Chiral Amplification and Helical-Sense Tuning by Mono- and Divalent Metals on Dynamic Helical Polymers
Chiral Amplification and Helical-Sense Tuning by Mono- and Divalent Metals on Dynamic Helical Polymers
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DOI：
10.1002/anie.201105769
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Riguera, Ricardo
中科院分区：
文献类型：
--
作者：
Freire, Felix;Seco, Jose Manuel;Riguera, Ricardo
通过外部刺激[1-4]控制诱导螺旋聚合物[1]中的螺旋偏置--即选择具有较好利手性的螺旋的可能性--已成为理想的目标[2，3]，因为这些材料作为手性传感器、分子器件、手性光学开关、用于信息存储的存储元件、手性催化剂和导电材料等的潜在应用。[1-3]自从Green等人[6]在多异氰酸酯中手性放大的开创性工作[6]以来，具有手性放大特性的螺旋聚合物引起了人们的极大关注。7]在这里，我们报道了一种新型的高动态的含手性侧链的聚苯乙炔(PPA)衍生物的合成和评价。这种聚合物结合了上述两个特征(选择性螺旋诱导和手性放大)，从而提供了一种用作金属阳离子价态传感器的材料。在本文报道的手性放大中，外部刺激-触发-是通过一价或二价金属阳离子(非手性试剂)的选择性配位来提供的，这样金属的价态决定了聚合物的右旋或左旋螺旋意义及其手性反应。[8]α-甲氧基苯乙酸(MPA)通过(C6H4)NH±C(=O)酰胺键连接到苯乙炔部分，是选择的手性支链。选择这个体系是因为：1)1，2-(酰胺基甲氧基)是某些阳离子很好的螯合部分(如CD和核磁共振研究所示)[9]和2)金属螯合改变了手性MPA酰胺的反周面/共周面(AP/SP)构象平衡。[9]用这种方法，我们合成了(R)和(S)-苯乙炔单体1和2(图1a)，我们评估了它们与一价和二价阳离子(Li+，Ca+，Ba2+，Mn2+)的配位能力。二价金属阳离子的加入引起了CD光谱的反转，表明构象从AP形式转变为SP形式。这一推论得到了旋光度和1H和
The controlled induction of a helix-sense bias in helical polymers [1] by external stimuli [1–4]—that is, the possibility of selecting a helix with a preferred handedness—has become a desirable goal [2, 3] owing to the potential applications of these materials as chiral sensors, molecular devices,[5] chiro-optical switches, memory elements for information storage, chiral catalysts, and conductive materials, amongst others.[1–3] Since the pioneering work by Green et al.[6] on the amplification of chirality in polyisocyanates, helical polymers with chiral amplification properties have attracted much attention.[1–3, 7] Herein we report the synthesis and evaluation of a new and highly dynamic poly (phenylacetylene)(PPA) derivative that bears chiral pendants. This polymer incorporates the two aforementioned features (selective helix induction and chiral amplification) to give a material that acts as a sensor for the valence of metal cations. In the amplification of chirality reported herein, the external stimulus—the trigger—is provided by the selective coordination of the pendants with mono-or divalent metal cations (achiral agents) in such a way that the valence of the metal determines the right-or lefthanded helical sense of the polymer and its chiroptical response.[8] α-Methoxyphenylacetic acid (MPA), connected to the phenylacetylene moiety through a (C6H4) ÀNHÀC (= O) amide bond, was the pendant of choice. This system was selected because: 1) the 1, 2-(amide carbonyl–methoxy) moiety is an excellent chelating moiety for certain cations (as shown by CD and NMR spectroscopy studies)[9] and 2) metal chelation is known to switch the antiperiplanar/synperiplanar (ap/sp) conformational equilibrium of chiral MPA amides.[9] In this way, the (R)-and (S)-MPA phenylacetylene monomers 1 and 2 (Figure 1 a) were prepared and we assessed their capacity to coordinate with mono-and divalent cations (Li+, Ca2+, Ba2+, Mn2+). The addition of divalent metal cations induced an inversion of the CD spectrum, indicating a conformational switch from the ap to the sp form. This inference was corroborated by optical rotation and by 1H and