(21), B0 = 16 418.105(26), and C0 = 14 649.084(28) MHz for 12CH231PH. The 101-000μA lines have also been detected for 13CH2PH, cis-CDHPH and trans-CHDPH. These data have enabled an accurate structure determination to be carried out which indicates: . The dipole moment components have been determined as μA = 0.731 (2), μB = 0.470 (3), μ = 0.869 (3) D for CH2PH; μA = 0.710 (2), μB = 0.509 (10), μ = 0.874 (7) D for CH2PD. 相似文献
17.
The new molecule 1-phosphabut-3-ene-1-yne, CH2=CHCP, produced by pyrolyzing prop-1-ene-3-phosphorus dichloride, CH2=CHCH2PCl2, was detected by microwave spectroscopy. The analysis of the rotational transitions indicates that the molecule is planar with constants: A0 = 46 694(24), B0 = 2807.7100(21), and C0 = 2645.8356(21) MHz. These rotational constants indicate that the structure of the vinyl group is essentially the same as that in CH2=CHCN and CH2=CHCCH; r(C---C) = 1.432 Å and (C=C---C) = 123.9°. The dipole moment parameters are μA = 1.181(2), μB = 0.074(1), and μ = 1.183(2) D. The vibrational satellite spectra for the C---CP bending modes indicate that ν11(a′) = 184 ± 30 cm−1 and ν15(a″) = 263 ± 30 cm−1. 相似文献
18.
The first structures of trifluorophosphine complexes of transition metals in an oxidation state greater than +1 are reported. 相似文献
19.
de Boer J Leonards PE Klungsøyr J McHugh B Nixon E McGovern E Rimkus GG 《Journal of AOAC International》2003,86(2):432-438
A comparison was made between electron capture negative ionization quadrupole mass spectrometry (ECNI-MS) and electron capture detection (ECD) with regard to repeatability and reproducibility for the gas chromatographic (GC) analysis of toxaphene congeners [chlorobornanes (CHBs)]. The tests, including standard solutions and several cleaned fish extracts, showed larger relative standard deviations (RSDs) for the repeatability of ECNI-MS but no differences in the reproducibility of the 2 techniques. The sensitivity of the GC-ECNI-MS was considerably better than that of GC/ECD. Four stepwise-designed comparative tests were also conducted on GC analysis, cleanup, and the complete method. The results showed that, according to the current state-of-the-art, coefficients of variation for the between-laboratory performance were not < 20% and were usually between 20 and 30%. In spite of separation problems, e.g., for CHB 26, which cannot be separated into a single-component peak, a 95% methyl 5% phenyl polysiloxane (CP Sil 8) column was preferred to more polar columns for the analysis of CHBs 26, 40, 41, 44, 50, and 62. CHB 62 was more difficult to determine than CHB 26 and 50. Addition of the CHBs 40, 41, and 44 to the standard set of 3 chlorobornanes (26, 50, and 62) resulted in more separation problems. A 3-step cleanup method was recommended. 相似文献
20.
Araujo MH Hitchcock PB Nixon JF Kuehner U Stelzer O 《Chemical communications (Cambridge, England)》2003,(9):1092-1093
Hydrozirconation of the eta 2-phosphaalkyne complex [Pt(dppe)(eta 2-tBuCP)] with [ZrHCl(eta 5-C5H5)2], followed by treatment with the chlorophosphaalkene ClP=C(SiMe3)2 affords the eta 2-2,3-diphosphabutadiene complex [Pt(dppe)(eta 2-tBuC(H)=PP=C(SiMe3)2]. In the presence of [Pt(PPh3)2] the latter undergoes an addition reaction with water to afford the structurally characterised Pt(II) complex [Pt(dppe)(tBuCH2P(O)HPC(SiMe3)2]. 相似文献