Simultaneous Two-Photon Absorption of the Thioguanosine Analogue 2′,3′,5′-Tri-O-acetyl-6,8-dithioguanosine with Its Potential Application to Photodynamic Therapy

Abstract

Milton Keynes MK7 6AA, United Kingdom ABSRACT 2',3',5'-Tri-O-acetyl-6,8-dithioguanosine (taDTGuo) is an analog of nucleoside and currently under investigation as a potential agent for photodynamic therapy (PDT). Excitation by simultaneous two-photon absorption of visible or near-infrared light would provide an efficient PDT for deep-seated tumors. The two-photon absorption spectrum of taDTGuo was obtained by optical-probing photoacoustic spectroscopy (OPPAS). A two-photon absorption band corresponding to the S 5 ←S 0 transition was observed at 556 nm, and the two-photon absorption cross section (2) was determined to be 26±3 GM, which was much larger than those of other nucleobases and nucleosides. Quantum chemical calculations suggested that the large (2) value of taDTGuo was responsible for large transition dipole moments and small detuning energy resulting from the thiocarbonyl group at 6-and 8-positions. This is the first 1

Excited States of Thio-2′-deoxyuridine Bearing an Extended π-Conjugated System: 3′,5′-Di-O-acetyl-5-phenylethynyl-4-thio-2′-deoxyuridine

“…Recently, we reported the two-photon absorption spectrum of a thionucleoside (2′,3′,5′-tri- O -acetyl-6,8-dithioguanosine) . Our simulated two-photon cross section peak of 1a was found to be about three times larger than that of the 6,8-dithioguanine .…”

“…Recently, we reported the two-photon absorption spectrum of a thionucleoside (2′,3′,5′-tri- O -acetyl-6,8-dithioguanosine) . Our simulated two-photon cross section peak of 1a was found to be about three times larger than that of the 6,8-dithioguanine . As 1a is part of 1c , 1c is expected to retain these desirable photo-properties, which would make 1c an excellent agent to induce the apoptosis for more deep-seated tumors.…”

“…The ϕ Δ values in the higher-order relaxation process assuming two-photon excitation is important to evaluate the potential of two-photon PDT as a photosensitizer for thionucleosides . Two-photon PDT has attracted much attention because of significant benefits such as much longer wavelength compared with one-photon excitation and spatial selectivity. − We simulated the two-photon absorption spectra of 1a , 3a (Figure ), and other pyrimidine derivatives (Figure S18).…”

“…Simulation of the two-photon absorption spectra was performed using sum-over state formalism summing all intermediate and final states considered in the calculation (20 excited states) . The dumping constant of the Lorentzian linewidth function was taken to be 0.25 eV . Solvent effects were modeled with the polarizable continuum model (PCM) for the ground- and the excited-states.…”

“…60 The dumping constant of the Lorentzian linewidth function was taken to be 0.25 eV. 61 Solvent effects were modeled with the polarizable continuum model (PCM) for the ground-and the excited-states.…”