Biomimetic Synchronized Motion of Two Interacting Macrocycles in [3]Rotaxane-Based Molecular Shuttles.

Noncovalent interactions between all the neighboring components in biomolecular machines are responsible for their synchronized motion and thus complex functions. This strategy has rarely been used in multicomponent molecular machines. Here, we report four [3]rotaxane-based molecular shuttles. Noncovalent interactions among the three components (two interacting macrocycles and one axle) not only cause a "systems-level" effect on the relative positions of the two macrocycles along the axle, but also result in a synchronized motion of the two macrocycles when adding partial amount of stimuli. Moreover, the intermediate state with one shuttled macrocycle even exist predominantly in the solution during the titration of stimuli, which is theoretically unexpected for the [3]rotaxane with two non-interacting rings. This biomimetic strategy may provide a method for constructing highly complex molecular machines.

Directional Shuttling of a Stimuli-Responsive Cone-Like Macrocycle on a Single-State Symmetric Dumbbell Axle.

Rotaxane-based molecular shuttles are often operated using low-symmetry axles and changing the states of the binding stations. A molecular shuttle capable of directional shuttling of an acid-responsive cone-like macrocycle on a single-state symmetric dumbbell axle is now presented. The axle contains three binding stations: one symmetric di(quaternary ammonium) station and two nonsymmetric phenyl triazole stations arranged in opposite orientations. Upon addition of an acid, the protonated macrocycle shuttles from the di(quaternary ammonium) station to the phenyl triazole binding station closer to its butyl groups. This directional shuttling presumably originates from charge repulsion and an orientational binding preference between the cone-like cavity and the nonsymmetric phenyl triazole station. This mechanism for achieving directional shuttling by manipulating only the wheels instead of the tracks is new for artificial molecular machines.

Light-Controlled Switching of a Non-photoresponsive Molecular Shuttle.

In this research, we report that the acid/base-switchable molecular shuttle without any photoresponsive group can be controlled photochemically by coupling to the indazole-based photoacid via an intermolecular proton-transfer process. The photocontrolled shuttling of the wheel can be conveniently monitored by following the fluorescent evolution during the photoirradiation.

Synthesis and DNA-binding affinities of protoberberine-based multivalent agents.

Three novel berberine derivatives bearing two, three, and four primary amino groups at C(9), respectively, were synthesized and characterized on the basis of ¹H- and ¹³C-NMR, MS, and HR-MS data. Their non-covalent binding with calf thymus (CT) DNA was investigated by means of spectrophotometric titration and ethidium bromide (EB) displacement experiments. The results indicated that these multivalent berberine derivatives exhibited up to 130-fold enhanced binding affinities relative to berberine, and thus, may be exploitable as potent DNA-binding agents.