Kinetics and mechanism of formation of nickel(II)porphyrin and its interaction with DNA in aqueous medium

Kinetics between 5,10,15,20-tetrakis(N-methylpyridium-4-yl)porphyrin and Ni 2+ species were investigated in aqueous solution at 25 ±1 °C in I = 0.10 M (NaNO 3 ). Speciation of Ni 2+ was done in I = 0.10 M (NaNO 3 ) for knowing distribution of Ni 2+ species with solution pH. Experimental data were compared with speciation diagram constructed from the values of hydrolysis constants of Ni 2+ ion. Speciation data showed that hexaaquanickel(II) ions took place in hydrolysis reactions through formation of [Ni(OH 2 ) 6-n (OH) n ] 2-n species with solution pH. According to speciation of Ni 2+ and pH dependent rate constants, rate expression can be written as: d[Ni(TMPyP) 4+ ]/dt = ( k 1 [Ni 2+ (aq) ] + k 2 [Ni(OH) + (aq) ] + k 3 [Ni(OH) 2 o (aq) ] + k 4 [Ni(OH) 3 - (aq) ])[H 2 TMPyP 4+ ], where k 1 , k 2 , k 3 and k 4 were found to be k 1 = (0.62 ± 0.22) × 10 -2 ; k 2 = (3.60 ± 0.40) × 10 -2 ; k 3 = (2.09 ± 0.52) × 10 -2 , k 4 = (0.53 ± 0.04) × 10 -2 M -1 s -1 at 25 ±1 °C, respectively. Formation of hydrogen bonding between [Ni(H 2 O) 5 (OH)] + and [H 2 TMPyP] 4+ causes enhanced reactivity. Rate of formation of [Ni(II)TMPyP] 4+ complex was to be 3.99 × 10 -2 M -1 s -1 in I = 0.10 M, NaNO 3 (25 ± 1 °C). UV-Vis and fluorescence data suggested that [Ni(II)TMPyP] 4+ and [H 2 (TMPyP)] 4+ interact with DNA via outside binding with self-stacking and intercalation, respectively. Graphic abstract SYNOPSIS Kinetics of tetrakis(1-methylpyridium-4-yl)porphyrin with Ni 2+ were studied in aqueous medium at 25 ±1 °C in I = 0.10 M (NaNO 3 ). Speciation data revealed the stepwise formation of [Ni(H 2 O) 6-n (OH) n ] 2-n species with solution pH. Kinetic results showed that [Ni(H 2 O) 5 (OH)] + is the most reactive species because of the formation of hydrogen bonding. UV-Vis/fluorescence data suggested that [Ni(II)TMPyP] 4+ and [H 2 TMPyP] 4+ interact with DNA via outside binding and intercalation, respectively.