Showing papers by "Jacqueline K. Barton published in 1987"

Evidence for altered DNA conformations in the simian virus 40 genome: site-specific DNA cleavage by the chiral complex lambda-tris(4,7-diphenyl-1,10-phenanthroline)cobalt(III)

Abstract: lambda-Tris(4,7-diphenyl-1,10-phenanthroline)cobalt(III), a photoactivated DNA-cleaving agent, is a small molecular probe of DNA structure. Because of its chirality, the complex cannot bind to regular right-handed B-form DNA but exhibits site-specific cleavage along the polymer strand at conformationally distinct sites such as those in a left-handed conformation. Both coarse and higher resolution mapping experiments using the chiral cobalt complex indicate intriguing conformational variations along the simian virus 40 genome. Highly specific cleavage is evident in the enhancer and promoter blocks and in the region downstream of 3' termini. A specific cleavage pattern borders an alternating purine/pyrimidine stretch within the enhancer, which was found earlier to bind anti-Z-DNA antibodies. Throughout the simian virus 40 genome, variations in structure delineated with the cobalt complex appear to correlate with regions important for control of gene expression.

Time-resolved resonance raman spectra of polypyridyl complexes of ruthenium(II)

Abstract: Time-resolved resonance Raman (TR/sup 3/) spectroscopy has recently evolved as a powerful tool for the investigation of the dynamics and structures of a variety of reactive intermediates, electronic excited states, biological systems, and enzyme-substrate complexes. In this communication, the authors report the TR/sup 3/ spectra of three ruthenium complexes of special importance because of three ruthenium complexes of special importance because of their binding ability to nucleic acids, because of their success as chiral probes that recognize the conformations and helicity of nucleic acids, and because of their potential to serve as models for the interaction of metal ions with nucleic acids. They report here the results of TR/sup 3/ and transient absorption experiments which demonstrate that the excited states of three Ru(II) complexes, tris(2,2'-bipyridyl)ruthenium(II) dichloride (I), tris(1,20-phenanthroline)-ruthenium(II) dichloride (II), and tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) dichloride (III), are indeed localized on the ligand.

Synthesis and spectroscopic characterization of the purple tris(phenanthrenequinone diimine)ruthenium(II) ion

Abstract: There has been considerable attention focused on the optical and electronic properties of ruthenium(II) polypyridyl complexes and on their rich excited-state chemistry because of their possible application in the design of photochemical sensitizers for solar energy conversion. The intense coloration and stability of the ruthenium(II) diimine complexes furthermore provide uniquely sensitive photophysical probes for solids, for surfaces, and, in their own laboratory, for biopolymers. While the detailed characterization of the ground- and excited-state electronic structures of bipyridyl and phenanthroline complexes of ruthenium(II) has proceeded, little attention has been given to other diimine complexes of ruthenium(II). The authors have examined complexes of the phenanthrenequinone diimine ligand to explore new photochemical electron transfer agents and to develop new photophysical probes for biopolymers.

Factors influencing the excited-state behavior of ruthenium(II) complexes adsorbed on aqueous laponite

Abstract: Conclusions The results reported in this paper show that liquid-flow microcalorimetry can be used together with a suitable analytical technique for the simultaneous determination of the enthalpy of displacement of solvent by solute at the solid/liquid interface and the adsorption isotherm. This combination of techniques should represent an additional and potentially valuable tool for the study of adsorption from solution at the solid/liquid interface. The enthalpy of displacement of sodium p(2-decyl)benzenesulfonate at a water/Bentheim sandstone interface is low and of the order of -5 kJ/mol. This points to very weak physisorption of the surfactant molecule onto the sandstone surface.

Time‐Resolved Resonance Raman Spectra of Polypyridyl Complexes of Ruthenium(II).

Abstract: Time-resolved resonance Raman (TR/sup 3/) spectroscopy has recently evolved as a powerful tool for the investigation of the dynamics and structures of a variety of reactive intermediates, electronic excited states, biological systems, and enzyme-substrate complexes. In this communication, the authors report the TR/sup 3/ spectra of three ruthenium complexes of special importance because of three ruthenium complexes of special importance because of their binding ability to nucleic acids, because of their success as chiral probes that recognize the conformations and helicity of nucleic acids, and because of their potential to serve as models for the interaction of metal ions with nucleic acids. They report here the results of TR/sup 3/ and transient absorption experiments which demonstrate that the excited states of three Ru(II) complexes, tris(2,2'-bipyridyl)ruthenium(II) dichloride (I), tris(1,20-phenanthroline)-ruthenium(II) dichloride (II), and tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) dichloride (III), are indeed localized on the ligand.

DNA-Mediated Photoelectron Transfer Reactions.

Abstract: The first enantioselective total synthesis of (-)-asperdiol has been accomplished in 15 steps from epoxygeranyl bromide. It is noteworthy that the trisubstituted epoxide was robust enough to survive the conditions for the nucleophilic displacement reactions which were used to form the C-12, C-13 and the '2-3, C-4 bonds. The epoxide also survived the reductive desulfonylation and the intramolecular Horner-Emmons reaction. Our assumption that the cyclization to the 14-membered ring in the desepoxy series would be more straightfoward than in the epoxy series, which provided the impetus for the synthesis of (+)-desepoxyasperdiol, was shown to be false. A number of the optically pure fragments which were used for the total synthesis of 1, particularly 4 and 7, will be useful for the synthesis of other cembranoids.