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The series of the β-ketoenoles (2 E ,5 Z ,7 E ,9 E )-2-(alkylamino)-6-hydroxy-10-phenyldeca-2,5,7,9-tetraen-4-ones with variation of the alkylamino tail groups was synthesized and studied as potential probes for the sensing of protein insoluble aggregates - amyloid fibrils. Depending on the structure of the alkylamino group, the dyes could increase their fluorescence intensity in the dozens of times in the presence of insulin fibrils. The compound with a 2-hydroxyethylamino substituent demonstrates the highest fluorescence response (up to 60 times) and good range of insulin fibril detection (1–50 μg/ml). In complexes with fibrils, the dyes possess fluorescence quantum yield values up to 15% and binding constant values of about 2 × 10 5 M −1 . The excitation and emission maxima of β-ketoenoles are located in the range 407–427 nm and 500–554 nm correspondingly. These compounds are weakly fluorescent when free and slightly sensitive to the native proteins insulin and bovine serum albumin. Thus β-ketoenoles are considered as prospective molecules for the fluorescent detection of amyloid aggregates of proteins. [ABSTRACT FROM AUTHOR]

The effect of various N,N ′-substituents in the molecule of benzothiazole trimethine cyanine dye on its ability to sense the amyloid aggregates of protein was studied. The dyes are low fluorescent when free and in the presence of monomeric proteins, but their emission intensity sharply increases in complexes with aggregated insulin and lysozyme, with the fluorescence quantum yield reaching up to 0.42. The dyes carrying butyl, hydroxyalkyl, and phenylalkyl groups as N,N ′-substituents possess the increased fluorescent sensitivity to fibrillar lysozyme, whereas the ones carrying quaternary amino groups are preferably sensitive to fibrillar insulin. This fluorescent sensitivity preference provided by the N,N ′-functional groups could be explained by the interaction between these groups and protein side chains. The strongest fluorescent response (up to 70 times) and the same sensitivity to aggregates of both proteins were exhibited by the dye D-51 carrying N -sulfoalkyl group. The studied cyanines allow the detection of fibrillar aggregates in the wide range up to 0.8 to 300 μg/ml and permit monitoring the protein aggregation kinetics with high reproducibility. The modification of trimethine cyanine dyes by functional substituents in N,N ′-positions is suggested as a tool for the design of fluorescent molecules with the enhanced fluorescent sensitivity to the fibrillar aggregates of proteins. [ABSTRACT FROM AUTHOR]