title: Two-Photon Spectroscopy as a New Sensitive Method for Determining the DNA Binding Mode of Fluorescent Nuclear Dyes.
abstract: A new optical strategy to determine the binding modes (intercalation vs groove binding) of small fluorescent organic molecules with calf thymus DNA was developed using two-photon absorption (TPA) spectroscopy. Two-photon excited emission was utilized to investigate a series of fluorescent nuclear dyes. The results show that TPA cross-sections are able to differentiate the fine details between the DNA binding modes. Groove binding molecules exhibit an enhanced TPA cross-section due to the DNA electric field induced enhancement of the transition dipole moment, while intercalative binding molecules exhibit a decrease in the TPA cross-section. Remarkably, the TPA cross-section of 4,6-bis(4-(4-methylpiperazin-1-yl)phenyl) pyrimidine is significantly enhanced (13.6-fold) upon binding with DNA. The sensitivity of our TPA methodology is compared to circular dichroism spectroscopy. TPA demonstrates superior sensitivity by more than an order of magnitude at low DNA concentrations. This methodology can be utilized to probe DNA interactions with other external molecules such as proteins, enzymes, and drugs.
authors.affiliation: †Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States.
authors.forename: Phi H
authors.initials: PH
authors.lastname: Doan
authors.affiliation: ‡Department of Chemistry, University of Miami, Coral Gables, Florida 33146, United States.
authors.forename: Demar R G
authors.initials: DR
authors.lastname: Pitter
authors.affiliation: †Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kocher
authors.affiliation: ‡Department of Chemistry, University of Miami, Coral Gables, Florida 33146, United States.
authors.forename: James N
authors.initials: JN
authors.lastname: Wilson
authors.affiliation: †Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States.
authors.forename: Theodore
authors.initials: T
authors.lastname: Goodson
mesh_terms: D000818:Animals; D002417:Cattle; D004247:DNA / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D017785:Photons; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D005456:Fluorescent Dyes; D004247:DNA; C427203:calf thymus DNA