Water Gelation of an Amino Acid-Based Amphiphile

• Published in: Chemistry : a European journal 2006-06, Vol.12 (19), p.5068-5074
• Main Authors: Das, Debapratim, Dasgupta, Antara, Roy, Sangita, Mitra, Rajendra Narayan, Debnath, Sisir, Das, Prasanta Kumar
• Format: Article
• Language: English
• Subjects: amino acids; Amino Acids - chemistry; amphiphiles; Anilino Naphthalenesulfonates; Cell Survival - drug effects; Circular Dichroism; Cross-Linking Reagents; Fluorescence; HeLa Cells; Humans; hydrogels; Hydrogels - chemical synthesis; Hydrogels - pharmacology; Hydrogen Bonding; Magnetic Resonance Spectroscopy; Microscopy, Electron, Scanning Transmission; Molecular Conformation; Spectrometry, Fluorescence; supramolecular chirality; Tetrazolium Salts; Thiazoles; Water - chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200501638

The water immobilization by a simple amino acid‐containing cationic surfactant was investigated. A variety of techniques, such as 1H NMR spectroscopy, circular dichroism (CD), steady‐state fluorescence spectroscopy, and field‐emission scanning electron microscopy (FESEM) were applied to determine the formation and architecture of the hydrogel. The new gelator with a minimum gelation concentration (MGC) of 0.3 % w/v shows prolonged stability and a low melting temperature (39 °C). 1H NMR experiments revealed that intermolecular hydrogen bonding between the amide groups and π–π stacking of the indole rings are the two regulating parameters for gelation. Furthermore, fluorescence studies with 8‐anilino‐1‐naphthalenesulfonic acid (ANS) as the probe indicate the participation of hydrophobicity during gelation. The luminescence study using both ANS and pyrene, along with FESEM results, indicate a critical concentration, well below the MGC, at which fibres begin to form. These cross‐link further to give thicker fibers, leading to the formation of a hydrogel (0.3 % w/v). This new hydrogelator expresses high supramolecular chirality, as evidenced by the CD spectra. In addition, the gelator molecule was found to be nontoxic up to a concentration of 4 mM (0.2 % w/v). The high supramolecular chirality, prolonged stability, low melting point, and biocompatibility of the molecule make it a focus of chemical and biological interest. The hydrogelation property of a simple amino acid‐based amphiphile (left) was investigated by means of spectroscopic and microscopic techniques. Intermolecular hydrogen bonding between amide NH and carbonyl oxygen, and π–π stacking between the indole rings, as well as hydrophobic interactions, were found to be responsible for the formation of a hydrogel that shows high supramolecular chirality (right).