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André Heeres

Publications and source records attributed to André Heeres.

4 recordsLinked to original sources
PubMed2005

Cyclohexane-based low molecular weight hydrogelators: a chirality investigation.

Seven new 1,3,5-cyclohexyltricarboxamide-phenylalanine derivatives were synthesized in order to investigate the effect of the amino acid chirality on the gelating properties of these small molecules in water. Gelation tests have shown that enantiomerically pure homochiral 1,3,5-cyclohexyltricarboxamide-L-phenylalanine is a non-hydrogelator as it crystallizes from water, whereas the heterochiral derivatives with either two L-phenylalanine moieties and one D-phenylalanine (LLD), or vice versa (DDL), are very good hydrogelators. Concentration-dependent gel-to-sol transition-temperature (T(gs)) curves for LLD or DDL gels show a sigmoidal behaviour, which is in contrast to the logarithmic curves generally observed for gels derived from low molecular weight gelators (LMWGs). Such sigmoidal behaviour can be related to interactions between fibre bundles, which give rise to intertwined bundles of fibres. Transmission electron microscopy (TEM) images of LLD and DDL gels show a network of thin, unbranched, fibre bundles with diameters of 20 nm. Right-handed twisted fibre bundles are present in the LLD gel, whereas left-handed structures can be found in the DDL gel. Each bundle of fibres consists of a finite number of primary fibres. Gels consisting of mixtures of gelators, LLD and DDL, and nongelators (LLL or DDD) were investigated by means of T(gs) measurements, CD spectroscopy and TEM. Results show that the incorporation of nongelator molecules into gel fibres occurs; this leads to higher T(gs) values and to changes in the helicity of the fibre bundles. Furthermore, it was found that peripheral functionalization of the homochiral derivatives LLL or DDD by means of a second amino acid or a hydrophilic moiety can overcome the effect of chirality; this process in turn leads to good hydrogelators.

Journal Article↗
PubMed2004

A synthetic strategy for novel nonsymmetrical bola amphiphiles based on carbohydrates.

A number of novel nonionic bolaform amphiphiles with nonidentical aldityl head groups, 1-(1-deoxy-D-galactitol-1-ylamino)-6-(1-deoxy-D-glucitol-1-ylamino)hexane, 1-(1-deoxy-D-mannitol-1-ylamino)-6-(1-deoxy-D-glucitol-1-ylamino)hexane, and 1-(1-deoxy-D-galactitol-1-ylamino)-6-(1-deoxy-D-mannitol-1-ylamino)hexane were synthesized by two successive reductive aminations involving 1,6-diaminohexane (1) and the appropriate D-aldohexoses (D-glucose, D-mannose, and D-galactose) using 5% Pd on carbon as the catalyst. Typical reaction conditions were 40 degrees C, 4MPa hydrogen and a reaction time of 4.5 h. The compounds were isolated as white solids in yields ranging from 39% to 72%. The intermediate aminoalditols, 1-(1-deoxy-D-glucitol-1-ylamino)-6-aminohexane and 1-(1-deoxy-D-galactitol-1-ylamino)-6-aminohexane were obtained as off-white solids in 80-85% yield. The bolaform amphiphiles containing 1-deoxy-D-glucitol head group(s) showed markedly lower melting points than the compounds with the 1-deoxy-D-mannitol and 1-deoxy-D-galactitol head groups, due to the presence of 1,3-syn interactions within the carbohydrate moiety. The novel bolaform compounds are potential starting materials for the synthesis of a broad range of gemini surfactants with nonidentical, carbohydrate-based head groups.

Biochemistry↗
PubMed2003

Orthogonal self-assembly of low molecular weight hydrogelators and surfactants.

The concurrent self-assembly of new 1,3,5-trisamide-cyclohexane-based low molecular weight hydrogelators and various surfactants in water leads to the formation of self-assembled fibrillar networks with encapsulated micelles. This prototype system presents an example of orthogonal self-assembly, that is, the independent formation of two different supramolecular structures, each with their own characteristics that coexist within a single system.

Amides↗