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Absolute rate constants for H-atom abstraction by OH radicals from cyclopropane, cyclopentane, and cycloheptane have been determined in the gas phase a t 298 K. Hydroxyl radicals were generated by flash photolysis of H,O vapor in the vacuum UV, and monitored by time-resolved resonance absorption a t 308.2 nm [OH(AL87+X'nl. The rate constants in units of cm3 mol-' s a t the 955% confidence limits were as follows: k(c-C3H,) = (3.74 -+ 0.83) x lo'', k(c-C5Hlo) = (3.12 5 0.23) x lo", k(c-C,H,,) = (7.88 5 1.38) x 10". A linear correlation was found to exist between the logarithm of the rate constant per C-H bond and the corresponding bond dissociation energy for several classes of organic compounds with equivalent C-H bonds. The correlation favors a value of D(c-C3H, -H) = (101 -+ 2) kcal mol-'.

We loaded a lignocellulosic substrate extracted from wheat bran with ferric ions. This new lowcost adsorbent was prepared for the adsorption and removal of arsenate and arsenite ions from aqueous systems. The loading process of Fe in this biomaterial was done by hydrolization of a ferric salt while an alkaline solution was added dropwise. The new material obtained has a high sensivity to arsenite and arsenate species. Here, we investigated the effect of contact time, pH, and Fe content on the adsorption of both arsenic ions on the new material. This adsorption was found to be highly pH-dependent, which can be explained on the basis of electrostatic interactions between ionic species in solution and the "FeOH surface groups. The maximum adsorption capacity of arsenite and arsenate species vary linearly with the amount of Fe loaded on the lignocellulosic substrate.

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