TY  - JOUR
A1  - Kröner, Dominik
A1  - Götze, Jan Philipp
T1  - Modeling of a violaxanthin-chlorophyll b chromophore pair in its LHCII environment using CAM-B3LYP
JF  - Journal of photochemistry and photobiology : B, Biology
N2  - 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.
KW  - CAM-B3LYP
KW  - Density functional theory
KW  - Light-harvesting complex II
KW  - Photosynthesis
KW  - Violaxanthin
KW  - Chlorophyll b
Y1  - 2012
U6  - https://doi.org/10.1016/j.jphotobiol.2011.12.007
SN  - 1011-1344
VL  - 109
IS  - 2
SP  - 12
EP  - 19
PB  - Elsevier
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Götze, Jan Philipp
A1  - Saalfrank, Peter
T1  - Quantum chemical modeling of the kinetic isotope effect of the carboxylation step in RuBisCO
JF  - Journal of molecular modeling
N2  - Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the most important enzyme for the assimilation of carbon into biomass, features a well-known isotope effect with regards to the CO2 carbon atom. This kinetic isotope effect alpha = k (12)/k (13) for the carboxylation step of the RuBisCO reaction sequence, and its microscopic origin, was investigated with the help of cluster models and quantum chemical methods [B3LYP/6-31G(d,p)]. We use a recently proposed model for the RuBisCO active site, in which a water molecule remains close to the reaction center during carboxylation of ribulose-1,5-bisphosphate [B. Kannappan, J.E. Gready, J. Am. Chem. Soc. 130 (2008), 15063]. Alternative active-site models and/or computational approaches were also tested. An isotope effect alpha for carboxylation is found, which is reasonably close to the one measured for the overall reaction, and which originates from a simple frequency shift of the bending vibration of (CO2)-C-12 compared to (CO2)-C-13. The latter is the dominant mode for the product formation at the transition state.
KW  - Cluster model
KW  - Dark reactions
KW  - Densityfunctional theory
KW  - Isotope effect
KW  - Photosynthesis
KW  - Quantum chemistry
KW  - RuBisCO
Y1  - 2012
U6  - https://doi.org/10.1007/s00894-011-1207-0
SN  - 1610-2940
VL  - 18
IS  - 5
SP  - 1877
EP  - 1883
PB  - Springer
CY  - New York
ER  -