Effect of acidity in TS-1 zeolites on product distribution of the styrene oxidation reaction

The role of Bronsted acidity of titanium silicalite zeolite (with different ratios of Si/Ti) in oxidation reactions of styrene has been investigated and discussed. For zeolites with Si/Ti > 42, most of the titanium is in the zeolite framework. These framework titanium species, which act both as the isolated titanium centers and as Bronsted acidity centers (together with the Bronsted acidity produced by the tetrahedral aluminum impurity introduced during synthesis), can catalyze both the epoxidation and the succeeding rearrangement reactions, thus promoting the formation of phenylacetaldehyde. With an increase in the titanium content of the zeolite, titanium will tend to stay outside the zeolite lattice, except for the TiOx nanophases which can be occluded in the zeolite channels or on the external surface. These non-framework titanium species are favorable for the carbon-carbon bond scission, leading to the production of additional benzaldehyde. The catalytic performances of these zeolites with different Si/Ti ratios are correlated here with their structural information by using solid-state NMR and UV-Vis methods. (C) 2003 Elsevier B.V. All rights reserved.

Theoretical studies of product polarization and state distributions of the H+HCl reaction

The angular momentum polarization and rotational state distributions of the H-2 and HCl products from the H + HCl reaction are calculated at a relative translational energy of 1.6 eV by using quasiclassical trajectories on two potential energy surfaces, one from G3 surface [T.C. Allison et al., J. Phys. Chem. 100 (1996) 13575], and the other from BW2 surface [W. Bian, H.-J. Werner, J. Chem. Phys. 112 (2000) 220]. Product rotational distributions obtained on the G3 potential energy surface (PES) are much closer to the experimental results (P.M. Aker et al., J. Chem. Phys. 90 (1989) 4795; J. Chem. Phys. 90 (1989) 4809) than the distributions calculated on the BW2 PES. The distributions of P(phi(r)) for the H-2 and HCl products obtained on the G3 PES are similar, whereas the rotational alignment effect of the H-2 product is stronger than that of the HCl product. In contrast to the polarization distributions obtained on the G3 PES, the rotational alignment effect of the two products calculated on the BW2 PES is similar. However, the abstraction reaction is dominated by out-of-plane mechanisms, while the exchange reaction is dominated by in-plane mechanisms. The significant difference of the product rotational polarization obtained on the G3 and BW2 PESs implies that the studies of the dynamical stereochemistry can provide a sensitive test for the accuracy of the PES. (C) 2002 Elsevier Science B.V. All rights reserved.

The Development of a Marine Natural Product-based Antifouling Paint

Problems with tin and copper antifouling compounds have highlighted the need to develop new environmentally friendly antifouling coatings. Bacteria isolated from living surfaces in the marine environment are a promising source of natural antifouling compounds. Four isolates were used to produce extracts that were formulated into ten waterbased paints. All but one of the paints showed activity against a test panel of fouling bacteria. Five of the paints were further tested for their ability to inhibit the settlement of barnacle larvae, Balanus amphitrite, and algal spores of Ulva lactuca, and for their ability to inhibit the growth of U. lactuca. Two paints caused a significant decrease in the number of settled barnacles. One paint containing extract of Pseudomonas sp. strain NUDMB50-11, showed excellent activity in all assays. The antifouling chemicals responsible for the activity of the extract were isolated, using bioassay guided fractionation, and their chemical structures determined.