Supramolecular salts assembled by melamine and two organic hydroxyl acids: synthesis, structure, hydrogen bonds, and luminescent property

Two novel supramolecular salts are synthesized by melamine and organic hydroxyl carboxylic acids. The structure prediction, purity, luminescent property, and thermal stability are investigated by theoretical and experimental analysis.

Bipyridine based metallogels: an unprecedented difference in photochemical and chemical reduction in the in situ nanoparticle formation

Metal co-ordination induced supramolecular gelation of low molecular weight organic ligands is a rapidly expanding area of research due to the potential in creating hierarchically self-assembled multi-stimuli responsive materials. In this context, structurally simple O-methylpyridine derivatives of 4,4'-dihydroxy-2,2'-bipyridine ligands are reported. Upon complexation with Ag(i) ions in aqueous dimethyl sulfoxide (DMSO) solutions the ligands spontaneously form metallosupramolecular gels at concentrations as low as 0.6 w/v%. The metal ions induce the self-assembly of three dimensional (3D) fibrillar networks followed by the spontaneous in situ reduction of the Ag-centers to silver nanoparticles (AgNPs) when exposed to daylight. Significant size and morphological differences of the AgNP's was observed between the standard chemical and photochemical reduction of the metallogels. The gelation ability, the nanoparticle formation and rheological properties were found to be depend on the ligand structure, while the strength of the gels is affected by the water content of the gels.

Solid state NMR studies of gels derived from low molecular mass gelators

Since its invention more than six decades ago, nuclear magnetic resonance (NMR) spectroscopy has evolved as an inevitable part of chemical as well as structural analysis of small molecules, polymers, biomaterials and hybrid materials. In the solution state, due to the increased viscosity of complex viscoelastic fluids such as gels, liquid crystals and other soft materials, the rate of molecular tumbling is reduced, which in turn affects the chemical shift anisotropy, dipolar and quadrupolar interactions. As a consequence the solution state NMR spectra show broad lines, and therefore, extracting detailed structural information is a challenging task. In this context, solid state (SS) NMR has the ability to distinguish between a minute amount of polymorphic forms, conformational changes, and the number of non-equivalent molecules in an asymmetric unit of a crystal lattice, and to provide both qualitative as well as quantitative analytical data with a short-range order. Therefore, SS NMR has continued to evolve as an indispensable tool for structural analysis and gave birth to a new field called NMR crystallography. Solid state cross polarization (CP) and high resolution (HR) magic angle spinning (MAS) NMR spectroscopy has been used to study weak interactions in polymer gels. However, the application of SS NMR spectroscopy to study gels derived from low molecular weight gelators has been limited until recently. In this review, we will focus on the importance of solid state NMR spectroscopy in understanding and elucidating the structure of supramolecular gels derived from low molecular weight gelators with selected examples.

Biocompatible hydrogelators based on bile acid ethyl amides

Four novel bile acid ethyl amides were synthetized using a well-known method. All the four compounds were characterized by IR, SEM, and X-ray crystal analyses. In addition, the cytotoxicity of the compounds was tested. Two of the prepared compounds formed organogels. Lithocholic acid derivative 1 formed hydrogels as 1% and 2% (w/v) in four different aqueous solutions. This is very intriguing regarding possible uses in biomedicine.

Bile acid-cysteamine conjugates: structural properties, gelation, and toxicity evaluation

Design, synthesis, and characterization of six novel bile acid-cysteamine conjugates together with investigation of their structural studies, gelation properties, and preliminary toxicity evaluation, are reported. Solid state properties of selected compounds were studied by means of X-ray diffraction and (13)C CPMAS NMR spectroscopy. N-(2-thioethyl)-3α,7α,12α-trihydroxy-5β-cholan-24-amide was shown to exhibit (pseudo)polymorphism, and a single crystal structure of its non-stoichiometric hydrate is reported herein. Cholyl and dehydrocholyl derivatives bearing three functionalities in their steroidal backbone were shown to undergo self-assembly leading to gelation in certain organic solvents. Preliminary morphology studies of the formed gels by scanning electron microscopy (SEM) were performed. The standard model mouse fibroblast cell line together with the MTT and NR tests were utilized for evaluating the toxicity of the prepared compounds. Lithocholyl, ursodeoxycholyl, and dehydrocholyl derivatives turned out to be relatively non-toxic in the conditions studied.