Effects of dehydration on light-induced conformational changes in bacterial photosynthetic reaction centers probed by optical and differential FTIR spectroscopy

► P+QA−/PQA IR spectra of reaction centers were analyzed in the 4000-1200 cm− 1 region. ► The effect of dehydration has been studied by controlling the relative humidity. ► Dehydration decreases difference bands attributed to bound water molecules. ► Dehydration affects vibrational modes of P and NH or OH groups of the protein. ► Spectral changes correlate with the stability of the light-induced P+QA− state.