0000000000068977
AUTHOR
Virpi Noponen
Stimuli-responsive bile acid-based metallogels forming in aqueous media
Abstract The synthesis and gelation properties of a picolinic acid conjugated bile acid derivative in the presence of metal salts along with the stimuli-responsiveness of the systems are reported. The gels are formed in the presence of Cu 2+ ions in the solvent systems composed of 30–50% of organic solvent (MeOH, acetonitrile, or acetone) in water. The gels respond to various stimuli: they can be formed upon sonication or shaking, and their gel–sol transformation can be triggered by a variety of chemical species. NMR, MS, and SEM techniques are exploited in order to gain a deeper insight on the self-assembled systems.
Self-assembly properties of bile acid derivatives of L-cysteine, L-valine and L-serine alkyl esters
Comprehensive self-assembly studies for nine bile acid amides of amino acid esters are reported. The number of the hydroxyl groups attached to the steroidal skeleton and the character of the amino acid ester moiety were used as variables when examining the self-assembly properties of the compounds. Two of the compounds were shown to undergo self-assembly leading to organogelation. In addition, preliminary self-assembly studies in aqueous mixtures of polar organic solvents were conducted. Microscopic methods (optical microscopy and scanning electron microscopy) were utilised in order to gain a deeper insight into the self-assembled structures. Furthermore, single-crystal X-ray structures for…
Bile acid–cysteamine conjugates: Structural properties, gelation, and toxicity evaluation
Abstract 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 13C 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 so…
Structural, Thermoanalytical and Molecular Modeling Studies on N-(3-hydroxypropyl) 3a,12a-Dihydroxy-5b-cholan-24-amide and Its Monohydrates
The synthetic method for preparing N-(3-hydroxypropyl) 3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-amide can lead to formation of at least three different crystal forms - an anhydrous compound and two monohydrates. The structural and thermal properties of these forms have been characterized by 13C-CP/MAS-NMR and IR spectroscopy, thermo- gravimetry, differential scanning calorimetry and by powder and single crystal x-ray crystallography. In addition, theoretical 13C-NMR chemical shift calculations were also performed for the anhydrous compound and for the first monohydrate, starting from single crystal structures and the structures of these species have now been verified. The first monohydra…
Bile acid alkylamide derivatives as low molecular weight organogelators: systematic gelation studies and qualitative structural analysis of the systems.
A series of amino- and hydroxyalkyl amides of bile acids have been synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), (1)H and (13)C nuclear magnetic resonance spectroscopy (NMR), as well as electrospray ionization mass spectrometry (ESI-MS) measurements. The ability of the synthesized molecules to promote gel formation was systematically investigated. Out of 396 combinations formed by 11 compounds and 36 different solvents, 22 gel-containing systems were obtained with 1% (w/v) gelator concentration. Apart from one exception, the gelator compounds were lithocholic acid derivatives. This challenges the general trend of bile acid-based physical gelators, accordin…
1 H,13 C, 19 F NMR, and ESI mass spectral characterization of two geminal difluorosteroids
Two geminal difluorosteroids, 3,3-difluoro-5β-cholan-24-oic acid (1) and 3,3-difluoro-5α-androstan-17-one (2), have been prepared from corresponding ketosteroids with diethylaminosulphurtrifluoride (DAST) treatment in moderate yields. The structures of 1 and 2 have been characterized by 1H, 13C, 19F NMR, and ESI mass spectral techniques. Copyright © 2008 John Wiley & Sons, Ltd.
Bile acid–amino acid ester conjugates: gelation, structural properties, and thermoreversible solid to solid phase transition
Design, synthesis, and gelation properties of three novel biocompatible bile acid–L-methionine methyl ester conjugates are presented. Two of the conjugates have been shown to undergo self-assembly leading to organogelation in certain aromatic solvents. The properties of these gels have been investigated by conventional methods typical for molecular gel studies along with 13C CPMAS NMR spectroscopic studies of the native gel. In addition, properties in solid and solution states for all three compounds have been investigated, and single crystal X-ray structures of all compounds determined. Furthermore, powder X-ray diffraction studies have revealed that compound 1 undergoes a dynamic and reve…
Novel two-step synthesis of gold nanoparticles capped with bile acid conjugates
Bile acids and their conjugates are physiologically important molecules. Syntheses and structure elucidation combined with investigation of properties and applications of bile acids and their derivatives are of academic interest. The concept of using bile acids and their conjugates in nanoscience is a novel idea, which opens up fascinating prospects. In this article, an easy and simple route for obtaining N-lithocholyl-L-(cysteine ethyl ester) (3), capable of effectively capping and stabilizing metal nanoparticles, is described. The whole synthetic route needs only two steps giving a moderate to good yield. The gold NPs are characterized by elemental analysis, UV spectroscopy, and TEM. Addi…
Recent advances in steroidal supramolecular gels
During the last decade or two the interest towards small molecules capable of self-assembly leading to gelation has increased intensively. The investigation of these supramolecular gels aims not only at understanding the fundamental processes underlying gel formation but also at development of new materials with a myriad of applications. Steroids are widely-spread natural products with a large and rigid steroidal nucleus combined with derivatizable functional groups leading to an adjustable polarity profile, which makes them attractive building blocks when designing novel low molecular weight gelators. Due to their unique properties, steroid-based supramolecular gels may find use in applica…