Lead toxicity and phosphate deficiency in chlamydomonas

The addition of lead salts to phosphate-containing Chlamydomonas reinhardtii media caused precipitation of Pb₃(PO₄)₂, effectively removing phosphate from solution. The effect of Pb²⁺ on growth of Chlamydomonas in liquid cultures depended strictly on the ratio of the equivalents of Pb²⁺ to phosphate present. When the amount of Pb²⁺ approached equivalency with phosphate, cell growth was initially slow as cells adhered to the surface of the precipitated Pb₃(PO₄)₂. Later, cells grew at a normal rate, spread throughout the solution, and reached the same densities obtained in the absence of Pb²⁺. Cells did not survive when the amount of Pb²⁺ in the culture exceeded the equivalents of phosphate.

Elemental analysis showed that in the presence of equivalent Pb²⁺ and phosphate, considerable Pb²⁺ remained in solution. The concentration of dissolved Pb²⁺ did not vary significantly when the amount of Pb²⁺ added to the culture was increased slightly, from an amount which permitted growth to an amount which completely prevented growth. The concentration of phosphate was decreased to an undetectable level when the amount of Pb²⁺ approached equivalency with phosphate.

In the presence of the chelating agent nitrilotriacetic acid, higher concentrations of Pb²⁺ remained in phosphate-containing media. The chelated Pb²⁺ did not retard the growth of Chlamydomonas.

It appears that Pb²⁺ is not toxic to Chlamydomonas, but kills cells by depriving them of phosphate.

     

NUCLEOLAR ORTHOPHOSPHATE IONS : Electron Microscope and Diffraction Studies

Lead acetate (3–10%, pH between 4.3 and 7.0, alone or containing 2% glutaraldehyde), when used as fixative, has been demonstrated to produce an intracellular microcrystalline precipitate of lead orthophosphate, Pb₅(PO₄)₃OH (lead hydroxyapatite). This confirms earlier work with the light microscope (6). In interphase cells the nucleoli are sharply delimited by the massive lead phosphate precipitate. Some diffuse precipitate is found in the nucleoplasm; it is always delimited by the nuclear membrane. Nucleolar localization of this orthophosphate pool is not a diffusion artifact; the pool is probably in a loosely bound state and is not retained by conventional fixatives. In maize root cells in advanced mitotic stages the lead phosphate crystals are seen distributed throughout the cytoplasm and also relatively concentrated on the late anaphase-early telophase chromosomes. This pool of inorganic phosphate anions may be involved in the mitotic cycle of chromatin condensation, and it may be partially responsible for the absence of mature ribosomes in the nucleolus through the chelation of divalent cations. It is evident that the siver-reducing component detected in the nucleoli of fixed cells (6) is a completely different substance.     

Transformation of galena to pyromorphite produces bioavailable sulfur for neutrophilic chemoautotrophy

The aqueous concentration of lead [Pb(II)] in geochemical environments is controlled by the solubility of Pb‐bearing minerals and their weathering products. In contaminated soils, a common method for in situ stabilization of Pb(II) is the addition of phosphate to convert more redox sensitive sulfide minerals into sparingly soluble pyromorphite [Pb₅(PO₄)₃X]. In this study, we conducted experimental studies to investigate the fate of reduced sulfur during the conversion of galena [PbS] to chloropyromorphite [Pb₅(PO₄)₃Cl]. Powder X‐ray diffraction analysis indicated that the reaction of phosphate with galena under oxic conditions resulted in the oxidation of sulfide and formation of elemental sulfur [S₈]. Under oxic abiotic conditions, the S₈ was retained in the solid phase, and negligible concentrations of sulfur as sulfide and thiosulfate were detected in the aqueous phase and only a small amount of sulfate. When PbS reacted in the presence of the chemoautotrophic organism Bosea sp. WAO, the S₈ in the secondary mineral was oxidized to sulfate. Strain WAO produced significantly more sulfate from the secondary S₈ than from the primary galena. Microscopic analysis of mineral–microbe aggregates on mineral‐embedded slide cultures showed that the organism was colocalized and increased in biomass over time on the secondary mineral surface supporting a microbial role. The results of this study indicate that stimulation of sulfur‐oxidizing activity may be a direct consequence of phosphate amendments to Pb(II)‐contaminated soils.     

Characterization of Lead in Soils of a Rifle/Pistol Shooting Range in Central Florida,USA

The distribution of lead in soil samples collected from both surface (0 to 10?cm) and profile (O 0 to 10?cm, E 11 to 30?cm, Eb 31 to 50?cm, Bw 51 to 100?cm, and C 181 to 200?cm) at a 14-year-old rifle/pistol shooting range located in central Florida were determined using EPA Method 3051a (microwave, HNO₃/HCl=3:1, v/v). In addition to total lead analysis, Toxicity Characteristic Leaching Procedure (TCLP) analysis was performed on corresponding samples to determine whether the soils would require special handling as hazardous waste if the soils were to be removed from the range. Total lead in surface soils varied from 330 to 17 850?mg Pb kg^?1, with the greatest concentration in the middle of the backstop berm. The TCLP tests indicated that lead in all surface soils exceeded the 5?mg Pb L^?1 critical level of federal regulation for solid wastes and hazardous wastes provided by the Resource Conservation and Recovery Act (RCRA) and would be characterized as hazardous waste. Sequential fractionation and X-ray diffraction (XRD) analyses revealed that lead carbonate existed predominantly (91.3%) in the berm soil. The weathering of lead bullets in the soil environments formed primarily as hydrocerussite (Pb₃(CO₃)₂(OH)₂), with small amounts of massicot (PbO) and cerussite (PbCO₃). However, the elevated soil pH, caused by the oxidization and transformation process of elemental lead in lead bullets, could be a significant factor in limiting the migration of lead in the soil.     

Synthesis and structural characterization of new one- and two-dimensional lead(II) coordination polymers; new precursors for preparation of pure phase lead(II) oxide nanoparticles via thermal decomposition

Two new lead(II) nitrate coordination polymers from ligand 1,2-di-(4-pyridyl)-ethylene (bpe), [Pb₂(μ-bpe)₃(μ-NO₃)₂(NO₃)₂]_n (1) and {[Pb(μ-bpe)(μ-NO₃)₂(NO₃)(H₂O)]·(Hbpe)·0.5(bpe)}_n (2), were synthesized. The compounds 1 and 2 were characterized by IR spectroscopy, elemental analyses and X-ray crystallography. The structures of 1 and 2 may be considered coordination polymers of lead(II) consisting of metallocyclic chains formed by bridging bpe ligands, making two- and one-dimensional array of Pb(NO₃)₂ and bpe, respectively. Pure phase PbO nano-particles were obtained by thermolyses of compounds 1-2 in oleic acid as surfactant at 180 and 200 °C under air atmosphere. The PbO nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).     

Fungal Bioweathering of Mimetite and a General Geomycological Model for Lead Apatite Mineral Biotransformations

Fungi play important roles in biogeochemical processes such as organic matter decomposition, bioweathering of minerals and rocks, and metal transformations and therefore influence elemental cycles for essential and potentially toxic elements, e.g., P, S, Pb, and As. Arsenic is a potentially toxic metalloid for most organisms and naturally occurs in trace quantities in soil, rocks, water, air, and living organisms. Among more than 300 arsenic minerals occurring in nature, mimetite [Pb₅(AsO₄)₃Cl] is the most stable lead arsenate and holds considerable promise in metal stabilization for in situ and ex situ sequestration and remediation through precipitation, as do other insoluble lead apatites, such as pyromorphite [Pb₅(PO₄)₃Cl] and vanadinite [Pb₅(VO₄)₃Cl]. Despite the insolubility of mimetite, the organic acid-producing soil fungus Aspergillus niger was able to solubilize mimetite with simultaneous precipitation of lead oxalate as a new mycogenic biomineral. Since fungal biotransformation of both pyromorphite and vanadinite has been previously documented, a new biogeochemical model for the biogenic transformation of lead apatites (mimetite, pyromorphite, and vanadinite) by fungi is hypothesized in this study by application of geochemical modeling together with experimental data. The models closely agreed with experimental data and provided accurate simulation of As and Pb complexation and biomineral formation dependent on, e.g., pH, cation-anion composition, and concentration. A general pattern for fungal biotransformation of lead apatite minerals is proposed, proving new understanding of ecological implications of the biogeochemical cycling of component elements as well as industrial applications in metal stabilization, bioremediation, and biorecovery.     

Interaction of the antitumor agent vanadocene dichloride with phosphate buffered saline

EPR study has shown that in aqueous solution the anticancer agent vanadocene dichloride (Cp₂VCl₂) interacts with phosphates contained in phosphate buffered saline (PBS). Chelate complex Cp₂VO₂PO₂H (|A_iso(V)|=189.0 MHz, |a_iso(P)|=81.5 MHz and g_iso=1.9862) is only one paramagnetic compound formed at the range about the physiological pH (6.3-7.8). Its structure was validated by comparison of observed and theoretical calculated HFC tensor (at the density functional level of theory).     

Inhibition of chlorophyll biosynthesis by lead in greeningPisum sativum leaf segments

Supply of 0.01 to 1.0 mM lead acetate to greening pea(Pisum sativum L.) leaf segments either in the absence or in the presence of inorganic nitrogen lowered total chlorophyll (Chl) content. During a time course study, there was not any appreciable effect of Pb²⁺ upto 4 h but thereafter Pb inhibited Chl synthesis. While supply of succinate, cysteine dithiothreitol, 5,5-dithio-bis-2-nitrobenzoic acid and NH₄C1 had no protective action against Pb²⁺ toxicity, and glycine, glutamate 2-oxoglutarate, MgCl₂, KH₂PO₄, CaCl₂, KC1 protected only partially, reduced glutathione (GSH) could completely overcome the inhibition of Chl biosynthesis by the metal. It is suggested that Pb²⁺ interferes with Chl biosynthesis through GSH availability     

Characterization of the mineral phosphate solubilizing activity of <Emphasis Type="Italic">Serratia marcescens</Emphasis> CTM 50650 isolated from the phosphate mine of Gafsa

The mineral phosphate solubilizing (MPS) ability of a Serratia marcescens strain, namely CTM 50650, isolated from the phosphate mine of Gafsa, was characterized on a chemically defined medium (NBRIP broth). Various insoluble inorganic phosphates, including rock phosphate (RP), calcium phosphate (CaHPO₄), tri-calcium phosphate (Ca₃(PO₄)₂) and hydroxyapatite were tested as sole sources of phosphate for bacterial growth. Solubilization of these phosphates by S. marcescens CTM 50650 was very efficient. Indeed, under optimal conditions, the soluble phosphorus (P) concentration it produced reached 967, 500, 595 and 326 mg/l from CaHPO₄, Ca₃(PO₄)₂, hydroxyapatite and RP, respectively. Study of the mechanisms involved in the MPS activity of CTM 50650, showed that phosphate solubilization was concomitant with significant drop in pH. HPLC-analysis of culture supernatants revealed the secretion of gluconic acid (GA) resulting from direct oxidation pathway of glucose when the CTM 50650 cells were grown on NBRIP containing glucose as unique carbon source. This was correlated with the simultaneous detection by PCR for the first time in a S. marcescens strain producing GA, of a gene encoding glucose dehydrogenase responsible for GA production, as well as the genes pqqA, B, C and E involved in biosynthesis of its PQQ cofactor. This study is expected to lead to the development of an environmental-friendly process for fertilizer production considering the capacity of S. marcescens CTM 50650 to achieve yields of P extraction up to 75% from the Gafsa RP.     

Solubilization of insoluble inorganic phosphates by a novel temperature-, pH-, and salt-tolerant yeast, <Emphasis Type="Italic">Rhodotorula</Emphasis> sp<Emphasis Type="Italic">.</Emphasis> PS4, isolated from seabuckthorn rhizosphere,growing in cold desert of Ladakh,India

The study was aimed to develop biofertilizer solubilizing inorganic phosphates for region experiencing temperature, pH and salt stressed conditions. A yeast strain PS4, which was temperature-, pH- and salt-tolerant and capable of solubilizing insoluble inorganic phosphate was isolated from rhizosphere of seabuckthorn (Hippophae rhamnoides L.), growing in the Indian Trans-Himalaya. Based on morphological, biochemical, whole cell FAME analysis and molecular characterization, strain PS4 was identified as Rhodotorula sp. The soluble phosphate production under optimal conditions at pH 7 and 30°C was 278.3 mg l⁻¹. Strain PS4 showed ability to solubilize insoluble phosphate under different stress conditions viz. 5–40°C temperature, 1–5% salt concentration and 3–11 pH range. Soluble phosphate production from Ca₃(PO₄)₂ under combined stress conditions at extreme values of temperature, pH and salt concentration showed 81.6–83.2% reduction as compare to optimal conditions after 5 days incubation. The strain solubilize Ca₃(PO₄)₂ to a great extent than FePO₄ and AlPO₄. The solubilization of insoluble phosphate was associated with drop in pH of the culture media. Inoculation of tomato seedling with the strain increased fruit yield, roots and shoot length. Rhodotorula sp. PS4 with phosphate-solubilizing ability under stress conditions appeared to be attractive for exploring their plant growth-promoting activity towards the development of microbial inoculants in stressed region.     

Two new bimetallic phosphates assembled from the 4-ring building units and influence of metal on the phase selectivity

Two new bimetallic phosphates [(CH₃)₂NH]_0.5[Zn_0.62Co_0.38PO₃OH] (ZnCoPO-CJ48) and [(CH₃)₂NH₂][Zn_2.3Mn_0.7(PO₄)₂(PO₃OH)]·H₃O (ZnMnPO-CJ49) have been solvothermally synthesized in the similar reaction system. ZnCoPO-CJ48 is a layered zinco-cobalt phosphate with neutral framework, its structure is constructed by the connection of Zn(Co)O₄ and PO₃OH tetrahedra forming a novel 2-D sheet with 3- and 4-rings. The alternating connection of Zn(Mn)O₄ and PO₄/PO₃OH tetrahedra results in the open framework of ZnMnPO-CJ49 with 16-ring extra-large channels. Notably, both compounds are featured by the 4-ring building units T₂P₂O₆(OH)₂ formed by the connection of two TO₄ tetrahedra and two PO₃OH tetrahedra. The 3-D structure of ZnMnPO-CJ49 can be viewed as the connection of zinc-manganese phosphate layers analogous to the layered structure of ZnCoPO-CJ48 by the 1-D edge-sharing 4-ring chains as the pillars. In this work, the synthetic conditions of these two compounds and the influence of metal on the phase selectivity have been discussed in detail.     

Lead Precipitation by Vibrio harveyi: Evidence for Novel Quorum-Sensing Interactions

Three pleiotropic, quorum sensing-defective Vibrio harveyi mutants were observed to precipitate soluble Pb²⁺ as an insoluble compound. The compound was purified and subjected to X-ray diffraction and elemental analyses. These assays identified the precipitated compound as Pb₉(PO₄)₆, an unusual and complex lead phosphate salt that is produced synthetically at temperatures of ca. 200°C. Regulation of the precipitation phenotype was also examined. Introduction of a luxO::kan allele into one of the mutants abolished lead precipitation, indicating that the well-characterized autoinducer 1 (AI1)-AI2 quorum-sensing system can block lead precipitation in dense cell populations. Interestingly, the V. harveyi D1 mutant, a strain defective for secretion of both AI1 and AI2, was shown to be an effective trans inhibitor of lead precipitation. This suggests that a previously undescribed V. harveyi autoinducer, referred to as AI3, can also negatively regulate lead precipitation. Experiments with heterologous bacterial populations demonstrated that many different species are capable of trans regulating the V. harveyi lead precipitation phenotype. Moreover, one of the V. harveyi mutants in this study exhibited little or no response to intercellular signals from other V. harveyi inocula but was quite responsive to some of the heterologous bacteria. Based on these observations, we propose that V. harveyi carries at least one quorum sensor that is specifically dedicated to receiving cross-species communication.     

Uranium phosphate biomineralization by fungi

Geoactive soil fungi were investigated for phosphatase‐mediated uranium precipitation during growth on an organic phosphorus source. Aspergillus niger and Paecilomyces javanicus were grown on modified Czapek–Dox medium amended with glycerol 2‐phosphate (G2P) as sole P source and uranium nitrate. Both organisms showed reduced growth on uranium‐containing media but were able to extensively precipitate uranium and phosphorus‐containing minerals on hyphal surfaces, and these were identified by X‐ray powder diffraction as uranyl phosphate species, including potassium uranyl phosphate hydrate (KPUO₆.3H₂O), meta‐ankoleite [(K_1.7Ba_0.2)(UO₂)₂(PO₄)₂.6H₂O], uranyl phosphate hydrate [(UO₂)₃(PO₄)₂.4H₂O], meta‐ankoleite (K(UO₂)(PO₄).3H₂O), uramphite (NH₄UO₂PO₄.3H₂O) and chernikovite [(H₃O)₂(UO₂)₂(PO₄)₂.6H₂O]. Some minerals with a morphology similar to bacterial hydrogen uranyl phosphate were detected on A. niger biomass. Geochemical modelling confirmed the complexity of uranium speciation, and the presence of meta‐ankoleite, uramphite and uranyl phosphate hydrate between pH 3 and 8 closely matched the experimental data, with potassium as the dominant cation. We have therefore demonstrated that fungi can precipitate U‐containing phosphate biominerals when grown with an organic source of P, with the hyphal matrix serving to localize the resultant uranium minerals. The findings throw further light on potential fungal roles in U and P biogeochemistry as well as the application of these mechanisms for element recovery or bioremediation.     

Production,Purification and Properties of Ribonuclease from Aspergillus niger

Aspergillus niger NRC–A–1–233 was cultivated by the shaking method. The optimal cultural conditions for ribonuclease (RNase) production were: composition of medium: sucrose, 15%; NH₄NO₃, 0.2%; KH₂PO₄, 0.1%; MgSO₄·7 aq., 0.025%; initial pH, 2.2; shaking conditions: 50 ml of medium /500 ml flask; cultivation time, 120 hr. The RNase was purified by acid clay treatment and chromatography on DEAE-cellulose and Sephadex G–75 columns. The purified RNase was homogeneous by ultracentrifuge and disc electrophoresis.

The molecular weight of the RNase was estimated to be 28,500 on SDS-polyacrylamide gel and its isoelectric point was 2.8 by Ampholine electrofocusing method. Digestion rate of RNA by the RNase was 100%. The RNase did not have an exact base specificity and produced four kinds of 3′-nucleotides from yeast RNA.     

New open-framework phosphate and phosphite compounds of gallium

Five new open-framework compounds of gallium have been synthesized by hydrothermal methods and their structures determined by single crystal X-ray diffraction studies. The compounds, [C₈N₄H₂₆][Ga₆F₄(PO₄)₆], I, [C₅N₃H₁₁][Ga₃F₂(PO₄)₃]·H₂O, II, [C₆N₃H₁₉][Ga₄(C₂O₄)(PO₄)₄(H₂PO₄)]·2H₂O, III, [Ga₂F₃(HPO₄)(PO₄)]·2H₃O, IV, and [C₃N₂H₅]₂[Ga₄(H₂O)₃(HPO₃)₇], V, possess three-dimensional structures. All the compounds are formed by the connectivity between the Ga polyhedra and phosphite/phosphate units. The observation of SBU-6 (I and II) and spiro-5 (IV) secondary building units (SBUs) are noteworthy. The flexibility of the formation of gallium phosphate frameworks has been established by the isolation of two related structures (I and II) from the same SBU units but different organic amines. Some of the present structures have close resemblance to the gallium phosphate phases known earlier. The compounds have been characterized by CHN analysis, powder XRD, IR, and TGA.     

On the molecular mechanisms of the acid-induced dissociation of hydroxy-apatite in water

The enamel/saliva interface is mimicked by the comparably much simpler model of (001) surfaces of hydroxy-apatite ( Ca₁₀(PO₄)₆(OH)₂ ) in contact with aqueous solution. At neutral pH, the dissociation of ions is penalized by more than 150 kJ mol^-1 giving rise to very stable apatite-water interfaces. This picture changes drastically with decreasing pH, as the protonation of phosphate and hydroxide ions lowers the free energy of calcium ions dissociation. Our simulations suggest the mechanism of acid-induced apatite decomposition to i) require a considerable degree of protonation of the apatite surface. The first ion dissociation step ii) involves calcium ions which electrostatic binding has been locally destabilized through phosphate and hydroxide protonation. The depletion of calcium ions embedding the anions then allows iii) the dissociation of the anionic species. Along this line, the protective role of fluoride in caries prevention is related to the stabilization of the calcium triangles embedding the OH^-/F^- ions.     

The Amount of Phosphate Solubilization Depends on the Strain,C-Source,Organic Acids and Type of Phosphate

Although production of organic acids (OAs) is usually mentioned as the main mechanism of phosphate solubilization, the relationship between carbon sources (C-sources) and OAs produced during phosphate-solubilization by microorganisms is still poorly understood. We evaluated the influence of different C-sources on FePO₄·2H₂O and Ca₃(PO₄)₂ solubilization by bacteria and on the identity/quantity of the OAs produced. Our results showed that the amount of phosphate solubilization depends on the strain, C-source, OAs, and type of phosphate. Among the five strains under study isolated from cowpea nodules (Rhizobium tropici strain UFLA 03-08, Acinetobacter sp. strain UFLA 03-09, Paenibacillus kribbensis strain UFLA 03-10, P. kribbensis strain UFLA 03-106, and Paenibacillus sp. strain UFLA 03-116), three of them solubilized Ca₃(PO₄)₂ in all C-sources. The influence of C-sources on Ca₃(PO₄)₂-solubilization increased in the following order: cellulose?<?lactose?<?mannitol?<?glucose. A significant positive correlation between the amount of phosphorus solubilized from Ca₃(PO₄)₂ and the concentration of total OAs in the presence of glucose and mannitol was observed for these three strains. In the presence of glucose, the highest solubilization rates are associated with high concentrations of tartaric acid, and in the presence of mannitol, are associated with maleic acid. Only one strain produced OAs in the medium with lactose and Ca₃(PO₄)₂, but there was no OAs in the medium containing cellulose. Despite the production of OAs, albeit in small concentrations, in all the C-sources investigated, FePO₄·2H₂O-solubilization was not observed. Thus, a relationship among C-sources, OAs, and phosphate solubilization was not always verified.     

Factors influencing phosphate exchange across the sediment-water interface of eutrophic reservoirs

The results of a survey of the sediment chemistry of 7 East Anglian reservoirs are presented as part of a regional study on the assessment and control of eutrophication. The influence of water quality (dissolved oxygen, pH, temperature) on phosphate (PO₄) adsorption by sediment from hypertrophic Ardleigh Reservoir is also examined. Extractable phosphate-P (extr.-P) varied between 92 and 383 mg kg^–1 dry matter. Extractable P varied between 5.3 and 16.6% of the total phosphate-P (Tot. P) content and increased with the concentration of dissolved reactive phosphate-P (DRP) in the overlying water column. Organically complexed iron (organic Fe) was the determinand which correlated most closely with phosphate adsorption capacity, PAC (r = 0.8). Organic Fe was also related inversely to Extr. P. The rate and extent of PO₄ adsorption by Ardleigh Reservoir sediment increased with the initial concentration of DRP and adsorption equilibria were reached after 24 h. The equilibrium DRP concentration, [DRP], was 0.7 mg P 1^–1 under aerobic conditions indicative of a high potential for PO₄ exchange. The rate and extent of PO₄ adsorption was greater at 7 °C than at 22 °C PO₄ adsorption increased markedly with dissolved oxygen status. Ardleigh sediment exhibited a marked buffering capacity to a change in pH; however, PO₄ adsorption was greatest at an equilibrium pH of 5.6 and decreased progressively either side of this pH value.Options for the artificial control of sediment PO₄ release are discussed in relation to the seasonal variation in sediment PO₄ exchange observed for Ardleigh Reservoir.     

Aqueous acid-base chemistry involving dioxovanadium(V) complexes of 2,6-pyridinedimethanol, and the X-ray structures of Na[VO2{2,6-(OCH2)2NC5H3}] · 4H2O and [1-H-2,6-(HOCH2)2NC5H3]Cl

Reaction of NH₄VO₃ with 2,6-pyridinedimethanol in water at 85 °C followed by the room temperature addition of HCl (aq) yields [HVO₂(pydim)]_x (pydim = 2,6-pyridinedimethanolato dianion), as a sparingly soluble off-white solid. This acid may be deprotonated by titration with NaOH (aq), yielding Na[VO₂(pydim)] · 4H₂O, which has been structurally characterized by single-crystal X-ray diffraction. Treating Na[VO₂(pydim)] · 4H₂O with HCl (aq) regenerates [HVO₂(pydim)]_x, but reaction with additional NaOH (aq) displaces the pyridinedimethanolato ligand from the vanadium center. Similarly, treating [HVO₂(pydim)]_x with excess HCl (aq) strips the pyridinedimethanolato ligand from the vanadium center and yields the adduct [H₃(pydim)]⁺Cl⁻ as one component in a mixture of products. This adduct has been structurally characterized by single-crystal X-ray diffraction. The optimum pH range for stable dioxovanadium(V) complexes stabilized by the 2,6-pyridinedimethanolato ligand is at least 1.5-9.4.     

Effect of temperature and pH on absorption of carbon dioxide by a free level of mixed solutions of some buffers

The rate of absorption of carbon dioxide by solutions of NaHCO₃, KH₂PO₄, hydrogencarbonate, phosphate and borate buffers at 20, 30 and 40°C was determined manometrically. The absorption rate increases for all buffers tested with increasing pH. The CO₂ absorption rate by KH₂PO₄ and by the phosphate buffer at low pH is lower than that of water. For other buffers tested it is equal to or higher than that of water, especially at higher temperatures.