| Abstract
| - Complexes formed between G-quadruplex (G4)-conformed oligonucleotides and four ethidium derivativeswere studied by surface-enhanced Raman spectroscopy(SERS) to detail the topology of complexes that support aG4 stabilization. Ethidium bromide (EB), which presentsa weak ability to stabilize oligonucleotides in G4 conformation, displayed no SERS intensity modification whenbound to G4, as compared with the free EB. Threeethidium derivatives have been selected due to theirhigher ability to stabilize G4 than EB. Bound with G4-conformed oligonucleotides, SERS intensity of these threeethidiums decreased by factors of about 6, 3.5, and 15.The high SERS quenching was interpreted as a loss ofaccessibility of silver colloids for G4-bound ethidiums.This could represent a new selective parameter useful toidentify G4-stabilizing molecules. To apraise the role ofthe oligonucleotide sequence on the interaction mode,complexes were formed with eight G4-conformed oligonucleotides in which the three loops were either 5‘-TTA-3‘ or 5‘-AAA-3‘. Spectra of ethidiums were sensitive toboth lateral loops, opposite to the 3‘ and 5‘ G4 ends. Thesequence of these loops are believed to be selective in theinteraction mode of ethidiums for G4.
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