Interaction of dendrimers (artificial proteins) with biological hydroxyapatite crystals.

This investigation sets out to mimic protein-crystal interaction during biomineralization with the use of artificial proteins (dendrimers). It is hypothesized that these interactions depend on the surface charge of hydroxyapatite crystals. This was investigated with the use of dendrimers with capped surfaces of different charges to probe the surface. We used AFM images of crystal-bound dendrimers to determine the distribution of the surface charge, and its magnitude was correlated to the binding capacity of the dendrimers to the surface. The binding capacity of the dendrimers in ascending order at pH 7.4 was: acetamide-capped, -NHC(O)CH3, neutral charge; carboxylic-acid-capped, -COOH, negative charge; and amine-capped, -NH2, positive charge. AFM images of the crystals showed dendrimers spaced equally along the crystal. The results suggest that the crystal surface has alternating bands of positive and negative charge or a differential charge array, i.e., alternating bands of either more or less positive or negative charge.

Determination of spherosiloxane cluster bonding to Si(100)-2 x 1 by scanning tunneling microscopy.

Scanning tunneling microscopy is used to determine the bonding geometry of the spherosiloxane cluster, H(8)Si(8)O(12) , on Si(100)-2 x 1. The images obtained are consistent with monovertex bonding to the Si(100)-2 x 1 surface via activation of a single Si-H bond. Filled and empty state images show good agreement with calculations of the electron density distribution of the cluster as well as the Psi(2) highest occupied molecular orbital and lowest unoccupied molecular orbital surface plots of the cluster.

Infrared Study of H(10)Si(10)O(15) Chemisorbed on a Si(100)-2x1 Surface.

Reflection-absorption infrared spectroscopy of the model interface derived from H(10)Si(10)O(15) on Si(100)-2x1 is presented. The spectra obtained are compared to the H(8)Si(8)O(12)-derived model interface and discussed in terms of the soft X-ray photoemission spectroscopy obtained for cluster-derived interfaces.

Active Role of a Germylene Ligand in Promoting Reactions of Platinum Complexes with Oxygen and Sulfur Dioxide.

The reaction of (Et(3)P)(2)PtGe[N(SiMe(3))(2)](2) with dioxygen yields (Et(3)P)(2)Pt(&mgr;-eta(2)-O(2))Ge[N(SiMe(3))(2)](2) (1). Exposure of 1 to light resulted in a rearrangement to (Et(3)P)(2)PtO(2)Ge[N(SiMe(3))(2)](2) (2a), the first example of a bidentate, dianionic germanate ligand. The isomerization was judged to occur via an intramolecular O-O bond scission and rotation of the Pt-Ge bond. No free germylene was detected, and the reaction was found to be zero order. An analogue of 2a was prepared by direct reaction of (Ph(3)P)(2)PtO(2) with Ge[N(SiMe(3))(2)](2) yielding (Ph(3)P)(2)PtO(2)Ge[N(SiMe(3))(2)](2) (2b). Addition of SO(2) to 1 results in the formation of the bridging sulfate (Et(3)P)(2)Pt(&mgr;-eta(2)-SO(4))Ge[N(SiMe(3))(2)](2) (3). An infrared spectroscopy study of the sulfate reaction was performed using oxygen-18. The results indicate that direct insertion of SO(2) into the O-O bond does not occur. Formaldehyde was also observed to insert into the Pt-O bond of 1 giving (Et(3)P)(2)Pt(&mgr;-eta(2)-OCH(2)OO)Ge[N(SiMe(3))(2)](2) (5).