title: Electronic interactions in helical stacked arrays of the modified DNA base pyrrolocytosine.
abstract: The thermal stability and ultraviolet and circular dichroism spectra of nine synthetic DNA hairpins possessing one or more (P)C-G base pairs ((P)C = pyrrolocytosine) have been investigated. One group of hairpins possess 1-5 sequential (P)C-G base pairs while another group possess two (P)C-G base pairs separated by 1-3 A-T base pairs. The first group displays a nearly linear dependence of UV and exciton-coupled circular dichroism (EC-CD) band intensity upon the number of neighboring chromophores, whereas the second group shows weak EC-CD only at the shortest distances between non-neighboring chromophores. This result stands in marked contrast to the exciton coupling seen between stilbene chromophores separated by as many as a dozen base pairs. The weak exciton coupling between non-neighboring (P)C chromophores, like that of the natural nucelobases, is attributed to their relatively weak electronic transition dipoles.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
authors.forename: Prakash P
authors.initials: PP
authors.lastname: Neelakandan
authors.forename: Martin
authors.initials: M
authors.lastname: McCullagh
authors.forename: George C
authors.initials: GC
authors.lastname: Schatz
authors.forename: Frederick D
authors.initials: FD
authors.lastname: Lewis
mesh_terms: D020029:Base Pairing; D002942:Circular Dichroism; D003596:Cytosine / Q000031:analogs & derivatives* / Q000737:chemistry*; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D004583:Electrons; D055029:Inverted Repeat Sequences; D009690:Nucleic Acid Conformation; D011758:Pyrroles / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013267:Stilbenes / Q000737:chemistry
chemical_list: D011758:Pyrroles; D013267:Stilbenes; D003596:Cytosine; D004247:DNA