Fluorescein, Eosin

Fig. 6 General structure of xanthene dyes containing fluorescein, eosin, and rhodamine...

Various pH sensors have been built with a fluorescent pH indicator (fluorescein, eosin Y, pyranine, 4-methylumbelliferone, SNARF, carboxy-SNAFL) immobilized at the tip of an optical fiber. The response of a pH sensor corresponds to the titration curve of the indicator, which has a sigmoidal shape with an inflection point for pH = pK , but it should be emphasized that the effective pKa value can be strongly influenced by the physical and chemical properties of the matrix in which the indicator is entrapped (or of the surface on which it is immobilized) without forgetting the dependence on temperature and ionic strength. In solution, the dynamic range is restricted to approximately two pH units, whereas it can be significantly extended (up to four units) when the indicator is immobilized in a microhetero-geneous microenvironment (e.g. a sol-gel matrix). 

Johansen et al. compared fluorescein, Eosin, Rose Bengal, and Rhodamine B. The system included the electron acceptor, methyl viologen, mv2 + which does not oxidize the dyes (nor are there dye-mv2+ complexes involved) but which reacts with the semireduced radicals formed by reduction of the dyes. The reaction scheme, in the presence of a platinum catalyst, is shown in Eqs. (32)—(35). 

In the Mau scheme fluorescein, Eosin, and Rose Bengal are used in combination to collect the light [272], In a related process developed by Gratzel, microparticles of collodial platinum are used as the reducing surface [273]. 

The substitution of l-chloro-2-naphthoxide ion by sulfite ion in water can also be initiated by visible light (436 nm) with the complex [Ru(bipy)2]Cl as the sensitizer and the complex [Co(bipy)3](C104)2 as the intermediate electron carrier3315. Another possibility is a dye photoinitiated reaction. In the latter example, the excited triplet of the dye (fluorescein, eosine or erythrosine) receives an electron from S03 2 whose radical anion (S03) reacts with halonaphthoxides to give finally the substitution product33c. 

The standard solutions of three organic dyes, rhodamine B, fluorescein, eosin Y and their mixtures were prepared with 2.5xl0 mol/l NaOH. The two-way EM/EX matrices of size... 

Clegg and co-workers used fluorescein as donor and tetramethylrhoda-mine as acceptor (Rq = 45 A), attaching the dyes to the 5 ends of complementary DNA strands. Others have also used fluorescein-eosin. The ability to measure the relatively long distances of a 20-mer (end-to-end distance of approximately 72 A plus linker lengths) required careful measurement and analysis of the sensitized emission (discussed above in the section on measurement). They took care to ensure that the local environment around the dyes was constant for all samples. They also adjusted the dye linker length to ensure that at least one of the dyes was rotationally mobile. (The fluorescein had a low steady-state anisotropy of... 

Fluorescein Eosin Erythrosine Rhodamine B Rose Bengal Anthracene Pyrene Perylene Triphenylene Anthraquinone... 

The presence of fluorescent groups such as pyrene, fluorescein, eosin etc. may also give characteristics to the protein or hgand that were previously not present. For example, such groups on ligands generally decrease water solubility and sometimes cause the compound to adsorb to the walls of plastic containers and cuvettes. 

Those not resolvable, as Fluorescein, Eosine, Nile Blue, Methylene Blue, Magdala Red, etc. 

Xanthene Compounds. Ghosh et al. have quantified the excited state(s) injection and direct molecule-to-particle dynamics of several xanthene compounds (fluorescein, eosin Y, erythrosine B and rose bengal) adsorbed to TiOa nanoparticles (Ramakrishna, 2001). The strong electronic coupling thought necessary for the ultrafast electron injection was previously observed by time-resolved resonance Raman spectroscopy, for eosin Y bonded to a Ti02 surface (Rossetti, 1984). A mechanistic scheme for interfacial electron transfer... 

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