Phthalocyanines naturally occurring

Phthalocyanine complexes are organic macrocycles with 18 7t-electrons, structurally resembling the naturally-occuring porphyrins complexes [1-3], Electrodes modified with transition metal (notably Fe, Co, Mn, Ni) phthalocyanine (MPc, Fig.l) complexes have continued to generate immense research interests because of their well-established electrocatalytic properties [3-6],... 

Copper phthalocyanine (1) was developed in the 1930s and is the most commonly used blue organic pigment in the coatings, paint, and printing inks industry. Phthalocyanine forms complexes with numerous metals. Various complexes with 66 chemical elements are known. Phthalocyanines are structurally related to naturally occurring dyes such as hemoglobin and chlorophyll A. 

The phthalocyanines are structurally similar to naturally occurring porphyrins such as hemoglobin (5), chlorophyll a, and vitamin B12. Phthalocyanines themselves do not occur in nature. 

In such a large subject, this article can only focus on certain aspects, namely those that involve complexation with inorganic substrates. We only consider the synthetic macrocycles, with emphasis on transition metal complexation. Aza, oxa, and, to a lesser extent, thia and phospha macrocycles are also covered. The naturally occurring porphyrins, corrins, corphins, chlorins, and phthalocyanins, as well as the cyclodextrins, are not included. Because of the general complexity of macrocychc systems and the resulting complicated systematic names, commonly used abbreviations or simplified names will be employed. This review will encompass the synthesis, thermodynamics, stmcture, and applications of macrocychc ligands. 

Phthalocyanines and metallophthalocyanines have been intensively studied as discotic liquid crystals,but porphyrins have received less attention. The first examples of porphyrin discotic phases were based on naturally occurring uroporphyrins but showed a very narrow discotic LC range. However, octa—substituted porphyrins can show discotic meso-phases over a broad temperature range, the LC phase being stabilised by metal insertion into the porphyrin, e.g. zinc. These materials are organic semiconductors whose LC properties allow them to form highly ordered thin films in the solid state. Emission, excitation and absorption spectra in... 

The most extensively studied chelates proposed as models of the naturally occurring systms utilizing molecular oxygen and most synthetic catalyst for the dioxygen reduction ate transition metal phthalocyanines, tetrasubstituted poif ytins and tetraazaannulenes. The N4 chelates exilat the highest activity. 

Naturally occurring free radicals in phthalocyanine, chlorophyll and haemoglobin derivatives Naturally occurring free radicals in phthalocyanine and other biological substances... 

Tetrapyrrolic macrocycles, such as porphyrin, consisted of four pyrrole units bonded by different bridges, for example methene in the case of porphyrins and aza-methene in the case of phthalocyanines [1]. These ligands can complex metal ion transition and the synthesized metallocomplexes are extremely stable [2, 3]. While some metalloporphyrins constitute the redox center of naturally occurring proteins, like heme in hemoglobin, metallophthalocyanines are purely synthetic molecules. The (electro) chemical properties of MN4 complexes have been widely studied and have been particularly used for the catalysis of several electrochemical reactions in homogeneous solutions [4]. It was shown that the electrochemical properties of a... 

In general, the electron transfer reaction (Reaction 2) controls the over-all rate of reaction, and the nature of the catalyst has a profound effect on the kinetics of oxidation (23). Thus Wallace et al. (23) have compared the catalytic efficiencies of metal phthalocyanines with metal pyrophosphates, phosphates, phosphomolybdates, and phosphotungstates. The activity of metal pyrophosphates was ascribed to the ease of electron transfer through the metal coordination shell, the reaction being suggested to occur at the solid pyrophosphate-liquid interface. On the other hand, the catalytic effectiveness of a series of metals, added to solution as simple salts, has been explained in terms of their ability to form soluble complexes containing thiols (13). It was not clear whether the high rates of oxidation were caused by the solubility of metal complexes or by the peculiar nature of the thiol complexes. 

Providing phthalocyanines with chiral bulky heli-cenes at the periphery (29) also results in helical aggregates.165 Aggregation in chloroform occurs upon addition of ethanol as was observed with UV—Vis spectroscopy, while CD spectroscopy revealed the helical nature of the columnar aggregates. Calculations have indicated that two phthalocyanines need to be rotated to allow a favorable intermolecular distance of 3.4 A, because of the bulky helicenes. As such, phthalocyanines provided with racemic helicenes cannot stack in such a defined manner, because of the steric hindrance of the racemic side groups. Aggregation of a smaller analogue of 29, a triphen-ylene-based porphyrazine, has been shown to occur as well.166... 

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