Temperature dependence of absorption and fluorescence spectra of bacteriochlorophylls in vivo and in vitro

Abstract

The “short wave” far-red absorption bands (795–825 nm) of bacteriochlorophyll in photosynthetic red bacteria are sharpened but not shifted upon cooling, the “long wave” far-red bands (840–890 nm) are sharpened less but shifted appreciably towards longer wavelengths. The fluorescence bands are shifted about as much as the corresponding “long wave” absorption bands. Warming results in changes in the opposite direction. The temperature effects are reversible.

With bacteriochlorophyll dissolved in a number of polar solvents, the temperature-induced shift of the yellow band is more pronounced than that of the far-red band; with colloidal and adsorbed bacteriochlorophyll, the 840-nm red band upon cooling shifts, by a similar amount as the 850-nm band in some, though not all, measured bacterial species, while the shift of the 780 nm and yellow band is small. The possible interference of temperature effects with the interpretation of results on absorption in terms of photochemical activity is discussed.