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Chiral Material (chiral + material)
Selected AbstractsMesoporous Silicas by Self-Assembly of Lipid Molecules: Ribbon, Hollow Sphere, and Chiral MaterialsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2008Haiying Jin Abstract Using lipids (N -acyl amino acids) and 3-aminopropyltriethoxysilane as structure- and co-structure-directing agents, mesoporous silicas with four different morphologies, that is, helical ribbon (HR), hollow sphere, circular disk, and helical hexagonal rod, were synthesized just by changing the synthesis temperature from 0,°C to 10, 15, or 20,°C. The structures were studied by electron microscopy. It was found that 1),the structures have double-layer disordered mesopores in the HR, radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2D-hexagonal mesopores in the disklike structure and helical rod, respectively; 2),these four types of mesoporous silica were transformed from the flat bilayered lipid ribbon with a chain-interdigitated layer phase through a solid,solid transformation for HR formation and a dissolving procedure transformation for the synthesis of the hollow sphere, circular disk, and twisted morphologies; 3),the mesoporous silica helical ribbon was exclusively right-handed and the 2D-hexagonal chiral mesoporous silica was excessively left-handed when the L -form N -acyl amino acid was used as the lipid template; 4),the HR was formed only by the chiral lipid molecules, whereas the 2D-hexagonal chiral mesoporous silicas were formed by chiral, achiral, and racemic lipids. Our findings give important information for the understanding of the formation of chiral materials at the molecular level and will facilitate a more efficient and systematic approach to the generation of rationalized chiral libraries. [source] Convergent Synthesis of Both Enantiomers of 4-Hydroxypent-2-ynoic Acid Diphenylamide for a Thrombin Receptor Antagonist Sch,530348 and Himbacine AnaloguesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Alex Zaks Abstract Sch,530348 and many himbacine analogues were prepared by using 4-hydroxypent-2-ynoic acid diphenylamide as the only chiral material. We developed deracemization methods to prepare both enantiomers of this propargyl alcohol. These methods involved a resolution followed by inversion. The objective for the resolution step was to obtain the desired enantiomer as an ester, and undesired enantiomer as an alcohol. With (R)-selective lipase, this was achieved by transesterifcation for (R)-alcohol, and ester hydrolysis for (S)-alcohol. The undesired enantiomer was inverted through the corresponding tosylate to yield the desired enantiomer as the ester. Deprotection of the ester gave enantiopure alcohol as the product. These methods not only overcame the 50% yield limit in resolution, but also eliminated the need to remove the undesired enantiomer. [source] Spontaneous segregation on a hybrid chiral surfaceJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2008Szabelski Abstract Segregation of enantiomers in two-dimensional adsorbed layers is a process that is usually controlled by anisotropic directional interactions between adsorbed molecules. In this contribution, we propose a simple theoretical model in which the chiral segregation occurs even though the lateral interactions are neglected. In particular, we consider a solid surface composed of two domains with different patterns of active sites being mirror images of each other. The domains of opposite handedness represent crystal facets of a composite chiral material which are adjoined to form a heterochiral adsorbing surface. To explore equilibrium properties of the system, we use Canonical Ensemble Monte Carlo method for a square lattice. The influence of factors such as energetic properties of the surface and density of the adsorbed layer on the extent of separation is examined. The obtained results indicate that effective two-dimensional separation on the hybrid chiral surface assumed in our model can be achieved only at sufficiently low adsorbate densities. The results also suggest that the segregation on the hybrid surface would be a promising method of enantiodiscrimination for those chiral molecules which do not exhibit strong lateral interactions. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008 [source] Development of synthetic double helical polymers and oligomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2009Yoshio Furusho Abstract There is growing interest in the design and synthesis of artificial helical polymers and oligomers, in connection with biological importance as well as development of novel chiral materials. Since the discovery of the helical structure of isotactic polypropylene, a significant advancement has been achieved for synthetic polymers and oligomers with a single helical conformation for about half a century. In contrast, the chemistry of double helical counterparts is still premature. This short review highlights the recent advances in the synthesis, structures, and functions of double helical polymers and oligomers, featuring an important role of supramolecular chemistry in the design and synthesis of double helices. Although the artificial double helices reported to date are still limited in number, recent advancement of supramolecular chemistry provides plenty of structural motifs for new designs. Therefore, artificial double helices hold great promise as a new class of compounds. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5195,5207, 2009 [source] Mesoporous Silicas by Self-Assembly of Lipid Molecules: Ribbon, Hollow Sphere, and Chiral MaterialsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2008Haiying Jin Abstract Using lipids (N -acyl amino acids) and 3-aminopropyltriethoxysilane as structure- and co-structure-directing agents, mesoporous silicas with four different morphologies, that is, helical ribbon (HR), hollow sphere, circular disk, and helical hexagonal rod, were synthesized just by changing the synthesis temperature from 0,°C to 10, 15, or 20,°C. The structures were studied by electron microscopy. It was found that 1),the structures have double-layer disordered mesopores in the HR, radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2D-hexagonal mesopores in the disklike structure and helical rod, respectively; 2),these four types of mesoporous silica were transformed from the flat bilayered lipid ribbon with a chain-interdigitated layer phase through a solid,solid transformation for HR formation and a dissolving procedure transformation for the synthesis of the hollow sphere, circular disk, and twisted morphologies; 3),the mesoporous silica helical ribbon was exclusively right-handed and the 2D-hexagonal chiral mesoporous silica was excessively left-handed when the L -form N -acyl amino acid was used as the lipid template; 4),the HR was formed only by the chiral lipid molecules, whereas the 2D-hexagonal chiral mesoporous silicas were formed by chiral, achiral, and racemic lipids. Our findings give important information for the understanding of the formation of chiral materials at the molecular level and will facilitate a more efficient and systematic approach to the generation of rationalized chiral libraries. [source] | ||||||||||