Xingguo Liang

Photoregulation of the Formation and Dissociation of a DNA Duplex by Using the cis-trans Isomerization of Azobenzene.

The duplex-forming activity of an oligonucleotide has been photoregulated by making use of the isomerization of an azobenzene moiety in the side chain. When the azobenzene moiety is isomerized from the trans form to the cis form upon photoirradiation, the melting temperature of the duplex between the oligonucleotide and its complementary counterpart is significantly lowered, and the duplex is largely dissociated into two single-stranded oligonucleotides (shown schematically).

Photocontrol of DNA Duplex Formation by Using Azobenzene-Bearing Oligonucleotides

The duplex‐forming activities of oligonucleotides can be photomodulated by incorporation of an azobenzene unit. Upon isomerizing the trans‐azobenzene to the cis form by irradiation with UV light, the Tm value of the duplex (with the complementary DNA) is lowered so that the duplex is dissociated. The duplex is formed again when the cis‐azobenzene is converted to the trans‐azobenzene by irradiation with visible light. The photoregulation is successful irrespective of the position of the azobenzene unit in the oligonucleotides. The trans‐azobenzene in the oligonucleotides intercalates between two DNA base pairs in the duplexes and stabilizes them because of a favorable enthalpy change. The nonplanar structure of a cis‐azobenzene is unfavorable for such an interaction. These photoresponsive oligonucleotides are promising candidates for the regulation of various bioreactions.

Photoregulation der Bildung und Dissoziation eines DNA‐Duplexes durch cis‐trans‐Isomerisierung einer Azobenzoleinheit

Die Neigung eines Oligonucleotids zur Duplexbildung wurde photoreguliert, indem die Isomerisierung einer Azobenzoleinheit in der Seitenkette genutzt wurde. Nach der Isomerisierung der Azobenzoleinheit von der trans- zur cis-Form durch Bestrahlung liegt die Schmelztemperatur des Duplexes aus dem Oligonucleotid und seinem komplementaren Gegenstuck wesentlich niedriger, und der Duplex ist weitgehend in zwei Einzelstrang-Oligonucleotide dissoziiert (schematisch gezeigt).

meta-Aminoazobenzene as a thermo-insensitive photo-regulator of DNA-duplex formation

Abstract meta -Aminoazobenzene has been introduced in the side chain of oligonucleotides as a photo-responsive molecule. Compared with the para -aminoazobenzene which was previously used, the thermal cis→trans isomerization was much slower: the half-lives of the cis- isomers of m - and p -aminoazobenzene were 13.2 h and 20 min at 50°C, respectively. By using the present oligonucleotides, duplex formation and dissociation was efficiently regulated on photo-irradiation without being disturbed by the thermal isomerization.

Phenylazonaphthalene as a superb photo-regulator for DNA-triplex formation

Phenylazonaphthalene was tethered to the 5′-end of oligo(T) as photo-responsive moiety for the photo-regulation of DNA-triplex formation. The melting temperature of DNA-triplex changed as greatly as 40.5°C on trans↔cis isomerization of phenylazonaphthalene. This change was much greater than that achieved by azobenzene.

DNA–Naphthyl Red conjugate as a visualizing probe of DNA hybridization

The Naphthyl Red moiety, conjugated to DNA, shows distinct chromism by hybridization with its complementary DNA. Single-stranded DNA involving the Naphthyl Red moiety exhibits an orange color and has lambda(max) at 466 nm at pH 7.0. The absorption maximum is shifted towards 545 nm by the presence of its complementary DNA, and the color of the solution changes from orange to magenta accordingly.