Complexes Formed in Solution Between Vanadium(IV)/(V) and the Cyclic Dihydroxamic Acid Putrebactin or Linear Suberodihydroxamic Acid

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• 作者：Amalie A. H. Pakchung ; Cho Zin Soe ; Tulip Lifa ; Rachel Codd
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：July 4, 2011
• 年：2011
• 卷：50
• 期：13
• 页码：5978-5989
• 全文大小：1148K
• 年卷期：v.50,no.13(July 4, 2011)
• ISSN：1520-510X

文摘

An aerobic solution prepared from V(IV) and the cyclic dihydroxamic acid putrebactin (pbH₂) in 1:1 H₂O/CH₃OH at pH = 2 turned from blue to orange and gave a signal in the positive ion electrospray ionization mass spectrometry (ESI-MS) at m/z_obs 437.0 attributed to the monooxoV(V) species [V^VO(pb)]⁺ ([C₁₆H₂₆N₄O₇V]⁺, m/z_calc 437.3). A solution prepared as above gave a signal in the ⁵¹V NMR spectrum at 未_V = 鈭?43.3 ppm (VOCl₃, 未_V = 0 ppm) and was electron paramagnetic resonance silent, consistent with the presence of [V^VO(pb)]⁺. The formation of [V^VO(pb)]⁺ was invariant of [V(IV)]:[pbH₂] and of pH values over pH = 2鈥?. In contrast, an aerobic solution prepared from V(IV) and the linear dihydroxamic acid suberodihydroxamic acid (sbhaH₄) in 1:1 H₂O/CH₃OH at pH values of 2, 5, or 7 gave multiple signals in the positive and negative ion ESI-MS, which were assigned to monomeric or dimeric V(V)鈥?or V(IV)鈥搒bhaH₄ complexes or mixed-valence V(V)/(IV)鈥搒bhaH₄ complexes. The complexity of the V-sbhaH₄ system has been attributed to dimerization (2[V^VO(sbhaH₂)]⁺ 鈫?[(V^VO)₂(sbhaH₂)₂]²⁺), deprotonation ([V^VO(sbhaH₂)]⁺ 鈥?H⁺ 鈫?[V^VO(sbhaH)]⁰), and oxidation ([V^IVO(sbhaH₂)]⁰ 鈥揺^{鈥?/sup> 鈫?[VVO(sbhaH₂)]+) phenomena and could be described as the sum of two pH-dependent vectors, the first comprising the deprotonation of hydroxamate (low pH) to hydroximate (high pH) and the second comprising the oxidation of V(IV) (low pH) to V(V) (high pH). Macrocyclic pbH₂ was preorganized to form [VVO(pb)]+, which would provide an entropy-based increase in its thermodynamic stability compared to V(V)鈥搒bhaH₄ complexes. The half-wave potentials from solutions of [V(IV)]:[pbH₂] (1:1) or [V(IV)]:[sbhaH₄] (1:2) at pH = 2 were E_1/2 鈭?35 or 鈭?52 mV, respectively, which differed from the expected trend (E_1/2 [VO(pb)]+/0 < VV/IV鈥搒bhaH₄). The complex solution speciation of the V(V)/(IV)鈥搒bhaH₄ system prevented the determination of half-wave potentials for single species. The characterization of [VVO(pb)]+ expands the small family of documented V鈥搒iderophore complexes relevant to understanding V transport and assimilation in the biosphere.}