A SHORT-LIVED INTERMEDIATE IN THE PHOTO-ENZYMATIC REDUCTION OF PROTOCHLOROPHYLL(IDE) INTO CHLOROPHYLL(IDE) AT A PHYSIOLOGICAL TEMPERATURE

The reduction of protochlorophyll(ide) into chlorophyll(ide) has been studied by flash absorption spectroscopy at 21°C, with a time resolution of 0.5 µs. The absorption changes have been recorded in the range 670–720 nm after the first and subsequent flashes given to an extract of etiolated bean leaves. At 695 nm the flash-induced absorption increase has its maximum value immediately after the flash and then partly decays with a half-time of about 7–10 µs. A complementary behaviour is observed at 675 nm where the absorption change is very small at time zero and then increases to a stationary value with a half-time of about 6–9 µs. From measurements at several wavelengths it is concluded that a species with an absorption peak around 695 nm is formed immediately after the flash and is then transformed into a stable species with an absorption peak around 675 nm. Measurements at lower temperatures, down to—50°C, show that the transformation is much slowed down at decreased temperatures. The species absorbing at 695 nm (P₆₉₅) is attributed to an intermediate in the photoreduction of protochlorophyll(ide) P_639,650 into chlorophyll(ide) P₆₇₆. When the protochlorophyll(ide) is photoreduced before the flash illumination, the newly formed chlorophyll(ide) gets to a triplet state, which decays with a half-time of 15 µs at 21°C. This result shows that carotenoid molecules do not exert their protective role at this stage of chlorophyll (Chi) formation.     

Unique Thermal Structural Phase Transitions Exhibited by Unsymmetrical Organometallic Gold(III)-Dithiolene Complexes with Pentylthio and Hexylthio Groups

Unsymmetrical gold(III)-dithiolene complexes are potential candidates for molecular materials that exhibit thermal structural phase transitions. In this study, unsymmetrical ppy-gold(III) (ppy⁻=C-deprotonated-2-phenylpyridine(−)) complexes [AuC5] and [AuC6] coordinated by dithiolene ligands containing tetrathiafulvalene (TTF) skeletons with pentylthio (2-{bis(pentylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate(2−)) and hexylthio groups (2-{bis(hexylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate(2−)) were synthesized. Both complexes exhibited a large absorption band at approximately 508 nm, owing to intramolecular ligand-to-ligand charge transfer. One-dimensional columnar structures with head-to-tail molecular arrangements around the metal ions were constructed in the crystals. The flexible alkylthio groups were intercalated into crystalline spaces between dithiolene ligands in the columns. [AuC5] exhibits a simple phase transition at 198 °C between crystalline and isotropic phases irreversibly. The crystalline phase of [AuC6] observed at 25 °C melted at 148 °C. Another crystalline phase grew above 148 °C with a very slow crystallization rate from the liquid phase and was completely transformed into an isotropic phase at 200 °C.     

ENERGY TRANSFER FROM PHYCOBILINS TO CHLOROPHYLL a IN HEAT-STRESSED CELLS OF Anacystis nidulans: CHARACTERIZATION OF THE LOW TEMPERATURE 683 nm FLUORESCENCE EMISSION BAND*

Abstract— Heat-induced changes of the characteristics of fluorescence spectra of Anacystis nidulans cells were studied after 39°C-grown cells were heated at 55°C. Heat-treatment of the cells induced no changes in the absorption properties or photosystem I-catalyzed cytochrome oxidation, but induced a dramatic change in the fluorescence characteristics of the cells. The low temperature fluorescence emission spectra of heated cells showed a large increase of fluorescence emission at683–685 nm (F683) and at 695 nm, while the bands at 660 nm (allophycocyanin) and at 718 nm (chlorophyll a of photosystem I) were not affected when the cells were excited with light absorbed by phycobilins. When the cells were heated for various periods, a progressive increase of the intensity of F683 occurred with the loss in oxygen evolution capacity. The increase of the F683 band was observed prior to the increase of the F695 band. Quenching of emission spectra by the addition of quinones indicates that the F683 band emanated mainly from a long wavelength form of allophycocyanin. Excitation spectra of heated cells measured at 77 K showed that light absorbed by phycobilins was effective in exciting F685, F695, and F715 emission. A possible energy distribution pathway in Anacystis nidulans is discussed.     

FLUORESCENCE SPECTROSCOPY OF A P700-CHLOROPHYLL-PROTEIN COMPLEX*

Abstract. Chlorophyll-protein complexes enriched in the Photosystem I reaction center chlorophyll (P700) exhibit a fluorescence emission maximum at 696 nm at - 196°C The height of this 696 nm emission relative to the emission at 683 nm from antenna chlorophyll a increases proportionally with the P700 concentration while the total fluorescence yield of the complex decreases. The 696 nm emission could possibly be from an absorbing form of antenna chlorophyll a that may be somewhat enriched along with P700 in Photosystem I fractions. However, evidence resulting from glycerol treatment which appears to decrease the rate of resonance energy transfer between antenna chlorophyll and P700 favors the hypothesis that the emission comes from a photooxidized P700 dimer (Chl⁺-Chl) absorbing near 690 nm. In turn, this fluorescence evidence provides additional support for the model of a P700 dimer involving exciton interaction. Absorption in the wavelength region of 450 nm specifically excites emission at 696 nm from the P700-chlorophyll complex.     

TEMPERATURE DEPENDENCE OF PICOSECOND FLUORESCENCE KINETICS OF A CYANOBACTERIAL PHOTOSYSTEM I PARTICLE*

Picosecond time-resolved fluorescence of photosystem I particles isolated from Synechococcus sp. was recorded in the wavelength range from 680 nm to 736 nm for temperatures of 6°C to 42°C and - 100°C using the single-photon-timing technique. By global analysis of the data we found four contributing lifetime components at the higher temperatures (T₁ ' 12 ps, T₁= 35 ps, T₃ ' 65 ps, T₄ ' 1000 ps). We attribute T₁ to an energy transfer between two pigment pools, T₂ to the charge separation process in the reaction center, component T₃ is assigned to aggregate and T₄ to uncoupled chlorophyll emission. The corresponding decay-associated spectra are presented. We also applied a target analysis procedure to fit parameters of a kinetic model directly to the data. The resulting rate constants and species-associated spectra are discussed. The data indicate substantial spectral heterogeneity in the antenna with at least three substantially different chlorophyll pools. The overall exciton decay kinetics (by charge separation) is trap-limited.     

Main‐chain viologen polymers with organic counterions exhibiting thermotropic liquid‐crystalline and fluorescent properties*

A series of viologen polymers with bromide, tosylate, and triflimide as counterions were prepared by either the Menshutkin reaction or metathesis reaction in a common organic solvent. Their polyelectrolyte behavior in methanol was determined by solution viscosity measurements, and their chemical structures were determined by Fourier transform infrared and Fourier transform NMR spectroscopy. They were characterized for their thermotropic liquid‐crystalline properties with a number of experimental techniques. Each of the viologen polymers with organic counterions had a low melting transition or fusion temperature above which it formed either a high‐order smectic phase or a low‐order smectic phase. Each of them also exhibited a smectic‐to‐isotropic transition. The ranges of the liquid‐crystalline phase were 80–88 °C for viologen polymers with tosylate as a counterion and 120–146 °C for viologen polymers with triflimide as a counterion. They had excellent thermal stability. The ranges of thermal stability were 288–329 °C for viologen polymers with tosylate as a counterion and 343–350 °C for viologen polymers with triflimide as a counterion. The fluorescence property for all of the viologen polymers in either aqueous or methanol solution was also included in this study. For example, the viologen polymer containing the 4,4′‐bipyridinium and p‐xylyl units along the backbone of the polymer chain with triflimide as a counterion had an absorption spectrum (λ_max = 265 nm), an excitation spectrum (λ_ex values = 357, 443, and 454 with monitoring at 533 nm), and an emission spectrum (λ_em = 536 nm with excitation at 430 and 450 nm) in methanol. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 659–674, 2002; DOI 10.1002/pola.10134     

Solid State Nuclear Magnetic Resonance Studies of the Thermochromic Phase Transition of the Polydiacetylene from the Bis-n-Propylurethane of 5,7-Dodecadiyne-1,12-diol

The polydiacetylene (PDA) from the bis-n-propylurethane of 5,7-dodecadiyne-1,12-diol (PUDO) undergoes a first order phase transition near 135°C that is associated with a color change from blue at temperatures below the transition to red at temperatures above the transition. We have studied PDA-PUDO by solid state ¹³C nuclear magnetic resonance (NMR) spectra using cross polarization and magic angle spinning (CP-MAS) techniques at temperatures between 25° and 140°C. As observed previously, the acetylene carbon shift moves up field as the temperature is raised above the transition temperature. In addition, near 130°C, the oxymethylene carbon shows 3 resonances, indicating multiple side chain conformations as the PDA undergoes the phase transition.     

QUANTUM YIELD RATIO OF THE FORWARD and BACK LIGHT REACTIONS OF BACTERIORHODOPSIN T LOW TEMPERATURE and PHOTOSTEADY-STATE CONCENTRATION OF THE BATHOPRODUCT K*

The maximum photosteady state fraction of K, x_K^max, and the ratio of the quantum yields of the forward and back light reactions, trans-bacteriorhodopsin (bR) hArr; K, φ_bR/φ_K, were obtained by measuring the absorption changes produced by illumination of frozen water-glycerol (1:2) suspensions of light-adapted purple membrane at different wavelengths at -165°C. An independent method based on the second derivative of the absorption spectrum in the region of the β-bands was also used. It was found that The quantum yield ratio (0.66 ± 0.06) was found to be independent of excitation wavelength within experimental error in the range510–610 nm. The calculated absorption spectrum of K has its maximum at603–606 nm and an extinction 0.85 ± 0.03 that of bR. At shorter wavelengths there are P-bands at 410, 354 and 336 rim. Using the data of Hurley et al. (Nature 270,540–542, 1977) on relative rates of rhodopsin bleaching and K formation, the quantum yield of K formation was determined to be 0.66 ± 0.04 at low temperature. The quantum efficiency of the back reaction was estimated to be 0.93 ± 0.07. These values of quantum efficiencies of the forward and back light reactions of bR at - 165°C coincide with those recently obtained at room temperature. This indicates that the quantum efficiencies of both forward and back light reactions of bacteriorhodopsin are temperature independent down to -165°C.     

PHOTOPHYSICAL PROPERTIES OF CHLOROPHYLL a LANGMUIR-BLODGETT MULTILAYER FILMS

Abstract— Multilayer Langmuir-Blodgett films of chlorophyll u and chlorophyll a in L-α-phosphatidylcholine dipal-mitoyl matrix have been prepared. The films were protected by covering them with eight layers of stearic acid to ensure high film stability during the light illumination. Based on the time-resolved fluorescence measurements a model with two types of chlorophyll arrangement was developed. One arrangement could be attributed to an aggregated state and the other to a homogeneously distributed state. Transient absorption in the wavelength range from 380 and 740 nm and the time range from 0.1 to 100 μ s were measured. The chlorophyll a radicals and the triplet state were observed and their lifetimes estimated.     

New technique of processing highly oriented poly(vinylidene fluoride) films exclusively in the β phase

Oriented β‐phase films were obtained by utilizing two different techniques: conventional uniaxial drawing at 80 °C of predominantly α‐phase films, and by drawing almost exclusively β‐phase films obtained by crystallization at 60 °C from dimethylformamide (DMF) solution with subsequent pressing. Wide angle X‐ray diffraction (WAXD) and pole figure plots showed that with the conventional drawing technique films oriented at a ratio (R) of 5 still contained about 20% of phase α, a crystallinity degree of 40% and β‐phase crystallographic c ‐axis orientation factor of 0.655. Drawing at 90 °C and with R = 4 of originally β‐phase films results in exclusively β‐phase films with crystallinity degree of 45% and orientation factor of 0.885. Crystalline phase, crystallinity degree, and crystallographic c‐axis orientation factor of both phases were also determined for α‐phase oriented films obtained by drawing α‐phase films at 140 °C. For films drawn at 140 °C the α to β phase transition drops to about 22%. Reduction in crystallinity degree with increasing R is more pronounced at draw temperature of 140 °C compared with 80 °C. Moreover, for both phases the c ‐axis orientation parallel to the draw direction is higher at draw temperature of 140 °C than at 80 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2793–2801, 2007     

THE MAJOR INTRINSIC LIGHT-HARVESTING PROTEIN OF Amphidinium: CHARACTERIZATION AND RELATION TO OTHER LIGHT-HARVESTING PROTEINS

A major light-harvesting complex (LHC) has been obtained from thylakoids of Amphidinium carterae solubilized with digitonin or decylmaltoside and separated by sucrose-gradient centrifugation. The digitonin-LHC forms a dark brown band at -17% sucrose and the decylmaltoside LHC one at -7% sucrose. Excellent energy transfer is retained from chlorophyll c and carotenoid to chlorophyll a. Absorbance and fluorescence excitation spectra show the existence of two major forms of chlorophyll c, one absorbing at 634 nm and the other at 649 nm. Linear dichroism spectra show the Q_y transition of both forms of chlorophyll c to be aligned at <35° to the membrane plane. On sodium dodecylsulfate polyacrylamide gels the complex resolves as a single band of 19 kDa. A partial amino acid sequence shows the N-terminus to be unblocked but modified; there is a persistent ambiguity of Ser/Asn at residue 4 and evidence for multiple but very similar polypeptides within the 19 kDa band. The peptide has strong identity with the N-terminal regions of LHC from Phaeodactylum and Pavlova and LHC 1 of higher plants. Antibodies to the 19 kDa peptide react weakly with LHC of brown algae, diatoms and Prymnesiophytes but not with those of higher plants or Cryptophytes.     

Synthesis of new wide nematic diaryl-diacetylenes containing thiophene-based heteromonocyclic and heterobicyclic structures,and their birefringence properties

New monocyclic and bicyclic thiophene-based diaryl-diacetylene liquid crystal (LC) materials were synthesised and demonstrated to exhibit wide enantiotropic nematic phases. One thiophenyl-benzene derivative, in particular, displayed a stable nematic phase across a temperature range of over 100°C. The birefringence properties of the compounds were measured using a multiple-beam interference (MBI) method, with the highest value found to be for the same thiophenyl-benzene molecule (Δn = 0.57, 550 nm) at 10°C above the crystal-to-nematic transition temperature. Furthermore, the effects of the cyclic structure on the mesomorphic behaviours, transition temperatures, and birefringence properties were investigated in detail from both experimental and theoretical viewpoints.     

Thermal behavior of the composite xerogels of zirconium oxyhydroxide and silicic acid

Gels were prepared via sol?Cgel method by addition of zirconium oxychloride solution into sodium metasilicate (SZ) and sodium metasilicate solution into zirconium oxychloride (ZS) at varying final pH. Si/Zr molar ratio equaled 1/1. Synthesized gels were dried with calcium chloride until they reached a constant mass. SEM and nitrogen adsorption analysis have shown that SZ gels have surface area 175?C200?m^2?g^?1, consist of 20?C30?nm grains. ZS samples have surface area about 1?m^2?g^?1, consist of grains smaller than 10?nm. Thermal and X-ray phase analysis have shown that transition of amorphous ZrO₂ to crystalline form shifts from 430 to 850?C870?°C for SZ gels. Unlike zirconia gels phase transitions that proceed in order: ??amorphous (430?°C)??tetragonal (800?°C)??monoclinic (1,000?°C) phases??, the monoclinic phase in ZS gels appears immediately after transition from amorphous to crystalline state; the tetragonal phase in SZ samples is stable until 1,000?°C.     

Thermosensitive phase behavior and drug release of in situ gelable poly(N-isopropylacrylamide-co-acrylamide) microgels

In situ gelable poly(N-isopropylacrylamide-co-acrylamide) microgels were prepared by precipitation polymerization in the presence of various amounts of N,N′-methlenebisacrylamide as a crosslinker. The diameters of microgels were in the range of 200–300 nm with narrow distributions as determined by photo correlation spectroscopy. The equilibrium swelling ratio and thermosensitive properties of the microgels increased with decreasing crosslinker content. The volume phase transition of microgels dispersions at high concentrations were investigated by phase diagrams. The microgels dispersions experienced four phases when the temperature was increased: semitranslucent swollen gel, clear flowable suspension, cloud flowable suspension, and white shrunken gel. The related phase transition temperatures were influenced by crosslinker content and the concentration of the microgel dispersions. Herein, the gelation temperature was changed by more than 20 °C, shrinking temperatures were slightly changed by about 3 °C, and cloud point temperatures showed almost no change. The three phase transition temperatures of microgels dispersed in phosphate-buffered saline solutions were lower than that in water. As drug carriers, the release rates of bleomycin from bleomycin-loaded microgel dispersions exhibited diffusion control at human body temperature.     

Temperature effect on the structure and characteristics of ZnS-based quantum dots

The synthesis of zinc sulfide (ZnS) quantum dots (QDs) by microwave heating in a water-ethanol medium is proposed. The effect of the synthesis temperature (80 °C, 100 °C, 120 °C, and 150 °C) on the QD characteristics is examined. Based on the analysis of X-ray diffraction profiles the conclusion is drawn that the hexagonal ZnS phase of wurtzite type with an average nanocrystal size of 2.6-3.7 nm forms in the synthesized QDs. The nanocrystallite size is found to increase with the QD synthesis heating temperature. The analysis of X-ray absorption spectra (XANES) at the zinc K-edge indicates a higher crystallinity of the QD samples prepared at higher synthesis temperatures. The combined analysis of X-ray diffraction profiles, optical diffuse reflectance spectra, and X-ray absorption spectra implies the following possible QD structure: the pure hexagonal ZnS phase of wurtzite type in the bulk of nanoparticles and the amorphous ZnO phase in the surface layer of nanoparticles.     

Photophysical and electrochemical characterization of new poly(arylene vinylene) copolymers containing quinoline or bisquinoline segments

Four new fluorescent conjugated vinylene‐copolymers incorporating quinoline or bisquinoline segments along the backbone were synthesized by Heck coupling. Three of them were fluorenevinylene‐copolymers and contained quinoline ( PQFV , PQFVT ) or bisquinoline segments ( PBQFV ). One of them ( PBQPV ) was phenylenevinylene‐copolymer and contained bisquinoline segments. All the copolymers were soluble in common organic solvents and had relatively low glass transition temperature (T_g = 50–56 °C for fluorenevinylenes and T_g < 25 °C for phenylenevinylene). In THF solutions, the quinoline‐containing copolymers showed absorption maxima at 411–420 nm while the bisquinoline‐containing ones exhibited maxima at 357–361 nm. The emission maxima of solutions were 465–490 nm. The copolymers showed high quantum yields up to 64%. The films exhibited absorption and emission maxima in the range of 371–437 nm and 480–521 nm, respectively. All copolymers revealed reversible reduction with electron affinity of 2.66–3.53 eV and irreversible oxidation scans with ionization potential of 5.39–5.53 eV. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3370–3379, 2009     

Preparation and characterization of polyimides containing triaryl imidazole side groups

A novel triaryl imidazole‐containing diamine, 3,5‐diamino‐N‐(4‐(4,5‐diphenyl‐1H‐imidazol)phenyl)benzamide, was successfully synthesized via the condensation of 4‐(4,5‐diphenyl‐1H‐imidazol)benzenamine and 3,5‐dinitrobenzoyl chloride, followed by reduction of the dinitro compound. A series of new aromatic polyimides with pendent triaryl imidazole moieties were prepared from the reaction of this diamine with various tetracarboxylic dianhydrides by a conventional two‐step polymerization process via thermal and chemical imidizations. The polyimides were obtained in quantitative yields with inherent viscosities of 0.21–0.44 dL/g. All the polymers are readily soluble in polar organic solvents. Flexible and strong films of polyimides were obtained by solution casting. The glass transition temperature of these polymers was in the range of 261–264°C. They were fairly stable up to a temperature around 300°C and lost 10% weight at 408°C under nitrogen. The ultraviolet–visible absorption spectra showed that all of the polymers had absorption maxima around 320 nm with a fluorescence emission maxima around 388–407 nm in N‐methyl‐2‐pyrrolidinone solution. Cyclic voltammograms of the polyimides revealed an oxidation wave with a peak around 1.7 V. Copyright © 2016 John Wiley & Sons, Ltd.     

In Situ Formation of Dual‐Phase Thermosensitive Ultrasmall Gold Nanoparticles

A novel method for the in situ synthesis of dual‐phase thermosensitive ultrasmall gold nanoparticles (USGNPs) with diameters in the range of 1–3 nm was developed by using poly(N‐isopropylacrylamide)‐block‐poly(N‐phenylethylenediamine methacrylamide) (PNIPAM‐b‐PNPEDMA) amphiphilic diblock copolymers as ligands. The PNPEDMA block promotes the in situ reduction of gold precursors to zero‐valent gold and subsequently binds to the surface of gold nanoparticles, while PNIPAM acts as a stabilizing and thermosensitive block. The as‐synthesized USGNPs stabilized by a thermosensitive PNIPAM layer exhibit a sharp, reversible, clear–opaque transition in aqueous solution between 30 and 38 °C. An unprecedented finding is that these USGNPs also show a reversible soluble–precipitate transition in nonpolar organic solvents such as chloroform at around 0 °C under acidic conditions.     

CONTROL OF CHLOROPHYLL b BIOSYNTHESIS BY PHYTOCHROME

In the mustard seedling cotyledons, chlorophyll b appears from the very beginning in white light provided that a red light pulse pretreatment was given 12 h prior to the onset of white light. The red light pulses act through phytochrome. Without pretreatment no chlorophyll b is detectable at least during the first 60 min after the onset of white light (25°C). Biogenesis of chlorophyll b specifically depends on the action of phytochrome during the pre-steady state period as well as during the steady state period of chlorophyll accumulation. In light pulse experiments, it was found that formation of chlorophyll b takes place stoichiometrically at the cost of chlorophyll(ide) a.     

Synthesis and properties of nanocrystalline materials based on LaPO<Subscript>4</Subscript>

A study of the processes in which lanthanum orthophosphate nanocrystalline powders with rhabdophane and monazite structure and crystallite size of about 10 nm are formed demonstrated that, at temperatures of up to 500°C, nanocrystalline lanthanum orthophosphate with rhabdophane structure loses crystal hydrate water and is transformed at 520–540°C to a nanocrystalline phase with monazite structure. This transition is not associated with as change in the crystallite size because nanocrystals of the anhydrous lanthanum orthophosphate phase with monazite structure retain a size of about 10 nm both at the instant of the structural transformation and up to temperatures of 600–700°C. The technological modes were determined in which nanocrystalline lanthanum orthophosphate powders with monazite structure can be obtained and the powders are used for sintering of ceramic materials with porosity on the level of 5–7%.