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首页> 外文OA文献 >Mixed adenine/guanine quartets with three trans-a2Pt II (a=NH3 or MeNH2) cross-links: Linkage and rotational isomerism, base pairing, and loss of NH3
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Mixed adenine/guanine quartets with three trans-a2Pt II (a=NH3 or MeNH2) cross-links: Linkage and rotational isomerism, base pairing, and loss of NH3

机译：具有三个反式a2Pt II（a = NH3或MeNH2）交联的腺嘌呤/鸟嘌呤四联体：链接和旋转异构，碱基配对和NH3丢失

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摘要

Of the numerous ways in which two adenine and two guanines (N9 positions blocked in each) can be cross-linked by three linear metal moieties such as trans-a2PtII (with a=NH3 or MeNH2) 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(NH3)2(N7-9-EtA-N1) 2}{Pt(MeNH2)2(N7-9-MeGH)}2] [(ClO4)6]·3H2O (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(NH3)2(N7-9-EtA-N1) 2}{Pt(MeNH2)2(N7-9-MeGH)2}] [(ClO4)6]·[(9-MeGH)2]·7 H 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 1 a (with NH3 ligands only), undergo loss of an ammonia ligand and formation of NH4 + when dissolved in [D6]DMSO. From the analogy between the behavior of 1 and 1 a it is concluded that a NH3 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 [D6]DMSO. It is proposed that the proton responsible for formation of NH4 + 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 NH3 by DMSO. This displacement is the most energetically costly step, but it is compensated by the proton transfer to NH3 and formation of U(-H+) species, which exhibits an intramolecular hydrogen bond between the deprotonated N6H- of one adenine and the N6H2 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. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
机译：在许多方式中，两个腺嘌呤和两个鸟嘌呤（每个N9位置均被封闭）可以通过三个线性金属部分（例如，trans-a2PtII（具有a = NH3或MeNH2））交联，以生成具有排他性金属的开放金属化嘌呤四重态通过N1和N7位点的配位，详细研究了一种连接异构体。异构体反式，反式，反式-[{Pt（NH3）2（N7-9-EtA-N1）2} {Pt（MeNH2）2（N7-9-MeGH）} 2] [（ClO4）6]·3H2O （1）（具有9-EtA ＝ 9-乙基腺嘌呤和9-MeGH ＝ 9-甲基鸟嘌呤）从水中结晶，并且就三核阳离子而言，发现其呈固态的扁平Z形。在过量的9-MeGH存在下，蜿蜒状的结构，反式，反式，反式-[{Pt（NH3）2（N7-9-EtA-N1）2} {Pt（MeNH2）2（N7-9- MeGH）2}] [（ClO4）6]·[（9-MeGH）2]·7 H 2O（2）形成，其中两个额外的9-MeGH核碱基氢键合到两个（9）-MeGH的鸟嘌呤鸟嘌呤配体上1.化合物1以及类似的络合物1a（仅具有NH 3配体），当溶解在[D6] DMSO中时，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原子的NH3配体丢失了。在这种DMSO溶液中添加1-甲基胞嘧啶（1-MeC）可揭示1-MeC与中心Pt的配位。以类似的方式，9-MeGH可以与[D6] 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，该过程伴随阳离子从Z-型变为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，并且它最好在DMSO取代NH3之前发生。这种置换是最耗费能量的步骤，但可以通过将质子转移到NH3和形成U（-H +）来补偿，该置换在一个腺嘌呤的去质子化N6H-和另一个腺嘌呤的N6H2基团之间显示出分子内氢键腺嘌呤。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（方形，矩形，梯形）和平面度。 ©2014 WILEY-VCH Verlag GmbH＆Co. KGaA，Weinheim。

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