Joseph M. Simard

Inhibition of chymotrypsin through surface binding using nanoparticle-based receptors.

Efficient binding of biomacromolecular surfaces by synthetic systems requires the effective presentation of complementary elements over large surface areas. We demonstrate here the use of mixed monolayer protected gold clusters (MMPCs) as scaffolds for the binding and inhibition of chymotrypsin. In these studies anionically functionalized amphiphilic MMPCs were shown to inhibit chymotrypsin through a two-stage mechanism featuring fast reversible inhibition followed by a slower irreversible process. This interaction is very efficient, with a K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{i}^{app}}}\end{equation*}\end{document} = 10.4 ± 1.3 nM. The MMPC–protein complex was characterized by CD, demonstrating an almost complete denaturation of the enzyme over time. Dynamic light scattering studies confirm that inhibition proceeds without substantial MMPC aggregation. The electrostatic nature of the engineered interactions provides a level of selectivity: little or no inhibition of function was observed with elastase, β-galactosidase, or cellular retinoic acid binding protein.

Formation and pH-controlled assembly of amphiphilic gold nanoparticles

Alkanethiolate-protected gold nanoclusters are solublized through place exchange reaction with ω-thiocarboxylic acids.

Reversible Regulation of Chymotrypsin Activity Using Negatively Charged Gold Nanoparticles Featuring Malonic Acid Termini

Negatively charged gold nanoparticles featuring 2-(10-mercapto-decyl)-malonic acid were synthesized using the Murray place-displacement reaction. These water-soluble malonate gold mixed monolayer protected clusters (MMPCs) effectively bind and inhibit chymotrypsin based on complementary electrostatic surface recognition. The effect of increasing ionic strength on inhibition was also studied. It was observed that addition of high ionic strength solutions to protein-nanoparticle complexes show almost complete restoration of protein activity. The conformational change of chymotrypsin upon binding to the MMPC was investigated using fluorescence spectrometry and circular dichroism, thus correlating structural changes with enzyme activity.