title: Hydrogelation Induced by Change in Hydrophobicity of Amino Acid Side Chain in Fmoc-Functionalised Amino Acid: Significance of Sulfur on Hydrogelation.
abstract: Although a few Fmoc-functionalised amino acids (Fmoc-AA) are capable of forming hydrogels, the exact levels of hydrophobicity, hydrogen bonding, and ionic nature of the Fmoc-AA gelator required for hydrogel formation remains uncertain. Here, the role of hydrophobicity of amino acid side chain, particularly in the formation of hydrogel, was studied by using Fmoc-norleucine (Fmoc-Nle) and its simple sulfur analogues such as Fmoc-methionine (Fmoc-M) in which the γCH2 of Fmoc-Nle is replaced by sulfur. Results indicate that Fmoc-M forms thermally reversible hydrogels in water (pH ca. 6.8), whereas Fmoc-Nle fails to display any gelation under similar conditions. The result suggests that substitution of the sulfur atom likely reduces the hydrophobicity of the alkyl side chain in Fmoc-Nle to the optimum level, which is sufficient to induce supramolecular hydrogelation in Fmoc-M. The difference in the self-association behaviour of Fmoc-M and Fmoc-Nle emphasise the importance of weak noncovalent interaction between side chains (in addition to the hydrogen-bond and aromatic interactions) to stabilise supramolecular self-assembly of Fmoc-functionalised compounds. The current observations provide a lead to the design of new sulfur-based low molecular weight gelators for various potential applications.
authors.affiliation: Bioorganic Chemistry Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai-, 600020, India), Phone: +91 44 24437224, Fax: +91 44 24911589.|Academy of Scientific and Innovative Research (AcSIR), Council of Scientific and Industrial Research (CSIR), New Delhi, 110 001, India.
authors.forename: Samala Murali Mohan
authors.initials: SM
authors.lastname: Reddy
authors.affiliation: Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai-, 600036, India.
authors.forename: Pramod
authors.initials: P
authors.lastname: Dorishetty
authors.affiliation: Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai-, 600036, India.
authors.forename: Abhijit P
authors.initials: AP
authors.lastname: Deshpande
authors.affiliation: Bioorganic Chemistry Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai-, 600020, India), Phone: +91 44 24437224, Fax: +91 44 24911589. ganesh@clri.res.in.|Academy of Scientific and Innovative Research (AcSIR), Council of Scientific and Industrial Research (CSIR), New Delhi, 110 001, India. ganesh@clri.res.in.
authors.forename: Ganesh
authors.identifier: http://orcid.org/0000-0003-1096-4201
authors.initials: G
authors.lastname: Shanmugam
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002942:Circular Dichroism; D005449:Fluorenes / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008715:Methionine / Q000737:chemistry; D018625:Microscopy, Atomic Force; D046529:Microscopy, Electron, Transmission; D013455:Sulfur / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D000596:Amino Acids; D005449:Fluorenes; D020100:Hydrogels; C016456:N(alpha)-fluorenylmethyloxycarbonylamino acids; D014867:Water; D013455:Sulfur; D008715:Methionine
keywords: amino acids; gels; mechanical properties; self-assembly; sulfur