Aq Complex Research Articles

Formation of Chlorine in the Atmosphere by Reaction of Hypochlorous Acid with Seawater.

The highly reactive dihalogens play a significant role in the oxidative chemistry of the troposphere. One of the main reservoirs of these halogens is hypohalous acids, HOX, which produce dihalogens in the presence of halides (Y-), where X, Y = Cl, Br, I. These reactions occur in and on aerosol particles and seawater surfaces and have been studied experimentally and by field observations. However, the mechanisms of these atmospheric reactions are still unknown. Here, we establish the atomistic mechanism of HOCl + Cl- → Cl2 + OH- at the surface of the water slab by performing ab initio molecular dynamics (AIMD) simulations. Main findings are (1) This reaction proceeds by halogen-bonded complexes of (HOCl)···(Cl-)aq surrounded with the neighboring water molecules. (2) The halogen bonded (HOCl)···(Cl-)aq complexes undergo charge transfer from Cl- to OH- to form transient Cl2 at neutral pH. (3) The addition of a proton to one proximal water greatly facilitates the Cl2 formation, which explains the enhanced rate at low pH.

High-order Cu(II) chloro-complexes in LiCl brines: Insights from density function theory and molecular dynamics

Cu(II) complexation by chloride is relevant to the transport of copper in near-surface geologic environments, yet the existence of high-order Cu(II) chloro-complexes still remains in dispute. In this study, the structure characteristics and stabilities of [CuClx]2−xaq (x=3, 4, 5) complexes have been investigated using density functional theory (DFT) methods and molecular dynamics (MD) simulations. [CuCl3]− and [CuCl4]2− species can both be tracked, while the [CuCl5]3−aq complex cannot be recorded during MD simulations of trace Cu2+ in chloride-rich brines. DFT calculations indicate that contact ion pair (CIP) conformers of [CuCl3]− species are less stable than its solvent separated ion pair (SSIP) conformers, in which one Cl− stays in the second coordination sphere of the centered Cu2+. MD simulations also reveal that the SSIP conformer is apt to appear in the aqueous solution than its CIP conformer. It seems that the third Cl− is more likely in the second coordination shell of center Cu2+ in [CuCl3]−. Meanwhile, the characteristic peak around 385nm resolved in UV–Vis spectra experiments, which was attributed to the [CuCl3]− complex, could also be resulted from some SSIP structures of the [CuCl3]− complex. In MD simulations, the complex [CuCl4]2−aq is found more stable than [CuCl3]−aq. The surrounding water molecules around [CuClx]2−xaq (x=3, 4) enhance their stabilities in Cl− brines, especially for [CuCl4]2−aq. The hydration shell of [CuCl4]2−aq species is more intact than that of [CuCl3]2−aq, and the residence time of a water molecule in the second coordination sphere of Cu ion in the [CuCl4]2−aq complex is also obviously longer than that of [CuCl3]−aq. The [CuCl4]2−aq complex can even be recorded in the less concentrated (6.33m)Cl− solution, while the [CuCl3]−aq complex is tracked only in the 16.32mCl− brine. Meanwhile, the possibilities of [CuCl3]−aq and [CuCl4]2−aq complexes found in 16.32mCl− solutions both decrease with increasing temperature, [CuCl3]−aq cannot be recorded during our simulations at 373K and 423K, and only few [CuCl4]2−aq at 423K.

Synthesis and characterization of novel ion-imprinted polymeric nanoparticles for very fast and highly selective recognition of copper(II) ions

This work reports the preparation of new Cu 2+ ion-imprinted polymeric nanoparticles using 1-hydroxy-4-(prop-2′-enyloxy)-9,10-anthraquinone (AQ) as a vinylated chelating agent. The Cu 2+ ion found to form a stable 1:1 complex with AQ in methanol solution. The resulting Cu 2+–AQ complex was copolymerized with ethyleneglycol dimethacrylate, as a cross-linking monomer, via precipitation polymerization method. The imprint copper ion was removed from the polymeric matrix using a 0.1 mol L −1 HNO 3 solution. The Cu 2+-imprinted polymeric nanoparticles were characterized by IR spectroscopy, scanning electron microscopy (SEM) and N 2 adsorption–desorption isotherms. The SEM micrographs showed colloidal nanoparticles of 60–100 nm in diameter and slightly irregular in shape. Optimum pH for maximum sorption was 7.0. Sorption and desorption of Cu 2+ ion on the IIP nanoparticles were quite fast and achieved completely over entire investigated time periods of 2–30 min. Maximum sorbent capacity and enrichment factor of the prepared IIP for Cu 2+ were 73.8 μmol g −1 and 56.5, respectively. The relative standard deviation and limit of detection ( C LOD = 3 S b/ m) of the method were evaluated as 2.6% and 0.1 ng mL −1, using inductively coupled plasma-atomic emission spectrometry, respectively. It was found that the imprinting technology results in increased affinity of the prepared material toward Cu 2+ ion over other metal ions with the same charge and close ionic radius. The relative standard deviations for six and twenty replicates with the same nanoparticles were found to be 1.7% and 2.1%, respectively.

Bioaccumulation and distribution of silver in four marine teleosts and two marine elasmobranchs: influence of exposure duration, concentration, and salinity

The bioaccumulation of waterborne silver (added as AgNO 3) was compared amongst drinking (teleosts: rainbow trout, tidepool sculpin, plainfin midshipmen, and English sole) and non-drinking marine fish (elasmobranchs: Pacific spiny dogfish and long nose skate) exposed to 14.5 μg/l Ag for 21 days in 30-ppt seawater. In addition, 21-day exposures were performed on trout, midshipmen, and sculpin at 0 (control), 1.5, 14.5, and 50 μg/l Ag to evaluate the effect of silver concentration, and on sculpins acclimated to 18 and 30 ppt salinity and sampled periodically up to 21 days to evaluate the effects of salinity and exposure duration. A 48-h acute exposure (250 μg/l Ag) was also carried out on sculpins at 10, 18, 24, and 30 ppt. The 1.5-and 14.5-μg/l Ag levels are of regulatory importance, but are several orders of magnitude higher than normal environmental levels. Silver uptake occurred in all exposures, but internal accumulations were less than proportional to exposure concentration (1.5–50.0 μg/l Ag), and tended to saturate over time, suggesting that physiological regulation occurred. Control (non-exposed) fish exhibited measurable levels of silver in all tissues (10–200 μg Ag/kg wet weight), suggesting that they accumulate silver from the natural environment throughout their lifetimes. After 21-day exposure to 14.5 μg/l Ag, silver levels increased 2–20-fold in most tissues of all species, with the greatest concentrations occurring in the livers of teleosts (order: liver>gills≥intestines>white muscle) and the gills of elasmobranchs (order: gills>liver>white muscle>intestines). Rainbow trout accumulated more silver than the other teleosts, and were the only species to suffer significant mortality, effects likely associated with added salinity stress. Accumulations were fairly uniform amongst the other teleosts. Similar concentrations in gills and intestines suggested that both branchial and intestinal uptake occurred, with the latter potentially dominant; indeed sole exhibited no silver build-up in the gills. The two elasmobranchs exhibited no silver build-up in intestines but much higher levels in gills, indicating that in the absence of drinking, only branchial uptake occurs. Nevertheless, based on whole liver content, the elasmobranchs accumulated silver 5–15-fold faster than the three teleosts. Over 21-day exposures (1.5–50.0 μg/l Ag) in sculpin, salinity markedly affected silver accumulation, with tissue-specific levels approximately 6-fold higher at 18, than at 30 ppt. However, there was negligible effect of salinity on silver accumulation during 48 h at 250 μg/l Ag. Silver bioaccumulation appears to be markedly affected by speciation. At lower salinities, or higher [Ag], a neutral charged AgCl aq complex exists in the water, allowing for increased bioaccumulation to occur. At higher salinity, only less bioavailable, negatively-charged AgCl n 1− n complexes are present (AgCl 2 −, AgCl 3 2−, AgCl 4 3−).

Spectral Investigation of Stability of the Peroxo Complexes M2[V2O2(O2)4H2O] . aq (M = N(CH3)4, N(C4H9)4) in Solutions

Infrared spectra of solutions of M2[V2O2(O2)4H2O] . aq (M = N(CH3)4, N(C4H9)4) in heavy water and acetonitrile indicate that in concentrated solutions (c >= 0.5 mol dm-3) the asymmetric structure of the [V2O2(O2)4H2O]2- anion remains preserved for some time. Electronic spectra suggest that in more dilute solutions (c = 10-3-10-4 mol dm-3) of the M2[V2O2(O2)4H2O] . aq complexes in water and acetonitrile the dinuclear ion decomposes faster to [VO(O2)2H2O]-, followed by a relatively slow liberation of the peroxidic oxygen and formation of vanadate ions. The dinuclear complex is more stable in dilute chloroform solutions. The 51V NMR spectrum of an aqueous solution of [N(CH3)4]2[V2O2(O2)4H2O] (c = 1.3 mol dm-3) taken after a partial decomposition suggests the simultaneous presence of [V2O2(O2)4H2O]2-, [VO(O2)2H2O]-, (VnO3n)n- (n = 4, 5, 6), [HmV10O28](6-m)-, and other unidentified species.

Fe(II)‐substituted horse liver alcohol dehydrogenase, a model for non‐heme iron enzymes

The catalytic Zn(II) ion of horse liver alcohol dehydrogenase (EE isozyme) was replaced by Fe(II), providing a novel iron protein with the unusual coordination of Fe(II) to two cysteines residues, one histine residue and water. The electronic structure of iron in this system was characterized by Mössbauer spectroscopy at various temperatures as well as applied magnetic fields and analysed in terms of the spin Hamiltonian formalism. The novelty we found is an unusually weak spin coupling (/J/ less than 0.1 cm-1) of a paramagnet (S = 1) with iron (S = 2). From EPR and biochemical studies we conclude that the corresponding chemical species is triplet oxygen (O2). The quantitative determination of the coupling energy was possible utilizing the competition between Zeemann interaction and spin coupling at weak magnetic fields and low temperature. Oxidation experiments followed by Mössbauer spectroscopy showed that the spin-coupled system is an outer-sphere Fe(II) . (O2)aq complex occurring as an intermediate during a Fe(II)-catalyzed dioxygen activation. We observed two additional Fe(II) species after treatment with O2 and dithionite. The spin Hamiltonian parameters of iron in the coupled system are presented. The results are compared with those of iron in other non-heme iron proteins.

Complexation of bases and phosphates of nucleic acid components by transition metal ions

Complexation of transition metal ions, Mn(II), Co(II) and Ni(II), by nucleic acid components (bases, nucleosides and nucleotides) has been studied by various polarographic methods (dc, NP, DP and ac). The Ni(II) electroreduction process was investigated in detail due to the unique effect of splitting of polarographic waves or peaks, which was attributed to the reduction of (Ni 2+-base) aq complexes and hydrated nickel ion Ni aq 2+. The following order of stability constants of (Ni 2+-base) aq complexes was observed for the bases in nucleosides: guanine > 5-methylcytosine ∼ adenine > cytosine ∼ 5-methyluracil. Complexation of Ni(II) by phosphate groups does not lead to splitting of the Ni(II) electroreduction waves or peaks, thus enabling a distinction between complexation of bases and phosphate groups in nucleotides. Complexation of the base and phosphate group in cytosine-containing nucleotide is similar but a much stronger complexation of the base was found in guanine nucleotide, thus confirming the order of (Ni 2+ -base) aq complexes derived from studies of nucleosides.

Complexation of bases and phosphates of nucleic acid components by transition metal ions

Complexation of transition metal ions, Mn(II), Co(II) and Ni(II), by nucleic acid components (bases, nucleosides and nucleotides) has been studied by various polarographic methods (dc, NP, DP and ac). The Ni(II) electroreduction process was investigated in detail due to the unique effect of splitting of polarographic waves or peaks, which was attributed to the reduction of (Ni 2+—base) aq complexes and hydrated nickel ion Ni 2+ aq. The following order of stability constants of (Ni 2+—base) aq complexes was observed for the bases in nucleosides: guanine > 5-methylcytosine ∼ adenine > cytosine ∼ 5-methyluracil. Complexation of Ni(II) by phosphate groups does not lead to splitting of the Ni(II) electroreduction waves or peaks, thus enabling a distinction between complexation of bases and phosphate groups in nucleotides. Complexation of the base and phosphate group in cytosine-containing nucleotide is similar but a much stronger complexation of the base was found in guanine nucleotide, thus confirming the order of (Ni 2+—base) aq complexes derived from studies of nucleosides.

Application of polarography to the study of complexation and stacking interactions of bases in the BZ helical transition of poly[d(GC)] and poly[d(G-m 5C)] induced by Ni(II) and Mn(II)

The complexation of polynucleotides, poly[d(GC)] and poly [d(G-m 5C)], by transition metal ions, Ni(II) and Mn(II), was studied by polarographic methods (dc and DP) at the conditions of the BZ helical transition of these polymers. In the case of Ni(II), the appearance of two peaks or waves corresponding to the reduction of (Ni 2+-base) aq complex and Ni 2+ aq, respectively, allows the monitoring of the complexation of the bases independently from the complexation of phosphate groups of polynucleotides. The changes in the stacking interactions of nucleic acid bases in nucleosides and dinucleotides in the presence of Ni(II) and Mn(II) were studied by ac polarography, as changes in “pits” or “wells” on double layer capacitance curves due to adsorption and association of bases on the electrode. Simultaneously, changes in complexation of these metal ions with the addition of nucleic acid components were monitored by DPP. The results were used to predict the stacking interactions in the B and Z form of poly[d(GC)] and [poly[d(G-m 5C)]. It was found that there exists a good correlation between the stacking pattern predicted from our ac polarographic data and that known from crystal structure data of these polynucleotides. The nature of the B to Z transition was explained as a change in stacking interactions between nucleic acid bases due to their complexation by transition metal ion. The proposed mechanism of the B to Z transition of polynucleotides resembles Calladine and Drew's explanation of the B to A transition based on the analysis of appropriate crystal structures.

Application of polarography to the study of complexation and stacking interactions of bases in the B–Z helical transition of poly[d(G–C)] and polyld(G-m 5 C)] induced by Ni(II) and Mn(II)

The complexation of polynucleotides, poly[d(G–C)] and poly [d(G-m 5 C)], by transition metal ions, Ni(II) and Mn(II), was studied by polarographic methods (dc and DP) at the conditions of the B–Z helical transition of these polymers. In the case of Ni(II), the appearance of two peaks or waves corresponding to the reduction of (Ni 2+-base) aq complex and Ni aq 2+, respectively, allows the monitoring of the complexation of the bases indepently from the complexation of phosphate groups of polynucleotides. The changes in the stacking interactions of nucleic acid bases in nucleosides and dinucleotides in the presence of Ni(II) and Mn(II) were studied by ac polarography, as changes in “pits” or “wells” on double layer capacitance curves due to adsorption and association of bases on the electrode. Simultaneously, changes in complexation of these metal ions with the addition of nucleic acid components were monitored by DPP. The results were used to predict the stacking interactions in the B and Z form of poly[d(G-C)] and poly[d(G-m 5 C)]. It was found that there exists a good correlation between the stacking pattern predicted from our ac polarographic data and that known from crystal structure data of these polynucleotides. The nature of the B to Z transition was explained as a change in stacking interactions between nucleic acid bases due to their complexation by transition metal ion. The proposed mechanism of the B to Z transition of polynucleotides resembles Calladine and Drew's explanation of the B to A transition based on the analysis of appropriate crystal structures.

Influence of an americium solid phase on americium concentrations in solutions

Americium-241 concentrations in solutions contacting contaminated sediments for up to 2 yr were measured as a function of pH. Steady-state concentrations were reached within a few days. The solubility-limited Am concentration was found to decrease approximately 10-fold with one unit increase in pH. The log equilibrium constant for the solubility of Am (soil) solid [Am (soil) + H + ⇌ Am (aq complex) +] was found to be −4.12. The predictions based upon thermodynamic data suggest that Am (aq complex) + is likely to be Am(OH) 2 +. Although the chemical formula of Am (soil) was not determined, it does not appear to be Am(OH) 3(a). Published data on sorption coefficients of Am by different rocks, soils, and minerals were critically evaluated. Final Am solution concentrations calculated from the sorption coefficients of a variety of earth materials with several solutions agreed well with the concentrations predicted from the solubility of Am (soil) solid, indicating that the sorption coefficient data are controlled by Am precipitation.

SO2 oxidation in aqueous solutions of Cu(II)

Kinetic studies of SO2 oxidation by Cu(II) complexes in aqueous solutions containing halide ions X(X=Cl−, Br− and I−) indicate that the highest activity is observed for mixed chloro-iodo complexes of Cu(II). A reaction mechanism is suggested where the principal role is assigned to CuX 4 2− aq complexes and HSO3 radicals.