It is a hot field to make natural molecular motors, namely motor proteins, applicable to nanotechnology especially nano-transportation. In order to accomplish such an application it is important to precisely regulate the motile function of natural motor proteins at molecular and macroscopic scales. In the present work we first confirmed that photo-responsive non-nucleoside triphosphates (AzoTP and its analogues) instead of the original energy molecule adenosine triphosphate (ATP) could drive myosin, one of motor proteins in our body. Furthermore we could control the driving velocity of the molecular motor reversibly by the photoisomerization of an azobenzene group in the non-nucleoside molecule. We also demonstrated the photo-regulation of muscle fibers containing myosin-action motor system using the fore mentioned non-nucleoside molecule. These demonstrations became possible by our original design of the energy molecule where the base aromatic and the ribose units in ATP were exchanged with azobenzene and some linkers, respectively. We believe the present work not only accelerate the progress of the study of soft molecular machines, but also provide a new tool for the study of the mechanism of motor functions of motor proteins. An illustration summarizing our present accomplishment was used as an inside cover of the issue where our article is included of Organic and Biomolecular Chemistry.

Constructing molecular machines with controllable movements has been an important goal in chemistry and nanotechnology and the pioneers in this field have been recognized with the Nobel Prize in Chemistry this year. Molecular machines will most likely be used in nanomedicine and the development of things such as new materials, sensors and energy storage systems. One way to construct useful molecular machines is to combine natural molecules ? such as proteins or DNAs in our body ? with synthetic molecules in order to control the functions of the natural molecules. Building on previous work that allowed to achieve complete control over ON/OFF switching of the movement of a nanomachine, we developed a molecular system which allows free control of the motion of single microtubules. This new work was featured as Nanotechnology Spotlight in a nanotechnology portal site, Nanowerk. The figure on the left is a schematic illustration of the transportation of single microtubule on kinesin coated surface in the presence of photoresponsive inhibitor. Under 365 nm local light irradiation selected microtubule was translocated, while almost arresting ambient microtubules under 510 nm. The movie of this event was recorded during observation on a fluorescent optical microscope.

Recently we demonstrated the reversible photoregulation of the kinesin motor activity using azobenzene tethered peptide (azo-peptide) composed of eleven amino acids derived from the tail domain of the kinesin (K. R. Sunil Kumar et al. ACS Nano, 2014, 8(5), 4157-4165). To know the mechanism of the photoswitchable inhibition, structure-property relationship study of the array of azo-peptides was carried out by incorporating the structural modifications at the peptide unit and at the photoresponsive unit. Our study gave the important information about the vital amino acids responsible for the inhibition, types of interactions involved in inducing the inhibition and the substituent group presenting on azobenzene exhibiting higher photoswitchability. As a result, a new, more efficient photoresponsive inhibitor of kinesin featuring relatively short peptide unit (-Arg-Ile-Pro-Lys-Ala-Ile-Arg-OH) coupled to an azobenzene unit substituted with an OMe group at the para position was obtained. This piece of work will be helpful in the molecular designing of the photoresponsive inhibitors for the applications in artificial nanotransportation systems, in the study and treatment of diseases etc. Interaction of the photoresponsive inhibitor with the kinesin motor domain and the reversible isomerization of the azo unit triggered by light are presented in this picture which was featured in the cover page of the journal 'Organic and Biomolecular Chemistry' published by Royal Society of Chemistry.

In our body, molecular machines with a nano meter size are working. If we took them out from our body and artificially regulated the motile function, it would lead to the actualization of “flexible and compact machine” which is totally different from the present hard and bulky machines. We developed a new photoresponsive inhibitor for kinesin, one of natural molecular machines, and succeeded in complete ON-OFF photo-switching of the motile property of kinesin by adding the inhibitor. This work was featured as Nanotechnology Spotlights in a nanotechnology portal site, Nanowerk.

The figure on the left is a schematic drawing of photo-stimulated switching of the movement of microtubules driven by kinesin in the presence of our photoresponsive inhibitor. The movie is showing the movement of microtubules observed on a fluorescent optical microscope. During the observation, 1 sec irradiation each of UV or blue light was applied to switch the state of motility between ON and OFF. The total length of the whole observation was 5 min.

We developed a methane derivative having two identical azobenzene substituents and demonstrated that detectable point chirality was generated and ceased upon photo-induced E/Z isomerization of one of the azobenzene substituents. The study may contribute to the study of the origin of enantio-pure molecules in nature and to the development of optical materials regulating polarized lights which is used for 3D displays. This work was featured in Nature Chemistry as highlight(PDF) and ChemViews Magazene as News.

Our review article on the photochromic regulation of liquid crystals was published in Journal of Photochemistry and Photobiology C as an “Invited Review Paper”. The left is an included schematic drawing by Nishad, a PhD student in our lab showing the entire field of the review.

We synthesized a planar chiral azobenzene, which induces chiral nematic phase in commercially available nematic liquid crystals and the change in the reflection color of the thin film of the chiral nematics from blue to red via green by ultra violet light and vice versa by visible light. Our achivement is featured as a highlight in Nature's web site.

A Japanese chemicals company, Tokyo Chemical Industry (TCI), started selling our newly developed photochromic compounds as reagents for laboratory experiments.
(Catalogue number: D3618, D3619)

Our work was introduced in Noteworthy Chemistry of the ACS's web site

Our paper on the cholestric liquid crystal with cholesterol and butadiene moieties responding to light and temperature was introduced in the "Highlights"of
Chemistry & Industry.  （full article）
＊This study was done on the joint
research with Dr. Suresh Das from
Regional Research Laboratory in India under India (DST)-Japan (JSPS) Joint Research Program.

This study was introduced in the papers below,

22/06/2006　Nikkei Business Daily
22/06/2006　Nikkan Kogyo Shinbun
22/06/2006　The Chemical Daily
07/07/2006　The Science News
26/07/2006　The Semiconductor Industry News