Mechanical stability of bivalent transition metal complexes analyzed by single-molecule force spectroscopy.

Manuel Gensler,Jürgen P Rabe,Maurice Taszarek,Christian Eidamshaus,Hans-Ulrich Reissig

doi:10.3762/bjoc.11.91

Abstract

Multivalent biomolecular interactions allow for a balanced interplay of mechanical stability and malleability, and nature makes widely use of it. For instance, systems of similar thermal stability may have very different rupture forces. Thus it is of paramount interest to study and understand the mechanical properties of multivalent systems through well-characterized model systems. We analyzed the rupture behavior of three different bivalent pyridine coordination complexes with Cu2+ in aqueous environment by single-molecule force spectroscopy. Those complexes share the same supramolecular interaction leading to similar thermal off-rates in the range of 0.09 and 0.36 s−1, compared to 1.7 s−1 for the monovalent complex. On the other hand, the backbones exhibit different flexibility, and we determined a broad range of rupture lengths between 0.3 and 1.1 nm, with higher most-probable rupture forces for the stiffer backbones. Interestingly, the medium-flexible connection has the highest rupture forces, whereas the ligands with highest and lowest rigidity seem to be prone to consecutive bond rupture. The presented approach allows separating bond and backbone effects in multivalent model systems.

Highlights

In a multivalent molecular system, two partners interact with each other through two or more non-covalent equivalent interaction centers
In the present work we address the question, if it is possible to tune the balanced interplay between most-probable rupture forces and rupture lengths by changing the backbone connection of the pyridine model system into more flexible analogues
By performing dynamic force spectroscopy (DFS) according to the KBE model we show that the rupture length may be similar to the monovalent rupture length for the system with medium flexibility 2b (2 sp3 carbons in the backbone, rb = 0.30 nm) and even larger for the system with high flexibility 2c (3 sp3 carbons + 2 ether groups in the backbone, rb = 1.12 nm)

Summary

Introduction

In a multivalent molecular system, two partners interact with each other through two or more non-covalent equivalent interaction centers. This principle is important in biochemistry [1] and supramolecular chemistry [2], but still not fully understood on the level of individual non-covalent interactions [3]. Synthetic supramolecular systems are ideal for a quantitative analysis of multivalency on the level of single molecules, because specific ligand design can be used to study selected parameters [4,5]. The mechanical stability of a molecular system is characterized by its rupture forces under a given loading rate.

Objectives

Results

Conclusion