Symmetry and dynamics of molecular rotors in amphidynamic molecular crystals

Abstract

Rotary biomolecular machines rely on highly symmetric supramolecular structures with rotating units that operate within a densely packed frame of reference, stator, embedded within relatively rigid membranes. The most notable examples are the enzyme FoF1 ATP synthase and the bacterial flagellum, which undergo rotation in steps determined by the symmetries of their rotators and rotating units. Speculating that a precise control of rotational dynamics in rigid environments will be essential for the development of artificial molecular machines, we analyzed the relation between rotational symmetry order and equilibrium rotational dynamics in a set of crystalline molecular gyroscopes with rotators having axial symmetry that ranges from two-to fivefold. The site exchange frequency for these molecules in their closely related crystals at ambient temperature varies by several orders of magnitude, up to ca. 4.46 × 10 8 s −1 .solid-state NMR | line shape analysis | spin-lattice relaxation | molecular design | crystal engineering

Synthesis and characterization of dissymmetric molecular rotors based on 1,4-diethynylphenylene rotators and steroidal/trityl type stators

“…Garcia-Garibay and co-workers recently reported the synthesis of symmetric molecular rotors with triphenylsilyl stators, exploiting that the C sp2 -Si bond length (1.86 Å ) [27] is longer than C sp2 -C sp3 (1.48 Å ) [17]. Particularly, the deuterated phenylene rotor was crystallized by slow evaporation of dichloromethane resulting in a single crystal solvent-free sample.…”

“…Efforts to control the rotational motion were based on the use of rotators with higher axial symmetry [17] to reduce the activation energies and on changes of the static components. Stators with a wide variety of architectures capable of isolating the rotary part such as triptycenes [18], pentiptycenes [19], MOFs [20], self-assembled structures [21], and steroids [22,23] have been investigated.…”

Well-Tempered Metadynamics as a Tool for Characterizing Multi-Component, Crystalline Molecular Machines

“…Experimentally, UV-vis spectroscopy 10,12 and increasingly, NMR, [18][19][20][21][22][23][24][25][26] have given insight into the molecular processes involved and their approximate rates. Because these systems and their functions are relatively well defined, they are also ideal targets for theoretical approaches, although covering the range of time scales at which they function, typically from GHz to Hz, 27 is problematic even for modern simulation techniques.…”

Electrochemically addressable trisradical rotaxanes organized within a metal–organic framework

“…This phenomenon was not an entirely unfamiliar one. The changes in dynamic behavior that can be expected on transitioning from working in solution, where molecules are free to tumble randomly, to crystalline materials, where they are highly ordered and densely packed, has been investigated systematically (35,36) by Miguel Garcia-Garibay (Fig. 1) for several years.…”

“…An extended strut, wherein 1,5-naphtho-p-phenylene [36]crown-10 (NPP36C10) was grafted into its midriff before being catenated with CBPQT 4+ cyclophanes has been used (18) in the preparation of MOF-1030, which constitutes an example of the ordering of MIMs within a well-defined 3D solid matrix. The catenated MOF-1030, however, brings the prototypically active switching machinery in the struts to a standstill!…”