Synthesis, spectral properties, and antitumor activity of a new axially substituted phthalocyanine complex of zirconium(IV) with citric acid

The new axially substituted phthalocyanine (pc) complex of zirconium(IV) with citric acid is reported. It has been shown that the replacement of two Cl-atoms with two citric acid fragments takes place as the result of the reaction between [ZrCl2(pc)] and citric acid. The complex [Zr(citrate)2(pc)] was formed. The spectroscopic properties of the synthesized compound in DMSO, RPMI 1640 medium with and without fetal calf serum (FCS), H2O, and buffer (Tris) solutions have been described. Antitumor activity of this compound has been studied. The cytostatic activity was observed in the concentration range of 6.1-9.0x10(9) molecules [Zr(citrate)2(pc)]/cell and occurred in 4-6 h after treatment with [Zr(citrate)2(pc)] solution.     

Synthesis, structure, spectroscopic properties, and electrochemical behavior of mixed ligand bis(β-ketoesterato)zirconium (IV) and -hafnium (IV) phthalocyaninates

The synthesis of new zirconium and hafnium mixed ligand phthalocyanine complexes PcM(β-ketoester)₂, where M-Zr (IV), Hf (IV); Pc - the dianion of phthalocyanine, and β-ketoester - the out planed ligand, is reported. The obtained complexes are characterized by ¹H NMR, IR, UV-Vis spectroscopy and cyclic voltammetry. ¹H NMR and elemental analysis confirm the substitution of two Cl atoms for two β-ketoester fragments to the central atom of the macrocycle. The data of ¹H NMR, UV-Vis spectroscopy have allowed us to conclude that two β-ketoester ligands are in the cis geometry to the phthalocyanine plane. X-ray crystallography for bis(isopropyl 3-oxobutanoato)hafnium(IV)phthalocyanine confirms this conclusion. The central macrocycle of the phthalocyanine ligand is not exactly planar (deviations from the least-square plane exceed 0.15 Å) and has the conformation of an essentially flattened crown. The Hf(1) atom is 1.349(3) above this least-square plane. Cyclic voltammetry investigation shows that the introduction of two β-ketoester ligands to the central atom of phthalocyanine complex leads to both chemical and electrochemical stabilization of the whole Pc system.     

Study of tetraphenylporphyrins as modifiers of insulin amyloid aggregation

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.     

Activity of Zn and Mg phthalocyanines and porphyrazines in amyloid aggregation of insulin

Formation of the deposits of protein aggregates—amyloid fibrils in an intracellular and intercellular space—is common to a large group of amyloid‐associated disorders. Among the approaches to develop of therapy of such disorders is the use of agents preventing protein fibrillization. Polyaromatic complexes—porphyrins and phthalocyanines—are known as compounds possessing anti‐fibrillogenic activity. Here, we explore the impact of related macrocyclic complexes—phthalocyanines (Pc) and octaphenyl porphyrazines (Pz) of Mg and Zn—on aggregation of amyloidogenic protein insulin. Pz complexes are firstly reported as compounds able to affect protein fibrillization. The effect of Pc and Pz complexes on the kinetics and intensity of insulin aggregation was studied by the fluorescent assay using amyloid sensitive cyanine dye. This has shown the impact of metal ion on the anti‐fibrillogenic properties of macrocyclic complexes—the effect on the fibrillization kinetics of Mg‐containing compounds is much more pronounced comparing to that of Zn analogues. Scanning electron microscopy experiments have demonstrated that filamentous fibrils are the main product of aggregation both for free insulin and in the presence of macrocyclic complexes. However, those fibrils are distinct by their length and proneness to lateral aggregation. The Pc complexes cause the increase in variation of fibrils length 0.9 to 2.7 nm in opposite to 1.4 to 2.0 nm for free insulin, whereas Pz complexes cause certain shortening of the fibrils to 0.8 to 1.6 nm. The averaged size of the fibrils population was estimated by dynamic light scattering; it correlates with the size of single fibrils detected by scanning electron microscopy.     

Studies of anti-fibrillogenic activity of phthalocyanines of zirconium containing out-of-plane ligands

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.     

Trimethine cyanine dyes as fluorescent probes for amyloid fibrils: The effect of N,N′-substituents

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.     

Synthesis and spectral properties of Zr(IV) and Hf(IV) phthalocyanines with β-diketonates as axial ligands

The series of new zirconium(IV) and hafnium(IV) phthalocyanines with various β-dicarbonyl ligands were prepared via direct interaction between di(chloro)zirconium(IV) or hafnium(IV) phthalocyanines and free β-diketones and also with 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one. The structure of the obtained bis(β-dicarbonilato) zirconium(IV) and hafnium(IV) phthalocyanines was studied by two dimension ¹H NMR spectroscopy (COSY, NOESY, ROESY). Absorption and fluorescence spectroscopic studies have been investigated in various solvents. Analyzed compounds of concentration range below 10^?5 mol/dm³ do not aggregate in the organic solvents. Fluorescence quantum yields (Φ_F) and natural life times (τ) of zirconium phthalocyanine complexes have been calculated in toluene, DMSO and THF.