Fine‐Tuning Supramolecular Assemblies by Controlling Micellar Aggregates

Abstract

Supramolecular assembly can be used to fabricate complex functional materials by organizing simple building blocks. However, it is difficult to control the hierarchical assembly across multiple length scales. The correlation of a supramolecular gel network and a pre‐gelling aggregate will help to understand how a molecular‐level assembly is translated into a higher order. Here, a functional dipeptide 2NapFF is used that can assemble in different micellar structures at high pH by varying the counterion. Replacing the counterions with a divalent calcium salt results in a cross‐linked gel network, or an interesting analog “gel noodles.” The physical properties of the gel noodles can be varied by choosing specific micellar assemblies as the pre‐gel. The mechanical rigidity of the gel networks is compared by nanoindentation and tensile testing, and the pattern to the structures of the micelles observed by small‐angle X‐ray scattering is correlated. The supramolecular assembly can be fine‐tuned by using different micelles as the pre‐gel without affecting the inherent gel‐state properties.

Metal Cross-Linked Supramolecular Gel Noodles: Structural Insights and Antibacterial Assessment

“…Achieving such controlled alignment is critical for enhancing the functionality of the constituent groups in supramolecular systems. Although numerous attempts have been made to assemble highly aligned supramolecular systems, the success is mostly limited to producing short-length fibers or ribbons or films. ,,,, In contrast, our gel noodles can be extended into significantly longer threads with very high persistence length, allowing for postsynthetic manipulations like folding or weaving …”

“…15,17,18,29,43 In contrast, our gel noodles can be extended into significantly longer threads with very high persistence length, allowing for postsynthetic manipulations like folding or weaving. 39 The gel noodles were prepared by extruding 2NapFF solutions (20 mg/mL, pH 10.5 adjusted with NaOH) from a syringe pump into a rotating 0.5 M solution of various metal chlorides (Figure S4). A high metal ion concentration was maintained to ensure saturation and to test the relative efficiency of each metal cation in stabilizing the noodles.…”

“…Considering prior examinations of 2NapFF-calcium bulk gels and noodles, our initial assessment involved gels derived from 2NapFF in combination with other Group 2 metals, magnesium and strontium chloride. We fixed the 2NapFF concentration at 20 mg/mL, and the pH was adjusted to 10.5 (±0.05 in all cases) using NaOH, based on our previous report that these conditions were suitable for stable bulk gel and noodle formation . The gel formation strongly depends on the molar ratio of the gelator to the cross-linker, so we standardized a 1:1 molar ratio of 2NapFF to the metal chlorides for bulk gel analysis.…”

Methods of changing low molecular weight gel properties through gelation kinetics

“…Similarly, the Adams groups have reported the impact of different counterions on the assembly of 2NapFF. 62 Both metal (Li + , Na + , K + , Rb + , and Cs + ) and non-coordinating organic (tetra- n -butylammonium (TBA) and benzyltrimethylammonium (BTMA)) ions were used to access different micellar structures at high pH. Differences in the micellar aggregation were evident from viscosity measurements.…”

“…3,58 Another advantage is that due to their hydrophobicity, the pre-gelled state may contain micellar aggregates (such as spherical, cylindrical, and worm-like micelles) above the critical micelle concentration and Krafft temperature. 59–62 How these molecules pack is dependent on their size and shape, but also on the non-covalent interactions present. 60,61 Owing to their weak nature, these interactions can be tuned by parameters such as temperature, ionic strength, or pH, thus impacting the bulk properties of the pre-gelled solution.…”