CHLOROPHYLLS IN POLYMERS. II. PHEOPHYTIN a IN POLYMERS and THE INFLUENCE OF STRETCHING ON THE STATE OF CHLOROPHYLLS IN ANHYDROUS POLYMER FILMS

Abstract— In the first part of this study the spectral properties of pheophytin a in rigid, unstretched anhydrous polyvinyl alcohol and nitrocellulose films have been studied in order to establish the influence of the central magnesium atom on the state of chlorophylls in polymer systems. The absorption, fluorescence, excitation spectra and fluorescence intensity decays in the polymer films and in the solutions from which they are cast are reported. It is shown that pheophytin a aggregate formation is influenced by the nature of the polymer system. An aggregate of pheophytin a is found in polyvinyl alcohol films over a wide concentration range. On the other hand, pheophytin a exists in the monomeric form in unstretched nitrocellulose films at concentrations below 6 × 10^-6 mol/g.
In the second part of this work, the influence of stretching of the films on the state and distribution of embedded chlorophyll pigments, is described. Here we show that the chlorophyll a molecules are found to undertake a heterogenous distribution in polyvinylalcohol matrices, since stretching partially disrupts the pocket-like structures present in unstretched films. In contrast, chlorophyll a and pheophytin a molecules can be embedded in a monomeric state in nitrocellulose matrices and moreover they remain homogeneously distributed upon stretching. The chlorophyll/nitrocellulose system is concluded to be a useful model system for studies of donor-donor energy transfer processes.     

SPECTROSCOPIC STUDY OF CHLOROPHYLL a IN ORGANIC SOLVENTS AND POLYMERIZED ANHYDROUS POLYVINYL MATRIX

In this paper we present a spectroscopic study of chlorophyll a in solutions and in anhydrous polyvinyl alcohol films. Absorption, excitation and emission spectra, combined with fluorescence lifetime and time-resolved anisotropy measurements show that chlorophyll a in anhydrous polyvinyl alcohol films exists in a purely monomeric state. Furthermore, it appears that the monomeric chlorophyll a exhibits an efficient excitation energy transfer in this polyvinyl alcohol matrix. These results are rationalized in terms of a model in which the chlorophyll a molecules are located within pockets, formed by the polymer chains. It is concluded that the chlorophyll a-anhydrous polyvinyl alcohol film is a suitable system for studying energy transfer processes, especially because the factors governing energy transfer such as mutual orientation and separation of the molecules can easily be controlled.     

Effect of Microwave Irradiation on the Cross-Linking of Polyvinyl Alcohol

The possibility of dehydration (cross-linking) of polyvinyl alcohol upon microwave irradiation of thin polymer films was examined. The properties of polyvinyl alcohol samples treated by convection heating and irradiation were compared. Immobilization of polyvinyl alcohol on polymer matrices by microwave irradiation was studied.     

Phosphatidylcholine-induced reactivation of photosystem II membranes pretreated with Triton X-100

Triton X-100-induced inactivation and phosphatidylcholine-induced reactivation of photosystem II (PSII) membranes were investigated using oxygen electrode, variable fluorescence and spectroscopic techniques including absorption and circular dichroism spectroscopy. Incubation of the PSII membrane with Triton X-100 reduced the oxygen-evolving rate, modified the variable chlorophyll fluorescence kinetics, changed the protein secondary structures, altered the chlorophyll binding state to proteins and decreased the excitonic interaction of chlorophyll molecules. Phosphatidylcholine addition did not change the protein secondary structures, but could partially reactivate the reduced oxygen-evolving rate, and partly reversed the variable fluorescence parameters, the chlorophyll binding state and the excitonic interaction of the chlorophyll molecules. The results indicate that the phosphatidylcholine environment can optimize the tertiary structures of PSII.     

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.     

PREPARATION AND PROPERTIES OF CHLOROPHYLL/WATER-SOLUBLE MACROMOLECULAR COMPLEXES IN WATER. STABILIZATION OF CHLOROPHYLL AGGREGATES IN THE WATER-SOLUBLE MACROMOLECULE

Abstract— As an artificial model compound of the chlorophyll-protein complex in vivo , the chlorophyll/water-soluble macromolecular complexes were prepared by using synthetic linear polymers of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and a natural polymer of bovine serum albumin (BSA). By the method described here, it is possible to prepare an aqueous chlorophyll (Chl)-macromolecular complex solution of a desired Chi aggregate, such as: Chi a (670), Chi a (740) and Chi b ; and with a desired relative content and concentration. These procedures for preparing such complexes will have wide applicability for technical use in Chi studies. For example, extremely diluted aqueous complex solutions of at least 1 × 10^-4% wt Chi a (670 or 740)-macromolecular complex / wt can be obtained without changing the spectral features. From viscosity measurements, the structures of the complexes were inferred: (1) for a linear macromolecular (PVA or PVP) complex, a Chi species is tightly surrounded by a chain of the polymer causing shrinkage of the chain; (2) globular BSA molecules surround Chi species to form a large complex. The mechanism of stabilization of Chi aggregates in thylakoid membrane was discussed concerning an analogy to the complexes studied here.     

Visible-light-excited long-lived organic room-temperature phosphorescence of phenanthroline derivatives in PVA matrix by H-bonding interaction for security applications

Organic room-temperature phosphorescence (RTP) materials are very attractive, but there is still a challenge to achieve RTP for their practical applications under visible light excitation (λ > 400 nm) because of the implement for the most organic RTP is under ultraviolet light. Herein, a simple tactics for inhibiting the vibrational dissipation of three amorphous phenanthroline derivatives by doping them into polyvinyl alcohol (PVA) matrix was utilized to afford visible-light excitation RTP. By using this method, on account of the mutual H-bonding and confinement effect with PVA matrix, a series of organic RTP materials with blue-green phosphorescence emission were obtained under visible-light excitation. The afterglow colors of RTP materials can be adjusted by co-doping the available fluorescence dyes (RhB or Rh6G) into the PVA films through a triplet-to-singlet Förster resonance energy transfer. However, the H-bonding is easily broken by water molecules resulting in the RTP phenomenon disappears. Hence, Aphen-epoxy resin composite system was constructed to overcome this drawback. It is shown that the composite still has good phosphorescence properties after soaking in water for 7 days. The superior RTP of the amorphous phenanthroline derivatives in processable polymer matrices endows these materials with a highly potential for the night warning clothing coating and information encryption.     

SPECTROSCOPIC AND ORIENTATIONAL PROPERTIES OF CHLOROPHYLL a AND CHLOROPHYLL b IN LIPID MEMBRANES

Abstract
Linear dichroism and fluorescence depolarization measurements on chlorophyll a and chlorophyll b molecules incorporated into macroscopically oriented multibilayers of the plant lipid digalactosyldiacylglycerol (DGDG) are presented. The results are combined with measurements of fluorescence anisotropy to obtain both the order parameters describing the orientational statistics and the directions of the absorption and emission transition moments in the frame of the molecules. The problem presented by the overlapping nature of the absorption and emission bands is overcome by determining the fluorescence depolarization at the two maxima of the emission spectrum.     

POLARIZED PHOTO ACOUSTIC SPECTRA OF PHYCOBILISOMES IN POLYVINYL ALCOHOL FILMS

Abstract— Phycobilisomes from Porphyridium cruentum , suspended in polyvinyl alcohol were found to be highly stable, and had normal absorption and fluorescence spectra. Intact phycobilisomes had a major emission peak at 680 nm, whereas upon partial dissociating the major emission was at 580 nm. Incorporation of phycobilisomes in thin polyvinyl alcohol films facilitated examination by photoacoustic spectroscopy. The photoacoustic spectra had a broad absorption maximum at 545–565 nm (phycoerythrin), which resolved as two peaks (545 and 563 nm) in absorption spectra. Stretching of films resulted in apparent chromophore reorientation in partially dissociated, but not in intact phycobilisomes. Only in dissociated phycobilisomes was observed a differential chromophore orientation at 685 nm by polarized fluorescence, which is attributed to a change in orientation of the terminal phycobilisome pigment relative to phycoerythrin.     

Influence of substituted 1,4-anthraquinones on the chlorophyll fluorescence and photochemical activity of pea thylakoid membranes

The effect of substituted 1,4-anthraquinones on the photochemical activity and chlorophyll fluorescence of thylakoid membranes was examined. Both the fluorescence and the photochemical activity depend on the 1,4-anthraquinone substituent. Stronger quinone-induced quenching of the chlorophyll fluorescence than quinone-induced changes in the activity of photosystem II is observed. The type (Cl or Br) and the position (Cl) of the chalogen atom strongly influence the degree of inhibition of PSII electron transport and the quenching of chlorophyll fluorescence. The data suggest that the quenching of chlorophyll fluorescence is due rather to the interaction of the 1,4-anthraquinones and chlorophyll molecules than to an indirect effect caused by stimulation of the photochemistry.     

Large edge-excitation red shift for a merocyanine dye in poly(vinyl alcohol) polymer matrix

The observed large edge-excitation red shift of the fluorescence of a merocyanine dye in a polyvinyl alcohol polymer matrix is explained in terms of a matrix that is rigid enough at room temperature to prevent complete equilibration between different solvation sites.     

EXCITATION TRANSFER BY CHLOROPHYLL a IN MONOLAYERS AND THE INTERACTION WITH CHLOROPLAST GLYCOLIPIDS*

In mixed monolayers with purified chloroplast glycolipids and other colorless lipids, chlorophyll a fluorescence exhibits a decrease in quantum efficiency with increasing chlorophyll concentration. The fluorescence, which is strongly polarized in dilute films, becomes progressively depolarized as the area fraction of chlorophyll increases, and it is completely depolarized in a pure chlorophyll a monolayer. The observed behavior is consistent with an inductive resonance mechanism of energy transfer among the chlorophyll molecules with a critical transfer distance of 20–90 Å, depending on the model chosen for the energy transfer mechanism. The purified glycolipids–mono-and digalactosyl diglycerides and sulfoquinovodiglyceride–separately form stable, compressible monolayers of the liquid-expanded type on an aqueous subphase and in an atompshere of nitrogen. At maximum compression the three glycolipids occupy areas of 55, 80 and 47 A²-molecule^-1, respectively, in the monolayer. Mixed monolayers of chlorophyll a with, separately, the monogalactolipid and the sulfolipid behave upon compression as two-dimensional solutions. The fluorescence polarization at high chlorophyll concentrations in mixed monolayers indicates that several of the lipid diluents facilitate local ordering of the pigment molecules.     

Fluorescence properties of nanosized sulfides

The absorption spectra of nanosized sulfides and selenides (ZnS, CdS, CuS, Cu₂S, AgS, In₂S₃, SnS, PbS, Sb₂S₃, FeS, CoS, NiS, CdSe, and Ag₂Se) showed one absorption band with a maximum at wave-lengths shorter than 300 nm. The UV fluorescence spectra of all of these nanosized sulfides in a polyvinyl alcohol film contained maxima at 380–440 nm. Nanosized sulfides are thus characterized by a very large (up to 15000 cm⁻¹) Stokes shift of fluorescence. In a polyvinyl alcohol film, a decrease in the concentration of cadmium sulfide from 0.05 to 0.002 M led to a threefold increase in the fluorescence intensity. The dependence of the degree of fluorescence buildup on the sulfide concentration is nearly linear. An increase in sulfide concentration to more than 5 × 10⁻³ M in solution led to a complete coagulation of particles.     

Electrochemical Polymerization of Aniline in Polyamide and Polyvinyl Alcohol Matrices

The electrochemical polymerization of aniline was studied in polymer matrices (polyamid-12 and polyvinyl alcohol) on an electrode in the potential cycling mode from –0.2 to +0.8 V vs. SCE. The indices of this process such as the potentials and currents of the polyaniline redox peaks, polymerization rate, and properties of the conducting composite formed depend on the nature of the matrix polymer and are a function of the extent of interaction of this matrix polymer with aniline and polyaniline.     

近红外聚乙烯醇荧光高分子材料的制备及性能

以一种方酸菁染料、水溶性石墨烯和聚乙烯醇为原料,设计合成了在近红外区具有强荧光(660~665 nm)特性及良好的光热稳定性的方酸菁/聚乙烯醇二元和方酸菁/石墨烯/聚乙烯醇三元高分子材料;与在水中相比,方酸菁染料在聚乙烯醇中的最大紫外-可见吸收和荧光波长红移,荧光强度和光稳定性大幅提高;石墨烯的存在增强了材料的光稳定性。     

聚醋酸乙烯酯乳液冻融稳定改性的机理

冻融稳定性;聚乙烯醇缩甲醛;保护胶体;聚醋酸乙烯酯乳液冻融稳定改性的机理     

pH-Responsive amorphous room-temperature phosphorescence polymer featuring delayed fluorescence based on fluorescein

Numerous researchers have paid attention to achieve metal-free phosphorescence by exploring new structures or new mechanisms. Herein, a facile way is introduced to endow a common fluorescence dye, tetrabromofluorescein (4Br-Flu), some fabulous optical characteristics such as dual emission including thermally activated delayed fluorescence, room-temperature phosphorescence (RTP), and the excellent pH-sensitivity. Shortly, 4Br-Flu with good light-emitting properties is composed into the polymer system. The multiple bromine atoms promote the spin-orbit coupling effect and facilitate triplet excitation. Especially, the hydrogen bonding network of the polymer restricts the molecular motion of 4Br-Flu so that the system can emit long-wavelength RTP when 4Br-Flu is doped into polyvinyl alcohol or co-polymerized with acrylamide. Due to the reversible transformation of protonation and deprotonation, the 4Br-Flu based polymer responded to acid and alkali like a phosphorescent switch which makes it an excellent hydrogen chloride/ammonia gas leak detector in dry environment.     

INFLUENCE OF ELECTRIC FIELDS ON FLUORESCENCE QUENCHING OF CHLOROPHYLL a IN NEMATIC LIQUID CRYSTAL MATRIX

Abstract— An electric field enhances the yield of fluorescence of chlorophyll in a liquid crystal solvent. The presented data suggest that the electric field effect is caused by the decrease in the efficiency of fluorescence quenching by ions. Quenching of each polarized component of fluorescence of chlorophyll molecules oriented by the liquid crystal matrix is different. The relative increase in fluorescence yield due to the applied electric field is stronger for a fluorescence component polarized parallel to the direction of liquid crystal orientation than for the perpendicular component.     

Residual water in polyvinyl alcohol

The state of sorbed water molecules in the matrix of polyvinyl alcohol is investigated via the methods of static sorption, DSC, TGA, IR Fourier spectroscopy, ¹H NMR spectroscopy, and quantum-chemical simulation. It is shown that the sorption of water by polyvinyl alcohol characterized by an S-shaped isotherm is described by the double-sorption model. It is established that the low diffusion coefficients and extremely low rates of desorption processes observed in the range of low activities are determined by a shift of the equilibrium toward the formation of hydrogen-bonded complexes of water molecules with hydroxy groups of the polymer. A mechanism for the behavior of residual water in hydrophilic polymers is suggested. It implies that differences between polymers are determined only by the quantity of residual water immobilized in “traps” and the energy of hydrogen-bond formation.     

Fluorescence and energy transfer in polyvinyl carbazole

A model is proposed to explain the kinetics of fluorescence and energy transfer in thin films of polyvinyl carbazole based on the migration of monomer excitons with activator molecules, dimers, and excimer forming sites competing as traps for the exciton energy.