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Title: Interaction of ethambutol with transition metal ions in solution: Formation constants and stereochemical configurations of the Cu(II), Ni(II), Co(II) and Zn(II) complexes and underlying biological implications
Authors: Bhattacharyya, R G
Paul, U K
Chatterjee, A B
Bag, S P
Issue Date: Oct-1990
Publisher: NISCAIR-CSIR, India
Abstract: Ethambutol (ETB), reacts with aqueous Cu2+, Co2+ and Ni2+ at pH 11 producing [M(H2O)4ETB]2+ (M=Cu, Co) and [Ni2(OH)2(H2O)4(ETB)2]2+. Nickel (II) at pH 9, however, forms [NiL4ETB]2+, where the ligand L is H2O or NH3 depending on whether Na4OH or NH4OH is used to maintain the pH. Spectrophotometric and potentiometric studies suggest that metal-ligand [ETB] formation constant is highest in the case of Cu(II), and DG0 accompanying the Cu-ETB complex formation is also the most negative. The Cu(II), Ni(II) and Co(II) complexes have pseudooctahedral structure as is apparent from their solution magnetic susceptibility and ligand field spectra. Dq (ETB) is exceedingly large for Cu(II), followed by that for Ni(II) and Co(II). The solution data have been corroborated by isolating the BPh4 salts of the complex cations, viz., [M(H2O)4ETB](BPh4)2 (M=Cu, Co, Ni), [Ni(NH3)4ETB](BPh4)2, [Zn(H2O)2(ETB)](BPh4)2 and [Ni2(OH)2(H2O)4(ETB)2](BPh4)2.These salts have been characterized by elemental analysis, molar conductance, magnetic susceptibility, EPR (for Cu(II) complex), infrared and UV-visible spectroscopy. The mode of coordination of ETB is also supported by the IH NMR data of Zn(II) complex. This in vitro study is quite consistent with the idea that ETB treatment depletes Cu2+ in the physiological system.
Page(s): 986-995
ISSN: 0975-0975(Online); 0376-4710(Print)
Appears in Collections:IJC-A Vol.29A(10) [October 1990]

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