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71.
Summary A global LSER model that relates HPLC retention to mobile phase composition and pH is tested for a varied group of solutes,
both neutral and ionizable, in a polymeric column and methanol-water mobile phases. It is compared to the local LSER model
developed only for a given mobile phase, i.e., a fixed organic modifier content, and to the global LSER model set only for
neutral solutes. The global LSER model for neutral and ionizable solutes requires a few supplementary parameters over the
other models tested, but it accounts for retention under any experimental conditions for a given column and methanol-water
mobile phases, describing properly the interactions established in the HPLC system (hydrophobicity, hydrogen-bond acidity
and basicity, dipolarity/polarizability…).
This paper is number 13 of a series with the same general title: “Retention of Ionizable Compounds on HPLC” published in various
journals. 相似文献
72.
The three-dimensional structure of human cytochrome P450 3A4 was modeled based on crystallographic coordinates of four bacterial P450s: P450 BM-3, P450cam, P450terp, and P450eryF. The P450 3A4 sequence was aligned to those of the known proteins using a structure-based alignment of P450 BM-3, P450cam, P450terp, and P450eryF. The coordinates of the model were then calculated using a consensus strategy, and the final structure was optimized in the presence of water. The P450 3A4 model resembles P450 BM-3 the most, but the B helix is similar to that of P450eryF, which leads to an enlarged active site when compared with P450 BM-3, P450cam, and P450terp. The 3A4 residues equivalent to known substrate contact residues of the bacterial proteins and key residues of rat P450 2B1 are located in the active site or the substrate access channel. Docking of progesterone into the P450 3A4 model demonstrated that the substrate bound in a 6-orientation can interact with a number of active site residues, such as 114, 119, 301, 304, 305, 309, 370, 373, and 479, through hydrophobic interactions. The active site of the enzyme can also accommodate erythromycin, which, in addition to the residues listed for progesterone, also contacts residues 101, 104, 105, 214, 215, 217, 218, 374, and 478. The majority of 3A4 residues which interact with progesterone and/or erythromycin possess their equivalents in key residues of P450 2B enzymes, except for residues 297, 480 and 482, which do not contact either substrate in P450 3A4. The results from docking of progesterone and erythromycin into the enzyme model make it possible to pinpoint residues which may be important for 3A4 function and to target them for site-directed mutagenesis. 相似文献
73.
Structures with AIB2? and BaAl4?type Units. I The Compounds Sr4Pd5P5 and Sr2Pd3P3 Sr4Pd5P5 (Cmcm, a = 4.177(1) Å, b = 31.377(5) Å, c = 8.581(2) Å, Z = 4) und Sr2 Pd3P3(Pmmm, a = 4.199(1) Å, b = 4.212(1) Å, c = 34.227(4) Å, Z = 4) have been prepared by heating the elements. Both structures contain exclusively units characteristic for the AIB2? and BaAl4?type. The ratio between isolated P-atoms and P2?pairs is interpreted with an ionic splitting of the formulas. 相似文献
74.
John L. Spouge 《Journal of statistical physics》1983,31(2):363-378
This paper gives the equilibrium distribution of polymer sizes for Flory'sA
g
RB
f–g model of polymerization. In this model, the polymers are composed of structural units withg functional groups of the typeA and (f-g) functional groups of the typeB. Reaction is subject to three conditions: (1) Functional groups of the typeA react only with those of typeB, and vice versa. (2) Intramolecular reactions do not occur [and therefore only branched-chain (noncyclic) polymers and formed]. (3) Subject to conditions (1) and (2), all functional groups are equally reactive. The derivation employs Stockmayer's statistical mechanical method (first used on Flory'sRA
f model), coupled with a recursion giving the number of distinct polymers which may be assembled fromk units of theA
g
RB
f–g type. We also give distributions for a limiting case of theA
g
RB
f–g model, the so-calledA
g
RB
model. This paper completes the solution of the Smoluchowski coagulation equation (monodisperse case) for the kernelsa
ij =A + B(i +j)+ Cij. The proof will be given in another publication. 相似文献
75.
H. C. Öttinger 《Colloid and polymer science》1987,265(2):101-105
The idea of consistently averaging the hydrodynamic interaction and its various consequences for Hookean dumbbells are reviewed. For long chains this idea can be used to generalize the Rouse-Zimm model for polymer solutions. Unlike the usual Rouse-Zimm model, the new model for steady shear flow predicts a nonzero second normal stress coefficient and shear rate dependent material functions. In the limit of long chains, the viscosity and the normal stress coefficients are universal functions of the reduced shear rate.This paper was presented at the Frühjahrstagung des Fachausschusses Polymerphysik der Deutschen Physikalischen Gesellschaft at Kaiserslautern (West Germany), March 12–14, 1986. 相似文献
76.
Oleg A. Raitman Andrei B. Kharitonov Maya Zayats Eugenii Katz Itamar Willner 《Analytica chimica acta》2004,504(1):101-111
Crosslinked films consisting of the acrylamide-acrylamidophenylboronic acid copolymer that are imprinted with recognition sites for β-nicotinamide adenine dinucleotide (NAD+), β-nicotinamide adenine dinucleotide phosphate NADP+, and their reduced forms (NAD(P)H), are assembled on Au-coated glass supports. The binding of the oxidized cofactors NAD+ or NADP+ or the reduced cofactors NADH or NADPH to the respective imprinted sites results in the swelling of the polymer films through the uptake of water. Surface plasmon resonance (SPR) spectroscopy is employed to follow the binding of the different cofactors to the respective imprinted sites. The imprinted recognition sites reveal selectivity towards the association of the imprinted cofactors. The method enables the analysis of the NAD(P)+ and NAD(P)H cofactors in the concentration range of 1×10−6 to 1×10−3 M. The cofactor-imprinted films associated with the Au-coated glass supports act as active interfaces for the characterization of biocatalyzed transformations that involve the cofactor-dependent enzymes. This is exemplified with the characterization of the biocatalyzed oxidation of lactate to pyruvate in the presence of NAD+ and lactate dehydrogenase using the NADH-imprinted polymer film. 相似文献
77.
Yoshihiko Ito Yoshinori Inubushi Toru Sugaya Takeo Saegusa 《Journal of organometallic chemistry》1977,137(1):1-9
Reaction of carboxamides with Cu2O in the presence of t-butyl isocyanide gave new chelated copper(I) complexes, which probably are formed by the insertion of t-butyl isocyanide into the coppernitrogen bond of copper(I) amide isonitrile complexes, which were initially produced from the carboxamides and Cu2Ot-butyl isocyanide complex. The same chelated copper(I) complexes were prepared more readily by the reaction of the corresponding N-trimethylsilyl-carboxamides with Cu2Ot-butyl isocyanide complex. Reactions of the copper(I) complexes thus obtained with alkylating agents, such as alkyl halides, alkyl tosylates and triethyloxonium tetrafluoroborate, also were described. 相似文献
78.
W. Ren 《Colloid and polymer science》1992,270(10):990-998
Inverse relaxation is studied for hard elastic polypropylene (HEPP), rubber and non-elastic polypropylene. The results show that contractive stress, stress, and internal friction are three essential factors related to the phenomenon. A three-element model in which each element has a definite meaning is proposed to describe this phenomenon. The results also show that, in the first cyclic deformation, relaxation time increases with the increase of recovery for all the materials, which indicates that recovery viscosity increases with the increase of recovery, but the stress rising amplitude (SRA) of inverse relaxation has a maximum in the recovery range. Analysis indicates that SRA equals recovery internal friction (RIF) for ideal material in which stress is solely a function of strain, independent of paths, and approximately equals RIF for non-ideal material at a given strain. From this principle it is found that the order of the work counteracted by RIF for the four materials is the same as that of their second hysteresis loop, and the RIF of HEPP has a sudden increase at the later recovery range. 相似文献
79.
Shu-Liang Zang Qing-Guo Zhang Ming Huang Bin Wang Jia-Zhen Yang 《Fluid Phase Equilibria》2005,230(1-2):192-196
This paper reports that an ionic liquid (IL) has been prepared by directly mixing InCl3 and 1-methyl-3-ethylimidazolium chloride (EMIC) with molar ratio 1/1 under dry argon atmosphere. The densities, and surface tension of the pure IL were determined at temperature range of 293.15 to 343.15 ± 0.1 K. The volumetric properties and the properties of surface for ionic liquid based on group III were discussed by Glasser's theory and Yang's interstice model. 相似文献
80.
Cellulose: the structure slowly unravels 总被引:5,自引:0,他引:5
ANTOINETTE C. O'SULLIVAN 《Cellulose (London, England)》1997,4(3):173-207
This article attempts to bring together basic and complex information which has been gathered on cellulose structure, principally
that of native cellulose, over the last few decades. Even though advances have been made in the field of crystallography,
powder crystallography cannot yield a definitive cellulose structure and single crystal diffraction is not possible due to
the lack of suitable crystals. Knowledge obtained on the biosynthesis of native cellulose and on the polymorphy of cellulose
and its derivatives help our understanding of ultrastructure. Many inconsistencies between early crystallographic studies
of native cellulose have been clarified by the discovery that two polymorphs (α and β) of cellulose I exist. Models of the
possible ultrastructural arrangements within native cellulose have been put forward over the decades; with advancement in
technology, computer simulations of small and large systems are being created to test the viability of these ultrastructural
models. It is hoped that this review will aid in the understanding of the complexity and uncertainties that still exist in
this subject.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献