Stability of Aqueous Suspensions of COOH-Decorated Carbon Nanotubes to Organic Solvents, Esterification, and Decarboxylation.

Carbon nanotubes are among the most widely used nanosystems, and stability of carbon nanotube suspensions is critical for nanotechnology and environmental science. Remaining in aqueous environment alone misses important factors that regulate colloidal stability in the presence of electrolytes. Indeed, introduction of (80-95) vol % organic solvents leads to sharp changes in suspension properties depending on the solvent. For example, the critical coagulation concentrations for a given inorganic or organic coagulating ion can change by 2 orders of magnitude when going from dimethyl sulfoxide to acetonitrile. We establish and explain these trends by Lewis acid-base interactions and show that a strong interaction extending beyond the standard theory of aggregation plays an important role.

1-(8-Bromo-2-methyl-4-thioxo-3,4,5,6-tetra-hydro-2H-2,6-methano-1,3-benzoxazocin-11-yl)ethanone.

In the title compound, C(14)H(14)BrNO(2)S, there are two similar non-equivalent mol-ecules in the asymmetric unit, displaying three chiral centres each. In the crystal structure, they are linked by inter-molecular N-H⋯O hydrogen bonds to form infinite chains, which are in turn connected by weak Br⋯H and S⋯H inter-actions.

Selectivity of 7-alkoxycoumarins as probe substrates for rat hepatic cytochrome P450 forms is influenced by the substitution pattern on the coumarin nucleus.

1. The O-dealkylation of 7-alkoxycoumarins is widely used as an assay to characterize cytochrome P450 (CYP) activity. These substrates can also undergo oxidative attack at additional sites on the coumarin nucleus, which may influence their apparent selectivity for particular CYP forms. 2. Accordingly, the effect of blockade of these additional sites was investigated on the selectivity towards rat hepatic CYP forms, with emphasis on the CYP1A and 2B forms. 3. Blockade of the 3-/4- and 6-positions resulted in substrates for which the CYP1A1/2 selectivity of the unsubstituted 7-alkoxycoumarins was altered to a CYP2B selectivity; this was achieved with little overall change in the molecular dimensions of the substrate. Limited analysis of other inducible CYP forms indicated at most only small effects of structure modification on activity. 4. The findings suggest that the sensitivity of probe substrates for CYP forms may be limited by the occurrence of competing side reactions of the substrate, and that better probes may be derived by blocking the sites of these side reactions.