Mechanical Tuning of Aggregated States for Conformation Control of Cyclized Binaphthyl at the Air–Water Interface

Abstract

An air–water interface enables molecular assemblies and conformations to be controlled according to their intrinsic interactions and anisotropic stimuli. The chirality and conformation of binaphthyl derivatives have been controlled by tuning molecular aggregated states in solution. In this study, we have tuned molecular aggregated states of monobinaphthyldurene (MBD) by applying different mechanical stimuli to control the conformation at the air–water interface. Density functional theory calculations indicate that MBD exists essentially in two conformations, namely, 1-MBD (most stable) and 2-MBD (less stable). MBD was mechanically dissolved in appropriate lipid matrices using the Langmuir–Blodgett (LB) method, while pure MBD was self-assembled at the dynamic air–water interface in the absence of or by applying vortex motions (vortex LB method). In MBD mixed monolayer, surface pressure–molecular area measurements and atomic force microscopy observations suggest that separate lipids and MBD phases transform to mixed phases induced by the dissolution of MBD into the lipid matrices during mechanical compression at the air–water interface. Circular dichroism measurements indicate that molecular conformation changes from 1-MBD to 2-MBD in passing from a separated phase to a mixed MBD/lipid phase. In addition, the molecular aggregated states and conformations of MBD depend on the spreading volume and vortex flow rate when applying the vortex LB method. Molecular conformations and aggregated states of MBD could be controlled continuously by applying a mechanical stimulus at the air–water interface.

Mechanical control of molecular machines at an air–water interface: manipulation of molecular pliers, paddles

“…The conformation of BBD and MBD, where a binaphthyl molecule is cross-linked with durene, can be controlled using mechanical stimuli in soft and well-miscible lipids but not in poorly miscible and hard lipids ( Table 2 ) [ 29 , 30 ]. Because MBD and BBD do not form two-dimensional monolayers but three-dimensional aggregates by themselves, it is assumed that their molecular conformations are moderately dispersed and modified in lipids with better miscibility.…”

“…The molecular conformations of binaphthyl molecules were also controlled in lipid matrices. M. Ishii et al formed monolayers of MBD [ 30 ], a binaphthyl molecule cross-linked with durene, and its dimer, BBD [ 29 ], mixed with various lipid matrices at the air – water interface and mechanically controlled their molecular conformations ( Figure 7 ). DFT calculations revealed that MBD and BBD have three main conformers: the most stable 1-conformers, 2-conformers with energies of a small kcal mol −1 , and unstable flat conformers.…”

Molecular machines working at interfaces: physics, chemistry, evolution and nanoarchitectonics

“…On the other hand, the molecular aggregation state of monobinaphthyl durene can be tuned by applying different mechanical stimuli to control its conformation at the air-water interface. 118 For example, the molecular conformation and aggregation state of monobinaphthyl durene could be continuously controlled by applying mechanical stimuli such as vortex motion at the air-water interface. These results provide various insights into the regulation of the dynamic behavior of molecular machines driven by mechanical stimuli at the liquid interfaces.…”

Molecular Machines and Microrobots: Nanoarchitectonics Developments and On-Water Performances

“…At the air-water interface, it is possible to control the conformation of the target molecule depending on the environment, such as the state of miscibility with the mixed lipid. Similarly, the aggregation state of monobinaphthyl durene molecules was controlled by applying different mechanical stimuli at the air-water interface [ 195 ]. When the vortex LB method [ 196 , 197 ] is applied to the water surface, the molecular aggregation state and conformation of the monobinaphthyl durene molecules depend on the molecular density and vortex flow velocity at the interface.…”