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1.
Fontana Jose D. Franco Valeria C. De Souza Silvio J. Lyra Ivone N. De Souza Angelita M. 《Applied biochemistry and biotechnology》1991,28(1):341-351
Caffeine and related xanthines were identified as potent stimulators for the bacterial cellulose production in A. xylinum. These compounds are present in several plants whose infusions are useful as culture-medium supplements for this acetobacterium.
The proposed target for these native purine-like inhibitory substances is the novel diguanyl nucleotide phosphodiesterase(s) that participate(s) in the bacterial cellulogenic complex.
A better understanding of this feature of A. xylinum physiology may facilitate the preparation of bacterial cellulose pellicles, which are applied as a biotechnological tool in the treatment of skin burns and other dermal injuries.
相似文献2.
Campo VL Carvalho I Allman S Davis BG Field RA 《Organic & biomolecular chemistry》2007,5(16):2645-2657
This study describes the synthesis of the alpha- and beta-linked N-acetyllactosamine (Galp-beta-1,4-GlcNAc; LacNAc) glycosides of threonine (LacNAc-Thr). LacNAc-a-Thr was prepared by direct chemical coupling of a 2-azido-2-deoxy-lactose disaccharide donor to a suitable partially protected threonine unit. In contrast, stepwise chemical generation of beta-linked N-acetylglucosamine followed by enzymatic galactosylation to give LacNAc-beta-Thr proved effective, whereas use of a 2-azido-2-deoxy-lactose donor in acetonitrile failed to give the desired beta-linked disaccharyl glycoside. This study illustrates that it is possible to overcome the inherent stereoselection for 1,2-trans chemical glycosylation with a GlcNAc donor, and that the well-established preference of bovine beta-1,4-galactosyltransferase for beta-linked acceptor substrates can also be overcome. Using this knowledge, short glycopeptide fragments based on T. cruzi mucin sequences, Thr-Thr-[LacNAcThr]-Thr-Thr-Gly, were synthesised. All LacNAc-based compounds outlined were shown to serve as acceptor substrates for sialylation by T. cruzi trans-sialidase. 相似文献
3.
Ivone M. R. Trigo Miguel A. D. Gonçalves Rolando C. S. Dias Mário Rui P. F. N. Costa 《Macromolecular Symposia》2008,271(1):107-119
A general kinetic approach allowing the prediction of the molecular architecture of non-linear polymers is applied to the study of the copolymerization of methyl methacrylate (MMA) with ethylene glycol dimethacrylate (EGDMA). Dynamic predictions of molecular weight distributions, sequence length distributions and mean square radius of gyration are possible before and after gelation. A set of experiments concerning the copolymerization of MMA and EGDMA was carried out in toluene solution at 60 °C for which classic radical kinetics is a good approximation. The time evolution of key polymer properties was followed using a SEC system with a refractive index detector coupled with MALLS allowing the determination of absolute weight average molecular weight and apparent molecular size distributions as well as z-average radius of gyration. Special focus was given to assess the influence of the initial amount of cross-linker on the dynamics of the non-linear structure build-up of these products. A kinetic scheme comprising 23 different chemical species and 76 chemical reactions was used in the modeling studies of this chemical system. Most of the kinetic parameters used in the simulations have been collected from previous studies. For experiments at low monomer conversion (up to about 0.5) a good agreement between predictions and experimental measurements is observed for molecular weights and z-average radius of gyration by fitting a small number of parameters describing gel effect (with a conversion dependent but chain length independent termination rate parameter) and the relative propagation on pendant double bonds. However, predicted values of weight-average molecular weights and z-average radius of gyration before gelation are too low at higher monomer conversions with non-linear systems. The likely cause is the presence of intramolecular reactions which should not be neglected in these circumstances. 相似文献
4.
Ivone Peres Sandra Rocha Joana A. Loureiro Maria do Carmo Pereira Galya Ivanova Manuel Coelho 《Journal of nanoparticle research》2012,14(9):1-11
We report a simple and effective supercritical fluid route to uniformly load ultrafine metal nanoparticles on the hydrophobic surfaces of graphene sheets. In the presence of supercritical carbon dioxide, PtRu alloy nanoparticles are decorated evenly on functionalized graphene sheets (FGSs) upon the reduction of organic platinum (II) and ruthenium (III) precursors, and its application as an electrocatalyst for methanol oxidation is studied. Transmission electron microscopy observation shows that highly dispersed PtRu metallic nanoparticles with an average size of about 3.11?nm are uniformly and densely distributed on the hydrophobic surface of FGSs. X-ray diffraction patterns demonstrate that the particles had a face-centered cubic crystal structure, and X-ray photoelectron spectroscopy analysis indicates the existence of zero-valence metals. Compared with the widely used Vulcan XC-72 carbon black, the PtRu/FGS composites exhibit superior catalytic activity and stability for methanol oxidation. The huge surface area of graphene and uniform distribution of nanosized metal particles are two critical factors for the significantly enhanced electrocatalytic efficiency. The findings suggest that the supercritical fluid method is highly efficient in preparing graphene-supported metallic catalysts, and FGSs serve as a favorable electrocatalytic carrier for direct methanol fuel cells. 相似文献
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The dark matter in the Universe might be composed of superheavy particles (mass greater, similar 10(10) GeV). These particles can be detected via nuclear recoils produced in elastic scatterings from nuclei. We estimate the observable rate of strongly interacting supermassive particles (simpzillas) in direct dark matter search experiments. The simpzilla energy loss in Earth and in the experimental shields is taken into account. The most natural scenarios for simpzillas are ruled out based on recent EDELWEISS and CDMS results. The dark matter can be composed of superheavy particles only if these interact weakly with normal matter or if their mass is above 10(15) GeV. 相似文献
8.
Marcos A. Scapin Vera L. R. Salvador Marycel E. B. Cotrim Maria A. F. Pires Ivone M. Sato 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(3):807-811
Uranium silicide (U3Si2), 20% 235U enriched powder, is an intermetallic compound used as nuclear fuel material, which is the state-of-the-art among nuclear fuel materials used in modern research reactors. It is produced by IPEN and used as nuclear fuel of the IEA-R1 reactor (IPEN/CNEN, São Paulo, Brazil); U3Si2 has 92.3 wt% Utotal and 7.7 wt% Si. The qualification of this material requires chemical and physical tests such as Si and Utotal content, isotope ratio, impurities, density, specific surface area and particle size determination. The Si and Utotal were determined by gravimetric and volumetric procedures. Usually, these classical methods require a long time for analyses and are expensive. The objective of this study was to establish a fast and efficient analytical method to meet ISO/IEC 17025:2005 requirements in the Si and Utotal determination. The X-ray fluorescence techniques (XRF) were chosen to allow a direct and non-destructive analysis, what is the main advantage compared to other instrumental techniques, since previous chemical treatments are not necessary. In this study, the performance of the wavelength dispersive (WDXRF) and energy dispersive (EDXRF) X-ray fluorescence techniques was evaluated. Furthermore, two different sample preparation procedures, plain powdered and pressed powdered, were evaluated. Statistical tools were used to evaluate the results and a comparison between these results and the conventional methods was done. 相似文献
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da Silva VB Kawano DF Gomes Ada S Carvalho I Taft CA da Silva CH 《The journal of physical chemistry. A》2008,112(38):8902-8910
In this work, we have used molecular dynamics, density functional theory, virtual screening, ADMET predictions, and molecular interaction field studies to design and propose eight novel potential inhibitors of CDK2. The eight molecules proposed showed interesting structural characteristics that are required for inhibiting the CDK2 activity and show potential as drug candidates for the treatment of cancer. The parameters related to the Rule of Five were calculated, and only one of the molecules violated more than one parameter. One of the proposals and one of the drug-like compounds selected by virtual screening indicated to be promising candidates for CDK2-based cancer therapy. 相似文献
10.
Gupta A Heimann AS Gomes I Devi LA 《Combinatorial chemistry & high throughput screening》2008,11(6):463-467
Antibodies are components of the body's humoral immune system that are generated in response to foreign pathogens. Modern biomedical research has employed these very specific and efficient molecules designed by nature in the diagnosis of diseases, localization of gene products as well as in the rapid screening of targets for drug discovery and testing. In addition, the introduction of antibodies with fluorescent or enzymatic tags has significantly contributed to advances in imaging and microarray technology, which are revolutionizing disease research and the search for effective therapeutics. More recently antibodies have been used in the isolation of dimeric G protein-coupled receptor (GPCR) complexes. In this review, we discuss antibodies as powerful research tools for studying GPCRs, and their potential to be developed as drugs themselves. 相似文献