The Molecular Mechanics of Quantized Valence Bonds

A new force field, Quantized Valence Bonds′ Molecular Mechanics (QVBMM) has been included in the molecular modeling program STR3DI.EXE. The QVBMM force field successfully embraces and implements all of the pivotal concepts in VSEPR theory and uniquely integrates lone pairs into molecular mechanics. QVBMM facilitates a detailed analysis of the stereo-electronic effects that contribute to the structural and conformational preferences of organic molecules in their ground states, including those molecules that possess the common heteroatoms. The design, parameterization and application of the force field to a few representative molecules is discussed. The anomeric effect is also briefly examined.     

Pathology of experimental Sarcocystis falcatula infections of canaries (Serinus canarius) and pigeons (Columba livia)

Sarcocystis falcatula is an apicomplexan parasite with a broad range of avian intermediate hosts. The pathology and pathogenesis of infection with this parasite has been studied experimentally in the budgerigar (Melopsittacus undulatus). The present study quantitatively examines the pathology of this parasite in canaries (Serinus canarius) and pigeons (Columba livia) and compares it with that found in budgerigars. The general progression of merogony and cyst formation is similar qualitatively to that seen in budgerigars, but it differs quantitatively. The principal site of precystic merogony is in pulmonary endothelial cells. The magnitude of pulmonary meront burdens (at similar inoculated dosages) varies in different intermediate host species. Merogony is less persistent than in budgerigars. Among the various species of birds, the magnitude of precystic merogony correlates differently with the magnitude of skeletal muscle cyst burdens. The distribution of cyst burdens among various muscles also differs. The composition of inflammatory cells differs among various avian species' response to S. falcatula. Pathologic changes quantitatively parallel tissue meront burdens (except possibly in the liver of canaries), resulting in an interstitial pneumonitis, hepatitis, and mild inflammatory lesions of other organs.     

Free Radical-Induced Tandem Base Damage in DNA Oligomers

A new tandem base lesion has been identified in two DNA oligomers, namely d(GpT) and d(CpGpTpA), exposed to X-irradiation in deoxygenated aqueous solution. In this lesion the C6 carbon atom of thymine is hydroxylated and a covalent link is formed between the C5 carbon atom of thymine and the C8 carbon atom of the adjacent guanine base. In addition, further evidence in the form of mass spectrometric data is presented confirming the structures of previously reported tandem base lesions that are produced by ionizing radiation in the presence of oxygen. New data is presented on the prevalence of a previously reported tandem base lesion in which the methyl carbon atom of thymine is covalently linked to the C8 carbon atom of the adjacent guanine base. The free radical-initiated processes by which tandem base damages are generated are discussed. To date four different radiation-induced tandem base lesion have been identified. The evidence suggests that tandem base damage is a significant component of free radical-induced DNA damage.