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 ring E ester system interacting with the pi-system of the macrocycle. In this work, we compared the effect of lauryldimethylamine-N-oxide (LDAO) and alkaline pH on both the near infrared and the ultraviolet region of the LHII spectrum from Ectothiorhodospira sp. While LDAO induces only a shift of the 850 nm band arising from the Qy transition of the bacteriochlorophyll a, alkaline pH also causes a concomitant and reversible 10-nm shift from 258 to 248 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 11.7.