The red chlorophyll catabolite (RCC) is an inefficient sensitizer of singlet oxygen – photochemical studies of the methyl ester of RCC

Abstract

The red chlorophyll catabolite (RCC) is a proposed cryptic intermediate of chlorophyll (Chl) breakdown in higher plants. Its accumulation in higher plants is believed to be metabolically suppressed, as RCC is commonly suspected to efficiently sensitize for the formation of the cell poison singlet oxygen (¹O₂). We report here a study on luminescence of the methyl ester of RCC (Me-RCC) and of its capacity to generate ¹O₂ in ethanolic solution. A solution of Me-RCC fluoresces at room temperature with a maximum near 670 nm and features a fluorescence spectrum with pronounced vibrational spacing at 77 K. As shown here, sensitization of the generation of ¹O₂ by Me-RCC in an oxygen-saturated solution in hexadeutero-ethanol occurs with a maximal quantum yield of only about 0.015. This low quantum yield suggests that the specific catabolic suppression of the accumulation of RCC during Chl breakdown is not primarily a countermeasure against the formation of ¹O₂ by RCC in the plant, but has other crucial reasons mainly.