Gold nanoparticles with a single carboxylic acid group on the surface were prepared from a solid phase place exchange reaction and then coupled to polylysine using an in situ activation agent, diisopropylcarbodiimide (DIPCDI). The covalent amide bond linkage between the nanoparticles and polylysine and the ring closure of the polylysine chain have led to the formation of a nanoparticle/polymer hybrid material with "nanonecklace" structures.

A novel solid phase synthetic strategy was developed in this work for controlled functionalization of gold nanoparticles.

We herein report a systematic study of solid-phase place exchange reactions for the synthesis of gold nanoparticles with a single surface functional group. This approach is based on a “catch and release” mechanism to control the number of functional groups attached to the nanoparticle surface. Bifunctional thiol ligands with a carboxylic end group were first immobilized on a solid polymer support in a controlled density. The density was low enough that neighboring thiol ligands were far apart from each other. When the modified polymer support was incubated in a butanethiol-protected nanoparticle solution, a one-to-one place exchange reaction took place between the polymer-bound thiol ligands and the nanoparticles. After cleaving off from the solid support, nanoparticles with a single carboxylic group were obtained as the major product. By varying the solid supports and reaction conditions, we succeeded to obtain monofunctional gold nanoparticles with enhanced yield and high purity.

The optical limiting performance of a covalently bonded gold nanoparticle (approximately 2 nm)/polylysine hybrid material (AuNP-PLL) was investigated using 4.1 ns laser pulses at 532 nm. The hybrid material exhibits enhanced optical limiting in comparison to individual nanoparticles, presumably due to the interparticle electromagnetic interactions between particles in close proximity. Reverse saturable absorption and/or free carrier absorption were found to be the dominant contributor(s) to the optical limiting of the hybrid material.

The kinetics of the reaction of aliphatic isocyanate with water were investigated with hexyl isocyanate as a model compound. The kinetic study was carried out with a titration method to determine the concentration of the isocyanate group as a function of time. Gas chromatography was used to augment the kinetic data obtained from the titration method. The effects of an organic acid [p-toluene sulfonic acid monohydrate (p-TSA)], a tertiary amine {diazabicyclo[2.2.2]octane (DABCO)}, and an organotin compound [dibutyltin dilaurate (DBTDL)] on the reaction were investigated for the conversion of isocyanate to a urea. Under the reaction conditions in this study, urea was the only product observed. The rate constants indicated that p-TSA had low catalytic activity, DABCO had intermediate catalytic activity, and DBTDL had high catalytic activity. A reaction mechanism was proposed for each of the catalysts.