Kinetics of zinc ion incorporation in base into a centrally aprotic beta-octabrominated cationic water-soluble porphyrin and its monolithium complex

Synthesis, Acid-Base Properties, Kinetics and Mechanism of Cu2+ Incorporation into Water-Soluble Highly Substituted Porphyrins

The synthesis, acid-base properties, and kinetics of Cu[Formula: see text] incorporation into water-soluble highly substituted porphyrins were studied. The basicity increased and the stepwise acid-base equilibrium was clarified by increasing the number of phenyl groups at the [Formula: see text] position, and the basicity of a dodeca-substituted porphyrin increased with the ionic strength. The metalation reaction of the dodeca-substituted porphyrin with Cu[Formula: see text] in aqueous solution revealed a biphasic absorbance change at 453 nm. Plots of [Formula: see text] or[Formula: see text] vs. the Cu[Formula: see text] concentration and of log ([Formula: see text] or[Formula: see text]/[Formula: see text] 0) vs. the ionic strength show that [Formula: see text] is dependent on the Cu[Formula: see text] concentration and ionic strength, while [Formula: see text] is independent of these parameters. These results confirm the stepwise metalation mechanism and the existence of an intermediate in aqueous solution, which is indicated by the biphasic absorbance change at 453 nm.

Direct measurement of equilibrium constants for water-soluble porphyrin with copper(II) and cobalt(II) by differential pulse anodic stripping voltammetry (DPASV)

Because of high stability constants and slow metalation rate of porphyrins, it is difficult to determine stability constants of metalloporphyrins correctly. We propose here a new method for the determination of the stability constant of Cu(II) or Co(II) with 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin, H2(OBTMPyP(4))4+ , by differential pulse anodic stripping voltammetry (DPASV) using a gold working electrode. The concentrations of free Cu(II) or Co(II) ion as low as 10-7–10-8 M were determined directly in equilibrium with H2(OBTMPyP(4))4+ of 10-7–10-8 M under optimum DPSAV conditions of rotating disk gold electrode, deposition of metals, stripping of metals, potential pulse amplitude and pulse width. Furthermore effects of supporting electrolytes, time for the attainment of chemical equilibrium and determination methods (standard addition and calibration curve methods) of total free metal ions were considered. Tetramethylammonium chloride, (CH3)4N+Cl-(TMAC) , showed the lowest detection limit of metals among other electrolytes such as Na2SO4 , NaNO3 , NaCl : 0.5 ppb for Cu(II) at I = 0.1 ((CH3)4N+Cl-) . The stability constants of K s defined as M2+ + P2- = MP ( M = Cu(II) and Co(II) , and H2P = H2(OBTMPyP(4))4+ ) were 1013.93 and 109.47 M-1 for Cu(II) and Co(II) , respectively, at I = 0.1 (CH3)4N+Cl-) and 25 °C. The working electrode was also electrochemically activated at higher potential affording to lower detection limit of metal ions as well as to measure cyclic voltammetry of metal ions, porphyrin and metalloporphyrin as low as 10-5 M. The values of E ap (vs. Ag/AgCl ) of Cu2+ , H2(OBTMPyP(4))4+ and Cu(OBTMPyP(4))4+ were 345, 338 and 425, respectively.