Molecular Dynamics Study of Crystalline Molecular Gyroscopes

Molecular machines and rotors are important functional components in all living organisms, playing critical roles in processes such as muscle contraction, cell division, motility, supporting cellular metabolism, vesicle and neuronal transport, as well as signaling and energy processing in cellular membranes. 7 High efficiency, flexibility, and robustness of biological nanomachines have stimulated significant experimental efforts to develop artificial molecular devices with potentially wide applications in nanotechnology, material science, and medicine. 21 Although many synthetic successes in this area have been reported, direct application of molecular motors and rotors in technology is still far away from the practical realization mainly because fundamental mechanisms of functioning of such systems are not well understood yet. One of the most promising directions in creating artificial molecular machines has been investigations of molecular rotors systems. Different systems that include molecular rotors working in solutions, 25 in liquid crystals, on surfaces, 35 and in solid-state medium 43 have been reported in various experimental studies. These works have stimulated multiple theoretical investigations of mechanisms and properties of molecular rotors. 50 These studies allowed researchers to understand better the dynamics of many molecular rotors at the single-molecule level. However, many fundamental questions concerning microscopic mechanisms of functioning of such systems remain unanswered. A new class of molecular rotors functioning in solid-state environment has been developed recently. 42 These materials, known as amphidynamic crystals (also called molecular gyroscopes), have been created synthetically by designing systems where strong translational interactions are uncoupled from internal rotational motions. Thermally activated internal rotations in these solid-state molecular systems have been confirmed via temperature-dependent nuclear magnetic resonance (NMR) dynamic analysis. In another study, it was argued that higher symmetry order to the rotator segment must lead to lower rotational barriers. However, analysis of experimental observations indicates that symmetry alone can only partially explain some dynamic features ofmolecular rotations. In this paper, we present a theoretical investigation of amphidynamic crystals concentrating on the role of intramolecular interactions, vibrations, coupling, and flexibility of different segments. Our goal here is to develop a simple theoretical approach that would combine minimalist computational method with phenomenological arguments in order to get qualitative understanding of physical-chemical mechanisms of underlying phenomena.