Institute of General Food Chemistry, Technical University of Lodz, Lodz, Poland.
Inorg Chem. 2011 Feb 7;50(3):883-99. doi: 10.1021/ic101475x. Epub 2011 Jan 12.
The complexation of V(IV)O(2+) ion with 10 picolinate and quinolinate derivatives, provided with the donor set (N, COO(-)), was studied in aqueous solution and in the solid state through the combined application of potentiometric (pH-titrations), spectroscopic (EPR, UV/vis and IR spectroscopy), and computational (density functional theory (DFT) calculations) methods. Such derivatives, that form potent insulin-enhancing V(IV)O(2+) compounds, are picolinic (picH), 6-methylpicolinic (6-mepicH), 3-methylpicolinic (3-mepicH), 5-butylpicolinic or fusaric (fusarH), 6-methyl-2,3-pyridindicarboxylic (6-me-2,3-pdcH(2)), 2-pyridylacetic (2-pyacH), 2-quinolinecarboxylic or quinaldic (quinH), 4-hydroxyquinoline-2-carboxylic or kynurenic (kynurH), 1-isoquinolinecarboxylic (1-iqcH) and 3-isoquinolinecarboxylic (3-iqcH) acid. On the basis of the potentiometric, spectroscopic, and DFT results, they were divided into the classes A, B, and C. The ligands belonging to class A (3-mepicH, 1-iqcH, 2-pyacH) form square pyramidal complexes in aqueous solution and in the solid state, and those belonging to class B (picH, fusarH, 3-iqcH) form cis-octahedral species, in which the two ligands adopt an (equatorial-equatorial) and an (equatorial-axial) arrangement and one water molecule occupies an equatorial site in cis position with respect to the V═O bond. Class C ligands (6-mepicH, 6-me-2,3-pdcH(2), quinH, kynurH) yield bis chelated species, that in water are in equilibrium between the square pyramidal and trans-octahedral form, where both the ligand molecules adopt an (equatorial-equatorial) arrangement and one water is in trans position with respect to the V═O group. The trans-octahedral compounds are characterized by an anomalous electron paramagnetic resonance (EPR) response, with A(z) value being reduced by about 10% with respect to the prediction of the "additivity rule". DFT methods allow to calculate the structure, (51)V hyperfine coupling constant (A(z)), the stretching frequency of V═O bond (ν(V═O)), the relative stability in aqueous solution, and the electronic structure and molecular orbital composition of bis chelated complexes. The results were used to explain the biotransformation of these potent insulin-enhancing compounds in blood serum.
本文通过电位（pH 滴定）、光谱（电子顺磁共振、紫外/可见和红外光谱）和计算（密度泛函理论（DFT）计算）方法的综合应用，研究了 V(IV)O(2+)离子与 10 个吡啶酸盐和喹啉酸盐衍生物的络合作用，这些衍生物提供了供体（N、COO(-)）。这些衍生物形成了有效的胰岛素增强 V(IV)O(2+)化合物，包括吡啶酸（picH）、6-甲基吡啶酸（6-mepicH）、3-甲基吡啶酸（3-mepicH）、5-丁基吡啶酸或呋咱酸（fusarH）、6-甲基-2,3-吡啶二甲酸（6-me-2,3-pdcH(2)）、2-吡啶基乙酸（2-pyacH）、2-喹啉羧酸或喹哪啶酸（quinH）、4-羟基喹啉-2-羧酸或犬尿酸（kynurH）、1-异喹啉羧酸（1-iqcH）和 3-异喹啉羧酸（3-iqcH）。基于电位、光谱和 DFT 结果，它们被分为 A、B 和 C 类。属于 A 类的配体（3-mepicH、1-iqcH、2-pyacH）在水溶液和固态中形成四方锥络合物，属于 B 类的配体（picH、fusarH、3-iqcH）形成顺式八面体物种，其中两个配体采用（赤道-赤道）和（赤道-轴向）排列，一个水分子占据顺式位置相对于 V═O 键的赤道位。C 类配体（6-mepicH、6-me-2,3-pdcH(2)、quinH、kynurH）生成双螯合物种，在水中处于四方锥和反式八面体形式之间的平衡，其中两个配体分子采用（赤道-赤道）排列，一个水分子位于 V═O 基团的反式位置。反式八面体化合物的电子顺磁共振（EPR）响应具有异常特征，A(z)值相对于“加和规则”的预测降低了约 10%。DFT 方法可以计算结构、（51）V 超精细耦合常数（A(z)）、V═O 键的伸缩频率（ν(V═O)）、在水溶液中的相对稳定性以及双螯合络合物的电子结构和分子轨道组成。这些结果用于解释这些有效的胰岛素增强化合物在血清中的生物转化。
