Dicyanomethylene-squaraine

Fig. 1 Absorption and emission spectra of Cy3, CyS, Cy7, oxo-squaraine 13b (part 3 of this chapter) and dicyanomethylene squaraine 41j (part 4 of this chapter) in water (pH 7.4)...

Squaraine dyes 10b, 39a, 39b, 41a, 41c, 41d, and 41e were used to measure different proteins such as BSA, HSA, ovalbumin, avidin from hen egg white, lysozyme, and trypsin (Fig. 12) [58]. It is difficult to predict correlations between the dyes structures and the affinity or sensitivity of the dyes for different proteins. All squaraine probes exhibit considerable fluorescence increases in the presence of BSA. Dicyanomethylene-squaraine 41c is the brightest fluorescent probe and demonstrates the most pronounced intensity increase (up to 190 times) in presence of BSA. At the same time, the fluorescent response of the dyes 10b, 39a, 39b, 41a, 41c, 41d, and 41e in presence of other albumins (HSA and ovalbumin) is, in general, significantly lower (intensity increases up to 24 times). Dicyanomethylene-squaraine 41a and amino-squaraines 39a and 39b are the most sensitive probes for ovalbumin. Dyes 41d, 10b, and 41e containing an A-carboxyalky I -group demonstrate sufficient enhancement (up to 16 times) in the presence of avidin. Nevertheless, the presence of hydrolases like lysozyme or trypsin has only minor effects on the fluorescence intensity of squaraine dyes. 

The dicyanomethylene-squaraine dye 41e was found to be highly sensitive to trace protein-lipid interactions [109]. Lysozyme association with the lipid bilayer leads to a noticeable decrease in the fluorescence intensity of 41e. In a separate... 

The commercially available dicyanomethylene squaraine dye Seta-670-mono-NHS showed extremely low blinking effects and good photostability when used in single-molecule studies of multiple-fluorophore labeled antibodies [113]. Seta-670-mono-NHS and Seta-635-NH-mono-NHS were covalently labeled to antibodies and used in a surface-enhanced immunoassay [114]. From the fluorescence intensity and lifetime changes determined for a surface that had been coated with silver nanoparticles, both labeled compounds exhibited a 15- to 20-fold... 

The photostability of ring-substituted squaraines, especially dicyanomethylene-and f/no-squaraines is, in general, higher compared to oxo-squaraines and cyanines (Fig. 2). Increasing of the number of sulfo groups further improves the photostability of these dyes the photostability for hydrophilic dyes increases in the order 10b < 13b < Cy5 < 41h < 41i 41j < 41f < 41g [18]. Thio-squaraine dyes... 

Due to their displayed higher photostability, indolenine-based cyanines and squaraines are preferred for the design of fluorescent tracers. Dicyanomethylene- and thio-squaraines with substituted squaraine oxygens also show potential as highly photostable fluorescent probes. 

Figure 5.8 Molecular structures of substituted squaraines mono(dicyanomethylene) squarate 25 frans-bis(dicyanomethylene)squarate 26 c/s-bis(dicyanomethylene)squarate 27 tris(dicyanomethylene)squarate 28 and tetraquis(dicyanomethylene)squarate 29.

In addition to the two crystal structures obtained in this study, six other coordination compounds have been synthesized and characterized [73, 84]. A complete spectroscopic study was performed involving squaraines 1,3- and 1,2-disubstituted with dicyanomethylene groups and four different transition metals cobalt, manganese, zinc, and nickel. The Raman and infrared spectra of all these complexes with both ligands reveal that the ligands exhibit an inverted symmetry element, meaning that the bands which are seen with one technique are not seen with the other, and vice versa. The complexation did not affect the molecular symmetry (in the case of the trans dianion) or the solid-state structure (in the case of the cis dianion). 

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