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VII complexes- model studies for vanadium in ascidians
VANADIIJM
407
ELEC~ICAI, INVESTIGAl’ION OFVI“/VIII/VII COMPLEXESMODEL STUDIES FOR VANADIUM INASCIDIANS
1006 M.Hecht, Technical Sciences,
R.Meier University of Leipzig, PO Box 66, D-O-Leipzig,
Department Germany
of Natural
The fact that some ascidians accummuiate vanadium ion specifically to a level exceeding four million times that present in sea water is an unusual phenomenon and the fact that they are only the such a high level is a mystery. Recent careful reinvestigations of the content, distribution, and valency of the vanadium in several tissues of ascidians clearly show the following Cl]: (i) the highest amounts of vanadium being present in the blood cells in concentrations of up to z 100 mM (ii)tp=valency observed usally is a mixture of VI” and We have recently shown that using voltammetry specication is possible both for mixtures of VI” as and Vm as well different protolytic Vm-species [2]. Because there is still a big controversy in the literature mainly regarding the pH- value inside the ascidians blood cells and the question if the vanadium ions are complexed or we are offering here a model study of the not CL31, interaction of VI” ligand V= and VII with the diethylenetriaminepenttaacetic acid (DTPA) to demonstrate the ease of vanadium speciation with voltammetry. As completion, potentiometric and spectroscopic titrations were conducted.The titration of VmDTPA2with acid is accompanid with an intramolecular rearrangement of one of the terminal iminodiaceto (IDA) groups. The pKa value of the equilibrium VmDTPA2- + H+ F V=DTPAH(1) plots and pHwas determined by both evaluation of E1/2potentiometric titrations yielding pKa=3.59. As soon as the appropriate protonated, nitrogen of the ligand is rearrangement of one terminal IDA-residue takes place. On the other hand, this opens up the possibility of and VmDTPA2quantitative determination of V=DTPAHusing fast scan differential pulse polarography, because the kinetics of the concomitant “protonationbond breakingrearangementprocess” is sluggish. [l] H.Michibata and H.Sakurai "Vanadium in Ascidians", ch.IX. in "Vanadium in Biological Systems", pp 153, N.D.Chasteen (ed.) Kluwer, Dordrecht 1990. [2] R.Meier et al., Anal.Chim.Acta 236 (1990) 315. [3] S.Lee, K.Nakanishi and K.Kustin, Biochim.Biophys.Acta m (1990) 311.
407
ELEC~ICAI, INVESTIGAl’ION OFVI“/VIII/VII COMPLEXESMODEL STUDIES FOR VANADIUM INASCIDIANS
1006 M.Hecht, Technical Sciences,
R.Meier University of Leipzig, PO Box 66, D-O-Leipzig,
Department Germany
of Natural
The fact that some ascidians accummuiate vanadium ion specifically to a level exceeding four million times that present in sea water is an unusual phenomenon and the fact that they are only the such a high level is a mystery. Recent careful reinvestigations of the content, distribution, and valency of the vanadium in several tissues of ascidians clearly show the following Cl]: (i) the highest amounts of vanadium being present in the blood cells in concentrations of up to z 100 mM (ii)tp=valency observed usally is a mixture of VI” and We have recently shown that using voltammetry specication is possible both for mixtures of VI” as and Vm as well different protolytic Vm-species [2]. Because there is still a big controversy in the literature mainly regarding the pH- value inside the ascidians blood cells and the question if the vanadium ions are complexed or we are offering here a model study of the not CL31, interaction of VI” ligand V= and VII with the diethylenetriaminepenttaacetic acid (DTPA) to demonstrate the ease of vanadium speciation with voltammetry. As completion, potentiometric and spectroscopic titrations were conducted.The titration of VmDTPA2with acid is accompanid with an intramolecular rearrangement of one of the terminal iminodiaceto (IDA) groups. The pKa value of the equilibrium VmDTPA2- + H+ F V=DTPAH(1) plots and pHwas determined by both evaluation of E1/2potentiometric titrations yielding pKa=3.59. As soon as the appropriate protonated, nitrogen of the ligand is rearrangement of one terminal IDA-residue takes place. On the other hand, this opens up the possibility of and VmDTPA2quantitative determination of V=DTPAHusing fast scan differential pulse polarography, because the kinetics of the concomitant “protonationbond breakingrearangementprocess” is sluggish. [l] H.Michibata and H.Sakurai "Vanadium in Ascidians", ch.IX. in "Vanadium in Biological Systems", pp 153, N.D.Chasteen (ed.) Kluwer, Dordrecht 1990. [2] R.Meier et al., Anal.Chim.Acta 236 (1990) 315. [3] S.Lee, K.Nakanishi and K.Kustin, Biochim.Biophys.Acta m (1990) 311.