No abstract

No abstract

No abstract

No abstract

Uma série de calcogeno ésteres, 1a, 6a e 6b foi obtida em uma rota sintética conveniente. A análise de microscopia óptica de luz polarizada (POM) e calorimetria diferencial de varredura (DSC) mostrou que estes calcogeno ésteres apresentam uma ampla faixa de mesofase nemática. Além disso, espectros de absorção na região do UV-Vis em solução (ca.10 -5 mol L -1 ) também foram obtidos de maneira a se obter a diferença de energia entre os orbitais moleculares HOMO-LUMO, para posterior comparação com os resultados teóricos. Os valores calculados para o gap de HOMO-LUMO estão de acordo com os valores experimentais obtidos, onde a eletronegatividade do heteroátomo (O, S e Se) deve ser o principal fator para a localização do máximo de absorção. Um estudo teórico foi realizado utilizando cálculos de DFT/B3LYP com método híbrido de Becke aplicando uma correlação funcional de Lee-Yang-Parr (B3LYP) com a base DGDZVP a fim de avaliar algumas propriedades físico-químicas relacionadas com o mesomorfismo e as propriedades eletrônicas espectrais. Através da síntese destes compostos, a influência do átomo de calcogênio nas propriedades fotofísicas e mesomórficas pôde ser avaliada de uma forma mais precisa.A series of chalcogeno esters 1a, 6a and 6b have been synthesized in a straightforward manner. Polarized-light optical microscopy (POM) and differential scanning calorimetry (DSC) showed that these chalcogeno esters displayed a wide nematic range of mesophase. In addition, UV-Vis in solution (ca.10 -5 mol L -1 ) was applied in order to obtain the HOMO-LUMO gap for further comparison with the theoretical results. The calculated values to the HOMO-LUMO gap are in excellent agreement with the experimental results, where the electronegativity of the heteroatom (O, S and Se) seems to play a fundamental role in the absorption maxima location. A theoretical study was performed using a DFT/B3LYP calculations with Becke's three-parameter hybrid method applying the Lee-Yang-Parr functional correlation (B3LYP) with DGDZVP basis set in order to evaluate some physical chemistry data related with mesomorphic and spectral eletronic properties. By synthesizing these compounds we were able to get a more precise description about the influence of the chalcogen atom on the mesomorphic and photophysical properties. Rampon et al. 2101 Vol. 21, No. 11, 2010 The biological and medicinal properties of selenium and organoselenium compounds are increasingly appreciated, mainly due to their antioxidant, antitumor, antimicrobial and antiviral properties. 4 Besides, the synthesis of peptides containing selenocysteine is rapidly gaining interest with the discovery of an increasing number of proteins containing this aminoacid. Keywords 5Chalcogeno esters (thiol, selenol and tellurol esters) are useful synthetic intermediates that have been employed, for example, as acylating reagents, building blocks for heterocyclic compounds, precursors of acyl radicals and anions, as well asymmetric aldol reactions. However, rare are the examples where these compounds a...

A collection of 3,5-disubstituted isoxazolines have been synthesized by 1,3-dipolar [3+2] cycloaddition reactions. Some isoxazolines were selected and transformed into liquid crystals. These new liquid crystals exhibit nematic and smectic C mesophases.

This work reports the synthesis of new fatty N-acylamino acids and N-acylamino esters from the C16:0, C18:0, C18:1, and C18:1(OH) fatty acid families and demonstrates the activity of these compounds as organogel agents. Compounds were heated and dissolved in various solvents (n-hexane, toluene, and gasoline). Only saturated C16:0 and C18:0 derived from alanine were able to form gels in toluene, and saturated C16:0 derived from phenylalanine showed gelation in n-hexane. This is the first evidence that fatty N-acylamino esters and N-acylamino acid derivatives of L-serine and fatty acids C16:0, C18:0, and C18:1 are able to form gels with hexane. This observation confirms the importance of the hydroxyl group in the segment derivative of L-serine in forming good gels.

[reaction: see text] The synthesis of liquid crystal series 9a-d was achieved using the Buchwald protocol and Sonogashira reaction.