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81.
The adsorption of lipoteichoic acid onto the surface of titanium dioxide is shown to be heterogeneous. 31P CPMAS solid-state NMR reveals two distinct phosphate species. The chemical shift anisotropy, asymmetry parameter, and rotating-frame spin-lattice relaxation suggest that 50% of the phosphates are bound to the surface. The remaining phosphates also exhibit restricted molecular motion, but do not have a direct surface bond. 相似文献
82.
Santos E Schühle DT Jones H Schmickler W 《Langmuir : the ACS journal of surfaces and colloids》2005,21(14):6406-6421
The nonlinear optical properties of self-assembled monolayers obtained from bonding two different alpha-functionalized terthiophenes (alpha-T3) to (111) silver electrode surfaces have been investigated using second harmonic generation (SHG). The two (alpha-T3) compounds used were functionalized with alkane chains of different lengths (C8 and C4), and each was terminated with a thiol anchoring group. A nitrile group was attached to the terminal thiophene ring of the (alpha-T3) compound with the C4 chain. The orientation of the polarization of the incident beam was changed systematically and gradually between "p" and "s" orientation and the SH signal (isotropic and anisotropic contributions) analyzed in both directions ("P" and "S"). The symmetry of the system was reduced by the presence of the adlayers from C3v to C3. The dependence on the applied potential and the incident wavelength has also been studied. The relative magnitudes and phases of the various second-order tensor elements have been estimated and compared with the values for a bare surface. A resonance process in the (alpha-T3) pi moiety has been investigated, and from this, the effective "band-gap" energies of the organic semiconductor SAMs (i.e., the energy difference between the pi-pi bands) have been estimated. 相似文献
83.
Charles C. Wu Robert W. Lenz 《Journal of polymer science. Part A, Polymer chemistry》1972,10(12):3555-3567
The thermal ring-opening reactions, autoxidation and hydrogenation of polymethy-lenecyclobutene (PMCB) and poly-1-methyl-3-methylenecyclobutene (PMMCB), were investigated. Both polymers were prepared by cationic polymerization and consisted almost entirely of 1,5-repeating units containing cyclobutene rings in the polymer backbone. Both polymers showed well behaved exothermic processes at elevated temperatures which apparently resulted in crosslinking. These processes were investigated by differential scanning calorimetry and interpreted to involve thermal ring-opening reactions. Autoxidation occurred very rapidly in PMCB but much more slowly in PMMCB as predicted by Bolland's rules. Attempts to hydrogenate the cyclobutene rings in both polymers resulted in the occurrence of hydrogenolysis in PMCB and little or no reaction with PMMCB for a Pd-catalyzed reaction and partial hydrogenation of the latter for a diimide reaction. 相似文献
84.
Chemical species present in reducing waters have the potential to produce severe negative interferences by consuming the chloramine T (CT) which is used as the oxidising agent in the phenol red-based calorimetric method for trace bromide analysis. Mn(2+) and Fe(2+) were found not to interfere at concentrations up to 200muM. However, hydroxylamine (NH(2)OH), which can be present in both ground-and surface-waters, exerts a strong negative interference. A method involving pre-treatment with permanganate and hydrogen peroxide has been developed for the destruction of NH(2)OH prior to adding the colour reagents. The procedure is not only compatible with the chemistry of the calorimetric method, but is also robust and technically easy to implement. 相似文献
85.
Carbonyl 2 + 2 photoaddition occurs selectively to the alkene moiety of 3-(4-methyl-3-pentenoxy)pyridine. Photolysis of alkene containing pyridines in acetophenone gives rise to an oxetane which is obtained with extremely high diastereoselectivity as shown by analysis of the major 2 + 2 photoproduct. A second photoproduct, 2,3-dihydroxy-2,3-diphenylbutane, is obtained as a result of acetophenone coupling. 相似文献
86.
Photocycloadditlon of (+)-isoplperltenone and cyclobutene-1-carboxylic acid gives an adduct which upon reduction with NaCNBH3 followed by thermolysis yields an isomer of isoaristolactone in an overall yield of 26%. 相似文献
87.
Charles E. Reid 《International journal of quantum chemistry》1972,6(2):383-386
It is a standard theorem of group representation theory that the dimension of an irreducible representation is a divisor of the order of the group. This paper gives a new, relatively simple proof, intended to make the theorem understandable to readers unfamiliar with algebraic integers. 相似文献
88.
S. A. Catlow G. L. Troyer D. R. Hansen R. A. Jones 《Journal of Radioanalytical and Nuclear Chemistry》2005,263(3):599-603
Summary Long-term risk assessment of residual and disposed nuclear fuel reprocessing waste requires good knowledge of component isotopes with long half-lives. For example, the accuracy of the accepted 126Sn half-life of approximately 100,000 years is insufficient for desired risk assessments. From modeling and sampling, 126Sn is known to exist in Hanford nuclear waste. Excess portions of waste characterization samples were used to isolate 126Sn for measurement of its half-life. Isolation was performed with ion-exchange resins. The resulting 126Sn was gamma-assayed with a hyperpure germanium spectrometer for decay photon identification and activity values. An inductively coupled plasma/mass spectrometer was used to measure the atom quantity of the isolated 126Sn. The separation chemistry, observed gamma energies, and calculated half-life are presented. The half-life of 126Sn estimated in this work is (2.33±0.10) . 105 years. 相似文献
89.
Charles S. Kahane 《Integral Equations and Operator Theory》1984,7(1):96-117
The integral operator which sends f (ζ) into $$\int_{|\xi |< 1} {\tfrac{{f(\xi )}}{{|x - \xi |^{p - 1} }}} d\xi = g(x)(|x|< 1)$$ x and ζ ∈ RP, is shown to map the space of functions f (ζ) on |ζ|<1, square integrable with respect to the weight (1-|ξ|2)1/2 one to one onto the space of functions g (x) on |x|<1 which possess gradients δg(x) in the sense of distribution theory, with both g(x) and δg(x) being square integrable with respect to the weight (1-|x|2)1/2. This extends to p≥3 a result of P. Wolfe's in the case p=2. 相似文献
90.
The molecular structure of 1,1,1,2-tetrafluoroethane is studied using gas-phase electron diffraction data collected on the Balzers KDG2 instrument. Effective least-squares refinement of the geometry is achieved with values for vibrational amplitudes transferred from normal coordinate calculations on related molecules. The following values for the main independent geometrical parameters are obtained (ra values with e.s.d. in parentheses): C-C = 1.501(4) Å, C-H = 1.077 (15) Å, C-F(CH2F) = 1.389(6) Å, C-F(CF3) = 1.334 (2) Å, ∠CCH= 106.1(12)°, ∠CCF(CH2F)= 112.3(4) Å, ∠CCF(CF3)= 110.4(2). Other angles are ∠FCF = 108.6 (2)° and ∠FCH = 111.4(15)°, with ∠HCH constrained at 109.4°. The ra bond lengths of all the fluoroethanes are compared. 相似文献