ANALYSIS OF MICROSECOND FLUORESCENCE YIELD AND DELAYED LIGHT EMISSION CHANGES AFTER A SINGLE FLASH IN PEA CHLOROPLASTS: EFFECTS OF MONO- AND DIVALENT CATIONS

Abstract. New results are presented on the effects of mono- and divalent cations on concurrent changes in the microsecond yields and kinetics of chlorophyll a fluorescence and delayed light emission, and the light saturation curve for the latter at 100 μs, following a 10 ns flash at 337 nm. (1) The fluorescence yield increases exponentially from 3 to 30 μs (lifetime, τ, 6.4 ± 0.6/μs), and decays biphasically between 50 and 800μs. (2) The delayed light emission decays biphasically with two exponential phases: fast phase, T= 7–10μs, and slow phase, T= 33–40μs. (3) The light saturation curve for 100μs delayed light emission is satisfactorily represented by a one-hit Poisson saturation curve. (4) Addition of 5 mM NaCl to salt-depleted chloroplasts decreases (by as much as 40%) the yields of μs fluorescence and delayed light emission, and the subsequent addition of 5mM MgCl₂ increases the yields (≤2 × over samples with only NaCl). (5) The fluorescence yield rise and delayed light emission decay kinetics are independent of low concentrations of cations. The lifetime of the fast phase of fluorescence decay changes from ?90μs to ?160μs, when Na⁺ or Na⁺+ Mg²⁺ are added. Based on a detailed analysis presented in this paper, the following conclusions regarding the effects of low concentrations (few mM) of mono-and divalent cations in sucrose-washed chloroplasts at room temperature are made: (a) Na⁺ decreases (?6%) and Mg²⁺ increases (? 20% compared with the Na⁺ sample) the sensitization of photosystem II photochemistry: this effect is small, but significant. (b) Na⁺ increases and Mg²⁺ decreases the efficiency for radiationless transitions in singlet excited Chl a in the antenna and closed reaction center of PS II; this includes non-radiative energy transfer to PS I, intramolecular intersystem crossing and internal conversion. The ratio of the sum of the rate constants for radiationless transitions to that for fluorescence increases by ? 2-fold upon the addition of Na⁺, and is completely reversed by the addition of Mg²⁺. (c) The rate constant for the re-oxidation of Q^- decreases (about 50%) in the presence of Na⁺ or Na⁺+ Mg²⁺. These conclusions imply that cations produce multiple changes in the primary photoprocesses of PS II at physiological temperatures. It is proposed that these changes are mutually independent and can co-exist.     

Voltammetric Behavior of Arsenic(III) in the Presence of Sodium Diethyl Dithiocarbamate and Its Determination in Water and Highly Saline Samples by Adsorptive Stripping Voltammetry

This paper describes the voltammetric behavior of As(III) at the hanging mercury drop electrode (HMDE) in the presence of sodium diethyl dithiocarbamate (SDDC) and a new voltammetric method for the determination of As(III) at trace levels. The method is based on the adsorptive deposition of a As(III) complex with SDDC at ?0.45 V (vs. Ag/AgCl) on the HMDE in acidic medium of 0.01 mol L^?1 HCl (pH 2.0) and its cathodic stripping during the potential scan (100 mV s^?1). The linear range for the determination of As(III) in the presence of SDDC (4 μmol L^?1) in water samples was between 1 and 10 μg L^?1 for a deposition time of 300 s (r=0.994) and between 10 and 100 μg L^?1 for a deposition time of 60 s (r=0.999). For the determination of As(III) in dialysis concentrate samples, the linear range was between 5 and 25 μg L^?1 for a deposition time of 180 s (r=0.992) and between 10 and 100 μg L^?1 for a deposition time of 60 s (r=0.996). Detection limits of 0.3 and 2.2 μg L^?1 in water and dialysis concentrate samples were calculated for the method using a deposition time of 300 and 180 s, respectively. Recovery values between 93.0 and 110.0% for As(III) added to deionized, mineral, seawater (synthetic and real) and dialysis concentrate samples prove the satisfactory accuracy and applicability of the procedure.     

A simple and sensitive continuous hydride generation system for the determination of arsenic and selenium by atomic absorption and atomic fluorescence spectrometry

The development and optimization of a continuous hydride generation system for atomic absorption spectrometry (a.a.s.) and atomic fluorescence spectrometry (a.f.s.) is described. Sodium tetrahydroborate(III) solution and sample solution are delivered by two small peristaltic pumps to a gas/liquid separator. The evolved hydrides are swept to a miniature argon/hydrogen diffusion flame burning on a borosilicate glass tube. Detection limits (2σ) obtained for arsenic are 0.8 ng ml^-1 by a.a.s. and 0.34 ng ml^-1 by a.f.s., and for selenium 0.5 ng ml^-1 by a.a.s. and 0.13 ng ml^-1 by a.f.s. Linear working ranges are typically 1–100 ng ml^-1 with a typical measurement time of 1 min per sample or standard.     

Rate constants for the reactions of O3 and OH radicals with a series of alkynes

Rate constants for the reactions of O₃ and OH radicals with acetylene, propyne, and 1-butyne have been determined at room temperature. The rate constants obtained at 294 ± 2 K for the reactions of O₃ with acetylene, propyne, and 1-butyne were (7.8 ± 1.2) × 10^?21 cm³/molecule · s, (1.43 ± 0.15) × 10^?20 cm³/molecule · s, and (1.97 ± 0.26) × 10^?20 cm³/molecule · s, respectively. The rate constants at 298 ± 2 K and atmospheric pressure for the reactions with the OH radical, relative to a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10^?12 cm³/molecule · s, were determined to be (8.8 ± 1.4) × 10^?13 cm³/molecule · s, (6.21 ± 0.31) × 10^?12 cm³/molecule · s, and (8.25 ± 0.23) × 10^?12 cm³/molecule · s for acetylene, propyne, and 1-butyne, respectively. These data are discussed and compared with the available literature rate constants.     

Kinetics of the reactions of O3 and OH radicals with furan and thiophene at 298 ± 2 K

Rate constants for the reactions of O₃ and OH radicals with furan and thiophene have been determined at 298 ± 2 K. The rate constants obtained for the O₃ reactions were (2.42 ± 0.28) × 10^?18 cm³/molec·s for furan and <6 ×10^?20 cm³/molec·s for thiophene. The rate constants for the OH radical reactions, relative to a rate constant for the reaction of OH radicals with n-hexane of (5.70 ± 0.09) × 10^?12 cm³/molec·s, were determined to be (4.01 ± 0.30) × 10^?11 cm³/molec·s for furan and (9.58 ± 0.38) × 10^?12 cm³/molec·s for thiophene. There are to date no reported rate constant data for the reactions of OH radicals with furan and thiophene or for the reaction of O₃ with furan. The data are compared and discussed with respect to those for other alkenes, dialkenes, and heteroatom containing organics.     

Oligonucleotide Analogues with Integrated Bases and Backbone

The thiomethylene‐linked U*[s]U⁽*⁾ dimers 9 – 14 were synthesized by substitution of the 6‐[(mesyloxy)methyl]uridine 6 by the thiolate derived from the uridine‐5′‐thioacetates 7 and 8 followed by O‐deprotection. Similarly, the thiomethylene‐linked A*[s]A⁽*⁾ dimers 9 – 14 were obtained from the 8‐(bromomethyl)adenosine 15 and the adenosine‐5′‐thioacetates 16 and 17 . The concentration dependence of both H? N(3) of the U*[s]U⁽*⁾ dimers 9 – 14 evidences the formation of linear and cyclic duplexes, and of linear higher associates, C(8 or 6)CH₂OH and/or C(5′/II)OH groups favouring the formation of cyclic duplexes. The concentration dependence of the chemical shift for both H₂N? C(6) of the A*[s]A⁽*⁾ dimers 18 – 23 evidences the formation of mainly linear associates. The heteroassociation of U*[s]U⁽*⁾ to A*[s]A⁽*⁾ dimers is stronger than the homoassociation of U*[s]U⁽*⁾ dimers, as evidenced by diluting equimolar mixtures of 11 / 20 and 13 / 22 . A 1 : 1 stoichiometry of the heteroassociation is evidenced by a Job's plot for 11 / 20 , and by mole ratio plots for 9 / 18, 10 / 19, 12 / 21, 13 / 22 , and 14 / 23 .     

Two-color excitation of NO in a supersonic free jet. Autoionization of high rydberg states

High Rydberg states of NO above the ionization limit have been measured for the isolated molecule in a supersonic free jet by two-color multiphoton ionization. Three Rydberg series (ns, np and nf) were identified, which appeared by rotational and the vibrational autoionization. The rotational structures of the 13s(υ = 1), 13p(υ = 1) and 12f(υ = 1) states have been analyzed in detail. The fluorescence dip spectra for the intermediate A²Σ⁺(3sσ) state have been measured simultaneously and the cross sections of the one-photon absorption to the high Rydberg states from the A²Σ⁺(υ = 1) state have been determined.     

ARE THERE SEVERAL PHOTORECEPTORS INVOLVED IN PHOTOTROPISM OF Phycomyces blakesleeunus? KINETIC STUDIES OF DICHROMATIC IRRADIATION*

Abstract— Photogeotropic equilibrium angles were measured for Phycomyces blakesleeanus wild type firstly by means of dichromatic fluence rate response curves using simultaneous irradiation with near threshold 450 nm reference light (constant at 1.2 × 10^?8 W m^?2) and variable fluence rates of test light (498–630 nm) from the same side. These curves showed minima for test light fluence rates that were close to the photogeotropic threshold for these wavelengths. Secondly, the time course of this inhibitory effect was studied with both the inductive reference 450 nm light (2 × 10^?-⁷ W m^?2) and the test light (606 or 450 nm) given as light pulses of 2 s duration (2 s light/48 s dark periods for 6 h). The dark period between the onset of the inductive reference light and test light pulses was varied between 0 and 48 s. No inhibitory effects were observed for simultaneous pulses; however, inhibitory effects were demonstrated for delay times of 2 s and 20 s for 606 nm as well as 450 nm test light. If the test light pulses were given immediately before the inductive reference light, only 606 nm test light was effective in producing a significant inhibitory effect. The results are discussed with regard to a multichromophoric photoreceptor system and to the wavelength dependence of the effects observed. The data and conclusions favor a photoreceptor system with at least two separate chromophoric absorptions of the blue light receptor type, one acting positively, the other acting inhibitorily, and at least one other photoreceptor of presumably minor influence.     

Diabatic molecular states and the shielded diatomic orbital method. Evolution of two-interacting state systems for molecular hydrogen

Within Lichten's method, shielded diatomic orbitals (SDO's) are proposed as a basis for building-up diabatic molecular states in the single configurati approximation. The determination of SDO's i.e. eigenfunctions in prolate spheroidal coordinates of the two-center problem with a parametric shielding potential is extended to mono-excited states of many-electron diatomic systems, the shielding potential being obtained from simple electrostatic considerations. Four diabatic molecular states of H₂ are investigated i.e. ¹Σ_g⁺ (2pσ², 1Σ_g⁺ (1s,σ 2sσ), ¹Σ_u⁺(1sσ,4Pσ), ¹Σ_u⁺ (1sσ, 4fσ) using a minimal basis of SDO'S. The dynamical evolution of the nuclei for the two sets ¹Σ_g and ¹Σ_u⁺ of two interacting states is described in both the diabatic and the corresponding adiabatic representation.     

SPIN TRAPPING OF THE SUPEROXIDE RADICAL BY 4-(N-METHYLPYRIDINIUM) t-BUTYL NITRONE

The synthesis of 4-(N-methylpyridinium) t-butyl nitrone (4-MePyBN) and its use as a spin trap for superoxide radicals produced in aqueous solutions is reported (a^N= 13.78 G, a^H_ß= 1.65 G, and g = 2.0091). The half-life of the spin adduct as a function of pH (83 s at pH 5.5, 78 s at pH 7.0, and 65 s at pH 8.0) the effects of iron salts, diethylenetriaminepentacetic acid (DETAPAC), and superoxide dismutase were examined, and comparisons made between 4-MePyBN and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as spin trapping agents for the superoxide radical.     

Approximate Self-Consistent Molecular Orbital Theory I S-P Separation Model Modification of CNDO-MO

A newly developed approximate self-consistent molecular orbital formulation, so called: ‘s–p separation model CNDO-MO method’, is proposed. The Pariser Parr¹⁾ and Nishimoto Mataga²⁾ approximations are separately applied to the ns and np (n=l to 3) AO's. The MO's of both closed and open shell cases are formulated. It seems to be a good method for molecular structure interpretation for both polar and nonpolar compounds.     

Determination of Se(IV) in On‐Line System by Cathodic Stripping Voltammetry

A sensitive and selective on‐line voltammetric procedure for determination of traces of Se(IV) is presented. The pulsed potential accumulation was proposed for minimization of interferences of surface active substances and foreign ions. The calibration plot was linear from 1×10^?9 mol L^?1 to 4×10^?8 mol L^?1 for accumulation time of 180 s. The relative standard deviation was 6.1% (n=5) for a Se(IV) concentration of 1×10^?8 mol L^?1. The detection limit estimated from (3 σ) for an accumulation time of 180 s was about 4×10^?10 mol L^?1. The validation of the procedure proposed was made by a recovery tests for tap and river water samples.     

Catalytic Adsorptive Stripping Voltammetry of Cobalt in the Presence of Dimethylglyoxime and Nitrite at In Situ Plated Lead–Copper Film Electrode

A lead‐copper film electrode was proposed for Co(II) determination by catalytic adsorptive stripping voltammetry. The electrode was plated in situ and hence the exchange of a solution after plating step was not required. At optimized conditions the calibration graph for Co(II) was linear from 5×10^?10 to 2×10^?8 mol L^?1 for accumulation time of 15 s. The relative standard deviation for Co(II) determination at concentration 5×10^?9 mol L^?1 was 4.1%. The detection limits for Co(II) were 1.2×10^?10 and 1.0×10^?11 mol L^?1 for an accumulation time of 15 and 180 s, respectively. The method was applied to Co(II) determination in certified reference material and other water samples.     

Comparative Study of Influence of Experimental Configuration on Densities of Active Species in the Early Afterglows of N2/(0–2.5%)H2 HF Flowing Plasmas

Afterglows of mixed gas of N₂ and H₂(0–2.5%) flowing microwave discharges in a 5 mm diameter tube connected to a 5 L reactor via a tube of 1.8 cm diameter and 50 cm long, have been studied using optical emission spectroscopy. The obtained results at the entrance of the afterglow tube of 1.8 cm diameter: Short time afterglow (SA), (10^–3 s) and inside the 5 L reactor: Long time afterglow (LA), (10^–2 s) were then compared. It was found that, in N₂ at 2 Torr, 0.5 slpm, the active specie density ratios had a constant value of 10^–2 for N/N₂, but decreased respectively from 10^–3 to 10^–4 for N₂ (X,v?>?13)/N₂ and from 10^–6 to 10^–8 for N⁺₂ /N₂. By directly connecting the discharge tube inside the 5 L reactor, the density increases by 10 for N₂ (X,v?>?13) and by 10² for N₂⁺ by changing the afterglow from LA(10^?2 s) to a SA(10^–3 s). Moreover and by adding 1% of H₂ to N₂, the N/N₂ and H/H₂ ratios had constant values of 1% and 0.2% respectively. The SA(10^–3 s) appeared to be more efficient for surface treatments than the LA (10^–2 s).

     

Atomic absorption spectrometric determination of copper in calcium carbonate scale and carbonate rocks by direct atomization of solid samples

Powdered samples (1 mg) are mixed with 1 mg of powdered graphite and copper is determined by atomic absorption spectrometry in a miniature graphite cup placed in a graphite crucible. Optimum conditions were drying at 200 °C (30 s), ashing at 900 °C (30 s), atomizing at 2700 °C (15 s) and cleaning at 2800 °C (10 s). Samples were powdered to 1–10 μm particle size. Magnesium, manganese and iron did not interfere. The effect of calcium carbonate was eliminated by the graphite addition. Results for copper (0.5–5 μg g^?1) in the scale and rocks agreed well with values obtained for dissolved samples. Relative standard deviations (n=10) were 4.9% for 1.2 μg g^?1 copper and 14.8% for 0.577 μg g^?1.     

New Potassium- and Cesium-selective Ionophoric Bis(crown ether)s Derived from Xanthene-4,5-dicarboxylic Acid

A series of bis(crown ether)sbased-upon a xanthene-4,5-dicarboxylic acid skeletonwas prepared and their ionophoric properties towardalkali metal cations were investigated. Bis(crownether)s bearing 15-crown-5 and 18-crown-6 moietiesexhibited pronounced extraction efficiencies towardK⁺ and Cs⁺ ions, respectively, and theextraction constant estimated by solvent extractionstudies was as high as 10⁹ for the 2-K⁺ and 3-Cs⁺ systems. Using UVtitration of potassium picrate with 2 in THF, thecomplex was found to have a structure of a completelyencapsulated guest in the host. In transportexperiments, the bis(crown ether)s showed nosignificant selectivity pattern compared withextraction results, again implying the strongcomplexation of bis(crown ether)s. Ion-selectiveelectrode studies also demonstrated that the selectiveionophoric properties of 2 toward K⁺ werereminiscent of the natural antibiotic valinomycinexcept for a somewhat slow response.     

α- and γ-Regiocontrol and Enantiospecificity in the Copper-Catalyzed Substitution Reaction of Propargylic Phosphates with Grignard Reagents

The regioselectivity (r.s.) and enantiospecificity (e.s.) of the substitution reactions of secondary propargylic alcohol derivatives using reagents derived from ArMgBr and Cu salts were studied. First, the picolinate, 3-methylpicolinate, and diethylphosphonate derivatives of Ph(CH₂)₂CH(OH)C≡CTMS were reacted with PhMgBr/CuCN in ratios of 2.5:2.7–2.5:0.25. The use of 2.5:0.25 ratio in THF/DME (6:1) at 0 °C for 1 h afforded the α-substitution product from the phosphate with ≥98 % r.s. and 99 % e.s. CuBr⋅Me₂S gave similar selectivity. The reaction system was then applied to phosphates derived from R¹CH(OH)C≡CR² and ArMgBr to obtain synthetically sufficient r.s. and e.s. values with R²=TMS, Ph, whereas iPr was borderline in terms of size as an R¹ substituent. The presence of a substituent at the o-position of Ar marginally affected the selectivity. We also found that the use of PhMgBr/Cu(acac)₂ in a 2:1 ratio in THF produced the γ-substitution products (allenes) with high r.s. and e.s.     

Li<Superscript><Emphasis Type="Bold">+</Emphasis></Superscript> Transport Mechanism in Oligo(Ethylene Oxide)s Compared to Carbonates

Molecular dynamics simulations have been performed on oligo(ethylene oxide)s of various molecular weights doped with the lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) in order to explore the mechanism of Li⁺ transport in materials covering the range from liquid electrolytes to prototypes for high molecular weight poly(ethylene oxide)-based polymer electrolytes. Good agreement between MD simulations and experiments is observed for the conductivity of electrolytes as a function of molecular weight. Unlike Li⁺ transport in liquid ethylene carbonate (EC) that comes from approximately equal contributions of vehicular Li⁺ motion (motion together with solvent) and Li⁺ diffusion by solvent exchange, Li⁺ transport in oligoethers was found to occur predominantly by vehicular motion. The slow solvent exchange of Li⁺ in oligo(ethylene oxide)s highlights why high molecular weight amorphous polymer electrolytes with oligo(ethylene oxide)s solvating groups suffer from poor Li⁺ transport. Ion complexation and correlation of cation and anion motion is examined for oligoethers and compared with that in EC.