Biomedical subjects
S D Christian
Publications and source records attributed to S D Christian.
The binding of deoxyguanosine to polycytidylic acid: an application of the thermodynamic model of monomer-polymer complex formation.
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Temperature dependence of the interfacial behavior of uracil derivatives.
The effect of temperature on the interfacial behavior of uracil, thymine and 1,5-dimethyluracil has been used to characterize the thermodynamics of adsorption of these compounds at a mercury electrode-aqueous electrolyte interface. Between 4.5 degrees C and 40 degrees C all three compounds exhibit two adsorption regions. The first, a dilute layer where the molecules adsorb in a flat orientation on the electrode surface. The second, a compact layer where the molecules adsorb in a perpendicular orientation. The thermodynamic constants characterizing formation of these surface layers have been deduced.
Potential and structure controlled interfacial behavior of uracil derivatives.
The adsorption and related interfacial behavior of uracil, various methylated uracil derivatives, uridine, uridine-5'-monophosphate and uridine-3'5'-cyclic monophosphate has been studied by surface electrochemical measurements at a mercury electrode. All uracil derivatives exhibit an initial "dilute" adsorption region where the virtually flat uracil residue is absorbed flat on the electrode surface. In the case of uracil and its methylated derivatives the area occupied by one molecule is about 60-70 A2. Uracil, thymine and 1,5-dimethyluracil exhibit a second adsorption region where they rearrange on the surface and adopt a perpendicular orientation and occupy about 40 A2 per molecule. In this perpendicular orientation the uracils are bound to the electrode through the N(3)-H or perhaps N(1)-H functions in a manner similar to their Watson-Crick bonding in nucleic acids. When in the perpendicular orientation the adsorbed molecules undergo extensive stacking (association) interactions, again similar to those observed between adjacent bases in nucleic acids. The ability of a uracil derivative to undergo a surface reorientation is critically dependent on electrode potential, bulk-solution concentration and molecular structure.
The binding of adenosine to polyuridylic acid in which uracil residues are chemically altered.
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Interfacial behavior of uracil derivatives.
The adsorption of a number of methylated uracil derivatives and of 5-fluorouracil has been studied by surface electrochemical methods at a mercury electrode. All derivatives exhibit an initial or dilute adsorption region where they are adsorbed flat on the electrode surface and are bound by pi-electron overlap with the electrode. Uracil, thymine, 1,5-dimethyl-uracil, 5,6-dimethyluracil, 1,5,6-trimethyluracil and 5-fluorouracil undergo a surface reorientation from the initial flat solution activities for each compound. An unsubstituted N(3)-H group is an absolute requirement for a uracil derivative to be capable of adopting the perpendicular surface stance. In the perpendicular orientation the uracil derivative appears to be bound to the electrode primarily via a N(3)-H--(-) electrode bond although a similar but weaker hydrogen bond can be formed via the N(1)-H group for certain compounds.
A model for the binding of adenosine to polyuridylic acid.
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Charge transfer complexes of purines and pyrimidines. 9-Cyclohexyladenine-iodine in organic solvents and in the solid state.
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