[Investigation of the initial steps of protochlorophyllide photoreduction in etiolated plants]. / Issledovanie nachal'nykh stadii fotogidrirovaniia protokhlorofillida v ztiolirovannykh rasteniiakh.

The irreversible nonfluorescent product of the protochlorophyllide photoreduction with the wide electronic band at 705 nm was discovered. The P705 product through the intermediate products with the fluorescence max at 695 nm and 687 nm turns into Chl684 678, as the result of heating in darkness. The P705, P695, P687 products quench protochlorophyllide fluorescence with great efficiency. Analysis of the intermediate product properties allow to propose a new photoreduction mechanism that includes energy transfer to the trapping center where the charge transfer is performed, nonradiative energy dissipation in the charge-transfer complex, and protonation and disproportionation of the pigment anion-radicals.

[Mixed aggregation of pigments with participation of bacteriochlorophyll]. / Smeshannaia agregatsiia pigmentov s uchastiem bakteriokhlorofilla.

In binar mixture of solvents (dioxane--water, 1 : 4) the spectral-luminescent investigation of the regularities of mixed association and the energetic interaction between molecules of bacteriochlorophyll (BChl) and its analogs (chlorophyll a--Chl, protochlorophyll--PChl, 4-vinyl-protochlorophyll--4VPChl) under variation of donor-acceptor ratio (0,001 less than or equal to CD/CA less than or equal to 1) in the polymer complex was conducted. The essential role of the elementary cell structure of the mixed associate was discovered: the associate of individual BChl did not possess measurable fluorescence whereas the introduction of PChl, 4VPChl and Chl admixture (approximately greater than 1%) into BChl aggregate resulted in the appearance of a BChl fluorescent ability. It was suggested that admixture and BChl molecules formed dimer cells in which the excitation nonradiative deactivation probability was strongly decreased in comparison with individual BChl aggregate. These cells are the centres of mixed associates emission. It was shown that under conditions of effective energy migration in the system of nearly arranged centres with a high degree of orientation the excitation trapping probability strongly depended on the resonance conditions for transition density--transition density interaction between partners of aggregation.

[Spectral-luminescent properties of separate aggregated forms of pigments in solutions]. / Spektral'no-liuminestsentnye svoistva otdel'nykh agregirovannykh form pigmentov v rastvorakh.

The aggregated forms of protochlorophyll a (PChl), 4-vinyl-protochlorophyll a (4VPChl) and chlorophyll a (Chl) in binar mixtures of dioxane-water was investigated. The aggregates are oligomer particles of pigment molecules having considerable degrees of fluorescence polarisation which points to their ordered structure. Two types of fluorescent associates I and II have been discovered. By its electronic spectrum I is similar to the molecular pigment but has smaller quantum yield B congruent to 10(-2) and the lifetime of fluorescence tau congruent to 3--4.10(-9) sec. Associates of type I spontaneously transform into associates of type II which have narrower bands of electronic spectrum than the monomer, very low B congruent to 10(-3)--10(-4) and tau congruent to 2--4.10(-10) sec. In contrast with the decreasing of B and the band intensities in CD spectrum conditioned by rotational strength increase by factor of 100 under transformation from I to II. It follows from these data that the antibatic connection possibly exists between excitation deactivation in associates and their optical activity. From data on splitting the associate CD spectra of type I and II the excitation interaction energy V12 congruent to 75 cm-1 was estimated. The reasons of increasing of rotational strength under transformation from I to II and the overturn of the sign dependence of bands in CD spectrum in some cases are discussed.

[Isolation and identification of protochlorophylls obtained by oxidation of corresponding chlorophylls]. / Vydelenie i identifikatsiia protokhlorofillov poluchennykh okisleniem sootvetstvuiushchikh khlorofillov.

Protochlorophyll with a high yield is isolated under oxidation of chlorophyll a by tetrachloro-o-quinone. A pigment, designated as protochlorophyll b, is isolated by the same way from chlorophyll b. A method of purification of the pigments obtained is worked out, their properties are studied and their structures are identified. The proposed method can be recommended for isolation of protochlorophyll a and b.

[Relationship between chlorophyll concentration and the energy reaction between protochlorophyll and chlorophyll in mixed associations]. / Izuchenie énergeticheskogo vzaimodeistviia mezhdu protokhlorofillom i khlorofillom v smeshannykh assotsiatakh v zavisimosti ot kontsentratsii khlorofilla.

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.

[Aggregation of 4-vinyl-protochlerophyll and protochlorophyll in solutions]. / Osobennosti agregatsii 4-vinil-protekhlorofilla i protokhlorofilla v rastvorakh

The addition of water to dioxane solution of protochlorophyll (PChl) and 4-vinyl-protochlorophyll (4VPChl) results in a number of transformations related with pigment molecule associations into polymer formations and with their conversion. By variation of pigment concentration and composition of binar mixture of solvents a set of aggregated forms with different electronic spectra can be obtained. At the first stage the monomeric pigment converts into polymer with long-wavelenght absorption maximum of 633 nm (P633). During 1-3 hours P633 converts into other aggregated forms: either P639 or P645 depending on the proportion of dioxane and water. The pigment aggregates are characterized by fluorescence (quantum yield less than or equal to 1%) with maxima close to the main maxima of absorption spectra. Alongside with the main aggregated forms of PChl and 4VPChl the presence of a small number of longer-wavelength aggregates in solutions is established by fluorescence spectra. The investigation of dependence of fluorescence spectra on excitation wavelength, as well as of fluorescence excitation spectra of pigments in binary mixture shows that the long-wavelength aggregates can form part of complex associate and be effective trapping centres of electronic excitation of shorter wavelength aggregated forms. The phenomenon of 4VPChl association in concentrated solutions of castor oil (c greater than-10(-2) m/l) is discovered, which is especially marked after a long storage of the solutions at lower temperature (t=-2 degrees C). Under these conditions the two aggregated forms P640 and P650 alongside with monomer are present. The aggregate P650 is characterized by fluorescence with maximum of 655 nm and spectrally similar to the natural form of photoactive protochlorophyll. The experimental data show that the protochlorophyll pigments form a set of aggregated forms and that the medium conditions favour the predominance of some of the forms and their interconversion. The results obtained evidence that the main reason of the long-wavelength shift of electronic spectra for PChl natural forms is the intermolecular interaction related with the association of pigment monomeric molecules.

[Migration of electron excitation energy in mixed associates of chlorophyll and its derivatives]. / Migratsiia energii elektronnogo vozbuzhdeniia v smeshannykh accotsiatakh khlorofilla i ego proizvodnykh

The intracomplex migration is investigated of electron excitation energy between molecules which are a part of a mixed associate. Weakly fluorescent and nonfluorescent associates of chlorophyll and its analogues as well as of bacteriochlorophyll and neoxanthine have been used as donors and acceptors. The migration of excitation energy with variation of quantum yield of donor emission from 5-10(-3) to less than or equal to 10(-4) and also with very weak overlapping of luminescence and absorption spectra for the pair D leads to A is experimentally discovered by luminescence excitation spectra of mixed pigment aggregates. A specific disturbing action of Pd and Cu ions on chlorophyll a luminescence with formation of mixed complexes of chlorophyll with Pd-pheophytin a and Cu-pheophytin b is observed. The presence of Pd and Cu ions in the structure of the mixed complexes gives rise to a considerable reduction of chlorophyll apparently due to increasing intersystem crossing probability in the chlorophyll molecule. The probability of intracomplex energy migration in systems under investigation amounts to approximately 10(12) sec-1 according to the obtained estimations. The probable mechanism of energy migration in mixed associates is discussed. The obtained results may be used for elucidation of a possible role of the mixed aggregates and effective intracomplex migration of excitation energy in photosynthetic apparatus of green plants.