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Amyloid fibrils are widely studied both as target in conformational disorders and as basis for the development of protein-based functional materials. The three Zr phthalocyanines bearing dehydroacetic acid residue (PcZr(L1)2) and its condensed derivatives (PcZr(L2)2 and PcZr(L3)2) as out-of-plane ligands were synthesized and their influence on insulin fibril formation was studied by amyloid-sensitive fluorescent dye based assay, scanning electron microscopy, fluorescent and absorption spectroscopies. The presence of Zr phthalocyanines was shown to modify the fibril formation. The morphology of fibrils formed in the presence of the Zr phthalocyanines differs from that of free insulin and depends on the structure of out-of-plane ligands. It is shown that free insulin mostly forms fibril clusters with the length of about 0.3-2.1 μm. The presence of Zr phthalocyanines leads to the formation of individual 0.4-2.8 μm-long fibrils with a reduced tendency to lateral aggregation and cluster formation (PcZr(L1)2), shorter 0.2-1.5 μm-long fibrils with the tendency to lateral aggregation without clusters (PcZr(L2)2), and fibril-like 0.2-1.0 μm-long structures (PcZr(L3)2). The strongest influence on fibrils morphology made by PcZr(L3)2 could be explained by the additional stacking of phenyl moiety of the ligand with aromatic amino acids in protein. The evidences of binding of studied Zr phthalocyanines to mature fibrils were shown by absorption spectroscopy (for PcZr(L1)2 and PcZr(L2)2) and fluorescent spectroscopy (for PcZr(L3)2). These complexes could be potentially used as external tools allowing the development of functional materials on protein fibrils basis., Competing Interests: The authors have declared that no competing interests exist.

Amyloid fibrils are rigid β-pleated protein aggregates that are connected with series of harmful diseases and at the same time are promising as base for novel nanomaterials. Thus, design of compounds able to inhibit or redirect those aggregates formation is important both for the biomedical aims and for nanotechnology applications. Here, we studied the effect of tetraphenylporphyrins (metal free, their Cu and Pd complexes, and those functionalized by carboxy and amino groups on periphery) on insulin amyloid self-assembling. The strongest impact on insulin aggregation was demonstrated by a metal-free porphyrin bearing four carboxy groups. This compound strongly suppresses insulin aggregation (about 88% reduction in amyloid-sensitive probe emission) inducing formation of fibrils with the length close to this of free insulin (1.7 ± 0.6 μm as compared with 1.4 ± 0.4 μm, respectively) with an essentially reduced tendency to lateral aggregation. Contrarily, the presence of tetraphenylporphyrin containing four amino groups only slightly affects fibrils' morphology and makes weaker impact on insulin aggregation yield (about 44% reduction). This is explained by the ability of aromatic carboxy groups of 5,10,15,20-(tetra-4-carboxyphenyl)porphyrin to interact with complementary protein-binding groups and thus stabilize the supramolecular complex. For 5,10,15,20-(tetra-4-aminophenyl)porphyrin, full protonation takes place in acidic medium of protein aggregation reaction; this results in the high positive charge of TPPN4 (equal or close to +6) and hence higher contribution of coulombic repulsion to interaction of TPPN4 with insulin. One more possible mechanism of the lower inhibition effect of TPPN4 as compared with TPPC4 could be the more restricted possibility of the former as compared with the latter to form H bonds with insulin groups. It was also shown that metal-free, Pd-containing, and Cu-containing tetraphenylporphyrins without peripheral substituents make almost the same impact on the protein self-assembling. We suppose this to be due to coordination saturation of these metal atoms., (© 2019 John Wiley & Sons, Ltd.)

Series of phthalocyanines of zirconium containing lysine, citric, nonanoic acid residues and dibenzolylmethane groups as out-of-plane ligands are firstly studied as inhibitors of fibrillogenesis using cyanine-based fluorescent inhibitory assay. It was shown that studied phthalocyanines at concentration of 20μM inhibited aggregation reaction on 38.5-57.6% and inhibitory activity of phthalocyanines depended on the chemical nature of out-of-plane ligand. For the most active compound PcZrLys(2) (zirconium phthalocyanine containing lysine fragment) the efficient inhibitor concentration was estimated to be 37μM. AFM studies have shown that in the presence of PcZrLys(2) the inhibition of fibrils formation and formation of spherical oligomeric aggregates took place. Due to the ability of phthalocyanines to decrease efficiently protein aggregation into the amyloid fibrils, modification of phthalocyanine molecules via out-of-plane substitutions was proposed as approach for design of anti-fibrillogenic agents with required properties., (Copyright © 2011. Published by Elsevier Ltd.)

The self-association of proteins into insoluble filamentous aggregates – amyloid fibrils – is associated with a range of protein deposition disorders. With the aim of developing fluorescent probes sensitive to amyloid aggregates, a new series of derivatives of (2Z,5Z,7E)-6-hydroxy-2-(alkylamino)-8-arylocta-2,5,7-trien-4-one dyes was synthesized. These dyes are less sensitive to native amyloidogenic proteins, such as insulin or lysozyme, while they have the ability to exhibit a pronounced fluorescence response in the presence of amyloid fibrils of these proteins depending on the structure of the dye tail groups. The dyes associated with the fibrils show green-yellow emission (495–540 nm) and rather large Stokes shift values (68–125 nm). Upon binding to the fibrils, the fluorescence quantum yields of the dyes could increase by a hundred times up to 0.18–0.47, and the fluorescence intensity decay time strongly enhances up to 0.9–1.3 ns. These features make ketoenoles attractive as probes for the detection of amyloid fibrils; besides, the efficiency of these dyes for real-time monitoring of the kinetics of protein aggregation is shown. The best sensing properties were shown by dyes 2 and 9 bearing short amino tail groups (correspondingly 2-methoxyethyl and 2-hydroxyethyl) and a 4-substituted phenyl moiety at the other end of the ketoenole backbone. [ABSTRACT FROM AUTHOR]