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Nitroxide Spin-Label Quenching of Fluorophore’s Triplet Stateas a Tool for Studying Diffusion Mediated Reactions in LipidMembranes
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
Department of Biochemistry and Biophysics, Stockholm University.
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(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

In this work, we introduce an approach to study bimolecularinteractions in model lipid bilayers and biologicalmembranes, which exploits the influence of membrane-associatedElectron Spin Resonance (ESR) labels on the fluorescencesignal of likewise membrane-bound fluorophoremarkers. It is shown how one can exploit the high detectionsensitivity of the fluorescence signal without loosing the abilityto follow low-frequency molecular interactions, takingplace on a time scale well beyond that of the fluorescencelifetimes. The approach utilizes triplet state monitoring byFluorescence Correlation Spectroscopy (FCS), whereby thefluctuations in a strong fluorescence signal is used to characterizetransition rates to and from the lowest triplet stateof the fluorophores, which take place on a time scale 3 to 6orders of magnitude slower than the fluorescence lifetimesof the fluorophores. FCS measurements were performed onthe dye Lissamine Rhodamine B (LRB) in aqueous solutionsand bound to a lipid in a liposome, and in the presence of differentlocal concentrations of the ESR label TEMPO. Bothin the aqueous solution and in the lipid membrane measurements,the measured relative changes in the singlet-triplettransitions rates were found to well reflect the collisionalfrequencies between the LRB and TEMPO molecules. Theproposed approach, allowing low-frequency interactionsto be monitored with a bright fluorescence signal offers abroad applicability, both in terms of read-out means, typesof molecular interactions that can be followed, and in whatenvironment these interactions can be measured. From thispoint of view, it can prove useful for a broad category ofmolecular interaction studies.

Keyword [en]
Fluorescence correlation spectroscopy, FCS, triplet state, TEMPO, quenching, diffusion, membrane
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-12343OAI: oai:DiVA.org:kth-12343DiVA: diva2:309815
Note
QC20100617Available from: 2010-04-12 Created: 2010-04-08 Last updated: 2010-06-17Bibliographically approved
In thesis
1. Photo-induced dark states influorescence spectroscopy – investigations & applications
Open this publication in new window or tab >>Photo-induced dark states influorescence spectroscopy – investigations & applications
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on investigations of transient dark states of fluorescentmolecules using spectroscopic techniques. The main purpose is to show andconvince the reader that transient dark states are not always a nuisance, butalso represent an additional source of information. Several studies with fluorescencecorrelation spectroscopy were performed, all related to non-fluorescentstates such as triplet state or isomerized states.Photobleaching is one of the main problems in virtually all of the fluorescencetechniques. In this thesis, mechanisms that retard photobleaching arecharacterized. Several compounds, antioxidants and triplet state quenchers,which decrease photobleaching, are studied, and guidelines for achieving optimalfluorescence brightness using these compounds are presented.Triplet state quenching by several compounds was studied. Detailed investigationsof the fluorescence quencher potassium iodide demonstratedthat for some of fluorophores, except of quenching, there is fluorescence enhancementmechanism present. In agreement with the first publication inthis thesis, antioxidative properties were found to play an important role inthe fluorescence enhancement. Quenching of the triplet state is proposedas a tool for monitoring diffusion mediated reactions over a wide range offrequencies.Specially designed fluorophores combining high triplet yields with reasonablefluorescence brightness and photostability were characterized forpossible applications in novel super-resolution imaging techniques based onfluorescence photoswitching. Except of benefits for imaging techniques, photoinducedswitching to non-fluorescent states could be used for monitoringmolecular diffusion, which was also demonstrated in this thesis.Studies of the triplet state kinetics of fluorophores close to dielectric interfaceswere performed using fluorescence spectroscopy. The analysis of thetriplet state kinetic can provide information about the local microenvironmentand electrostatic interactions near dielectric interfaces.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. vii, 111 p.
Series
Trita-FYS, ISSN 0280-316X ; 2010:20
Keyword
fluorescence correlation spectroscopy, triplet state, isomerisation, photobleaching, quenching, diffusion, total internal reflection, interface
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-12372 (URN)978-91-628-8108-5 (ISBN)
Public defence
2010-04-29, FA31, Albanova University Center, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20100414Available from: 2010-04-14 Created: 2010-04-12 Last updated: 2011-01-20

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