Chiral Gelator Research Articles

Chiral Gelators Constructed from 11‐Aminoundecanoic (AUDA), Lauric and Amino Acid Units. Synthesis, Gelling Properties and Preferred Gelation of Racemates vs. the Pure Enantiomers

AbstractA new class of efficient low molecular weight gelator molecules has been designed by combining 11‐aminoundecanoic acid (AUDA), lauric acid and aromatic and aliphatic amino acid units in the same molecule. This yields a special class of fatty acid amphiphiles with core chiral centres and hydrogen bonding sites. Some of the compounds with terminal carboxylic acid and sodium carboxylate functions exhibited ambidextrous gelation properties, being able to form gels both with highly polar solvents (water, DMSO) and also with highly lipophilic solvents, including two hydrocarbon fuels. At variance with several recent observations that the enantiomers are generally more efficient gelators than the corresponding racemates, some of the racemic gelators prepared in this work were found to be capable of gelling up to 16 times larger volumes of certain solvents than the pure enantiomers. Temperature‐dependent FTIR and 1H NMR studies of the gels formed by derivatives with terminal carboxylic acid groups and lipophilic solvents revealed that intermolecular hydrogen bonding between amidic and carboxylic acid units was involved in the self‐assembly of gel aggregates. Additional strong stabilization of the aggregates was observed in the gelators possessing terminal sodium carboxylate groups, and this was attributed to the electrostatic and ion‐dipole interactions between the sodium carboxylate groups. This additional stabilization appears to be responsible for considerably higher thermal stability of the latter gels in relation to those formed by gelators with terminal carboxylic acid groups. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Chiral Amplification of the Structure and Viscoelasticity of a Supramolecular Polymeric System Consisting of N,N‘,N‘‘-Tris(3,7-Dimethyloctyl)Benzene-1,3,5-Tricarboxamide and n-Decane

The influence of a chiral gelator molecule, N,N‘,N‘‘-tris-(S)-(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide ((S)DO3B), on the structure in the formation of supramolecular polymers and viscoelasticity was examined in an organogel system consisting of a racemic mixture of the gelator molecule, N,N‘,N‘‘-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide (DO3B), and n-decane. In the absence of the chiral gelator, equal amounts were observed of the right- and left-handed helicities of the formed columnar supramolecular polymers. Addition of (S)DO3B markedly induced one helicity in excess, due to the Majority Rule effect. Although there are two possibilities, (1) left- and right-handled helices within single supramolecular polymers and (2) mixtures of homochiral supramolecular helical polymers, the viscoelasticity of the system supports the former. Without (S)DO3B, 60% of the amide groups of the gelators formed hydrogen bonding in the system; upon increasing the relative (S)DO3B composition (relative to the ...

Synthesis of polymer gel with chiral helical cavity by molecular imprinting using bifunctional vinyl monomers

The molecular imprinting method was applied for synthesizing gels with a chiral helical cavity using various bifunctional vinyl monomers, such as α-(benzyloxymethyl)acrylic acid derivatives as a monomer, and one-handed helical (+)-poly(diphenyl-2-pyridylmethyl methacrylate) as a template. The chiral gels were almost quantitatively prepared after removal of the template polymer by hydrolysis of the ester groups. The obtained gels exhibited chiral resolution powers toward various racemates, such as trans-stilbene oxide and Tröger's base, and the substituents on the phenyl group of the monomer significantly affected the recognition ability. The observed separation factors were higher than those of the gels prepared from the mono-functional vinyl monomer, methacrylic acid.

MEMBRANE-ASSISTED CHIRAL RESOLUTION OF PHARMACEUTICALS: IBUPROFEN SEPARATION BY ULTRAFILTRATION USING BOVINE SERUM ALBUMIN AS CHIRAL SELECTOR

The chiral separation of ibuprofen has been performed by ultrafiltration in solutions containing the protein bovine serum albumin (BSA) as a chiral selector. The effectiveness of optical resolution was characterized in terms of enantiomeric enrichment and solute recovery in the permeate. Working conditions, including parameters of feed solution and hydrodynamic conditions, which can influence thermodynamic equilibrium and nonselective solute binding, have been investigated with regard to the separation effectiveness. Enantioselectivity is strongly pH-dependent and reaches a maximal value at pH 9.0–9.2. It was established that nonspecific interactions also played a significant role in total ibuprofen binding, decreasing both enantioselectivity and solute recovery in permeates. Nonspecific interactions are suppressed in the presence of organic solvents (acetonitrile, methanol) in the feed solution thereby increasing the solute recovery in the permeate. Increase in BSA content in the feed solution results in an increase of both enantioselectivity and solute binding. In ultrafiltration-based chiral separation, concentration polarization and gel formation worsen enantioselectivity and increase solute binding. A consequent enrichment of enantiomers was illustrated in a multi-stage chiral resolution. After six stages of separation, the permeate contains more than 95% of (S)-ibuprofen. Regeneration of both BSA and bound enantiomer may be fulfilled in the same ultrafiltration system by ultrafiltration of alkaline solutions.

Helical aggregates from a chiral organogelator

A new class of pyrene based organogelators has been discovered, and a chiral gelator of this type has been shown to form helical aggregates upon gelation.

Chiral Recognition in Bis-Urea-Based Aggregates and Organogels through Cooperative Interactions.

Chiral recognition in organogels occurs in the coassembly of the chiral gelator 1 with the chiral guest molecule 2. The diastereomeric aggregates formed from (R,R)-2 with (R,R)-1 or (S,S)-1 were found to be truly different in structure and strength. Cooperativity makes a major contribution to the chiral recognition in this system.

Switchable mirrors of chiral liquid crystal gels

Chiral nematic liquid crystal compositions containing mono- and di-acrylates in mixtures with non-reactive liquid crystal molecules were produced. Defect-free planar macroscopic alignment of the molecules was induced between uniaxially rubbed substrates. Polymerization of the acrylate groups was initiated photochemically leading to the formation of a new class of chiral gels consisting of a lightly cross-linked network containing non-reactive molecules. In this way, the chiral pitch and, hence, the reflection colour became permanently fixed. Under the influence of an electric field the gels could be switched to the homeotropic state and reverted to the planar defect-free state upon removal of the electric field. Depending on the composition of the gel, either the position of the reflection band remained the same while its magnitude and/or width decreased, or its position shifted to smaller wavelengths with increasing electric field. Some of the gels showed sharp switching characteristics with a hysteresis making them suitable for passive matrix addressing with a high degree of multiplexability. The gels also showed fast switching times as they reverted to the defect-free optical state upon removal of the electric field. The phase structure of the gels was studied using dielectric spectroscopy which showed that the gels have an inhomogeneous structure.

ChemInform Abstract: Enzymatic Synthesis of a Chiral Gelator with Remarkably Low Molecular Weight.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Sugar-integrated gelators of organic fluids: on their versatility as building-blocks and diversity in superstructures

Three 1-O-methyl-4, 6-O-benzylidene derivatives of monosaccharides (D-glucose, D-galactose and D-mannose) were synthesised: they acted as versatile gelators of various organic fluids, indicating that saccharides are useful as potential building-blocks for molecular design of chiral gelators.

Enzymatic synthesis of a chiral gelator with remarkably low molecular weight

In one enzymatic step, two products of low molecular weight are obtained: one is a gelator of organic solvents, the other crystallizes to form an extended hydrogen-bondednetwork.

Functional organic gels. Enantioselective elution using chiral gels from amino acid-derived lipids

Abstract The L-glutamic acid-derived lipids form organic gels in benzene, which show enantioselective elution of N-dansyl L-phenylalanine from organic gels to aqueous phases. Differential scanning calorimetry and circular dichroism measurements demonstrate that this enantioselectivity occurred through highly-oriented structures of aggregated lipids like those of aqueous lipid membrane systems.

A Novel Low Molecular Weight Chiral Gelator for Apolar Organic Solvents

AbstractThe synthesis, molecular structure, and properties of a new chiral gelforming agent 1 are described. Key structural features in 1 are a γ‐alkoxybutyro‐lactone tetralin moiety and an angular phenylsulphone unit. The new low molecular weight gelator 1 can reversibly form stable gels in low concentrations (e.g., 1:800 for n‐hexane) with isopropanol and a variety of apolar organic solvents. The gels were studied with differential scanning calorimetry and a combination of electron microscopy techniques, which revealed a highly ordered three‐dimensional network of entangled fibers. X‐ray analysis showed that the aggregation of 1 leads to a helical structure in the solid state. Nonchiral analogues 2 and 3 were unable to initiate gel formation.

Gelation of silicone fluids using 1,3:2,4-dibenzylidene sorbitol

A variety of silicone fluids have been found to gel using low concentrations (typically < 4 wt.%) of 1,3:2,4-dibenzylidene sorbitol (DBS). DBS is known to be a chiral gelator for many organic solvents. Gels were formed when small amounts of DBS were introduced into the silicone fluids either by heating to high temperatures or at ambient temperatures with the use of a co-solvent. Optical and electron microscopy of neat silicon–DBS gels (concentration as low as 0.005 wt.%), revealed the formation of two types of fibrous network. One consisted of ribbon-like macrofibres (average width, ca. 2–3 µm) present in the opaque region of the gels and the other consisted of dense intertwined microfibres (average width, ca. 100 nm) present in the clear portion of the gels. The gels prepared in the presence of a co-solvent consisted only of the microfibrous network. N-Methylpyrrolidone was found to be a very effective co-solvent for the phenyl-containing siloxanes producing firm clear gels. Dynamic mechanical measurements indicated that the storage modulus (G′) of these gels increased with increasing DBS content over the range 1–6 wt.% DBS. Comparison with propylene glycol–DBS gels showed the silicone gels to differ in that they comprised mostly an isotropic phase with no detectable crystalline phase present.

ChemInform Abstract: CHIRAL AGGREGATION PHENOMENA. 4. A SEARCH FOR STEREOSPECIFIC INTERACTIONS BETWEEN HIGHLY PURIFIED ENANTIOMERIC AND RACEMIC DIPALMITOYL PHOSPHATIDYLCHOLINES AND OTHER CHIRAL SURFACTANTS IN MONOLAYERS, VESICLES, AND GELS

Chemischer InformationsdienstVolume 13, Issue 18 Article ChemInform Abstract: CHIRAL AGGREGATION PHENOMENA. 4. A SEARCH FOR STEREOSPECIFIC INTERACTIONS BETWEEN HIGHLY PURIFIED ENANTIOMERIC AND RACEMIC DIPALMITOYL PHOSPHATIDYLCHOLINES AND OTHER CHIRAL SURFACTANTS IN MONOLAYERS, VESICLES, AND GELS E. M. ARNETT, E. M. ARNETTSearch for more papers by this authorJ. M. GOLD, J. M. GOLDSearch for more papers by this author E. M. ARNETT, E. M. ARNETTSearch for more papers by this authorJ. M. GOLD, J. M. GOLDSearch for more papers by this author First published: May 4, 1982 https://doi.org/10.1002/chin.198218089AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue18May 4, 1982 RelatedInformation

Outer-Sphere Ligand Exchange Chromatography on Bonded Chiral Silica Gel

Abstract A bonded chiral phase for HPLC, obtained by reaction between a porous silica gel modified with N(aminoethylamino)propyl groups, and A(+)[Co(en)2(NO2)] Br, was prepared in order to sepa rate optical isomers by a outer-sphere complex mechanism. The extent of the stereoselectivity of this support was tested by sampling racemates of organics acids and of tris-oxalate complexes of cobalt(III) and chromium(III). Good resolution was achieved when strong interactions of the solute (tri-oxalates complexes) with the support were involved.