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91.
An amperometric method for the determination of thiocarbamyl sulphonamides has been developed, based on the cleavage of the S-N bond by hydriodic acid. The method can also be applied for the cleavage of the S-S bond in thiuram disulphides and dibenzothiazyl disulphide, and thus provides a useful means for the estimation of these compounds as well. 相似文献
92.
Frost RL Erickson KL 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(1-2):51-56
The hydrotalcite minerals stitchtite, iowaite and desautelsite together with the arsenate exchanged takovite and arsenate exchanged hydrotalcite have been studied using near-IR reflectance spectroscopy. Each mineral has its own characteristic NIR spectrum enabling recognition of the particular hydrotalcite. As such the technique has application in the field for the analysis and identification of hydrotalcites. Hydrotalcites have proven useful as an anion exchange material. Takovite and hydrotalcite were used to exchange carbonate anions by arsenate. Three Near-IR spectral regions are identified: (a) the high wavenumber region between 6400 and 7400 cm(-1) attributed to the first overtone of the fundamental hydroxyl stretching mode, (b) the 4800-5400 cm(-1) region attributed to water combination modes of the hydroxyl fundamentals of water, and (c) the 4000-4800 cm(-1) region attributed to the combination of the stretching and deformation modes of the MOH units of the hydrotalcites. NIR spectroscopy enables the separation of the hydroxyl bands of the water and M-OH units for the hydrotalcites. Compared with the NIR spectroscopy of the structural units of the hydrotalcites namely gibbsite and brucite, the bands are broad. 相似文献
93.
Millar AJ Doonan CJ Smith PD Nemykin VN Basu P Young CG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(11):3255-3267
Intermediates in the oxygen atom transfer from Mo(VI) to P(III), [Tp(iPr)MoOX(OPR3)] (Tp(iPr) = hydrotris(3-isopropylpyrazol-1-yl)borate; X = Cl-, phenolates, thiolates), have been isolated from the reactions of [Tp(iPr)MoO2X] with phosphines (PEt3, PMePh2, PPh3). The green, diamagnetic oxomolybdenum(IV) complexes possess local C(1) symmetry (by NMR spectroscopy) and exhibit IR bands assigned to nu(Mo==O) (approximately 950 cm(-1)) and nu(P==O) (1140-1083 cm(-1)) vibrations. The X-ray crystal structures of [Tp(iPr)MoOX(OPEt3)] (X = OC6H4-2-sBu, SnBu), [Tp(iPr)MoO(OPh)(OPMePh2)], and [Tp(iPr)MoOCl(OPPh3)] have been determined. The monomeric complexes exhibit distorted octahedral geometries, with coordination spheres composed of tridentate fac-Tp(iPr) and mutually cis monodentate terminal oxo, phosphoryl (phosphine oxide), and monoanionic X ligands. The electronic structures and stabilities of the complexes have been probed by computational methods, with the three-dimensional energy surfaces confirming the existence of a low-energy steric pocket that restricts the conformational freedom of the phosphoryl ligand and inhibits complete oxygen atom transfer. The reactivity of the complexes is also briefly described. 相似文献
94.
Preparation and characterization of individual peptide-wrapped single-walled carbon nanotubes 总被引:3,自引:0,他引:3
Zorbas V Ortiz-Acevedo A Dalton AB Yoshida MM Dieckmann GR Draper RK Baughman RH Jose-Yacaman M Musselman IH 《Journal of the American Chemical Society》2004,126(23):7222-7227
Two challenges for effectively exploiting the remarkable properties of single-walled carbon nanotubes (SWNTs) are the isolation of intact individual nanotubes from the raw material and the assembly of these isolated SWNTs into useful structures. In this study, we present atomic force microscopy (AFM) evidence that we can isolate individual peptide-wrapped SWNTs, possibly connected end-to-end into long fibrillar structures, using an amphiphilic alpha-helical peptide, termed nano-1. Transmission electron microscopy (TEM) and well-resolved absorption spectral features further corroborate nano-1's ability to debundle SWNTs in aqueous solution. Peptide-assisted assembly of SWNT structures, specifically in the form of Y-, X-, and intraloop junctions, was observed in the AFM and TEM images. 相似文献
95.
Frost RL Duong L Weier M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(8-9):1853-1859
A series of tungstate bearing minerals including scheelite, stolzite, ferberite, hübnerite, wolframite, russellite, tungstenian wulfenite and cuprotungstite have been analyzed by Raman microscopy. The results of the Raman spectroscopic analysis are compared with published data. These minerals are closely related and often have related paragenesis. Raman microscopy enables the selection of individual crystals of these minerals for spectroscopic analysis even though several of the minerals can be found in the same matrix because of the pargenetic relationships between the minerals. The Raman spectra are assigned according to factor group analysis and related to the structure of the minerals. These minerals have characteristically different Raman spectra. The nu1(Ag) band is observed at 909 cm(-1) and although the corresponding nu1(Bu) vibration should be inactive a minor band is observed around 894 cm(-1). The bands at 790 and 881 cm(-1) are associated with the antisymmetric and symmetric Ag modes of terminal WO2. The band at 695 cm(-1) is interpreted as an antisymmetric bridging mode associated with the tungstate chain. The nu4(Eg) band was absent for scheelite. The bands at 353 and 401 cm(-1) are assigned as either deformation modes or as r(Bg) and delta(Ag) modes of terminal WO2. The band at 462 cm(-1) has an equivalent band in the infrared at 455 cm(-1) assigned as delta(as)(Au) of the (W2O4)n chain. The band at 508 cm(-1) is assigned as nu(sym)(Bg) of the (W2O4)n chain. 相似文献
96.
Chekmenev EY Xu RZ Mashuta MS Wittebort RJ 《Journal of the American Chemical Society》2002,124(40):11894-11899
We report here (13)C(alpha) chemical shielding parameters for central Gly residues in tripeptides adopting alpha-helix, beta-strand, polyglycine II, and fully extended 2 degrees structures. To assess experimental uncertainties in the shielding parameters and the effects of (14)N-(13)C(alpha) or (15)N-(13)C(alpha) dipolar coupling, stationary and magic angle spinning (MAS) spectra with and without (15)N decoupling were obtained from natural abundance and double-labeled samples containing [2-(13)C, (15)N]Gly. We find that accurate (<1 ppm uncertainty) shielding parameters are measured with good sensitivity and resolution in (15)N decoupled 1D or 2D MAS spectra of double-labeled samples. Compared to variations of isotropic shifts with peptide angles, those of (13)C(alpha) shielding anisotropy and asymmetry are greater. Trends relating shielding parameters to the 2 degrees structure are apparent, and the correlation of the experimental values with unscaled ab initio shielding calculations has an rms error of 3 ppm. Using the experimental data and the ab initio shielding values, the empirical trends relating the 2 degrees structure to shielding are extended to the larger range of torsion angles found in proteins. 相似文献
97.
The reaction of 2-arylpyridinecarboxaldimine [RH4C6NC(H)Py, L (1)] with hydrated RuX3 (X = Cl, Br) in boiling C2H5OH affords dark crystals of RuX2L2. Two geometrical isomers of the compound have been isolated and characterized by analytical and spectroscopic data. The trans isomer of RuCl2L2 shows a single sharp band for ν(Ru---Cl), whereas two bands are observed for the corresponding cis isomer. The highresolution 1H NMR spectra of the isolated complexes are reported and completely assigned. All the complexes have multiple t2→π*(L) transitions in the visible region. Each of the complexes display a quasi-reversible oxidative response due to an RuIII/RuII couple in the range 0.25–0.40 V vs S.C.E. at a platinum working electrode. The formal potentials of this couple obey the Hammett relationship. The ligand-based irreversible oxidations are also briefly noted. 相似文献
98.
The feasibility of remote sensing by means of two-photon excited molecular fluorescence was investigated by using a single 115-m multimode optical fibr.Because of modal dispersion and reflecton of Rayleigh scatter, time-resolved detection ws required to resolve the weak fluorescence from the relatively intense laser background. The bare-ended probe, which both delivered the excitation and collected the fluorescence emission, was employed to detect an analyte in an optically dense environment. For a fixed amount of fluorophore, the solvent was continuously changed from 90% (w/w) ethanol (non-absorbing) to 100% acetone (absorbing). The result was a flurorescence signal constant to within 5%. Quantitation via one-photon excitatation using a 50-cm optical fiber demonstrated the characteristic inner filter roll-off of optically dense systems. Because of th elarge attenuation of the waveguide in the ultraviolet range, remote sensing via one-photon excited fluorescence proved impossible. However, linear calibration plots for the nonlinear excitation process were obtained from micromolar to near saturation levels. Sources of interference were isolated, and the extension to a single-mode fiber was made. 相似文献
99.
Summary [NiL2X2] (L =N,N-dimethyl-1,2-ethanediamine; X = Cl–, CF3CO
2
–
, CC13CO
2
–
and CBr3CO
2
–
), [NiL2C2O4] · H2O and [NiL2X2] · 2 H2O (X = Br–, 0.5 SO
4
2–
and 0.5 SeO
4
–
) have been synthesised and their thermal studies carried out. Thermally induced phase transition phenomena are noticed in [NiL2X2] (X = CF3CO
2
–
and CCl3CO
2
–
) and their probable mechanisms are described. [NiL2X2] (X = Br–, 0.5 SO
4
2–
and 0.5 SeO
4
2–
) and [NiLX2] (X = Cl–, 0.5 C2O
4
2–
and 0.5 SO
4
2–
) have been prepared by solid state pyrolysis from the respective parent diamine complexes. [NiL2X2] have been made in solid state by temperature arrest technique from [NiL2(CX3CO2)2] (X = Cl– and Br–). 相似文献
100.
Gervais C Dupree R Pike KJ Bonhomme C Profeta M Pickard CJ Mauri F 《The journal of physical chemistry. A》2005,109(31):6960-6969
13C, 14N, 15N, 17O, and 35Cl NMR parameters, including chemical shift tensors and quadrupolar tensors for 14N, 17O, and 35Cl, are calculated for the crystalline forms of various amino acids under periodic boundary conditions and complemented by experiment where necessary. The 13C shift tensors and 14N electric field gradient (EFG) tensors are in excellent agreement with experiment. Similarly, static 17O NMR spectra could be precisely simulated using the calculation of the full chemical shift (CS) tensors and their relative orientation with the EFG tensors. This study allows correlations to be found between hydrogen bonding in the crystal structures and the 17O NMR shielding parameters and the 35Cl quadrupolar parameters, respectively. Calculations using the two experimental structures for L-alanine have shown that, while the calculated isotropic chemical shift values of 13C and 15N are relatively insensitive to small differences in the experimental structure, the 17O shift is markedly affected. 相似文献