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51.
Dr. Ruth Matesanz Dr. José Fernando Diaz Dr. Francisco Corzana Andrés G. Santana Dr. Agatha Bastida Dr. Juan Luis Asensio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(10):2875-2889
The most common mode of bacterial resistance to aminoglycoside antibiotics is the enzyme‐catalysed chemical modification of the drug. Over the last two decades, significant efforts in medicinal chemistry have been focused on the design of non‐ inactivable antibiotics. Unfortunately, this strategy has met with limited success on account of the remarkably wide substrate specificity of aminoglycoside‐modifying enzymes. To understand the mechanisms behind substrate promiscuity, we have performed a comprehensive experimental and theoretical analysis of the molecular‐recognition processes that lead to antibiotic inactivation by Staphylococcus aureus nucleotidyltransferase 4′(ANT(4′)), a clinically relevant protein. According to our results, the ability of this enzyme to inactivate structurally diverse polycationic molecules relies on three specific features of the catalytic region. First, the dominant role of electrostatics in aminoglycoside recognition, in combination with the significant extension of the enzyme anionic regions, confers to the protein/antibiotic complex a highly dynamic character. The motion deduced for the bound antibiotic seem to be essential for the enzyme action and probably provide a mechanism to explore alternative drug inactivation modes. Second, the nucleotide recognition is exclusively mediated by the inorganic fragment. In fact, even inorganic triphosphate can be employed as a substrate. Third, ANT(4′) seems to be equipped with a duplicated basic catalyst that is able to promote drug inactivation through different reactive geometries. This particular combination of features explains the enzyme versatility and renders the design of non‐inactivable derivatives a challenging task. 相似文献
52.
Krzysztof K. Zborowski Ibon Alkorta Jose Elguero Leonard M. Proniewicz 《Structural chemistry》2012,23(2):595-600
An extension of the harmonic oscillator model of aromaticity (HOMA) model to systems with carbon–boron bonds is presented. Model parameters were estimated using experimental and theoretical bond lengths. It is shown that both approaches produce very similar HOMA models. In the second part of the article, the aromaticity levels of several model compounds containing carbon–boron bonds are calculated using the previously obtained parameters. The results of these calculations are compared with those provided by other aromaticity indices. The aromaticity of boron-containing compounds is also compared with the aromaticity of analogous compounds containing carbon and nitrogen. 相似文献
53.
C. Lavilla A. Alla A. Martínez de Ilarduya E. Benito M.G. García‐Martín J.A. Galbis S. Muñoz‐Guerra 《Journal of polymer science. Part A, Polymer chemistry》2012,50(16):3393-3406
Random poly(hexamethylene terephthalate‐co‐galactarate)s and poly(dodecamethylene terephthalate‐co‐galactarate)s copolyesters covering the whole range of compositions were obtained with weight‐average molecular weights of ~30,000–50,000 g mol?1 by melt polycondensation. They were thermally stable above 300 °C, and displayed Tg in the +20 to ?20 °C range with values steadily decreasing with the content in galactarate units. All the copolyesters were semicrystalline with Tm between 50 and 150 °C and those made from dodecanediol were able to crystallize from the melt at a crystallization rate depending on composition. Copolyesters containing up to 50% of galactaric units retained the crystal structure of their respective polyterephthalate homopolyesters, whereas they adopted the structure of the respective polygalactarates when the content in Galx units reached 70%. Stress‐strain essays revealed decay in the mechanical parameters as the aromatic units were replaced by Galx. Incubation in aqueous buffer revealed that hydrolysis of the polyesters were largely enhanced by copolymerization and evidenced the capacity of the Galx unit for making aromatic polyesters susceptible to biodegradation. A detailed NMR analysis complemented by SEM observations indicated that hydrolysis took place by preferred splitting of galactarate ester bonds with releasing of alkanediol and Galx‐diacid. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
54.
55.
56.
Generalized solutions are defined for stochastic evolution equations of the formdY
t
=A
*
Y
t
dt + dZ
t
on the nuclear triplel(R
d
) L2(R
d
) l(R
d
), whereA does not mapl(R
d
) into itself. One case which is treated in detail involvesA = –(–)
/2
,0 < < 2. This example arises as the Langevin equation for the fluctuation limit of a system of particles migrating according to a symmetric stable process and undergoing critical branching in a random medium.The research of D. A. Dawson was supported by the Natural Sciences and Engineering Research Council of Canada. L. G. Gorostiza's research was supported in part by CONACyT Grants PCEXCNA-040319 and 140102 G203-006, Mexico. 相似文献
57.
The classes ofL
1-matrices,L
2-matrices,L
3-matrices andW-matrices are introduced to study solvability of a linear complementarity problem via solving a linear program. Three sufficient
conditions are presented to guarantee that a linear complementarity problem is solvable via a linear program. The new sufficient
conditions are weaker than the ones introduced by Mangasarian. This fact is also illustrated by an example.
Partially supported by NSFC.
This author is also with College of Business Administration of Human University as a Lotus chair professor. 相似文献
58.
In this work we show that the energy associated to the linear three-dimensional magneto-elastic system decays polynomially to zero as time goes to infinity, provided the initial data is smooth enough. 相似文献
59.
60.
Luiza Amália Moraes Luis Romero Grados 《Journal of Mathematical Analysis and Applications》2003,281(2):575-586
Let Au(BG) be the Banach algebra of all complex valued functions defined on the closed unit ball BG of a complex Banach space G which are uniformly continuous on BG and holomorphic in the interior of BG, endowed with the sup norm. A characterization of the boundaries for Au(BG) is given in case G belongs to a class of Banach spaces that includes the pre-dual of a Lorentz sequence space studied by Gowers in Israel J. Math. 69 (1990) 129-151. The non-existence of the Shilov boundary for Au(BG) is also proved. 相似文献