Resonance energy transfer structure

More recently, the method of scanning near-field optical microscopy (SNOM) has been applied to LB films of phospholipids and has revealed submicron-domain structures [55-59]. The method involves scanning a fiber-optic tip over a surface in much the same way an AFM tip is scanned over a surface. In principle, other optical experiments could be combined with the SNOM, snch as resonance energy transfer, time-resolved flnorescence, and surface plasmon resonance. It is likely that spectroscopic investigation of snbmicron domains in LB films nsing these principles will be pnrsned extensively. 

The intramolecular distances measured at room temperature with the AEDANS FITC pair were similar in the Ca2Ei and E2V states [297]. Ca and lanthanides are expected to stabilize the Ej conformation of the Ca -ATPase, since they induce a similar crystal form of Ca -ATPase [119,157] and have similar effects on the tryptophan fluorescence [151] and on the trypsin sensitivity of Ca -ATPase [119,120]. It is also likely that the vanadate-stabilized E2V state is similar to the p2 P state stabilized by Pi [418]. Therefore the absence of significant difference in the resonance energy transfer distances between the two states implies that the structural differences between the two conformations at sites recorded by currently available probes, fall within the considerable error of resonance energy transfer measurements. Even if these distances would vary by as much as 5 A the difference between the two conformations could not be established reliably. 

Jovin, T. and Arndt-Jovin, D. (1989). FRET microscopy Digital imaging of fluorescence resonance energy transfer. Application in cell biology. In Cell Structure and Function by Microspectrofluorometry (Kohen, E., JG, H. and Ploem, J., eds.). Academic Press, London, pp. 99-117. 

Medintz, I L., Konnert, J.H., Clapp, A.R., Stanish, I., Twigg, M.E., Mattoussi, H., Mauro, J.M., and Deschamps, J.R. (2004) A fluorescence resonance energy transfer-derived structure of a quantum dot-protein bioconjugate nanoassembly. Proc. Natl. Acad. Sci. USA 101(26), 9612-9617. 

The already critical need for molecular-scale compositional mapping will increase as more complex structures are assembled. Currently, electron microscopy, scanning probe microscopy (SPM) and fluorescence resonance energy transfer (FRET) are the only methods that routinely provide nanometer resolution. 

The Na+ sensor M-9 has a structure analogous to that of compound E-4, but instead of two identical pyrene fluorophores, it contains two different fluorophores with a pyrene group and an anthroyloxy group. Resonance energy transfer (see Chapter 9) from the former to the latter is then possible because of the spectral overlap between the fluorescence spectrum of the pyrene moiety and the absorption spectrum of the anthroyloxy moiety. Upon addition of Na+ to a solution of M-9 in a mixture of MeOH and THF (15 1 v/v), the fluorescence of the anthroyloxy group increases significantly compared with that of the pyrene group, which permits a ratiometric measurement. 

In 1994 and 1995, two crystal structures of hammerhead ribozymes [31,32] and a structural analysis based on fluorescence resonance energy transfer studies [41] were published. In case of the crystal structure analyses, both ribozyme variants contained certain modifications that had been introduced to avoid self-cleavage [31,32]. In one case a DNA-analog of the substrate oligonucleotide was used [31], in the other case the all-RNA substrate contained a I -O-CR modification at the attacking 2 -OH group to avoid cleavage in the crystal [32] for reviews see [8,42,43]. 

A notable exception are chemisorbed complexes in zeolites, which have been characterized both structurally and spectroscopically, and for which the interpretation of electronic spectra has met with a considerable success. The reason for the former is the well-defined, although complex, structure of the zeolite framework in which the cations are distributed among a few types of available sites the fortunate circumstance of the latter is that the interaction between the cations, which act as selective chemisorption centers, and the zeolite framework is primarily only electrostatic. The theory that applies for this case is the ligand field theory of the ion-molecule complexes usually placed in trigonal fields of the zeolite cation sites (29). Quantum mechanical exchange interactions with the zeolite framework are justifiably neglected except for very small effects in resonance energy transfer (J30). ... 

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