Catalysis and Nanomaterials Laboratory

16. B. Sitharaman, S. Asokan, I. Rusakova, M. S. Wong and L. J. Wilson, "Nanoscale Aggregation Properties of Neuroprotective Carboxyfullerene (C3) in Aqueous Solution" Nano Lett. 4, 1759-1762 (2004). DOI:10.1021/nl049315t

Water-soluble malonic acid derivatives of C60 are known to have potent antioxidant activity with potential medical applications as neuroprotective agents. It is commonly assumed that e,e,e tris-malonic acid-C60 (or C3) exists as discrete molecules solubilized in aqueous solution. In this work, C3 is revealed to aggregate in water. The aggregation properties have been studied as a function of concentration, temperature, and pH by dynamic light scattering (DLS). The C3 aggregates are polydisperse under physiological conditions, do not vary much in size as a function of concentration or temperature, and tend to larger sizes at low pH values. Transmission electron microscopy (TEM) and cryo-TEM have been used to visualize the morphology of the nanocrystalline aggregates. The results suggest that 40−80 nm aggregates of C3, not individual C3 molecules, are responsible for their neuroprotective action in cells.

15. V. S. Murthy, J. N. Cha, G. D. Stucky and M. S. Wong, "Charge-driven Flocculation of Poly-L-Lysine - Gold Nanoparticle Assemblies Leading to Hollow Microspheres" J. Am. Chem. Soc., 126, 5292-5299 (2004). DOI: 10.1021/ja038953v

An unusual aggregation phenomenon that involves positively charged poly(l-lysine) (PLL) and negatively charged gold nanoparticles (Au NPs) is reported. Discrete, submicrometer−sized spherical aggregates are found to form immediately upon combining a PLL solution with gold sol (diameter ≈ 14 nm). These PLL−Au NP assemblies grow in size with time, according to light scattering experiments, which indicates a dynamic flocculation process. Water-filled, silica hollow microspheres (outer diameter ≈ microns) are obtained upon the addition of negatively charged SiO2 NPs (diameter ≈ 13 nm) to a suspension of the PLL−Au NP assemblies, around which the SiO2 NPs form a shell. Structural analysis through confocal microscopy indicates the PLL (tagged with a fluorescent dye) is located in the interior of the hollow sphere, and mostly within the silica shell wall. The hollow spheres are theorized to form through flocculation, in which the charge-driven aggregation of Au NPs by PLL provides the critical first step in the two-step synthesis process (“flocculation assembly”). The SiO2 shell can be removed and re-formed by decreasing and increasing the suspension pH about the point-of-zero charge of SiO2, respectively.

14. M. S. Wong and W. V. Knowles, "Surfactant-Templated Mesostructured Materials: Synthesis and Compositional Control" in Nanoporous Materials - Science and Engineering; G. Q. Lu and X. S. Zhao, Eds.; Imperial College Press: London; Chapter 5, pp. 125-164 (2004).

Abstract not available

13. V. S. Murthy, R. K. Rana, J. Yu and M. S. Wong, "Self-assembly of Inorganic Nanoparticles and Polyelectrolytes into Micron-sized Hollow Sphere Structures" PMSE Preprints 90, 632-633 (2004).

The compositional variety in surfactant-templated mesostructured and mesoporous materials widened tremendously since the initial reports on MCM-41 and M41S aluminosilicate mesoporous molecular sieve materials came out. In this chapter the current state of synthesis and compositional control of mesostructured and mesoporous metal oxides is presented. New surfactant templating synthesis routes, especially those that lead to the formation of non-silicates, are described, and a comprehensive update on the available types of such materials is presented. General trends are noted, which could provide insights towards surfactant-templated materials as yet synthesized.