Hydrogen generation through indirect biophotolysis in batch cultures of the nonheterocystous nitrogen-fixing cyanobacterium Plectonema boryanum.

The nitrogen-fixing nonheterocystous cyanobacterium Plectonema boryanum was used as a model organism to study hydrogen generation by indirect biophotolysis in nitrogen-limited batch cultures that were continuously illuminated and sparged with argon/CO(2) to maintain anaerobiosis. The highest hydrogen-production rate (i.e.

Amide bond cleavage: acceleration due to a 1,3-diaxial interaction with a carboxylic acid.

To independently assess the contribution of ground-state pseudoallylic strain to the enormous rates of amide bond cleavage in tertiary amide derivatives of Kemp's triacid, we have studied four amide derivatives of (1alpha-3alpha-5beta)-5-tert-butyl-1,3-cyclohexanedicarboxylic acid. Our results demonstrate that absent pseudoallylic strain, a 1,3-diaxial interaction of an amide with a carboxylic acid leads to only a 2400-fold increase in the rate of amide bond cleavage as compared with the rate of hydrolysis of an unactivated peptide bond.