bacteriochlorophylls and chlorophyll-b

The role of the environment in excitation energy transport in the pigment-protein complexes (PPCs) of photosynthetic organisms is a widely investigated topic. The spectral density is a key component in understanding this protein-pigment interaction; however, the typical approach for calculating spectral density, combining molecular dynamics with quantum chemistry (QC) calculations, suffers from the geometry mismatch problem, arising from the structural inconsistency between the force field (FF) and the QC calculation. Existing parameterization methods demand much time-consuming manual inputs, limiting the number of systems that can be studied. We present a method, utilizing force matching for the autoparameterization of new pigment FFs for the use in spectral density calculations of PPCs, and apply the method to three pigments. The use of these optimized FFs in spectral density computation results in a notable difference in comparison to the original FF.

Topics: Bacteria; Bacterial Proteins; Bacteriochlorophyll A; Chlorophyll; Chlorophyll A; Chlorophyll Binding Proteins; Light-Harvesting Protein Complexes; Molecular Dynamics Simulation; Quantum Theory

Bacteriochlorophyll(BChl)-f which has not yet been found in natural phototrophs was prepared by chemically modifying chlorophyll-b. The retention time of reverse-phase high-performance liquid chromatography of the synthetic monomeric BChl-f as well as its visible absorption and fluorescence emission spectra in a solution were identified and compared with other naturally occurring chlorophyll pigments obtained from the main light-harvesting antenna systems of green sulfur bacteria, BChls-c/d/e. Based on the above data, BChl-f was below the level of detection in three strains of green photosynthetic bacteria producing BChl-e.

Topics: Bacteriochlorophylls; Chlorobi; Chlorophyll; Chromatography, High Pressure Liquid; Spinacia oleracea

From time integration of the electron dynamics under a density functional tight binding Hamiltonian in the presence of external time varying electric fields, we obtain the absorption spectra of a series of chlorophylls and bacteriochlorophylls. We obtain good agreement with the observed experimental energies as well as with fully ab initio results in the literature for the main absorption bands. As a first step towards an atomistic description of energy transfer between chromophores in photosynthetic antenna systems we calculate the coupling energy between the excitations of two chlorophyll a molecules as a function of the distance as well as the transfer of energy between these when one of them is subjected to laser illumination.

Topics: Absorption; Bacteriochlorophylls; Chlorophyll; Chlorophyll A; Energy Transfer; Photosynthesis; Thermodynamics

Mg(II)-porphyrin-ligand and (bacterio)chlorophyl-ligand coordination interactions have been studied by solution and solid-state MAS NMR spectroscopy. (1)H, (13)C and (15)N coordination shifts due to ring currents, electronic perturbations and structural effects are resolved for imidazole (Im) and 1-methylimidazole (1-MeIm) coordinated axially to Mg(II)-OEP and (B)Chl a. As a consequence of a single axial coordination of Im or 1-MeIm to the Mg(II) ion, 0.9-5.2 ppm (1)H, 0.2-5.5 ppm (13)C and 2.1-27.2 ppm (15)N coordination shifts were measured for selectively labeled [1,3-(15)N]-Im, [1,3-(15)N,2-(13)C]-Im and [1,3-(15)N,1,2-(13)C]-1-MeIm. The coordination shifts depend on the distance of the nuclei to the porphyrin plane and the perturbation of the electronic structure. The signal intensities in the (1)H NMR spectrum reveal a five-coordinated complex, and the isotropic chemical shift analysis shows a close analogy with the electronic structure of the BChl a-histidine in natural light harvesting 2 complexes. The line broadening of the ligand responses support the complementary IR data and provide evidence for a dynamic coordination bond in the complex.

Topics: Bacteriochlorophyll A; Bacteriochlorophylls; Carbon Isotopes; Chlorophyll; Chlorophyll A; Histidine; Imidazoles; Isotope Labeling; Light-Harvesting Protein Complexes; Magnesium; Magnetic Resonance Spectroscopy; Molecular Structure; Nitrogen Isotopes; Photosynthesis; Rhodobacter sphaeroides; Spectrophotometry, Infrared; Spinacia oleracea

Measurements of dipole strengths of chlorophylls in solution are reviewed and correlated. The refractive index dependence is found to be expressible in a simple empirical fashion that does not rely on the concept of vacuum dipole strength. The index dependence in some respects contradicts the dependence expected on the basis of effective field theories.

Topics: Bacterial Proteins; Bacteriochlorophylls; Chlorophyll; Chlorophyll A; Refractometry; Solutions; Static Electricity

The Willstätter allomerization reaction of chlorophylls (Chl) has posed a difficult problem in Chl and photosynthesis research over the past 90 years. Here, we present strong additional evidence, based on (18)O-labeling and mass spectrometry, for the previously published free-radical allomerization (FRA) mechanism (Hynninen, Z. Naturforsch. 1981, 36b, 1010-1016). This mechanism is also complemented now by describing two alternative pathways for the formation of 13(2)(S/R)-hydroxy-Chl a. The results from the (18,18)O(2)-experiments suggest that the predominant route for the formation of the 13(2)(S/R)-hydroxy-Chl a under essentially anhydrous conditions (anhydrous Chl and thoroughly dried methanol) is the homolytic cleavage of the C-13(2)-hydroperoxide intermediate. However, if Chl dihydrate and undried methanol are used in the reaction mixture, the direct route from the Chl C-13(2) radical to 13(2)(S/R)-hydroxy-Chl a can be predicted to become significant. The results from the (18,18)O(2)-allomerization experiments described in this paper also verified that the 13(2)(S/R)-methoxy-lactone derivatives and the 15-glyoxylic acid derivative of Chl a incorporated each a single (18)O-atom, whereas 13(2)(R/S)-methoxy-Chl a remained unlabeled. Consequently, these allomers are formed via the pathways previously suggested in the original FRA mechanism. The possible factors contributing to the control of the allomerization reactions are considered. Finally, the relationship between the allomerization reactions of Chl a and those of Chl b and BChl a is briefly discussed.

Topics: Bacteriochlorophyll A; Carbon Isotopes; Chlorophyll; Chlorophyll A; Chromatography, High Pressure Liquid; Dimerization; Energy Transfer; Kinetics; Mass Spectrometry; Molecular Structure; Oxygen Isotopes; Photosynthesis; Phytolacca dodecandra; Stereoisomerism; Structure-Activity Relationship

Topics: Bacteria; Bacteriochlorophylls; Biochemical Phenomena; Biochemistry; Chlorobium; Chlorophyll; Chlorophyll A; Hydrogen; Magnetic Resonance Spectroscopy; Research; Rhodospirillum