Wavelength shifts correlation between near infrared and ultraviolet regions of the LHII bacteriochlorophyll spectrum from Ectothiorhodospira sp.

Bacteriochlorophyll a has a maximum at 258 nm previously related to the rin g E ester system interacting with the rr system of the macrocycle. In this work, we compared the effect of lauryldimethylamine-N-oxide (LDAO) and alka line pH on both the near infrared and the ultraviolet region of the LHII sp ectrum from Ectothiorhodospira sp. While LDAO induces only a shift of the 8 50 nm band arising from the ey transition of the bacteriochlorophyll a, alk aline pH also causes a concomitant and reversible 10-nm shift from 258 to 2 48 nm. Both shifts have similar apparent pKs (12.3 and 12.6, respectively). Interestingly, the presence of NaCl reduces these pKs values to 11.4 and 1 1.7.