Extinction coefficients of bacteriochlorophylls $d$ and $e$ in organic solvents for quantitative spectrophotometric determination of pigments of phototrophic green sulphur bacteria

The extinction coefficients of bacteriochlorophylls $d$ and $e$ in several organic solvents were determined and compared with the coefficients of related compounds – chlorophylls $a$ and $b$. In some solvents (ethanol, isopropanol, acetone-ethanol (7 : 2) and acetone-methanol (7 : 2) – for bacteriochlorophyll $d$, in isopropanol and acetone-ethanol (7 : 2) – for bacteriochlorophyll $e$), extinction coefficients were determined for the first time. Spectrophotometric formulas for quantitative measurement of bacteriochlorophylls $d$ and $e$ in different solvents are given. The method of dynamic light scattering revealed the absence of noticeable aggregation of bacteriochlorophyll molecules in acetone and ethanol to a concentration of 0.14 g/l. The obtained data expand the possibilities of the spectrophotometric method for quantifying the pigments of phototrophic bacteria.