Advances and Novel Perspectives on Colloids, Hydrogels, and Aerogels Based on Coordination Bonds with Biological Interest Ligands

Abstract

This perspective article shows new advances in the synthesis of colloids, gels, and aerogels generated by combining metal ions and ligands of biological interest, such as nucleobases, nucleotides, peptides, or amino acids, among other derivatives. The characteristic dynamism of coordination bonds between metal center and biocompatible-type ligands, together with molecular recognition capability of these ligands, are crucial to form colloids and gels. These supramolecular structures are generated by forming weak van der Waals bonds such as hydrogen bonds or π–π stacking between the aromatic rings. Most gels are made up of nano-sized fibrillar networks, although their morphologies can be tuned depending on the synthetic conditions. These new materials respond to different stimuli such as pH, stirring, pressure, temperature, the presence of solvents, among others. For these reasons, they can trap and release molecules or metal ions in a controlled way allowing their application in drug delivery as antimicrobial and self-healable materials or sensors. In addition, the correct selection of the metal ion enables to build catalytic or luminescent metal–organic gels. Even recently, the use of these colloids as 3D-dimensional printable inks has been published. The elimination of the solvent trapped in the gels allows the transformation of these into metal–organic aerogels (MOAs) and metal–organic xerogels (MOXs), increasing the number of possible applications by generating new porous materials and composites useful in adsorption, conversion, and energy storage. The examples shown in this work allow us to visualize the current interest in this new type of material and their perspectives in the short-medium term. Furthermore, these investigations show that there is still a lot of work to be done, opening the door to new and interesting applications.

Metal–organic gels and their derived materials for electrochemical applications

“…[54][55][56] Besides carboxylates, several organic ligands are used to assemble MOGs, including pyridines [59][60][61][62][63] and ligands of biological interest. 45 MOGs are built from various metal ions, including transition metal ions, 64 lanthanide ions, [65][66][67][68] and main group metal ions. [69][70][71] The diverse building blocks (metal ions and organic linkers) allow the adjustable chemical structures of MOGs.…”

“…Although there are some recent review articles in the eld of MOGs, 16,[42][43][44][45][46] a review that comprehensively focuses on the electrochemical applications of MOGs is not available. In this review, we survey the up-to-date research development of MOGs and their applications in the electrochemical elds to promote future breakthroughs (Fig.…”

FF Activates Nucleation for Aggregation in Aqueous Medium: A Key Insight of Amyloid Plaque Formation

“…[13][14][15] Peptide-based hydrogels are biocompatible soft materials formed by water-swollen networks, and have many applications, from the formulation of membranes to the optimization of tools for delivery of drugs and/or diagnostic agents. [10][11][12]16] However, its structural-morphological and hence functional properties are deeply affected by the amino acid composition of its primary sequence. [16,17] It has already been reported that Fmoc-diphenylalanine (Fmoc-FF) can form hydrogels with selfassembling properties under physiological condition.…”

Structuration and deformation of colloidal hydrogels

“…Moreover, they should have a high resistance to cracking. The mechanical behavior of these soft materials is currently an important research area and several groups [6][7][8][9][10] have proposed strategies to improve their mechanical properties; for example, reducing heterogeneities in the network in order to reduce nucleating centers for cracks or enhancing the energy dissipation during crack propagation 11,12 . Most hydrogels are chemical hydrogels as they are formed through covalent bonding which implies sophisticated chemistry.…”