Cationic fluorescent probes

Greene, F. 1984. Interactions of anionic and cationic fluorescent probes with proteins The effect of charge. J. Protein Chem. 3 167-180. 

The cationic fluorescent probes used in this study. 

Kollmannsberger M, Rurack K, Resch-Genger U, Daub J (1998) Ultrafast charge transfer in amino-substituted boron dipyrromethene dyes and its inhibition by cation com-plexation a new design concept for highly sensitive fluorescent probes. J Phys Chem A 102 10211-10220... 

The molecules used as fluorescent probes for cations, including H+, are nonluminescent, but become fluorescent when bonded to the cation. 

Delmond S, Letard JF, Lapouyade R et al (1996) Cation-triggered photoinduced intramolecular charge transfer and fluorescence red-shift in fluorescence probes. New J Chem 20 861-869... 

Li YQ, Bricks JL, Resch-Genger U et al (2006) Bifunctional charge transfer operated fluorescent probes with acceptor and donor receptors. 2. Bifunctional cation coordination behavior of biphenyl-type sensor molecules incorporating 2, 2 6, 2"-terpyridine acceptors. J Phys Chem A 110 10972-10984... 

The discovery of crown ethers and cryptands in the late sixties opened new possibilities of cation recognition with improvement of selectivity, especially for alkali metal ions for which there is a lack of selective chelators. Then, the idea of coupling these ionophores to chromophores or fluorophores, leading to so-called chromoionophores and fluoroionophores, respectively, emerged some years later l9) As only fluorescent probes are considered in this chapter, chromoionophores will not be described. 

The development of fluorescent probes for anion recognition has been very limited so far in comparison with those for cations. Most of the presently available methods of detection of anions based on fluorescence involve quenching, redox reactions, substitution reactions, ternary complex formation(15) and thus cannot be considered as recognition methods. For instance, the fluorescent sensors that are used for the determination of chloride anions in living cells are based on collisional quenching of a dye by halide ions 6-methoxy-iV-(sulfopropyl)quinoliniuni and... 

At the present time, there is a striking contrast between the extensive development of fluorescent probes for cation recognition and the limited number of available probes for anions notwithstanding the great need for the latter. This is due to the difficulty of the design of selective anion receptors progress made in the relevant field of supra-molecular chemistry will certainly lead in the future to new selective fluorescent signaling receptors of anions. 

The interaction of ACh with the Torpedo nAChR. The data shown compare the equilibrium binding parameters obtained from fluorescence studies using covalently attached fluorescent probes and those obtained from radiolabelled [ H]ACh binding studies or functional measurements of cation flux. These data support a model in which the Torpedo nAChR carries sites of different affinities for ACh. We have previously suggested that occupancy of the lower affinity sites leads to channel activation whereas the higher affinity sites may play a role in desensitization processes... 

Figure 1. (Bottom) Diagram of the electrostatic potential adjacent to a membrane bearing a positive charge. The zeta potential is the potential at the hydrodynamic plane of shear, which should be about 2 A from the surface of the membrane. (Top) Schematic of the location of the probe molecules used to detect the potential produced by the adsorption of calcium and other alkaline earth cations to membranes formed from PC. The divalent cation cobalt and the amphipathic, anionic, fluorescent probe TNS will sense the potential at the interface. The non-actin-Rf complex will sense the potential in the center of the membrane.

Yet the relationship between solute chemical structure and diffusion is not always simple. Werner et al. [248] conducted fluorescence correlation spectroscopic studies of three fluorescent probes in l-butyl-3-methylimidazolium hexafluorophosphate. The probes were chosen to be of comparable molecular structure, but possessed positive, negative, and neutral charges. The authors found that while the neutral probe diffused more rapidly than the cationic probe, the anionic probe diffused the most quickly. 

A demonstration of the single molecule detection at the liquid-liquid interface was reported for the fluorescent probe of l,l/-dioctadecyl-3,3,3/,. 3 -tetramethyI i ndoearboeyan i ne (Dil), which is a monovalent cation with two Cig alkyl chains. Thus, it has high adsorptivity at the dodecane-water interface. 

QUATRISOFT LM 200,a cationic celluloslc polymer with hydrophobic groups,Is a product of Union Carbide Corporation as Is the cationic celluloslc polymer. Polymer JR. Both have a molecular weight In excess of 100,000. Tergltol NP 10, a nonyl phenol ethoxylate used In this study Is also a product of Union Carbide Corporation. Sodium dodecyl sulfate Is a high purity sample purchased from EM Science Corporation. Pyrene which Is used as a fluorescence probe was obtained from Aldrich Chemicals Co. 

The phosphorescence of trivalent cations (as analogues of Ca ) is also widely used in binding studies. The photobinding of phenothiazine derivatives has been studied for different types of biological membranes. The specificity of binding is low, although general, and can be used to identify and localize membrane proteins. The influence of Ca " and phase behaviour in synaptosomal lipids have been examined by the steady-state fluorescence polarization of A fluorescent probe of the tumour promoter phorbol... 

The fluorescent probe 4-aminophthalimide (63) was employed by several authors to study micelles. Samanta and coworkers187,188 used it to study micellization of common cationic (SDS), anionic (cetyltrimethylammonium bromide) and neutral (Triton-X 100) aqueous surfactants, and the same systems were also studied by Datta, Mandal and coworkers189 19°. The critical micelle concentration could be determined and it was found that the probe binds to the micelle water interface or to the cyclodextrin cavities that have also been studied187,188. Water-in-oil microemulsions of Triton-X 100 in a mixture of benzene and hexane showed190 the probe to reside in the water core of the reversed micelles, the polarity of which differs much from that of bulk water. 

CONCLUSIONS This Study shows that fluorescence probing techniques are useful and powerful tools for investigation of conformational transitions of polyelectrolytes as induced by cationic surfactants, pH or other means. Studies on the interaction of cationic probes with polyelectrolytes provide useful information on the intermediates that lie between A states and B states. It is concluded that the conformational transition induced by pH is a progressive process over several pH units. Studies on the interaction of cationic surfactants with PMA at pH 8 show that the aggregates formed are large loose structures, while the interior of the aggregate has a hydrophobicity that is similar to that of a micelle. 

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