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71.
Gehanne S Cecconi D Carboni L Righetti PG Domenici E Hamdan M 《Rapid communications in mass spectrometry : RCM》2002,16(17):1692-1698
We describe a simple approach for the relative quantification of individual proteins within a mixture. The method is based on the differential labelling of the mixtures by use of a commercially available acrylamide and deuterium-labelled [2,3,3'-d(3)]-acrylamide to alkylate proteins prior to two-dimensional (2-D) gel electrophoresis. The tryptic digests of the separated proteins were subjected to reflector matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis and the relative peak heights of cysteine-containing peptides were used to quantify their precursor proteins. This approach was tested for the relative quantification of proteins within an artificial mixture of standard proteins and for proteins observed in a 2-D map of rat serum. A good correlation was found between the measured ratios derived from MALDI-TOF data and those theoretically calculated prior to 2-D analysis via known mixing ratios of the two alkylating reagents. The described procedure has proved to be effective for comparative measurements of protein abundances within the investigated mixtures. 相似文献
72.
A laser flash photolysis study of the spectral properties and beta-scission reactions of a series of ring-substituted cumyloxyl radicals has been carried out. All cumyloxyl radicals display a broad absorption band in the visible region of the spectrum, which decays on the microsecond time scale, leading to a strong increase in absorption in the UV region of the spectrum, which is attributed to the corresponding acetophenone formed after beta-scission of the cumyloxyl radicals. The position of the visible absorption band is red-shifted by the presence of electron-donating ring substituents, while a blue-shift is observed in the presence of electron-withdrawing ring substituents, suggesting that + R ring substituents promote charge separation in the excited cumyloxyl radical through stabilization of the partial positive charge on the aromatic ring of an incipient radical zwitterion. Along this line, an excellent Hammett-type correlation between the experimentally measured energies at the visible absorption maxima of the cumyloxyl radicals and sigma(+) substituent constants is obtained. A red-shift is also observed on going from MeCN to MeCN/H(2)O for all cumyloxyl radicals, pointing toward a specific effect of water. The ring substitution does not influence to a significant extent the rate constants for beta-scission of the cumyloxyl radicals, which varies between 7.1 x 10(5) and 1.1 x 10(6) s(-1), a result that suggests that cumyloxyl radical beta-scission is not governed by the stability of the resulting acetophenone. Finally, k(beta) increases on going from MeCN to the more polar MeCN/H(2)O 1:1 for all cumyloxyl radicals, an observation that reflects the increased stabilization of the transition state for beta-scission through increased solvation of the incipient acetophenone product. 相似文献
73.
N-[1-(Phenylsulfonyl)alkyl]oxazolidin-2-ones are successfully prepared by condensation of the corresponding optically active oxazolidin-2-ones with aldehydes and benzenesulfinic acid. At low temperature, in the presence of titanium tetrachloride, these sulfones are converted into N-acyliminium ions, which react with allyltrimethylsilane with a variable degree of stereoselectivity. The best results are obtained with (R)-5,5-dimethyl-4-phenyloxazolidin-2-one as a chiral auxiliary. Cleavage of the oxazolidin-2-one ring with lithium/ammonia affords the corresponding homoallylamines, which reveal an absolute configuration opposite that expected on the basis of the usual steric effects. A complexation of the Lewis acid with the N-acyliminium ion may be responsible of this rather unusual stereochemical outcome. 相似文献
74.
Photoluminescence excitation spectroscopy and scanning-tunneling spectroscopy are used to study the electronic states in CdSe quantum rods that manifest a transition from a zero-dimensional to a one-dimensional quantum-confined structure. Both optical and tunneling spectra show that the level structure depends primarily on the diameter of the rod and not its length. With increasing diameter, the band gap and the excited state level spacings shift to the red. The level structure was assigned using a multiband effective-mass model, showing a similar dependence on rod dimensions. 相似文献
75.
In the early 1930s, Wiener proved that if f(x) is a strictlypositive periodic function whose Fourier series is absolutelyconvergent, then the Fourier series of g(x)=1/f(x) is also absolutelyconvergent [8, pp. 1014]. This phenomenon can be easilyunderstood nowadays using Banach algebra techniques (see, forexample, [4, pp. 202203]). In fact, these techniquesallow us to study the absolute convergence of g(x)=F(f(x)),where F is holomorphic in an open subset of C that containsthe range of f(x) (for xR). In this context, Wiener's originalproblem corresponds to the choice F(z)=1/z. In this work we want to analyse the constraints on the simultaneousrate of vanishing of the Fourier coefficients f(n) and (n) asn. We shall focus on g=1/f, but we shall also study the generalcase g=F(f). In either case, there are obviously no constraintswhen f is a constant function. Although this problem does not seem to be directly related touncertainty inequalities for the Fourier Transform, we observethat there are some analogies, both in the nature of the resultsand in the proof techniques. The general fact with which weare dealing is that f(n) and (n) cannot vanish too quickly atthe same time as n, unless f(x) is constant. The general factthat underlies uncertainty inequalities is that a non-periodicfunction (x) and its Fourier Transform circ;(u) cannot vanishtoo quickly at the same time as x and u, unless (x) is zero(almost everywhere). For a simple introduction to some aspectsof uncertainty inequalities, see [5]; for a thorough and recentintroduction to this vast subject, see [3]. 1991 MathematicsSubject Classification 42A05, 42A16, 42A99. 相似文献
76.
Enrico Schlesinger 《Transactions of the American Mathematical Society》1999,351(7):2731-2743
We prove a version of the Halphen Speciality Theorem for locally Cohen-Macaulay curves in . To prove the theorem, we strengthen some results of Okonek and Spindler on the spectrum of the ideal sheaf of a curve. As an application, we classify curves having index of speciality as large as possible once we fix the degree of and the minimum degree of a surface containing .
77.
Enrico Massa 《General Relativity and Gravitation》1974,5(5):573-591
The general theory of space tensors is applied to the study of a space-time manifoldsV
4 carrying a distinguished time-like congruence Γ. The problem is to determine a physically relevant spatial tensor analysis
over (V
4, Γ), in order to proceed to a correct formulation of Relative Kinematics and Dynamics.
This is achieved by showing that each choice of
gives rise to a corresponding notion of ‘frame of reference’ associated with the congruence Γ. In particular, the frame of
reference (Γ, ∇*) determined by the standard spatial tensor analysis
is shown to provide the most natural generalization of the concept of frame of reference in Classical Physics.
The previous arguments are finally applied to the study of geodesic motion inV
4. As a result, the general structure of the gravitational fields in the frame of reference (Γ, ∇*) is established.
This work was assisted by funds from the C.N.R. under the aegis of the activity of the National Group for Mathematical Physics. 相似文献
78.
Enrico C. Poggio 《Annals of Physics》1973,81(2):481-518
An alternate method of renormalizing a quartic self-interacting boson theory has been developed. We find that one can obtain finite renormalized expressions for the perturbation theory contributions to the Green's function without carrying out limiting procedures. As a consequence of the analysis, one is able to renormalize explicitly the field energy-momentum tensor to all orders. There exists a one-parameter family of renormalized tensors. The method will allow for a simple determination of the asymptotic “zero-mass” theory. 相似文献
79.
Enrico Abignente Paolo De Caprariis Michele Liguori 《Journal of heterocyclic chemistry》1983,20(6):1597-1599
Some new 4,5-dihydro-5-oxoisoxazole derivatives were synthesized as part of a study to prepare potential antiinflammatory agents. The reaction of the diethyl ester of 3-oxopentanedioic acid with hydroxylamine afforded the 3-hydroxyimino derivative, which was then cyclized to the title compound. This reacted with diazomethane to give a couple of isomeric methyl derivatives, namely methyl 2,5-dihydro-2-methyl-5-oxo-3-isoxazoleacetate and methyl 5-methoxy-3-isoxazoleacetate. Reaction of these compounds with ammonia gave the corresponding acetamides. All compounds were characterized by elemental analysis, uv, ir, and 1H-nmr spectra. 相似文献
80.