Wirgau Joseph I, Spasojević Ivan, Boukhalfa Hakim, Batinić-Haberle Ines, Crumbliss Alvin L
Department of Chemistry, Duke University, Box 90346, Durham, North Carolina 27708-0346, USA.
Inorg Chem. 2002 Mar 25;41(6):1464-73. doi: 10.1021/ic0109795.
pK(a) values for the hydroxamic acid, alpha-NH(3)(+), and epsilon-NH(3)(+) groups of L-lysinehydroxamic acid (LyHA, H(3)L(2+)) were found to be 6.87, 8.89, and 10.76, respectively, in aqueous solution (I = 0.1 M, NaClO(4)) at 25 degrees C. O,O coordination to Fe(III) by LyHA is supported by H(+) stoichiometry, UV-vis spectral shifts, and a shift in nu(CO) from 1648 to 1592 cm(-1) upon formation of mono(L-lysinehydroxamato)tetra(aquo)iron(III) (Fe(H(2)L)(H(2)O)(4)(4+)). The stepwise formation of tris(L-lysinehydroxamato)iron(III) from Fe(H(2)O)(6)(3+) and H(3)L(2+) was characterized by spectrophotometric titration, and the values for log beta(1), log beta(2), and log beta(3) are 6.80(9), 12.4(2), and 16.1(2), respectively, at 25 degrees C and I = 2.0 M (NaClO(4)). Stopped-flow spectrophotometry was used to study the proton-driven stepwise ligand dissociation kinetics of tris(L-lysinehydroxamato)iron(III) at 25 degrees C and I = 2.0 M (HClO(4)/NaClO(4)). Defining k(n) and k(-n) as the stepwise ligand dissociation and association rate constants and n as the number of bound LyHA ligands, k(3), k(-3), k(2), k(-2), k(1), and k(-1) are 3.0 x 10(4), 2.4 x 10(1), 3.9 x 10(2), 1.9 x 10(1), 1.4 x 10(-1), and 1.2 x 10(-1) M(-1) s(-1), respectively. These rate and equilibrium constants are compared with corresponding constants for Fe(III) complexes of acetohydroxamic acid (AHA) and N-methylacetohydroxamic acid (NMAHA) in the form of a linear free energy relationship. The role of electrostatics in these complexation reactions to form the highly charged Fe(LyHA)(3)(6+) species is discussed, and an interchange mechanism mediated by charge repulsion is presented. The reduction potential for tris(L-lysinehydroxamato)iron(III) is -214 mV (vs. NHE), and a comparison to other hydroxamic acid complexes of Fe(III) is made through a correlation between E(1/2) and pFe.
在25℃、离子强度I = 0.1 M（高氯酸钠）的水溶液中，发现L-赖氨酸异羟肟酸（LyHA，H₃L²⁺）的异羟肟酸基团、α-NH₃⁺基团和ε-NH₃⁺基团的pK(a)值分别为6.87、8.89和10.76。LyHA与Fe(III)的O,O配位作用得到了H⁺化学计量学、紫外-可见光谱位移以及在形成单（L-赖氨酸异羟肟酸根）四（水）合铁（III）（Fe(H₂L)(H₂O)₄⁴⁺）时ν(CO)从1648 cm⁻¹移至1592 cm⁻¹的支持。通过分光光度滴定对Fe(H₂O)₆³⁺和H₃L²⁺逐步形成三（L-赖氨酸异羟肟酸根）合铁（III）的过程进行了表征，在25℃、I = 2.0 M（高氯酸钠）条件下，logβ₁、logβ₂和logβ₃的值分别为6.80(9)、12.4(2)和16.1(2)。采用停流分光光度法研究了在25℃、I = 2.0 M（高氯酸/高氯酸钠）条件下三（L-赖氨酸异羟肟酸根）合铁（III）质子驱动的逐步配体解离动力学。将k(n)和k(-n)定义为逐步配体解离和缔合速率常数，n为结合的LyHA配体数，k₃、k₋₃、k₂、k₋₂、k₁和k₋₁分别为3.0×10⁴、2.4×10¹、3.9×10²、1.9×10¹、1.4×10⁻¹和1.2×10⁻¹ M⁻¹ s⁻¹。以线性自由能关系的形式将这些速率和平衡常数与乙酰异羟肟酸（AHA）和N-甲基乙酰异羟肟酸（NMAHA）的Fe(III)配合物的相应常数进行了比较。讨论了静电作用在这些形成高电荷Fe(LyHA)₃⁶⁺物种的络合反应中的作用，并提出了由电荷排斥介导的交换机制。三（L-赖氨酸异羟肟酸根）合铁（III）的还原电位为 -214 mV（相对于标准氢电极），并通过E(1/2)与pFe之间的相关性对其与其他Fe(III)异羟肟酸配合物进行了比较。
