Dicyclohexylurea derivatives of amino acids as dye absorbent organogels and anion sensors.

Dicyclohexyl urea (DCU) derivatives of amino acids Fmoc-Phe-DCU (M1), Fmoc-Phg-DCU (M2) and Fmoc-Gaba-DCU (M3) have been shown to form phase selective, thermoreversible and mechanically robust gels in a large range of organic solvents. This is the first report of low molecular weight gelators (LMWG) from DCU derivatives of amino acids. The self-assembly mechanism of the organogels has been probed using concentration dependent 1H NMR, DMSO titration 1H NMR, fluorescence, FTIR, PXRD and FESEM techniques. Self-assembly leading to gelation process is mainly driven by hydrophobicity and π-π stacking interactions in between Fmoc groups. Interestingly, the gels can absorb several kinds of organic dyes efficiently and can be reused for dye absorption for multiple cycles. Additionally, M1-M3 act as sensors for anions like fluoride, acetate and hydroxide, for which they have specific fluorescence response. Gel formation by M1-M3 is completely arrested in the presence of fluoride. The possible binding mode of fluoride has been delineated using DFT studies. Calculations suggest, involvement of urea NH in a six membered intramolecular hydrogen bond, rendering it unavailable for fluoride binding. Backbone -NH of the amino acids of M1-M3 is responsible for fluoride binding. The reported small, economically viable, synthetically facile molecules not only enrich the repertoire of LMWG molecules, but can have multifaceted applications.

Co-assembly of charge complementary peptides and their applications as organic dye/heavy metal ion (Pb2+, Hg2+) absorbents and arsenic(iii/v) detectors.

Learning from nature, molecular self-assembly has been used extensively to generate interesting materials using a bottom up approach. The enthusiasm in this field of research stems from the unique properties of these materials and their diverse applications. The field has not been limited to studying assembly of similar types of molecules but extended to multi component systems via the co-assembly phenomenon. We have designed two charge complementary peptides to study their co-assembly in mechanistic detail in the present work. The cooperative self-assembly is mainly driven by electrostatic interaction that is aided by aromatic interactions, hydrogen bonding interactions and hydrophobic interactions. The hydrogels obtained have been employed in waste water remediation. Both the self-assembled and co-assembled hydrogels are capable of removal of different kinds of organic dyes (cationic, anionic and neutral) and toxic metal ions (Ni2+, Co2+, Pb2+ and Hg2+) individually and as a mixture from water with high efficiency. Additionally, the peptides developed in this study can act as ion sensors and detect arsenic in its most toxic (III/V) oxidation states. Molecular understanding of the assembly process is of fundamental importance in the rational design of such simple, robust yet economically viable materials with versatile and novel applications.

Peptide Hydrogels as Platforms for Sustained Release of Antimicrobial and Antitumor Drugs and Proteins.

A charged synthetic peptide-based noncytotoxic hydrogelator was employed in encapsulation, storage, and sustainable release of different kinds of drugs, namely, ciprofloxacin (CP), an antibiotic; 5-fluorouracil (5-FU), an anticancer drug and proteins like lysozyme and bovine serum albumin (BSA). Hydrogelation of the peptide and its coassembly with the drug molecules were studied to obtain mechanistic details. All of the different cargos were capable of sustained and efficient release from the delivery platform. The drugs were found to retain their activity post release, while the proteins showed complete retention of their secondary structure. While about 80% CP was released at physiological pH over a period of 3 days, 5-FU was better released (73%) at an acidic pH (5.5) in comparison to the physiological pH (68%). Lysozyme was better released (82%) than BSA (43%) owing to the smaller size of the former and negative charge on the latter. Such biocompatible multicargo-releasing platforms from simple economically viable biomaterials, capable of sustained and tissue-specific release of cargo, are extremely promising in topical delivery of therapeutics.

Self-Assembly Mechanism of a Peptide-Based Drug Delivery Vehicle.

We report the mechanism of the concentration-dependent self-assembly of a tetrapeptide. Peptide Boc-Trp-Leu-Trp-Leu-OMe self-assembles to form discrete nanospheres at a low concentration. Tryptophan side chains point outwards of the nanospheres while leucine side chains point towards the core of the nanospheres. The nanospheres fuse together to become microspheres with the increase in the peptide concentration. At higher concentrations of the peptide, the microspheres start clustering. This is stabilized by the aromatic interactions between the side chains of the tryptophan residues that cover the outer surface of the peptide microspheres. In addition to behaving like the conventional hollow sphere-based drug delivery vehicles which entraps the drug and performs stimuli-responsive release, this prototype can interact, stabilize, and intercalate hydrophobic dye carboxyfluorescein and anti-cancer drug curcumin even on the surface through aromatic interactions. The dye/drug can be released in acidic pH and in the presence of physiologically relevant ions such as potassium.

Extracellular Pectinase from a Novel Bacterium Chryseobacterium indologenes Strain SD and Its Application in Fruit Juice Clarification.

Pectinase is one of the important enzymes of industrial sectors. Presently, most of the pectinases are of plant origin but there are only a few reports on bacterial pectinases. The aim of the present study was to isolate a novel and potential pectinase producing bacterium as well as optimization of its various parameters for maximum enzyme production. A total of forty bacterial isolates were isolated from vegetable dump waste soil using standard plate count methods. Primary screening was done by hydrolysis of pectin. Pectinase activity was determined by measuring the increase in reducing sugar formed by the enzymatic hydrolysis of pectin. Among the bacterial isolates, the isolate K6 exhibited higher pectinase activity in broth medium and was selected for further studies. The selected bacterial isolate K6 was identified as Chryseobacterium indologenes strain SD. The isolate was found to produce maximum pectinase at 37°C with pH 7.5 upon incubation for 72 hours, while cultured in production medium containing citrus pectin and yeast extract as C and N sources, respectively. During enzyme-substrate reaction phase, the enzyme exhibited its best activity at pH of 8.0 and temperature of 40°C using citrus pectin as substrate. The pectinase of the isolate showed potentiality on different types of fruit juice clarification.