Magnetically Aligned Supramolecular Hydrogels

Abstract

The magnetic-field-induced alignment of the fibrillar structures present in an aqueous solution of a dipeptide gelator, and the subsequent retention of this alignment upon transformation to a hydrogel upon the addition of CaCl2 or upon a reduction in solution pH is reported. Utilising the switchable nature of the magnetic field coupled with the slow diffusion of CaCl2, it is possible to precisely control the extent of anisotropy across a hydrogel, something that is generally very difficult to do using alternative methods. The approach is readily extended to other compounds that form viscous solutions at high pH. It is expected that this work will greatly expand the utility of such low-molecular-weight gelators (LMWG) in areas where alignment is key.

Using solution state NMR spectroscopy to probe NMR invisible gelators

“…14 We showed that the magnitude of the line splitting observed, the residual quadrupolar coupling (RQC), depends not only on the relative alignment of the gelator aggregates but also on the nature of the surface interaction between the aggregates and the deuterated solutes. This anisotropy manifests as splittings of the NMR resonances of deuterated probe molecules present in solution (D 2 O and/or water miscible deuterated organic solvents) that transiently interact with the gelator aggregates.…”

“…Such regions are apparent in the final gel (Fig. The isotropic peak first becomes apparent on the 14 NH 4 + resonance after approximately 700 minutes and on the IPA resonance after 500 minutes (ESI, † Section 6). The isotropic component of the IPA resonance in this gel is ca.…”

Supramolecular biofunctional materials

“…Due to the dynamic nature of noncovalent interactions, the biofunctional materials based on supramolecular hydrogels exhibit stimuli responsiveness to various physical, chemical, or biological stimuli, like temperature,[58] ultrasound,[59, 60] light,[61] magnetic field,[62] pH,[63–65] ionic strength,[66, 67] redox agent,[68] ligand-receptor interactions, [69–72], enzymes (Figure 2A),[25, 73–80] and many other reaction agents and catalysts. [81–83] Utilizing this property, one is able to not only control the self-assembly/disassembly process as in situ response to external stimuli for desired biomedical applications, but also to generate chemical, physical, and biological sensors for the detection of various external stimuli.…”

“…[88] Although light is a physical stimulus, chemical reactions and structural changes, in most cases, also occur to initiate the light-triggered sol-gel or gel-sol transition, and the resulting conformation of the molecules typically favor more compact stacking when a hydrogel forms. An interesting but much less used physical trigger is magnetic field,[62, 89, 90] which is contactless, homogeneously effective over the whole sample and can produce structured materials with different sizes. However, this technique heavily relies on the (dia)magnetic susceptibility of the sample and the strength of the applied magnetic field.…”

“…However, this technique heavily relies on the (dia)magnetic susceptibility of the sample and the strength of the applied magnetic field. [62] The adjustment of pH serves as the most common and convenient chemical process for preparing supramolecular hydrogels. The protonation or deprotonation mediated by changing pH directly influences not only the intensity and strength of hydrogen bonding between hydrogelators, but also the conformations of the hydrogelators to promote the rearrangement of the molecular stacking.…”