Aggregation of chlorophylls a and b in polymer films and monolayers (original) (raw)
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CHLOROPHYLLS IN POLYMERS. I. STATE OF CHLOROPHYLL a IN UNSTRETCHED POLYMER SYSTEMS
Photochemistry and Photobiology, 1995
Model systems for the study of energy transfer processes are useful for the elucidation of the various factors governing the mechanism of energy transfer in photosynthetic systems. Here we describe the characterization of two systems, consisting of chlorophyll a incorporated in anhydrous nitrocellulose and polyvinylalcohol films. First, optical spectroscopy and time-resolved fluorescence techniques are used to characterize the state of the chlorophyll molecules in the films. We find that in nitrocellulose films the state of chlorophyll a depends strongly on the ratio of nitrocellulose to dimethylsulfoxide in the solutions from which the films are cast. The state of chlorophyll a in polyvinylalcohol films does not depend on the amount of polymer originally dissolved in dimethylsulfoxide. In these films the pigment is monomeric at low concentrations of chlorophyll a, but aggregates are formed at much lower concentrations than in nitrocellulose. The latter fact is explained by the existence of pockets in polyvinylalcohol, leading to high local concentrations. To further test the suitability of the nitrocellulose polymer films as model systems for energy transfer processes, time-resolved fluorescence anisotropy profiles are measured in dependence of the concentration of pigments in the matrix. Fits of the observed decay profiles to the predicted decay show good correspondence, as long as no traps are present. Furthermore, the fitted decay times yield the correct value of the Forster radius R, as compared to the value obtained spectroscopically. We thus conclude that the chlorophyll a-nitrocellulose system can be very appropriate for the study of energy transfer processes between photosynthetic pigment, since the pigments are uniformally distributed in the matrix.
Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences, 1972
By means of the Langmuir-Blodgett technique, monomolecular layers containing chloroplast pigments and lipids have been prepared and transferred from a water surface to solid substrates for spectroscopic study. The absorption spectra of such monolayers of pure chlorophyll a and b have been characterized on several different surfaces. Phytol and M 2+ -1:1 stearate–oleate have been used as inert, transparent layer diluents for the chlorophylls to enable the effect of pigment concentration on the absorption and fluorescence spectra to be studied. Self-quenching of the fluorescence of both chlorophylls has been observed and the chromophore separation at the half-quenching concentration is compared with similar data for monolayers on the surface of water, as well as solid and solution systems. Energy transfer between chlorophyll b and a within a monolayer has also been investigated, and found to involve essentially irreversible transfer of excitation energy from b to a . Experiments invol...
European Journal of Biochemistry, 1991
The binding of cytochrome c to an insoluble monolayer of chlorophyll a was studied. Surface pressure (n), surface potential ( A V) and ['4C]cytochrome c surface-concentration (r) isotherms were measured versus molecular area (a) in mixed films. Compared to the successive-addition method, this procedure allows the formation of homogeneous mixed films. The cytochrome c is incorporated into a chlorophyll a monolayer, compressed at a surface pressure of 20 mN . m-'. On expansion, the quantity of protein incorporated into the monolayer gradually increases. Subsequent compression-expansion cycles result in similar isotherms, distinct from that measured during the first expansion. All surface properties measured, but more specifically the surface radioactivity of ['4C]cytochrome c, indicate the irreversibility of protein incorporation into the chlorophyll a monolayer. In fact, surface properties of the binary film are completely different from the properties of either of the pure components. As a result, calculated values of surface potentials for mixed films using the additivity law deviate from experimentally measured potentials. The absorption and fluorescence spectra of mixed films transferred onto a solid substrate by the Langmuir-Blodgett technique, indicate a dilution effect of chlorophyll a by cytochrome c. However, the dilution effect cannot be detected by the fluorescence lifetimes of pure chlorophyll a and mixed chlorophyll a-cytochrome c films, both shorter than 0.2 ns. This provides support for the existence of an energytransfer mechanism between chlorophyll a monomer and chlorophyll a aggregates which could serve as an energy trap. The role of the protein could be related to that of the matrix.
The Influence of Strong and Weak Acid Upon Aggregation and Pheophytinization of Chlorophyll a and B
Indonesian Journal of Chemistry, 2010
Chlorophyll is green pigment that can be found in plant chloroplast. Higher plants usually have two kinds of chlorophylls, chlorophyll a and b. These green pigments are easily degraded by temperature, light intensity, oxygen, acid, and water. Water causes aggregation of chlorophyll, while acid causes pheophytinization of chlorophyll. Aggregation and pheophytinization process of chlorophyll are influenced by solvents. This study was conducted to observe the spectral difference of aggregated chlorophyll in acetone and methanol upon pheophytinization by strong (HCl) and weak acid (CH 3 COOH), in comparison to the non-aggregated chlorophyll. Observation of spectral pattern was carried out using double beam spectrophotometer CARY 50 at 350-1100 nm. The result shows that pheophytinization of chlorophyll a and b causes hypsochromic shift, particularly at Soret band. There are new peak formations in Qx region, specifically at 506 and 535 nm for pheophytinized-chlorophyll a, and at 371, 435, 526 and 599 nm for pheophytinized-chlorophyll b.
Fluorescence studies of Langmuir--Blodgett films of chlorophyll a mixed with phytol
Journal of Photochemistry and …, 1991
The fluorescence properties of chlorophyll a mixed with phytol (in a 1:lOO molar ratio) were studied in Langmuir-Blodgett films. Fluorescence excitation and fluorescence emission spectra of the chlorophyll a-phytol system in Langmuir-Blodgett films, prepared from an argon-saturated subphase, have maxima at 444 nm and 684 nm respectively. Two lifetime components describe the state of chlorophyll a in Langmuir-Blodgett films: T, =5.18 ns (33%) and r2 = 1.83 ns (67%); these are assigned to single molecules of chlorophyll c1 and to hydrated dimers or oligomers of chlorophyll a respectively. For films prepared from an oxygen-saturated subphase, the maxima of the fluorescence excitation and fluorescence emission spectra of the chlorophyll a-phytol system are shifted to 423 nm and 678 nm respectively. The lifetime components in the time-resolved fluorescence decay curve of the film are r1 = 3.81 ns (54%) and r2 = 1.56 ns (46%). The observed changes in the fluorescence parameters of the chlorophyll a-phytol Langmuir-Blodgett films are discussed in view of the chemical effect of molecular oxygen on the mixed chlorophyll a-phytol monolayer at the air-water interface.
Chloroplast Pigments: Structure, Function, Assembly and Characterization
Plant Growth and Regulation - Alterations to Sustain Unfavorable Conditions, 2018
Chlorophyll and carotenoid are vital components that can be found in the intrinsic part of chloroplast. Their functions include light-harvesting, energy transfer, photochemical redox reaction, as well as photoprotection. These pigments are bound non-covalently to protein to make pigment-protein supercomplex. The exact number and stoichiometry of these pigments in higher plants are varied, but their compositions include chlorophyll (Chl) a, Chl b, lutein, neoxanthin, violaxanthin, zeaxanthin and β-carotene. This chapter provides introduction to the structure and photophysical properties of these pigments, how they assemble as pigment-protein complexes and how they do their functions. Various common methods for isolation, separation and identification of chlorophylls and carotenoid are also discussed.
Biochemistry, 1998
The influence of aggregation on triplet formation in the light-harvesting pigment-protein complex of photosystem II of green plants (LHCII) has been studied with time-resolved laser flash photolysis. The aggregation state of LHCII has been varied by changing the detergent concentration. The triplet yield increases upon disaggregation and follows the same dependence on the detergent concentration as the fluorescence yield. The rate constant of intersystem crossing is not altered by disaggregation, and variations of the triplet yield appear to be due to aggregation-dependent quenching of singlet excited states. The efficiency of triplet transfer in LHCII aggregates from chlorophyll (Chl) to carotenoid (Car) is 92 (7% at room temperature and 82 (6% at 5 K, and does not change upon disaggregation. The Chl's that do not transfer their triplets to Car's seem to be bound to LHCII and are capable of transfering/accepting their singlet excitations to/from other Chl's. Two spectral contributions of Car triplets are observed: at 525 and 506 nm. Disaggregation of macroaggregates to small aggregates reduces by 10% the relative contribution of Car triplets absorbing at 525 nm. This effect most likely originates from a decreased efficiency of intertrimer Chl-to-Car triplet transfer. At the critical micelle concentration, at which small aggregates are disassembled into trimers, the interactions between Chl and Car are changed. At room temperature, this effect is much more pronounced than at 5 K.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1978
Absorption and fluorescence spectra in the red region of water-soluble chlorophyll proteins, Lepidium CP661, CP663 and Brassica CP673, pigment System II particles of spinach': chloroplasts and chlorophyll a in diethylether solution at 25°C were analyzed by the curve-fitting method (French, C.S., Brown, J.S. and Lawrence, M.C, (1972) Plant Physiol. 49, 421--429). It was found that each of the chlorophyll forms of the chlorophyll proteins and the pigment System II particles had a corresponding fluorescence band with the Stokes shift ranging from 0.6 to 4.0 nm.
In order to obtain information on the organization of the pigment molecules in chlorophyll (Chl) a/b/c-containing organisms, we have carried out circular dichroism (CD), linear dichroism (LD) and absorption spectroscopic measurements on intact cells, isolated thylakoids and purified light-harvesting complexes (LHCs) of the prasinophycean alga Mantoniella squamata. The CD spectra of the intact cells and isolated thylakoids were predominated by the excitonic bands of the Chl a/b/ c LHC. However, some anomalous bands indicated the existence of chiral macrodomains, which could be correlated with the multilayered membrane system in the intact cells. In the red, the thylakoid membranes and the LHC exhibited a welldiscernible CD band originating from Chl c, but otherwise the CD spectra were similar to that of non-aggregated LHC II, the main Chl a/b LHC in higher plants. In the Soret region, however, an unusually intense (+) 441 nm band was observed, which was accompanied by negative bands between 465 and 510 nm. It is proposed that these bands originate from intense excitonic interactions between Chl a and carotenoid molecules. LD measurements revealed that the Q Y dipoles of Chl a in Mantoniella thylakoids are preferentially oriented in the plane of the membrane, with orientation angles tilting out more at shorter than at longer wavelengths (9³ at 677 nm, 20³ at 670 nm and 26³ at 662 nm); the Q Y dipole of Chl c was found to be oriented at 29³ with respect to the membrane plane. These data and the LD spectrum of the LHC, apart from the presence of Chl c, suggest an orientation pattern of dipoles similar to those of higher plant thylakoids and LHC II. However, the tendency of the Q Y dipoles of Chl b to lie preferentially in the plane of the membrane (23³ at 653 nm and 30³ at 646 nm) is markedly different from the orientation pattern in higher plant membranes and LHC II. Hence, our CD and LD data show that the molecular organization of the Chl a/b/c LHC, despite evident similarities, differs significantly from that of LHC II. ß 0005-2728 / 00 / $^see front matter ß 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 5 -2 7 2 8 ( 0 0 ) 0 0 1 0 1 -8