Crystal structure of the supramolecular linear polymer formed by the self-assembly of mono-6-deoxy-6-adamantylamide-beta-cyclodextrin

Mono-6-deoxy-6-adamantylamide-beta-cyclodextrin - dimethylformamide - 15H(2)O, C53H85NO35.C3H7NO.15H(2)O, crystallizes in the orthorhombic space group P2(1)2(1)2(1). The adamantyl group is inserted into the cyclodextrin cavity of the adjacent molecule, entering by the side of the secondary hydroxy rim, thus forming a supramolecular linear polymer by self-assembly. Adjacent macrocycles are linked into columns by hydrogen bonds involving the nearest glucose residues, and the structure is further stabilized by their involvement in hydrogen bonding with water molecules which reside in channels surrounding the polymer columns, thus acting as bridges between the cyclodextrin units. The centroid of the adamantyl group lies below the plane formed by the seven glycosidic O atoms of the host cyclodextrin, excluding water molecules from the secondary side of beta-cyclodextrin (beta-CD). Between the adamantyl group and the primary hydroxy rim of the cyclodextrin cavity lies a dimethylformamide molecule, which shields the hydrophobic adamantyl group from the primary hydroxy rim of its carrying beta-CD and excludes water molecules from the primary side of the beta-CD cavity

Supramolecular structures generated by a p-tert-butylphenyl-amide derivative of cholic acid: From vesicles to molecular tubes

The formation of supramolecular structures initiated by a p-tert-butylphenyl-amide derivative of cholic acid is investigated. The initial spherical vesicles, with a rather low effective bending constant, collapse into necklaces that self-transform into tubules of small diameter. Finally, molecular tubes are generated (see figure). During the process, the geometrical constraints of fixed surface area and fixed enclosed volume are obeyed

Thermodynamics of formation of host-guest supramolecular polymers

The interactions between three beta-cyclodextrin hosts (having 1-3 binding sites) and two adamantyl guests (having 1-2 binding sites) have been studied by ITC, ROESY, static and dynamic light scattering (SLS and DLS), and AFM and TEM techniques. The enthalpy and free energy values (determined from ITC experiments) evidence that the single interaction between one binding site of the guest and one binding site of the host is independent of the number of binding sites of the interacting species. The average values are Delta H degrees = -26.6 +/- 2.3 kJ mol(-1) and Delta G degrees = -30.4 +/- 3.2 kJ mol(-1), indicating that the process is mainly enthalpy driven. In all cases, the experimental molar ratio (from ITC experiments) agrees with the expected one from the number of binding sites of both the host and guest. The formation of polymer-like entities was demonstrated by SLS, DLS, AFM, and TEM measurements. The structure of polymers is linear when both the host and the guest are ditopic entities and dendritic (or Cayley tree type) when the host and the guest have three and two binding sites, respectively

New lamellar structure formed by an adamantyl derivative of cholic acid

The self-aggregation of the sodium salt of a new adamantyl amide of the 3 beta-amino derivative of cholic acid (Na-AdC) in aqueous solution has been investigated by surface tension, dynamic light scattering, fluorescence, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) measurements. These last two techniques suggest that a lamellar phase, consisting of charged bilayers of Na-AdC separated by solvent and periodically stacked, is formed in aqueous solution. The structure of the bilayer is inferred from the resolution of the crystal of the compound in its acid form. The adamantyl moieties, which are mutually interlocked, reside in the central region of the bilayer, and the carboxylic groups are directed toward the hydrophilic region. The structure is open enough to allow water molecules to interact with a fluorescence probe located at the central hydrophobic region

Kinetics of formation of supramolecular tubules of a sodium cholate derivative

We report a kinetic study of the supramolecular tubule formation of the bile salt derivative [3 beta, 5 beta, 7 alpha, 12 alpha]-3-(4-t-butylbenzoilamine)-7,12-dihydroxycholan-24-oic acid sodium salt (Na-tbutPhC). At high bicarbonate buffer concentration (pH similar to 10) this salt shows gelator properties. Starting from gels or viscous solutions, the tubule formation is triggered by increasing the temperature beyond the critical value of 34-36 degrees C. For gels, when the process takes place, the transition to sols occurs. The process is easily triggered and can be followed by several techniques. We used static light scattering (SLS), circular dichroism (CD), small angle X-ray scattering (SAXS) along with transmission electron (TEM) and optical microscopies. The CD results show that fibrils with a clockwise arrangement of the bile salt derivative are present in the samples at room temperature. When the tubule formation starts, evolutions of the CD and SLS profiles are observed indicating that the formation process begins with the aggregation of the fibrils accompanied by a simultaneous peculiar reciprocal reorientation of the surfactant molecules. After that, as pointed out by the long time evolution of the curves, a slow transformation towards the final well defined tubules occurs, involving an adjustment of the molecular packing. In the meanwhile, the slow ordering of the tubule walls in well spaced layers takes place, as inferred by SAXS. The TEM images show that short disordered tubules are formed, because of the aggregation of fibrils, in the beginning. Moreover they highlight a final elongation of the tubules taking place without a further aggregation of fibrils. Optical microscopy frames, collected during the process, point out that the tubules grow singly even at quite a high concentration, thus supporting the data interpretation