Time-dependent gel to gel transformation of a peptide based supramolecular gelator

Abstract

A dipeptide with a long fatty acid chain at its N-terminus gives hydrogels in phosphate buffer in the pH range 7.0-8.5. The hydrogel with a gelator concentration of 0.45% (w/v) at pH 7.46 (physiological pH) provides a very good platform to study dynamic changes within a supramolecular framework as it exhibits remarkable change in its appearance with time. Interestingly, the first formed transparent hydrogel gradually transforms into a turbid gel within 2 days. These two forms of the hydrogel have been thoroughly investigated by using small angle X-ray scattering (SAXS), powder X-ray diffraction (PXRD), field emission scanning electron microscopic (FE-SEM) and high-resolution transmission electron microscopic (HR-TEM) imaging, FT-IR and rheometric analyses. The SAXS and low angle PXRD studies substantiate different packing arrangements for the gelator molecules for these two different gel states (the freshly prepared and the aged hydrogel). Moreover, rheological studies of these two gels reveal that the aged gel is stiffer than the freshly prepared gel.

A Ferrocene–Tryptophan Conjugate: The Role of the Indolic Nitrogen in Supramolecular Assembly

“…For molecule B, the dihedral angles include theta=2.3(3)°, omega=76.1(15)°, beta(O1B)=1.8(14)°, and beta(O5B)=6.4(13)°. Here, our peptide is completely ordered, causing the formation of a nanofibrillar network structure owing to the intra‐ and intermolecular hydrogen bonding . This supports the role intermolecular hydrogen bonding in the assembly of the compound into a supramolecular network structure.…”

“…This is observed in the structures showni nF igure 2a,band d. The second type of intermolecularb ondingi ncludes one of the amide nitrogen atoms, in the middle of the two Trps ide chains, and the carbonyl group nearest the ferrocenem oiety 14)8,a nd beta(O5B) = 6.4(13)8.H ere, our peptide is completely ordered, causing the formation of an anofibrillar network structure owing to the intra-and intermolecular hydrogen bonding. [14,33,34] This supports the role intermolecular hydrogen bondingi nt he assembly of the compound into a supramolecular network structure. An umber of structural parametersi ncluding hydrogen bonding, bondd istances,a nd torsion angles are presented in Tables S1 and S2 in the Supporting Information.…”

“…For compound 1 , an N−H stretching band centered at 3289 cm −1 was observed. This suggests that the NH group is involved in hydrogen‐bonding interactions in the assembled state . The appearance of a C=O stretching band of the amide centered at 1656 cm −1 also indicates that the hydrogen‐bonded structure is present in the assembled state.…”

“…This suggeststhat the NH group is involved in hydrogen-bonding interactionsi nt he assembled state. [33] The appearance of a C=Os tretching band of the amide centered at 1656 cm À1 also indicates that the hydrogen-bonded structure is presenti nt he assembled state. Another peak at 1739 cm À1 is characteristico f the C=Os tretcho ft he ester group.…”

Controlling self-assembly of diphenylalanine peptides at high pH using heterocyclic capping groups

“…Whereas microscopy techniques such as transmission electron microscopy (TEM) and atomic force microscopy (AFM) are liable to suffer from the presence of sample preparation artefacts, small angle scattering is conducted on the native hydrogel, providing an accurate statistical three dimensional perspective of the actual hydrogel structure. SANS measurements have been extensively used to probe the native structure of peptide-based hydrogels, most often on hydrogel samples which already exhibit a well-defined network151617181920212223242526. Less well studied is small angle scattering on transitions within gelators; however there are examples of SANS being used to examine the transition of a hexapeptide from ribbons to fibers27 and using SANS to look at the evolution of a pyromellitamide organogel over several days28.…”