Formation of water-chlorophyll clusters in dilute samples of chlorophyll-a in ether at low temperature

Abstract

Simultaneously measured absorption (ABS) and magnetic circular dichroism (MCD) spectra of the Q-bands of chlorophyll-a (Chl-a) in ether over 150-186 K reveal that the species that forms at low temperature is a chlorophyll hydrate rather than a diether complex. We have recently proposed a new assignment paradigm for the spectra of chlorophillides which, for the first time, quantitatively accounts for a wide range of observed data. Observations performed at low temperature in ether have historically been very important for the interpretation of the spectra of Chl-a. While our assignment for this system initially anticipated only small spectral changes as the temperature is lowered, significant changes are known to occur. Extensive CAM-B3LYP time-dependent density-functional theory (TD-DFT) calculations verify that the observed spectra of the hydrated species conforms to expectations based on our new assignment, as well as supporting the feasibility of the proposed hydration reactions. Show more