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131.
This review highlights the basis of gradient reversed-phase high-performance liquid chromatography (RP-HPLC) of ionogenic analytes.We describe pH-gradient RP-HPLC in strict theoretical terms, with examples of experiments to provide improvements in analyte separations and peak shapes, and an original method of pKa determination.Finally, we present the concept of the combined pH/organic-modifier gradient mode of RP-HPLC and illustrate it with applications. It allows optimization of separation of ionogenic analytes, along with a method for determining their biorelevant physico-chemical parameters [e.g., hydrophobicity (log kw) and acidity (pKa)]. The method is applicable to drugs and other xenobiotic mixtures, including individual analytes of interest assayed in biological fluids. 相似文献
132.
The oxidative degradation of phenothiazine derivatives (PTZ) by manganese(III) was studied in the presence of a large excess
of manganese(III)-pyrophosphate (P2O7
2−), phosphate (PO4
3−), and H+ ions using UV–vis. spectroscopy. The first irreversible step is a fast reaction between phenothiazine and manganese pyrophosphate
leading to the complete conversion to a stable phenothiazine radical. In the second step, the cation radical is oxidized by
manganese to a dication, which subsequently hydrolyzes to phenothiazine 5-oxide. The reaction rate is controlled by the coordination
and stability of manganese(III) ion influenced by the reduction potential of these ions and their strong ability to oxidize
many reducing agents. The cation radical might also be transformed to the final product in another competing reaction. The
final product, phenothiazine 5-oxide, is also formed via a disproportionation reaction. The kinetics of the second step of
the oxidative degradation could be studied in acidic phosphate media due to the large difference in the rates of the first
and further processes. Linear dependences of the pseudo-first-order rate constants (k
obs) on [MnIII] with a significant non-zero intercept were established for the degradation of phenothiazine radicals. The rate is dependent
on [H+] and independent of [PTZ] within the excess concentration range of the manganese(III) complexes used in the isolation method.
The kinetics of the disproportionation of the phenothiazine radical have been studied independently from the further oxidative
degradation process in acidic sulphate media. The rate is inversely dependent on [PTZ+.], dependent on [H+], and increases slightly with decreasing H+ concentration. Mechanistic consequences of all these results are discussed. 相似文献
133.
Pawe? Niedzia?kowski Tadeusz Ossowski Rados?aw Majewski Zdzis?awa Nowakowska Grzegorz Schroeder 《Monatshefte für Chemie / Chemical Monthly》2011,89(3):1121-1129
Abstract
In this work, the synthesis of various thiol-functionalized anthraquinone compounds is presented. The studied compounds were characterized by mass spectrometry and the main fragmentation pathways are discussed. The compounds studied formed stable self-assembled monolayers (SAMs) in the gold surface. The parameters for the reduction processes in the gold surface of the studied new anthraquinones were determined by cyclic voltamperometry tests. 相似文献134.
135.
We propose an efficient approach to the problem of multi-degree reduction of rectangular Bézier patches, with prescribed boundary control points. We observe that the solution can be given in terms of constrained bivariate dual Bernstein polynomials. The complexity of the method is O(mn1n2) with m ? min(m1, m2), where (n1, n2) and (m1, m2) is the degree of the input and output Bézier surface, respectively. If the approximation—with appropriate boundary constraints—is performed for each patch of several smoothly joined rectangular Bézier surfaces, the result is a composite surface of global Cr continuity with a prescribed r ? 0. In the detailed discussion, we restrict ourselves to r ∈ {0, 1}, which is the most important case in practical application. Some illustrative examples are given. 相似文献
136.
Our work is a foundational study of the notion of approximation in Q-categories and in (U,Q)-categories, for a quantale Q and the ultrafilter monad U. We introduce auxiliary, approximating and Scott-continuous distributors, the way-below distributor, and continuity of Q- and (U,Q)-categories. We fully characterize continuous Q-categories (resp. (U,Q)-categories) among all cocomplete Q-categories (resp. (U,Q)-categories) in the same ways as continuous domains are characterized among all dcpos. By varying the choice of the quantale Q and the notion of ideals, and by further allowing the ultrafilter monad to act on the quantale, we obtain a flexible theory of continuity that applies to partial orders and to metric and topological spaces. We demonstrate on examples that our theory unifies some major approaches to quantitative domain theory. 相似文献
137.
Results on the existence and non-existence of nontrivial
\mathbb L1{\mathbb L^1}-solutions of the refinement equation
f(x)=òW|detK(w)|f(K(w)x-L(w))dP(w)f(x)={\int\limits_{\Omega}}|\det K(\omega)|f(K(\omega)x-L(\omega))dP(\omega) 相似文献
138.
We develop the concept of integral Menger curvature for a large class of nonsmooth surfaces. We prove uniform Ahlfors regularity and a C1,λ-a priori bound for surfaces for which this functional is finite. In fact, it turns out that there is an explicit length scale R>0 which depends only on an upper bound E for the integral Menger curvature Mp(Σ) and the integrability exponent p, and not on the surface Σ itself; below that scale, each surface with energy smaller than E looks like a nearly flat disc with the amount of bending controlled by the (local) Mp-energy. Moreover, integral Menger curvature can be defined a priori for surfaces with self-intersections or branch points; we prove that a posteriori all such singularities are excluded for surfaces with finite integral Menger curvature. By means of slicing and iterative arguments we bootstrap the Hölder exponent λ up to the optimal one, λ=1−(8/p), thus establishing a new geometric ‘Morrey–Sobolev’ imbedding theorem.As two of the various possible variational applications we prove the existence of surfaces in given isotopy classes minimizing integral Menger curvature with a uniform bound on area, and of area minimizing surfaces subjected to a uniform bound on integral Menger curvature. 相似文献
139.
Cui Yunan Hudzik Henryk Kaczmarek Radosław Kolwicz Paweł 《Aequationes Mathematicae》2019,93(1):311-343
Aequationes mathematicae - The paper deals with F-normed functions and sequence spaces. First, some general results on such spaces are presented. But most of the results in this paper concern... 相似文献
140.
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