SPECTRAL ANALYSIS OF CHLOROPHYLL a AGGREGATES IN THE PRESENCE OF WATER-SOLUBLE MACROMOLECULES

Abstract— The absorption and fluorescence spectra of chlorophyll a (Chi a) aggregates formed in aqueous solutions of polyvinyl alcohol) (PVA), polyvinyl pyrrolidone) (PVP), and bovine serum albumin (BSA) were analyzed by curve-fitting methods in the wavelength region from 650 to 800 nm. The results indicated that the aggregation of Chi a to polymeric forms such as (Chia–2H₂0), was suppressed in the presence of the macromolecules. The suppression was due to a coordination of macromolecule bound ligands to Chi a and was strongest in BSA and weaker in PVA. There were differences in the spectra even though the same types of polymeric Chi a forms were observed due to characteristically different composition of these forms. Fluorescence patterns indicated that energy was transferred from the shorter to the longer wavelength forms.     

IN VIVO FLUORESCENCE SPECTROSCOPY OF CHLOROPHYLL IN VARIOUS UNRIPE AND RIPE FRUIT

—Low temperature (77 K) fluorescence emission spectra of slices obtained from the peel and various layers of the pericarp were recorded for fruits which remain green or undergo color break during ripening.
Fluorescence emission peaks characteristic of the photosystem II antennae (λ_F 686 nm) and reaction center (λ_F 696 nm), as well as of the photosystem I antenna (λ_F 730-740 nm), were present in the peel and all parts of the green pericarp of ripe kiwi, avocado and cantaloupe, as well as in ripe tomato and tangerine after color break. The pattern of the fluorescence emission spectra of all samples except that of the kiwi fruit was similar to that obtained from green photosynthetic tissue of leaves, indicating a normal organization of the chlorophyll-containing complexes of thylakoidal membranes. This pattern is characterized by a significantly higher emission at 730-740 nm relative to that of the 696 and 686 nm peaks. In contradistinction, the fluorescence emission at 686 and 696 nm was higher than that at 730 nm in the kiwi fruit, indicating a reduction in the size of the photosystem I antenna chlorophyll. In the innermost yellowish layers of the kiwi pericarp, a further loss of this antenna occurred, as well as disorganization of the photosystem II complex. The above conclusions are suggested also by measurements of variable fluorescence kinetics.
The results presented here indicate that fluorescence spectroscopy might be used as a tool for the study of chlorophyll organization during the growth and ripening periods of fruit.     

POLARIZED SITE-SELECTION SPECTROSCOPY OF CHLOROPHYLL a IN DETERGENT

Monomeric chlorophyll a (Chl a ) was obtained from the isolated core antenna complex CP47 of photo-system II after incubation with the detergent triton X-100 and was studied by low-temperature polarized light spectroscopy with the aim to obtain model spectra for Chi a in intact photosynthetic complexes. Evidence is presented by circular dichroism and anisotropy measurements that the isolated chlorophyll is monomeric. The absorption bandwidths are relatively large compared to those found in photosynthetic complexes due to inhomogeneous broadening introduced by the detergent. By selective laser excitation at low temperature, considerable narrowing can be achieved. A number of vibrational bands are resolved in the site-selected, polarized absorption and fluorescence emission spectra. The emission spectrum of Chi a in detergent-damaged CP47 is compared with that of Chi a in the intact light-harvesting complex of photosystem II (LHC-II) from green plants. The spectra are remarkably similar indicating that the low-temperature thermal emitter in LHC-II has spectral properties that are very similar to those of monomeric Chl a .     

REACTIVITY OF CHLOROPHYLL a/b-PROTEINS AND MICELLAR TRITON X-100 COMPLEXES OF CHLOROPHYLLS a OR b WITH BOROHYDRIDE

The reaction of several plant chlorophyll-protein complexes with NaBH₄ has been studied by absorption spectroscopy. In all the complexes studied, chlorophyll b is more reactive than Chi a, due to preferential reaction of its formyl substituent at C-7. The complexes also show large variations in reactivity towards NaBH₄ and the order of reactivity is: LHCI > PSII complex > LHCII > PSI > P700 (investigated as a component of PSI). Differential pools of the same type of chlorophyll have been observed in several complexes.
Parallel work was undertaken on the reactivity of micellar complexes of chlorophyll a and of chlorophyll b with NaBH₄ to study the effect of aggregation state on this reactivity. In these complexes, both chlorophyll a and b show large variations in reactivity in the order monomer > oligomer > polymer with chlorophyll b generally being more reactive than chlorophyll a. It is concluded that aggregation decreases the reactivity of chlorophylls towards NaBH₄ in vitro, and may similarly decrease reactivity in naturally-occurring chlorophyll-protein complexes.     

PHYSICAL AND CHEMICAL PROPERTIES OF CHLOROPHYLL RCI EXTRACTED FROM PHOTOSYSTEM I OF SPINACH LEAVES AND FROM GREEN ALGAE

Abstract— A new chlorophyll, designated chlorophyll RCI (Chi RCI), with absorption and fluorescence properties different to other known chlorophylls, has been extracted from photosystem I (PSI) sub-chloroplast particles of the green alga Scenedesmus obliquus; it was suggested that this chlorophyll is either the chromophore ofP–700 or the chromophore of another holochrome associated in a 1:1 molar ratio withP–700. We now report the extraction and isolation of a chlorophyll from PSI particle preparations from spinach leaves with properties identical to those of Chi RCI from Scenedesmus. Its molar ratio toP–700 measured in vivo is again approximately 1:1. Chlorophyll RCI is further characterized by its fluorescence characteristics and redox behaviour. Molecular weight determinations show that Chi RCI has a mol wt 35 units higher than that of chlorophyll a (Chi a).     

Preparation of Polymer Nanofibers Containing Silver Nanoparticles by Using Poly(N‐vinylpyrrolidone)

Summary: Poly(N‐vinylpyrrolidone) (PVP) was used in two methods to prepare polymer nanofibers containing Ag nanoparticles. The first method involved electrospinning the PVP nanofibers containing Ag nanoparticles directly from the PVP solutions containing the Ag nanoparticles. N,N‐Dimethylformamide was used as a solvent for the PVP as well as a reducing agent for the Ag⁺ ions in the PVP solutions. In the second method, poly(vinyl alcohol) (PVA) aqueous solutions were electrospun with 5 wt.‐% of the PVP containing Ag nanoparticles. The Ag nanoparticles were evenly distributed in the PVA nanofibers. PVP containing Ag nanoparticles could be used to introduce Ag nanoparticles to other polymer nanofibers that are miscible with PVP.

TEM image of a PVA nanofiber electrospun with 5 wt.‐% of the PVP containing Ag nanoparticles.     

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.     

FOURIER-TRANSFORM INFRARED SPECTROSCOPIC STUDY OF THE STRUCTURE OF CHLOROPHYLL a and CHLOROPHYLL b IN HIGHLY DILUTE WATER-SATURATED CARBON TETRACHLORIDE SOLUTIONS

Abstract— Fourier-transform (FT) infrared (IR) absorption spectra have been measured for chlorophyll a (Chi a ), chlorophyll b (Chi b ), pheophytin a (Pheo a ), and pheophytin b (Pheo b ) in highly dilute (10^-5-10^-6 M ) water-saturated carbon tetrachloride solutions. Frequencies of IR bands due to C=O stretching modes of the 9-keto group indicate that Chi a assumes largely a dimeric structure in the concentrated (10^-2-10^-3 M ) water-saturated carbon tetrachloride solutions but it remains mostly a monomer with one or two coordinated water molecules in dilute (10^-5-10^-6 M ) solutions. Although it seems that Chi b also assumes predominantly dimeric form in concentrated solutions and monomelic form in dilute solutions, the relative intensity change of two C=O stretching bands ascribed to the free and coordinated 3-aldehyde groups with decreasing concentration suggests that the aldehyde group is also involved in formation of the dimer. The relative intensity of two C=O stretching bands due to the free and coordinated aldehyde groups changes significantly for Pheo b in water-saturated carbon tetrachloride solutions. This observation suggests that some of Pheo b also assume dimeric form via the aldehyde group in concentrated solutions.     

ON THE NATURE OF CHLOROPHYLL a IN AQUEOUS MICELLAR SYSTEMS

Abstract— Absorption and fluorescence spectra of chlorophyll a in aqueous micellar solutions were studied. Solutions in anionic micelles gave an absorption band at 740 nm, attributable to microcrystal- line chlorophyll a. Solutions in cationic and nonionic micelles do not show this band. The positions of the spectral bands in anionic micelles and the possible structure of microcrystalline form are discussed. A comparison is made of the behaviour of microcrystalline form in hydrocarbon solvents and in micellar solutions.     

Successive interaction of pairs of soluble organics with nanosilica in aqueous media

Successive interaction of different pairs of water-soluble polymers (poly(ethylene glycol) (PEG), poly(vinyl pyrrolidone) (PVP), poly(vinyl alcohol) (PVA)), proteins (bovine serum albumin (BSA), ovalbumin, gelatin, and ossein), and smaller organics such as lecithin (1-stearoyl-2-oleoyl phosphatidylcholine, SOPC) and Aethonium (1,2-ethylene-bis(N-dimethyl carbodecyl oxymethyl) ammonium dichloride) with nanosilicas A-300 (S(BET)=232 and 297 m(2) g(-1)) and A-50 (S(BET)=52 m(2)g(-1)) was studied using dynamic light scattering, adsorption, and infrared (FTIR) spectroscopy methods. Time-dependent rearrangement of particle size distributions (PSDs) depicts appearance of both smaller and larger aggregates for silica/PEG(I-first adsorbate)/BSA(II-second adsorbate) and silica/PVP(I)/BSA(II) (i.e., BSA adsorbs onto PEG/silica or PVP/silica) than that for silica/organic compound I. However, in the cases of PVA(I)-BSA(II) and PVA(I)-SOPC(II) a similar effect is not observed because only increased aggregation occurs. The successive equilibrium adsorption of similar pairs shows a diminution of the adsorption of the second compound (gelatin, ovalbumin) with increasing amount of the first adsorbed polymer (PEG or PVP).     

电池结构对叶绿素电池光电性质的影响

叶绿素是绿色植物中吸收太阳能进行光合作用的主要色素,它在可见光范围内有很好的吸收特性^[1]。人们为了充分利用太阳能为人类造福开始了光合作用模拟,70年代后以叶绿素为光敏剂的研究成了科学家的热门课题。     

Studies on the structural transitions and self-organization behavior of polyacrylic acids with complementary polymers in aqueous solution by laser flash photolysis method using the triplet state of covalently bound phenosafranine

The conformational transition of polyacrylic acids and the formation of interpolymer complexes with synthetic polymers in aqueous solution are investigated using the triplet state of the cationic dye phenosafranine covalently attached to the polymer chain. Laser excitation of the phenosafranine dye covalently bound to polymethacrylic acid at 532 nm shows that the absorption spectrum of the triplet state shifts to red region by 40 nm as compared to that of the free dye in aqueous solution and the triplet state lifetime is enhanced by 20-fold. Laser flash excitation shows that the environment of the triplet state of the dye bound to the polyelectrolyte at pH ?5.5 in aqueous solution is more rigid and less polar resulting in a highly compact globular nature of the polymer. The decay of the triplet state of the dye bound to the polymer is attributed to the quenching of the excited state by the carboxylate groups of polyacrylic acids and to the decay process of the triplet in the tightly coiled polymer environment in the pH range 2.0–5.0. The spectra of the triplet dye molecules bound to the polymer at different degree of ionization of the polyelectrolyte suggest that the structural transition from compact globular structure to stretched rod like structure is cooperative involving a series of structural transitions. The observation of diprotonated triplet state of the PMAA bound dye at higher pH (i.e. pH ∼7.0) reveals the existence of an intermediate structure akin to a micellar segment in PMAA prior to the formation of elongated linear chain. The self-organization of PMAA adduct formation with complementary macromolecules, PVP, PEO and PVA primarily due to hydrogen bonding makes the environment of the dye in the adduct more compact and rigid; in particular poly(vinylpyrrolidone), PVP, has the tendency to form more compact interpolymer complex at pH 4.5 than poly(vinyl alcohol), PVA, and poly(ethylene oxide), PEO as revealed from the laser flash photolysis studies of the polymer bound dye using triplet state of the phenosafranine as the marker.     

水溶性高分子对聚紫罗精光致变色性能的影响

用光谱法研究了四种水溶性高分子(聚乙烯吡咯烷酮PVP、聚乙烯醇PVA、明胶、聚丙烯酰胺PAM)对聚丁基紫罗精溴化物(PBV)的光致变色行为的影响。PBV的变色(还原)速率按PVP>明胶>PVA>PAM的顺序递减。在聚乙烯醇介质中,PBV的还原为二级反应。测定了暗回复(退色)速率,发现其服从一级反应规律,用电子顺磁共振法得到同样的结果。     

ON THE FORMATION OF PHOTOSYNTHETIC MEMBRANES IN BEAN PLANTS*

Abstract— The formation of lamellar chlorophyll-protein complexes I and II, solubilized by sodium dodecyl sulfate, was studied by hydroxylapatite column chromatography during greening of etiolated Phaseohis vulgaris leaves.
The protein moiety of both complexes preexists in the prolamellar body of etiolated tissue. The complex II to complex I protein ratio is of the order of 0.5. During greening in intermittent illumination the 'proto'-chloroplast is agranal, and contains 'primary' thylakoids and chlorophyll a (Chl a ). At this stage the complex II to complex I protein ratio increases only slightly. Further greening of the plant tissue in continuous illumination results in grana, Chi b (chlorophyll b ) and more Chl a formation. The complex II to complex I protein ratio in unfractionated thylakoids is now of the order of 2.5, while in grana it is of the order of 4.0.
The binding of chlorophyll formed during greening to the protein moiety of the two complexes is found to be selective. The Chi a selectively formed under intermittent illumination is more strongly bound to the complex I protein. The Chi b and Chl a formed in continuous illunination are found bound to both complex I and complex II proteins.
Analysis by hydroxylapatite column chromatography of subchloroplast fractions obtained by different fractionation procedures have shown that these two chlorophyll-protein complexes are most probably derived from the PSI (photosystem I) and PSII (photosystem II) particles of the photosynthetic membrane. These findings suggest that PSI units are assembled ahead of PSII units. Moreover, they indicate that the complex I protein is the main protein component in the prolamellar body membranes, the 'primary' thylakoids. and the stroma lamellae, while in the grana membranes the major protein is the complex II protein. Finally our results show that formation of the photosynthetic membranes is a multi-step process.     

FAR-INFRARED SPECTRA OF LANGMUIR-BLODGETT FILMS OF CHLOROPHYLL a,CHLOROPHYLL b,PHEOPHYTIN a and THEIR ADDUCTS WITH WATER and DIOXANE*

Fourier transform infrared spectra in the low frequency region (500–150cm^?1) of Langmuir-Blodgett films of chlorophyll a (Chi a), chlorophyll b (Chi b) and pheophytin a have been studied. Correlations between spectral changes in monolayer and multilayers of Chi a and Chi b and their adducts with water and dioxane have been established. Spectroscopic evidence has indicated that, although there are no individual absorption bands that can be assigned to pure Mg-nitrogen and/or Mg-oxygen stretching or bending modes, there are several bands in the400–200 cm^?1 region of the spectra containing considerable contributions from metal-nitrogen and metal-oxygen vibrational modes. These specific vibrations exhibit marked intensity changes and shifts upon water and dioxane interaction. The different states of chlorophyll aggregation in Langmuir-Blodgett mono- and multilayers films resulted in noticeable changes in their far-IR spectra.     

ENERGY TRANSFER FROM CHLOROPHYLL b TO CHLOROPHYLL a IN A HYDROPHOBIC MODEL SYSTEM

Abstract— Chlorophyll a and chlorophyll b purified by high-performance liquid chromatography (HPLC) were subsequently adsorbed on the surface of a pellicular reverse phase packing normally used in HPLC. The granule surface is reacted with octadecyl groups and furnishes an hydrophobic substrate for pigment adsorption. Reflectance spectra of chlorophyll a and chlorophyll b , each adsorbed at average spacings of about 11 nm² per molecule, had red region maxima at 664 and 643nm respectively. Fluorescence excitation spectra for 740nm emission from these surfaces peaked at about 420nm for chlorophyll a and 460nm for chlorophyll b. Adsorbed pigments excited at either of the two wave lengths had a single fluorescence emission peak at 683nm for chlorophyll a and at 664nm for chlorophyll b. A surface having both pigments adsorbed in approximately equal amounts with an overall average spacing of about 5.6nm² per molecule also had peaks at 420 and 460nm in the excitation spectrum. However, excitation of adsorbed molecules on this (latter) surface, at either 420 or 460nm, produced emission with the single chlorophyll a peak at 683nm. It is concluded that, under the conditions of our experiment, exciting adsorbed chlorophyll b contributes strongly to emission from adsorbed chlorophyll a.     

PHOTOVOLTAIC EFFECT OF CHLOROPHYLL a–QUINONE SYSTEMS IN MULTILAYER ARRAYS

Abstract— Photovoltaïc cells made of an array of chlorophyll a (Chi a ) monolayers between an aluminum and a silver electrode have been analyzed. These cells are characterized by charge carrier production due to the dissociation of singlet excitons. The exciton diffusion length λ∼ 300 ± 100 Å. The optimum thickness of these cells consists of an array of 44 monolayers for which a power conversion efficiency η= 0.038% and a quantum yield ø= 0.49% has been measured at 678 nm using an incident light intensity of 0.3 W/m². In these cells, about 60% of the collected charges are generated by the exciton dissociation in the bulk of the semiconductor and 40% by the exciton dissociation at the aluminum electrode. The behaviour of Chl a photovoltaïc cells doped with two quinones has also been analyzed. The two quinones are vitamin K¹ and N,N-distearoyl-1,4-diaminoanthraquinone (SAQ). The photovoltaic properties of Chi a remain practically unchanged when quinone is not in the same monolayer as Chi a. But when Chi a and quinone are in the same monolayer, up to a molecular ratio of 1:0.3, there is a drastic decrease in the efficiencies and quantum yields of the cells. The photovoltaïc behaviour varies in parallel with the extinction of Chi a fluorescence by the quinones in contrast with what is reported for strong electron acceptors adsorbed on photoconductors. An electron transfer from the singlet state of Chi a to the quinones is proposed on the basis of the variation in the quantum yield for current production with the energy of the incident photon.     

聚乙烯醇水溶液反复冷冻过程中的溶剂化效应

采用示差扫描量热技术(DSC)对聚乙烯醇(PVA)水溶液反复冰冻过程中的溶剂化效应进行研究.引入水化数的概念来表征溶剂化效应的大小.结果表明不同浓度区间的PVA水溶液其在反复冰冻过程中溶剂化效应显著不同,主要归因于高分子链分子内和分子间缠结程度对溶剂分子"参与"溶剂化的程度和方式的不同.作者把极稀高分子溶液的研究结果拓展到高分子稀溶液或亚浓溶液区间,阐述了高分子溶液中高分子链的物理图像.冷冻次数的增加导致链间缠结增加,部分溶剂则被包裹在由链间缠结点所形成的网圈内成为分子链的一部分.溶液溶剂化程度的变化受到包裹溶剂与高分子链脱溶剂化的综合影响.     

PROTECTION OF CHLOROPHYLL a BY CAROTENOID FROM PHOTODYNAMIC DECOMPOSITION

Abstract— The order of inhibition of the photooxidation of chlorophyll a in ethanol and ethanol-benzene is as follows: β-carotene, α-tocopherol, benzoquinone, DABCO, menadione, cholesterol and KI. The quenching of singlet oxygen by β-carotene occurs by a collisional quenching mechanism with a diffusion-controlled rate of 1.7 × 10¹⁰ M ^-1 s^-1. Photodecomposition of Chi a is faster in ethanol-D₂O than in ethanol-H₂O. Photoirradiation (660 nm) of the peridinin-Chl a -protein complex, a photosynthetic light-harvesting pigment isolated from marine dinoflagellates, did not show any photo-decomposition of its Chi a in H₂O or D₂O, even after an extended period (12 h) of irradiation. However, the carotenoid, peridinin, in the photosynthetic antenna pigment was photobleached (ca. 10%) during the irradiation. We conclude that the singlet oxygen formed as a result of the Chi photosensitization is immediately quenched by the low-lying triplet state of four peridinin molecules (per Chl a ) bound within the same protein crevice. The carotenoid thus effectively protects Chl a from photodynamic damage, providing a direct proof for the protective role of carotenoids in the photosynthetic pigment complex.     

Effect of an anionic surfactant on the complexation of some nonionic polymers with iodine in aqueous media

Complexation of some water soluble nonionic polymers, namely, polyvinylalcohol (PVA), polyvinylpyrrolidone (PVP), and hydroxypropyl cellulose (HPC), with iodine has been studied in aqueous and aqueous sodiumdodecylsulfate (SDS) solution. While the complexation was indicated by a red shift of the tri-iodide band in case of PVP or HPC, the PVA-iodine complex showed its characteristic band around 500 nm. It was observed for the first time that presence of SDS led to complete break down of the PVA-iodine complex and its characteristic blue color. The presence of monomers of SDS, however, appeared to favor the formation of the iodine complex with PVP or HPC. Addition of n-propanol, which is known to prevent the formation of gels or microgels in polymer solutions, was found to enhance the polymer-iodine complex. Gels of pure HPC and HPC with iodine both in presence and absence of SDS have been prepared and studied.