Binding of Stimuli-Responsive Ruthenium Aqua Complexes with 9-Ethylguanine

Atsuki Maeda; Jun-Ya Tokumoto; Soichiro Kojima; Keiichi Fujimori; Takayo Moriuchi-Kawakami; Masanari Hirahara

doi:10.1021/acsomega.3c05343

Binding of Stimuli-Responsive Ruthenium Aqua Complexes with 9-Ethylguanine

ACS Omega. 2023 Sep 26;8(40):37391-37401. doi: 10.1021/acsomega.3c05343. eCollection 2023 Oct 10.

Authors

Atsuki Maeda¹, Jun-Ya Tokumoto¹, Soichiro Kojima¹, Keiichi Fujimori¹, Takayo Moriuchi-Kawakami¹, Masanari Hirahara¹

Affiliation

¹ Department of Applied Chemistry, Faculty of Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi Ward, Osaka 535-8585, Japan.

Abstract

Stimuli-responsive ruthenium complexes proximal- and distal-[Ru(C₁₀tpy)(C₁₀pyqu) OH₂]²⁺ (proximal-1 and distal-1; C₁₀tpy = 4'-decyloxy-2,2':6',2″-terpyridine and C₁₀pyqu = 2-[2'-(6'-decyloxy)-pyridyl]quinoline) were experimentally studied for adduct formation with a model DNA base. At 303 K, proximal-1 exhibited 1:1 adduct formation with 9-ethylguanine (9-EtG) to yield proximal-[Ru(C₁₀tpy)(C₁₀pyqu)(9-EtG)]²⁺ (proximal-RuEtG). Rotation of the guanine ligand on the ruthenium center was sterically hindered by the presence of an adjacent quinoline moiety at 303 K. Results from ¹H NMR measurements indicated that photoirradiation of a proximal-RuEtG solution caused photoisomerization to distal-RuEtG, whereas heating of proximal-RuEtG caused ligand substitution to proximal-1. The distal isomer of the aqua complex, distal-1, was observed to slowly revert to proximal-1 at 303 K. In the presence of 9-EtG, distal-1 underwent thermal back-isomerization to proximal-1 and adduct formation to distal-RuEtG. Kinetic analysis of ¹H NMR measurements showed that adduct formation between proximal-1 and 9-EtG was 8-fold faster than that between distal-1 and 9-EtG. This difference may be attributed to intramolecular hydrogen bonding and steric repulsion between the aqua ligand and the pendant moiety of the bidentate ligand..