Incorporation of methyl group on azobenzene for the effective photo-regulation of hybridization and suppression of thermal isomerization.

We have synthesized azobenzene-tethered DNAs and have successfully photo-regulated various DNA functions. In the present study, we synthesized azobenzenes substituted with methyl group for still more effective photo-regulation of DNA hybridization. In trans-form, mono substituted azobenzene at ortho position stabilized the DNA duplex more efficiently than the other mono-substituted ones. In contrast, melting temperature (T(m)) for 2-methylazobenzene was lower in cis-form. As a result, change of T(m) (DeltaT(m)) induced by trans-cis isomerization became larger than that of unmodified azobenzene. Furthermore, di-substituted azobenzene at both ortho positions exhibited even larger DeltaT(m). Quite interestingly, thermal cis-to-trans isomerization of this azobenzene was about 10-fold slower than that of unmodified one. Thus, introduction of methyl group at 2, 6 positions raised both photo-regulatory activity and thermal stability of cis-form.