Dissolved organic matter in water of Daugava river

New ICT-dyes for Membrane StudiesO.Zhytniakivska* 1 , V.Trusova 1 , G.Gorbenko 1 , T.Deligeorgiev 2 , S.Kaloyanova 2 , N.Lesev 21 V.N. Karazin Kharkiv National University, 4 Svobody Sq., Kharkiv, 61077, Ukraine;2 Faculty of Pharmacy and Chemistry, University of Sofia, Sofia, Bulgariae-mail: olya_zhitniakivska@yahoo.comDuring the past decades fluorophores which can undergo photoinduced intramolecular chargetransfer (ICT dyes) find increasing application in biological sciences. Fluorophores whichexhibit ICT state are widely used in different areas, including the development of solar cellsand chemosensing. High sensitivity of these compounds to the environmental polarityprovokes their use as fluorescent microenvironmental sensors, particularly, in the studies ofmembrane structure and protein-lipid interactions.The present study was undertaken to evaluate the sensitivity of newly synthesized ICT dyes,referred to here as ICT2, ICT4, ICT3 and ICT5, whose structures are given in Fig.1, to thechanges in physicochemical properties of lipid bilayer. At the first step of the study wecompared the lipophilic properties of the ICT-dyes and their sensitivity to the membraneenvironment. Fluorescence spectra of these dyes were recorded in buffer solution (5 mM Naphosphate,pH 7.4) and liposomal suspension. It appeared that only ICT2 and ICT4 arecapable of fluorescing, while ICT3 and ICT5 are non-fluorescent. ICT4 fluorescencedecreases, while emission maximum is shifted from 435 nm in buffer to about 420 nm on thedye transfer from the aqueous to lipid phase. On the contrary, the binding of ICT2 to themodel membranes was followed by the fluorescence increase without any shift of theemission maximum. Moreover, fluorescence quantum yield of ICT2 exhibited tenfoldincrease in the lipid bilayer compared to the buffer solution, while that of ICT4 decreasedabout twice.H 3 COCH 3 SO 4ISNCH 3SNCH 3NNCH 3CH 3OACHS3NNCH 3(CH 2 ) 3 NH 2 HBrCDFig. 1. Structure of the dyes ICT2 (A), ICT4 (B), ICT3(C) and ICT5 (D)To characterize ICT2-lipid binding quantitatively, at the next step of the study we determinedthe dye partition coefficient KPfor different lipid systems. The values of KPwere found tofall in the range (0.4 – 1.5)×10 4 indicating that the examined dyes possess high lipidassociatingability. Analysis of the partition coefficients shows that inclusion of anioniccardiolipin and cholesterol into phosphatidylcholine bilayer gives rise to the increase ofpartition coefficient relative to the neat phosphatidylcholine membrane.To summarize, a comparison of the fluorescence properties of the four newly synthesized ICTcompounds revealed that despite being structurally similar, these dyes display differentspectral and lipid-associating behavior. ICT2 was featured by the most effective partitioninginto lipid phase coupled with considerable increase of the fluorescence quantum yield. Therecovered properties of ICT2 allowed us to recommend this dye for further use in membranestudies. This work was supported by the grant from Fundamental Research State Fund ofUkraine (project number F.41.4/014).ISNCH 3 SO 4CH 3OCH 3B- 36 -