Eosin-5 -isothiocyanate

Figure 14.2. Chemical structures of some commonly used organic fluorescent probes 1, fluorescein-5-isothiocyanate (FITC) 2, tetramethylrhodamine-5-isothiocyanate (TRITC) 3, 5-carboxyrhodamine B 4, rhodamine X isothiocyanate (XRITC) 5, malachite green isothiocyanate 6, eosin-5-isothiocyanate 7, 1-pyreneisothiocyanate 8, 7-dimethylaminocoumarin-4-acetic acid 9, CY5.180Su.

Eosine, E-00007 Eosin-5-iodoacetamide, see 1-00054 Eosin-5-isothiocyanate, see T-00016 Eosin-5-maleimide, see T-00017... 

The localization of the sensitizer has a significant effect on the photodynamic activity. Eosin is scarcely taken up by cells, and Pooler and Girotti [131] report that Eosin isothiocyanate is 50-100 times more efficient for inducing photohemolysis of human erythrocytes. The spectral properties and quantum yields for singlet oxygen production are identical for both compounds. Therefore, they attribute the difference in photodynamic activity to the ability of the isothiocyanate derivative to bind covalently to band 3 protein. 

The photoswitchable complexation and decomplexation properties of n donor-acceptor complexes between xanthene dyes and photoisomerizable bipyridinium salts has been used to generate an optoelectronic interface (Figure Eosin isothiocyanate (24) was covalently linked to an... 

The photoswitchable complexation/dissociation properties of n donor-acceptor complexes between xanthene dyes and photoisomerizable bipyrid-inium salts have been used to generate an optoelectronic interface [97] (Fig. 28). Eosin isothiocyanate (52) was covalently linked to an electrode surface via a thiourea bond (Fig. 28A). The electron acceptor 3, 3 -bis(N-methylpyridinium) azobenzene 53 was used as the photoisomerizable component. The association constants of the n donor-acceptor complexes generated between eosin and 53a or 53b in solution correspond to Ka — 8.3 x 103 M-1 and Ka — 3.4 x 103 M 1, respectively. The analysis of complexation on the functionalized surface was accomplished by quartz crystal microbalance measurements. The frequency change (Af) of a piezoelectric quartz crystal on which a mass change Am occurs is given by the Sauerbrey equation (Eqn. 1) ... 

It is known, however, that isothiocyanates on their own can form stable self-assembled monolayers on gold (Section V.E), and amine-terminated monolayers were reported to show unusually low reactivity towards electrophilic reagents329,330. It is therefore possible that the observed immobilization of eosin is due not to reaction with amino groups, but to either insertion of the eosin isothiocyanate into a disordered layer of cysteamine, or even replacement of cysteamine monolayer with the molecules of S=C=N—eosin. Because the experimental data on reactions in gold-thiol monolayers are scarce, chemical transformations described in this section should be interpreted with some caution. 

In this paper we outline a series of experiments where we have investigated the conformation of isolated and membrane bound CF1 by means of spectroscopic techniques (4,5,6). For these studies CF1 was covalently labeled with a spectroscopic probe, eosin-isothiocyanate, which preferentially reacts with aminogroups from lysine (5). Upon excitation by a short laser flash the dye can be efficiently transformed into a relatively long lived triplet state. Spectroscopic detection of this triplet state allows to follow conformational changes of the enzyme in either of two ways ... 

The triplet lifetime depends on the access of Op to a given binding site of eosin isothiocyanate in the host profein. Thus, the triplet lifetime reflects the proximity of a binding site to the bulk medixim and/or the flexibility of protein chains which cover a binding site. 

ABEI, M(4-ami nobutyl )-Methylisolu mi nol BSA, bovine serum albumin CL, chemiluminescence DNPO, tas-(2,4-dinitrophenyl)oxalate ECL, electrogenerated chemiluminescence EMMA, electrophoretically mediated microanalysis EY, eosine Y FR, lluorescamine HRP, horseradish peroxidase ILITC, isoluminol isothiocyanate LOD, limit of detection RITC, rhodamine B isothiocyanate TCPO, Mv-(2,4,6-trichlorophenyl)oxalate TEA, triethylamine TRITC, tetramethylrhodamine isothiocyanate. 

Certain fluorescent compounds, such as formycin nucleotides and eosin, behave as noncovalently binding ATP analogs, and their fluorescence increases upon association with the ATPases. The transition from the Na+-form to the K+-form of Na+-K+-ATPase gives rise to a decrease in fluorescence from these probes. The fluorescence of fluorescein isothiocyanate (FITC) bound covalently at the nucleotide site of Na+-K+-ATPase (Table 3) also decreases in relation to transition from the Na+-form to the K+-form. With the noncovalent as well as with the covalently-binding probes the fluorescence decrease probably reflects the structural change in the nucleotide site associated with the reduced nucleotide affinity in the E2 form (see above). By contrast, when FITC is attached to the SR Ca2+-ATPase (at the residue homologous to the FITC-binding residue in Na+-K+-ATPase) the fluorescence increases upon removal of Ca2+. Most likely this relates to the above discussed difference between Na+-K+-ATPase and Ca2+-ATPase with respect to the existence of a stable E2 form with low affinity for nucleotide. 

Figure 21-12. Plot of In(kigt) vs. the driving force (Eo-o) for back electron transfer to the cation radical of the compounds. Eo-o is a linear function of—d G. The compounds are (a) eosin yellowish (EOY), (b) dibromo fluorescein (DBF), (c) fluorescein isothiocyanate (FITC), (d) fluorescein (FLU), and (f) 5(6)-carboxyfluorescein (56CF) (taken with permission from Ramakrishna, 2001).

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