Peptide-Based Gel in Environmental Remediation: Removal of Toxic Organic Dyes and Hazardous Pb2+ and Cd2+ Ions from Wastewater and Oil Spill Recovery.

A dipeptide-based synthetic amphiphile bearing a myristyl chain has been found to form hydrogels in the pH range 6.9-8.5 and organogels in various organic solvents including petroleum ether, diesel, kerosene, and petrol. These organogels and hydrogels have been thoroughly studied and characterized by different techniques including high-resolution transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and rheology. It has been found that the xerogel obtained from the peptide gelator can trap various toxic organic dyes from wastewater efficiently. Moreover, the hydrogel has been used to remove toxic heavy metal ions Pb2+ and Cd2+ from wastewater. Dye adsorption kinetics has been studied, and it has been fitted by using the Freundlich isotherm equation. Interestingly, the gelator amphiphilic peptide gels fuel oil, kerosene, diesel, and petrol in a biphasic mixture of salt water and oil within a few seconds. This indicates that these gels not only may find application in oil spill recovery but also can be used to remove toxic organic dyes and hazardous toxic metal ions from wastewater. Moreover, the gelator can be recycled several times without significant loss of activity, suggesting the sustainability of this new gelator. This holds future promise for environmental remediation by using peptide-based gelators.

Self-Assembling Peptide-Based Hydrogel: Regulation of Mechanical Stiffness and Thermal Stability and 3D Cell Culture of Fibroblasts.

A histidine-containing peptide-based amphiphile (P1) forms a transparent hydrogel within a pH range of 5.5 to 8.5 in phosphate buffer solution. Interestingly, thermal stability and mechanical stiffness are modulated by incorporating different types of dicarboxylic acids into the hydrogels. Inclusion of succinic acid with the molar ratio 2:1 (peptide:dicarboxylic acid) yields improved properties compared to the other tested dicarboxylic acids such as oxalic, glutaric and octanedioic acids. Transmission electron microscopic (TEM) images show the assembly of nanospheres is responsible for the hydrogel obtained from the assembly of native peptide. However, a morphological transformation takes place from nanosphere to nanofibers, when the peptide gels with succinic acid. XRD and FT-IR studies reveal interactions between peptide amphiphiles and the acids are responsible for the formation of a two-component hydrogel. Gel stiffness is enhanced considerably upon the addition of succinic acid to P1 with a 1:2 molar ratio. The two-component gel consisting of peptide and succinic acid has been successfully used for three-dimensional cell culture using mouse fibroblast cell line (NIH-3T3). This indicates future promise for the application of such peptide-based gels as tunable biomaterials in cell culture and regenerative medicine.

Amino-Acid-Based Metallo-Hydrogel That Acts Like an Esterase.

A histidine-based amphiphile containing a C14 fatty acyl chain, N- histidyl N'-myristry ethyl amine (AM1, 14.7 mM) forms hydrogels in the presence of Fe3+ (within the range 1.47 to 4.41 mM) and Hg2+ (within the range 3.67 to 11.02 mM) ions in aqueous dispersions at pH 6.6 (27 °C). The imidazole ring of the histidine residue plays a vital role to interact with these metal-ions. The thermal and mechanical stability of these metallo-hydrogels can be tuned by changing the proportion of amphiphile to metal ion ratio (1:0.1 to 1:0.3 for Fe3+-containing gel and 1:0.25 to 1:0.75 for Hg2+-containing gel). The metallo-hydrogels were characterized by different spectroscopic and microscopic techniques, low- and wide-angle powder X-ray diffraction, and small-angle X-ray scattering studies. FT-IR and NMR spectroscopic studies indicate the participation of the imidazole ring in metal-ion binding. Low- and wide-angle powder X-ray diffraction and small-angle X-ray scattering data are in favor of a layered structure of the supramolecular assembly of the AM1 in the presence of metal-ions. Both, the amphiphiles and the metal ion induced hydrogels reveal catalytic activity of p-nitrophenyl esters hydrolysis for the acetyl, n-butyl and n-octyl esters . Ferric ion containing metallo-hydrogel exhibits higher catalytic activity than the corresponding AM1 aggregate in the absence of metal ions.

Copper-catalyzed C-H functionalization of pyridines and isoquinolines with vinyl azides: synthesis of imidazo heterocycles.

Copper(I) iodide-catalyzed oxidative C(sp(2))-H functionalization of pyridines and isoquinolines for the synthesis of imidazo[1,2-a]pyridines and 2-phenylimidazo[2,1-a]isoquinolines with vinyl azides under mild aerobic conditions is reported. Good selectivity for 3-substituted pyridines and single isomer formation with isoquinolines were observed.