Farkas Etelka, Szabó Orsolya, Parajdi-Losonczi Péter L, Balla György, Pócsi István
Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4010 Debrecen, POB 21, Hungary.
MTA-DE Homogenous Catalysis and Reaction Mechanisms Research Group, Debrecen, Hungary.
J Inorg Biochem. 2014 Oct;139:30-7. doi: 10.1016/j.jinorgbio.2014.06.005. Epub 2014 Jun 11.
Manganese(II) and manganese(III) complexes of the exocyclic desferricrocin (H3DFCR) and endocyclic triacetylfusarinine C (H3TAF) in solution have been studied by using pH-potentiometry, UV-Vis spectrophotometry, relaxometry and cyclic voltammetry. A comparison between the present results and the corresponding ones for the open-chain analogues, desferrioxamine B (DFB) and desferricoprogen (DFC), shows (i) The dissociation processes of H3DFCR occur in the expected pH-range (pH7-10.5), but hydrogen bonding is assumed to be responsible for a quite low proton dissociation constant (pK=4.18) of H3TAF and also an unusually high one (10.59). (ii) Moderate stability complexes with 1:1 Mn(II) to ligand ratio are formed with all four siderophores. (iii) The coordination of the three hydroxamates of a siderophore takes place in stepwise processes, except the case of desferricrocin, with which, large-extent overlapping of the processes occurs. (iv) Out of the four tris-chelated [ML] type complexes, the complex of DFCR is the most compact, as it is indicated by the relaxivity values. (v) Following the stoichiometric oxidation of the Mn(II)-siderophore complexes at pH≥9, tris-chelated Mn(III) complexes are formed. To make a comparison between the stability of the Mn(III) and the corresponding Fe(III) complexes of DFCR and TAF, the determination of the stability of the Fe(III) complexes under our condition has also been performed, by using UV-Vis spectrophotometry. Comparable stability of the corresponding complexes was found. (vi) Correlation study of the stability constants resulted in estimation of the constant of the Mn(III) monohydroxo complex, for which there was no data in the literature under our conditions.
已通过pH电位滴定法、紫外可见分光光度法、弛豫测量法和循环伏安法对溶液中环外去铁铁载体（H3DFCR）和环内三乙酰富萨里宁C（H3TAF）的锰（II）和锰（III）配合物进行了研究。将目前的结果与开链类似物去铁胺B（DFB）和去铁铁载体蛋白（DFC）的相应结果进行比较，结果表明：（i）H3DFCR的解离过程发生在预期的pH范围内（pH 7 - 10.5），但氢键被认为是H3TAF质子解离常数相当低（pK = 4.18）以及一个异常高的值（10.59）的原因。（ii）所有四种铁载体均形成了1:1 Mn（II）与配体比例的中等稳定性配合物。（iii）除去铁铁载体蛋白的情况外，铁载体的三个异羟肟酸酯的配位过程是分步进行的，而去铁铁载体蛋白的配位过程存在很大程度的重叠。（iv）在四种三螯合[ML]型配合物中，DFCR的配合物最为紧密，弛豫率值表明了这一点。（v）在pH≥9时，Mn（II）-铁载体配合物进行化学计量氧化后，形成了三螯合Mn（III）配合物。为了比较DFCR和TAF的Mn（III）配合物与相应Fe（III）配合物的稳定性，还通过紫外可见分光光度法在我们的条件下测定了Fe（III）配合物的稳定性。发现相应配合物具有可比的稳定性。（vi）稳定性常数的相关性研究得出了Mn（III）单羟基配合物常数的估计值，在我们的条件下，文献中没有该数据。
