Methods for regulating peptide conformation by non-harmful light stimuli can be useful for remotely controlling cellular functions in vitro. Here, we synthesized a series of p-heteroatom-substituted azobenzenes and studied their photoisomerization properties. The trans-isomer of p-sulfur-substituted azobenzene was effectively isomerized by visible light irradiation and the cis-isomer was thermally stable at physiological temperature. We developed a novel visible light sensitive amino acid (AZO), via p-sulfur-substituted azobenzene, and utilized it as a photosensitive modulator of the SV40 nuclear localization signal (NLS). The cellular uptake of the AZO-NLS conjugate was controlled by visible light irradiation. Our technology can be utilized for regulating not only the cellular uptake, but also the function of peptides within cells by non-harmful visible light irradiation.

The anion radicals of syn- and anti-[2.2](2,6)azulenophane, (1) and (2), [2.2](1,3)azulenophane, (3), and [2](1,3)-azuleno[2]paracyclophane, (4), all produced by alkali metal reduction in various solvents, have been investigated by ESR and ENDOR spectroscopy. They exist in the ion pair with cations in the solutions, except for 4\ewdot which exists in 1,2-dimethoxyethane with Na+. Their ion pairing tendency is appreciably higher than that of the naphthalenophane anion radicals. The unpaired electron in these ion pairs localizes mostly on an azulene ring (in 1\ewdot, 2\ewdot, and 3\ewdot, close to a cation). The polarization effects due to the pairing with the cations are much larger than those in the naphthalenophane anion radicals, and increase in the order 1\ewdot≤2\ewdot≤3\ewdot, indicating that the smaller the inter-layer orbital overlap, the larger the polarizability. The unpaired electron of 4\ewdot localizes mostly on the azulene ring even in the free anion.

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