The anaerobic filtration of dairy waste: Results of a pilot trial

Results are presented from a pilot scale (4·3 m³) upflow anaerobic filter for the treatment of the wastewater from ice-cream manufacture. The reactor was completely mixed by gas production but the solids or sludge held within the reactor were shown to be affected by the liquid velocities. The reactor was subject to a number of organic and hydraulic shocks and this reduced the consistency of COD removal. Daily loading rates varied from 0 to 18 kg COD/m³/day but with an average load of 5·5 kg/m³/day the mean COD removal was 70%. This was compared with previous work and shown to be a typical performance for an anaerobic filter. Alkalinity and carboxylic acid data are also presented and were within the normal, stable, operating range. Previous research on the anaerobic treatment of industrial effluents has shown alkalinity to be the most important factor controlling reliability.     

Determination of kinetic constants for a two-stage anaerobic upflow packed-bed reactor for dairy wastewater

A two-stage upflow packed-bed (reactors in series) system was used for the treatment of dairy wastewater. Nylon pads were used as supporting media for the biomass. This investigation aimed at the determination of various kinetic constants for substrate, biomass and biogas based on various models. The maximum loadings that could be applied to reactor I and reactor II were 14·29 and 5·0 kg of chemical oxygen demand (COD) per m³ per day, respectively. The maximum COD removal efficiencies at various loading rates were in the ranges of 93·8–98·5% and 72·5–84% for the two reactor systems, respectively. The combined biogas yield was between 0·196 and 0·386 m³ gas/kg COD_a.     

肇庆市某污水厂CASS工艺的调试与运行性能

对肇庆市某新建城市污水处理厂进行工艺调试,研究了其CASS系统对进水的处理效果.结果表明,调试阶段,进水COD_Cr、BOD₅、NH₄⁺-N和TP浓度分别为117.3～446.4 mg·L^-1、60.5～225.9 mg·L^-1、7.6～34.3 mg·L^-1和1.85～5.49 mg·L^-1,对应地,出水浓度分别为18.6～63.2 mg·L^-1、8.0～29.2 mg·L^-1、2.0～8.8 mg·L^-1和0.22～0.83 mg·L^-1.正常运行并优化工艺后,出水BOD₅、NH₄⁺-N和TP可达标排放.CASS池微生物数量丰富,正常运行阶段每克干污泥中,细菌、酵母菌和霉菌总数分别高达4.2×10¹⁰±1.8×10¹⁰CFU、2.5×10⁷±1.8×10⁷CFU和3.6×10⁶±2.6×10⁶CFU.     

Quantification of pathogenic micro-organisms in the sludge from treated hospital wastewater

The sludge from hospital waste treatment facilities is a potential source of infectious organisms. The average numbers of micro-organisms in the sludge of hospital wastewater in Taiwan were as follows: total count 8·1 × 10⁷ cfu g⁻¹ (dry weight of sludge), and 1·4 × 10⁶, 3·6 × 10⁵, 1·6 × 10⁵, 2·2 × 10⁵ and 5·5 × 10⁴ cfu g⁻¹ (dry weight of sludge) for total coliforms, faecal coliforms, faecal streptococci, Pseudomonas aeruginosa and Salmonella spp., respectively . Salmonella spp. were detected in 37% (10 of 27) of the sludges from hospital wastewaters. Therefore, the treatment of such sludge to reduce pathogenic micro-organisms should be considered.     

Rate of electron transfer between plastocyanin, cytochrome ƒ, related proteins and artificial redox reagents in solution

The rate of electron transfer between reduced cytochrome ƒ and plastocyanin (both purified from parsley) has been measured as k = 3.6 · 10⁷ M⁻¹ · s⁻¹, at 298 °K and pH 7.0, with activation parameters ΔH^‡ = 44 kJ · mole⁻¹ and ΔS^‡ = +46 J · mole⁻¹ · °K⁻¹. Replacement of cytochrome ƒ with red algal cytochrome c-553, Pseudomonas cytochrome c-551 and mammalian cytochrome c gave rates at least 30 times slower: k = 5 · 10⁵, 7.5 · 10⁵ and 1.0 · 10⁶ M⁻¹ · s⁻¹, respectively.

Similar measurements made with azurin instead of plastocyanin gave k = 6 · 10⁶ and approx. 2 · 10⁷ M⁻¹ · s⁻¹ for reaction of reduced azurin with cytochrome ƒ and algal cytochrome respectively.

Rate constants of 115 and 80 M⁻¹ · s⁻¹ were found for reduction of plastocyanin by ascorbate and hydroquinone at 298 °K and pH 7.0. The rate constants for the oxidation of plastocyanin, cytochrome ƒ, Pseudomonas cytochrome c-551 and red algal cytochrome c-553 by ferricyanide were found to be between 3 · 10⁴ and 8 · 10⁴ M⁻¹ · s⁻¹.

The results are discussed in relation to photosynthetic electron transport.     

Pretreatment of beet molasses to increase pullulan production

Pretreatment of beet molasses with cation exchange resin, sulphuric acid, tricalcium phosphate, potassium ferrocyanide, and ethylenediaminetetraacetic acid and disodium salt (EDTA) to increase the production of pullulan was investigated. Among the above techniques used for the removal of heavy metals, sulphuric acid treatment gave better results regarding polysaccharide concentration, polysaccharide yield, and sugar utilization. Aureobasidium pullulans grown on beet molasses produced a mixture of pullulan and other polysaccharides. The pullulan content of the crude polysaccharide was 30–35%. The addition of nutrients improved the production of polysaccharide. A maximum polysaccharide concentration (32·0±1·0 g litre⁻¹) was achieved in molasses solution (70 g litre ¹ initial sugar concentration, pH 6·5–7·5) treated with sulphuric acid and supplemented with K₂HPO₄ 0·5%, -glutamic acid 1%, olive oil 2·5% and Tween 80 0·5%. In this case, the highest values of biomass dry weight (33·8±1·0 g litre⁻¹), polysaccharide yield (63·5±2·5%), and sugar utilization (97·5±1·5%) were obtained at pH 6·5, 3·5, and 4·5–7·5, respectively.     

Kinetics and equilibria of Ga(III)---thiocyanate complex formation. Mechanism of ligand substitution reactions of Ga(III) in aqueous solution

The kinetics and equilibria of complex formation by Ga(III) with NCS⁻ in aqueous solution have been measured over a range of acidities and temperatures, the contributing paths to the reaction resolved, and their rate constants and activation parameters determined. The hydrolysis equilibria required to carry out this resolution of kinetic behaviour have also been measured.

Unlike the other reported complexation reactions of Ga(III) in aqueous solution, the separate reaction pathways can be assigned with no ambiguity. At 25 °C and ionic strength 0.5 M, the observed forward rate constant for the complex formation is described by {k₁ + k₂K_1h/[H⁺] + k₃K_1hK_2h/[H⁺]²} M⁻¹ s⁻¹. For these conditions, the first and second successive hydrolysis constants of Ga(H₂O)₆³⁺ are given by pK_1h = 3.69 ± 0.01 and pK_2h = 3.74 ± 0.04. The rate constants corresponding to the reactions of the species Ga(H₂O)₆³⁺, Ga(H₂O)₅(OH)²⁺ and Ga(H₂O)₄(OH)₂⁺ with NCS⁻ are k₁ = 57 ± 4 M^{−1 −1}, k₂ = (1.08 ± 0.01) × 10⁵ M⁻¹ s⁻¹ and k₃ = 3 × 10⁶ M⁻¹ s⁻¹ respectively. The complexation equilibrium quotient [GaNCS²⁺]/([Ga³⁺][NCS⁻]) has been independently determined by spectrophotometric titration to be 20.8 ± 0.3 M⁻¹ at 25 °C and ionic strength 0.5 M.

These kinetic results lead to an interpretation of the data, and a reinterpretation of other data for aquo-Ga(III) complex formation kinetics from the literature which support the assignment of a dissociative interchange mechanism for these reactions rather than the associative activation mode sometimes proposed.     

Phosphorylation of an actin · tropomyosin · troponin complex from human skeletal muscle

A human skeletal actin · tropomyosin · troponin complex was phosphorylated in the presence of [γ-³²P]ATP, Mg²⁺, adenosine 3′:5′-monophosphate (cyclic AMP) and cyclic AMP-dependent protein kinase (protein kinase). Phosphorylation was not observed when the actin complex was incubated in the absence of protein kinase or 1 μM cyclic AMP. In the presence of 10⁻⁷ M Ca²⁺ and protein kinase 0.1 mole of [³²P]phosphate per 196 000 g of protein was incorporated. This was two-fold higher than the [³²P]phosphate content of a rabbit skeletal actin complex but two-fold lower than that of a bovine cardiac actin complex. At high Ca²⁺, 5 · 10⁻⁵ M, little change in the phosphorylation of a human skeletal actin complex occurred. Phosphoserine and phosphothreonine were identified in the [³²P]phosphorylated actin complex. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that 60% of the label was associated with the tropomyosin binding component of troponin. The inhibitory component of troponin contained 16% of the bound [³²P]phosphate. Increasing the Ca²⁺ concentration did not significantly decrease the [³²P]phosphate content of the phosphorylated proteins in the actin complex. No change in the distribution of phosphoserine or phosphothreonine was observed. Half maximal calcium activation of the ATPase activity of reconstituted human skeletal actomyosin made with the [³²P]phosphorylated human skeletal actin complex was the same as a reconstituted actomyosin made with an actin complex incubated in the absence of protein kinase at low or high Ca²⁺.     

A convenient electrochemical preparation of reduced methyl viologen and a kinetic study of the reaction with oxygen using an anaerobic stopped-flow apparatus

1. Single reduced methyl viologen (MV^.+) acts as an electron donor in a number of enzyme systems. The large changes in extinction coefficient upon oxidation (λ_max 600 nm; MV^.+, = 1.3 · 10⁴ M⁻¹ · cm⁻¹; oxidised form of methyl viologen (MV²⁺), = 0.0) make it ideally suited to kinetic studies of electron transfer reactions using stopped-flow and standard spectrophotometric techniques.

2. A convenient electrochemical preparation of large amounts of MV^.+ has been developed.

3. A commercial stopped-flow apparatus was modified in order to obtain a high degree of anaerobicity.

4. The reaction of MV^.+ with O₂ produced H₂O₂ (k > 5 · 10⁶ M⁻¹ · s⁻¹, pH 7.5, 25 °C). H₂O₂ subsequently reacted with excess MV^.+ (k = 2.3 · 10³ M⁻¹ · s⁻¹, pH 7.5, 25 °C) to produce water. The kinetics of this reaction were complex and have only been interpreted over a limited range of concentrations.

5. The results support the theory that the herbicidal action of methyl viologen (Paraquat, Gramoxone) is due to H₂O₂ (or radicals derived from H₂O₂) induced damage of plant cell membrane.     

Biological phosphorus removal in sequencing batch reactor with single-stage oxic process

The performance of biological phosphorus removal (BPR) in a sequencing batch reactor (SBR) with single-stage oxic process was investigated using simulated municipal wastewater. The experimental results showed that BPR could be achieved in a SBR without anaerobic phase, which was conventionally considered as a key phase for BPR. Phosphorus (P) concentration 0.22–1.79 mg L⁻¹ in effluent can be obtained after 4 h aeration when P concentration in influent was about 15–20 mg L⁻¹, the dissolved oxygen (DO) was controlled at 3 ± 0.2 mg L⁻¹ during aerobic phase and pH was maintained 7 ± 0.1, which indicated the efficiencies of P removal were achieved 90% above. Experimental results also showed that P was mainly stored in the form of intracellular storage of polyphosphate (poly-P), and about 207.235 mg phosphates have been removed by the discharge of rich-phosphorus sludge for each SBR cycle. However, the energy storage poly-β-hydroxyalkanoates (PHA) was almost kept constant at a low level (5–6 mg L⁻¹) during the process. Those results showed that phosphate could be transformed to poly-P with single-stage oxic process without PHA accumulation, and BPR could be realized in net phosphate removal.     

Reduction of ferricytochrome c by hydrogen atoms: Evidence for intramolecular transfer of reducing equivalent

Direct evidence obtained by means of the technique of pulse radiolysis-kinetic spectrometry, with measurements in the time range 10⁻⁶ to 1 s, is presented that, consequent upon reaction of a single H-atom with a single molecule of ferricytochrome c, a reducing equivalent is transmitted via the protein structure to the ferriheme moiety. Such transmission accounts for at least 70% of the total reduction of the ferri to the ferro state of cytochrome c. The remainder of the total reduction takes place without stages resolvable on the time scale of these experiments. Reduction brought about by H atoms appears to follow a different course than reduction by hydrated electrons. In the latter case, intramolecular transmission of reducing equivalents could not be demonstrated (Lichtin, N. N., Shafferman, A. and Stein, G. (1973) Biochim. Biophys. Acta 314, 117–135).

Not every H-atom reacts with ferricytochrome c at a site which results in conversion of the Fe(III) state to the Fe(II) state. Approximately half of reacting H-atoms do not produce reduction.

The following second order rate constants have been determined in solutions of low ionic strength at 20±2 °C: k[H+ferricytochrome c] = (1.0±0.2) · 10¹⁰ M⁻¹ · s⁻¹ at pH 3.0 and 6.7; k[H+ferrocytochrome c] = (1.3±0.2) · 10¹⁰ M⁻¹ · s⁻¹ at pH 3.0; k[e⁻_aq + ferrocytochrome c] = (1.9±0.4) · 10¹⁰ M⁻¹ · s⁻¹ at pH 6.7.     

Production d'NH4 par la crevette Crangon crangon L. dans deux écosystémes côtiers. approche expérimentale et étude de l'influence du sédiment sur le taux d'excrétion

Estimation of the ammonia production of the shrimp C. crangon in two littoral ecosystems (oligotrophic sand and eutrophic mud) was determined in winter and summer conditions from laboratory observations in experimental microcosms. The ammonia excretion rate of C. crangon was not influenced by either the sediment type or the ammonia concentration of the overlying water; on the other hand, the mean excretion rate and the response to initial handling stress increased markedly as shrimp were deprived of soft substratum.

The daily ammonia production of C. crangon was 16 μmol NH₃ · g ⁻¹ wet wt · day ⁻¹ in winter and 40 μmol in summer. A gross production of 12 μmol NH₃ · m⁻² · day ⁻¹ and 300–700 μmol μ m⁻² · day⁻¹, respectively, could be expected in the two ecosystems studied. This would account for 5% (winter) and 2–4% (summer) of the total NH⁺₄ flux at the sediment-water interface. The contribution of the excretion of all macrofauna to the NH⁺₄ flux from the sediment is discussed.     

Mg2+ ion effect on conformational equilibrium of poly A . 2 poly U and poly A poly U in aqueous solutions

Differential UV spectroscopy and thermal denaturation were used to study the Mg²⁺ ion effect on the conformational equilibrium in poly A · 2 poly U (A2U) and poly A · poly U (AU) solutions at low (0.01 M Na⁺) and high (0.1 M Na⁺) ionic strengths. Four complete phase diagrams were obtained for Mg²⁺–polynucleotide complexes in ranges of temperatures 20–96 °C and concentrations (10⁻⁵–10⁻²) M Mg²⁺. Three of them have a ‘critical’ point at which the type of the conformational transition changes. The value of the ‘critical’ concentration ([Mg_t²⁺]_cr=(4.5±1.0)×10⁻⁵ M) is nearly independent of the initial conformation of polynucleotides (AU, A2U) and of Na⁺ contents in the solution. Such a value is observed for Ni²⁺ ions too. The phase diagram of the (A2U+Mg²⁺) complex with 0.01 M Na⁺ has no ‘critical’ point: temperatures of (3→2) and (2→1) transitions increase in the whole Mg²⁺ range. In (AU+Mg²⁺) phase diagram at 0.01 M Na⁺ the temperature interval in which triple helices are formed and destroyed is several times larger than at 0.1 M Na⁺. Using the ligand theory, a qualitative thermodynamic analysis of the phase diagrams was performed.     

Structure and characterization of platinum(II) and platinum(IV) complexes with protonated nucleobase ligands

The reaction of H₂[PtCl₆] · 6H₂O and (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O (18C6 = 18-crown-6) with 9-methylguanine (MeGua) proceeded with the protonation of MeGua forming 9-methylguaninium hexachloroplatinate(IV) dihydrate (MeGuaH)₂[PtCl₆] · 2H₂O (1).The same compound was obtained from the reaction of Na₂[PtCl₆] with (MeGuaH)Cl.On the other hand, the reaction of guanosine (Guo) with (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O in methanol at 60 °C proceeded with the cleavage of the glycosidic linkage and with ligand substitution to give a guaninium complex of platinum(IV), [PtCl₅(GuaH)] · 1.5(18C6) · H₂O (2).Within several weeks in aqueous solution a slow reduction took place yielding the analogous guaninium platinum(II) complex, [PtCl₃(GuaH)] · (18C6) · 2Me₂CO (3).H₂[PtCl₆] · 6H₂O and guanosine was found to react in water, yielding (GuoH)₂[PtCl₆] (4) and in ethanol at 50 °C, yielding [PtCl₅(GuoH)] · 3H₂O (5).Dissolution of complexes 2 and 5 in DMSO resulted in the substitution of the guaninium and guanosinium ligands, respectively, by DMSO forming [PtCl₅(DMSO)]⁻.Reactions of 1-methylcytosine (MeCyt) and cytidine (Cyd) with H₂[PtCl₆] · 6H₂O and(H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O resulted in the formation of hexachloroplatinates with N3 protonated pyrimidine bases as cation (MeCytH)₂[PtCl₆] · 2H₂O (6) and (CydH)₂[PtCl₆] (7), respectively. Identities of all complexes were confirmed by ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopic investigations, revealing coordination of GuoH⁺ in complex 5 through N7 whereas GuaH⁺ in complex 3 may be coordinated through N7 or through N9. Solid state structure of hexachloroplatinate 1 exhibited base pairing of the cations yielding (MeGuaH⁺)₂, whereas in complex 6 non-base-paired MeCytH⁺ cations were found. In both complexes, a network of hydrogen bonds including the water molecules was found. X-ray diffraction analysis of complex 3 exhibited a guaninium ligand that is coordinated through N9 to platinum and protonated at N1, N3 and N7. In the crystal, these NH groups form hydrogen bonds N–HO to oxygen atoms of crown ether molecules.     

Performance evaluation of a 1 m modified, fixed-dome Deenbandhu biogas plant under hilly conditions

The performance of a 1 m³ daily gas-production-capacity, modified, Deenbandhu biogas plant was evaluated under hilly conditions. The modified plant had a digester volume of 2·65 m³ with 55 days hydraulic retention time (HRT) as against a volume of 2·45 m³ with 50·96 days HRT of the Action for Food Production (AFPRO) design. All the constructional items used in the modified plant were in accordance with the recommendations of AFPRO except the number of bricks, i.e. 625 in the modified design as against 800 in the AFPRO design. The rates of biogas production in October 1993 and January 1994 were 0·0357 and 0·0282 m³/kg feed (wet weight of dung); respectively. Thus the modified plant had a gas production efficiency of 70·5–89·4% of its rated capacity. All other functional parameters were within the optimum limits recommended for successful operation of any anaerobic digester.     

Reaction of myosin with salicylaldehyde I. The effect of salicylaldehyde on the physicochemical properties of myosin

The specificity and nature of the reaction between salicylaldehyde and myosin and the effect of salicylalation on the molecular parameters of myosin were studied. The following observations were made.

1. 1. The reaction of salicylaldehyde with the lysyl residues of myosin is specific, since no salicylaldehyde is bound if the lysyl residues of myosin are trinitrophenylated.

2. 2. Salicylaldehyde is bound by myosin through the formation of an azomethine linkage (Schiff's base). This was established from the measured difference absorption spectrum of the myosin-salicylaldehyde complex.

3. 3. Three groups of lysyl residues can be distinguished with respect to the reaction with salicylaldehyde, namely, (a) residues with high association constant (K_ass = 1.8 ± 0.9·10⁵ M^-1), (b) residues with moderate association constant (K_ass = 2.2·10³ M^-1) and (c) residues that react with salicylaldehyde only after the denaturation of the protein. Their numbers could be estimated as 10 ± 5, 130 ± 5 and 260 ± 5 per mole myosin, respectively. The first group of residues was found to be absent from heavy and light meromyosin, the proteolytic fragments of myosin.

4. 4. The reaction is reversible. The complex formation rate constant, evaluated from the formula for second order reaction, is 2.2 sec^-1·M^-1, and the decomposition rate constant for first order reaction is 1.1·10^-3 sec^-1 at 22°.

5. 5. The reaction is pH dependent, the reaction yield increasing at higher pH.

6. 6. The solubility of myosin at low ionic strength decreases with increasing degree of salicylalation at slightly alkaline pH.

7. 7. The intrinsic viscosity of myosin does not change on salicylalation.

8. 8. A second peak due to polymerization appears on the sedimentation profile of the protein if more than 70 lysyl residues are salicylalated per mole of myosin.

Uptake of corticosterone into isolated rat liver cells: Possible involvement of Na/K-ATPase

Isolated rat hepatocytes posses a saturable glucocorticoid uptake system with high affinity (K_d value = 2.8 ± 0.7 × 10⁻⁸ M; 318,000 ± 80,000 binding sites per cell; 317 fmol/mg protein). The initial rates of uptake decrease by about 30–40% if the cells are incubated simultaneously with [³H]corticosterone and either SH-reagents (N-ethylmaleimide and p-chloromercuriphenylsulphonate, 1 mM), metabolic inhibitors (2,4-dinitrophenol, 1 mM; and antimycin, 0.1 mM) or the Na⁺/K⁺-ATPase-inhibitors, ouabain and quercetine. These Na⁺/K⁺-ATPase-blockers exert half-maximal inhibition at 3 × 10⁻⁷ and 3 × 10⁻⁶ M, respectively. A slight increase in K⁺ concentration and a corresponding decrease in Na⁺ in the medium leads to a significant reduction in the initial uptake rate. The uptake system from the rat hepatocytes shows a clear steroid specificity, being different from the intracellular receptor. Corticosterone and progesterone are the strongest competitors, cortisol, 5- and 5β-dihydrocorticosterone, 11-deoxycorticosterone, cortisone and testosterone have an intermediate effect and only weak competition is exerted by dexamethasone and by the mineralocorticoid, aldosterone. Estradiol and estrone sulphate as well as the synthetic glucocorticoid triamcinolone acetonide are unable to inhibit initial corticosterone uptake.     

Biochemical and biophysical studies on cytochrome aa3 VIII. Effect of cyanide on the catalytic activity

1. 1. Cyanide inhibits the catalytic activity of cytochrome aa₃ in both polarographic and spectrophotometric assay systems with an apparent velocity constant of 4·10³ M⁻¹·s⁻¹ and a K_i that varies from 0.1 to 1.0 μM at 22 °C, pH 7·3.

2. 2. When cyanide is added to the ascorbate-cytochrome c-cytochromeaa₃−O₂ system a biphasic reduction of cytochrome c occurs corresponding to an initial K_i of 0.8 μM and a final K_i of about 0.1 μM for the cytochrome aa₃−cyanide reaction.

3. 3. The inhibited species (a²+a₃³⁺HCN) is formed when a²⁺a₃³⁺ reacts with HCN, when a²⁺a₃²⁺HCN reacts with oxygen, or when a³⁺a₃³⁺HCN (cyano-cytochrome aa₃) is reduced. Cyanide dissociates from a²⁺a₃³⁺HCN at a rate of 2·10⁻³ s⁻¹ at 22 °C, pH 7.3.

4. 4. The results are interpreted in terms of a scheme in which one mole of cyanide binds more tightly and more rapidly to a²⁺a₃³⁺ than to a³⁺a₃³⁺.

Copper-Ligand Interactions and Physiological free Radical Processes. Part 2. Influence of Cu2+ Ions on Cu+-Driven Oh Generation and Comparison with Their Effects on Fe2+-Driven Oh Production

In our search to establish a reference ·OH production system with respect to which the reactivity of copper(II) complexes could then be tested, the influence of free Cu²⁺ ions on the Cu⁺/H₂O₂ reaction has been investigated.

This influence depends on the C_Cu²⁺/C_Cu⁺ ratio. At low Cu²⁺ concentrations, ·OH damage to various detector molecules decreases with increasing Cu²⁺ concentrations until C_Cu²⁺/C_Cu⁺ reaches unity. Above this value, ·OH damage increases sharply until C_Cu²⁺/C_Cu⁺ becomes equal to 5 with salicylate and 2 with deoxyribose, ratios for which the protective effect of Cu²⁺ cancels. Finally, at higher concentrations, Cu²⁺ ions logically add their own ·OH production to that normally expected from Cu⁺ ions. The possible origin of this unprecedented alternate effect has been discussed. The possible influence of Cu⁺ ions on the generation of ·OH radicals by water gamma radiolysis has also been tested and, as already established for Cu²⁺ in a previous work, shown to be nonexistent. This definitely confirms that either form of ionised copper cannot scavenge ·OH radicals in the absence of a Iigand.     

Bipyridylium quaternary salts and related compounds. V. Pulse radiolysis studies of the reaction of paraquat radical with oxygen. Implications for the mode of action of bipyridyl herbicides

1. Rate constants for reduction of paraquat ion (1,1′-dimethyl-4,4′-bipyridy-lium, PQ²⁺) to paraquat radical (PQ⁺·) by e⁻_aq and CO₂⁻· have been measured by pulse radiolysis. Reduction by e⁻_aq is diffusion controlled (k = 8.4·10¹⁰ M⁻¹·s⁻¹) and reduction by CO₂⁻· is also very fast k = 1.5·10¹⁰ M⁻¹·s⁻¹).

2. The reaction of paraquat radical with oxygen has been analysed to give rate constants of 7.7·10⁸ M⁻¹·s⁻¹ and 6.5·10⁸ M⁻¹·s⁻¹ for the reactions of paraquat radical with O₂ and O₂⁻·, respectively. The similarity in these rate constants is in marked contrast to the difference in redox potentials of O₂ and O₂⁻· (− 0.59 V and + 1.12 V, respectively).

3. These rate constants, together with that for the self-reaction of O₂⁻·, have been used to calculate the steady-state concentration of O₂⁻· under conditions thought to apply at the site of reduction of paraquat in the plant cell. On the basis of these calculations the decay of O₂⁻· appears to be governed almost entirely by its self-reaction, and the concentration 5 μm away from the thylakoid is still 90% of that at the thylakoid itself. Thus, O₂⁻· persists long enough to diffuse as far as the chloroplast envelope and tonoplast, which are the first structures to be damaged by paraquat treatment. O₂⁻· is therefore sufficiently long-lived to be a candidate for the phytotoxic product formed by paraquat in plants.