Characteristics of mixed association and deactivation of electron excitation in chlorophyll-pheophytin complexes

The regularities of the individual and mixed association of chlorophylls (Chl a, PChl a) with pheophytin (Pheo) were investigated. The complex studies of optical activity, spectral--luminescent and energetic characteristics of aggregates were carried out in mixture of solvents aceton-water (1:49). The formation of pigment mixed associates leads to intracomplex energy transfer from Chl (or PChl) to Pheo. It is shown that the efficiencies of such process, determined by independent ways via the luminescence quenching of energy donor or the emission sensibilization of acceptor, are identical. The energy migration mechanism is the inductive resonance one in studied complexes. The main patterns of the electronic excitation energy deactivation in such systems are discussed. The obtained results are analysed taking into account the contemporary background of the role of pheophytin in the primary processes of photosynthesis.     

Relationship between chlorophyll concentration and the energy reaction between protochlorophyll and chlorophyll in mixed associations

In the paper results are presented of investigation of protochlorophyll (PChl) and chlorophyll (Chl) mixed associations and of interaction between them within the polymer molecular complex, which forms in mixture of water-dioxane (1 : 4). The initial PChl concentration in all solutions was constant (CPChl = 1 . 10(-5) m/l), and Chl concentration varied from 1.10(-8) m/l up to 2.10(-5) m/l. It is shown that with the rise of Chl proportion in the mixed aggregate the rearrangement of both donor (PChl) and acceptor (Chl) components of complex takes place. The luminescence quenching of PChl and the sensitization of Chl emission in mixed pigment associates were investigated of different Chl levels and the evaluation of efficiency of intracomplex electronic excitation energy transfer, determined from quenching and sensibilization, was performed. Similar dependence of energy transfer effectiveness on Chl concentration, determined by the two above-mentioned methods shows that the excitation migration in an associate takes place without losses. An analysis of results permits to conclude that a small trapping efficiency of PChl excitation by the acceptor part of the complex may be connected with the existence of the prerelaxation reverse energy transfer from Chl to PChl in mixed pigment associates. On the basis of the obtained data a mechanism of energy transfer from protochlorophyllide to chlorophyllide in etiolated leaves and homogenates is discussed.     

Excitation dynamics in strongly bounded associates of B800–850 and B800–830 complexes from photosynthetic purple bacterium Thiorhodospira sibirica

Strongly bounded associates of B800–850 (LH2) and B800–830 (LH3) complexes from photosynthetic purple bacterium Thiorhodospira sibirica were investigated. It was shown that associates contain 8–10 complexes (LH2:LH3 ≈ 1:1). Absorption spectra of the monomer LH2 and the monomer LH3 complexes were calculated. Excitation of B800 absorption band of associates results in: (i) intracomplex excitation energy transfer from B800 to B830 or B850 with time constant of about 500 fs; (ii) intercomplex excitation energy transfer from B820 band of LH3 complex to B850 band of LH2 complex with time constant of about 2.5 ps; (iii) excitation deactivation in B850 band of LH2 complex with time constant of about 800 ps. Signal polarization at long-wavelength side of associates absorption spectrum near 900 nm was negative (?0.1). The interaction of LH3 and LH2 complexes in associates is, to some extent, analogous to the interaction of LH2 and LH1 complexes in chromatophores. Time constant of excitation energy transfer between LH3 and LH2 complexes in associates may be regarded as a minimal time constant for energy transfer between the peripheral and core antenna complexes.     

The photophysical behavior of mixed transition metal-uranyl complexes with polyketonate ligands. The vibronically isolated uranyl chromophore

The uranyl excited-state lifetimes and luminescence spectra have been examined for a series of bis- triketonate and bis-tetraketonate uranyl— transition metal complexes at low temperatures. The energies of the vibronic components of the uranyl luminescence were found to be dependent on the complexing ligand, but they did not depend significantly on the neighboring transition metal (Cu, Co, Fe, Ni, Zn, Pd). The band shape was sometimes markedly dependent on the metal. Emission quantum yields varied over a 100-fold range. Emission lifetimes varied by less than a factor of three, despite the fact that most of the transition metals are potential quenchers, and despite the existence of a low energy ligand-to-metal charge-transfer excited state in the tetraketonate complexes. The vibronic isolation of the uranyl excited state from other molecular excited states in these complexes is attributed to a large nuclear reorganizational barrier for entry into or escape from the potential energy surface of the electronically excited uranyl moiety. Population of the uranyl excited state results in an increase in the UO bond length, and the UO nuclear motions are not activated by other low energy electronic excited states of the polyketonate complexes.     

Study of different types of chlorophyll a aggregates in solutions and films by absorption and luminescence derivative spectroscopy]

The second derivative of absorption, fluorescence and fluorescence excitation spectra of chlorophyll a in concentrated solutions and films was investigated. More than 14 forms of pigment aggregates, which can be divided into two types--with narrow 8-10nm) and wide (25-40nm) low temperature (-196 degrees C) spectra bands, were found. For the most part of the aggregated forms, the position and half width of the bands, as well as the Stokes shift and relative quantum yield were determined. The comparison of the spectral characteristics points to the indentity of the aggregates and corresponding native forms of Chl. a. It is shown that the universal relationship between absorption and fluorescence bands in applicable to the aggregates of the two types and the energy of resonance interaction between monomers in the aggregates is evaluated.     

Effect of intramolecular interaction on the electron excitation state of nucleic acid components

A theoretical and experimental investigation of absorption and luminescence features of crystals and aggregates of nucleic acid bases were carried out. The long wavelength low intensity bands in UV-absorption nd excitation spectra, bathochromic shift of fluorescence spectra, the change of correlation between the intensity of fluorescence and phosphorescence spectra were obtained. The interpretation of these experimental results was proposed on the basis of pair interaction calculations (exciton-resonance and charge-resonance) in different conformations of cytosine dimers. The energy transfer after excitation at lambda 280 and 312 nm was investigated in nucleic acid base aggregates.     

Study of spectral and luminescent manifestations of the aggregation of thymine chromophores in aqueous solutions of polythymidylic acid at room temperature in connection with the task of photochemical record of information on thymine

Luminescence and excitation luminescence spectra of water solutions of polythymidylic acid at room temperature were studied. Three luminescence bands at different excitation wavelengths were observed: at 338 nm, which was known earlier, and two new bands, at 320 and 350 nm. The study of excitation luminescence spectra that have not been studied earlier led us to interpret the band at 320 nm as a band of chromophores that do not interact, the band at 338 nm as a band of photochemically most active densely packed stacking dimers (absorption band exciton splitting approximately 4000 cm(-1)), and the band at 350 nm as a band of photochemically inactive big stacking aggregates (n > or = 10, exciton splitting approximately 8000 cm(-1)). Changes in optical density at 270 nm of poly-T water solutions after consecutive irradiations with UV light at 297+302 and 248 nm were studied. The causes of incomplete reversibility are discussed.     

Determination of Fluorescence Polarization of Double Chromophore Complexes

Polarized fluorescence of rigid double-chromophore complexes with intracomplex energy exchange between chromophores was analyzed, and the formula for the degree of polarization derived for the case of steady-state excitation: P = (3 cos²θ - 1 + 2A)/(3 + cos²θ + 4A). In this formula θ is the angle between the transition dipole moments of chromophores in complexes, and A is the parameter dependent on the spectroscopic features of chromophores and energy migration rates. The case of excitation by a δ-pulse was also analyzed, and a formula for fluorescence polarization kinetics was derived.As an example of the application of the derived formulae, the polarized fluorescence spectra and their picosecond kinetics were calculated for the β-subunits of the blue-green algae Agmenellum quadruplicatum. The results obtained were compared with experimental measurements of Mimuro et al. (1986, Biochim. Biophys. Acta848, 155-166) and found to match these data well.     

Luminescence of bacteriorhodopsin from Halobacterium halobium and its connection with the photochemical conversions of the chromophore

Red luminescence of purple membranes from Halobacterium halobium cells in suspension, dry film or freeze-dried preparations was studied and its emission, excitation and polarization spectra are reported. The emission spectra have three bands at 665–670, 720–730 and at 780–790 nm. The position (maximum at 580 nm) and shape of the excitation spectra are close to those of the absorption spectra. The spectra depend on experimental conditions, in particular on pH of the medium. Acidification increases the long wavelength part of the emission spectra and shifts the main excitation maximum 50–60 nm to the longer wavelength side. Low-temperature light-induced changes of the absorption, emission and excitation spectra are presented. Several absorbing and emitting species of bacteriorhodopsin are responsible for the observed spectral changes. The bacteriorhodopsin photoconversion rate constant was estimated to be about 1 · 10¹¹ s^?1 at ? 196°C from the quantum yields of the luminescence (1 · 10^?3) and photoreaction (1 · 10^?1). The temperature dependence of the luminescence quantum yield points to the existence of two or three quenching processes with different activation energies. High degree of luminescence polarization (about 45–47%) throughout the absorption and fluorescence spectra and its temperature independence show that there is no energy transfer between bacteriorhodopsin molecules and no chromophore rotation during the excitation lifetime. In carotenoid-containing membranes, energy migration from the bulk of carotenoids to bacteriorhodopsin was not found either. Bacteriorhodopsin phosphorescence was not observed in the 500–1100 nm region and the emission is believed to be fluorescence by nature.     

Luminescence of bacteriorhodopsin in purple membranes from Halobacterium haolbium cells]

Red luminescence of purple membranes from Halobacterium halobium cells was found out, and its emission, excitation and polarization spectra were investigated. Simultaneous parallel measurements of absorption and luminescence changes in one sample brought about by the action of light were also carried out. The bands in the spectra can be attributed to a number of bacteriorhodpsin (BR) forms: BR(595,520), BR(650,575),BR(600-620), BR(700,625), BR(730,660) BR(780,695), where the number above is the position of the luminescence maxima, below--that of absorption. Proceding from the quantum yield of the luminescence (10(-3)) and of photoreaction (10(-1)) of BR, the photoisomerization rate constant of the latter was estimated (10(11) sec(-1). The temperature dependence of the luminescence quantum yield points to the existence of two or three quenching processes with different activation energies. BR phosphorescence was not observed in the region 500-1100 nm. High degree (36%) os luminescence polarization shows that there is no homogeneous energy transfer between BR molecules, or there is regularity in orientation of their dipoles. Energy migration from the bulk of carotenoids to BR was not found. However limited heterogeneous transfer between the different BR forms cannot be ruled out. The absence (or limitation) of migration indicated that there is a spatial separation of the chromophores. Data on possible participation of triplet states in the BR photoconversions are discussed.     

Interactions of the anticancer antibiotic altromycin B with copper(II), palladium(II) and platinum(II) ions and in vitro activity of the formed complexes

Interaction of the anticancer antibiotic altromycin B with Cu(II), Pd(II) and Pt(II) ions was studied using 1H-NMR, EPR, electronic absorption and circular dichroism spectroscopy. The results derived from NMR studies where that the Pt(II) and Pd(II) ions interact with the nitrogen atom of the dimethylamino group of the C(10)-disaccharide, while the C(2)-epoxide group does not participate and remains intact. Cu(II) ions interact in a different way with altromycin B as was concluded by EPR and circular dichroism spectra. Altromycin B coordinates to the Cu(II) ions via the oxygen atoms of the C(11) phenolic and the C(12) carbonyl group while the nitrogen atom does not participate in the complexation. The presence of these metal ions improves the stability of altromycin B in solution. These complexes were studied in vitro against K562 leukemia sensitive and doxorubicin-resistant cells and GLC4 lung tumor cells, sensitive and doxorubicin-resistant. The activity of the complexes compared to the free drug is improved against resistant cells and is affected moderately against sensitive cells. Finally, 20% of platinum added as altromycin B metal complex entered GLC4 cells.     

Effect of DNAase on fluorescent properties of pigment-protein complexes, contained in photosystem II

It was found that chlorophyll fluorescence spectra and spectra of fluorescence excitation of pigment-protein complexes of photosystem II are affected by treatment with DNase. Pigment-protein complexes were isolated from pea thylakoid membranes. Spectra were measured at room temperature. It was shown that the treatment with DNase leads to a 30% increase in fluorescence yield at excitation in chlorophyll absorption bands in the fraction containing CP47, CP43, and CP29, and also in the fraction containing reaction center complexes with minor contaminations of light-harvesting complexes. Upon excitation at 260-300 nm and in the region of 500 nm, a diminishing of fluorescence yield takes place. These results suggest that pigments and/or pigment-protein complexes are bound to nucleic acids. This association, by influencing the pigment properties, can participate in the photoregulation of biochemical reactions through changes in the thermal dissipation of excited chlorophyll molecules.     

Complexes produced by associated forms of porphyrin bound with hydrophobic-hydrophilic copolymer and transition metal ions

Properties of protonated dimeric forms of meso-tetraphenylporphine (TPP) and meso-tetra(p-aminophenyl)porphine (TAPP) bound with copolymer and also complexes produced by associated TAPP bound with copolymer, Mn2+, and Fe3+ are investigated by absorption, luminescence, and Raman spectroscopy. According to absorption spectra of protonated dimers of TPP, three dimeric forms of the porphyrin are observed in the ground state. However, selective excitation of these forms according to the fluorescence spectra reveals only two dimeric forms in the excited state. In contrast, similar selective excitation of TAPP bound with copolymer in aqueous-dioxane solution results in weak changes in the fluorescence spectra, nevertheless, there is strong interaction between porphyrin and macromolecular carboxyl groups in the ground state. In the case of the formation of the complexes between associated TAPP bound with copolymer, Mn2+ and Fe3+, a new band in the near IR region with a maximum at 840 nm is built up in the fluorescence spectrum. However, this near IR emission is completely quenched when new strong vibrational bands at approximately 1800 and 1900 cm-1 are revealed in the resonance Raman spectra of the complexes. The observed effects are explained in terms of direct participation of water molecules involved in the water-porphyrin dimeric complex in the processes of transformation of excitation energy. The involvement of water in this dimeric complex can lead to redistribution of flows of the energy degradation when transition metal ions play a role of the agent which enhances the trapping properties of the porphyrin-metal-ions complexes.     

Fluorescence Analysis of 7-Aminoactinomycin–Telomeric Oligonucleotide d[AGGG(TTAGGG)<Subscript>3</Subscript>] Complexes

Interactions of 7-aminoactinomycin D (a fluorescent analogue of actinomycin D, an anticancer antibiotic) and two structural forms of the model guanine-rich telomeric oligonucleotide d[AGGG(TTAGGG)₃] have been studied. We have shown that 7-aminoactinomycin D induces fluorescence in two G-quadruplex structures formed with the presence of potassium or sodium ions. The enthalpy of the interaction between the phenoxasone chromophore of the antibiotic and the telomeric oligonucleotide as determined by analysis of excitation spectra is 5.5 kcal/mol. This value differs little from those obtained for complexes with guanine, adenine, or thymine aggregates (6–7 kcal/mol). In the oligonucleotide, the antibiotic is located within dynamic cavities. Therefore, 7-aminoactinomycin D is not released from telomeric structures to the aqueous phase spontaneously or even by photoexcitation, but it is easily released from the surface of aggregates of the respective nucleobases. The entropy term of the interaction energy calculated as a difference between the total energy determined from the binding constant and the enthalpy determined from excitation spectra constitutes approximately 30% for the telomeric oligonucleotide and is virtually null in interactions with nucleobase aggregates.     

Steady-state luminescence investigation of the binding of Eu(III) and Tb(III) ions with synthetic peptides derived from plant thionins

This work reports Eu(III) and Tb(III) luminescence titrations in which the lanthanide ions were used as spectroscopic probes for Ca(II) ions to determine the metal binding ability of Ac-NESVKEEGGW-NH(2) and Ac-NESVKEDGGW-NH(2). These decapeptides correspond to the putative calcium binding region of the plant antifungal proteins SI-alpha1 from Sorghum bicolor and of Zeathionin from Zea mays, respectively. The luminescence spectra for the Eu(III)-decapeptide system (red emission) with the excitation at the Trp band at 280 nm showed an enhancement of the intensities of the 5D(0)-->7F(J) transitions (where J=0-4) with increments of Eu(III) ion concentration. The photoluminescence titration data of the terbium ion (green emission) in the decapeptide solutions showed intensification of the 5D(4)-->7F(J) transitions (J=0-6), similar to that observed for the Eu(III) ion. Thus, energy transfer from Ac-NESVKEEGGW-NH(2) and Ac-NESVKEDGGW-NH(2) to the trivalent lanthanide ions revealed that these peptides are capable of binding to these metal ions with association constants of the order of 10(5) M(-1). The amino acid derivative Ac-Trp-OEt also transferred energy to Tb(III) and Eu(III) ions as judged from the quenching of tryptophan luminescence. However, the energy transfers were significantly lower. Taken together the luminescence titration data indicated that Ac-NESVKEEGGW-NH(2) and Ac-NESVKEDGGW-NH(2) bind efficiently to both trivalent lanthanide ions and that these ions may be used as probes to distinguish an anionic peptide from a neutral amino acid derivative.     

Spectroscopic properties of the main-form and high-salt peridinin-chlorophyll a proteins from Amphidinium carterae

The main-form (MFPCP) and high-salt (HSPCP) peridinin-chlorophyll a proteins from the dinoflagellate Amphidinium carterae were investigated using absorption, fluorescence, fluorescence excitation, two-photon, and fast-transient optical spectroscopy. Pigment analysis has demonstrated previously that MFPCP contains eight peridinins and two chlorophyll (Chl) a molecules, whereas HSPCP has six peridinins and two Chl a molecules [Sharples, F. P., et al. (1996) Biochim. Biophys. Acta 1276, 117-123]. Absorption spectra of the complexes were recorded at 10 K and analyzed in the 400-600 nm region by summing the individual 10 K spectra of Chl a and peridinin recorded in 2-MTHF. The absorption spectral profiles of the complexes in the Q(y) region between 650 and 700 nm were fit using Gaussian functions. The absorption and fluorescence spectra from both complexes exhibit several distinguishing features that become evident only at cryogenic temperatures. In particular, at low temperatures the Q(y) transitions of the Chls bound in the HSPCP complex are split into two well-resolved bands. Fluorescence excitation spectroscopy has revealed that the peridinin-to-Chl a energy transfer efficiency is high (>95%). Transient absorption spectroscopy has been used to measure the rate of energy transfer between the two bound Chls which is a factor of 2.9 slower in HSPCP than in MFPCP. The kinetic data are interpreted in terms of the F?rster mechanism describing energy transfer between weakly coupled, spatially fixed, donor-acceptor Chl a molecules. The study provides insight into the molecular factors that control energy transfer in this class of light-harvesting pigment-protein complexes.     

Pigment compositions,spectral properties,and energy transfer efficiencies between the xanthophylls and chlorophylls in the major and minor pigment-protein complexes of photosystem II

Absorption, fluorescence, and fluorescence excitation spectra have been measured from CP26, CP29, and monomeric and trimeric LHCIIb light-harvesting complexes isolated from Photosystem II subchloroplast particles from spinach. The complexes were purified using a combination of isoelectric focusing and sucrose gradient ultracentrifugation. The chlorophyll (Chl) and xanthophyll pigment compositions were measured using high-performance liquid chromatography (HPLC). Using the pigment compositions from the HPLC analysis as a starting point, the absorption spectral profiles of the complexes have been reconstructed from the individual absorption spectra obtained for each of the pigments. Also, the fluorescence excitation spectra of the complexes have been deconvoluted. The data reveal the energy transfer efficiencies between Chl b and Chl a and between specific xanthophylls and Chl a in the complexes. The spectral analyses reveal the underlying features of the highly congested spectral profiles associated with the complexes and are expected to be beneficial to researchers employing spectroscopic methods to investigate the mechanisms of energy transfer between the pigments bound in these complexes.     

Protein-protein interactions of light-harvesting pigment protein from spinach chloroplasts. I.Ca-2+ binding and its relation to protein association.

The role of divalent cations in the regulation of the distribution of excitation energy between the two photosystems involved in green plants photosynthesis has led us to search for a better understanding of how such phenomena might occur at the molecular level. Since small changes in orientation of and distance between pigment molecules could greatly affect the distribution of excitation energy, we have decided to study the effects of ions on the light-harvesting pigment protein from spinach chloroplasts. The light-harvesting pigment protein is shown to have two types of binding sites for Ca-2+. Binding studies and analytical ultracentrifugation indicate that site I (K-d equals 2.5 mu-M, n equals 1.5-4.0 mu-mol Ca-2+ bound/mg chlorophyll) is lost as the protein associates. Site II (K-d equals 32 mu-M, n equals 9,5 mu-mol Ca-2+/mg chlorophyll) is not affected by the association of the protein. This site is responsible, however, for a further divalent cation-dependent association of the protein. The possible role of this protein in grana stacking and control of spillover is discussed.     

Fluorinated β-diketone-based Sm(III) complexes: spectroscopic and optoelectronic characteristics

The synthesis and characterization of a series of octa-coordinated Sm(III) complexes with 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione (TFNB) and 2,2′-bipyridine (Bpy) derivatives as ancillary ligand are described here. The complexes were analyzed by elemental, spectroscopic such as infrared spectroscopy, ¹H NMR, and thermogravimetric analyses. The fluorinated TFNB ligand absorbs in the range from 200 to 400 nm. The complexes show the sharp and structured Sm-based emissions in visible region upon irradiation in UV range. Excitation spectra of complexes show similarity to the absorption spectra of ligands suggesting that excitation energy is transferred from ligands to Sm(III) centre by the antenna effect. Photoluminescence emission spectra and colour parameters affirmed that the complexes show luminescence in orange–red region. These luminous Sm(III) complexes might be applied as emissive layer in organic electroluminescent devices.     

Excitation spectra of chlorophyll fluorescence in spinach and barley chloroplasts at 4 K

Excitation spectra of chlorophyll a fluorescence in chloroplasts from spinach and barley were measured at 4.2 K. The spectra showed about the same resolution as the corresponding absorption spectra. Excitation spectra for long-wave chlorophyll a emission (738 or 733 nm) indicate that the main absorption maximum of the photosystem (PS) I complex is at 680 nm, with minor bands at longer wavelengths. From the corresponding excitation spectra it was concluded that the emission bands at 686 and 695 nm both originate from the PS II complex. The main absorption bands of this complex were at 676 and 684 nm. The PS I and PS II excitation spectra both showed a contribution by the light-harvesting chlorophyll $\text{a}\text{b}$ protein(s), but direct energy transfer from PS II to PS I was not observed at 4 K. Omission of Mg²⁺ from the suspension favored energy transfer from the light-harvesting protein to PS I. Excitation spectra of a chlorophyll b-less mutant of barley showed an average efficiency of 50–60% for energy transfer from β-carotene to chlorophyll a in the PS I and in the PS II complexes.