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91.
92.
Casey Kukielski Krishnagopal Maiti Sayantan Bhaduri Sandra Story Dev P. Arya 《Tetrahedron》2018,74(33):4418-4428
A library of mono- and di-amino acid peptidic-aminoglycosides (PAs), with kanamycin and neomycin as the model aminoglycosides, was systematically and rapidly synthesized via solid phase peptide synthesis. Aminoglycosides were first converted into N-Boc protected carboxylic acids and fifteen l-amino acids were then used in the diversification of the full library. The approach outlined describes a rapid synthetic procedure where >200?PA compounds can be synthesized in a few months with 85–95% purity. UV thermal denaturation assessed the binding stabilization by PAs to model human and bacterial A-site rRNA sequences. Significant differences were found in thermal melting profiles among PAs that were attributed to specific amino acid sequences. Neomycin PAs lead to a much larger variation in the stabilization of A-site rRNA sequences (ΔTm?=?2.6–17.1?°C) as compared to kanamycin PAs (ΔTm?=?0.4–4.3?°C). Kanamycin PAs had little activity against Gram-negative and Gram-positive bacteria as compared with neomycin PAs that had significant antibacterial activity with MIC ranging from 2 to 16?μM. 相似文献
93.
Anna Thoma Ashutosh Dahal Aayush Regmi Alecia Valencia Veronika Viner Rafael Cueto Blane Baker Patrick Bunton John A. Pojman 《Journal of polymer science. Part A, Polymer chemistry》2011,49(19):4261-4266
For the first time, electron paramagnetic resonance spectroscopy was used to compare numbers and distributions of radicals produced in frontal free‐radical polymerization of multifunctional acrylates and methacrylates to those produced by bulk free‐radical polymerization. A comparison of radical concentrations was performed for individual polymers and selected copolymers of trimethylolpropane trimethacrylate (TMPTMA), 1,6‐hexanediol diacrylate, trimethylolpropane triacrylate, and pentaerythritol tetraacrylate (PETA). Frontally polymerized samples showed a large spike in intensity at the point of initiation. Within a few centimeters, the radical signal diminished to a steady state. The radical concentration remained almost constant over 3 months under helium in flame‐sealed tubes. The types of radicals were similar to those in bulk polymerization. For both TMPTMA and PETA, frontally polymerized samples had significantly higher numbers of radicals than did the bulk‐prepared samples, achieving concentrations as high as 8.7 × 10?3 mol/kg in the frontally prepared samples of TMPTMA. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
94.
We study a 3-dimensional, dual-field, fully explicit method for the solution of dispersive Maxwell's equations in the time domain on unstructured, tetrahedral grids. In a previous paper, we investigated the element level time domain (ELTD) algorithm for solving electromagnetic problems with parameters independent of the excitation frequency content, i.e. nondispersive materials. The suitability of the ELTD method for the numerical analysis of nanometer structured systems in the optical frequencies was thoroughly studied. This paper introduces the generalization of the method and its implementation as a computer code for problems with dispersive material properties. We profit from the ELTD formulation in conjunction with the auxiliary differential equation (ADE) approach for modeling dispersion. Examples with analytical solutions are solved and verified in order to benchmark the method. Eventually, to demonstrate the potential of the method, we consider the structure of a single field emitter and solve for the electromagnetic fields when illuminated by a plane wave. We have obtained a flexible and versatile method of 2nd order accuracy that is applicable to both dispersive and nondispersive problems with a wide range of nano-optical configurations. 相似文献
95.
S. K. Arya Tanvi Vats Shailesh N. Sharma Kulvir Singh A. K. Narula 《Journal of Thermal Analysis and Calorimetry》2012,107(2):555-560
In this study, we have studied the stability of TiO2–CdSe nanocomposites in which the individual moieties are linked using a bifunctional linker (mercaptopropionic acid). Nanoparticles
of TiO2 and CdSe are synthesized by sol–gel and one pot methods. The equimolar amount of the above particles is utilized to prepare
nanocomposites with and without linker. These samples are characterized for their structural, thermal, and optical properties
using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TG), Fourier transform infra-red
spectroscopy (FTIR), and UV–Vis spectroscopy. The average particle size of TiO2 and CdSe are 16 and 23 nm, respectively. The addition of a bifunctional linker shows remarkable effect on the properties
of TiO2–CdSe nanocomposites. 相似文献
96.
Cyclization reactions of lapachol (1) isolated from Heterophragma adenophyllum have been studied under microwave irradiation under different conditions using alumina (acidic, basic and neutral)/silica gel/montmorillonite (KSF and K-10) as solid support along with neat reaction using 2-3 drops of DMF giving naturally occurring dehydro-alpha-lapachone (2), alpha-lapachone (3), beta-lapachone (4) depending upon the nature of support and irradiation time. A novel naphthoquinone derivative adenophyllone (5) can be synthesized from lapachol using DMF under microwaves. 相似文献
97.
Current interest in the properties of materials having grains in the nanometer regime has led to the investigation of the
size-dependent properties of various dielectric and magnetic materials. We discuss two chemical methods, namely the reverse-micellar
route and the polymeric citrate precursor route used to obtain homogeneous and monophasic nanoparticles of several dielectric
oxides like BaTiO3, Ba2TiO4, SrTiO3, PbTiO3, PbZrO3 etc. In addition we also discuss the synthesis of some transition metal (Mn and Cu) oxalate nanorods using the reverse-micellar
route. These nanorods on decomposition provide a facile route to the synthesis of transition metal oxide nanoparticles. We
discuss the size dependence of the dielectric and magnetic properties in some of the above oxides 相似文献
98.
Reduction of epoxide into the corresponding saturated alcohol is an important synthetic transfornation. Various reagents t o bring about such a conversion have been reported in the literature1. An important aspect of such a transformation is the regioselective opening in case of unsymmetrical epoxides. Numerous modifications of the existing reducing agents have also been reported1 to meet with the regioselective requirements. Every reagent reported so far, to our knowledge, makes use of its hydride donating ability to effect the reduction. 相似文献
99.
The aqueous heterogeneous polymerization of methyl methacrylate (MMA) initiated by the Ce4+-glycolic acid (GA) redox system was studied at 35 × 0.2°C under a nitrogen atmosphere. The rate of monomer disappearance was proportional to [MMA]1[GA]1[Ce4+]°, and the rate of eerie ion disappearance was found to be directly proportional to [Ce4+] and [GA] but independent of [MMA]. The activation energy was found to be 34 kJ/mol. The molecular weight of polymethyl methacrylate increased with increasing [MMA] and decreased with increasing [oxidant]. The effect of increasing [H2SO4] on polymerization was also studied. The results are compared with those obtained for the aqueous homogeneous polymerization of acrylamide with the same redox pair. 相似文献
100.
Cheng Peng Piyush Arya Zhiyao Zhou Scott A. Snyder 《Angewandte Chemie (International ed. in English)》2020,59(32):13521-13525
The four contiguous all‐carbon quaternary centers of waihoensene, coupled with the absence of any traditional reactive functional groups other than a single alkene, render it a particularly challenging synthetic target among angular triquinane natural products. Here, we show that its polycyclic frame can be assembled concisely by using a strategically chosen quaternary center to guide the formation of the other three through judiciously selected C?C bond formation reactions. Those events, which included a unique Conia‐ene cyclization and a challenging Pauson–Khand reaction, afforded a 17‐step synthesis of the molecule in enantioenriched form. 相似文献