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Modeling of a violaxanthin–chlorophyll b chromophore pair in its LHCII environment using CAM-B3LYP

Paper ID Volume ID Publish Year Pages File Format Full-Text
30575 44488 2012 8 PDF Available
Title
Modeling of a violaxanthin–chlorophyll b chromophore pair in its LHCII environment using CAM-B3LYP
Abstract

Collecting energy for photosystem II is facilitated by several pigments, xanthophylls and chlorophylls, embedded in the light harvesting complex II (LHCII). One xanthophyll, violaxanthin (Vio), is loosely bound at a site close to a chlorophyll b (Chl). No final answer has yet been found for the role of this specific xanthophyll. We study the electronic structure of Vio in the presence of Chl and under the influence of the LHCII environment, represented by a point charge field (PCF).We compare the capability of the long range corrected density functional theory (DFT) functional CAM-B3LYP to B3LYP for the modeling of the UV/vis spectrum of the Vio + Chl pair. CAM-B3LYP was reported to allow for a very realistic reproduction of bond length alternation of linear polyenes, which has considerable impact on the carotenoid structure and spectrum. To account for the influence of the LHCII environment, the chromophore geometries are optimized using an ONIOM(DFT/6-31G(d):PM6) scheme.Our calculations show that the energies of the locally excited states are almost unaffected by the presence of the partner chromophore or the PCF. There are, however, indications for excitonic coupling of the Chl Soret band and Vio. We propose that Vio may accept energy from blue-light excited Chl.

► The influence of the protein environment on a violaxanthin/chlorophyll b pair of LHCII was studied. ► Two density functional theory methods were used and compared: CAM-B3LYP and B3LYP. ► Single chromophores, chromophore pairs, in vacuo, in solution and in the protein environment were studied. ► Results depend on the density functional, for both structure and spectrum, the environment plays a minor role. ► Indications for dipole coupling were found, the results may be connected to proposed blue-light induced quenching mechanisms.

Keywords
CAM-B3LYP; Density functional theory; Light-harvesting complex II; Photosynthesis; Violaxanthin; Chlorophyll b
First Page Preview
Modeling of a violaxanthin–chlorophyll b chromophore pair in its LHCII environment using CAM-B3LYP
Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 109, 2 April 2012, Pages 12–19
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering