Magnesium complexes of phthalocyanines (Pcs) and their aza-analogues have a great potential in medical applications or fluorescence detection. They are known to demetallate to metal-free ligands in acidic environments, however, detailed investigation of this process and its possible prevention is lacking. In this work, a conversion of lipophilic and water-soluble magnesium complexes of Pcs and tetrapyrazinoporphyrazines (TPyzPzs) to metal-free ligands was studied in relation to the acidity of the environment (organic solvent, water) including the investigation of the role of delivery systems (microemulsion or liposomes) in improvement in their acido-stability. The mechanism of the demetallation in organic solvents was based on an acidoprotolytic mechanism with the protonation of the azomethine nitrogen as the first step and a subsequent conversion to non-protonated metal-free ligands. In water, the mechanism seemed to be solvoprotolytic without any protonated intermediate. The water-soluble magnesium complexes were stable in a buffer with a physiological pH 7.4 while a time-dependent demetallation was observed in acidic pH. The demetallation was immediate at pH < 2 while the full conversion to metal-free ligand was done within 10 min and 45 min for TPyzPzs at pH 3 and pH 4, respectively. Incorporation of lipophilic magnesium complexes into microemulsion or liposomes substantially decreased the rate of the demetallation with the latter delivery system being much more efficient in the protection from the acidic environment. A comparison of two different macrocyclic cores revealed significantly higher kinetic inertness of magnesium TPyzPz complexes than their Pc analogues.

• Klíčová slova
• dissociation, liposomes, magnesium phthalocyanine,
• Publikační typ
• časopisecké články MeSH

New complexes of Zn(ii), Pd(ii) and Pt(ii) with Schiff bases are prepared in a one-step condensation of 4-(dibutylamino)-2-hydroxybenzaldehyde and 4,5-diaminophthalonitrile in the presence of a metal salt. The complexes possess efficient absorption in the blue-green part of the spectrum with molar absorption coefficients up to 98 000 M-1 cm-1. The Pt(ii) complex shows very strong red phosphorescence in anoxic solutions at room temperature with a quantum yield of 65% in toluene which places it among the brightest emitters available for this spectral range. The phosphorescence of the Pd(ii) complex under the same conditions is very weak (Φ < 1%) but is enhanced to Φ > 10% upon immobilization into polymers. Optical thermometers based on self-referenced lifetime read-out are prepared upon immobilization of the dyes into gas-blocking poly(vinylidene chloride-co-acrylonitrile). At 25 °C, the materials based on Pd(ii) and Pt(ii) complexes show sensitivities of -2.1 and -0.52%τ/K, respectively. Application of the sensors for imaging of temperature on surfaces (planar optode) and for monitoring of fast temperature fluctuations (fiber-optic microsensor) is demonstrated. Immobilized into a gas-permeable matrix, the Pt(ii) complex also performs as a promising oxygen-sensing material. The new systems are also attractive for imaging of oxygen or temperature with the help of multi-photon microscopy, due to a good match with the biological optical window and much better brightness under two photon excitation compared to that of the conventional Pt(ii) meso-tetra-(pentafluorophenyl)porphyrin.

• Publikační typ
• časopisecké články MeSH