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首页> 外文期刊>Chemistry: A European journal >Mixed Adenine/Guanine Quartets with Three trans-a_2Pt~(II) (a=NH_3 or MeNH_2) Cross-Links: Linkage and Rotational Isomerism, Base Pairing, and Loss of NH_3
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Mixed Adenine/Guanine Quartets with Three trans-a_2Pt~(II) (a=NH_3 or MeNH_2) Cross-Links: Linkage and Rotational Isomerism, Base Pairing, and Loss of NH_3

机译：具有三个反式-a_2Pt〜（II）（a = NH_3或MeNH_2）交联的腺嘌呤/鸟嘌呤混合四元组：链接和旋转异构，碱基配对和NH_3的损失

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摘要

Of the numerous ways in which two adenine and two guanines (N9 positions blocked in each) can be crosslinked by three linear metal moieties such as trans-a_2Pt~(II) (with a=NH_3 or MeNH_2) to produce open metalated purine quartets with exclusive metal coordination through N1 and N7 sites, one linkage isomer was studied in detail. The isomer trans,trans,trans-[{Pt(NH_3)_2(N7-9-EtA-N1)_2}{Pt- (MeNH_2)_2(N7-9-MeGH)}_2][(ClO_4)_6]·3H_2O (1) (with 9-EtA=9-ethyladenine and 9-MeGH=9-methylguanine) was crystallized from water and found to adopt a flat Z-shape in the solid state as far as the trinuclear cation is concerned. In the presence of excess 9-MeGH, a meander-like construct, trans,trans,trans-[{Pt(NH_3)_2(N7-9-EtA-N1)_2}{Pt(MeNH_2)_2(N7-9- MeGH)_2}][(ClO_4)_6]·[(9-MeGH)_2]·7H_2O (2) is formed, in which the two extra 9-MeGH nucleobases are hydrogen bonded to the two terminal platinated guanine ligands of 1. Compound 1, and likewise the analogous complex 1a (with NH_3 ligands only), undergo loss of an ammonia ligand and formation of NH_4~+ when dissolved in [D_6]DMSO. From the analogy between the behavior of 1 and 1a it is concluded that a NH_3 ligand from the central Pt atom is lost. Addition of 1- methylcytosine (1-MeC) to such a DMSO solution reveals coordination of 1-MeC to the central Pt. In an analogous manner, 9-MeGH can coordinate to the central Pt in [D_6]DMSO. It is proposed that the proton responsible for formation of NH_4~+ is from one of the exocyclic amino groups of the two adenine bases, and furthermore, that this process is accompanied by a conformational change of the cation from Z-form to U-form. DFT calculations confirm the proposed mechanism and shed light on possible pathways of this process. Calculations show that rotational isomerism is not kinetically hindered and that it would preferably occur previous to the displacement of NH_3 by DMSO. This displacement is the most energetically costly step, but it is compensated by the proton transfer to NH_3 and formation of U(-H~+) species, which exhibits an intramolecular hydrogen bond between the deprotonated N6H~- of one adenine and the N6H_2 group of the other adenine. Finally the question is examined, how metal cross-linking patterns in closed metallacyclic quartets containing two adenine and two guanine nucleobases influence the overall shape (square, rectangle, trapezoid) and the planarity of a metalated purine quartet.
机译：在许多方式中，两个腺嘌呤和两个鸟嘌呤（每个N9位置均受阻）可以通过三个线性金属部分（例如，trans-a_2Pt〜（II）（a = NH_3或MeNH_2））进行交联，从而生成具有通过N1和N7位点的唯一金属配位，详细研究了一种连接异构体。异构体反式，反式，反式-[{Pt（NH_3）_2（N7-9-EtA-N1）_2} {Pt-（MeNH_2）_2（N7-9-MeGH）} _ 2] [（ClO_4）_6]·从水中结晶出3H_2O（1）（具有9-EtA = 9-乙基腺嘌呤和9-MeGH = 9-甲基鸟嘌呤），就三核阳离子而言，发现其呈固态呈扁平Z形。在过量的9-MeGH存在下，蜿蜒状的构建体，反式，反式，反式-[{Pt（NH_3）_2（N7-9-EtA-N1）_2} {Pt（MeNH_2）_2（N7-9- MeGH）_2}] [（ClO_4）_6]·[（9-MeGH）_2]·7H_2O（2）形成，其中两个额外的9-MeGH核碱基氢键合到1的两个末端铂化鸟嘌呤配体上。当溶于[D_6] DMSO中时，化合物1以及类似的络合物1a（仅具有NH_3配体）会损失氨配体并形成NH_4〜+。从1和1a的行为之间的类比可以得出结论，中心Pt原子失去了NH_3配体。在这种DMSO溶液中添加1-甲基胞嘧啶（1-MeC）可显示1-MeC与中心Pt的配位。以类似的方式，9-MeGH可以与[D_6] DMSO中的中心Pt协调。提出负责形成NH_4〜+的质子来自两个腺嘌呤碱基的环外氨基之一，此外，该过程还伴随着阳离子从Z型到U型的构象变化。 。 DFT计算证实了提出的机制，并阐明了该过程的可能途径。计算表明，旋转异构现象在动力学上没有受到阻碍，并且优选在DMSO取代NH_3之前发生。这种置换是最耗费能量的步骤，但是可以通过质子转移到NH_3和形成U（-H〜+）物种来补偿，该置换在一个腺嘌呤的去质子化的N6H〜-和N6H_2基团之间显示出分子内氢键。其他腺嘌呤。最后，研究了这个问题，即在包含两个腺嘌呤和两个鸟嘌呤核碱基的封闭金属杂环四元组中，金属的交联方式如何影响金属化嘌呤四元组的整体形状（正方形，矩形，梯形）和平面度。

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