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We employed an azobenzene based non-nucleoside triphosphate, AzoTP, in a myosin-actin motile system and demonstrated its efficiency as an energy molecule to drive and photo-regulate the myosin-actin motile function at the macroscopic level along with an in vitro motility assay. The AzoTP in its trans state induced shortening of a glycerinated muscle fibre whilst a cis isomer had no significant effect. Direct photoirradiation of a cis-AzoTP infused muscle fibre induced shortening triggered by a locally photo-generated trans-AzoTP in the muscle fibre. Furthermore, we designed and synthesized three new derivatives of AzoTPs that served as substrates for myosin by driving and photo-regulating the myosin-actin motile function at the molecular as well as the macroscopic level with varied efficiencies.

Recently we demonstrated the photoregulation of the activity of kinesin-1 using an azobenzene-tethered peptide (azo-peptide: Azo-Ile-Pro-Lys-Ala-Ile-Gln-Ala-Ser-His-Gly-Arg-OH). To understand the mechanism behind this photoswitchable inhibition, here we studied the structure-property relationships of a range of azo-peptides through systematic variations in the structures of the peptide and azobenzene units. The vital peptide sequence for kinesin inhibition-mediated through electrostatic, hydrophobic and C-Hπ interactions-was the same as that for the self-inhibition of kinesin. We also identified substituents on the azobenzene capable of enhancing the photoswitchability of inhibition. As a result, we developed a new inhibitor featuring a relatively short peptide unit (-Arg-Ile-Pro-Lys-Ala-Ile-Arg-OH) and an azobenzene unit bearing a para-OMe group. In the trans form of its azobenzene unit, this finely tuned inhibitor stopped the kinesin-driven gliding motility of microtubules completely at a relatively low concentration, yet allowed gliding motility with a relatively high velocity in the cis form obtained after UV irradiation.

In this study, we synthesized asymmetric dimeric chiral molecules as photon-mode chiral switches for reversible tuning of self-assembled helical superstructures. The chiral switches bearing two mesogen units-cholesterol and azobenzene moieties connected through flexible alkylenedioxy bridges-were doped into nematic liquid crystals, resulting in a chiral nematic (cholesteric) phase. Under irradiation with UV light, photoisomerization of the azobenzene units led to unprecedented switching of the cholesteric pitch and helical twisting power (HTP, β), with a higher HTP found in the cis-rich state (bent-form) than in the trans-state (rod-form). We attribute this behavior to the elongated cybotactic smectic clusters disrupting the helical orientation of the molecules in the cholesteric liquid crystals; their reversible decay and reassembly was evidenced upon sequential irradiation with UV and visible light, respectively. In addition to the photoisomerization of the azobenzene units, the odd/even parity of the alkylenedioxy linkers of the dimeric dopants also had a dramatic effect on the transitions of the cybotactic smectic domains. On the basis of the large rotational reorganization of the cholesteric helix and HTP switching (Δβ/βini of up to 50%), we could control the macroscopic rotational motion of microsized glass rods upon irradiating the surface of a cholesteric liquid crystal film featuring a polygonal fingerprint texture using UV and visible light.

To apply motor proteins as natural nanomolecular machines to transporting systems in nanotechnology, complete temporal control over ON/OFF switching of the motility is necessary. We have studied the photoresponsive inhibition properties of azobenzene-tethered peptides for regulation of kinesin-microtubule motility. Although a compound containing a peptide having an amino acid sequence derived from the kinesin's C-terminus (a known inhibitor of kinesin's motor domain) and also featuring a terminal azobenzene unit exhibited an inhibition effect, the phototunability of this behavior upon irradiation with UV or visible light was only moderate. Unexpectedly, newly synthesized peptides featuring the reverse sequence of amino acids of the C-terminus of kinesin exhibited excellent photoresponsive inhibition. In particular, azobenzene-CONH-IPKAIQASHGR completely stopped and started the motility of kinesin-microtubules in its trans- and cis-rich states, respectively, obtained after irradiation with visible and UV light, respectively. A gliding motility system containing this photoresponsive inhibitor allowed in situ control of the motion of microtubules on a kinesin-coated glass substrate. It is expected that the present results on the photoresponsive nanomotor system open up new opportunities to design nanotransportation systems.

Motor enzymes such as F1-ATPase and kinesin utilize energy from ATP for their motion. Molecular motions of these enzymes are critical to their catalytic mechanisms and were analyzed thoroughly using a single molecule observation technique. As a tool to analyze and control the ATP-driven motor enzyme motion, we recently synthesized a photoresponsive ATP analog with a p-tert-butylazobenzene tethered to the 2' position of the ribose ring. Using cis/trans isomerization of the azobenzene moiety, we achieved a successful reversible photochromic control over a kinesin-microtubule system in an in vitro motility assay. Here we succeeded to control the hydrolytic activity and rotation of the rotary motor enzyme, F1-ATPase, using this photosensitive ATP analog. Subsequent single molecule observations indicated a unique pause occurring at the ATP binding angle position in the presence of cis form of the analog., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Three non-nucleoside triphosphates, one containing an azobenzene moiety, power a kinesin-microtubule system with high motile activity, with an observed maximum velocity of almost half of that obtained with ATP. The cis-trans photoisomerization of the azobenzene unit allows reversible and repeated control over the motile properties of kinesin.

Reversible fluorescence photoswitching of RSA-AZO dyad 1 was clearly demonstrated in an acidic aqueous solution. The fluorescence photoswitching mechanism is based on the reversible ring opening/closing reactions of the RSA unit induced by a photochromic pK(a) change along with the photoisomerization of the AZO unit.

The reversibly and repeatedly altered gliding motility of microtubules driven by kinesin on the photoresponsive monolayer surface is studied. It was confirmed that an azobenzene monolayer surface needs to have free amino terminal groups for the successful dynamic control of the motility of microtubule. The surface of the azobenzene monolayer with terminal amino groups can dynamically control the ATP hydrolysis activity of kinesin which resulted in the change in motility of the microtubules., (This journal is © The Royal Society of Chemistry 2012)

The gliding motility of microtubules driven by kinesin on the surface of an azobenzene monolayer presenting lysine terminal groups is reversibly and repeatedly altered upon photoisomerization of the monolayer., (© 2011 American Chemical Society)

A Ag(I) complex was prepared from azobenzenonaphthalenophane as a photoreactive multidentate ligand. The coordination of Ag(I) was reversibly controlled by photoisomerization of the azobenzene unit, and at the same time, Ag(I) accelerated the Z-E thermal isomerization of the azobenzene unit.

N-(L-valyl-L-valyl-L-valyl)azobenzene-4-carboxamide [Azo(LVal)(3)] is a low molecular weight gelator that forms a photofunctional fibrous assembled system; this assembly undergoes dispersion/reorganization upon trans-to-cis photoisomerization, which, as a result of the breaking and reforming of hydrogen bonds, induces reversible sol-gel transitions. In this paper, we describe the mechanism by which azobenzene isomerization induces the breaking and reorganization of these assembled systems. We applied Fourier transform infrared spectroscopy to investigate the effect of the irradiation time on the change in absorption intensity in the amide I region. The lifetime of the cis isomer influences the photoinduced breaking and reforming of hydrogen bonds between trivalyl units. Because the cis isomer of Azo(LVal)(3) had a long lifetime, its assemblies underwent reversible phototriggered dispersion and organization. In contrast, the lifetime of the cis isomer of 4'-dimethylamino-N-(L-valyl-L-valyl-L-valyl)azobenzene-4-carboxamide [pMR(LVal)(3)] was too short to disrupt the hydrogen bonds in its fibrous self-assembled system.