Rhodopin Glucoside Lab Report
Introduction
Carotenoids are natural pigments that exist in nature among both photosynthetic and non-photosynthetic organism. They serve many significant functions some of which are light harvesting and photoprotection in plants, promoting reproduction and survival in animals and providing substrates for biosynthesis of hormones and signalling molecules. In particular this essay will explore how the structure of rhodopin glucoside determines its function in light harvesting system LH2 of a purple photosynthetic bacteria Rhodopesudomonas acidophila.
Overall structure of Rhodopin glucoside
Rhodopin glucoside (RG) is the major carotenoid in LH2 complex of Rhs acidophila revealed by high solution structure of LH2 complex at 2.5 Å (McDermott et. …show more content…
The polyene chain of RG, a long system of conjugated double bonds determines the light absorption properties. Once rhodopin glucoside gets photo-activated, one of the low energy bonding ∏ electrons from the conjugated system gets excited to higher energy unoccupied ∏* anti-bonding orbital. This is often referred as ∏ to ∏* transition. Due to quantum nature of an electron only the frequency that corresponds to energy gap between the two states can be absorbed. In RG the ∏ electrons are highly delocalised over the chain length so energy required to bring out this transitions is reduced. This energy corresponds to wavelength of light of 400-500nm.This visible region is spectrally not covered by the bacteriochlorophyll molecules. Therefore by utilising mixture of different bacteriochlorophyll and carotenoids absorbing photons of different wavelengths, Rhs acidophila can efficiently utilise the entire spectrum of light. Hence more energy per quanta can be fed into reaction centre where photochemistry takes place. Interestingly the characteristic strong absorption by RG at 400-500nm is a result of transition of electrons from ground state (S0) to second singlet excited state (S2). In RG this transition is very strong corresponding to large delocalisation of electrons. Due to near symmetry structure of RG the transition from ground state to first single excited state (S1) is dipole forbidden (H. A. Frank, et.al 1991). Instead the S2 state of RG has a high dipole moment therefore readily absorb
Carotenoids are natural pigments that exist in nature among both photosynthetic and non-photosynthetic organism. They serve many significant functions some of which are light harvesting and photoprotection in plants, promoting reproduction and survival in animals and providing substrates for biosynthesis of hormones and signalling molecules. In particular this essay will explore how the structure of rhodopin glucoside determines its function in light harvesting system LH2 of a purple photosynthetic bacteria Rhodopesudomonas acidophila.
Overall structure of Rhodopin glucoside
Rhodopin glucoside (RG) is the major carotenoid in LH2 complex of Rhs acidophila revealed by high solution structure of LH2 complex at 2.5 Å (McDermott et. …show more content…
The polyene chain of RG, a long system of conjugated double bonds determines the light absorption properties. Once rhodopin glucoside gets photo-activated, one of the low energy bonding ∏ electrons from the conjugated system gets excited to higher energy unoccupied ∏* anti-bonding orbital. This is often referred as ∏ to ∏* transition. Due to quantum nature of an electron only the frequency that corresponds to energy gap between the two states can be absorbed. In RG the ∏ electrons are highly delocalised over the chain length so energy required to bring out this transitions is reduced. This energy corresponds to wavelength of light of 400-500nm.This visible region is spectrally not covered by the bacteriochlorophyll molecules. Therefore by utilising mixture of different bacteriochlorophyll and carotenoids absorbing photons of different wavelengths, Rhs acidophila can efficiently utilise the entire spectrum of light. Hence more energy per quanta can be fed into reaction centre where photochemistry takes place. Interestingly the characteristic strong absorption by RG at 400-500nm is a result of transition of electrons from ground state (S0) to second singlet excited state (S2). In RG this transition is very strong corresponding to large delocalisation of electrons. Due to near symmetry structure of RG the transition from ground state to first single excited state (S1) is dipole forbidden (H. A. Frank, et.al 1991). Instead the S2 state of RG has a high dipole moment therefore readily absorb