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Supramolecular hydrogels have a wide range of applications in the biomedical field, acting as scaffolds for cell culture, matrices for tissue engineering and vehicles for drug delivery. L-Phenylalanine (Phe) is a natural amino acid that plays a significant role in several physiological and pathophysiological processes (phenylketonuria and assembly of fibrils linked to tissue damage). Since Myerson et al. [ Chem. Eng. Commun. , 2002, 189 (8), 1079-1090] reported that Phe forms a fibrous network in vitro , Phe's self-assembly processes in water have been thoroughly investigated. We have reported structural control over gelation by introduction of a halogen atom in the aromatic ring of Phe, driving changes in the packing motifs, and therefore, dictating gelation functionality. The additional level of control gained over supramolecular gelation via the preparation of multi-component gel systems offers significant advantages in tuning functional properties of such materials. Gaining molecular-level information on the distribution of gelators between the inherent structural and dynamic heterogeneities of these materials remains a considerable challenge. Using multicomponent gels based on Phe and amino-L-phenylalanine (NH 2 -Phe), we will explore the patterns of ordered/disordered domains in the gel fibres and will attempt to come up with general trends of interactions in the gel fibres and at the fibre/solution interfaces. Phe and NH 2 -Phe were found to self-assemble in water into crystalline hydrogels. The determined faster dynamics of exchange between the gel and solution states of NH 2 -Phe in comparison with Phe were correlated with weaker intermolecular interactions, highlighting the role of head groups in dictating the strength of intermolecular interactions. In the mixed Phe/NH 2 -Phe systems, at a low concentration of NH 2 -Phe, disruption of the network was promoted by interference of the aliphatics of NH 2 -Phe with the electrostatic interactions between Phe molecules. At high concentrations of NH 2 -Phe, multiple-gelator hydrogels were formed with crystal habits different from those of the pure gel fibres. NMR crystallography approaches combining the strengths of solid- and solution-state NMR proved particularly suitable to obtain structural and dynamic insights into the "ordered" fibres, solution phase and fibre/solution interfaces in these gels. These findings are supported by a plethora of experimental (diffraction, rheology, microscopy and thermal analysis) and computational methods.

The possibility of using differential pre-heating prior to supramolecular gelation to control the balance between hydrogen-bonding and aromatic stacking interactions in supramolecular gels and obtain consequent systematic regulation of structure and properties is demonstrated. Using a model aromatic peptide amphiphile, Fmoc-tyrosyl-leucine (Fmoc-YL) and a combination of fluorescence, infrared, circular dichroism and NMR spectroscopy, it is shown that the balance of these interactions can be adjusted by temporary exposure to elevated temperatures in the range 313-365 K, followed by supramolecular locking in the gel state by cooling to room temperature. Distinct regimes can be identified regarding the balance between H-bonding and aromatic stacking interactions, with a transition point at 333 K. Consequently, gels can be obtained with customizable properties, including supramolecular chirality and gel stiffness. The differential supramolecular structures also result in changes in proteolytic stability, highlighting the possibility of obtaining a range of supramolecular architectures from a single molecular structure by simply controlling the pre-assembly temperature., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Stiff, elastic, viscous shear thinning aqueous gels are formed upon dispersion of low weight percent concentrations of cationically modified cellulose nanofibrils (CCNF) in water. CCNF hydrogels produced from cellulose modified with glycidyltrimethylammonium chloride, with degree of substitution (DS) in the range 10.6(3)-23.0(9)%, were characterised using NMR spectroscopy, rheology and small angle neutron scattering (SANS) to probe the fundamental form and dimensions of the CCNF and to reveal interfibrillar interactions leading to gelation. As DS increased CCNF became more rigid as evidenced by longer Kuhn lengths, 18-30 nm, derived from fitting of SANS data to an elliptical cross-section, cylinder model. Furthermore, apparent changes in CCNF cross-section dimensions suggested an "unravelling" of initially twisted fibrils into more flattened ribbon-like forms. Increases in elastic modulus (7.9-62.5 Pa) were detected with increased DS and 1 H solution-state NMR T 1 relaxation times of the introduced surface -N + (CH 3 ) 3 groups were found to be longer in hydrogels with lower DS, reflecting the greater flexibility of the low DS CCNF. This is the first time that such correlation between DS and fibrillar form and stiffness has been reported for these potentially useful rheology modifiers derived from renewable cellulose.

Phenylalanine is an important amino acid both biologically, essential to human health, and industrially, as a building block of artificial sweeteners. Our interest in this particular amino acid and its derivatives lies with its ability to form gels in a number of solvents. We present here the studies of the influence of halogen addition to the aromatic ring on the gelation properties and we analyse the crystal structures of a number of these materials to elucidate the trends in their behaviour based on the halogen addition to the aromatic group and the interactions that result.

Supramolecular hydrogels are composed of self-assembled solid networks that restrict the flow of water. l-Phenylalanine is the smallest molecule reported to date to form gel networks in water, and it is of particular interest due to its crystalline gel state. Single and multi-component hydrogels of l-phenylalanine are used herein as model materials to develop an NMR-based analytical approach to gain insight into the mechanisms of supramolecular gelation. Structure and composition of the gel fibres were probed using PXRD, solid-state NMR experiments and microscopic techniques. Solution-state NMR studies probed the properties of free gelator molecules in an equilibrium with bound molecules. The dynamics of exchange at the gel/solution interfaces was investigated further using high-resolution magic angle spinning (HR-MAS) and saturation transfer difference (STD) NMR experiments. This approach allowed the identification of which additive molecules contributed in modifying the material properties., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Correction for 'Substituent interference on supramolecular assembly in urea gelators: synthesis, structure prediction and NMR' by Francesca Piana et al., Soft Matter, 2016, 12, 4034-4043.

Eighteen N-aryl-N'-alkyl urea gelators were synthesised in order to understand the effect of head substituents on gelation performance. Minimum gelation concentration values obtained from gel formation studies were used to rank the compounds and revealed the remarkable performance of 4-methoxyphenyl urea gelator 15 in comparison to 4-nitrophenyl analogue 14, which could not be simply ascribed to substituent effects on the hydrogen bonding capabilities of the urea protons. Crystal structure prediction calculations indicated alternative low energy hydrogen bonding arrangements between the nitro group and urea protons in gelator 14, which were supported experimentally by NMR spectroscopy. As a consequence, it was possible to relate the observed differences to interference of the head substituents with the urea tape motif, disrupting the order of supramolecular packing. The combination of unbiased structure prediction calculations with NMR is proposed as a powerful approach to investigate the supramolecular arrangement in gel fibres and help understand the relationships between molecular structure and gel formation.