“High-Tech”-Anwendungen von supramolekularen nanostrukturierten Gelmaterialien - von der regenerativen Medizin bis hin zu elektronischen Bauelementen

Rationally Developed Organic Salts of Tolfenamic Acid and Its β-Alanine Derivatives for Dual Purposes as an Anti-Inflammatory Topical Gel and Anticancer Agent

A new series of primary ammonium monocarboxylate (PAM) salts of a nonsteroidal anti-inflammatory drug (NSAID), namely, tolfenamic acid (TA), and its β-alanine derivatives were generated. Nearly 67 % of the salts in the series showed gelling abilities with various solvents, including water (biogenic solvent) and methyl salicylate (typically used for topical gel formulations). Gels were characterized by rheology, electron microscopy, and so forth. Structure-property correlations based on single-crystal and powder XRD data of several gelator and nongelator salts revealed intriguing insights. Studies (in vitro) on an aggressive human breast cancer cell line (MDA-MB-231) with the l-tyrosine methyl ester salt of TA (S7) revealed that the hydrogelator salt was more effective at killing cancer cells than the mother drug TA (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay); displayed better anti-inflammatory activity compared with that of TA (prostaglandin E₂ assay); could be internalized within the cancer cells, as revealed by fluorescence microscopy; and inhibited effectively migration of the cancer cells. Thus, the easily accessible ambidextrous gelator salt S7 can be used for two purposes: as an anti-inflammatory topical gel and as an anticancer agent.

T-shaped monopyridazinotetrathiafulvalene-amino acid diad based chiral organogels with aggregation-induced fluorescence emission

A series of pyridazine coupled tetrathiafulvalene T-shaped derivatives with varying amino acid moieties have been synthesized and their gelation properties were studied in various organic solvents. Among these derivatives, two gelators bearing glycine or phenylalanine units display efficient gelation in aromatic and polar solvents. Interestingly, these gelators, except for the gelator containing two tryptophan units, are able to gel DMF via a solution-to-gel transformation when triggered with sonication for less than 20 s or cooled below zero. A number of experiments revealed that these gelator molecules self-assembled into elastically interpenetrating three-dimensional chiral fibrillar aggregates. Importantly, all of the resulting gels result in a dramatic enhancement of the fluorescence intensity compared with their hot solution in spite of the absence of a conventional fluorophore unit and the fluorescence was effectively quenched by the introduction of C60. Moreover, the gelators can be utilized for the removal of different types of toxic molecules, such as aromatic solvents and cationic dyes, from wastewater.

Supramolecular Self-Assembly of Histidine-Capped-Dialkoxy-Anthracene: A Visible-Light-Triggered Platform for Facile siRNA Delivery

Supramolecular self-assembly of histidine-capped-dialkoxy-anthracene (HDA) results in the formation of light-responsive nanostructures. Single-crystal X-ray diffraction analysis of HDA shows two types of hydrogen bonding. The first hydrogen bond is established between the imidazole moieties while the second involves the oxygen atom of one amide group and the hydrogen atom of a second amide group. When protonated in acidic aqueous media, HDA successfully complexes siRNA yielding spherical nanostructures. This biocompatible platform controllably delivers siRNA with high efficacy upon visible-light irradiation leading up to 90 % of gene silencing in live cells.

Supramolecular Gels by Design: Towards the Development of Topical Gels for Self-Delivery Application

Following a supramolecular synthon approach, simple salt formation has been employed to gain access to a series of supramolecular gelators derived from the well-known non-steroidal anti-inflammatory drug (NSAID) ibuprofen. A well-studied gel-inducing supramolecular synthon, namely primary ammonium monocarboxylate (PAM), has been exploited to generate a series of PAM salts by reacting ibuprofen with various primary amines. Remarkably, all of the salts (S1-S7) thus synthesized proved to be good to moderate gelators of various polar and nonpolar solvents. Single-crystal and powder X-ray diffraction studies established the existence of the PAM synthons in the gel network, confirming the efficacy of the supramolecular synthon approach employed. Most importantly, the majority of the salts (S2, S3, S6, and S7) were capable of gelling methyl salicylate (MS), an important ingredient found in many commercial topical gels. In vitro experiments (MTT and PGE2 assays) revealed that all of the salts (except S3 and S7) were biocompatible (up to 0.5 mm concentration), and the most suited one, S6, displayed anti-inflammatory ability as good as that of the parent drug ibuprofen. A topical gel of S6 with methyl salicylate and menthol was found to be suitable for delivering the gelator drug in a self-delivery fashion in treating skin inflammation in mice. Histological studies, including immunohistology, were performed to further probe the role of the gelator drug S6 in treating inflammation. Cell imaging studies supported cellular uptake of the gelator drug in such biomedical application.

Carbon-Nanotube-Mediated Electrochemical Transition in a Redox-Active Supramolecular Hydrogel Derived from Viologen and an l-Alanine-Based Amphiphile

A two-component hydrogelator (16-A)2 -V(2+) , comprising an l-alanine-based amphiphile (16-A) and a redox-active viologen based partner (V(2+) ), is reported. The formation the hydrogel depended, not only on the acid-to-amine stoichiometric ratio, but on the choice of the l-amino acid group and also on the hydrocarbon chain length of the amphiphilic component. The redox responsive property and the electrochemical behavior of this two-component system were further examined by step-wise chemical and electrochemical reduction of the viologen nucleus (V(2+) /V(+) and V(+) /V(0) ). The half-wave reduction potentials (E1/2 ) associated with the viologen ring shifted to more negative values with increasing amine component. This indicates that higher extent of salt formation hinders reduction of the viologen moiety. Interestingly, the incorporation of single-walled carbon nanotubes in the electrochemically irreversible hydrogel (16-A)2 -V(2+) transformed it into a quasi-reversible electrochemical system.

Hydrogelation and Crystallization of Sodium Deoxycholate Controlled by Organic Acids

The gelation and crystallization behavior of a biological surfactant, sodium deoxycholate (NaDC), mixed with l-taric acid (L-TA) in water is described in detail. With the variation of molar ratio of L-TA to NaDC (r = n(L-TA)/n(NaDC)) and total concentration of the mixtures, the transition from sol to gel was observed. SEM images showed that the density of nanofibers gradually increases over the sol-gel transition. The microstructures of the hydrogels are three-dimensional networks of densely packed nanofibers with lengths extending to several micrometers. One week after preparation, regular crystallized nanospheres formed along the length of the nanofibers, and it was typical among the transparent hydrogels induced by organic acids with pKa1 value <3.4. Small-angle X-ray diffraction demonstrated differences in the molecular packing between transparent and turbid gels, indicating a variable hydrogen bond mode between NaDC molecules.

Selective Extraction and In Situ Reduction of Precious Metal Salts from Model Waste To Generate Hybrid Gels with Embedded Electrocatalytic Nanoparticles

A hydrogel based on 1,3:2,4-dibenzylidenesorbitol (DBS), modified with acyl hydrazides which extracts gold/silver salts from model waste is reported, with preferential uptake of precious heavy metals over other common metals. Reduction of gold/silver salts occurs spontaneously in the gel to yield metal nanoparticles located on the gel nanofibers. High nanoparticle loadings can be achieved, endowing the gel with electrochemical activity. These hybrid gels exhibit higher conductances than gels doped with carbon nanotubes, and can be used to modify electrode surfaces, enhancing electrocatalysis. We reason this simple, industrially and environmentally relevant approach to conducting materials is of considerable significance.

pH-Cleavable Nucleoside Lipids: A New Paradigm for Controlling the Stability of Lipid-Based Delivery Systems

Lipid-based delivery systems are an established technology with considerable clinical acceptance and several applications in human. Herein, we report the design, synthesis and evaluation of novel orthoester nucleoside lipids (ONLs) for the modulation of liposome stability. The ONLs contain head groups with 3'-orthoester nucleoside derivatives featuring positive or negative charges. The insertion of the orthoester function in the NL structures allows the formation of pH-sensitive liposomes. ONL-based liposomes can be hydrolyzed to provide nontoxic products, including nucleoside derivatives and hexadecanol. To allow the release to be tunable at different hydrolysis rates, the charge of the polar head structure is modulated, and the head group can be released at a biologically relevant pH. Crucially, when ONLs are mixed with natural phosphocholine lipids (PC), the resultant liposome evolves toward the formation of a hexadecanol/PC lamellar system. Biological evaluation shows that stable nucleic acid lipid particles (SNALPs) formulated with ONLs and siRNAs can effectively enter into tumor cells and release their nucleic acid payload in response to an intracellular acidic environment. This results in a much higher antitumor activity than conventional SNALPs. The ability to use pH-cleavable nucleolipids to control the stability of lipid-based delivery systems represents a promising approach for the intracellular delivery of drug cargos.

An NMR study on the gelation of N,N′-bis(4-N-alkylo-xybenzoyl) hydrazine (4Dn) in two aromatic solvents

The diffusion of toluene can be accelerated at a particular gelator concentration while there is no diffusion acceleration in benzene.

Two-component supramolecular gels derived from amphiphilic shape-persistent cyclo[6]aramides for specific recognition of native arginine

A unique supramolecular two-component gelation system was constructed from amphiphilic shape-persistent cyclo[6]aramides and diethylammonium chloride (or triethylammonium chloride). This system has the ability to discriminate native arginine from 19 other amino acids in a specific fashion. Cyclo[6]aramides show preferential binding for the guanidinium residue over ammonium groups. This specificity was confirmed by both experimental results and theoretical simulations. These results demonstrated a new modular displacement strategy, exploring the use of species-binding hydrogen-bonded macrocyclic foldamers for the construction of two-component gelation systems for selective recognition of native amino acids by competitive host-guest interactions. This strategy may be amenable to developing a variety of functional two-component gelators for specific recognition of various targeted organic molecular species.

Supramolecular hydrogels made of basic biological building blocks

As a consequence of the self-assembly of small organic molecules in water, supramolecular hydrogels are evolving from serendipitous events during organic synthesis to become a new type of materials that hold promise for applications in biomedicine. In this Focus Review, we describe recent advances in the use of basic biological building blocks for creating molecules that act as hydrogelators and the potential applications of the corresponding hydrogels. After introducing the concept of supramolecular hydrogels and defining the scope of this review, we briefly describe the methods for making and characterizing supramolecular hydrogels. We then discuss representative hydrogelators according to the categories of their building blocks, such as amino acids, nucleobases, and saccharides, and highlight the applications of the hydrogels when necessary. Finally, we offer our perspective and outlook on this fast-growing field at the interface of organic chemistry, materials, biology, and medicine. By providing a snapshot for chemists, engineers, and medical scientists, we hope that this Focus Review will contribute to the development of multidisciplinary research on supramolecular hydrogels for a wide range of applications in different fields.