pH-dependent distribution of chlorin e6 derivatives across phospholipid bilayers probed by NMR spectroscopy

Vermathen, Martina; Marzorati, Mattia; Vermathen, Peter; Bigler, Peter (2010). pH-dependent distribution of chlorin e6 derivatives across phospholipid bilayers probed by NMR spectroscopy. Langmuir, 26(13), pp. 11085-94. Washington, D.C.: American Chemical Society 10.1021/la100679y

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The pH-dependent membrane adsorption and distribution of three chlorin derivatives, chlorin e6 (CE), rhodin G7 (RG), and monoaspartyl-chlorin e6 (MACE), in the physiological pH range (pH 6-8) were probed by NMR spectroscopy. Unilamellar vesicles consisting of dioleoyl-phosphatidyl-choline (DOPC) were used as membrane models. The chlorin derivatives were characterized with respect to their aggregation behavior, the pK(a) values of individual carboxylate groups, the extent of membrane adsorption, and their flip-flop rates across the bilayer membrane for pH 6-8. External membrane adsorption was found to be lower for RG than for CE and MACE. Both electrostatic interactions and the extent of aggregation seemed to be the main determinants of membrane adsorption. Rate constants for chlorin transfer across the membrane were found to correlate strongly with the pH of the surrounding medium, in particular, for CE and RG. In acidic solution, CE and RG transfer across the membrane was strongly accelerated, and in basic solution, all compounds were retained, mostly in the outer monolayer. In contrast, MACE flip-flop across the membrane remained very low even at pH 6. The protonation of ionizable groups is suggested to be a major determinant of chlorin transfer rates across the bilayer. pK(a) values of CE and RG were found to be between 6 and 8, and two of the carboxylate groups in MACE had pK(a) values below 6. For CE and RG, the kinetic profiles at acidic pH indicated that the initial fast membrane distribution was followed by secondary steps that are discussed in this article.

Item Type:

Journal Article (Original Article)


04 Faculty of Medicine > Department of Radiology, Neuroradiology and Nuclear Medicine (DRNN) > Institute of Diagnostic, Interventional and Paediatric Radiology > DCR Magnetic Resonance Spectroscopy and Methodology (AMSM)
08 Faculty of Science > Department of Chemistry, Biochemistry and Pharmaceutical Sciences (DCBP)

UniBE Contributor:

Vermathen, Peter, Bigler, Peter




American Chemical Society




Factscience Import

Date Deposited:

04 Oct 2013 14:07

Last Modified:

05 Dec 2022 14:00

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URI: (FactScience: 196958)

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