Abstract
Chitosan is a naturally occurring polysaccharide derived from chitin with a wide range of uses. Phthalocyanines are macroheterocyclic compounds that have a number of useful properties such as coloring and catalytic and antioxidant activity. Phthalocyanines are able to immobilize on chitosan, forming complexes with new useful properties. In this work, we evaluated the ability of phthalocyanines to increase the thermal stability of chitosan. Chitosan (CS) forms complexes with copper(II)-(CuPc) and cobalt(II)-(CoPc) tetrasulphophthalocyanines. The processes of destruction of chitosan (CS) and its complexes with sulphophthalocyanines CuPc and CoPc in oxidizing and inert atmospheres have been studied. It was established that, regardless of the atmosphere composition, the first chemical reactions taking place in the studied systems are elimination reactions. The latter ones in the case of chitosan and complex CS-CuPc lead to the formation of spatially crosslinked polymer structures, and it causes the release of CuPc from the polymer complex. It was found that in the case of CS-CoPc elimination reactions did not lead to the formation of crosslinked polymer structures but caused the destruction of the pyranose rings with a partial release of CoPc. Metallophthalocyanines showed antioxidant properties in the composition of complexes with chitosan, increasing the temperature of the beginning of glycosidic bond cleavage reaction by 30–35 °C in comparison with the similar characteristics for chitosan.
Highlights
Phthalocyanines are aromatic macroheterocyclic compounds capable of forming internal salts with almost all metals of the Periodic system
In [25], the ability of the mentioned polysaccharide consisting of N-acetyl Damine and D-glucosamine units to bind d-metal ions due to the formation of donor-acceptor bonds of the M←NH2 group of chitosan, with further synthesis of metal complexes of phthalocyanines (MPc) In Situ was used
Phthalonitrile was added to the resulting complex, and the reaction was carried out in a deep eutectic solvent (DES) at 150 ◦ C for 1 h
Summary
Phthalocyanines are aromatic macroheterocyclic compounds capable of forming internal salts with almost all metals of the Periodic system. In this case, the aromatic phthalocyanine macrocycle is an equatorial ligand. Among the factors determining the stability of complexes of phthalocyanines with metal ions, the geometric correspondence of the covalent radius of the metal cation and the diameter of the reaction cavity of the macro ring are of great importance. They determine the efficiency of the formation of σ- and π-coordination bonds (metal-phthalocyanine). The diameter of the phthalocyanine reaction center is about 2.8 Å [1] and it almost perfectly corresponds to the covalent radius of copper and cobalt atoms, which are 2.6 and 2.5 Å, respectively
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