排序方式: 共有68条查询结果,搜索用时 15 毫秒
1.
A more consistent, straightforward, and economical protocol for generation of stannylene species and their reaction with BnBr leading to products of O-monobenzylation of diols has been set. It has shown to be specially indicated for substrates bearing vicinal trans 1,2-diol moieties on cyclohexane backbones, which are more resistant to these transformations. Such protocol has been successfully applied to myo-inositol derivatives and acyclic diols. 相似文献
2.
3.
Menezes PH Gonçalves SM Hallwass F Silva RO Bieber LW Simas AM 《Organic letters》2003,5(10):1601-1604
[reaction: see text] Several (77)Se NMR experiments were performed by titrating a sample of selenides with the chiral shift reagent methylbenzylamine (MBA), followed by acquisition of (77)Se NMR spectra. Eventually, we observed the appearance of two anisochronous resonances, with a relatively large separation, from 37 to 56 Hz, corresponding to the formation of the diastereomeric complexes. This methodology avoids derivatization processes, and the studied compound can be easily recovered from the NMR tube. 相似文献
4.
Rafael Dias do Espírito Santo Rosineide Costa Simas Alviclér Magalhães Vanessa Gonçalves dos Santos Thais Regiani Ana Cristina Isler Natiza Graziele Martins Marcos Nogueira Eberlin Eduardo René Pérez González 《Journal of Physical Organic Chemistry》2013,26(4):315-321
Molecules containing the guanidinic nuclei possess several pharmacological applications, and knowing the preferred isomers of a potential drug is important to understand the way it operates pharmacologically. Benzoylguanidines were synthesized in satisfactory to good yields and characterized by NMR, Electrospray Ionization Mass Spectrometry (ESI‐MS) and Fourrier Transform InfraRed Spectroscopy techniques (FTIR). E/Z isomerism of the guanidines was studied and confirmed by NMR analysis in solution (1H‐13C Heteronuclear Single Quantum Coherence (HSQC) and Heteronuclear Multiple‐Bond Correlation (HMBC), 1H‐15N HMBC, 1H‐1H Correlation Spectroscopy (COSY) and Nuclear Overhauser Effect Spectroscopy (NOESY) experiments) at low temperatures. Compounds with p‐Cl and p‐Br aniline moiety exist mainly as Z isomer with a small proportion of E isomer, whereas compounds with p‐NO2 moiety showed a decrease in proportion of isomer Z. The results are important for the application of these molecules as enzymatic inhibitors. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
5.
Carlos Victor Montefusco-Pereira Maria José de Carvalho Ana Paula de Araújo Boleti Lorisa Simas Teixeira Humberto Reis Matos Emerson Silva Lima 《Applied biochemistry and biotechnology》2013,170(6):1367-1378
Diabetes mellitus is a metabolic disease characterized by abnormally high plasma glucose levels, leading to major complications, such as insulin resistance, obesity, hyperlipidemia, and hypertension, also with alterations in the immune and neuronal systems. Brazilian plants have been studied as important sources for new molecules with medicinal properties. The genus Passiflora known as “Maracujá” has been used as a traditional folk medicine for a long time, so an investigation was performed regarding an endemic kind of passion fruit (Passiflora nitida Kunth) from Amazonas, Brazil. Here, we aimed to determine its potential biological activity against metabolic syndrome, oxidative stress, pain, and inflammation. The hydroethanol leaf extract revealed an in vitro α-glucosidase inhibitory activity of 50 % inhibitory concentration (IC50)?=?6.78?±?0.31 μg/mL and an α-amylase inhibition of IC50?=?93.36?±?4.37. In vivo, experiments of different saccharide tolerance resulted in significant glycemia control and, with alloxan-diabetic mice, resulted in a decrease of total cholesterol, a hypoglycemic effect, and an antioxidant activity by thiobarbituric acid-reactive substances measurement. Also, it decreased the carrageenan-induced edema volume and the rate of writhing as a nociceptive response. These results indicate positive effects of P. nitida extract and its potential to inhibit metabolic syndrome. 相似文献
6.
Simas ER Gehlen MH Pinto MF Siqueira J Misoguti L 《The journal of physical chemistry. A》2010,114(47):12384-12390
Polyfluorene end-capped with N-(2-benzothiazole)-1,8-naphthalimide (PF-BNI) is a highly fluorescent material with fluorescence emission modulated by solvent polarity. Its low energy excited state is assigned as a mixed configuration state between the singlet S(1) of the fluorene backbone (F) with the charge transfer (CT) of the end group BNI. The triexponential fluorescence decays of PF-BNI were associated with fast energy migration to form an intrachain charge-transfer (ICCT) state, polyfluorene backbone decay, and ICCT deactivation. Time-resolved fluorescence anisotropy exhibited biexponential relaxation with a fast component of 12-16 ps in addition to a slow one in the range 0.8-1.4 ns depending on the solvent, showing that depolarization occurs from two different processes: energy migration to form the ICCT state and slow rotational diffusion motion of end segments at a longer time. Results from femtosecond transient absorption measurements agreed with anisotropy decay and showed a decay component of about 16 ps at 605 nm in PF-BNI ascribed to the conversion of S(1) to the ICCT excited state. From the ratio of asymptotic and initial amplitudes of the transient absorption measurement, the efficiency of intrachain ICCT formation is estimated in 0.5, which means that, on average, half of the excited state formed in a BNI-(F)(n)-BNI chain with n = 32 is converted to its low energy intrachain charge-transfer (ICCT) state. 相似文献
7.
Simas Sakirzanovas Artūras Katelnikovas Danuta Dutczak 《Journal of luminescence》2011,131(11):2255-2262
Complete and partial samarium reduction was achieved under strong reducing atmosphere by solid-state and combustion synthesis of Sr3.96Sm0.04Al14O25. Dependence of different fluxing agents on the formation of various strontium aluminates was examined. The samples were investigated by X-ray powder diffraction, temperature dependent luminescence decay and photoluminescence measurements. Excitation with UV radiation resulted in sharp and well resolved emission lines of samarium ions. Distinct temperature behavior for Sm2+ and Sm3+ were detected in the range of 100-500 K. Estimated emission thermal quenching values (TQ1/2) for divalent samarium were approximately 270 K while for trivalent state around 660 K. Measured luminescence decay values of Sm2+ are substantially lower than for Sm3+,≈1.7 and ≈2.7 ms, respectively. The spectral feature of Sm2+ emission spectrum indicates that dopant occupies low symmetry site in Sr4Al14O25 compound. 相似文献
8.
We investigate the presence of topological twistons in crystalline polyethylene. We describe crystalline polyethylene with a model that couples the torsional and longitudinal degrees of freedom of the polymeric chain by means of a system of two real scalar fields. This model supports topological twistons, which are described by exact and stable topological solutions that appear when the interaction between torsional and longitudinal fields is polynomial, containing up to the sixth power in the fields. We calculate the energy of the topological twiston, and the result is in good agreement with values obtained using numerical simulation methods. 相似文献
9.
Freire RO da Costa NB Rocha GB Simas AM 《The journal of physical chemistry. A》2006,110(17):5897-5900
The sparkle/AM1 model for the quantum chemical prediction of coordination polyhedron crystallographic geometries from isolated lanthanide complex ion calculations, defined recently for Eu(III), Gd(III), and Tb(III) (Inorg. Chem. 2005, 44, 3299) is now extended to La(III) and Lu(III). Thus, for each of the metal ions we chose a training set of 15 complexes that possess various representative ligands of high crystallographic quality (R factor < 0.05 Angstroms) and oxygen and/or nitrogen as coordinating atoms. In the validation procedure we used a set of 60 more La(III) coordination compound structures, as well as 15 more Lu(III) coordination compound structures, all of high crystallographic quality. For both the 75 La(III) compounds and the 30 Lu(III) compounds, the Sparkle/AM1 unsigned mean error, for all interatomic distances between the metal ions and the ligand atoms of the first sphere of coordination, is 0.08 Angstroms, thus comparable to the accuracy normally achievable by present day ab initio/ECP calculations, while being hundreds of times faster. 相似文献
10.