| Sol-gels have been utilized in many applications due to many desirable properties. A limitation of sol-gels is the gradual collapse of their structure with time. To address this problem, sol-gels were formed from tetramethoxysilane in the presence and absence of generation-zero poly(amidoamine) dendrimers (G0-PAMAM). To test the hypothesis that G0-PAMAM, which serves as a crosslinking agent, will stabilize the structure, the pore volume was monitored over a 52-week period. The premise was that the crosslinking will result in rapid densification. Nitrogen adsorption data stabilized after 25 weeks when G0-PAMAM was present. In its absence, the total pore volume continued to decrease over the entire period.;Phospholipids (PLs) determination is important in the food and pharmaceutical industries. Methods were developed for the detection of a PL, phosphatidylcholine (PC). Electrochemical oxidation of PC, was accomplished at a 4-aminothiophenol (ATP)-modified gold electrode coated with a layer-by-layer assembly of electrochemical catalyst (dirhodium phosphomolybdic acid), a trapping agent for PC (a cyclophane, CP, derivative, 1,4-xylylene-1,4-phenylene-diacetate), and a spacer (generation-4 polyamidoamine dendrimer, PAMAM). The hypothesized process was verified by quartz crystal microbalance measurements which showed that Au | ATP | CP | PAMAM | CP trapped (1.5 +/- 0.4)·10-9 mol cm -2 of PC. The oxidation of PC at 0.16 V vs. Ag | AgCl yielded a current that varied linearly with concentration over the range 1-50 muM.;Finally, an electrochemically assisted method for deposition of nm-scale films of porous silica was developed. In aqueous, un-buffered solution at a potential where H+ is generated in a tetraethylorthosilicate sol, nm-scale, insulating deposits of silica on electrodes are formed. Inclusion of beta-cyclodextrin in the sol provides conductivity, presumably by producing channels in the film. With the addition of a mediator, RhII, the electrochemical oxidation of PC is demonstrated; the process occurs without the passivation that otherwise precludes the voltammetric determination of PLs. Voltammetric current proportional to PC concentration in the range 1-100 muM is achieved with this electrode. |
