Hydroxy Ions Research Articles

Photoinduced electron doping of single-walled carbon nanotubes based on carboxamide photochemical reactions

Photoinduced electron doping of single-walled carbon nanotubes based on the formation of 1,3-dimethyl-2-arylbenzimidazole (DMBI) cations and hydroxy ions by photochemical reaction of DMBI oxides.

Review Article Recent Advances in Preventing Dental Erosion

Dental erosion is defined as an irreversible loss of dental hard tissue due to exposure to chelating agents or non-bacterial acids. The occurrence of this condition was noted and the incidence and prevalence of dental erosion has been increasingly documented.The Ant erosive agents such as Anacardic acid in which the key component is the cashewnut shell liquid is phenolic lipids. It is a mixture of molecules which are saturated and unsaturated. It is also considered to have an anti-microbial effect and has been studied for the treatment of cancer, oxidative damage, inflammation and obesity disorders. Other anti-erosive agent like Fluoride helps in tooth remineralization. Fluorapatite, rather than hydroxyapatite, forms during the process of remineralization when fluoride is found in oral fluids. In apatite crystal lattice formation, fluoride ions replace hydroxy ions. Fluorapatite, even under acidic conditions, is less soluble than hydroxyapatite, which helps to regenerate tooth enamel. Fluoride is therefore a stronger anti-erosive agent. Various Recent advances in anti-erosive agents are Calcium and phosphate, Casein phosphopeptide amorphous calcium phosphate (CPP-ACP), Protease inhibitors, Oils, Chitosan chitosan and Multivalent metal ions Various techniques to evaluate dental erosion are in vitro techniques and in vivo techniques. In vitro techniques are Scanning electron microscope, Surface Profilometry, Polarized Light Microscopyand Non-Contact Confocal Laser Scanning Microscopy (CLSM). And iv vivo techniques are Photographs Clinical review and indices. The most important point of treatment is identifying and removing the erosion factor, above all current materials and methods. Therefore, early identification of the lesions, evaluation and removal of the etiological variables are relevant topics.

STUDI KOMPUTASI REAKSI SUBTITUSI DARI 1-BROMOHEPTANA DENGAN ION HIDROKSI MENGGUNAKAN PENDEKATAN AB-INITIO

Substitution reaction is a simple reaction that can occur through the SN1 pathway. One of the reactions included in the substitution reaction is the reaction between alkane halides and hydroxy ions. The computational calculation has done for substitution reaction between 1-bromoheptane and hydroxy ion. The purpose of computational calculations is to obtain a stable structure, and thermodynamic aspect of the reaction. The calculation was using the ab-initio approach HF-SCF (Hatree Fock-Self Consistent Field) with 6-31G(d) as a basis set. The calculation is done in gas phase. The optimized structure of reactant is being in complex reactant. Gibbs Free energy from the calculation is about - 255.53 kJ/mol. It is mean that the reaction is happen spontaneously.

Sorption characteristics of iodide on chalcocite and mackinawite under pH variations in alkaline conditions

Abstract In terms of long-term safety for radioactive waste disposal, the anionic iodide (I-129) with a long half-life (1.6 × 106 yr) is of a critical importance because this radionuclide migrates in geological media with limited interactions. Various studies have been performed to retard the iodide migration. Recently, some minerals that are likely generated from waste container corrosion, have been suggested to have a considerable chemical interaction with iodide. In this study, chalcocite and mackinawite were selected as candidate minerals for underground corrosion materials, and an iodide sorption experiment were carried out. The experiment was performed under anoxic and alkaline conditions and the pH effects on the iodide sorption were investigated in the range of pH 8 to 12. The results showed that both minerals demonstrated a noticeable sorption capacity on iodide, and the distribution coefficient (Kd) decreased as the pH increased in the experimental condition. In addition, when the alkalinity increased higher than a pH of 12, the sorption capacity of both minerals decreased dramatically, likely due to the competition of hydroxy ions with the iodide. This result confirmed that chalcocite was an especially good sorbing media for iodide under alkaline conditions with a pH value of less than 12.

Poly(ionic liquid) binders as ionic conductors and polymer electrolyte interfaces for enhanced electrochemical performance of water splitting electrodes

A PIL blocks metals at the electrode, while it is permeable to water, hydroxy ions and the as-generated oxygen.

Electronic‐Structure Calculations of Cation‐Ordered II‐III Layered Double Hydroxides: Origin of the Distortion of the Metal‐Coordination Symmetry

Cation ordering brings down the crystal symmetry and introduces distortion into the coordination polyhedra around the divalent cations. In particular, edge sharing of the differently sized [M(OH)6] polyhedra causes a non‐uniform distension of the array of hydroxy ions. The question arises as to whether this distortion has its origin in the Jahn–Teller distortion of metal coordination or a 2D “Peierls”‐type distortion of the array of hydroxy ions. To address this question, DFT calculations were performed on the sulfate‐intercalated [Cu–Cr], [Zn–Cr], and [Zn–Al] layered double hydroxides (LDHs). An analysis of the density of states shows that the distortion of the Cu2+ coordination polyhedron is due to the Jahn–Teller effect, whereas the Zn2+ coordination polyhedron in [Zn–Al] LDH likely suffers a “Peierls”‐type distortion. In the [Zn–Cr] LDH, electronic‐structure calculations do not predict any distortion in the metal coordination, which is in agreement with experimental results that show only a slight departure from ideal symmetry.

Effect of pH on crystallization of nanocrystalline zirconia in a microwave-hydrothermal process

Nanocrystalline zirconia (ZrO2) was synthesized using a microwave-hydrothermal process. The effect of pH on the crystallization of the ZrO2 powders was investigated. The phase and microstructure of ZrO2 powders were examined using X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). Results show that pure m-ZrO2 can be obtained at low pH (pH<2). Pure t-ZrO2 is formed at pH = 7 and 14. The size of the ZrO2 crystals is in the range of 8-26 nm and decreases with increasing pH. The formation of m-ZrO2 results from the precipitation of ZrO2 from solution. The t-ZrO2 is formed through the in-situ structural rearrangement of amorphous Zr(OH)xOy. The stabilization of t-ZrO2 is attributed to the small crystal size and the adsorption of hydroxy ions on the surfaces of the crystals.

A novel peat-based biosorbent for the removal of phosphate from synthetic and real wastewater and possible utilization of spent sorbent in land application

Removal of potentially harmful phosphorus compounds from wastewater by adsorption onto biosorbents is a cost-effective alternative to the conventional treatment methods. Raw peat and peat modified with iron(III) hydroxy ions were used in this study to remove phosphate ions from synthetic solution and household wastewater. Interaction of iron(III) ions with carboxylic groups of peat occurred during peat modification, which was confirmed by the FTIR technique. The effect of the initial phosphate concentration, pH, contact time, temperature, and ionic strength was studied in batch experiments. It was found that the sorption capacity increased with the increasing temperature, i.e. the maximum sorption capacity of the modified peat was 9.64 mg P/g at 2°C and 11.53 mg P/g at 40°C, respectively, indicating the endothermic nature of the sorption. Besides, the Langmuir equation was used to describe the sorption isotherms quantitatively. Given that the spent biosorbent did not exhibit phytotoxicity and the concentration of heavy metals did not exceed the limit values, the phosphate-saturated modified peat may be utilized as an organic fertilizer in agricultural land application.

A molecular dynamics study on the nucleation of calcium phosphate regulated by collagen

Molecular dynamics (MD) simulations have been used to study calcium phosphate formation regulated by collagen in solution. In this study, a collagen-like peptide molecule has been mixed with different types of ions for simulations of the early stage of biomineralization. We have compared one system containing calcium ions, and hydrogen phosphate ions to the other system containing calcium ions, phosphate ions and hydroxy ions in a water box containing a peptide molecule (1CAG) in the center. After the simulations, the radical distance function and coordination number profiles show that calcium ions and phosphate ions attract each other and form stable clusters in both systems studied. The hydroxy ions are attracted by calcium ions and the distance between them is close to that in hydroxyapatite, which is considered to play important roles in the formation of hydroxyapatite. The current results provide a useful approach to study the scenario of mineralizing collagen using MD methods.

Electrochemical determination of dissolved oxygen based on three dimensional electrosynthesis of silver nanodendrites electrode

In this paper, a highly sensitive electrochemical sensor for dissolved oxygen was prepared. A glassy carbon electrode was modified with silver nanodendrites that were synthesized by electrochemical deposition on the electrode without the use of a surfactant or template. The electrode displayed efficient electrocatalytic reduction of dissolved oxygen to form hydroxy ions via a four-electron reduction pathway, and a significant decrease in the respective overvoltage. The sensor responded linearly to dissolved oxygen in the 1.0–66.7 μM concentration range, and had a remarkably good sensitivity (0.169 μA μM−1) at an applied potential of −300 mV (vs. Ag/AgCl). The lower detection limit was 0.043 μM (at the signal-to-noise ratio of 3), and the response time was 5 s. The good performance was attributed to the enlarged electro-active surface of the dendritic silver nanostructures and to the efficiency of electron transfer between dissolved oxygen and the electrode. The sensor also showed good reproducibility, long-term stability, and relative good selectivity.

Mechanism of cathodic reduction of cobalt pyrophosphate complex

Potentiostatic and potentiodynamic methods were employed to study the kinetics of electrochemical reduction of the pyrophosphate cobalt complex to the metal from electrolytes of various compositions in the atmosphere of hydrogen. The reaction orders of cobalt reduction with respect to pyrophosphate anions and hydroxy ions were found. A stage-by-stage mechanism of the cathodic reduction of cobalt was suggested.

Molecular Dynamics Simulation of the Early Stages of Nucleation of Hydroxyapatite at a Collagen Template

We have used molecular dynamics simulations to investigate the early processes in the nucleation of hydroxyapatite at a collagen template, by immersing a triple-helical collagen molecule in a stoichiometric solution of Ca2+, PO43–, and OH– ions, where we have observed the formation of calcium phosphate clusters at the collagen template. Electrostatic attractions were prevalent between calcium ions and oxygen atoms of the glycine and hydroxyproline residues, which were the starting point for the formation of the calcium phosphate clusters. Some phosphate ions form hydrogen-bonds with the hydroxy groups of hydroxyproline residues, whereas most of the hydroxy ions stay in solution, although some become attached to calcium phosphate clusters. The observed nucleation and clustering is too early in the hydroxyapatite formation process to show differentiation between distinct hydroxyapatite surfaces. However, calculations of the interaction of a collagen peptide with the (0001) and (0110) surfaces of hydroxyapa...

When Microbubble–Polyelectrolyte Complexes Overcharge: A Comparative Study Using Electrophoresis

Abstract We observed the charge reversal of microbubble–polyelectrolyte complexes using microscopic electrophoresis. The measured mobility of microbubbles with the addition of cationic poly(allylamine hydrochloride) exhibited unusual behaviors. The critical concentration of polyelectrolytes added for the charge reversal was not only weakly dependent on chain length but was also much larger than that of colloidal silica–polyelectrolyte complexes. We attribute the nonstoichiometric overcharging to the adsorption–desorption kinetics of hydroxy ions on the surface of genuine microbubbles.

The effects of different nitrogen compounds on the growth and microcystin production of Microcystis aeruginosa

The effects of different nitrogen compounds, which include bicine, sodium nitrate, ammonium chloride, glutamic acid and urea, on growth and microcystin (MC) production were studied in batch cultures. The results showed that growth and microcystin production were promoted by bicine, sodium nitrate and ammonium chloride and could not be supported by urea and glutamic acid. It is likely that the cells of Microcystis aeruginosa have no urease which can be utilized to decompose urea. Glutamic acid enters the cell and may interrupt the normal metabolic processes. This would inhibit growth and microcystin production, resulting in the death of the organism. Bicine kept the pH of the medium at about 8.5 and offered a preferential environment for growth and microcystin production. Ammonium chloride could be utilized by Microcystis aeruginosa indirectly. During the process of assimilation, hydroxy ions were continuously consumed, which would lead to a reduction in pH to less than 7 and retard growth and microcystin production. In the presence of sodium nitrate, the metabolic and biochemical mechanisms, which use sodium nitrate as a source of nutrition during the process of expanding vaccination, were impossible to change in a short time. Thus, sodium nitrate promoted growth and microcystin production.

The first polymeric thiogallate with lanthanide-containing counter cation, [Dy 2(en) 6(μ 2-OH) 2]Ga 4S 8

The title compound, [Dy 2(en) 6(μ 2-OH) 2]Ga 4S 8 (en = ethylenediamine), contains 1D infinite sinusoidal [ GaS 2 - ] n anions and hydroxy bridged dinuclear dysprosium complex cations. Two bridging hydroxy ions connect two inversion-related Dy 3+ ions to form a centrosymmetric dimer, in which a Dy 2O 2 rhomboidal core is formed. The title compound is the only example of the thiogallates with lanthanide-containing counter cation.

Routes to new hafnium(IV) tetraaryl porphyrins and crystal structures of unusual phosphate-, sulfate-, and peroxide-bridged dimers.

New routes for the synthesis of mono tetraaryl porphyrinato hafnium(IV) complexes, Hf(IV)Por(L)(2), are reported, where the secondary ligands, L, are determined by the method of purification. These synthetic routes cater to the solubility of the macrocycles and provide access to Hf(IV) complexes of meso tetraaryl porphyrins bearing diverse functional groups such as phenyl, tolyl, pyridyl, pentafluorophenyl, and carboxyphenyl. The latter three derivatives significantly expand the repertoire of hafnium porphyrinates. One route refluxes the porphyrin with HfCl(4) in 1-chloronaphthalene or in a mixed solvent of 1-chloronaphthalene and o-cresol. A second, solventless method is also reported wherein the porphyrin is mixed with Hf(cp)(2)Cl(2) and heated to give the metalated porphyrin in good yields. Simultaneous purification and formation of stable porphyrinato hafnium(IV) diacetate complexes, Hf(Por)OAc(2), is accomplished by elution over silica gel using 3-5% acetic acid in the eluent. Exchange of the acetate ligands for other oxo-bearing ligands can be nearly quantitative, such as p-aminobenzoate (PABA), pentanoate (pent), or octanoate (oct). Notably, we find that two to three of a variety of small multitopic dianions such as peroxo (O(2)(-2)), SO(4)(-2), and HPO(4)(-2) serve to bridge between two Hf(Por) moieties to form stable dimers. The crystal structures of this library of Hf(Por) complexes are reported, and we note that careful analysis of crystallography data reveals (Por)Hf(micro-eta(2)-O(2))(2)Hf(Por) rather than four bridging oxo or hydroxy ions.

A computational investigation of stoichiometric and calcium-deficient oxy- and hydroxy-apatites

Computer modelling techniques have been employed to qualitatively and quantitatively investigate the dehydration of hydroxyapatite to oxyapatite and the defect chemistry of calcium-deficient hydroxyapatite, where a number of vacancy formation reactions are considered. The dehydration of hydroxyapatite into oxyhydroxyapatite is calculated to be endothermic by E = +83.2 kJ mol(-1) in agreement with experiment, where thermal treatment is necessary to drive this process. Calcium vacancies are preferentially charge-compensated by carbonate ions substituting for phosphate groups (E = -5.3 kJ mol(-1)), whereas charge-compensating reactions involving PO4 vacancies are highly endothermic (E > or =652 kJ mol(-1)). The exothermicity of the charge compensation of a Ca vacancy accompanied by a PO4/CO3 substitution agrees with their co-occurrence in natural bone tissue and tooth enamel. Our calculations of a range of defect structures predict (i) that calcium vacancies as well as substitutional sodium and potassium ions would occur together with carbonate impurities at phosphate sites, but that other charge compensations by replacement of the phosphate groups are unfavourable, and (ii) that the hydroxy ions in the channel are easily replaced by carbonate groups, but that the formation of water or oxygen defects in the channels is thermodynamically unfavourable. Calculated elastic constants are reported for the defect structures.

Coordination ability of trans-cyclohexane-1,2-diamine-N,N,N′,N′-tetrakis(methylenephosphonic acid) towards lanthanide(iii) ions

The proton and metal complex equilibria of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetrakis(methylenephosphonic acid) (CDTP) with lanthanide(iii) ions, where Ln(III) = La(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Ho(III) and Lu(III) were studied. The stoichiometry, protonation and complex formation constants were determined by potentiometric titration at 25.0 degrees C and ionic strength of 0.1 mol dm(-3) (KCl). All metal ions form several species: [LnH4L]-, [LnH3L](2-), [LnH2L](3-), [LnHL](4-), [LnL](5-), [LnH(-1)L](6-) and [LnH(-2)L](7-) in the pH range between 2 and 11. The stability constants log beta(LnL) were found to be between 14.7 and 16.7. The studied complexes were also characterized by spectroscopic methods (31P NMR, UV-Vis absorption and emission spectroscopy). These studies allowed to reveal a distinct structural change of the Ln(III)-CDTP complex which occurs between protonated and hydroxy species in solutions at pH around 7.5. The major change is caused by the involvement of both nitrogen donors in the metal ion coordination occurring in ML species. The data obtained from UV-Vis spectroscopy allowed to draw conclusions about complex symmetry and to estimate a number of coordinated water molecules. The hydration number or more precisely the number of two OH oscillators was found to be approximately one in all species formed over the pH range between 5 and 10. The structure of the major hydroxy complex was supported by X-ray crystallographic data. The crystal structures of the Eu(III) and Tb(III) complexes clearly show that the CDTP ligand is coordinated to the Ln(III) ion by two nitrogen and four oxygen atoms in such a way that only one oxygen atom from each phosphonic group is placed in the lanthanide inner sphere. The monomeric complex anion is connected to a symmetry related ion through short hydrogen bonds formed by two hydroxy ions and one water molecule. In this way the two neighbouring anions form a quasi-dimer in which one of the Ln(III) ion is seven-coordinate (two N atoms, four O atoms and one hydroxy ion) and the other is eight-coordinate (two N atoms, four O atoms, one hydroxy ion and one water molecule).

Analysis of Toxic Aluminium Species in Natural Waters

Aluminium is known to be toxic to a wide range of aquatic organisms under certain conditions. Monomeric hydroxy ions have been found to be primarily responsible for aluminium aquatic toxicity. A survey of aluminium toxicity and a brief discussion of speciation schemes are presented. The fast reaction of Al3+ with pyrocatechol violet (PCV) followed by spectrophotometric analysis is a frequently used method for aluminium speciation. By using a flow system, one obtains fairly exact and reproducible control of the reaction time, and as a result it provides a direct method of analysis for “free” aluminium (including inorganic monomeric aluminium). The PCV-method has been adapted for the determination of aluminium in carbonate-rich natural waters using an improved buffering system. Thus it is possible to monitor aluminium concentrations in lake water as well as in pore water of the sediments of eutrophicated hardwater lakes that has been treated with aluminium salts as a restoration measure.

Formation and stability of schwertmannite in acidic mining lakes

Schwertmannite (ideal formula: Fe8O8(OH)6SO4) is typically found as a secondary iron mineral in pyrite oxidizing environments. In this study, geochemical constraints upon its formation are established and its role in the geochemical cycling of iron between reducing and oxidizing conditions are discussed. The composition of surface waters was analyzed and sediments characterized by X-ray diffraction, FTIR spectroscopy and determination of the Fe:S ratio in the oxalate extractable fraction from 18 acidic mining lakes. The lakes are exposed to a permanent supply of pyritegenous ferrous iron from adjacent ground water. In 3 of the lakes the suspended matter was fractionated using ultra filtration and analyzed with respect to their mineral composition. In addition, stability experiments with synthetic schwertmannite were performed. The examined lake surface waters were O2-saturated and have sulfate concentrations (10.3 ± 5.5 mM) and pH values (3.0 ± 0.6) that are characteristic for the stability window of schwertmannite. Geochemical modeling implied that i) the waters were saturated with respect to schwertmannite, which controlled the activity of Fe3+ and sulfate, and ii) a redox equilibrium exists between Fe2+ and schwertmannite. In the uppermost sediment layers (1 to 5 cm depth), schwertmannite was detectable in 16 lakes—in 5 of them by all three methods. FTIR spectroscopy also proved its occurrence in the colloidal fraction (1–10 kDa) in all of the 3 investigated lake surface waters. The stability of synthetic schwertmannite was examined as a function of pH (2–7) by a 1-yr experiment. The transformation rate into goethite increased with increasing pH. Our study suggests that schwertmannite is the first mineral formed after oxidation and hydrolysis of a slightly acidic (pH 5–6), Fe(II)-SO4 solution, a process that directly affects the pH of the receiving water. Its occurrence is transient and restricted to environments, such as acidic mining lakes, where the coordination chemistry of Fe3+ is controlled by the competition between sulfate and hydroxy ions (i.e. mildly acidic).