TERNARY COMPLEXES IN SOLUTION .35. INTRAMOLECULAR HYDROPHOBIC LIGAND LIGAND INTERACTIONS IN MIXED-LIGAND COMPLEXES CONTAINING AN ALIPHATIC AMINO-ACID
TERNARY COMPLEXES IN SOLUTION .35. INTRAMOLECULAR HYDROPHOBIC LIGAND LIGAND INTERACTIONS IN MIXED-LIGAND COMPLEXES CONTAINING AN ALIPHATIC AMINO-ACID
复制标题
DOI：
10.1021/ja00529a021
复制
发表时间：
1980-01-01
影响因子：
15
通讯作者：
SIGEL, H
中科院分区：
文献类型：
--
作者：
FISCHER, BE;SIGEL, H
M（Ar）（Aa）+型混合配体络合物，其中M2+ = Cu 2+或Zn 2+，Ar = 2，2“-联吡啶（bpy）或1，10-菲咯啉（phen），Aa- =丙氨酸酯、2-氨基丙酸酯（α-氨基丁酸盐）、正缬氨酸盐、正亮氨酸盐、缬氨酸盐、亮氨酸盐（leu）或异亮氨酸盐。电位测量揭示了稍高的形成趋势，表示为Δ。log Km = log .**图形 **。- log .**图形 **。对于以亮氨酸为氨基酸的系统，与以丙氨酸为氨基酸的系统相比。这种稳定性的增加归因于分子内疏水配体-配体之间的相互作用的芳环系统的bpy或phen和异丙基基团的亮氨酸。估计了疏水相互作用发生的开放和封闭形式之间的分子内异构体平衡的位置;例如，三元Zn（phen）（leu）+络合物在折叠态中存在约26%，即，封闭形式在不存在和存在Zn 2+的情况下对所述系统的1H NMR位移测量证实存在这样的疏水配体-配体相互作用，并且它们通过在2个反应物之间形成金属离子桥来促进。脂肪族氨基酸的侧链越长，末端甲基的高场位移越大，这是由于与三元复合物内的芳香族部分相互作用造成的。这些结果促使进行文献检索，很明显，例如，与M（phe）（ala）或M（phe）（gly）相比，M（苯丙氨酸）（酪氨酸）或M（苯丙氨酸）（正缬氨酸）具有增强的稳定性，这现在归因于分子内芳环堆积和疏水配体-配体相互作用。对于这些和其他系统（总共约40个），计算了封闭异构体的百分比;它们涵盖了高达约90%的整个范围。Δ G度从平衡常数计算的值与这种相互作用的理论预测吻合得很好。可能的生物影响进行了简要讨论。
Mixed ligand complexes of the type M(Ar)(Aa)+, where M2+ = Cu2+ or Zn2+, Ar = 2,2''-bipyridyl (bpy) or 1,10-phenanthroline (phen), and Aa- = alaninate, 2-aminopropionate (.alpha.-aminobutyrate), norvalinate, norleucinate, valinate, leucinate (leu), or isoleucinate, were studied by potentiometric pH titrations and 1H NMR. The potentiometric measurements reveal a slightly higher formation tendency, expressed as .DELTA. log Km = log .**GRAPHIC**. - log .**GRAPHIC**. for the systems with leucinate as amino acid compared to those with alaninate. This increase in stability is attributed to an intramolecular hydrophobic ligand-ligand interaction between the aromatic ring system of bpy or phen and the isopropyl group of leucine. The position of the intramolecular isomeric equilibrium between an open and closed form, in which the hydrophobic interaction occurs, was estimated; e.g., the ternary Zn(phen)(leu)+ complex exists about 26% in the folded, i.e., closed form. 1H NMR shift measurements of the mentioned systems in the absence and presence of Zn2+ confirmed that such hydrophobic ligand-ligand interactions exist and that they are promoted by the formation of a metal-ion bridge between the 2 reactants. The longer the side chain of the aliphatic amino acid, the larger is the upfield shift of the terminal methyl group(s), resulting from the interaction with the aromatic moiety within the ternary complex. These results prompted a literature search and it became evident that, e.g., M(phenylalaninate) (tyrosinate) or M(phenylalaninate) (norvalinate) have an enhanced stability, compared with M(phe)(ala) or M(phe)(gly), and this is now attributed to intramolecular aromatic-ring stacking and hydrophobic ligand-ligand interactions. For these and other systems (in total about 40) the percentages of the closed isomer were calculated; they cover the whole range till up to about 90%. The .DELTA.G.degree. values calculated from the equilibrium constants agree well with the theoretical predictions for such interactions. Possible biological implications are briefly discussed.