A novel supramolecular system that acts as a biomimetic receptor for neutral guests is presented. The functionalization of t-butyl-calix[6]arene (X 6 H 6 ) at the lower rim in alternate position by methyl (Me) and 2-methylene-1-methyl-1H-imidazole (Imme) yielded the new ligand X 6 Me 3 Imme 3 . It provided a neutral tris(imidazole) coordination site associated with a conic cavity, thereby mimicking the active center of zinc proteins. Upon reaction with Zn(ClO 4 ) 2 (H 2 O) 6 , an air-stable dicationic zinc-aqua complex [Zn(X 6 Me 3 Imme 3 )-(H 2 O)](ClO 4 ) 2 was obtained. The highly acidic Zn 2+ center was constrained in a tetrahedral environment with a labile site oriented toward the inside of the calix[6]arene structure. The hydrophobic pocket acted as a selective molecular funnel for neutral molecules. 1 H NMR spectroscopy studies showed the easy exchange of the aqua ligand for amines, alcohols, amides, or nitriles. The selectivity of the exchange process is based on both the guest's binding ability to the metal center and its shape and size. Two of these ternary complexes were characterized by X-ray diffraction analysis: [Zn(X 6 Me 3 Imme 3 )(NCC 2 H 5 )](ClO 4 ) 2 and [Zn(X 6 Me 3 Imme 3 )-(NH 2 C 7 H 15 )](ClO 4 ) 2 . Hydrogen bonds between the acidic protons of the coordinated guest and the calixarene phenoxyl group suggest an important role in the stabilization of these dicationic complexes that do not undergo deprotonation.
E. coli bacteria were encapsulated within silica gels and aged at room temperature in the absence of nutrients. Their viability was studied as a function of time using different viability tests. The plate count technique gives the number of culturable bacteria that remain able to form colonies in the presence of a culture medium. Their metabolic activity toward glycolysis was followed by 14 C titration and 13 C NMR spectroscopy. Several sol-gel matrices were tested in order to improve the viability of the trapped bacteria. The best results were obtained when encapsulation is performed in the presence of glycerol showing that almost 50% of the bacteria were still able to form metabolites after one month of ageing. Moreover, this study demonstrates that a wide range of viability tests can be adapted for use with cells encapsulated in mineral matrices. ExperimentalMaterials E. coli B (CIP-54125) was taken from the Institut Pasteur collection (Paris, France). Silica sources were sodium silicate solutions SiNa (27 wt% SiO 2 , 10 wt% NaOH from Riedel-de Hae ¨n) and colloidal silica (LUDOX HS-40 from Aldrich).
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