Force Spectroscopy of Metal-Crown Ether Multivalency: Effect of Local Environments on Energy Landscape and Sensing Kinetics

• Published in: Angewandte Chemie Vol. 127; no. 32; pp. 9345 - 9349
• Main Authors: Kuo, Ting-Yang, Tseng, Wei-Hsiang, Chen, Chun-hsien
• Format: Journal Article
• Language: English; German
• Published: Weinheim WILEY-VCH Verlag 03.08.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Alkali metals; Atomic force microscopy; Cations; Chemistry; Complexation; Ethers; Ionen-Molekül-Reaktionen; Kronenverbindungen; Landscapes; Molekulare Erkennung; Reaktionskinetik; Recognition; Sandwich-Komplexe; Spectroscopy
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201503948

Sandwich complexation involving alkali or alkaline‐earth metals, multivalency, and effects associated with local environments is widely encountered in biological and synthetic systems yet the mechanic properties remain unexplored. Herein, AFM (atomic force microscopy)‐based single‐molecule force spectroscopy is employed to investigate a classical model of Mn+[15C5]2, a metal cation hosted jointly by two 15‐crown‐5 moieties immobilized on both the substrate and the AFM tip. Factors reportedly promoting the recognition performance are examined. The rupture force required to break apart Mn+[15C5]2 is found to be in the order of tens of pico‐Newton, e.g., fβ=31 pN for K+[15C5]2. The presence of a second functional group, carboxylate, confers K+[15C5]2 with a longer lifetime (from 13 to 16 ms), faster association (from 0.4 to 1.3×106 M−1 s−1), and slower dissociation (from 77 to 62 s−1). The effect of local environments is significant on association yet less critical on dissociation pathways. Die mechanische Stärke von multivalenten Metall‐Kronenether‐Wechselwirkungen wird mittels Einzelmolekül‐Kraftspektroskopie quantitativ bestimmt. Die Bruchkraft liegt im zweistelligen Pikonewton‐Bereich. Dynamische Kraftspektroskopie zeigt, dass der Einfluss der unmittelbaren Umgebung auf die Assoziation deutlich, auf die Dissoziation jedoch relativ unbedeutend ist.