A polysaccharide, chitosan, was chemically modified to form a polyelectrolyte complex membrane with calcium alginate beads. A key factor in membrane for mation was found to be the viscosity average molecular weight (M v) of the chitosan. While unmodified chitosan (Mv = 12.1 x 105) formed thin and weak microcapsule membranes, when the Mv of the chitosan was reduced to 2.4 x 105, the polymer exhibited optimum membrane forming characteristics in terms of capsule strength and flexibility. The degree of deacetylation of chi tosan varied from 94.3% for the unmodified polymer to 93.2% for chitosan of Mv = 1.6 × 105. A substitution reaction sequence was developed in an attempt to modify the pendant amine of the practical grade polysaccharide. Reactive groups were coupled to the chitosan main chain following a two-step process; activation with a bromoacetyl halide and termination with a diamine [(NH2 (CH2)nNH2)] or methyl containing amine compound. Initial studies indicated that thin capsule membranes formed regardless of application of reaction se quence, distance of reactive groups from the main chain, or type of reactive group inserted. The permeability of the chitosan-alginate capsules was assessed, with various diffusing proteins. Membranes formed with chitosan Mv =0.5 × 106 excluded beta amylase, suggesting a membrane molecular weight cut-off of approximately 200,000.

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The reaction of atomic hydrogen with acetaldehyde has been studied with a discharge-flow system coupled to a time-of-flight mass spectrometer. The results are consistent with the mechanism Primary step: CH3CHO+H→CH3CO+H2;Secondary steps: CH3CO+H→CH2CO+H2,CH2CO+H→CH3CO*→CH3+CO,and CH3+H→ lim wallCH4. The rate constant for the abstraction of the aldehydic hydrogen in the primary step (1) for the isotopic modification CD3CDO+D has been determined directly to be 3.2±0.5×10−14 cc molecule−1·sec−1 at 300°K. Under the conditions studied, the major reaction of the acetyl radical is its further reaction with hydrogen atoms to form ketene (6). The final carbon containing products, CO and CH4, are formed from subsequent reactions of ketene with hydrogen atoms (10). The kinetic behavior of the products, CH2CO and CH4, confirms the role of ketene as a major intermediate species in this system. Isotopic studies further confirm that methane is formed from a reaction sequence of ketene with H atoms. The above mechanism is compatible with previous studies of this system, with the exception of a recent communication by Lambert, Christie, and Linnett (Chem. Commun. 1967, 338), who suggest a primary step that yields methane and the formyl radical, CHO, rather than Reaction (1).

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