Coordination compounds of cobalt porphyrins with nitrogen monoxide

Abstract

Complex formation of NO and the NO 2 -ion with cobalt porphyrins bearing various substituents in the porphyrin macrocycle, viz., tetraphenylporphine (1), β octabromo meso tetraphenylporphyrin (2), protoporphyrin IX (3), and 5,10,15,20 tetra(4N carboxymethylene pyridyl)porphyrin tetrabromide (4), was studied. The stability constants of the nitrosyl and nitrite extracomplexes in water and in ethanol were determined. Porphyrin 4 forms the most stable extracomplexes. Nitrogen monoxide is produced by enzymatic systems in mammals and acts as a versatile regulator of metabolic processes. 1-3 Nitrogen monoxide is found 4,5 to be an endogenic vasodilator and neurotransmitter and oppresses thrombocyte aggregation; the superoxide radical and NO during oxidative stress act in conjugation.Nitrogen monoxide is produced in biological systems by NO synthases from L arginine, which is classified as an enzyme forming the NO • free radical and citrulline as a by product. 6 In the organism nitrogen monoxide is rapidly oxidized to stable end products, NO 2 -and NO 3 -ions. The nitrite ion in vivo oxidizes oxyhemoglobin and cata lyzes reactions involving NO. The mechanism of toxic effect of nitrites is mainly attributed to the oxidation of hemoglobin to methemoglobin accompanied by the vio lation of oxygen transport to tissues due to which hemic hypoxia is developed. Nitrogen monoxide can coordinate to thiols, sulfur-iron proteins of plasma, secondary amines, and hemoglobin and be consumed in reactions with oxygen, superoxide radicals, and hemoglobin. 5-8 Therefore, non heme models of iron containing proteins are being developed and their nitrosyl complexes are un der study. 9 However, the single compensatory adjustment form of NO depositing and utilization is complex forma tion with hemoglobin that occurs via axial coordination on the protoheme. 10 Therefore, investigation of binding (axial coordination) processes of nitrogen monoxide and its metabolite (nitrite ion) by metal porphyrins in solu tions is key for understanding of the essence of biological processes involving NO.In the present work, we studied the equilibrium of formation of the axial NO and NO 2 -complexes with Co II porphyrins of different structural types: tetraphe nylporphine (1), β octabromo meso tetraphenylpor phyrin (2), protoporphyrin IX (3), and 5,10,15,20 tetra(4N carboxymethylenepiridyl)porphyrin tetrabro R = H (1), Br (2)

Variable Nitric Oxide Reactivity of Tropocoronand Cobalt(III) Nitrite Complexes as a Function of the Polymethylene Linker Chain Length

“…Previous reports detailing reactions of cobalt(III) centers with NO(g) describe reductive nitrosylation pathways, whereby cobalt(III) reacts with NO to form species that are formally {Co III –NO – } adducts. − A reductant such as butylamine is sometimes utilized in these reactions . We propose that, in reductive nitrosylation reactions between [Co(η 2 -NO 2 )(TC- n , n )] ( n = 4–6) and NO(g), nitrite may provide the electrons for cobalt mononitrosyl formation, generating • NO 2 as a byproduct.…”

Influence of the Ligand’s Basicity on the Kinetics of Complexation of 5,10,15,20-Tetra(trifluoromethyl) and 5,10,15,20-Tetra(iso-butyl)porphine with Copper Acetate

“…[1][2][3] Исследования уникальных свойств порфиринов могут послужить основой как для решения фундаментальных проблем (установление механизмов превращения и переноса энергии в процессе фотосинтеза, ферментативного катализа), так и многих практически важных вопросов (получение синтетических переносчиков кислорода, каталитически активных материалов и др.). [4][5][6][7][8][9][10][11][12] Многообразие практически значимых свойств порфиринов и их аналогов связано с особенностями их строения. Порфирины образуют устойчивые координационные соединения состава 1:1 (металл:лиганд) с большинством металлов (исключение составляют щелочные металлы).…”

“…Введение тех или иных заместителей может принципиально изменить как геометрические параметры молекулы, так и избирательно регулировать необходимые физико-химические свойства. [1,7,12] В связи с этим представляется весьма актуальной задача исследования влияния электронных и стерических эффектов заместителей порфиринового макроцикла на координационные, кислотно-основные и спектральные свойства порфиринов.…”