Normal-phase HPLC separation of possible biosynthetic intermediates of pheophytin a and chlorophyll a'.

Normal-phase HPLC conditions have been developed for separating the C17(3) isoprenoid isomers, which are expected to be formed as biosynthetic intermediates of chlorophyll (Chl) a, Chl a' (C13(2)-epimer of Chl a), pheophytin (Pheo) a and protochlorophyll (PChl). The application of these conditions to pigment composition analysis of greening etiolated barley leaves allowed us to detect, for the first time, the C17(3) isomers of Chl a', a possible constituent of the primary electron donor of photosystem (PS) I, P700, and those of Pheo a, the primary electron acceptor of PS II, in the very early stage of greening. The C17(3) isomer distribution patterns were approximately the same between Chl a and Chl a', but significantly different between Pheo a and Chl a', probably reflecting the similarity and difference, respectively, in the biosynthetic pathways of these pigment pairs.     

Reversed-phase HPLC determination of chlorophyll a' and naphthoquinones in photosystem I of red algae: existence of two menaquinone-4 molecules in photosystem I of Cyanidium caldarium.

Chlorophyll (Chl) a', the C13(2)-epimer of Chl a, is one of the two Chl molecules constituting the primary electron donor (P700) of photosystem (PS) I of a thermophilic cyanobacterium Synechococcus elongatus. To examine whether PS I of other oxygenic photosynthetic organisms in general contain one Chl a' molecule in P700, the pigment composition of thylakoid membranes and PS I preparations isolated from red algae Porphyridium purpureum and Cyanidium caldarium was examined by reversed-phase HPLC with particular attention to Chl a' and phylloquinone (PhQ), the secondary electron acceptor of PS I. The two red algae contained one Chl a' molecule at the core part of PS I. In PS I of C. caldarium, two menaquinone-4 (MQ-4) molecules were detected in place of PhQ used by higher plants and cyanobacteria. The 1:2:1 stoichiometry among Chl a', PhQ (MQ-4) and P700 in PS I of the red algae indicates that one Chl a' molecule universally exists in PS I of oxygenic photosynthetic organisms, and two MQ-4 molecules are associated with PS I of C. caldarium.     

P680 (P(D1)P(D2)) and Chl(D1) as alternative electron donors in photosystem II core complexes and isolated reaction centers

Low temperature (77-90 K) measurements of absorption spectral changes induced by red light illumination in isolated photosystem II (PSII) reaction centers (RCs, D1/D2/Cyt b559 complex) with different external acceptors and in PSII core complexes have shown that two different electron donors can alternatively function in PSII: chlorophyll (Chl) dimer P(680) absorbing at 684 nm and Chl monomer Chl(D1) absorbing at 674 nm. Under physiological conditions (278 K) transient absorption difference spectroscopy with 20-fs resolution was applied to study primary charge separation in spinach PSII core complexes excited at 710 nm. It was shown that the initial electron transfer reaction takes place with a time constant of ~0.9 ps. This kinetics was ascribed to charge separation between P(680)* and Chl(D1) absorbing at 670 nm accompanied by the formation of the primary charge-separated state P(680)(+)Chl(DI)(-), as indicated by 0.9-ps transient bleaching at 670 nm. The subsequent electron transfer from Chl(D1)(-) occurred within 13-14 ps and was accompanied by relaxation of the 670-nm band, bleaching of the Pheo(D1) Q(x) absorption band at 545 nm, and development of the anion-radical band of Pheo(D1)(-) at 450-460 nm, the latter two attributable to formation of the secondary radical pair P(680)(+)Pheo(D1)(-). The 14-ps relaxation of the 670-nm band was previously assigned to the Chl(D1) absorption in isolated PSII RCs [Shelaev, Gostev, Nadtochenko, Shkuropatov, Zabelin, Mamedov, Semenov, Sarkisov and Shuvalov, Photosynth. Res. 98 (2008) 95-103]. We suggest that the longer wavelength position of P(680) (near 680 nm) as a primary electron donor and the shorter wavelength position of Chl(D1) (near 670 nm) as a primary acceptor within the Q(y) transitions in RC allow an effective competition with an energy transfer and stabilization of separated charges. Although an alternative mechanism of charge separation with Chl(D1)* as the primary electron donor and Pheo(D1) as the primary acceptor cannot be ruled out, the 20-fs excitation at the far-red tail of the PSII core complex absorption spectrum at 710 nm appears to induce a transition to a low-energy state P(680)* with charge-transfer character (probably P(D1)(δ+)P(D2)(δ-)) which results in an effective electron transfer from P(680)* (the primary electron donor) to Chl(D1) as the intermediary acceptor.     

Energy transfer among dyes on particulate solids

Absorption and fluorescence properties of methylene blue (MB), a well-known singlet molecular oxygen photosensitizer, and its mixtures with pheophorbide-a (Pheo) sorbed on microgranular cellulose are studied, with emphasis on radiative and nonradiative energy transfer from Pheo to MB. Although pure MB builds up dimeric species on cellulose even at 2 x 10(-8) mol g(-1), addition of 2.05 x 10(-7) mol g(-1) Pheo largely inhibits aggregation up to nearly 10(-6) mol g(-1) MB. At the same time, the absorption spectrum of monomeric MB in the presence of Pheo differs from the spectrum in pure cellulose. Both effects reveal a strong influence of Pheo on the medium properties. A model relying entirely on experimental data is developed, through which energy transfer efficiencies can be calculated for thin and thick layers of dye-loaded cellulose. At the largest concentration of MB assuring no dye aggregation, nonradiative energy transfer efficiencies reach a maximum value of nearly 40%. This value is quite high, taking into account the low fluorescence quantum yield of Pheo, Phi = 0.21, and results from the existence of high local concentrations of the acceptor within the supporting material. These results show that large energy transfer rates can exist in a system devoid of any special molecular organization.     

Pulsed high-frequency EPR study on the location of carotenoid and chlorophyll cation radicals in photosystem II

When the primary electron-donation pathway from the water-oxidation complex in photosystem II (PS II) is inhibited, chlorophyll (Chl(Z) and Chl(D)), beta-carotene (Car) and cytochrome b(559) are alternate electron donors that are believed to function in a photoprotection mechanism. Previous studies have demonstrated that high-frequency EPR spectroscopy (at 130 GHz), together with deuteration of PS II, yields resolved Car(+) and Chl(+) EPR signals (Lakshmi et al. J. Phys. Chem. B 2000, 104, 10 445-10 448). The present study describes the use of pulsed high-frequency EPR spectroscopy to measure the location of the carotenoid and chlorophyll radicals relative to other paramagnetic cofactors in Synechococcus lividus PS II. The spin-lattice relaxation rates of the Car(+) and Chl(+) radicals are measured in manganese-depleted and manganese-depleted, cyanide-treated PS II; in these samples, the non-heme Fe(II) is high-spin (S = 2) and low-spin (S = 0), respectively. The Car(+) and Chl(+) radicals exhibit dipolar-enhanced relaxation rates in the presence of high-spin (S = 2) Fe(II) that are eliminated when the Fe(II) is low-spin (S = 0). The relaxation enhancements of the Car(+) and Chl(+) by the non-heme Fe(II) are smaller than the relaxation enhancement of Tyr(D)(*) and P(865)(+) by the non-heme Fe(II) in PS II and in the reaction center from Rhodobactersphaeroides, respectively, indicating that the Car(+)-Fe(II) and Chl(+)-Fe(II) distances are greater than the known Tyr(D)(*)-Fe(II) and P(865)(+)-Fe(II) distances. The Car(+) radical exhibits a greater relaxation enhancement by Fe(II) than the Chl(+) radical, consistent with Car being an earlier electron donor to P(680)(+) than Chl. On the basis of the distance estimates obtained in the present study and by analogy to carotenoid-binding sites in other pigment-protein complexes, possible binding sites are discussed for the Car cofactors in PS II. The relative location of Car(+) and Chl(+) radicals determined in this study provides valuable insight into the sequence of electron transfers in the alternate electron-donation pathways of PS II.     

Transmembrane charge transfer in photosynthetic reaction centers: some similarities and distinctions

This mini review presents a general comparison of structural and functional peculiarities of three types of photosynthetic reaction centers (RCs)--photosystem (PS) II, RC from purple bacteria (bRC) and PS I. The nature and mechanisms of the primary electron transfer reactions, as well as specific features of the charge transfer reactions at the donor and acceptor sides of RCs are considered. Comparison of photosynthetic RCs shows general similarity between the core central parts of all three types, between the acceptor sides of bRC and PS II, and between the donor sides of bRC and PS I. In the latter case, the similarity covers thermodynamic, kinetic and dielectric properties, which determine the resemblance of mechanisms of electrogenic reduction of the photooxidized primary donors. Significant distinctions between the donor and acceptor sides of PS I and PS II are also discussed. The results recently obtained in our laboratory indicate in favor of the following sequence of the primary and secondary electron transfer reactions: in PS II (bRC): Р(680)(Р(870)) → Chl(D1)(В(А)) → Phe(bPhe) → Q(A); and in PS I: Р(700) → А(0А)/A(0B) → Q(A)/Q(B).     

KINETIC STUDIES ON THE STABILIZATION OF THE PRIMARY RADICAL PAIR P680+ Pheo- IN DIFFERENT PHOTOSYSTEM II PREPARATIONS FROM HIGHER PLANTS*

Abstract— The stabilization of the primary radical pair P680+ pheophytin (Pheo)^- through rapid electron transfer from Pheo to the special plastoquinone of photosystem II (PS II), Q_A, was analyzed on the basis of time-resolved (40 ps) UV-absorption changes detected in different PS II preparations from higher plants. Lifetime measurements of¹Chi* fluorescence by single photon counting and a numerical analysis of the redox reactions revealed (1) at exciton densities required for light saturation of the stable charge separation, annihilation processes dominate the excited state decay leading to very similar lifetimes of ¹Chi* in systems with open and closed reaction centers and (2) the difference of absorption changes induced by actinic flashes of comparatively high photon density in samples with open and photochemically closed reaction centers, respectively, provides a suitable measure of the rate constant of QA formation. Conclusion 2 was confirmed in PS II membrane fragments by measurements at three wavelengths (280 nm, 292 nm and 325 nm) where the difference spectrum of Q^-_A formation exhibits characteristic features. The numerical evaluation of the experimental data led to the following results: (1) the rate constant of Q^-_A formation was found to be (300 ± 100 ps)^-1 in PS II membrane fragments and PS II core complexes deprived of the distal and proximal antenna and (2) an iron depletion treatment of membrane fragments does not affect these kinetics. The implications of these results are briefly discussed in terms of the PS II reaction pattern.     

Online Concentration by Head-column Field-amplified with Large-volume Sample Stacking Using Flow Injection-Capillary Electrophoresis for the Analysis of Four Active Components in Cold Medicines.

A simple, effective, and sensitive online concentration method for the detection of dextromethorphan hydrobromide (Dex), chlorphenamine hydrogen maleate (Chl), pseudoephedrine hydrochloride (Pse) and paracetamol (Par) based on flow injection-capillary electrophoresis (FI-CE) analysis with head-column field-amplified sample stacking and large-volume sample stacking was developed. The background electrolyte (BGE) was a solution composed of 55 mM borate-15% (v/v) acetonitrile (ACN) (pH 9.3). The sample was injected electrokinetically between plugs of water. Under the optimum conditions, about a 30-fold improvement in the concentration sensitivity relative to normal CE methods was achieved, giving low limits of detection (LOD) of 1.94 x 10(-5), 0.64 x 10(-5), 1.16 x 10(-5) and 2.84 x 10(-5) mg/mL for Dex, Chl, Pse and Par, respectively. The repeatability (defined as RSD) was 1.01, 1.91, 0.89 and 0.92% with the peak-area evaluation and 1.94, 3.98, 2.66 and 3.27% with the peak-height evaluation for Dex, Chl, Pse and Par, respectively. This method has been successfully applied to the analysis of commercial pharmaceutical preparations containing Dex, Chl, Pse and Par.     

DCMU-INDUCED STIMULATION OF PHOTOSYSTEM I ELECTRON TRANSPORT. INVOLVEMENT OF MEMBRANE STRUCTURAL CHANGES

DCMU-induced stimulation of the rate of photosystem I (PS I) electron transport in DCIPH₂→ MV photoreaction occurs through the action of DCMU on the rate-limiting step which contains the site of electron donation of DCIPH₂ (Ramanujam et al. , 1981). The magnitude of stimulation of the rate by 50 μ M DCMU decreased with increasing concentration of chlorophyll (Chl), implying that DCMU is stoichiometrically related to Chl with respect to the stimulation of the PS I rate.
DCMU-induced stimulation was sensitive to the ionic condition of the thylakoids, the effect being reduced at low cation concentration. Cation-induced scattering changes in thylakoid suspension were partially reversed by DCMU, and the percent Chl in the 10 K fraction of the thylakoid decreased upon addition of DCMU, indicating that grana structure is disrupted by DCMU. Hydroquinone-mediated reduction of cytochrome f in thylakoids in the dark was accelerated in the presence of DCMU. The DCMU effect was not observed in isolated PS I particles.
It is concluded that DCMU binds to the thylakoid membranes and brings about structural changes leading to unstacking of the thylakoids accompanied by an altered interaction of the electron transfer chain components with the added electron donor. This binding of DCMU must have an affinity lower than the well-known binding of DCMU to photosystem II (PS II), because the concentration required is markedly higher.     

Electron transfer through a prenucleated bimetalated alanine-based peptide helix

We have synthesized a 22 residue alanine-based peptide with a tris(bipyridyl)ruthenium(II) amino acid near the middle of the peptide which can act as a photoinducible electron donor. Two histidines spaced i, i + 4 near the C-terminus of the peptide were then cross-linked with a tetraammineruthenium(III) moiety to prenucleate the helix and provide an electron acceptor site. Introduction of the cross-link enhances the average helix content from 67% to 84% at 0 degrees C, as judged by circular dichroism spectroscopy. The temperature dependence of the mean molar residue ellipticity at 222 nm, [THETAV;](222), for the bimetalated peptide was fit to a modified Lifson-Roig helix-coil model to permit extraction of the population of helical conformation at each residue separating the electron donor and acceptor. On average, the residues between the donor and acceptor are 92% helical. Photoinduced electron transfer with a driving force of -1.0 eV and an estimated reorganization energy of 0.82 eV was measured by fluorescence quenching methods in H(2)O and D(2)O, yielding rate constants, k(ET), of 7 +/- 3 x 10(6) s(-)(1) and 5 +/- 1 x 10(6) s(-)(1) at 0 degrees C. Calculation of the electronic coupling matrix element, H(ab), with the Marcus equation yields a value of 0.19 +/- 0.4 cm(-)(1). Analysis in terms of the pathway model for electronic coupling indicates that this magnitude of H(ab) is consistent with the participation of hydrogen bonds in electronic coupling for an isolated alpha-helix.     

Solvent extraction of arsenic(V) with dispersed ultrafine magnetite particles.

The solvent extraction of arsenic(V) was investigated using heptane containing ultrafine magnetite particles and hydrophobic ammonium salt. Arsenic(V) was favorably extracted from aqueous solutions of pH ranging over 2-7, where the distribution ratio (10(3)) was independent of the pH. Although the addition of alkyl ammonium salt improved the phase separation, no notable influence was observed on the extraction of arsenic(V). Oleic acid suppressed the distribution ratio of arsenic(V) when the concentration exceeded 10(-2) M. Sulfate did not interfere with the extraction, while the presence of more than 10(-3) M phosphate decreased the distribution ratio. Metal cations including calcium(II), manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and lanthanum(III) did not give any serious interference up to the 10(-4) M level. According to equilibrium and kinetic studies, the extraction of arsenic(V) can be interpreted by the adsorption of H2AsO4- onto the surface of dispersed magnetite particles. The relationship between the amount of arsenic(V) extracted in the organic phase and that remaining in an aqueous phase followed a Langmuir-type equilibrium equation. The maximum uptake capacity was determined to be 4.8 x 10(-4) mol/g-magnetite (36 mg As/g). The arsenic(V) extracted in the organic phase was quantitatively recovered by back-extraction with an alkaline solution.     

CHARGE TRANSFER COMPLEXES OF PHEOPHYTIN a WITH NITROAROMATICS. ELECTRON TRANSFER FROM EXCITED SINGLET OF PHEOPHYTIN a TO NITROAROMATICS

Abstract— The interaction of pheophytin a (Pheo) with seven nitroaromatic acceptors of varying ring sizes and electron acceptor abilities has been studied both in the ground and excited states. The ground state association constants ( K ) of the 1: 1 complexes of donor (Pheo) and acceptors were found to increase with increasing electron affinities of the different acceptors. All the nitroaromatic compounds efficiently quench the singlet emission of Pheo and the quenching follows the Stern-Volmer (SV) relationship. The SV constants ( K _sv) for different quenchers follow the same order as that of the K values. The reduction potential of Pheo₊/Pheo_* obtained from the quenching data agrees well with the theoretically predicted value. A charge transfer interaction between the singlet excited state of Pheo and the nitroaromatics is suggested from the dependence of quenching rate constants on the electron affinities of the acceptors.     

Effects of metal and the phytyl chain on chlorophyll derivatives: physicochemical evaluation for photodynamic inactivation of microorganisms

Chlorophyll compounds and their derivatives containing metal or phytyl chain can be used as photosensitizer in photodynamic inactivation of microorganisms (PDI). So, the physicochemical properties and antimicrobial effect of chlorophyll derivatives were investigated: Mg‐chlorophyll (Mg‐Chl), Zn‐chlorophyll (Zn‐Chl), Zn‐chlorophyllide (Zn‐Chlde), Cu‐chlorophyll (Cu‐Chl), pheophytin (Pheo) and pheophorbide (Pheid). The photobleaching experiments showed photostability according to Cu‐Chl > Pheo ∼ Pheid ≫ Zn‐Chl ∼ Zn‐Chlde > Mg‐Chl. This order was discussed in terms of metal and the phytyl chain presences. Pheid and Zn‐Chl in aqueous Tween 80 solution exhibited highest singlet oxygen yield compared with the other derivatives. Chlorophyll derivatives (CD) with phytyl chain was limited by the self‐aggregation phenomenon at high concentrations, even in micellar systems (Tween 80 and P‐123). The antimicrobial effect of CD derivatives was investigated against Staphylococcus aureus, Escherichia coli, Candida albicans and Artemia salina. Pheid showed the best results against all organisms tested, Zn‐Chlde was an excellent bactericide in the dark and Cu‐Chl had no PDI effect. No correlation with CD uptake by microorganisms and darkness cytotoxicity was found. The physicochemical properties allied to bioassays results indicate that Mg‐Chl, Pheo, Zn‐Chl and Pheid are good candidates for PDI.     

Rapid ultra-trace determination of beryllium by gas chromatography

The electron capture detector has been used to measure ultra-trace quantities of beryllium separated as beryllium(II) trifluoroacetylacetonate by gas Chromatographic techniques. The lower limit of detectability is ca. 4 x 10(-13) g of beryllium. Calibration plots extend from 8 x 10(-13) to 4 x 10(-11) g of beryllium. Samples of beryllium in aqueous solution at four concentrations (1.18 x 10(-7), 1.18 x 10(-8), 2.95 x 10(-9), and 8.84 x 10(-10)g ml ) were analysed quantitatively by combining solvent extraction and gas chromatography. The distribution of beryllium during the extraction procedures was determined independently by use of radioactive beryllium-7, but the use of tracers is not required in the recommended procedure. Interference studies were made on cations and anions found in biological samples. At the concentrations used in the extraction procedure and the gas Chromatographic process, none of the fifteen ions studied interferes appreciably.     

Effects of acid and alkali on the light absorption, energy transfer and protein secondary structures of core antenna subunits CP43 and CP47 of photosystem II

The effects of acid and alkali treatment on the light absorption, energy transfer and protein secondary structure of the photosystem II core antenna CP43 and CP47 of spinach were investigated by the absorption spectra, fluorescence emission spectra and ciruclar dichroism spectra. It has been found that acid treatment caused the appearance of absorption characteristic of pheophytin a (Pheo a), whereas alkali treatment induced a new absorption peak at 642 nm. The energy transfer between β-carotene and chlorophyll a (Chl a) in CP43 was easily disturbed by alkali, whereas in CP47 was readily affected by acid. As to the effects on the secondary structure of proetins in CP43 and CP47, effects of acid were far less than those of alkali. Both acid and alkali disturbed the microenvironment of Chl a and interfered exciton interaction between Chl a molecules. It was suggested that acid and alkali affect the light absorption, energy transfer and protein secondary structure of CP43 and CP47 in a differenty way. H⁺ can permeate into the internal space of α-helix, change Chl a into Pheo a and disturb the microenvironment of pgiments without damaging the secondary structure of protein, whereas OH⁻ can induce the protein unfolding at first, then saponify Chl a to chlorophyllide and disturb the microenvironment of pigments.     

BASF 13.338 INDUCED CHANGES IN STRUCTURE and FUNCTION OF THE PHOTOSYNTHETIC APPARATUS OF WHEAT SEEDLINGS

Abstract— Growing wheat seedlings in the presence of BASF 13.338 [4-chloro-5-dimethylamino-2-phenyl-3(2H)pyridazinone], a PS II inhibitor of the pyridazinone group, brought about notable changes in the structure and functioning of photosynthetic apparatus. In BASF 13.338 treated plants, there was a decrease in the ratio of Chi a/Chl b, an increase in xanthophyll/carotene ratio and an increase in the content of Cyt b 559 (HP + LP). Chl/p700 ratio increased when measured with the isolated chloroplasts but not with the isolated PS I particles of the treated plants. The SDS-PAGE pattern of chloroplast preparations showed an increase in the CPII/CP I ratio. The F685/F740 ratio in the emission spectrum of chloroplasts at -196°C increased. The difference absorption spectrum of chloroplasts between the control and the treated plants showed a relative increase of a chlorophyll component with a peak absorption at 676 nm and a relative decrease of a chlorophyll component with a peak absorption at 692 nm for the treated plants. The excitation spectra of these chloroplast preparations were similar. Chloroplasts from the treated plants exhibited a greater degree of grana stacking as measured by the chlorophyll content in the 10 K pellet. The rate of electron transfer through photosystem II at saturating light intensity in chloroplast thylakoids isolated from the treated plants increased (by 50%) optimally at treatment of 125 μM BASF 13.338 as compared to the control. This increase was accompanied by an increase in (a) I₅₀ value of DCMU inhibition of photosystem II electron transfer; (b) the relative quantum yield of photosystem II electron transfer; (c) the magnitude of C550 absorbance change; and (d) the rate of carotenoid photobleaching. These observations were interpreted in terms of preferential synthesis of photosystem II in the treated plants. The rate of electron transfer through photosystems I and through the whole chain (H₂O → methyl viologen) also increased, due to an additional effect of BASF 13.338, namely, an increase in the rate of electron transfer through the rate limiting step (between plastoquinol and cytochrome f). This was linked to an enhanced level of functional cytochrome f. The increase in the overall rate of electron transfer occurred in spite of a decrease in the content of photosystem I relative to photosystem II. Treatment with higher concentrations (> 125 μM) of BASF 13.338 caused a further increase in the level of cytochrome f, but the rate of electron transfer was no greater than in the control. This was due to an inhibition of electron transfer at several sites in the chain.     

A new chemiluminescence system for determination of cobalt

The chemiluminescence of the reaction of tartaric acid with hydrogen peroxide in the presence of Co(II) in alkaline buffer media has been examined. The maximum emission wavelength is 460 nm. The kinetic curve of the chemiluminescence system has been modelled with a computer, and the reaction conditions have been optimized. Foreign ions, such as Fe(II), Cr(III) and Mn(II), interfere when present in more than 10-fold ratio to Co(II), but several ions can be tolerated when present in higher ratios to Co(II). The concentration range of linear response is from 3.5 x 10(-9) to 2.0 x 10(-6) g/ml, and the detection limit is 4 x 10(-11) g/ml. The procedure has been satisfactorily applied to determine trace cobalt in human blood serum.     

Spectrophotometric determination of mercury in soils with triphenyltetrazolium chloride

The formation of the acidocomplex of mercury(II) with triphenyl-tetrazolium chloride is studied spectrophotometrically in water-organic media. The composition of the complex is established as TTC:Hg:I = 1:1:1. The molar absorptivity (255) = (6.45 +/- 0.12) x 10(4) 1 mole(-1). cm(-1) is determined. The selectivity of the reaction is studied and the method for determination of mercury(II) 0.1-0.8 mug/ml is shown. Extraction investigations of the system discussed were carried out. The characteristic values for the extraction equilibrium and the equilibrium in the aqueous phase was determined: extraction constant K(ex) = 3.16 x 10(4), distribution constant K(D) = 20.67, and association constant = 1.53 x 10(3). 5 A rapid and sensitive extractive-photometric method for determination of mercury(II) in soil was developed. The determination was carried out without preliminary elimination of mercury.     

QUANTUM YIELDS AND KINETICS OF THE PHOTOBLEACHING OF HEMATOPORPHYRIN, PHOTOFRIN II, TETRA(4-SULFONATOPHENYL)-PORPHINE AND UROPORPHYRIN

Porphyrins used as sensitizers for the photodynamic therapy (PDT) of tumors are progressively destroyed (photobleached) during illumination. If the porphyrin bleaches too rapidly, tumor destruction will not be complete. However, with appropriate sensitizer dosages and bleaching rates, irreversible photodynamic injury to the normal tissues surrounding the tumor, which retain less sensitizer, may be significantly decreased. This paper surveys the quantum yields and kinetics of the photobleaching of four porphyrins: hematoporphyrin (HP), Photofrin II (PF II), tetra(4-sulfonatophenyl)porphine (TSPP) and uroporphyrin I (URO). The initial quantum yields of photobleaching, as measured in pH 7.4 phosphate buffer in air, were: 4.7 x 10(-5), 5.4 x 10(-5), 9.8 x 10(-6), and 2.8 x 10(-5) for HP, PF II, TSPP and URO respectively; thus, the rates of photobleaching are rather slow. Low oxygen concentration (2 microM) significantly reduced the photobleaching yields. However, D2O increased the yields only slightly, and the singlet oxygen quencher, azide, had no effect, even at 0.1 M. Photosensitizing porphyrins in body fluids, cells and tissues may be closely associated with various photooxidizable molecules and electron acceptors and donors. Therefore, selected model compounds in these categories were examined for their effects on porphyrin photobleaching. A number inhibited and/or accelerated photobleaching, depending on the compound, the porphyrin and the reaction conditions. For example, 1.0 mM furfuryl alcohol increased the photobleaching yields of HP and URO more than 5-fold, with little effect on PF II or TSPP. In contrast, the electron acceptor, methyl viologen, increased the photobleaching yield of TSPP more than 10-fold, with little accelerating effect on the other porphyrins. These results suggest that the mechanism(s) of the photobleaching of porphyrin photosensitizers in cells and tissues during PDT may be complex.     

CHLOROPHYLL b: AN INTEGRAL COMPONENT OF PHOTOSYSTEM I OF HIGHER PLANT CHLOROPLASTS

Abstract— An undissociated photosystem I complex may be isolated from spinach thylakoids by mild gel electrophoresis (CP1a) or Triton X-100. CP1a has a Chl a / b ratio of 11 and a Chl/P700 ratio of 120. while the Triton X-100 PS I complex (Chl a / b ratio of 5.9) has a larger antenna unit size (Chl/P700 ratio of 180). None of the Chl a / b -proteins of the main light-harvesting complex (apoproteins of 30–27 kD) are present in CP1a, and they account for less than 10% of the total chlorophyll in the Triton X-100 PS I complex. Instead, these PS I complexes have specific, but as yet little characterized, Chi a / b -proteins (apoproteins in the 26–21 kD range). With both PS I complexes, Chi b transfers light excitation to the 735 nm low temperature fluorescence band characteristic of photosystem I. We suggest that Chi b is an integral but minor component of photosystem I.