A comparative IR and NMR study of two low-molecular-weight organogels (LMWGs) based on aminoacid derivatives let us point out the hierarchy of the gelation assembly process. Different association states of corresponding organogelator molecules can be observed leading to the supramolecular organization of gel. A first hydrogen bond network of gelators leads to the formation of "head-to-tail" stacking-up, which can be assembled afterward one to the other by π-π stacking interactions. These small supramolecular aggregates (incipient precursor) are still visible in NMR spectra, and they represent, for example, 36% of the total amount of gelator in the case of the L-phenylalanine derivative (gelator 1) at 1 wt % in toluene. Finally, in the last step, the incipient precursor tends to form the expected 3D fibrillar network responsible for the gelation phenomenon. Temperature-dependent IR and NMR experiments allowed us to identify these different states clearly.

In recent years, the design of new low-molecular-weight gelators (LMWGs) has attracted considerable attention because of the interesting supramolecular architectures as well as industrial applications. In this context, the role of the organic solvent in determining the organogelation behavior is a central question. Herein we report the results of a systematic study of the organogelation behavior of amino acid derivatives in a wide range of solvents to establish a relationship between the nature of the solvent and the formation of the gel. We highlight that the majority of the gelified solvents are aromatic, except for carbon tetrachloride and tetrachloroethylene. In addition, different parameters related to the nature of the solvent were considered and their influence on the physical properties of gelation was evaluated. The hydrogen-bonding Hansen parameter (δ(h)) allows us to draw a narrow favorable δ(h) domain for gelation in the range of 0.2-1.4 (cal cm(-3))(1/2). Furthermore, a general increase of the Hildebrand parameter (δ) leads to the formation of poor gels (small gelation numbers, GNs) in aromatic solvents. Scanning electron microscopy (SEM) revealed that the gels prepared from (l)-phenylalanine and (l)-leucine derivatives in different solvents are composed of an entangled 3D fibrillar network, the diameter of which is only slightly influenced by the nature of the solvent.

This paper describes a new type of surface imprinting technique that combines the advantages of both the semi-covalent approach and one-stage miniemulsion polymerization. This process has been successfully applied for the preparation of glucose surface-imprinted nanoparticles. The selective artificial receptors for glucopyranoside were fully characterized by IR, TEM and BET analyses, and their molecular recognition abilities by binding experiments carried out in batch processes. The molecular affinity and selectivity of the glucose molecularly imprinted polymers were accurately quantified. These characteristics are essential for verification of the efficiency of the developed surface imprinting process. The imprinting effect was clearly demonstrated using the batch rebinding method. We have found that the glucose imprinted polymers produced using the optimized one-stage mini-emulsion exhibited quite fast kinetics of binding and equilibration with glucopyranoside templates, compared to polymers prepared by bulk polymerization technique, as well as extremely low levels of unspecific bindings. We also demonstrated that glucose molecular imprinted polymer (MIP) exhibited very good selectivity for its original template compared to other glycopyranoside derivatives, such as galactose. Finally, the extraction of the binding properties from isotherms of binding by fitting to the bi-Langmuir and Freundlich models allowed the determination of the affinity constant distribution of the binding sites. This imprinting protocol allowed the determination of an affinity constant (K(D)), involving exclusively H-bonding interactions, for the glucose MIP (P2C) with the best template 1, in CH3CN as the solvent system.