Cation amelioration of aluminum toxicity in wheat

Aluminum is a major constituent of most soils and limits crop productivity in many regions. Amelioration is of theoretical as well as practical interest because understanding amelioration may contribute to an understanding of the mechanisms of toxicity. In the experiments reported here 2-day-old wheat (Triticum aestivum L. cv Tyler) seedlings with 15-millimeter roots were transferred to solutions containing 0.4 millimolar CaCl₂ at pH 4.3 variously supplemented with AlCl₃ and additional amounts of a chloride salt. Root lengths, measured after 2 days in the test solutions, were a function of both Al activity and the cation activity of the added salt. Percent inhibition = 100 {Al³⁺}/({Al³⁺} + K_m + α{C}^β) where {Al³⁺} is the activity of Al³⁺ expressed in micromolar, {C} is the activity of the added cation expressed in millimolar, and K_m (= 1.2 micromolar) is the {Al³⁺} required for 50% inhibition in the absence of added salt. For Ca²⁺, Mg²⁺, and Na⁺ the values of α were 2.4, 1.6, and 0.011, respectively, and the values for β were 1.5, 1.5, and 1.8, respectively. With regard to relative ameliorative effectiveness, Ca²⁺ > Mg²⁺ ≈ Sr²⁺ K⁺ ≈ Na⁺. Other cations were tested, but La³⁺, Sc³⁺, Li⁺, Rb⁺, and Cs⁺ were toxic at potentially ameliorative levels. The salt amelioration is not solely attributable to reductions in {Al³⁺} caused by increases in ionic strength. Competition between the cation and Al for external binding sites may account for most of the amelioration.     

Assessing the phytotoxicity of mononuclear hydroxy-aluminum

Abstract Al³⁺ is an important rhizotoxic ion in acid soils around the world. Al³⁺ is in equilibrium with mononuclear hydroxy-Al species, such as AlOH²⁺ and AL(OH)₂⁺, but the toxicity of these species has not been determined. Polynuclear Al may also coexist with Al³⁺, and one of these species, AlO₄Al₁₂(OH)₂₄(H₂O)₁₂⁷⁴, is very toxic. In order to determine the toxicity of mononuclear hydroxy-Al we have reanalysed the results of previously published, solution-culture experiments and have performed new experiments. Several problems are inherent in these studies. At pH values less than 5.0, the activities of the mononuclear hydroxy-Al species are low relative to Al³⁺, but attempts to change the ratio by raising the pH generally initiate the formation of polynuclear Al. (We discovered that mononuclear solutions are stable for many days when {Al³⁺}/{H⁺}³≤ 10^8.8, where braces denote activities.) We avoided, or accounted for, polynuclear Al in our studies. In addition, we used up-to-date equilibrium constants to compute Al species, very simple culture media (generally containing CaCl₂, AlCl₃ and HCl as the only inputs), short-term (2d) growth, and an Al-sensitive wheat variety (Triticum aestivum L. cv. Tyler) that permitted low Al levels and, consequently, higher pH values without Al polymerization. Experiments were designed in which the solutions were constant in {Al³⁺} and variable in mononuclear hydroxy-Al or were orthonal (factorial) in {Al³⁺} and {AlOH²⁺}. Linear and nonlinear, simple and multiple, regression analyses of these and previous experiments failed to reveal any toxicity for mononuclear hydroxy-Al to Tyler wheat.     

Non-phytotoxicity of the aluminum sulfate ion, AlSO+4

Aluminum is a phytotoxic element in many soils and occurs in a variety of chemical species. In order to determine whether AlSO⁺₄ is toxic, seedlings of wheat (Triticum aestivum L. cv. Tyler) and red clover (Trifolium pratense L. cv. Kenland) were transferred to solutions containing controlled activities of Al³⁺, AlSO⁺₄, Na⁺ and Ca²⁺. Root elongation was inhibited by Al³⁺ (or mononuclear hydroxy-Al species that are in equilibrium with Al³⁺), but not by AlSO⁺₄. We assumed a formation constant (K_AlSO⁺₄= {AlSO⁺₄}/[{Al³⁺} {SO^2-₄}]; braces indicate activities} of 10^3.2 for AlSO⁺₄ in the computation of ionic activities, but use of K_AlSO⁺₄ values ranging from 10^2.8 to 10^3.6 had very little effect on the computed toxicities of Al³⁺ and AlSO⁺₄. Sulfate did not promote the formation of polynuclear Al complexes in our experiments. A practice in studies of Al phytotoxicity has been to attribute toxicity to mononuclear Al, but now it would seem advisable to exclude AlSO⁺₄. That AlSO⁺₄ is non-toxic, or is at least 10-fold less toxic than Al³⁺, has implications for the physiology of Al toxicity and for the use of sulfate salts in experimental work and in agriculture.     

Ionic and pH signalling from roots to shoots of flooded tomato plants in relation to stomatal closure

Soil flooding damages shoot systems by inhibiting root functioning. An example is the inhibition of water uptake brought about by decreased root hydraulic conductance. The extent of any resulting foliar dehydration this causes is limited by partial stomatal closure that begins within 4 h and is maintained for several days. Root to shoot signals that promote closure in flooded tomato plants have remained elusive but may include changes in solute delivery to the shoot by transpiration. Accordingly, we examined total osmolites and selected mineral ions in samples of xylem sap flowing at rates approximating whole plant transpiration. After 2.5 h flooding,delivery of total osmolites and of PO₄ ^3-SO₄ ^2-Ca²⁺K⁺NO₃ ^– and H⁺strongly decreased while Na⁺ remained excluded. Several hours later, deliveries of osmolites, PO₄ ^3-, SO₄ ^2-, Ca²⁺, and Na⁺ rose above control values, suggesting that, after approximately 10 h, root integrity became degraded and solute uptake de-regulated. Deliveries of NO₃ ^– remained below control values. Reducing or eliminating the supply of K⁺ to detached leaves to test the potential of decreased K⁺ delivery to close stomata proved negative. Decrease in H⁺ delivery was associated with sap alkalisation. However, raising the pH of buffer from 6.0 or 6.5 to 7.0 did not close stomata when tested in the presence of abscisic acid (ABA) at a concentration (10 mol m^–3) typical of the transpiration stream of flooded plants. It is concluded that despite their rapidity and scale, negative messages in the form of increased pH and decreased solute delivery from roots to shoots are, themselves, unlikely initiators of stomatal closure in flooded tomato plants.     

A web-accessible computer program for calculating electrical potentials and ion activities at cell-membrane surfaces

Aims

Increasing evidence indicates that plant responses to ions (uptake/transport, inhibition, and alleviation of inhibition) are dependent upon ion activities at the outer surface of root-cell plasma membranes (PMs) rather than activities in the bulk-phase rooting medium.

Methods

A web-accessible computer program was written to calculate the electrical potential (ψ) at the outer surface of root-cell PMs (ψ _PM). From these values of ψ _PM, activities of ion I with charge Z ({I ^Z}) can be calculated for the outer surface of the PM ({I ^Z}_PM). In addition, ψ and {I ^Z} in the Donnan phase of the cell walls (ψ _CW and {I ^Z}_CW) can be calculated.

Results

By reanalysing published data, we illustrate how this computer program can assist in the investigation of plant-ion interactions. For example, we demonstrate that in saline solutions, both Ca deficiency and Na uptake are more closely related to {Ca²⁺}_PM and {Na⁺}_PM than to {Ca²⁺}_b and {Na⁺}_b (activities in the bulk-phase media). Additional examples are given for Zn and P nutrition, Ni toxicity, and arsenate uptake.

Conclusions

The computer program presented here should assist others to develop an electrostatic view of plant-ion interactions and to re-evaluate some commonly-held views regarding mechanisms of ion transport, toxicity, competition among ions, and other phenomena.     

Medium optimization for a methanol utilizing bacterium based on chemostat theory

Summary In the productions of biomass and vitamin B₁₂ using methanol as the sole carbon source, it is necessary to use a medium in which methanol is the growth limiting substrate. Other inorganic salts should be in slight excess so that the yield of cells and the intracellular content of vitamin B₁₂ do not vary. From basic principles of chemostat culture, a medium was optimized for Pseudomonas AM-1 a methanol utilizing bacterium, for the concentrations of various inorganic salts. This was done in a series of chemostat cultures at a dilution rate of 0.1 h^–1. Optimum amounts of NH₄ ⁺, PO₄ ^3- and Mg²⁺ were estimated from the minimum concentration of the salt at which methanol became growth limiting. The optimum concentrations of Ca²⁺, Fe²⁺, Mn²⁺, and Zn²⁺ as a group were determined in the same way. Cu²⁺, Mo⁶⁺, Co²⁺ and B³⁺ are required at concentrations of g/l and they were not studied as these very low level can be introduced as contaminants from other salts. The optimum medium composition (in g/l) was as follows: (NH₄)₂SO₄, 1.0; H₃PO₄, 75×10^–3; MgSO₄ · 7H₂O, 30×10^–3; CaCl₂ · 2H₂O, 3.3×10^–3; FeSO₄ · 7H₂O, 1.3×10^–3, MnSO₄ · 4H₂O, 0.13×10^–3; ZnSO₄ · 7H₂O, 0.13×10^–3; CuSO₄ · 5H₂O, 40×10^–6; Na₂MoO₄, 40×10^–6; CoCl₂ · 6H₂O, 40×10^–6; H₃BO₃, 30×10^–6 and methanol 4.     

Influence of the culture medium constituents and inoculum size on the accumulation of blue pigment and cell growth of Lavandula spica

The effects of the concentration of PO₄ ^3-, NO₃ ^–, Fe ²⁺, sucrose and inoculum size on the accumulation of blue pigment and growth of suspension cultures of Lavandula spica D.C. ( L. latifolia Vill.), were studied. The combination of 2.5 mM PO₄ ^3-, 14.1 mM NO₃ ^–, 1 mM Fe ²⁺, 30 g l^–1 sucrose and 10 g l^–1fresh weight of inoculum, promoted a 7-fold enhancement on the productivity of blue pigment in comparison to the control medium. Among all the culture medium constituents tested, phosphate exerted the highest beneficial effect and Fe²⁺ showed to be essential for the accumulation of the pigment. High levels of sucrose (60 or 90 g l^–1) did not stimulate the accumulation of blue pigment. In these conditions, cell growth and cell viability were drastically affected.     

Modelling anion amelioration of aluminium phytotoxicity

There is good evidence for the ameliorating effect of SO₄ ^2- and F^- on the expression of Al phytotoxicity in acidic solutions. The role of OH^-, in both shifting Al speciation towards hydroxy-Al species and decreasing activities of H⁺ with increasing pH, is still controversially discussed. Grauer and Horst (1992) proposed a model based on the assumption that Al phytotoxicity is a function of the Al saturation (AlS) of exchange sites in the root apoplast and analyzed the predictions of the model in the case of cation amelioration, with special emphasis on H⁺. In this study the model is further developed by considering, in addition to Al³⁺, the complexation of Al with the anions OH^-, F^-, SO₄ ^2-, and Cl^- to form potentially toxic Al species. Association constants of these Al complexes with a ligand (L ^-) which is assumed to simulate the cation exchange sites in the root apoplast, were estimated. Affinity factors for binding to L ^- compared to Al³⁺ were derived from these estimated association constants, and values were, in a first approach, 0.79 for AlOH²⁺, 0.02 for Al(OH)₂ ⁺, and 0.13 for Al(OH)₃ ⁰ (or 0.03 choosing another hydrolysis constant). High toxicity of Al₁₃ (AlO₄Al₁₂(OH)₂₄(H₂O)₁₂ ⁷⁺) could be explained by diminished H⁺ amelioration and a high association constant to L ^-. From estimated association constants for Al-Cl complexes, low affinity factors for L ^- for these complexes were derived. Since the formation of these Al-Cl complexes is not favoured, Cl^- is predicted to have very little ameliorating effect. In the case of SO₄ ^2– and F^- complexes with Al, the derived affinity factors never exceeded 0.05 and, since formation of these complexes is favoured by high association constants, are thus in agreement with experimental results on ameliorating effects. The ranking of the anions for ameliorative effectiveness was estimated to be in the order of OH^->F^->SO₄ ^2–>Cl^-. Hydroxy amelioration in this context is restricted to the speciation effect, which is only significant above pH 4.     

Density Functional Geometry Optimization and Energy Calculations of Calcium(II)-Triphosphate Complexes. Polyphosphates as Possible Dissolving Agents for Calcium Pyrophosphate Dihydrate Crystals in Chondrocalcinosis Disease

Abstract

Geometry optimizations and energy calculations have been carried out via molecular orbital methods at the density functional B3LYP/LANL2DZ level on the molecules PO₃ ^?, OPO₃ ^3-, HOPO₃ ^2-, CH₃OPO₃ ^2-, H(CH₃OPO₃ ^?, O(PO₃)₂ ^4-, HO(PO₃)₂ ^3-, CH₂ (PO₃)₂ ^4-, (CH₃OPO₂)O(PO₃)^3-, O(PO₃)₃ ^5-, HO(PO₃)₃ ^4-, (PO₃)₃ ^3-, (CH₃OPO₂)O(PO₃)₂ ^3-, [Mg{O(PO₃)₂}]^2-, [Ca{O(PO₃)₂}]^2-, [Ca{CH₂ (PO₃)₂}]^2-, [Ca{CH₃OPO₂)O(PO₃)}]^?, [Ca(PO₃)₃]^?, [Ca{O(PO₃)₃}]^3-, and [Ca{CH₃OPO₂)O(PO₃)₂}]^2- with the aim to find reliable and easily accessible computational methods to simulate some phosphate-containing molecules of importance for the living cells and to study the energetics for protonation and metal-complex formation reactions. The analysis is part of a general investigation on phosphate-containing molecules as potential dissolving agents for calcium pyrophosphate dihydrate (CPPD) crystals which deposit in certain articular diseases. The basis set was expanded to 6–31G** for the P atoms for all the molecules investigated and to 6–31G* for the O atoms for OPO₃ ^3-. Calculations at the semi- empirical MNDO/d level were also carried out for comparison purposes on the free ligand molecules and on [Mg{O(PO₃)₂}]^2-. The density functional analysis reproduced well the geometry found at the solid state via X-ray diffraction. The analyses of the geometrical parameters and the total electronic energy of the molecules shows that O(PO₃)₂ ^4- and other di- and tri-phosphates are versatile ligands for divalent metal ions like Ca²⁺. The computed P-O-P bond angle for free O(PO₃)₃ ^4- is 180° and the conformation of the two PO₃ ^? groupings is staggered along the P…P vector. The linear arrangement for P-O-P is assisted by P-Oπ interactions. The bending of the P-O-P angle when accompanied by a slight P-O(b) elongation requires a very small amount of energy; 4.65 kcal/mol to pass from 180 to 140°, as calculated at the DFT level. The computed Ca-O and Mg-O bond distances for [M{O(PO₃)₂}]^2- are 2.378 and 2.079Å, when the metal ions link two oxygen atoms from each PO₃ group. The computed Ca-O bond lengths for [Ca{CH₃OPO₂)O(PO₃)}]^? are 2.482 (P_αO₂) and 2.358Å (P_βO₂), showing a significant lengthening for Ca-OP_α, when compared to the pyrophosphate derivative. The Ca-O bond lengths for [Ca{O(PO₃)₃}]^3- and [Ca{CH₃OPO₂)O(PO₃)2}]^2- are 2.251Å and 2.525 (P_αO₂), 2.407 and 2.338 (P_βO₂), and 2.251 and 2.228Å (P_γO₂), showing a shortening for the Ca-OPγ bond upon methylation. The (P_β)O-P_γ bond length increases significantly (0.09 Å) upon Ca(II) coordination to (CH₃OPO₂)O(PO₃)₂ ^4- via all the three PO₃ groups. This latter result suggests that metal complexes of linear organic-triphosphates have a larger tendency to release the P_γO₃ group when compared to the free ligand molecules. The electronic contribution to the energy of the complex formation reaction for [Ca{CH₂ (PO₃)₂}]^2- is only slightly higher (some 1.8 kcal) than that for [Ca{O(PO₃)₂}]^2-; but is much higher (some 63 kcal) than that relevant to the formation of [Ca{CH₃OPO₂)O(PO₃)₂}]^2-. Therefore the linear methyltriphosphates (and reasonably nucleoside triphosphates) are predicted to form metal complexes which are less stable than diphosphonate or inorganic diphosphate ligands, at least in the case the organic moiety does not have any appreciable coordination ability toward the metal. The energy of complex formation for [Ca{O(PO₃)₃}]^3- is much higher than that for [Ca{O(PO₃)₂}]^2- and [Ca(PO₃)₃}]^? (some 116 and 345 kcal, respectively). This is in part a rationale for the high dissolving ability (DA) toward CPPD crystals, shown by solutions of pentasodium tripolyphosphate. DA values of 65.4±3.0 μg Ca/mL were detected, via atomic absorption spectroscopy, in solutions of Na₅{O(PO₃)₃} 0.06 M after digestion (1.00 h, 37°C, pH 7.4) in the presence of CPPD crystals. Efficient non-toxic dissolving agents for CPPD crystals are needed to cure chondrocal-cinosis desease. The semi-empirical computations gave correct overall optimized structures and conformations for, at least, the free not-substituted ligands and the relevant Mg(II)-com- plexes. The optimized structure for [Mg{O(PO₃)₂}]^2- has computed P-O(t) and P-O(d) bond distances of 1.503 and 1.598Å, in perfect agreement with the results from DFT calculations.     

An OFF–ON–OFF type fluorescent probe based on a naphthalene derivative for Al3+ and F− ions and its biological application

A novel fluorescent probe‐based naphthalene Schiff, 1‐(C2‐glucosyl‐ylimino‐methyl)‐naphthalene‐2‐ol (L) was synthesized by coupling d ‐glucosamine hydrochloride with 2‐hydroxy‐1‐naphthaldehyde. It exhibited excellent selectivity and highly sensitivity for Al³⁺ in ethanol with a strong fluorescence response, while other common metal ions such as Pb²⁺, Mg²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Fe²⁺, Mn²⁺, Hg²⁺, Li⁺, Na⁺, K⁺, Fe³⁺, Cr³⁺, Zn²⁺, Ag⁺, Ba²⁺ and Ca²⁺ did not cause the same fluorescence response. The probe selectively bound Al³⁺ with a binding constant (K_a) of 5.748 × 10³ M^?1 and a lowest detection limit (LOD) of 4.08 nM. Moreover, the study found that the fluorescence of the L ? Al³⁺ complex could be quenched after addition of F^? in the same medium, while other anions, including Cl^?, Br^?, I^?, NO₂^?, NO₃^?, ClO₄^?, CO₃^2?, HCO₃^?, SO₄^2?, HSO₄^?, CH₃COO^?, PO₄^3?, HPO₄^2?, S^2? and S₂O₃^2? had nearly no influence on probe behaviour. Binding of the [L ? Al³⁺] complex to a F^? anion was established by different fluorescence titration studies, with a detection limit of 3.2 nM in ethanol. The fluorescent probe was also successfully applied in the imaging detection of Al³⁺ and F^? in living cells.     

Measured and modelled effects of temperature,dissolved oxygen and nutrient concentration on sediment-water nutrient exchange

Empirical models of sediment-water fluxes of NH₄ ⁺, NO₃ ^– were and PO₄ ^3– were formed based on published reports. The models were revised and parameters evaluated based on laboratory incubations of sediments collected from Gunston Cove, VA. Observed fluxes ranged from — 18 (sediments uptake) to 276 (sediment release) mg NH₄ ⁺ m^–2 day^–1, –17 to –509 mg NO₃ ^– m^–2 day^–1, and –16.4 to 8.9 mg PO₄ ^3– m^–2 day^–1. The model and observations indicated release of NH₄ ⁺ was enhanced by high temperature and by low DO. Uptake of NO₃ ^– was enhanced primarily by high NO₃ ^– concentration and to a lesser extent by high temperature and by low DO. Direction of PO₄ ^3– flux depended on concentration in the water. Release was enhanced by low DO. No effect of temperature on PO₄ ^3– flux was observed.     

Space–time configurations of solute input and biological uptake in river systems traversing limestone uplands (Yorkshire Dales,northern England)

Solute concentrations, including major plant nutrients, are surveyed from sampling during 1985–89 in river systems variably influenced by upland Dinantian (Carboniferous) limestone. Concentrations of most ions generally increase downstream, but there are widespread dilution effects after rainy periods for major ions and local depletions of mostly biological origin for major plant nutrients. In the upper reaches, these depletions develop mainly under low flow from the influence of benthic algae and macrophytes; they affect inorganic C as HCO₃ ^- plus dissolved gaseous CO₂ and soluble reactive forms of Si, N and P. Inflow – outflow differences of an upland lake result from biological influence on these constituents and also Ca⁺ and K⁺. Experimental injections of NH₄-N, PO₄-P and K⁺were made to an acid headwater of the River Swale, together with Na⁺ and Cl^- as supposed conservative reference ions. Uptake is insignificant for K⁺ but marked for NH₄-N and PO₄-P; the residual percentage decreases exponentially with time. Relative rates of net uptake per unit time are greater for P than for NH₄-N and larger under conditions of higher flow velocity and benthic algal growth. Although limestone is lacking in some headwater regions, where atmospheric inputs appear to predominate, overall its chemical denudation as Ca²⁺ and HCO₃ ^-provides most of the solute flux downstream, as well as in some karstic headwaters where the highest values are limited by CaCO₃ saturation.     

Tree species mediated soil chemical changes in a Siberian artificial afforestation experiment

Natural and human-induced changes in the composition of boreal forests will likely alter soil properties, but predicting these effects requires a better understanding of how individual forest species alter soils. We show that 30 years of experimental afforestation in Siberia caused species-specific changes in soil chemical properties, including pH, DOC, DON, Na⁺, NH₄ ⁺, total C, C/N, Mn²⁺, and SO₄ ^2-. Some of these properties –- pH, total C, C/N, DOC, DON, Na⁺ –- also differed by soil depth, but we found no strong evidence for species-dependent effects on vertical differentiation of soil properties (i.e., no species × depth interaction). A number of soil properties –- NO₃ ^–, N, Al³⁺, Ca²⁺, Fe³⁺, K⁺, Mg²⁺ and Cl^– –- responded to neither species nor depth. The six studied species may be clustered into three groups based on their effects on the soil properties. Scots pine and spruce had the lowest pH, highest C/N ratio and intermediate C content in soil. The other two coniferous species, Arolla pine and larch, had the highest soil C contents, highest pH values, and intermediate C/N ratios. Finally, the two deciduous hardwood species, aspen and birch, had the lowest C/N ratio, intermediate pH values, and lowest C content. These tree-mediated soil chemical changes are important for their likely effects on soil microbiological activities, including C and N mineralization and the production and consumption of greenhouse gases.     

Anoxic degradation of biogenic debris in sediments of eutrophic subalpine Lake Bled (Slovenia)

Anoxic degradation of sedimentary biogenic debris using closed sediment incubation experiments was studied in eutrophic subalpine Lake Bled (NW Slovenia) which, for most of the year, has an anoxic hypolimnion. Production rates of dissolved inorganic carbon (DIC), NH₄ ⁺, PO₄ ^3- and dissolved Si, and reduction rates of SO₄ ^2- were measured and anoxic mineralization rates were modelled using G-model. The depth profiles indicated major mineralization of biogenic debris and SO₄ ^2- reduction near the sediment surface. A comparison between depth integrated anoxic mineralization rates and diffusive benthic fluxes of DIC, NH₄ ⁺ and PO₄ ^3- showed that the anoxic incubation experiments provide a good estimate of N degradation of biogenic debris. The contributions of SO₄ ^2- reduction and acetate fermentation in NH₄ ⁺ production are about 30 and 70%, respectively. The DIC production accounted for only 15% of DIC benthic flux, indicating that methanogenesis and oxidation of methane provides 80% of this flux. Only about 30% of PO₄ ^3- was released because phosphate precipitated in the closed incubation experiments. The depth integrated production of Si accounts for 70–80% of Si benthic fluxes indicating intense dissolution of biogenic Si in the surficial lake sediment.     

Removal of inorganic ions from wastewaters by immobilized microalgae

Anabaena doliolum and Chlorella vulgaris immobilized on chitosan were more efficient at removing NO₃ ^–, NO₂ ^p–, PO₄ ^3– and CR₂O₇ ^2– from wastewaters than cells immobilized on agar, alginate, carrageenan or even free cells. Carrageenan-immobilized cells, however, were better at removing NH₄ ⁺ and Ni²⁺. The PO₄ ^3– uptake capacity was significantly increased in cells starved of PO₄ ^3– for 24 h. Agar-immobilized cells, though having good metal and nutrient uptake efficiency, had only a slow growth rate. Chitosan is recommended as an algal support for wastewater detoxification.The authors are with the Laboratory of Algal Biology, Department of Botany, Banaras Hindu University, Varanasi-221005, India     

Octanuclear {Co6W2} aggregate versus mixed valence {Co}3 cluster in the assembling of Co(phen)2Cl2 (phen = 1,10-phenanthroline) with octacyano metallates: A case of non-isostructurality between {W(CN)8}4− and {Nb(CN)8}4−

An unprecedented octanuclear aggregate, [{Co(phen)₂}₆{W(CN)₈}₂Cl₂] · 2Cl, 2, resulted from the assembling of {Co(phen)₂Cl₂}, 1, and {W(CN)₈}^4?. Surprisingly, the reaction with the paramagnetic {Nb(CN)₈}^4? unit did not afford the homologous {Co–Nb} cluster. Instead the latter building unit undergoes dissociation which led to the formation of a mixed-valence [{Co^II(phen)₂}{Co^III(phen)(CN)₄}₂], 3. This observation is in contrast to the usual trend that {Nb^IV(CN)₈}^4? forms compounds isostructural to that observed for {Mo^IV(CN)₈}^4? and {W^IV(CN)₈}^4?. The structures of the compounds 2 and 3 have been established by single crystal X-ray diffraction. Magnetic behaviors for compounds 1–3 are reported.     

Aluminum Enhances Melanin-Induced Lipid Peroxidation

The present study was conducted to characterize the possible interaction of Al³⁺ and Fe²⁺ with synthetic melanin in the potentiation of lipid peroxidation in liposomes and rat caudate-putamen homogenates. Al³⁺ stimulated melanin-initiated lipid peroxidation as measured by the production of 2-thiobarbituric acid-reactive substances (TBARS) and conjugated dienes. The effect of Al³⁺ was dependent on melanin (10–100 g/ml) and Al³⁺ (2.5–250 M) concentrations and no synergism between Fe²⁺ and Al³⁺ was observed. The prooxidant effect of Al³⁺ was partially inhibited by superoxide dismutase indicating the involvement of O ₂ ^- . Ga³⁺ and Be²⁺ which can increase NADH oxidation in the presence of O ₂ ^- , also were shown to stimulate melanin-initiated TBARS production. Based on the effect of Al³⁺ and other non redox metals, we suggest that Al³⁺ does not act through either the induction of melanin free radicals, or the induction of changes in membrane physical properties. Results show that Al³⁺ enhances melanin-initiated lipid peroxidation in part through an interaction with O ₂ ^- generated from the autoxidation of melanin. We speculate that Al³⁺ contributes to neuromelanin-mediated oxidative damage in dopaminergic neurons and subsequent neuronal degeneration and death in Parkinson's disease.     

Photocatalytic inactivation rate of phage MS2 in titanium dioxide suspensions containing various ionic species

In the TiO₂ photoreaction system, the coexistence of NO₃ ^–, SO₄ ^2–, PO₄ ^3–, K⁺ or Ca²⁺ each at 10–100 mM decreased the rate constant for phage MS2 inactivation, but Cl^–, Br^– or Na⁺ did not. The inhibitory effects of the ions could be elucidated by the proportional relation found between the rate constants and quantities of the phage on TiO₂ irrespective of the kinds of existing ions.     

Sequential liquid-liquid extraction of d-amino acid oxidase from Trigonopsis variabilis

A method for isolation of d-amino acid oxidase (DAAO) from disrupted Trigonopsis variabilis cells has been developed. In an aqueous two-phase system consisting of PEG6000 (220 g l^–1), potassium phosphate (110 g l^–1, K₂HPO₄ + KH₂PO₄ = 10.1:1, mol mol^–1) and dl-methionine (11 g l^–1), the major portion of cellular proteins (87%) was partitioned into the salt phase. By sequential extraction, 48% of DAAO was recovered in PEG phase, giving a yield of 211 U mg protein^–1.     

Effects of pH,phosphate and ammonia on the rate of uptake of nitrate and ammonia by freshwater phytoplankton

The effect of phosphate (PO₄ ⁺³) and pH in regulating nitrate (NO₃) and ammonia (NH₃ ⁺) uptake by phytoplankton was investigated in two Oklahoma lakes using ¹⁵N tracers. Addition of PO₄ ⁺³ above ambient concentrations had a negligible effect on the rate of uptake of NO₃ ^– or NH₃ ⁺. Manipulation of pH of lake water had little effect on uptake of either NO₃ ^– or NH₃ ⁺. A correlation analysis suggested that NO₃ ^– is not used by phytoplankton when NH₃ ⁺ concentrations exceed about 210 µg NH₃ ⁺-N(1)^–1.