CORRELATION BETWEEN DELAYED LIGHT EMISSION AND FLUORESCENCE OF CHLOROPHYLL a IN SYSTEM II PARTICLES DERIVED FROM SPINACH CHLOROPLASTS

Abstract— The induction transient of delayed light of chlorophyll a, excited by repetitive flashes (0.5 ms in duration) and emitted 0.1 - 1.2 ms after the flashes, was measured in system II particles derived from spinach chloroplasts. An uncoupler, gramicidin S, was always added to the particles in order to eliminate the influence of the phosphorylation system on the delayed light and to isolate a direct relationship between the delayed light emission and the primary photochemical reaction, except for the experiments described in the next paragraph. The yield of delayed light emission from the system II particles was found to be about three–times higher than that of chloroplasts on a chlorophyll content basis. System I particles, on the other hand, emitted much weaker delayed light than chloroplasts. Upon intermittent illumination, induction of delayed light in system II particles showed a decrease from the initial rise level to the steady-state level. The initial rise level was the maximum. The fluorescence induction, on the other hand, exhibited an increase from the initial rise level to the maximum steady-state level. The induction of both delayed light emission and fluorescence arrived at their final steady-state levels after the same period of illumination. Induction of delayed light emission was measured under various conditions that changed the oxidation-reduction state of the primary electron acceptor, X, of photoreaction II: by adding an electron acceptor and an inhibitor of electron transport, and by changing the light intensity. The state of A'was monitored by measuring the fluorescence yield. The yield of delayed light emission excited by each flash was found to depend on the amount of oxidized form of X present before the flash. To examine the role of the primary electron donor Y of photoreaction II in delayed light emission, effects of electron donors of photoreaction II such as Mn²⁺, hydroquinone and p-phenylenediamine were investigated. These agents were found to markedly decrease the yield of delayed light emission without altering the pattern of its induction. They had little effect on the induction of fluorescence. These findings are interpreted by a mechanism in which transformation of the reaction center from the form (X^-Y⁺) into (X Y) produces a singlet excitation of chlorophyll a that is the source of millisecond delayed light emission. This reaction is probably non–physiological and must be very slow if compared to the transformation of (X^-Y⁺) into (X^-Y). Since the form (X^-Y⁺) is produced when the excitation is transferred to the reaction center in the form (XY), it is expected in this scheme that the yield of delayed light emission should depend on the amount of the form (X Y) present before the excitation flashes. Electron donors stimulate transformation of the reaction center from (X^-Y⁺) into (X^-Y). Since this reaction competes with the process of delayed light emission, electron donors are expected to suppress delayed light emission.     

Angular dependence of Gaussian-Lobe orbitals. II. Set of axial Gaussian-Lobe orbitals

The topological properties of real spherical harmonic representations on the unit sphere have been found to provide a convenient tool to infer the lobe edifices which mimic these orbitals. The prohibitive number of lobes required in such an approach for l > 2, can be avoided in using only axial Gaussian-lobe orbitals (AGLO ). It is proved that 2l + 1 independent Y_lo-like functions correctly span the relevant Y_lm (m = ?l,l) subspace. The multipolar component analysis of any spatial arrangement of lobes is derived, and allows the optimization of the angular dependence of AGLO S. The cases of d- and f-orbitals are studied in detail and accurate optimized functions are proposed. This method can be easily extended to obtain the atomic orbitals of any azimuthal quantum number l-subspace.     

Vibrational heating effects in the flash photolysis of ozone

The vibrational temperature of ozone has been estimated during the flash photolysis of ozone under non-isothermal and strictly isothermal conditions, utilising the variation in extinction coefficient with temperature at two wavelengths. Vibrational temperatures measured in the range 300–970 K have been attributed to energy transfer from O₂

(³Σ_g^?) to ozone and the effect of this non-equilibrium vibrational excitation on the secondary reactions with non-zero activation energies is discussed.     

A study of characteristic fragmentation of isoflavonoids by using negative ion ESI-MSn

Isoflavone mono‐O‐glycosides were investigated by electrospray ionization tandem mass spectrometry with a quadrupole linear ion trap mass spectrometer in negative ion mode. Isoflavonoids having different positions of glycosylation or methylation were differentiated according to the relative abundances of Y₀^? and [Y₀? H]^?? ions generated from the [M ? H]^? ion. It is found that the site of glycosyl or methyl group significantly affects relative abundances of the Y₀^? and [Y₀? H]^?? ions. In addition, the characteristic ion [Y₀? 2H]^? was observed in the product ion spectrum of genistein 7‐O‐β‐D ‐glucoside and was also detected, together with the [Y₀? CH₃]^?? and [Y₀? H ? CH₃]^? ions in the product ion spectra of glycitin and 6‐methoxy genistein 7‐O‐β‐D ‐glucoside. The structures of isoflavonoids can be characterized and identified according to the formation of these diagnostic ions. The results obtained from this investigation can promote the rapid identification of isoflavonoids in crude plant extracts. Copyright © 2010 John Wiley & Sons, Ltd.     

Determination of traces of terbium and indium by candoluminescence in various matrices by using a rod technique

The candoluminescence of terbium and indium was studied in various matrices coated on CaO/CaSO₄ rods. Terbium was studied in Y₂O₃, Gd₂O₃, ThO₂ and La₂O₃. Calibration graphs were linear over different ranges, up to 90 ng in some cases, with 0.2–0.3 ng μl^?1 detection limits and 2.8–3.2% relative standard deviations (c.s.d.). The candoluminescence of indium in Y₂O₃, Gd₂O₃ and Al₂O₃ was also examined. Calibration graphs were linear over different ranges, up to 20 ng in some cases, with detection limits of 0.08 ng μl^?1 for Y₂O₃ and Al₂O₃ and 0.2 ng μl^?1 for Gd₂O₃ with r.s.d. of 2.5–2.9%. There are many interferences.     

Solution combustion synthesized Y2O3 nanoparticles and influence of Dy doping on their microstructural,optical, and photoluminescence characteristics

Dy-doped Y₂O₃ nanoparticles were synthesized by solution combustion route with urea as fuel, and their microstructural features were analyzed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The XRD study confirms the formation of a pure cubic phase of Y₂O₃, with the maximum textural coefficient along the (2 2 2) plane for the Dy-doped samples. The lattice fringes in the HRTEM image and the bright spotty rings in the selected area electron diffraction (SAED) pattern reveal the highly crystalline nature of the nanoparticles. From the diffuse reflectance spectroscopy, using Kubelka-Monk theory, the direct bandgap energy is estimated to be 5.61 eV for the undoped Y₂O₃, which is found to decrease upon Dy³⁺ doping. The room-temperature excitation spectra of the nanoparticles recorded at 575 nm emission wavelength comprise several excitation bands corresponding to the f-f transitions of Dy³⁺ ions in the host lattice. The photoluminescence spectra of the nanoparticles excited at the wavelength of 350 nm comprise three visible emission peaks at 477 nm (blue), 573 nm (yellow), and 666 nm (red). It has been concluded that the 0.5 mol% Dy-doped Y₂O₃ nanoparticles are the potential candidate to be used for solid-state luminescent device applications.     

A method for computer analysis of kinetics of competing first- and second-order reactions

Competing first- and second-order reactions of transient molecular species (e.g., triplet states and free radicals) are a common occurrence in kinetic studies such as flash photolysis and pulse radiolysis. We have developed a method for analyzing the decay kinetics of any species (Y) whose disappearance is described by ?dY/dt = k₁Y + k₂Y². The computer program (written in time-sharing BASIC) employs an iterative technique to obtain the least-squares estimates of the three parameters in the integrated rate equation.     

Electrostatic rigidity of polyelectrolytes from reparametrization invariance

The persistence length l_p of a polyelectrolyte chain can be represented as l_p = l_O + l_e where l_O is the bare persistence and I_e is the electrostatic contribution coming from the effects of electrostatic chain self-interactions. Using a reparametrization-invariant path integral model of semiflexible polymers we find that I_e depends on the ionic strength I as I_e ∼ I^−1/2. This result accords with experimental observations and recent Monte Carlo simulations. Reparametrization-invariance is apparently an essential constrainet in selecting acceptable models of semiflexible polymers.     

SIMPLE EXPLANATION OF THE MISSES IN THE COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION

Abstract —In the model of Forbush et at. (1971) the observed damping of the flash yield sequence of photosynthetic O₂ evolution was related to a certain percentage of ‘misses’ (α; i.e. centers not converted). The possibility of a miss was supposed to be equal for all states S_0.1,2,3. We propose a new model and a new recurrence law that gives better quantitative agreement with the O₂ yield oscillations observed in Chlorella during a sequence of flashes. We find a better fit with all experimental results by assuming very unequal misses; the misses occur nearly exclusively on S₂ (and also sometimes on S₃). In the simpler case of only one miss on one state, half of S₂ exists as an inactive form S₂₊^- because it is in apparent equilibrium with pool A. The active form of S₂ is converted to S₃ in a flash and the unchanged inactive form S₂₊^- explains the miss: S ₁ hv→S₂₊^-=S₂hv→S₃ (S₂₊^- is a transition state between S₁ to S₂ associated with Q^-). In the dark, the apparent equilibrium constant K_A between pool A and Q (i.e. S₀, S₁ in the dark) is very large; this explains why there is no miss on these states. In light, the experimental value of K_A between pool A and Q (i.e. S₂, S₃ in the light) is 1, and this explains why the misses are large for states S₂, S₃; i.e., S₂₊^-/S2- 1 and sometimes S₃₊^-/S₃?0–1. This new model predicts that the total number of active states ΣS_i=S₀+S₁+S₂+S₃ is an oscillating function of the flash number. This sum 2S, is also the number of trapping centers for excitons. As fluorescence is proportional to excitons that are not trapped, our model explains why the fluorescence oscillates as a function of the flash number. We find also that the initial rates of O₂ evolution after (n - 1) flashes vs the 02 yield of the n^th flash are not exactly on a straight line, which also favors our model.     

The sectioning of randomly branched filamentous structures

A theorectical analysis is given of the two-dimensional picture observed when a three-dimensional randomly branched fibrous structure is sectioned. The model adopted consists of randomly oriented, interconnected straight rods having either the same length or a defined distribution of lengths. Expressions are derived for the total number of fragments observed and their total apparant length per unit area projected in the plane of the section, together with the distribution function of the projectd lengths. However, the expression derived for the total projected length per unit area, one-fourth πtρ_l, where t is the section thickness and ρ_l the fiber length per unit volume in the three-dimensional stucture, is, however, independent of the above model. The theory is discussed in terms of electron microscopy which has been carried out by other workers on agarose gels.     

Exploratory flash vacuum pyrolysis of some cyclopentadienyliron complexes

At 500°C, flash vacuum pyrolysis of (η⁵-C₅H₅)₂Fe₂(CO)₄ provides a rapid, practical synthesis of the tetranuclear complex (η⁵-C₅H₅)₄Fe₄(μ₃-CO)₄: at higher temperatures, ferrocene is formed. Ferrocene itself undergoes little change under flash vacuum pyrolysis conditions, even at 725°C. Pivaloylferrocene is unchanged at 650°C but cracks to yield isobutene between 675 and 700°C; this reaction does not proceed by simple elimination since formylferrocene can be recovered unchanged under flash vacuum pyrolysis conditions which give substantial quantities of isobutene from pivaloylferrocene.     

β‐Y2Si2O7, a new thortveitite‐type compound,determined at 100 and 280 K

A new form of Y₂Si₂O₇ (diyttrium heptaoxodisilicate) has been synthesized which is isotypic with thortveitite, Sc₂Si₂O₇, and crystallizes in the centrosymmetric space group C2/m, both at 100 and 280 K. The Y³⁺ cation occupies a distorted octahedral site, with Y—O bond lengths in the range 2.239 (2)–2.309 (2) Å. The SiO₄ tetrahedron is remarkably regular, with Si—O bond lengths in the range 1.619 (2)–1.630 (2) Å. The bridging O atom of the Si₂O₇ pyrosilicate group shows a large anisotropic displacement perpendicular to the Si—O bond. Changes in lattice and structural parameters upon cooling are small with, however, a distinct decrease of the anisotropic displacement of the briding O atom. Structure solution and refinement in the non‐centrosymmetric space group C2 are possible but do not yield a significantly different structure model. The Si—O—Si bond angle of the isolated Si₂O₇ groups is 179.2 (1)° at 280 K in C2 and 180° per symmetry in C2/m. The C2/m structure model is favoured.     

Laser flash photolysis of carboxymethylcellulose in an aqueous solution

Laser flash photolysis with excitation at 248 nm was used to study photochemically derived changes of carboxymethylcellulose (CMC) in aqueous solutions. Transient absorption spectra of solutions after photolysis revealed a broad band with a maximum of approximately 720 nm, which could be ascribed to the signal of the hydrated electron. The interaction of the hydrated electron with CMC was slow (<10⁷ dm³ mol^?1 s^?1), but the OH radical, formed by the decomposition of H₂O₂, reacted with CMC at a high rate constant (9.5–11.0 × 10⁸ dm³ mol^?1 s^?1). The rate constant of the reactions of CMC with hydroxyl radicals depended on the conformation of the macromolecules, which was determined by the pH of the solution. Transient absorption was recorded at a wavelength shorter than 370 nm for CMC solutions photolyzed in the presence of H₂O₂. As a result of OH attack, long‐lived radicals were formed on CMC. The recombination of macroradicals led to the formation of crosslinking bonds between side‐chain groups, and as a result of it an insoluble gel arose in low‐pH solutions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 505–518, 2005     

CrIII-Phthalocyaninate: Darstellung,Eigenschaften und Kristallstruktur von l-Bis(triphenylphosphin)iminium-trans-di(nitrito(O))phthalocyaninato(2–)-chromat(III)

Cr^III Phthalocyaninates: Synthesis, Properties, and Crystal Structure of l-Bis(triphenylphosphine)iminium trans-Di(nitrito(O))phthalocyaninato(2–)chromate(III) [Cr(H₂O)₂Pc^2?]I_x reacts with excess (PNP)NO₂ in dimethylformamide to yield less soluble greenblack l-bis(triphenylphosphine)iminium trans-di(nitrito(O))phthalocyaninato(2–)chromate(III), ^l(PNP)^trans[Cr(ONO)₂Pc^2?], which crystallizes in the triclinic space group P1 (No. 2) with Z = 2. The Cr atom is in the center of the Pc^2? ligand and the two nitrite ions are monodentate O-coordinated in a mutually trans arrangement to the Cr atom. The Cr? O and Cr? N_iso bond distances are 1.9898(14) und 1.981(2) Å, respectively. The geometric data of the coordinated nitrite ion are: d(N? O) = 1.307(2) Å; d(N? O) = 1.205(2) Å; ?(O? N? O) = 113.7(2)°; ?(Cr? O? N) = 116.85(12)°. The non-bonding O atoms are trans to the Cr atom. The Pc^2? ligand is slightly saddled. Three weak spin-allowed trip-quartet(TQ) transitions (in 10³ cm^?1): TQ1 (8.20) < TQ2 (11.3) < TQ3 (20.33) and the characteristic π-π* transitions of the Pc^2? ligand: B (14.68) < Q₁ (27.1) < Q₂ (29.0) < N (35.4) are observed in the UV-VIS-NIR spectrum. Prominent luminescence spectra are obtained by excitation within the TQ1 region, in which the spin-forbidden trip-sextet transition at 7376 cm^?1 dominates at low temperatures (T < 50 K). The vibrational spectra are discussed. In coincidence of the excitation lines with TQ3, v_s(Cr? O) at 378 cm^?1 is selectively resonance Raman (RR) enhanced. v_as(Cr? O) is observed in the FIR spectrum at 391 cm^?1. The following internal vibrations (in cm^?1) of the nitrito ligand are in the MIR spectrum: v_as(N? O)/1447 > v_as(N? O)/1018/1029 > δ(O? N? O)/828 and in the RR-spectrum: v_s(N? O)/1410 > v_s(N? O)/952, the last followed by three overtones.     

Off-axis field approximations for ion traps with apertures

In recent work (Int. J. Mass Spec., vol. 282, pp. 112–122) we have considered the effect of apertures on the fields inside rf traps at points on the trap axis. We now complement and complete that work by considering off-axis fields in axially symmetric (referred to as “3D”) and in two dimensional (“2D”) ion traps whose electrodes have apertures, i.e., holes in 3D and slits in 2D. Our approximation has two parts. The first, E_noAperture, is the field obtained numerically for the trap under study with apertures artificially closed. We have used the boundary element method (BEM) for obtaining this field. The second part, E_{dueToAperture}, is an analytical expression for the field contribution of the aperture.In E_{dueToAperture}, aperture size is a free parameter. A key element in our approximation is the electrostatic field near an infinite thin plate with an aperture, and with different constant-valued far field intensities on either side. Compact expressions for this field can be found using separation of variables, wherein the choice of coordinate system is crucial. This field is, in turn, used four times within our trap-specific approximation.The off-axis field expressions for the 3D geometries were tested on the quadrupole ion trap (QIT) and the cylindrical ion trap (CIT), and the corresponding expressions for the 2D geometries were tested on the linear ion trap (LIT) and the rectilinear ion trap (RIT). For each geometry, we have considered apertures which are 10%, 30%, and 50% of the trap dimension. We have found that our analytical correction term E_{dueToAperture}, though based on a classical small-aperture approximation, gives good results even for relatively large apertures.     

A flash photolysis-resonance fluorescence study of the reaction of atomic hydrogen with molecular oxygen H + O2 + M → HO2 + M

Using the technique of flash photolysis-resonance fluorescence, absolute rate constants have been measured for the reaction H + O₂ + M → HO₂+M over a temperature range of 220–360°K. Over this temperature range, the data could be fit to an Arrhenius expression of the following form: The units for k_Ar are cm⁶/mole-s. At 300°K the relative efficiencies for the third-body gases Ar:He:H₂:N₂:CH₄ were found to be 1.0:0.93:3.0:2.8:22. Wide variations in the photoflash intensity at several temperatures demonstrated that the reported rate constants were measured in the absence of other complex chemical processes.     

FLUORESCENCE FROM MAJOR AND MINOR BACTERIOCHLOROPHYLL COMPONENTS IN VIVO*

Abstract— In the photosynthetic bacteria Chromatium, Rhoahpirillum rubrum, and Rhodopseudomonus spheroides the fluorescence of bacteriochlorophyll is probably free of contamination by a “fast” component of delayed emission, judging from the characteristics of the delayed light measured 3 msec after excitation. In Rps. spheroides the pigment P870, associated with photochemical reaction centers, is non-fluorescent in its photochemically active state. Fluorescence of P870 can be induced by either of two agencies that suppress its photochemical activity: exposure to Na₂S₂O₄ and (in a dry chromatophore film) dessication. The yield of fluorescence from the major (light harvesting) component of bacteriochlorophyll in vivo is brought to a common maximum value by conditions that suppress the photochemical activity of P870. In addition to dessication and exposure to Na₂S₂O₄ these conditions include saturating illumination and exposure to K₃Fe(CN)₆. Of these four treatments only the last two bleach the long wave absorption band of P870. These experiments support the following assertions: (1) P870 traps singlet excitation energy absorbed by the light harvesting BChl; the trapping function of P870 depends on its ability to initiate and participate in photochemistry. (2) Both dessication and exposure to Na₂S₂O₄ suppress the photochemical activity of P870 by blocking an event that proceeds directly from the excited singlet state in P870. (3) The fluoresecence of BChl in vivo is emitted almost entirely by a major (light harvesting) component.     

Warm white light from Y4MgSi3O13:Bi, Eu nanophosphor for white light-emitting diodes

Y₄MgSi₃O₁₃:Bi³⁺, Eu³⁺ nanophosphors have been prepared by a facile sol–gel method. The products have been characterized by X-ray diffraction, field-emission scanning electron microscopy and fluorescence measurements. The results show that the nanophosphors are of single phase hexagonal Y₄MgSi₃O₁₃ with size-distribution of 50–90 nm in diameter. White-light emission has been obtained from Bi³⁺ and Eu³⁺ co-doped Y₄MgSi₃O₁₃ nanophosphors upon excitation of 350 nm ultraviolet light. It is noted that Bi³⁺ ions can occupy two different Y³⁺ sites and generate different emissions from the ³p₁ → ¹s₀ transition. Warm white light has been obtained from Y₄MgSi₃O₁₃:Bi³⁺, Eu³⁺ nanophosphors according to Commission International de I’Eclairage (CIE) chromaticity coordinates and color temperature (T_c) with appropriately adjusted contents of Bi³⁺ and Eu³⁺. The results indicate that Y₄MgSi₃O₁₃:0.08Bi³⁺, 0.04Eu³⁺ (x = 0.31, y = 0.31, T_c = 6907 K) are potential nanophosphors for white light-emitting diodes (LEDs) applications.     

The flash photolysis of di-μ-oxo-bis(oxo-molybdate(V)) acid aqueous solutions in the presence of excess thiocyanate

The flash photolysis of the mono and di-thiocyanate complexes of μ-oxo bis(oxo-molybdenum(V)) (Mo₂O₄(NCS)_x(H₂O)_6?x^(2?x)+ where x = 1, 2) has been studied in the system composed of perchloric acid solutions of Mo₂O₄(H₂O)₆²⁺ in the presence of excess thiocyanate. Irradiation with light in the wavelength range 250–340 nm induced the formation of three reaction intermediates identified as μ-oxo-bis (oxo-molybdenum(V)) species: Mo₂O₃(H₂O)₈⁴⁺ (A), Mo₂O₃(NCS) (H₂O)₇³⁺ (B), and Mo₂O₃(NCS)₂(H₂O)₆²⁺ (C). A rapid equilibria between the transient species is established before they decay following a first order kinetics. Intermediate A is the only species effective in promoting the observed decay leading to the end products Mo(VI) and H₂. The relative absorption spectrum of species A, B, and C are reported, as well as the measured stability constants for the formation of B and C in the temperature range 20–45°C. An overall mechanism is proposed.     

COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION-II. DAMPING OF FLASH YIELD OSCILLATION,DEACTIVATION*

Abstract— A quantitative analysis is made of a linear 4-step model for photosynthetic O₂ evolution in which each photochemical trapping center or an associated enzyme cycles through 5 oxidation states (S₀, S₁, S₂, S₃, S₄). The overall reaction is: S₀→ S₄, S₄→ S₀+ O₂, where k_d= rate of dark reaction. Based on data obtained with isolated chloroplasts, four aspects were considered: (1) The two perturbations which damp the oscillation of the O₂ flash yield in a flash sequence given after a dark period-(a) a failure rate (α) of the trapping centers in the photochemical conversion (‘misses’) and (b) double effective excitations in a fraction (8) of the centers which are in the S₀ and S₁ states (‘double hits’). Best fit with the experimental data is obtained for α= 0.1, β=0.05. (2) The kinetics and the mechanism of deactivation—the loss of + charges (O₂ precursors) in the dark. The momentary distribution of the four oxidation states (S₀-_-S₃) in a sample can be computed from the O₂ yields of four consecutive flashes with corrections for a and β. The time course of the various states in the dark following specific preilluminations reveals that deactivation proceeds in single equivalent steps: S₃→S₂, S₂,→S₁. S₁, itself stable in the dark, is the end product of deactivation. The ground state S₀ cannot be formed by deactivation in the dark but is only formed during illumination. (3) The various ratios [S₀]/[S₁] which can be observed in a sample after deactivation following different preilluminations with flashes or continuous light. (4) The transients of the O₂ evolution rate in weak continuous light as observed after deactivation with or without flash preillumination. In all instances satisfactory agreement is found between the observations and the predictions of the model.