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The applicability of surface-enhanced Raman scattering (SERS) on silver nanoparticles for characterization of interaction between the phthalocyanine molecule and amyloid fibril was studied using the axially coordinated Hf phthalocyanine dichloride and fibrils of amyloidogenic protein insulin. The SERS spectra of the phthalocyanine were obtained; the analytical enhancement factor was estimated to be in the range from 4 to 6 × 104. An intensity enhancement in its SERS spectra caused by the presence of fibrillar insulin was observed. Deviation of this enhancement with the change of fibrillar insulin concentration was manifested. [ABSTRACT FROM AUTHOR]

Abstract: The activity of the boron cluster ‐ closo‐borates in protein amyloid fibrillization was first studied. For this, we explored the effect of dianionic compound [B12H12]2− on aggregation of amyloidogenic protein insulin by the circular dichroism spectroscopy, amyloid‐sensitive fluorescent dye based assay and transmission electron microscopy. It was shown that the presence of closo‐borate during fibrillization reaction speeds up the loss of the protein α‐helical structure. This effect of dianionic compound on protein fibrillization process is concentration‐dependent. Closo‐borate at low concentration (10 mM) enhances the intensity of insulin fibrillization, while at higher concentration (50 mM, 100 mM) fluorescent assay showed the decrease of this intensity. The morphology of fibrils formed in the presence of the boron dianion differs from that of free insulin, namely they are less branched and have the bigger diameter. Besides, closo‐borate‐induced fibrils have strong proneness to stick together forming large aggregated clots. [ABSTRACT FROM AUTHOR]

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]