Mareda Jiri, Matile Stefan
Department of Organic Chemistry, University of Geneva, Geneva, Switzerland.
Chemistry. 2009;15(1):28-37. doi: 10.1002/chem.200801643.
The recognition and transport of anions is usually accomplished by hydrogen bonding, ion pairing, metal coordination, and anion-dipole interactions. Here, we elaborate on the concept to use anion-pi interactions for this purpose. Different to the popular cation-pi interactions, applications of the complementary pi-acidic surfaces do not exist. This is understandable because the inversion of the aromatic quadrupole moment to produce pi-acidity is a rare phenomenon. Here, we suggest that pi-acidic aromatics can be linked together to produce an unbendable scaffold with multiple binding sites for anions to move along across a lipid bilayer membrane. The alignment of multiple anion-pi sites is needed to introduce a cooperative multi-ion hopping mechanism. Experimental support for the validity of the concept comes from preliminary results with oligonaphthalenediimide (O-NDI) rods. Predicted by strongly positive facial quadrupole moments, the cooperativity and chloride selectivity found for anion transport by O-NDI rods were consistent with the existence of anion-pi slides. The proposed mechanism for anion transport is supported by DFT results for model systems, as well as MD simulations of rigid O-NDI rods. Applicability of anion-pi slides to achieve electroneutral photosynthesis is elaborated with the readily colorizable oligoperylenediimide (O-PDI) rods. To clarify validity, scope and limitations of these concepts, a collaborative research effort will be needed to address by computer modeling and experimental observations the basic questions in simple model systems and to design advanced multifunctional anion-pi architectures.
阴离子的识别和传输通常通过氢键、离子对、金属配位和阴离子 - 偶极相互作用来实现。在此，我们详细阐述利用阴离子 - π相互作用来实现这一目的的概念。与常见的阳离子 - π相互作用不同，互补的π酸性表面尚无应用实例。这是可以理解的，因为使芳香四极矩反转以产生π酸性是一种罕见的现象。在此，我们提出π酸性芳烃可以连接在一起，形成一个不可弯曲的支架，具有多个阴离子结合位点，以便阴离子能沿着脂质双分子层膜移动。需要多个阴离子 - π位点的排列来引入协同多离子跳跃机制。对该概念有效性的实验支持来自寡聚萘二酰亚胺（O - NDI）棒的初步结果。由强正的面四极矩预测，O - NDI棒对阴离子传输所发现的协同性和氯离子选择性与阴离子 - π滑动的存在一致。阴离子传输的 proposed 机制得到了模型系统的密度泛函理论（DFT）结果以及刚性O - NDI棒的分子动力学（MD）模拟的支持。利用易于显色的寡聚苝二酰亚胺（O - PDI）棒阐述了阴离子 - π滑动在实现电中性光合作用方面的适用性。为了阐明这些概念的有效性、范围和局限性，需要通过计算机建模和实验观察来共同研究，以解决简单模型系统中的基本问题，并设计先进的多功能阴离子 - π结构。
