Supramolecular assemblies from amphiphilic homopolymers: Testing the scope

It has been shown by us in a recent communication that homopolymers, in which each repeat unit contains a hydrophilic and a hydrophobic head group, are capable of forming environment-dependent micellar or inverse micellar assemblies. A systematic structure-property relationship study is carried out here to test the scope of the design. We show here that the molecular design is indeed broadly applicable and that there is a significant gain in the critical aggregation concentrations of these polymers, as compared to the small molecule counterparts. We also show that the design can be tuned to achieve vesicle-type assemblies, which further expands the repertoire of amphiphilic homopolymers in a variety of areas. Characterizations of these assemblies have been carried out using transmission electron microscopy, dynamic light scattering, static light scattering, and dye incorporation experiments.     

Pipecolic acid-catalyzed direct asymmetric mannich reactions

[STRUCTURE: SEE TEXT] Mannich reactions between aldehydes and N-p-methoxyphenyl-protected alpha-imino ethyl glyoxylate have been performed using (S)-pipecolic acid as catalyst. The reactions give both syn- and anti-products (dr=1.4-2:1) with high enantioselectivities (>98% ee). In contrast, (S)-proline-catalyzed reactions give mainly syn-products with high enantioselectivities. Computational studies reveal that the energetic preference between the transition structures involving the s-cis-enamine and the s-trans-enamine is smaller for the pipecolic acid as compared to proline, yielding the (2S,3R)-anti and the (2S,3S)-syn Mannich product in nearly equal amounts.     

Low band gap thiophene-perylene diimide systems with tunable charge transport properties

Perylenediimide-pentathiophene systems with varied architecture of thiophene units were synthesized. The photophysical, electrochemical, and charge transport behavior of the synthesized compounds were studied. Both molecules showed a low band gap of ～1.4 eV. Surprisingly, the molecule with pentathiophene attached via β-position to the PDI unit upon annealing showed a predominant hole mobility of 1 × 10(-4) cm(2) V(-1) s(-1) whereas the compound with branched pentathiophene attached via β-position showed an electron mobility of 9.8 × 10(-7) cm(2) V(-1) s(-1). This suggests that charge transport properties can be tuned by simply varying the architecture of pentathiophene units.     

Configurational stability and transfer of stereochemical information in the reactions of enantioenriched organolithium reagents

The conversion of a prochiral methylene group into a stereogenic center by means of a lithiation/substitution sequence has emerged as a powerful synthetic transformation over the past 15 years. This reaction proceeds via a chiral organolithium intermediate, and the stereochemical fidelity of the overall reaction sequence is intimately dependent on the stereochemical behavior of the chiral organolithium as well as on the rate and stereochemical sense of the electrophilic substitution step. Chiral organolithium reagents were first reported by Letsinger, Curtin, and Applequist half a century ago. The lithiated intermediates in these early studies were not highly configurationally stable, and applications in stereoselective synthesis were not immediately forthcoming. The two decades that followed the 1980 report by Still and Sreekumar of a configurationally stable alpha-oxyorganolithium were marked by an increased interest in these reagents. As the synthetic applications of chiral organolithium reagents have grown, so have accompanying mechanistic studies of these intermediates which serve as the basis for this review.     

Mass spectral studies of some fructose containing oligosaccharide permethyl ethers

Mass spectrometry can be used to characterise fructofuranose units connected via C₂ to another sugar. The intensity of the m/e 101 and m/e 88 ions cannot be used to differentiate between furanose and pyranose ring forms in disaccharide permethyl ethers. The type of glycosidic linkage has considerable influence on the formation of these ions.     

The direct organocatalytic asymmetric mannich reaction: unmodified aldehydes as nucleophiles

The unprecedented application of unmodified aldehydes as nucleophilic donors in direct catalytic asymmetric Mannich-type reactions is disclosed in a full account. Our efforts in broadening the applicability of chiral pyrrolidine-based catalysts in direct asymmetric Mannich-type reactions led to the highly diastereo- and enantioselective and concise synthesis of functionalized alpha- and beta-amino acids, beta-lactams, and amino alcohols.     

Synthesis of dendrimers with multifunctional periphery using an ABB' monomer

A new methodology using an ABB' monomer for synthesizing dendrons with multiple functionalities in the periphery is described.     

Probing the periphery of dendrimers by heterogeneous electron transfer

The accessibility of the electroactive periphery was studied and compared for dendrimers and linear analogs by heterogeneous electron transfer using microelectrodes.