Ab initio calculations on large molecules using molecular fragments. Preliminary investigation of ethyl chlorophyllide a and related molecules

Spangler, Dale; McKinney, R. W.; Christoffersen, Ralph E.; Maggiora, Gerald M.; Shipman, Lester L.

doi:10.1016/0009-2614(75)80273-9

Cited by 35 publications

(5 citation statements)

References 14 publications

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“…56 The first ab initio calculations of ground state properties of porphins, chlorins and ethyl chlorophyllide were published by Christoffersen and Shipman together with electron density contour and electrostatic potential maps of these compounds. [57][58][59][60][61] Petke et al [49][50][51] introduced ab initio CI calculations of ethyl chlorophyllide a and ethyl pheophorphide a. Q y and Q x transitions were described with the use of four orbital model. Polarisation of the Q x transition was not correctly predicted.…”

Section: Introductionmentioning

confidence: 99%

Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes

Linnanto

Korppi-Tommola

2006

Phys. Chem. Chem. Phys.

145

164

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The present review describes the use of quantum chemical methods in estimation of structures and electronic transition energies of photosynthetic pigments in vacuum, in solution and imbedded in proteins. Monomeric Mg-porphyrins, chlorophylls and bacteriochlorophylls and their solvent 1:1 and 1:2 complexes were studied. Calculations were performed for Mg-porphyrin, Mg-chlorin, Mg-bacteriochlorin, mesochlorophyll a, chlorophylls a, b, c(1), c(2), c(3), d and bacteriochlorophylls a, b, c, d, e, f, g, h, plus several homologues. Geometries were optimised with PM3, PM3/CISD, PM5, ab initio HF (6-31G*/6-311G**) and density functional B3LYP (6-31G*/6-311G**) methods. Spectroscopic transition energies were calculated with ZINDO/S CIS, PM3 CIS, PM3 CISD, ab initio CIS, time-dependent HF and time-dependent B3LYP methods. Estimates for experimental transition energies were obtained from linear correlations of the calculated transition energies of 1:1 solvent complexes against experimentally recorded solution energies (scaling). According to the calculations in five-coordinated solvent complexes the magnesium atom lies out of the porphyrin plane, while in six-coordinated complexes the porphyrin is nearly planar. Charge densities on magnesium and nitrogen atoms were strongly dependent on the computational method deployed. Several dark states of low oscillator strength below the main Soret band were predicted for solvent complexes and chlorophylls and bacteriochlorophylls in protein environment. Such states, though not yet identified experimentally, might serve as intermediate states for excitation energy transfer in photosynthetic complexes. Q(y), Q(x) and Soret transition energies were found to depend on the orientation of the acetyl group and external pressure. A method to estimate site energies and dimeric interaction energies and to simulate absorption and CD spectra of photosynthetic complexes is described. Simulations for the light harvesting complexes Rhodospirillum molischianum, chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, and LHC-II of Spinacia oleracea are presented as examples.

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Section: Introductionmentioning

confidence: 99%

Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes

Linnanto

Korppi-Tommola

2006

Phys. Chem. Chem. Phys.

145

164

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“…For each of these molecules, an ab initio SCF-MO calculation has been carried out [6]. These molecules provide a good basis for assessing the effect of magnesium complexation, ring IV reduction, and addition of ring V and other peripheral substituents on the electronic structure of ethyl chlorophyllide a.…”

Section: Resultsmentioning

confidence: 99%

“…Although such an approach can and has been used on quite large chemical systems [6], direct examination of chlorophyll dimers and oligomers and related molecules using such techniques is not computationally feasible at present. However, there are several point-charge as well as other representations based directly on molecular fragment-type ab initio wave functions that are potentially useful, both for interpretive purposes and for an examination of the electrostatic interactions between dimers and oligomers.…”

Section: (3)mentioning

confidence: 99%

“…Toward this end, a series of quantum mechanical studies has been undertaken to probe the electronic and geometric structural features of chlorophyll and related molecules in both their monomeric and 119 oligomeric forms. Preliminary ab initio SCF-MO studies of ethyl chlorophyllide a, magnesium chlorin, magnesium porphine, and free-base porphine have been reported [6], and the donor properties of the three carbonyl groups of ethyl chlorophyllide a have been studied [7].…”

Section: Introductionmentioning

confidence: 99%

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Ab initio calculations on large molecules using molecular fragments: Comparison of charge distribution and molecular electrostatic potential for ethyl chlorophyllide a and related molecules

Oie

Maggiora

Christoffersen

2009

Int. J. Quantum Chem.

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An analysis of the electronic charge distributions of porphine and chlorin, their magnesium-substituted analogs, and ethyl chlorophyllide a has been carried out, using point-charge and symmetrically orthogonalized representations of ab initio molecular fragment SCF-MO wave functions. The results indicate that both representations provide essentially identical descriptions.Molecular electrostatic potential calculations have also k n carried out using the point-charge representation and from the wave function directly. Both approaches are in good agreement in regions beyond the van der Waals radius of the various atoms in the molecule.

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“…The ground state wavefunction is a single Slater determinant constructed from doubly occupied molecular orbitals which are linear combinations of floating spherical Gaussian orbitals (FSGO). The positions of the FSGO within the molecular fragments and the FSGO orbital radii were fixed in previous studies (16)(17)(18). The linear coefficients for the basis orbitals in each of the molecular orbitals were determined by the usual SCF procedure (20,21).…”

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confidence: 99%

Donor properties of the three carbonyl groups of chlorophyll a: ab initio calculations and 13C magnetic resonance studies.

Shipman¹,

Janson²,

Ray³

et al. 1975

Proc. Natl. Acad. Sci. U.S.A.

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The relative donor properties of the three carbonyl groups of chlorophyll a have been studied theoretically by a series of ab initio molecular fragment, floating spherical Gaussian orbital, self-consistent field calculations on ethyl chlorophyllide a and experimentally through a '3C magnetic resonance study on chlorophyll a. The approximate ground state electronic wavefunction of ethyl chlorophyllide a was perturbed by monopole and dipole point charges whose signs, magnitudes, and positions were chosen to mimic the coulombic interactions associated with carbonyl coordination to Mg. Because the polarizability of the ring V keto carbonyl binding site is substantially greater than that for the ester carbonyl binding sites, the ring V keto binding site binds with smallest binding energy for weak perturbations and with largest binding energy for strong perturbations. A comparison of '3C magnetic resonance chemical shifts in chlorophyll a monomer and dimer provides new experimental evidence that the donor-acceptor interactions that bind the chlorophyll dimer together involve a substantial participation by the ring V keto carbonyl and minimal participation by the two ester carbonyl groups, and thus are in agreement with conclusions derived from the ab initio calculations.The primary events (1) in photosynthesis are generally believed to occur within a photosynthetic unit (2-4) in which a large number of chlorophyll molecules act cooperatively. In the photosynthetic unit light energy is absorbed by antenna chlorophyll and converted into electronic excitation energy; this excitation energy is then transferred very efficiently (via excitons) to the photoreactive center (5) where charge separation occurs in a few special chlorophyll molecules (6).Chlorophyll a (Chl a) oligomers have been proposed (7) as realistic models for antenna chlorophyll. Infrared (8-10) and proton magnetic resonance studies (11)(12)(13) In the theoretical part of the present study we have calculated the coulombic binding energies of the three carbonyl functions of Chl a (ring V keto carbonyl at position 9, methyl ester or carbomethoxy carbonyl at position 10a, and ethyl ester or propionic carbonyl at position 7c) to gain an understanding of the relative donor abilities of the three carbonyl groups. The potential energy component of the free energy of monopole and dipole binding was computed through a series of twelve ab initio calculations in which first a monopole and then a dipole was brought up in turn to each of the three carbonyl groups along their C=O axes (Fig. 2) and the binding energy was calculated before and after polarization of the electron distribution.In the experimental part, we have compared 13C chemical shifts of the carbonyl carbon atoms and of carbon atoms in the vicinity of the potential donor functions in Chl a monomer and dimer by a titration procedure introduced by Closs et al. (11).Nuclear geometry of ethyl chlorophyllide a The nuclear geometry for the non-hydrogen atoms used in this study was taken from the x-ray ...

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Ab initio calculations on large molecules using molecular fragments. Preliminary investigation of ethyl chlorophyllide a and related molecules

Cited by 35 publications

References 14 publications

Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes

Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes

Ab initio calculations on large molecules using molecular fragments: Comparison of charge distribution and molecular electrostatic potential for ethyl chlorophyllide a and related molecules

Donor properties of the three carbonyl groups of chlorophyll a: ab initio calculations and 13C magnetic resonance studies.

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