Influence of solvent effects on Qy transitions in chlorophyll

Abstract

The most abundant and efficient light harvesting, energy transfer and transduction systems are found in nature within the process of photosynthesis. Although the processing sequences of an absorbed solar photon in the photosynthetic apparatus have been deciphered, the underlying physical basis of photosynthesis is not well understood yet. Our research aims to contribute to this understanding by characterising the level of organisation of the Light Harvesting II complexes (LHCII) and energy transfer systems when incorporated into artificial vesicles called PheroidTM. LHCII was extracted from spinach leaves in a 20 mM Tricine buffer to stabilise the proteins. Raman, FTIR and absorbance spectra of samples were compared. The Qy transitions of chlorophyll in the red (Qy) region of the absorption spectra appears to red-shift by 3.5 - 5.5 nm; indicating a possible change in organisation of the light harvesting system after incorporation into the PheroidTM. These shifts however could also be interpreted as bathochromic solvent effects due to the Tricine buffer. The objectives of this study were (1) to investigate whether the red-shifts were due to the Tricine buffer and (2) if so, whether the alternative use of a 20 mM K2HPO4 / KH2PO4 buffer could eliminate the bathochromic solvent effects. The Tricine buffer was dialysed out of the samples directly into a 20 mM K2HPO4 / KH2PO4 buffer to prevent denaturing of the LHCII proteins. Preliminary results indicated a lessening of the bathochromic effects with the K2HPO4 / KH2PO4 buffer.