Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
Photochem Photobiol Sci. 2018 Oct 10;17(10):1469-1476. doi: 10.1039/c8pp00240a.
Thioguanine is sensitive to UVA light and generates singlet molecular oxygen (1O2*) when exposed to UVA. Three thioguanosine derivatives, 2',3',5'-tri-O-acetyl-6-thioguanosine (ta6TGuo), 2',3',5'-tri-O-acetyl-8-thioguanosine (ta8TGuo), and 2',3',5'-tri-O-acetyl-6,8-dithioguanosine (taDTGuo) were explored photophysically and photochemically. Nanosecond transient absorption and time-resolved near-infrared emission measurements were carried out to investigate the characteristics of their excited triplet states in acetonitrile solution. The quantum yield of intersystem crossing (ΦISC), the intrinsic decay rate constant (k0), the quenching rate constant by 3O2 (kq) and the self-quenching rate constant (kSQ) of their triplet states were all determined. From the precise analysis of the quantum yield of 1O2* generation (ΦΔ) against the concentration of dissolved molecular oxygen, the fraction of the triplet states quenched by dissolved oxygen which gives rise to 1O2* formation (SΔ) was successfully obtained with high accuracy. The ΦΔ values at low oxygen concentrations reveal that these thioguanosines, particularly taDTGuo, can still effectively generate 1O2* at low molecular oxygen concentrations like carcinomatous microenvironments. These findings indicate that taDTGuo would perform well as a potential agent for photo-induced cancer therapies.
硫鸟嘌呤对 UVA 光敏感，暴露于 UVA 时光解可生成单重态氧（1O2*）。研究了三种硫鸟苷衍生物：2',3',5'-三-O-乙酰基-6-硫代鸟苷（ta6TGuo）、2',3',5'-三-O-乙酰基-8-硫代鸟苷（ta8TGuo）和 2',3',5'-三-O-乙酰基-6,8-二硫代鸟苷（taDTGuo）的光物理和光化学性质。通过纳秒瞬态吸收和时间分辨近红外发射测量研究了它们在乙腈溶液中激发三重态的特性。测定了系间穿越量子产率（ΦISC）、固有衰减速率常数（k0）、3O2 猝灭速率常数（kq）和三重态自猝灭速率常数（kSQ）。通过精确分析 1O2生成量子产率（ΦΔ）与溶解氧浓度的关系，成功地以高精度获得了由溶解氧猝灭的三重态分数（SΔ），该分数导致 1O2形成。在低氧浓度下的ΦΔ 值表明，这些硫鸟苷，特别是 taDTGuo，在类似癌组织微环境的低氧浓度下仍能有效地生成 1O2*。这些发现表明 taDTGuo 将成为光诱导癌症治疗的潜在有效药物。
