title: Acridine orange interaction with DNA: Effect of ionic strength.
abstract: The study of acridine orange (AO) spectral characteristics and the quenching of its singlet and triplet excited states by TEMPO radical at its binding to DNA in the function of the DNA concentration and in the absence and presence of NaCl is reported.
  
  
  
  The study was performed using steady-state and time resolved optical absorption and florescence, fluorescence correlation spectroscopy and resonant light scattering techniques.
  
  
  
  The presence of different species in equilibrium: AO monomers and aggregates bound to DNA, has been demonstrated, their relative content depending on the DNA and the AO concentrations. At high DNA concentration the AO monomers are protected against the contact with other molecules, thus reducing the AO excited state quenching. The addition of NaCl reduces the AO binding constant to DNA, thus reducing the AO and DNA aggregation.
  
  
  
  The interaction of AO with DNA is a complex process, including aggregation and disaggregation of both components. This modifies the AO excited state characteristics and AO accessibility to other molecules. The salt reduces the DNA effects on the AO excited state characteristics thus attenuating its effects on the AO efficacy in applications.
  
  
  
  This study demonstrates that the interaction of photosensitizers with DNA, depending on their relative concentrations, can both decrease and increase the photosensitizer efficacy in applications. The salt is able to attenuate these effects.
authors.affiliation: Departamento de Física, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, Vila Monte Alegre, CEP 14040-901 Ribeirão Preto, SP, Brazil.
authors.forename: André M
authors.initials: AM
authors.lastname: Amado
authors.affiliation: Departamento de Física, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, Vila Monte Alegre, CEP 14040-901 Ribeirão Preto, SP, Brazil.
authors.forename: Wallance M
authors.initials: WM
authors.lastname: Pazin
authors.affiliation: Departamento de Física, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, Vila Monte Alegre, CEP 14040-901 Ribeirão Preto, SP, Brazil.
authors.forename: Amando S
authors.initials: AS
authors.lastname: Ito
authors.affiliation: Emanuel Institute of Biochemical Physics, Russian Academy of Science, Kosygin st. 4, 117977 Moscow, Russia.
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Kuzmin
authors.affiliation: Departamento de Física, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, Vila Monte Alegre, CEP 14040-901 Ribeirão Preto, SP, Brazil. Electronic address: iouribor@usp.br.
authors.forename: Iouri E
authors.initials: IE
authors.lastname: Borissevitch
mesh_terms: D000165:Acridine Orange / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D009994:Osmolar Concentration; D012965:Sodium Chloride / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D012965:Sodium Chloride; D004247:DNA; D000165:Acridine Orange