PARTICLE SYNTHESIS AND PROPERTIES

Uniform Particles of Pure and Silica Coated Cholesterol

Dr. Egon Matijevic' (the Victor K. LaMer Professor of Colloid and Surface Science at Clarkson University) uses precipitation to prepare uniform crystalline colloidal cholesterol particles of narrow size distribution. This method consists of adding a miscible non-solvent (water) to cholesterol solutions of different alcohols and acetone, without any additives. The properties of the resulting particles depend in a sensitive way on the concentration of all reactants, temperature, pH, ionic strength, and aging time. See Figures 1 and 2. The major observed effects are due to the solubility of cholesterol, which is strongly affected by the solvent mixture and temperature.

Cholesterol represents one of the essential biochemical compounds in the animal kingdom, because it is involved in numerous body-functioning tasks that range from the synthesis of bile acids and steroid hormones in vivo to maintaining a proper transport balance within cellular membranes. However, due to the lack of ability to make cholesterol soluble from different sources by micellar, vesicular and bilayer cleansing agents in bile, as well as lipoprotein complexes in blood, this steroid may deposit on the vessel walls. This causes problematic health issues that include gallstone formation, intestinal lumen deposits, and artheriosclerotic plaque.

Figure 1. SEM of cholesterol particles prepared with 1-propanol as solvent using a standard precipitation procedure (SPP), sampled after10 minutes of reaction time.

Figure 2. SEM of cholesterol particles prepared using reactant concentrations as in the SPP, but with different temperature and aging conditions. These particles precipitated at 31 degrees C and aged at 37 degrees C for 5 hours.

In order to be able to control the deposition and dissolution of cholesterol, investigations of its crystallization in simple environments may be useful in providing information critical for medicine and chemotherapeutics. Also, uniform colloidal cholesterol particles of various morphologies could serve as excellent model systems for the evaluation of different factors on the properties and reactivity of this steroid. Professor Matijevic's work demonstrates that such dispersions can be obtained by using his method. Precipitation in a 1-propanol/water system yields stable dispersions of well-defined particles, which are used to evaluate the effects of different experimental parameters on their properties. Aging of stable dispersions results in multilayered aggregation of the primary platelets, the degree and rate of which are strongly affected by temperature and ionic strength (salt content in the environment). In addition, Professor Matijevic' has shown that colloidal cholesterol particles can be coated with homogeneous silica layers in order to alter their surface characteristics.

Professor Dan Goia's Research in Fine Metallic Particles Generates High Interest and Attracts Significant External Support

CAMP Professor Dan Goia is involved in the synthesis, characterization, and modification of ultra-fine and nanosize metallic and metal-composite particles with controlled size, shape, internal structure, composition, and surface properties. Besides already being used extensively in catalysis, electronics, metallurgy, and pigments, these materials are starting to impact many emerging technological fields such as medicine, biology, defense, nonlinear optics, energy generation, and magnetic storage. Professor Goia's research in this field over the past five years has resulted in 12 US, European, and worldwide patents and has attracted significant interest from both government agencies and industrial sponsors.