title: Chiral electronic transitions in fluorescent silver clusters stabilized by DNA.
abstract: Fluorescent, DNA-stabilized silver clusters are receiving much attention for sequence-selected colors and high quantum yields. However, limited knowledge of cluster structure is constraining further development of these "AgN-DNA" nanomaterials. We report the structurally sensitive, chiroptical activity of four pure AgN-DNA with wide ranging colors. Ubiquitous features in circular dichroism (CD) spectra include a positive dichroic peak overlying the lowest energy absorbance peak and highly anisotropic, negative dichroic peaks at energies well below DNA transitions. Quantum chemical calculations for bare chains of silver atoms with nonplanar curvature also exhibit these striking features, indicating electron flow along a chiral, filamentary metallic path as the origin for low-energy AgN-DNA transitions. Relative to the bare DNA, marked UV changes in CD spectra of AgN-DNA and silver cation-DNA solutions indicate that ionic silver content constrains nucleobase conformation. Changes in solvent composition alone can reorganize cluster structure, reconfiguring chiroptical properties and fluorescence.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Barbara , Santa Barbara, California 93106, United States.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Swasey
authors.forename: Natalia
authors.initials: N
authors.lastname: Karimova
authors.forename: Christine M
authors.initials: CM
authors.lastname: Aikens
authors.forename: Danielle E
authors.initials: DE
authors.lastname: Schultz
authors.forename: Anna J
authors.initials: AJ
authors.lastname: Simon
authors.forename: Elisabeth G
authors.initials: EG
authors.lastname: Gwinn
mesh_terms: D003116:Color; D004247:DNA / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry*; D055620:Optical Phenomena; D011789:Quantum Theory; D012834:Silver / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D014173:Transistors, Electronic
chemical_list: D012997:Solvents; D012834:Silver; D004247:DNA