In vitro preparation and characterization of a 700 nm absorbing chlorophyll-water adduct according to the proposed primary molecular unit in photosynthesis

Fong, Francis K.; Koester, Vaughn J.

doi:10.1016/0005-2728(76)90100-6

Cited by 81 publications

(20 citation statements)

References 22 publications

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“…Analyzing the line intensities at the canonical orientations indicate that the most probable configuration, in the LC matrix, is the partially folded dimer. This is in line with other observations [108][109][110] that only in the presence of hydrogen bonding molecules such as H20, the completely folded conformation exists [108][109][110].…”

Section: -"V" Z 8o~ssupporting

confidence: 81%

Spin polarized triplets oriented in liquid crystals

Levanon

1987

Reviews of Chemical Intermediates

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Section: -"V" Z 8o~ssupporting

confidence: 81%

Spin polarized triplets oriented in liquid crystals

Levanon

1987

Reviews of Chemical Intermediates

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“…Our results are entirely consistent with earlier deductions from solution studies on Chl a dimers and oligomers. The mass spectrometric data show that, contrary to opinions expressed in the literature (24)(25)(26)(27), (i) Chl a free of water can be readily obtained by simple procedures and (ii) the Chl a species absorbing maximally at t-680 nm contain no wateri.e., water is not an integral component of the (Chl a). oligomer structure.…”

Section: Resultscontrasting

confidence: 76%

Self-assembled chlorophyll a systems as studied by californium-252 plasma desorption mass spectroscopy

Hunt

Macfarlane

Katz

et al. 1980

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

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Self-assembled chlorophyll a and pheophytin a systems in thin solid films have been studied by 2'52Cf plasma desorption mass spectrometry (PDMS). The 252Cf-PDMS spectra of these films show monomer cation and anion molecular ions, ions of molecular aggregates, and positive and negative ion fragmentation patterns arising from the loss of various aliphatic side chains from the chlorin ring. Chlorophyll a films cast from dry carbon tetrachloride solution, in which chlorophyll a is known to occur as the dimer, produced an abundant dimer ion. The highest degree of chlorophyll a self-assembly was observed in chlorophyll a films cast from n-octane solutions. Oligomer ions extending upwards in size to the heptamer were detected in this system.It has long been recognized that the optical properties of chlorophyll in vivo are anomalous (1). Relative to a solution of chlorophyll in a polar solvent such as pyridine or diethyl ether, an environment in which chlorophyll is known to exist predominantly as monomer (2), the main red absorption band of chlorophyll in vivo is both red-shifted and broadened. Both the absorption and emission spectra are significantly different (3). The discrepancies are most often attributed (i) to aggregation of the pigment molecules or (ii) to specific chlorophyll-protein interactions. Krasnovskii (4), Brody and Brody (5, 6), and others have suggested that chlorophyll occurs in various states of aggregation in vivo, and that interactions between the chlorophyll molecules in the various aggregates perturb the electronic states of the chromophores and, thus, become the primary source of the spectral anomalies in vivo. Whether there are specific chlorophyll-protein interactions that can generate spectral shifts in the absence of pigment chromophore-chromophore interactions is still an unresolved question.The nature of the various red-shifted chlorophyll systems that can readily be prepared in the laboratory thus becomes relevant to the state of chlorophyll in vivo. Organic compounds with large delocalized 7r electron systems (e.g., chlorophyll) experience nonspecific 7r-7r intermolecular attractive dispersion forces that result in aggregation. In addition, chlorophyll is now recognized to have coordination properties (7) particularly conducive to the formation both of chlorophyll-chlorophyll (endogamous) adducts (8), and chlorophyll-nucleophile (exogamous) aggregates (9). Nuclear magnetic resonance (10, 11) and infrared (12) spectroscopy show that the central magnesium atom of chlorophyll with coordination number 4 (as shown in Fig. 1) is coordinatively unsaturated. The Mg atom thus has a strong tendency to acquire electrons by filling one or both of its axial positions with nucleophilic ligands that have lone pairs of electrons. At the same time, the keto C=O function in ring V has been shown to be an excellent nucleophile (12, 13). The

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“…band in the carbonyl region due to hydrogen bonding of tip keto carbonyl group. Fong and Koester have also observed 709 nm absorption by Chl a solutions in hydrocarbons containing water at low temperatures (18).…”

mentioning

confidence: 97%

Covalently linked chlorophyll a dimer: A biomimetic model of special pair chlorophyll

Wasielewski

Studier

Katz

1976

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

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The synthesis of a covalent dimer of chlorophyll a which possesses properties strikingly similar to those exhibited by P700 special pair chlorophyll in vivo is described. The covalent dimer is characterized by several spectroscopic techniques. Hydrogen bonding nucleophiles, such as water, primary alcohols, and primary thiols, are effective in generating a species from solutions of 10 ,sM covalent dimer in hydrophobic solvents which absorbs light near 700 nm. Formation of this in vitro special pair is a rapid, spontaneous process at room temperature. The range of nucleophiles which promote this process suggests that amino acid residues may function in a similar fashion to form P700 in chlorophyll-protein complexes. The photochemical properties of this in vitro special pair mimic those of in vivo P700 species. The 697 nm a sorption of the in vitro special pair undergoes photo-bleaching rapidly in the presence of iodine that results in the production of a cation radical which exhibits an electron spin resonance signal similar to that of oxidized P700 observed in Chlorella vulgaris. Investigations into the molecular organization of chlorophyll in green plants strongly suggest that the chlorophyll molecules act cooperatively in the primary light absorption process of photosynthesis (1-3). The light energy is captured by an extended array of antenna chlorophyll molecules that absorb strongly at 678 nm (4). The electronic excitation produced by the light absorption is transmitted via the antenna chlorophyll to a special pair of chlorophyll molecules absorbing at about 700 nm, that functions as a low energy trap (5). The trapping of the excitation energy by the P700 special pair results in one electron oxidation of the pair to yield the special pair cation radical, and an electron which ultimately furnishes the reducing potential of photosystem 1 (6). There is good evidence from studies in vivo that the species designated P700 is actually a pair of chlorophyll a (Chl a) molecules.In the visible spectra of systems in vivo, P700 undergoes bleaching upon illumination with red light to a greater extent than does P680 (7-10). The subsequent appearance of a photo-induced electron spin resonance signal of about 7 gauss linewidth with g = 2.0025 suggests the formation of P700t (11) Chl a. Two such interactions result in a structure possessing C2 symmetry with an approximate 8.9 A Mg-Mg distance and 3.6 A interplanar separation between the macrocycles. In this model, the carbomethoxy groups are pointed away from the center of the structure and the phytyl tails extend in similar directions from the macrocycles.Spectroscopic evidence indicates that the keto carbonyl group of Chl a is the primary nucleophilic donor moiety and is of principal importance in Chl a aggregation (14-16). This evidence also supports a minor role for the carbomethoxy group as a donor. Nevertheless, Fong has proposed a model (17) for the structure of the special pair based on the coordination of a water molecule to the magnesium of one Chl a molecu...

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In vitro preparation and characterization of a 700 nm absorbing chlorophyll-water adduct according to the proposed primary molecular unit in photosynthesis

Cited by 81 publications

References 22 publications

Spin polarized triplets oriented in liquid crystals

Spin polarized triplets oriented in liquid crystals

Self-assembled chlorophyll a systems as studied by californium-252 plasma desorption mass spectroscopy

Covalently linked chlorophyll a dimer: A biomimetic model of special pair chlorophyll

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