Solutions Of Chlorophyll Research Articles

Interaction between chlorophyll a and b-cyclodextrin derivatives in aqueous solutions

Cyclodextrins (CDs) are widely used as delivery systems of poorly water soluble drugs in pharmacological applications. The delivery system produces an increase of aqueous solubility of the drug and significant modifications in its physico-chemical and pharmacological properties. In this paper we report the results of our study on aqueous solutions of chlorophyll a, a natural pigment useful as sensitizer in the photodynamic therapy, and two CDs: hydroxypropyl- b-cyclodextrin and heptakis(2,6-di-O-methyl)-b-cyclodextrin. The interactions between chlorophyll and CDs and the effect produced by the presence of the CDs on the aggregation of chlorophyll were studied by calorimetric and UV-Vis spectrophotometric measurements respectively.

Interactions of Chlorophyll and Polypeptide Mixture with Bacterial Reaction Centres

In aqueous solutions of chlorophyll (Chl) a with synthesized polypeptides, at high ratios of Chl to polypeptides (about 75-150 µM to 500 µM) clusters of polypeptides and pigment molecules were formed. The main absorption maxima of more than one formed cluster were located at about 500 nm (Soret band) and in the region of 720-806 nm (red band). The formation of these clusters was fairly slow (some hours) at room temperature and even slower at 4 °C. The rate of cluster formation increased with the increase in Chl concentration. The addition of the even low amount of reaction centres (RCs), separated from the purple bacteria Rhodobacter sphaeroides, to the sample of Chl with polypeptides caused a very strong decrease in the efficiency of cluster formation, and a change in concentration ratios of various pigment-polypeptide aggregates. It was probably a competition between the interaction of Chl with polypeptides and with the RCs. The yield of thermal deactivation of the clusters was high, much higher than that for the RCs alone and it was different for various types of cluster. The clusters absorbing at 725-750 nm were fluorescent with maximum of emission at about 770 nm, whereas clusters absorbing at about 800 nm were nonfluorescent.

The Effect of a Magnetic Field on Photoinduced Electron Transfer in Solutions of Chlorophyll and Porphyrins

It is found that, with the action of photoexcitation and a variable magnetic field on halide-containing porphyrin solutions, a differential absorption is observed, whose spectra conform to the absorption spectra of cation radicals of pigments. It is shown that the effect increases linearly with an increase in the strength of a supplementary magnetic field (H) up to saturation (Hmax 200 ≈ G). The scheme of the photophysical and photochemical deactivation of the energy of electronic excitation for chlorophyll-like pigments in the presence of CCl4 is analyzed with allowance for the effect of the magnetic field on the intercombination conversion in an ion–radical pair. It is shown that solvate-separated ion radicals of the pigments in halide-containing solutions can be formed from the singlet state of tetrapyrrole molecules.

Oxygen uptake photosensitized by disorganized chlorophyll in model systems and thylakoids of greening barley.

Light-dependent oxygen uptake was observed and studied in thylakoids from early greening barley in comparison to oxygen uptake in chlorophyll solutions and in thylakoids from fully green leaves. Substantial oxygen uptake was observed in chlorophyll solutions supplemented with tryptophan, histidine, ascorbic acid or linoleic acid. This uptake was diminished by adding azide, beta-carotene and alpha-tocopherol, which are specific singlet-oxygen quenchers. Illuminated thylakoids from greening barley also exhibited marked oxygen uptake that, likewise, was strongly quenched by azide. In comparison, azide was found not to affect oxygen uptake that is associated with the methyl viologen-catalyzed Mehler reaction. It is reasoned that in the first two cases the oxygen uptake arises from chlorophyll-photosensitized activation of oxygen to the singlet state and its consumption by exogenous or endogenous substrates. In greening, we propose that disorganized chlorophyll photo-sensitizes the oxygen uptake.

Self-Defocusing Effects in an Ethanol Solution of Chlorophyll

The thermally induced optical nonlinearity in a chlorophyll ethanol solution is examined. A theory is presented which shows good agreement with experiment. The theory models an optically thick but physically thin medium whose only heat transport mechanism is conduction. An average n2 was found for the medium which corresponds well with previous results but the thermal medium is shown to be fundamentally different from a Kerr medium.

Photocurrent kinetics (in the microsecond time range) of chlorophyll a, chlorophyll b and stilbazolium merocyanine solutions in a nematic liquid crystal located in an electrochemical cell

The photosynthetic pigments chlorophyll a and chlorophyll b solutions in a nematic liquid crystal were located between semiconducting and metallic transparent electrodes and illuminated by lamp or laser light. Cells with two semiconducting electrodes were also investigated. Such systems represent models of biological membranes simulating their fluid and oriented structure. The kinetics of photocurrent generation in the time range from microseconds to minutes were measured. The action spectrum of the photocurrent effect was established. The kinetics of the photocurrent generated by laser flash photolysis in the chlorophyll solutions are complex and to some extent similar to the kinetics reported for thylakoids. For comparison, the photocurrent kinetics of stilbazolium merocyanine, a highly protonated dye, were also measured. In this case, on flash illumination, only one photocurrent peak was observed. This peak is due to electron tunnelling to the semiconducting electrode. In the case of the chlorophylls, several effects, such as charge displacement and migration of the ions, are superimposed giving a complex photocurrent generation. The results suggest that, in the case of chloroplasts, the kinetics of photopotential generation may be partially dependent on the membrane structure and fluidity.

Spectrofluorimetric method for the determination of large chlorophyll a/b ratios

A practical spectrofluorimetric calibration method at room temperature is described for determining large chlorophyll a/b ratios on direct extracts from plant material of pigments in 80% aqueous acetone, dimethyl sulfoxide, and N,N′-dimethylformamide. The method is based on the work of Boardman and Thorne [Boardman NK and Thorne SW (1971) Biochim Biophys Acta 253: 222–231] who used diethyl ether as solvent. We repeated the calibration in diethyl ether and find significantly different parameters for the calibration curve. The range of standards in this work included solutions with chlorophyll a/b ratios of 10–125 in dimethyl sulfoxide, and of 10–220 in the other solvents. Fluorescence emission spectra were found to be a highly sensitive method for assessing chlorophyll purity. We determined the limits of sensitivity for each solvent from the calibration data. The empirically determined slope of the calibration curve was shown to be related to intrinsic properties of the chlorophylls in solution; this allows predictions of the performance of the method in other solvents.

Theoretical and experimental studies of pump-induced probe deflection in a thermal medium

We analyze the deflection of a probe beam because of pump-probe interaction in a high-absorbing thermal medium. We extend the existing theory by accounting for translation of a finite-width probe because of deflection within the nonlinear sample. We also provide expressions for the number of resolvable angles of the probe for possible applications of the setup as a beam deflector and study conditions for the maximization of the deflection angle and the resolution. We present experimental results obtained with a solution of chlorophyll in ethanol as the thermal medium.

Singlet molecular oxygen and primary mechanisms of photo-oxidative damage of chloroplasts. Studies based on detection of oxygen and pigment phosphorescence

SynopsisPhotogeneration of singlet oxygen molecules (1O2), their vibrationally excited stateand dimols (1O2)2has been shown by measuring photosensitised delayed luminescence in pigment-containing media. All singlet oxygen species are formed as a result of energy transfer to O2from triplet pigment molecules. Monomeric pigment molecules are the most efficient singlet oxygen generators. The1O2quantum yields are 40–80% in aerobic solutions of monomeric chlorophylls and pheophytins. Pigment aggregation causes a strong decrease in singlet oxygen production. The1O2quantum yield in chloroplasts has been estimated using literature and experimental data on formation of the chlorophyll triplet states in the photosynthetic apparatus. The most probable value is 0.1%. One of the major sources of singlet oxygen is likely to be the triplet states of newly formed pigment molecules which are not quenched by carotenoids and can be detected by measuring low-temperature pigment phosphorescence. Quenching of singlet oxygen by the thylakoid components has been analysed and the1O2lifetime estimated. The data suggest that carotenoids and chlorophylls are the most efficient physical1O2quenchers and the1O2lifetime is about 70 ns in thylakoids. The quantum yield of1O2-induced pigment photodestruction was estimated to be about 10−6–10−5. This value is close to the quantum yield of chlorophyll photobleaching experimentally observed in aerobic suspensions of isolated chloroplasts. The intensity of pigment phosphorescence at 77 K correlates with the rate of chlorophyll photobleaching in plant materials. The data suggest that1O2generation by the pigment triplet states is the most likely reason for chloroplast photodamage. The intensity of pigment phosphorescence can be used as an index of the degree of plant photo-oxidative stress.

Effect of exciting wavelength on the quantum yield of a photochemical reaction of polyatomic molecules in halomethane solutions

UDC 541.14 Systems including halo-derivatives of methane as the primary electron acceptor are used to study reactions of one-electron oxidation of photosynthetic pigments and to develop media for optical recording of information [I]. A number of hypotheses have been discussed relative to the possible mechanisms for the dependence of the efficiency of quenching of fluorescence and photoreaction of organoluminophors in the presence of halo-derivatives of methane on the wavelength of the exciting radiation. Thus, for example, in the opinion of Lewis and Ware [2], the dependence of the efficiency of quenching of fluorescence of anthracene by carbon tetrachloride on the exciting wavelength is due to formation of donor-acceptor complexes (exciplexes). However, Leite and Razi Nagvi [3] assume that this effect is connected with formation of a donor-acceptor complex in the ground state rather than in the excited state. We have observed that the quantum yield of the photochemical reaction of 3- and 4-aminophthalimides in the presence of carbon tetrachloride depends on the wavelength of the exciting light [4]. We hypothesized that this dependence is a consequence of the direct decomposition of CC14 under the action of UV radiation and the reaction of the photodecomposition products of tetrachloromethane reacting with phthalimides. In principle, the dependence of the efficiency of quenching of fluorescence and the quantum yield of the reaction on the wavelength of the exciting radiation in halomethane solutions may be also due to the fact that the given process has a rate on the order of the vibrational relaxation or internal S n- + S l conversion. In order to resolve the question concerning the effect of the wavelength of the exciting light on the quantum yield of the photoreaction, it seemed expedient to study halomethane solutions of chlorophyll a and porphyrins. Tetrapyrrole pigments have intense absorpton bands both in the UV and in the visible regions of the spectrum, which allows us to significantly increase the spectral range to be studied. In [5], it was shown that the photoreaction of chlorophyll and porphyrins in halomethane solutions upon irradiation in the longwavelength absorption band is due to electron transfer from the S l state of the pigments to the CCI 4 with formation of the radical cation of the pigment and the radical anion of the halomethane. The solutions were irradiated in a quartz one-centimeter cuvette by a DKSSh-1000 xenon lamp through a diffraction monochromator, and also individual lines of the ILK-120 krypton

Theoretical and experimental studies of propagation of beams through a finite sample of a cubically nonlinear material

Propagation of an externally focused or defocused Gaussian beam in a cubically nonlinear material is studied analytically and experimentally. The theoretical analysis is applied to determine the sign and magnitude of n2 for a material by means of a single-beam experiment with a finite nonlinear sample within which propagational diffraction cannot be neglected. Experimental results for a solution of chlorophyll in ethanol are reported. Based on available theory, an average n2 can be defined for a nonlinearity of thermal origin, and this value is found to be in good agreement with experimental results. Finally, the theoretical analysis and the experimental results of a double-beam experiment performed to determine the sign and magnitude of n2 are also presented.

Model calculations for laser-induced dichroism for molecules in solution

Dichroism in solutions of chlorophyll a in hexane is induced with laser radiation which creates an anisotropy in the spatial distribution of ground and excited states. The dichroism is probed with another laser beam by allowing the direction of polarization of this beam to change with respect to that of the beam which induces the anisotropy and the wavelengths of the two light beams are tuned to different absorption bands of the chlorophyll molecule. Model calculations are performed for the anisotropy and a comparison is made with experiment.

Self-focusing and self-trapping in new types of Kerr media with large nonlinearities

Self-focusing and self-trapping of light in common liquid media such as Chinese tea, Chinese herbal medicine, and solutions of chlorophyll have been observed. These materials are found to be new types of natural Kerr media, and their nonlinear coefficients have been determined. Laser-heating-induced self-phase modulation in these materials has also been observed.

Chlorophyll fluorescence lifetime studies of greening in yellow mutants of Chlamydomonas reinhardtii: Assembly of the Photosystem I core complex

Changes in the functional organization of chlorophyll occur during light-dependent chlorophyll accumulation in yellow mutants of Chlamydomonas reinhardtii . These changes were studied using single-photon counting techniques to determine the chlorophyll fluorescence decay kinetics at various times after transfer of de-greened cultures to the light Several different yellow mutants were analyzed: y-1, a photoautotrophic strain; LM18-al2b, a Photosystem-II (PS II) -deficient derivative of y- 1; and C2, a strain deficient in both Photosystem I (PS I) and PS II. The results demonstrate that the residual chlorophyll present in de-greened cultures has a similar organization, independent of the chlorophyll-protein composition of the fully greened strains. Relative to the composition in light-grown cultures, the chlorophyll present in de-greened cells is enriched in chlorophyll b and has fluorescence decay kinetics similar to monomeric chlorophyll in solution. The reaction-center core complexes accumulate preferentially during the first 2 h of greening, and the light-harvesting complexes beginto accumulate more rapidly thereafter. After 5–6 h, during the stage of maximal chlorophyll accumulation rate, reaction centers and antenna complexes accumulate in constant proportions. The PS I reaction-center core complex has a constant apparent size of about 130 Chl/P-700 at all stages of greening under the conditions we examined.

Determination of the aggregate size in detergent solution of the light-harvesting chlorophyll a/b-protein complex from chloroplast membranes

The molecular mass of an oligomeric integral membrane protein, the light-harvesting chlorophyll a/b-protein complex from the photosynthetic membranes of chloroplasts, has been determined in detergent solution by analytical ultracentrifugation and measurement of the density increment at constant chemical potential of all diffusible solutes. The technique used eliminates any problems resulting from detergent binding to the protein, is independent of the particular detergent used (in this case the nonionic n-octyl beta-D-glucopyranoside), and gives the apparent weight-average molecular mass at different protein concentrations, allowing extrapolation to zero concentration. It means that the solutions of the complex must be brought to dialysis equilibrium with the solvent detergent solution and also requires a reliable method for measuring the protein concentration, for which amino acid analysis was used. The detergent-solubilized complex was a trimer that dissociated into monomers and dimers at low protein concentration. The accurate concentration determinations also allowed the molar chlorophyll-to-protein ratio to be measured as 15, corresponding to 8 chlorophyll a and 7 chlorophyll b molecules.

Study of primary photochemical processes in halomethane solutions of chlorophyll a by kinetic absorption and EPR spectroscopy methods

The authors studied the primary photochemical processes and the electron donor-acceptor properties of chlorophyll a and carbon tetrachloride by using kinetic absorption and EPR spectroscopy. The induced absorption spectra were studied on lamp and laser pulsed photolysis systems. The EPR spectra were recorded on an E-12 radiospectrometer. The pulsed photoexcitation of chlorophyll a in carbon tetrachloride led to substantial changes in the absorption in the visible spectra.

PICOSECOND ABSORPTION SPECTROSCOPY OF CHLOROPHYLL A DIHYDRATE

Abstract— The solution of chlorophyll a in hexane with more than 70% of chlorophyll molecules in the form of the dihydrate (CHl‐a.2H2O)n is investigated at room temperature by picosecond absorption technique. The transient difference spectra and the kinetic dependences of the absorption changes are measured for several excitation and probe wavelengths. Creation of a new state with blue‐shifted absorption band is observed in the system after excitation. A model of the behaviour of the system after excitation is proposed and checked by comparison of the computer‐simulated spectral and time dependences with the experimental data. According to the model, about 30% of excited molecules are in the state with the 0.046 eV shift of the absorption band in comparison with the ground state absorption. The lifetime of this state has 170‐ps component. The rest of the excited molecules are in the first excited state with the decay time component of 37 ps.

Comparison of methods for the determination of chlorophyll in estuarine sediments

Five methods for the determination of the chlorophyll content in solutions of pure chlorophyll and pigmentextracts of estuarine sediments were compared. If only chlorophyll a was present, fluorometric, spectrophotometric as well as HPLC-methods yielded reliable results. In samples containing a mixture of pigments, the spectrophotometric method appears to be preferable to the fluorometric determination, unless the relation between spectrophotometer and fluorometer readings is checked regularly. However, in pigment extracts that contain a mixture of pigments, the most reliable results will be obtained with the HPLC-technique because interference by the various pigments in the extract is excluded as they are separated before quantification. Similar results are reported from the literature for phytoplankton. The conclusions drawn from the analysis of samples from the water column are thus also valid for sediments containing chlorophyll in addition to large amounts of organic matter.

Selective Observation of Chlorophyll c in Whole Cells of Diatoms by Resonant Raman Spectroscopy

A surface scanning technique was used to obtain resonant Raman spectra from chlorophylls in solution and in whole cells of diatoms at 80 K. When in vivo samples are excited at 457.9 nm, chlorophyll c becomes observable in the recorded Raman spectra, as shown by comparison with in vitro measurements. In the field of photosynthetic research this becomes Interesting, as chlorophyll c can hardly be detected in electronic absorption spectra from whole cells, even at low temperatures, because of its weak Q bands compared with other plant chlorophylls. Chl a spectra were obtained with the use of 441.6-nm excitation. Working with two-channel recording, we eliminated the solvent contribution from the Raman spectra of pigments in vitro. Moreover, the technique facilitates detection of Raman excitation profiles from pigment lines in vivo at low temperatures by use of a nonresonating reference in the second sample chamber.

Temperature Induced Spectral Changes of Chlorophyll in Micelles and Solution

Effects of temperature on the spectral properties of chlorophyll in solution and in micelles are reported. After correcting for the volume expansion coefficient of the solvent, it is observed that temperature has no detectable effects on the spectral properties of chlorophyll (between 14 °C to 35 °C). Solutions examined include acetone, chloroform and ethyl alcohol. It is concluded that the temperature induced change in refractive index, of the solvent, has no significant affect on the chlorophyll spec­trum. In micelles containing chlorophyll there are significant temperature induced spectral changes. Heating and cooling results in an irreversible redistribution of monomeric and oligomeric forms of chlorophyll.