title: Interaction of the antibiotic norfloxacin with ionic micelles: pH-dependent binding.
abstract: The interaction of the antimicrobial drug norfloxacin (NFX) with anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB) micelles was studied using the intrinsic spectroscopic properties of NFX to obtain association constants and molecular modifications. Nonionic Tween(®) 20 micelles were also investigated, but the spectroscopic properties of NFX did not detect interactions with these micelles, and quenching by iodide suggested a weak association constant around 47 M(-1). For SDS and CTAB, UV-Vis absorption spectroscopy, steady-state and time-resolved fluorometry were monitored as a function of surfactant concentration ranging from the premicellar to micellar region. It was found that cationic (pH 4.0) and zwitterionic NFX (pH 7.4) associate with SDS micelles, with binding constants equal to 5.4 × 10(3) and 1.7 × 10(3) M(-1), respectively. Premicellar interaction slightly decreases the critical micelle concentration of SDS. Association of anionic NFX (pH 10.6) is very weak. The fluorescence spectrum and lifetime showed that SDS-associated NFX is cationic and that the heterocycle penetrates the interfacial environment of decreased polarity. Cationic CTAB micelles do not bind cationic NFX, and the association constant with zwitterionic NFX is two orders of magnitude lower than that of SDS micelles. From a pharmacological point of view, it is important that at neutral pH, NFX presented a two orders of magnitude higher affinity for anionic than for cationic sites, and did not interact significantly with nonionic or zwitterionic micelle interfaces.
authors.affiliation: Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, RJ, Brazil, gabriel.muniz@fis.puc-rio.br.
authors.forename: Gabriel Silva Vignoli
authors.initials: GS
authors.lastname: Muniz
authors.forename: Letícia Regina
authors.initials: LR
authors.lastname: Teixeira
authors.forename: Sonia Renaux Wanderley
authors.initials: SR
authors.lastname: Louro
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D008823:Micelles; D009643:Norfloxacin / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D007477:Ions; D008823:Micelles; D012967:Sodium Dodecyl Sulfate; D009643:Norfloxacin
references.citation: Int J Pharm. 2003 Feb 18;252(1-2):149-57
references.pmid: 12550790
references.citation: Biochim Biophys Acta. 1990 Feb 28;1031(1):111-42
references.pmid: 2155023
references.citation: Photochem Photobiol. 2006 Jan-Feb;82(1):64-70
references.pmid: 16076246
references.citation: Eur J Med Chem. 2002 Jun;37(6):443-60
references.pmid: 12204471
references.citation: J Fluoresc. 2011 Sep;21(5):1933-40
references.pmid: 21573968
references.citation: Am Fam Physician. 2000 May 1;61(9):2741-8
references.pmid: 10821154
references.citation: Chem Soc Rev. 2003 Jul;32(4):238-50
references.pmid: 12875030
references.citation: Photochem Photobiol. 1996 Sep;64(3):496-500
references.pmid: 8806228
references.citation: Biochim Biophys Acta. 2008 Nov;1778(11):2535-43
references.pmid: 18809375
references.citation: Int J Antimicrob Agents. 2000 Sep;16(1):5-15
references.pmid: 11185413
references.citation: Biochim Biophys Acta. 1994 Mar 23;1190(2):319-28
references.pmid: 8142432
references.citation: Biophys J. 2008 Apr 15;94(8):3035-46
references.pmid: 18178657
references.citation: Curr Top Med Chem. 2009;9(11):981-98
references.pmid: 19747119
references.citation: J Pharm Biomed Anal. 1998 Dec;18(4-5):859-63
references.pmid: 9919988