Certain alkyl l-O and l-S glycosides with hydrocarbon chain lengths greater than hexyl have been shown to form thermotropic liquid crystals at temperatures between 60 and 100[ddot]C. These are believed to be members of a large class of alkyl and acyl carbohydrate mesogens which, apart from their intrinsic value as potentially useful solid-state materials, could provide a variety of structurally accessible model systems for studying the phase transitions in the cell-membrane glycolipids.

Carbohydrate liquid crystals

Complexation of the crown ether receptor of the benzo-15-crown-5 benzoate 6[6,7,9,10,12,13,15,16octahydro-1,4,7,10,13-pentaoxabenzocyclopentadecen-2-ylmethyl 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate]6 with NaCF3SO3 and KCF3SO3 destabilizes the crystalline phase of 6 and induces the self-assembly of a supramolecular cylindrical channel-like architecture which displays an enantiotropic thermotropic disordered hexagonal columnar (Φh) mesophase Characterization of this supramolecular architecture was performed by a combination of differential scanning calorimetry (DSC), X-ray scattering, thermal optical polarized microscopy, DC conductivity and molecular modelling A model is proposed in which a stratum of the column is formed by ca 58 molecules of 6 with their benzo-15-crown-5 receptors placed side-by-side in the centre of the column and their melted alkyl tails radiating towards its periphery endo-Recognition generated via the benzo-15-crown-5 receptor upon complexation, and exo-recognition provided by the tapered 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate fragment of 6(most probably functioning via hydrophobichydrophobic interactions) provide the driving force for the self-assembly of this channel-like supramolecule This mechanism of self-assembly resembles that of tobacco mosaic virus (TMV)

Molecular recognition directed self-assembly of supramolecular cylindrical channel-like architectures from 6,7,9,10,12,13,15,16-octahydro-1,4,7,10,13-pentaoxabenzocyclopentadecen-2-ylmethyl 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate

This article presents a reoptimization of the GROMOS 53A6 force field for hexopyranose-based carbohydrates (nearly equivalent to 45A4 for pure carbohydrate systems) into a new version 56A(CARBO) (nearly equivalent to 53A6 for non-carbohydrate systems). This reoptimization was found necessary to repair a number of shortcomings of the 53A6 (45A4) parameter set and to extend the scope of the force field to properties that had not been included previously into the parameterization procedure. The new 56A(CARBO) force field is characterized by: (i) the formulation of systematic build-up rules for the automatic generation of force-field topologies over a large class of compounds including (but not restricted to) unfunctionalized polyhexopyranoses with arbritrary connectivities; (ii) the systematic use of enhanced sampling methods for inclusion of experimental thermodynamic data concerning slow or unphysical processes into the parameterization procedure; and (iii) an extensive validation against available experimental data in solution and, to a limited extent, theoretical (quantum-mechanical) data in the gas phase. At present, the 56A(CARBO) force field is restricted to compounds of the elements C, O, and H presenting single bonds only, no oxygen functions other than alcohol, ether, hemiacetal, or acetal, and no cyclic segments other than six-membered rings (separated by at least one intermediate atom). After calibration, this force field is shown to reproduce well the relative free energies of ring conformers, anomers, epimers, hydroxymethyl rotamers, and glycosidic linkage conformers. As a result, the 56A(CARBO) force field should be suitable for: (i) the characterization of the dynamics of pyranose ring conformational transitions (in simulations on the microsecond timescale); (ii) the investigation of systems where alternative ring conformations become significantly populated; (iii) the investigation of anomerization or epimerization in terms of free-energy differences; and (iv) the design of simulation approaches accelerating the anomerization process along an unphysical pathway.

A reoptimized GROMOS force field for hexopyranose‐based carbohydrates accounting for the relative free energies of ring conformers, anomers, epimers, hydroxymethyl rotamers, and glycosidic linkage conformers

Data on the synthesis, structures and properties of ionic, coordination, organometallic and organoelement compounds with liquid-crystal properties are surveyed. The substances examined are new in the chemistry of the liquid-crystal compounds. Their potential applications are described. The bibliography includes 211 references.

http://iopscience.iop.org/article/10.1070/RC1993v062n04ABEH000019/pdf

Metal-containing liquid-crystal phases

Carbohydrate liquid-crystals

The isotypic crystal form for the smectogenic p-n-alkoxybenzoic acids has been determined by room-temperature single-crystal x-ray diffraction analyses for the acids having 7, 8, 9, and 10 carbon atoms in the alkyl chain. The molecules are present in the crystals as centrosymmetric hydrogen-bonded dimers. The alkyl chains adopt an all-trans extended conformation but a gauche-relation of the ether oxygen and C(γ) about the C(α)-C(β) bond of the chains imparts a markedly non-linear and non-planar conformation to the molecules. With these chain lengths, adoption of this conformation makes possible an imbricated stratified layer structure in which the alkyl chains and the central aromatic nuclei are segregated into separate close-packed strata. Antiparallel interdigitation of chains in adjacent layers gives a 2:1 ratio of chains to nuclei in the strata. Evidence is presented that the molecules in the smectic mesophase probably retain the conformation found in the crystal and it is shown that the chan...

An X-Ray Study of the p-n-Alkoxybenzoic Acids. Part VI. Isotypic Crystal Structures of Four Smectogenic Acids Having Seven, Eight, Nine, and Ten Alkyl Chain Carbon Atoms

X-ray structure analyses have been carried out at room temperature for a crystalline modification of p-n-hexoxybenzoic acid (60BAC) which undergoes four solid-solid transitions on heating before yielding a nematic phase, and for a form of p-n-octoxybenzoic acid, different from that previously reported, which undergoes a single solid-solid transition before yielding a smectic phase. In both crystals the molecules are present as centrosymmetric hydrogen-bonded dimers. The alkyl chains are in the all-trans extended conformation but the dimers have a non-planar conformation arising from a gauche-relation of the ether oxygen and C(γ) about the C(α)-C(β) bond of the chain. This molecular conformation is the same as that found in other crystalline modifications of homologous members. The dimers in each structure are arranged in identical stacks along the crystal b-axes, and in projection down that axis are arranged in parallel staggered rows in a head-to-tail fashion in 8OBAC, but in an alternating head...

An X-Ray Study of the p-n-Alkoxybenzoic Acids. Part VII. Crystal Structures of Related Forms of p-n-Hexoxy- and p-n-Octoxy-Benzoic Acids

The crystal structures of p-n-propoxy- and p-n-pentoxy-benzoic acids (3OBAC and 5OBAC) have been determined at room temperature by single-crystal x-ray analysis. Both crystals have sheet structures. Within each sheet the molecules are arranged as hydrogen-bonded dimers in head-to-tail fashion in parallel staggered rows. The long axes of the aromatic nuclei are almost normal to crystal b. The alkyl chains are in planar extended form, but the ether oxygen and C(γ) are in a gauche relation about the C(α)-C(β) bond of the chain. The stacking of sheets is slightly different in 3OBAC which undergoes a solid-solid transition before yielding a nematic phase, than in 5OBAC which transforms directly to the nematic state. The tight face-to-face overlap of phenyl rings characteristic of the crystal structures of the two lowest homologs in the series, which are non-mesogenic at atmospheric pressure, is absent in these crystal structures where the ring planes in adjacent sheets are inclined to one another by a...

An X-Ray Study of the p-n-Alkoxybenzoic Acids. Part V. Crystal Structures of the Nematogenic Acids Having Three and Five Alkyl-Chain Carbon Atoms

The effect upon molecular packing of increasing chain length in a homologous series of mesogens has been examined in the case of the p-n-alkoxycinnamic acids by determination of the crystal structures of the four nematogenic acids having two, four, six, and eight carbon atoms in the alkyl chain. The chains have the all-trans extended conformation, and the molecules exist in the crystal as planar hydrogen-bonded dimers. The dimers are arranged in end-to end fashion in parallel rows. Similar side-to-side packing of pairs of dimmers is found in each crystal structure giving a good fit between adjacent aromatic cores, but the amplitudes of thermal vibration of the chain carbon atoms increase markedly with increasing chain length, indicating a low packing efficiency for these moieties.

Paul Hartley

Papers

An X-Ray Study of the p-n-Alkoxybenzoic Acids. Part VI. Isotypic Crystal Structures of Four Smectogenic Acids Having Seven, Eight, Nine, and Ten Alkyl Chain Carbon Atoms

An X-Ray Study of the p-n-Alkoxybenzoic Acids. Part VII. Crystal Structures of Related Forms of p-n-Hexoxy- and p-n-Octoxy-Benzoic Acids

An X-Ray Study of the p-n-Alkoxybenzoic Acids. Part V. Crystal Structures of the Nematogenic Acids Having Three and Five Alkyl-Chain Carbon Atoms

An X – Ray Study of the p-n-Alkoxycinnamic Acids. Part III.1

Structure of methyl 6-deoxy-α-d-idopyranoside