Dramatic Specific‐Ion Effect in Supramolecular Hydrogels

Abstract

We report on a pronounced specific-ion effect on the intermolecular and chiral organization, supramolecular structure formation, and resulting materials properties for a series of low molecular weight peptide-based hydrogelators, observed in the presence of simple inorganic salts. This effect was demonstrated using aromatic short peptide amphiphiles, based on fluorenylmethoxycarbonyl (Fmoc). Gel-phase materials were formed due to molecular self-assembly, driven by a combination of hydrogen bonding and π-stacking interactions. Pronounced morphological changes were observed by atomic force microscopy (AFM) for Fmoc-YL peptide, ranging from dense fibrous networks to spherical aggregates, depending on the type of anions present. The gels formed had variable mechanical properties, with G' values between 0.8 kPa and 2.4 kPa as determined by rheometry. Spectroscopic analysis provided insights into the differential mode of self-assembly, which was found to be dictated by the hydrophobic interactions of the fluorenyl component, with comparable H-bonding patterns observed in each case. The efficiency of the anions in promoting the hydrophobic interactions and thereby self-assembly was found to be consistent with the Hofmeister anion sequence. Similar effects were observed with other hydrophobic peptides, Fmoc-VL and Fmoc-LL. The effect was found to be less pronounced for a less hydrophobic peptide, Fmoc-AA. To get more insights into the molecular mechanism, the effect of anions on sol-gel equilibrium was investigated, which indicates the observed changes result from the specific-ion effects on gels structure, rather than on the sol-gel equilibrium. Thus, we demonstrate that, by simply changing the ionic environment, structurally diverse materials can be accessed providing an important design consideration in nanofabrication via molecular self-assembly.

Self-Assembled Peptide Nanofibers Encapsulated with Superfine Silver Nanoparticles via Ag+ Coordination

“…9 According to previous reports, in most cases, no matter whether the fluorenyl group was in monomers or within aggregates, there was always 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 the two states. 6,9,10,27 However, an exception occurred in the present system. The characteristic signal with the maximum emission at 320 nm ( Figure S6a) was generated by monomeric fluorenyl.…”

“…The characteristic signal with the maximum emission at 320 nm ( Figure S6a) was generated by monomeric fluorenyl. 6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 the three peaks shift to 1700 cm −1 , 1636 cm −1 and 3286 cm −1 , respectively, indicating the formation of carboxylate and the hydrogen bonding, which may be formed between the -C=O and -N-H groups of two Fmoc-GCE molecules. 30 In addition, the peaks at 1412 cm −1 and 1532 cm −1 of Fmoc-GCE respectively assigned to symmetric and antisymmetric stretching of carboxyl shift to 1368 cm −1 and 1542 cm −1 , respectively, in Fmoc-GCE/Ag + complex, denoting the presence of coordination between the carboxylate groups and Ag + ions.…”

“…With tunable numbers and sequences of amino acids, peptides are promising building blocks in molecular self-assembly which can be modulated by external conditions including temperature, 5 ionic strength, 6 enzymes, 7 etc. The oligopeptides possessing fragments of conjugated aromatic components can easily self-organize by taking advantage of -stacking.…”

Salt-Induced Control of Supramolecular Order in Biocatalytic Hydrogelation

“…Although the exact mechanism behind this effect is not fully understood, it can be rationalized by considering electrostatic screening of the charges, ion binding, and its implication to hydrophobic interactions, as discussed in our recent work. 52 The present study demonstrates that highly complex self-assembly behavior occurs when combining the effects of salts, protein templating, and catalysis. Insight into these behaviors is useful in controlling and directing peptide self-assembly toward desired nanomaterials.…”

Preparation and chiral recognition of thermosensitive poly(N-isopropylacrylamide) microgels containing modified L-phenylalanine groups

“…The chiral recognizable capacity of such polymers may originate from the chiral structures and/or ordered secondary structures of polymers. Many natural compounds or macromolecules have been adopted to form chiral recognizable sites, such as amino acids [10] , cholesterols [11] , peptides [12,13] , sugars [14][15][16] , and celluloses [17] derivatives. Among them, L-amino acids and their derivatives are widely used because of their diversified structures, low costs, comprehensive applicability and feasibility [18,19] .…”