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A series of β-amino acid containing tripeptides has been designed and synthesized in order to develop oligopeptide-based, thermoreversible, pH-sensitive, and proteolytically stable hydrogels. The Fmoc [N-(fluorenyl-9-methoxycarbonyl)]-protected tripeptides were found to produce hydrogels in both pH 7 and 2 buffers at a very low concentration (<0.2% w/v). It has been shown that the Fmoc group plays an important role in the gelation process. Also a dependence of gelation ability on hydrophobicity of the side chain of the Fmoc-protected α-amino acid was observed. The effect of the addition of inorganic salts on the gelation process was investigated as well. Spectroscopic studies indicated formation of J-aggregates through π-π stacking interactions between Fmoc groups in solution as well as in the gel state. In the gel phase, these self-assembling tripeptides form long interconnected nanofibrils leading to the formation of 3-dimensional network structure. The hydrogels were characterized by various techniques, including field emission electron microscopy, transmission electron microscopy, atomic force microscopy, rheology, Fourier transform IR, circular dichroism (CD), and wide-angle X-ray diffraction (WAXD) spectroscopy. The CD studies and WAXD analyses show an antiparallel β-sheet structure in the gel state. l-Phenylalanine and l-tyrosine containing tripeptides formed helical aggregates with handedness opposite to those containing l-valine and l-leucine residues. The mechanical stability of the hydrogels was found to depend on the hydrophobicity of the side chain of the tripeptide as well as on the pH of the solution. Also, the tripeptides exhibit in vitro proteolytic stability against proteinase K enzyme. [ABSTRACT FROM AUTHOR]

In our recent reports, we have shown that when a poly(ethylene glycol) (PEG) chain is covalently linked to any ionic group, the resultant molecule behaves like an amphiphile. Depending upon the nature of ionic head groups, they self-assemble to form micelles or vesicles, in which the PEG chain constitutes the micellar core or vesicle bilayer. In this study, we intend to examine what happens when both hydrocarbon (HC) and PEG chains are attached to a carboxylate head group. Therefore, we have synthesized two novel amphiphiles in which a PEG and a HC chain is covalently linked to l-cysteine. The surface activities and the solution behavior of the sodium salts of these amphiphiles were investigated at neutral pH. The amphiphiles self-organize to form large unilamellar vesicles in dilute solutions, which transformed into small micelles at higher concentrations. The HC chains of the molecules have been shown to constitute the bilayer membrane of the vesicles and core of micelles. In acidic pH, the amphiphiles were found to form large disklike micelles. The thermodynamic parameters of self-assembly formation were also measured by isothermal titration calorimetry. The vesicle and micelle formation was found to be spontaneous and thermodynamically favorable. The thermal stability of the micelles at neutral and acidic pH was studied. The addition of cholesterol was observed to increase the physical stability of vesicles. [ABSTRACT FROM AUTHOR]

Two new l-cysteine-derivedzwitterionic amphiphiles withpoly(ethylene glycol) methyl ether (mPEG) tail of different chainlengths were synthesized and their surface activity and self-assemblyproperties were investigated. In aqueous phosphate buffered solutionof pH 7.0, the amphiphiles were observed to form stable unilamellarvesicles, the bilayer membrane of which is constituted by the mPEGchains. The vesicle phase was characterized by a number of methodsincluding fluorescence spectroscopy, dynamic light scattering, andtransmission electron microscopy. The thermodynamics of self-assemblywas also studied by isothermal titration calorimetry through measurementsof the standard Gibbs free energy change (ΔG°m), standard enthalpy change (ΔH°m) and standard entropy change (ΔS°m) of micellization. The self-assembly process wasfound to be entropy-driven, which implies that the mPEG chain behaveslike a hydrocarbon tail of conventional surfactants. The effects ofpH, temperature, salt, and aging time on the bilayer stability werealso investigated. Encapsulation and pH-triggered release of modelhydrophobic and hydrophilic drugs is demonstrated. [ABSTRACT FROM AUTHOR]

A series of l-cysteine-derived double hydrocarbonchainamphiphilic gelators l-(3-alkyl-carbamoylsulfanyl)-2-(3-alkylurido)propionicacid with different hydrocarbon chain lengths (C6–C16) wasdesigned and synthesized. These gelators efficiently gelate only aromaticsolvents. The gelation ability increased with the increase of chainlength up to C14, but then it dropped with further increase of chainlength. The C12 and C14 derivatives also gelled ethanol/water mixtures.The gels were characterized by a number of methods, including FT-IR,NMR, and XRD spectroscopy, electron microscopy, and rheology. Theamphiphiles were observed to form either flat lamellar or ribbonlikeaggregates in aromatic solvents as well as in ethanol/water mixtures.The gelation in all the solvents employed was observed to be thermoreversible.The gel-to-sol transition temperature as well as mechanical strengthof the organogels were observed to increase with the hydrocarbon chainlength. Both types of gels of C8–C16 amphiphiles have gel-to-soltransition temperatures above the physiological temperature (310 K).FT-IR and variable temperature 1H NMR measurements suggestedthat van der Waals interactions have major contribution in the gelationprocess. The gel-to-sol transition temperature and mechanical strengthof the organogels in ethanol/water mixtures was observed to be higherthan those of benzene organogel. [ABSTRACT FROM AUTHOR]