Racemic atropisomeric N,N-chelate ligands for recognizing chiral carboxylates via Zn(II) coordination: structure, fluorescence, and circular dichroism.
Racemic atropisomeric N,N-chelate ligands for recognizing chiral carboxylates via Zn(II) coordination: structure, fluorescence, and circular dichroism.
复制标题
DOI：
10.1021/ic801269z
复制
发表时间：
2008-10
影响因子：
4.6
通讯作者：
T. McCormick;Suning Wang
中科院分区：
文献类型：
--
作者：
T. McCormick;Suning Wang
已经发现两种外消旋阻转异构的N，N ′-螯合配体，双{3，3 ′-[N-Ph-2-（2 ′-py）吲哚基]}（1）和双{3，3 ′-N-4-[N-2-（2 ′-py）吲哚基]苯基-2-（2 ′-py）吲哚基}（2），能够区分Zn（（R）-BrMeBu）2和Zn（（S）-BrMeBu）2的对映异构体，其中BrMeBu = O2 CCH（Br）CHMe 2，在约10 μ M浓度范围具有明显和强烈的CD光谱响应。计算研究证实，（R）-1-Zn（（R）-BrMeBu）2或（S）-1-Zn（（S）-BrMeBu）2非对映体比（R）-1-Zn（（S）-BrMeBu）2或（S）-1-Zn（（R）-BrMeBu）2更稳定。此外，计算研究表明（S）-1-Zn（（S）-BrMeBu）2和（S）-1-Zn（（R）-BrMeBu）2的CD光谱是相似的。(1)H NMR光谱证实，对于1和2的两种络合物，这两种非对映异构体以约2：1的比例存在于溶液中。因此，外消旋配体1和2对手性羧酸锌（II）的不同CD响应归因于一种非对映体的优先形成。通过模型化合物1-Zn（tfa）2和2-Zn（tfa）2（tfa = CF 3CO 2（-））的晶体结构确定了锌（II）盐与配体1和2的结合模式，其中Zn（II）离子被配体中的两个中心吡啶基螯合。荧光滴定实验与各种锌（II）盐表明，阻转异构体配体的荧光光谱显示阴离子依赖性的变化。已发现锌（II）与阻转异构体配体的N，N '-螯合位点的结合强度在外消旋阻转异构体配体对不同手性羧酸锌（II）衍生物的选择性识别中起关键作用。
Two racemic atropisomeric N,N'-chelate ligands, bis{3,3'-[N-Ph-2-(2'-py)indolyl]} (1) and bis{3,3'-N-4-[N-2-(2'-py)indolyl]phenyl-2-(2'-py)indolyl} (2), have been found to be able to distinguish the enantiomers of Zn((R)-BrMeBu)2 and Zn((S)-BrMeBu)2 where BrMeBu = O2CCH(Br)CHMe2, with a distinct and intense CD spectral response at approximately the 10 microM concentration range. Computational studies established that the (R)-1-Zn((R)-BrMeBu)2 or (S)-1-Zn((S)-BrMeBu)2 diastereomer is more stable than (R)-1-Zn((S)-BrMeBu)2 or (S)-1-Zn((R)-BrMeBu)2. In addition, computational studies showed that the CD spectra of (S)-1-Zn((S)-BrMeBu)2 and (S)-1-Zn((R)-BrMeBu)2 are similar. (1)H NMR spectra confirmed that these two diastereomers exist in solution in about a 2:1 ratio for both complexes of 1 and 2. The distinct CD response of the racemic ligands 1 and 2 toward the chiral zinc(II) carboxylate is therefore attributed to the preferential formation of one diastereomer. The binding modes of the zinc(II) salt with ligands 1 and 2 were established by the crystal structures of the model compounds 1-Zn(tfa)2 and 2-Zn(tfa)2 (tfa = CF3CO2(-)), where the Zn(II) ion is chelated by the two central pyridyl groups in the ligand. Fluorescent titration experiments with various zinc(II) salts showed that the fluorescent spectrum of the atropisomeric ligand displays an anion-dependent change. The zinc(II) binding strength to the N,N'-chelate site of the atropisomeric ligand has been found to play a key role in the selective recognition of different chiral zinc(II) carboxylate derivatives by the racemic atropisomeric ligands.