Radiation chemical investigations on aqueous solutions of C60(OH)18

The ultraviolet-visible absorption spectrum of C₆₀(OH)₁₈ in water showed an absorption band with λ_max = 215 nm and other characteristic absorption bands of C₆₀ are not observed. The singlet-singlet and triplet-triplet absorption bands are not observed in the 400–900 nm region. It has low reactivity with e_aq⁻ and formed an absorption band with λ_max = 580 nm. The hydroxyl radicals react with a bimolecular rate constant of 2.4×10⁹ dm³ mol⁻¹ s⁻¹ and showed an absorption band at 540 nm.     

INTERMEDIATES IN THE PHOTOCONVERSION OF FUNCTIONAL PHYTOCHROME IN FERN SPORES OF Dryopteris-I DEMONSTRATION AND QUANTITATIVE CHARACTERIZATION OF THE PHOTOCHROMIC SYSTEM Pr⇔ Ii700USING NANOSECOND-LASER PULSES*,†

Abstract— Spores of Dryopteris paleacea and D. filix-mas are positively photoblastic with an optimum in the action spectrum around 665 nm. Light is perceived by phytochrome and the relationship between germination and mole fraction of the far-red-absorbing form of this pigment, P_fr, was investigated with saturating irradiations between 662 and 747 nm under low-fluence-rate conditions. These control irradiations establish a proportion of the total phytochrome, P,_tot, as P_fr with P_fr/P_tot–φ at equilibrium. These φ -values were calculated according to data for native oat phytochrome (Kelly and Lagarias, 1985, Biochemistry 24, 6003) and the spectral characteristics of the interference filters. With this method a linear relationship could be found between φ and germination from 2 to 70% for D. paleacea and from 2 to 90% for D. filix-mas, if probit germination was plotted vs probit φ This correlation formed the basis of investigating the phytochrome photoconversion by dye-laser pulses of 380 ± 30 ns under high-fluence-rate conditions, and thus to test quantitatively the impact of the photoreversibility of intermediate reactions of the photoconversion and the red-absorbing form of phytochrome, P_fr on the final P_fr-level. Spore germination was initiated by a single-laser pulse in the range from 592 to 700 nm. The most effective wavelengths were 649 and 660 nm in both species, and at saturation maximal germination (ca. 50%) was obtained from 592 to 665 nm for D. paleacea or ca. 60% germination from 592 to 670 nm for D. filix-mas. Both saturation levels correspond to a ø-value between 0.40 and 0.45. This significantly diminished photoconversion is a consequence of the high-fluence-rate conditions during the laser pulse which establishes the photochromic system between P_r and a set of very early intermediates, Iⁱ_700, (= P_r? Iⁱ₇₀₀). This system can be described by the extinction coefficients of P_r and the intermediates Iⁱ₇₀₀, and by the quantum yields, 4,φ for the forward and reverse reactions as φ If φ is calculated, assuming a quantum yield of 1:1 for both reactions and with the extinction coefficients of P_r and Iⁱ_7(l() (= lumi-R) given by Eilfeld and Riidiger (1985, Z. Naturforsch. 40c , 109), significantly higher values are calculated for / as compared to φ found in the control experiments. These results can be explained either: (i) with a quantum yield ratio φ_pr-φ1700: φ_1700φpr=1:1 and an assumed additional dark reaction leading from Iⁱ₇₀₀ or later intermediates back to P_r: or (ii) with a quantum yield ratio φ_{pr φ 1700}: φ_{1700 φpr}=1:2. In this case all Iⁱ₇₀₀ have to relax to P_fr. In this case all Iⁱ₇₀₀ have to relax to P_fr.     

IDENTIFICATION OF TRYPTIC CHROMOPEPTIDES OF PHYTOCHROME ON SODIUM DODECYL SULFATE GELS: IMPLICATIONS FOR STRUCTURE

Abstract— After electrophoresis on sodium dodecyl sulfate polyacrylamide gels, bleached chromopeptides of phytochrome can have their blue color restored by soaking the gels in 20% trichloroacetic acid. The blue bands have a broad absorption maximum between 630 and 655 nm, characteristic of denatured phytochrome. The restored color retains most of its intensity for up to 2 h, but gradually bleaches again until it disappears completely within 24 h. This visualization method is used to identify the number and sizes of phytochrome chromopeptides produced by limited tryptic digestion. The results reveal some structural requirements for photoreversibility and are consistent with a model of phytochrome structure that predicts a high degree of symmetry within the native subunit.     

PHOTOREGULATION OF LOGARITHMIC FLUENCE-RESPONSE CURVES FOR PHYTOCHROME CONTROL OF CHLOROPHYLL FORMATION IN PISUM SATIVUM L*

Abstract— Logarithmic fluence-response curves for red (660 nm) and far red (730 nm) light induction of rapid chlorophyll a (Chi a) accumulation in pea seedlings (Pisum sativum L. cv. Early Alaska) indicate extreme light sensitivity in dark-grown seedlings. The energy requirement for onset of 660 nm light induction is less than 20 μJ m^-2 and for 730 nm is about 1 mJ m^-2. De-etiolation produced by a saturating exposure of red light (3–8 kJ m^-2) 24 h prior to the construction of the logarithmic fluence-response curves resulted in approximately a 3 fold increase in slope for 660 nm light, whereas the energy requirement for onset of induction shifted to about 100 mJ m^-2. In such de-etiolated plant material, far red applied at low incident energies almost completely lost its inductive capacity. The inductive capacity of far red applied as high irradiance over a long period of time (16h) appeared not to be affected by the de-etiolation treatment. Reciprocity failed for both dark-grown and de-etiolated seedlings upon exposures exceeding 1,000s. Nearly identical results were obtained for seedlings de-etiolated by red exposures immediately followed by far red (4.8 kJ m^-2), although this treatment did not lead to any significant decrease in spectrophotometrically measurable phytochrome. Therefore, no simple correlation was observed between the level of phytochrome present and the sensitivity of seedlings for induction of rapid Chl a accumulation. In order to explain this apparent phytochrome paradox the possibility was tested and ruled out for changes in the degree of synchronization of seedlings, or for induction of some sort of circadian rhythmicity in light sensitivity being involved. In addition, no correlation was observed between induction of morphogenic development and changing light sensitivity. These results formed, therefore, additional support for a model for phytochrome action involving its intracellular transport and local concentration during the process of seedling de-etiolation.     

Stabilization of phytochrome intermediates by low temperature

Abstract— The photocon versions between the red-absorbing form (P_r) and the far-red absorbing form (P_fr) of phytochrome were examined at low temperatures. Partially purified preparations of the chromoprotein were examined in phosphate buffer and in 25 per cent buffer plus 75 per cent glycerol. Actinic irradiation of P, below – 150°C produces an intermediate with maximum absorbance near 695 nm, R₆₉₅. Actinic irradiation of R₆₉₅ converts it back to P. Above – 150°C R₆₉₅ decays to a low extinction form of phytochrome, R, which in turn decays to P_fr upon further warming. Light absorption by P_fr below – 150°C results in the formation of an intermediate form of phytochrome with maximum absorbance near 660 nm, FR₆₆₀. FR₆₆₀ decays upon warming to a lower extinction form, FR'. which in turn decays to P_r on continued warming. No evidence was obtained to suggest that any of the observed intermediate states are involved in more than one direction of phytochrome photocon version.     

Pulse radiolysis study on the initial processes of radiation-induced cationic polymerization of styrene and α-methylstyrene

Initial processes of radiation-induced cationic polymerization of styrene and α-methylstyrene have been studied by means of microsecond pulse radiolysis. For styrene, absorption bands caused by the monomer cation radical St⁺? appear at 630 and 350 nm in a mixture of isopentane and n-butyl chloride at about ?165°C. In parallel with the decay of St⁺?, three absorption bands appear in the near-infrared (IR) region, and at 600 and 450 nm. The IR and 600 nm bands are assigned to the associated dimer cation radical St₂⁺?, and the 450 nm band to the bonded dimer cation radical St-St⁺?. The kinetic behavior of these species shows that reaction of St⁺? with styrene monomer forms both St₂⁺? and St-St⁺?. With the decay of St-St⁺?, another absorption band appears at 340 nm, and the lifetime of this band is relatively long. The 340 nm band may be due to carbonium ions of the growing polystyrene. For α-methylstyrene, the monomer cation radical (at 690 and 350 nm), the associated dimer cation radical (in the near-IR region and at 620 nm) and the bonded dimer cation radical (at 480 nm) behave in a manner similar to that of the corresponding styrene species. The absorption band caused by carbonium ions of growing poly(α-methylstyrene) appears at 340 nm.     

Gamma irradiation induced photochemical reactions in V-doped borate glasses

Glasses of the composition XNa₂O · 4Al₂O₃ (96-X) B₂O₃ (mole%) where X = 10, 20, 30 to which 0.03 g V₂O₅ per 100 g glass was added, were prepared by normal melting. Their absorption characteristics together with the corresponding V-free base glasses were determined before and after gamma irradiation. The characteristic spectra of the unirradiated glasses show absorption bands at 315, 470, 560–580, 610–650, 700–870, and 860–1000 nm, indicating the presence of vanadium ions in more than one oxidation state, viz, V⁵⁺, V⁴⁺, and V³⁺. Gamma irradation of V-containing glasses causes the formation of color centers in the glass matrices, with absorption bands at 330, 500, and 610 nm, and photoreduced [V³⁺] and [V²⁺] ions with absorption bands at 350–355 and 530–570 and 520 nm, respectively. Photoreduced [V⁴⁺] may also be formed, giving rise to absorptions at 690–700 and 750–800 nm. The induced vanadium ions are found to absorb at shorter wavelengths than the intrinsic ones. An explanation based on the difference in the field energy of the two states is given.     

ACTION SPECTRA OF PHYTOCHROME IN VIVO*

Abstract— A method is described to determine spectral properties of phytochrome in vivo. For photochrome in 7-day-old dark-grown Cucurbita pepo L. seedlings the mole fraction of the far-red-absorbing form (P_fr) present at photoequilibrium at 664 nm was found to be 0.76 ± 0.02 in vivo. Based on reflectance measurements, the photon fluence rate just below the surface of the cotyledons was calculated. Local rates of photoconversion for known local fluence rates were measured across cotyledons after non-saturating irradiations with wavelengths between 544 and 781 nm and in situ molar photoconversion coefficients were obtained. In contrast to purified oat phytochrome, the in situ molar photoconversion coefficients for P_fr show a strong shoulder between 660 and 700 nm. The maximum of P_fr absorption is at 726 nm. An isosbestic point of phytochrome is found at 686 nm. The mole fraction of P_fr present at photoequilibrium with 686 nm light is 0.58. The ratio of photoconversion quantum yields (that for P_r→ P_fr divided by that for P_fr→ P_r) is 1.38 ± 0.06.     

The triplet state of 4-nitronaphthylamine

Nanosecond spectroscopic and kinetic studies of 4-nitronaphthylamine (4-NO₂NA) in aerated and deaerated nonpolar solvents at room temperature show a transient species with absorption maxima at 470 and 665 nm. The rate constant for the decay of this species in deaerated benzene is 6.7 × 10⁵ sec^?1, while in aerated benzene solutions the species is quenched by oxygen with arate constant k = 2.0 × 10⁹M^?1·sec^?1. The transient absorption at 470and 665 nm is assigned to the lowest triplet excited state of 4-NO₂NA. In polar solvents, however, electronic excitation of 4-NO₂NA does not lead to any detectable transient absorption between 400 and 800 nm for the temperature range of 25 to ?150°C. This is attributed to lack of intersystem crossing of 4-NO₂NA in polar solvents.     

Results of studies of potential light spectrum effects on human performance

Abstract— Sensitization of the phytochrome-mediated germination at 20°C of lettuce seeds (Lactuca sativa L. cv. Grand Rapids) by pretreatment at 4°C, 28°C, or on 1% ethanol, was studied. The 660 nm fiuence-response characteristics were similarly biphasic for all sensitizing treatments and displayed responses at very low fluences (VLFR) as well as responses characteristic of non-sensitized seeds at 10000-fold higher, low fluences (LFR). Maximum VLFR increased with the duration of sensitizing treatments. However, the fluence ranges required for the two types of responses remained relatively constant. These and additonal responses of sensitized seeds to 730 nm fluences were compared to simulations of a mechanism involving a receptor, X, and based on the dimeric structure of phytochrome in which each monomer is independently phototransformed from the inactive (P_r) to the active (P_fr) form. The fluence requirements for phytochrome photoconversion in seeds were determined to be similar to those of purified Avena phytochrome in vitro, on which photochemical parameters for the simulations were based. The analyses suggest that P_r:P_fr-Xand P_fr:P_fr-X are responsible, respectively, for the VLFR and the LFR, and that sensitization involves membrane influences on the activity of P_r:P_r-X. They also suggest the concentration of X to be about 0.001 that of total phytochrome dimer in this system.     

Preparation and Spectral Analysis of Nickel-containing Aluminophosphate Molecular Sieves of Type-5

Diffuse reflectance spectroscopy was used to studynickel ion positions in the aluminophosphate molecularsieves of the AlPO-5 type. Nickel ions wereintroduced into the reactant mixture of thealuminophosphate and the synthesis carried outhydrothermally through various methods of gel, clearsolution and diluted suspension. The visibleabsorption spectra obtained of the dried, hydrated andcalcined materials were studied. A distinct andwell-defined triplet absorption band observed at about625, 580 and 540 nm was assigned to tetrahedralframework-substituted nickel(II) ions. A relativelystrong band at about 400 nm and two broad bands withsimilar intensity at 730 and 660 nm were assigned tooctahedral nickel species. These 730 and 660 nm bandsare observable only in the sample where nickel cationswere incorporated merely in the octahedralextra-framework sites by ion-exchange treatment ofSAPO-5. According to the synthesis procedure used,the amount of tetrahedral framework-substituted nickelions in comparison with octahedral ones can beevaluated from the intensities of the characteristicbands of the 4- and 6-coordinated nickel ions. Thereis much more octahedral nickel compared with thetetrahedral ones estimated in the light of theintensity data taking into account the absorptivitiesof nickel (II) symmetries. This work showed thatusing our synthesis procedure of a dilutedsuspension will result in preparing NiAPO-5 molecular sieve with more nickel cationsincorporated in the framework sites ofthe aluminophosphate. A very small quantity of thesecations remain in their sites at temperatures as highas 550°C.     

Side‐chain effects on phenothiazine‐based donor–acceptor copolymer properties in organic photovoltaic devices

A series of new phenothiazine‐based donor–acceptor copolymers, P1 and P2, were synthesized via a Suzuki coupling reaction. The weight‐averaged molecular weights (M_w) of P1 and P2 were found to be 16,700 and 16,100, with polydispersity indices of 1.74 and 1.39, respectively. The UV–visible absorption spectra of the polymer thin films contained three strong absorption bands in the ranges 318–320 nm, 430–436 nm, and 527–568 nm. The absorption peaks at 320 and 430 nm originated mainly from the phenothiazine‐based monomer units, and the longer wavelength absorption band at 527–568 nm was attributed to the increased effective conjugation length of the polymer backbones. Solution‐processed field‐effect transistors fabricated with these polymers exhibited p‐type organic thin film transistor characteristics. The field‐effect mobilities of P1 and P2 were measured to be 1.0 × 10^?4 and 7.5 × 10^?5 cm² V^?1 s^?1, respectively, with on/off ratios in the order of 10⁴ for all polymers. A photovoltaic device in which a P2/PC₇₁BM (1/3) blend film was used as the active layer exhibited an open‐circuit voltage (V_OC) of 0.70 V, a short‐circuit current (J_SC) of 6.79 mA cm⁽², a fill factor of 0.39, and a power conversion efficiency of 1.86% under AM 1.5 G (100 mW cm^?2) illumination. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

THE TEMPERATURE DEPENDENCE OF Pfr ACTION GOVERNS THE UPPER TEMPERATURE LIMIT FOR GERMINATION IN LETTUCE

In most cultivars of lettuce (Lactuca saliva L,), red light acting through the red/far-red reversible phytochrome system promotes full germination within the20–30°C range, but at progressively higher temperatures germination declines sharply. The relationship between this upper ternperature limit for germination and the temperature dependence of phytochrome action was investigated in Grand Rapids lettuce. In fresh seeds the GT₅₀ (temperature giving half maximal germination) was ca 29–30°C. In these seeds, escape from far-red reversibility did not occur at 35°C, a temperature above the GT₅₀, but occurred rapidly at 27°C, a temperature below the upper limit. Increasing periods of dark pretreatment at high temperature (35°C) or increasing concentrations of the germination inhibitor coumarin caused a progressive decline in the GT₅₀, Escape from photoreversibility did not occur at 27°C in seeds in which the GT₅₀ had been reduced to less than 25°C by coumarin or by prolonged high temperature pretreatment. These results indicate that there is a close correlation between the position of the upper temperature limit for germination, and the temperature dependence of phytochrome action. We conclude that factors that alter the upper temperature limit for germination do so by changing the temperature dependence of phytochrome action.     

RED/FAR-RED PHOTOREVERSIBILITY: NOT AN APPROPRIATE PHYTOCHROME ASSAY FOR RED-LIGHT PREIRRADIATED CORN COLEOPTILES

Abstract— Based on measurements with a single beam spectrophotometer, it has been found that subsequent red/far red irradiation cycles, which are usually given to monitor phytochrome content by dual wavelength spectroscopy, induce chlorophyll-related absorption changes in maize coleoptiles. Therefore, the difference signal, usually measured between 730 and 800 nm or 660 and 730 nm after saturating red and far red irradiations, does not represent solely the phytochrome content of preirradiated samples.     

THE BLUE ANOMALOUS EMISSION OF LARGE AND SMALL PHYTOCHROME*

–Small and immunoaffinity-purified large phytochrome (P_r and P_fr) show a so-called anomalous fluorescence with λ^em_max= 470 and 440 nm, respectively, when irradiated within the blue absorption band. Model studies indicate that this emission arises from a dipyrromethenone partial structure produced by a nucleophilic addition to the central carbon C-10 of the bilindione chromophore. The anomalous emitter of phytochrome is thus similar to one bilirubin conformer which has previously been found to contribute to the absorption and emission of the bile pigment.     

Synthesis,crystal structure,absorption properties,photoelectric behavior of organic–inorganic hybrid (CH3NH3)2CoCl4

Lead‐free and organic–inorganic hybrid (CH₃NH₃)₂CoCl₄ [(MA)₂CoCl₄] single crystal and thin film are prepared. The single crystal diffraction data of (MA)₂CoCl₄ are assigned to monoclinic, P2(1)/C space group (7.6590 × 12.6908 × 10.89350 Å, 90.0 × 96.5320 × 90.000). The absorption edge of (MA)₂CoCl₄ reaches 730 nm. The band gap for (MA)₂CoCl₄ is determined to be approximately 1.63 eV. To the best of our knowledge, this is the first study on (MA)₂CoCl₄ for optoelectronic applications. A low‐cost photodetector based on (MA)₂CoCl₄ thin film is efficient under different monochromatic light from 330 nm to 400 nm with different chopping frequencies (1.33–60 Hz). The strongest photoresponse (I_on ? I_off) is under 330 nm monochromatic light with 1.33 Hz according to our optimal condition. The calculational results by density functional theory show that the narrow valence bands and conduction bands are derived from the 3p orbitals of Cl and 3d orbitals of Co.     

Effect of temperature on frying oils: infrared spectroscopic studies

Frying oils were studied by Fourier-transform infrared (FT-IR) spectroscopy, in the range 4,000–200 cm^?1, at different temperatures, in the liquid and solid states. The infrared spectrum at 15 °C was similar to that at 200 °C. The band at 730 cm^?1 which was assigned to the rocking mode of (–CH₂) disappeared at higher temperature because of the rotational isomerism which occurred in the oil structure. The activation energy (E _a) of the disappearing (–CH₂) band, calculated by use of the chemical dynamic method using the Arrhenius equation, is 8.45 kJ mol^?1. The enthalpy difference (ΔH) between the two rotational isomer bands of the conformational structures of the oil at 730 and 1,790 cm^?1, at different high temperatures, was also calculated, by use of the Van’t Hoff equation; the value obtained was ?10.85 kJ mol^?1.     

Investigation of excited‐state properties of fluorene–thiophene oligomers by the SAC‐CI theoretical approach

Excited states of fluorene‐ethylenedioxythiophene (FEDOT) and fluorene‐S,S‐dioxide‐thiophene (FTSO2) monomers and dimers were studied by the symmetry‐adapted cluster (SAC)‐configuration interaction (CI) method. The absorption and emission peaks observed in the experimental spectra were theoretically assigned. The first three excited states of the optimized conformers, and the conformers of several torsional angles, were computed by SAC‐CI/D95(d). Accurate absorption spectra were simulated by taking the thermal average for the conformers of torsional angles from 0° to 90°. The conformers of torsional angles 0°, 15°, and 30° mainly contributed to the absorption spectra. The full width at half‐maximum of the FEDOT absorption band is 0.60 eV (4839 cm^?1), which agrees very well with the experimental value of 0.61 eV (4900 cm^?1). The maximum absorption wavelength is located at 303 nm, which is close to those of the experimental band (327 nm). The calculated absorption spectrum of FTSO2 showed two bands in the range of 225–450 nm. This agrees very well with the available experimental spectrum of a polymer of FTSO2, where two bands are detected. The excited‐state geometries were investigated by CIS/6‐31G(d). These showed a quinoid‐type structure which exhibited a shortening of the inter‐ring distance (0.06 Å for FEDOT and 0.04 Å for FTSO2). The calculated emission energy of FEDOT is 3.43 eV, which agrees very well with the available experimental data (3.46 eV). The fwhm_E is about 0.49 eV (3952 cm^?1), while the experimental fwhm is 0.43 eV (3500 cm^?1). For FTSO2, two bands were also found in the emission spectrum. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Transient spectrum from nanosecond pulse radiolysis of liquid ammonia

In addition to the absorption of the ammoniated electron, the transient absorption spectrum of irradiated liquid ammonia contains two ultraviolet bands at 250 nm and 320 nm. The latter is shown to be due neither to the NH₂^? ion nor to NH singlet. There is conflicting evidence concerning its possible assignment to NH triplet. The C value of the ammoniated electron has been found to be 3.0 at ?48°C. At ?45°C, the ammoniated electron decays with concurrent first and second order kinetics and it reacts with Cu²⁺ with the rate constant 1.5 × 10¹¹$\text{l}$ mole^?1 sec^?1.     

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.