Behaviours of trinitratonitrosyl complexes of ruthenium in dilute nitric acid solutions (author's transl)

This study aimed to elucidate the protolysis and condensation processes of the Ru complexes in relation to the concentration of nitric acid. The compositions of the dissociated and undissociated complexes were determined by the extraction with tributyl phosphate (TBP) and absorption spectroscopy in order to follow the rather rapid protolysis reaction of the complexes. The test solutions were prepared by dissolving the freshly obtained complexes into 0.50-0.001 M nitric acid solutions. The amounts of the undissociated complexes were determined at different elapses of time in the test solutions. The protolysis became significant when the concentration was below 0.15 M, and the dissociation rate suddenly increased at this concentration. At the concentrations above 0.2 M, the absorption peak of the complexes at 480 nm survived even after 144 hours. But below 0.15 M, the formation of dissociation products by protolysis was observed after the disappearance of the absorption peak. The amount of dissociation products rapidly increased after the preparation of the test solution as the concentration decreased below 0.15 M.     

Kinetic study of uranium speciation in model solutions and in natural waters using Competitive Ligand Exchange Method

Kinetic speciation of uranium in model solutions containing uranium and humic acid (HA) and in natural waters has been investigated by Competitive Ligand Exchange Method (CLEM). In alkaline freshwaters, most of uranium species were uranium-carbonate species, which were labile in the CLEM experiment. The uranium speciation of every sample was characterized either as “labile” or “non-labile” uranium complexes depending on the dissociation rate coefficients of the complexes. The results showed that as the U(VI)/HA ratio was decreased, the dissociation rate coefficients decreased and the labile fraction decreased as well. When the U(VI)/HA ratio was 0.1, the labile fraction of the U(VI)-HA increased with increasing pH; however, there was no pH effect on the dissociation of U(VI)-HA complexes at lower U(VI)/HA ratios. Chelex-100 had some limitations in its use for the study of dissociation of U(VI)-HA complex at very low U(VI)/HA ratios. By developing an analytical method and procedure for quantitative determination of kinetic parameters for the dissociation of uranium-HA complexes in model solutions and natural waters, this work has made a substantial contribution to analytical chemistry.     

Formation of unsaturated C3 hydrocarbons by the protolysis of magnesium sesquicarbide with ammonium halides

The protolysis of magnesium sesquicarbide, Mg2C3, with inorganic acids provides an interesting alternative to the more common hydrolysis of ionic carbides for obtaining their respective hydrocarbons. In particular, protolysis reactions with ammonium halides as precursors for hydrogen halides were investigated using in situ methods such as TGA/sDTA/MS and high-temperature XRPD. The protolysis reactions with NH4F and NH4Cl revealed two different reaction mechanisms yielding C3H4 and the respective magnesium halides as expected products. In the case of NH4Cl, intermediate phases that have not been previously observed, specificly (NH4)2MgCl4 (I4/mmm) and two modifications of NH4MgCl3 (P63/mmc), were structurally characterized.     

Spectrophotometric analysis of simultaneous protolysis equilibria

Simultaneous protolysis equilibria can be spectrophotometrically analysed easily by means of absorbance diagrams. The dissociation constants K(1) and K(2) can be determined directly from distinct points on the absorbance diagram by correlation with a photometric titration plot of absorbance vs. pH. Furthermore, from the absorbance diagram the ratio K (2)K (1) can be evaluated from the ratio of corresponding sides, and pH-measurement is not necessary. The titration systems of a mixture of 2-nitroso-l-naphthol-4-sulphonic acid with P-nitrophenol, and a mixture of P-nitrophenol with o-nitrophenol have been analysed by these methods, and are described as examples.     

Protolysegleichgewichte zwischen Aquo- und Hydroxohalogenokomplexen von Osmium(lV)

Equilibrium of Protolysis between Aquo- and Hydroxo-Halogeno Complexes of Osmium (IV) The equilibrium of protolysis between the monaquo complexes [OsCl₅(H₂O)]^?,[OsBr₅(H₂O)]^?, trans-[OsC1₄I(H₂0)]^?, cis-[0sC1₃I₂(H₂O)]^?, prepared by hydrolysis, and the corresponding monhydroxo complexes is studied by measurement of the absorption spectra as function of pH. The protolysis constants decrease as the trans-effect of the ligand opposite to the aquo group increases. The properties of the aquo and hydroxo complexes are described.     

Mechanism of action of anticancer titanocene derivatives: an insight from quantum chemical calculations

Titanocene derivatives exhibit high potential in the treatment of cisplatin-resistant tumor types. Density functional theory calculations were performed on the hydrated form of five drug candidates differing in the pendant arms attached to the aromatic rings. A qualitative correlation has been found between the experimentally measured anticancer activity of alkylammonium-functionalized titanocene derivatives and the computed free energy change of the proton-induced dissociation reaction of these compounds. The results indicate that differences in the cytotoxic activities could be related to the solvation properties of the protolysis products, whereas no correlation was found with gas-phase properties of these molecules. Contrary to the free energy change of the protolysis reaction, other molecular properties, such as the geometrical parameters or the binding energies of the cyclopentadienyl rings in solution, do not correlate with the in vitro cytotoxic activity of these drug candidates.     

Kinetic studies of nickel speciation in model solutions of a well-characterized humic acid using the competing ligand exchange method

Publications on the binding characteristics of metals with humic acid (HA) are sparse. Here we investigated the release of nickel from Ni(II)-HA complexes using model solutions of three different [Ni(II)]/[HA] mole ratios at three different pH values; we also compared the results with those of [Ni(II)]/[FA] complexes from previous work in this laboratory. Ligand exchange kinetics using the competing ligand exchange method (CLEM) were studied using two different techniques: graphite furnace atomic absorption spectrometry (GFAAS) with Chelex 100 resin as the competing ligand, and adsorptive cathodic stripping voltammetry (AdCSV) with dimethylglyoxime as the competing ligand to measure the rate of dissociation of Ni(II)-HA complexes. The results of the kinetic studies showed that as the [Ni(II)]/[HA] mole ratio was decreased, the rate of dissociation of Ni(II)-HA complexes decreased, and the proportion of free Ni²⁺ ions plus very labile nickel complexes decreased while the proportion of the less labile kinetically distinguishable components increased. Generally, the rate of dissociation of Ni(II)-HA complexes was slower than that of Ni(II)-FA complexes. Studies on the validity of the kinetic model showed that the concentrations of chemical species varied in a reasonable way with pH and the [Ni(II)]/[HA] mole ratios, indicating that the kinetically distinguishable components have chemical significance and the kinetic model is valid.     

Dynamic NMR properties of DOTA ligand: variable pH and temperature 1H NMR study on [K(HxDOTA)](3-x)- species

The (1)H NMR spectra of [H(x)DOTA]((4-x)-) species are reported as a function of pH and temperature in aqueous solution. The spectra show line broadening both in ligand proton signals and also in the water proton signal by titration with KOH solution. The formation of different [K(H(x)DOTA)]((3-x)-) complexes is found to be responsible for this behaviour. At high pH the usual fluxional motions, i.e. the ring inversion and the change in the acetate arms' helicity, which are also characteristic for other but inert metal-DOTA complexes, have been detected. However, because of the kinetic lability of K(+)-O and K(+)-N coordinative bonds a new type of rearrangement appears. This new motion requires breaking of coordinative bonds in the complex and can be described as a certain type of "ring slewing" around the ring C-C bonds. At low temperature (about 270 K) the ring slewing slows down and becomes negligible compared with the ring inversion and the change in the arms' helicity. These two latter processes have the same rate. When the temperature is higher (about 320 K) the ring slewing accelerates and its rate exceeds the rate of ring inversion. At this temperature the change in the acetate arms' helicity has the same rate as the ring slewing. Additionally, in the pH range 4-5 a slow intermolecular proton exchange process has been observed between the water and the dissociable protons of [K(H(x)DOTA)]((3-x)-). A water-assisted proton exchange mechanism is proposed on the basis of the activation parameters. This finding supports the previously suggested slow proton motion hypothesis for the formation of DOTA complexes.     

Host-guest complexation affected by pH and length of spacer for hydroxyazobenzene-modified cyclodextrins

Three modified beta-cyclodextrins appended with a hydroxyazobenzene as a dye unit, 1, 2, and 3, each incorporating a different length spacer between the beta-CD and the dye unit with a bis(propyl(oxyethylene)), butylene, and amide bond spacer, respectively, were synthesized in order to investigate their spectroscopic changes induced by pH and host-guest complexation as well as to investigate their conformations and guest-binding properties by means of absorption and induced circular dichroism spectroscopies in aqueous solutions. All hosts accommodated the dye unit in their own CD cavities with an orientation parallel to the CD axis, forming intramolecular complexes. When the pH of the solution changed, the structure changed in response to pH without conformational changes. Existing as the phenol form under acidic condition, they were converted to the yellow phenolate form by dissociation of a proton of the hydroxyl group in the dye unit with increasing pH (pK(a1); 7.62 for 1, 7.44 for 2, 8.00 for 3). Further increase in pH led to the dissociation of the ammonium proton in the secondary amine group in the spacer of 1 and 2 (pK(a2); 8.76 for 1, 8.67 for 2). Upon addition of 1-adamantanol (AN) as a guest, all hosts accommodated AN in their CD cavities, forming 1:1 host-guest inclusion complexes. The complexation phenomena were accompanied with changes in the conformation of the hosts, in which the dye units of 1 and 2 are excluded to outside of the cavity, but not for 3. The dye unit of 3 remained in the cavity, where the guest was also included partly. Therefore, the guest-binding abilities of 1 and 2 were larger than that of 3, which has poor binding ability. The binding constants of 1, 2, and 3 for AN are estimated to be 7400, 1940, and 140 M(-1) at pH 3.2, respectively. However, the guest-binding abilities of 1 and 2 were dependent on the pH of the solution. The ability of 1 under weak alkaline condition was stronger than under acidic or alkaline conditions, while that of 2 increased with increasing pH. Under the condition from neutral to weak alkaline media, 1 and 2 demonstrated color changes from colorless to yellow upon formation of inclusion complexes. When 1-adamantanecarboxylic acid (AC) was used as the charged guest, 1 and 2 bound to AC with a larger binding constant than AN. On the other hand, 1 and 2 bound to 1-adamantineamine (AA) with a smaller binding constant than AN. All these results demonstrate that the complexation phenomena depend on the pH of the solution as well as the length of the spacer of the hosts and that the electrostatic interaction between the host and the guest is also important for forming a stable complex.     

Accurate determination of low pK values by (1)H NMR titration

The NMR titration methodology to determine acid dissociation constants in aqueous solutions is extended for pK(a) values between 0 and 2, where potentiometric titrations are no longer applicable. (1)H NMR spectra are acquired for single samples of constant acid concentration (e.g. 0.02M), controlled ionic strength (I=1M with HNO(3)/NaNO(3)) and varying pH. To avoid biased pH readings due to the acid error of the glass electrode, true, concentration-based pH values are deduced by combination of the charge balance equation with information from (1)H NMR chemical shifts of the investigated acid. The method has been tested on histidine (pK(1)=1.83+/-0.02) and yielded the dissociation constant of dichloroacetic acid (pK=1.06+/-0.01) for the first time with good accuracy and precision. Dichloroacetic acid is recommended as an NMR spectroscopical "indicator molecule" for in situ monitoring the pH in strong acidic solutions of other equilibrium systems.     

Thermodynamic stability and acidic properties of platinum(II) and palladium(II) bromide complexes

The instability constants of the platinum(II) and palladium(II) bromide complexes have been determined by potentiometry. The thermodynamic stability has been found to depend on the geometric structure of the complex and the nature of the central atom. The acid dissociation constants of the aqua complexes have been determined from pH measurements of the equilibrated solutions.     

Gallium(III) complexes of DOTA and DOTA-monoamide: kinetic and thermodynamic studies

Given the practical advantages of the (68)Ga isotope in positron emission tomography applications, gallium complexes are gaining increasing importance in biomedical imaging. However, the strong tendency of Ga(3+) to hydrolyze and the slow formation and very high stability of macrocyclic complexes altogether render Ga(3+) coordination chemistry difficult and explain why stability and kinetic data on Ga(3+) complexes are rather scarce. Here we report solution and solid-state studies of Ga(3+) complexes formed with the macrocyclic ligand 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, (DOTA)(4-), and its mono(n-butylamide) derivative, (DO3AM(Bu))(3-). Thermodynamic stability constants, log K(GaDOTA) = 26.05 and log K(GaDO3AM(Bu)) = 24.64, were determined by out-of-cell pH-potentiometric titrations. Due to the very slow formation and dissociation of the complexes, equilibration times of up to ～4 weeks were necessary. The kinetics of complex dissociation were followed by (71)Ga NMR under both acidic and alkaline conditions. The GaDOTA complex is significantly more inert (τ(1/2) ～12.2 d at pH = 0 and τ(1/2) ～6.2 h at pH = 10) than the GaDO3AM(Bu) analogue (τ(1/2) ～2.7 d at pH = 0 and τ(1/2) ～0.7 h at pH = 10). Nevertheless, the kinetic inertness of both chelates is extremely high and approves the application of Ga(3+) complexes of such DOTA-like ligands in molecular imaging. The solid-state structure of the GaDOTA complex, crystallized from a strongly acidic solution (pH < 1), evidenced a diprotonated form with protons localized on the free carboxylate pendants.     

Effects of various competing ligands on the kinetics of trace metal complexes of Laurentian Fulvic Acid in model solutions and natural waters

The objective of this work was to study the effects of the following Ligands: Chelex-100, Dowex MAC-3 and Dowex 50WX-8 using Competing Ligand Exchange Method. This objective was achieved by investigating complex dissociation kinetics of trace metals: Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Mn(II) and Pb(II) of a well-characterized Laurentian Fulvic Acid (LFA) in model solutions and in a natural waters of Lake Heva (Québec, Canada). The effects of variation in the competing ligands (including their quantities) on the complex dissociation kinetics were quantitatively characterized by their first-order dissociation rate coefficients. The kinetic lability of the metal complexes varied with the metal-to-LFA ratio, as expected from the theory of metal complexes of the chemically and physically heterogeneous complexants, LFA. The general trend in the metal-binding by the above competing ligands was: Dowex 50WX-8 > Chelex-100 > Dowex MAC-3. However, no difference was found between the Dowex 50WX-8 and Chelex-100 for Cd(II), Zn(II), and Co(II). The results revealed the importance of the quantity of Chelex-100 as a competing ligand in the metal(II)-LFA complexation, on the dissociation kinetics of these complexes in model solutions. By developing Competing Ligand Exchange Method as an analytical technique, for studying the relative affinities of the above competing ligands for metals complexation in natural waters this work has made a substantial contribution to analytical chemistry.     

Anion exchange liquid chromatography--inductively coupled plasma-mass spectrometry detection of the Co2+, Cu2+, Fe3+ and Ni2+ complexes of mugineic and deoxymugineic acid

Phytosiderophores, such as mugineic and deoxymugineic acid, are produced by graminaceous plant species in response to Fe deficiency conditions normally experienced in calcareous and alkaline non-calcareous soils. As these phytosiderophores have the ability to form thermodynamically stable complexes with other metal cations present in the growing medium, they have also been implicated in the transport and bioavailability of these metals in the environment. However, routine analytical methodology to detect the various metal complexes formed by these phytosiderophores is lacking. Therefore, as these complexes are negatively charged over a wide range of pH values, anion exchange liquid chromatography (AE LC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS) was investigated as a means to separate and quantify these complexes. The metal-phytosiderophore complexes were prepared at pH 7 and separated by NaOH or NH4NO3 gradient elution on a Dionex AS11 anion exchange column. Of the metals tested only the Co2+ and Ni2+ complexes of mugineic and deoxymugineic acid were detected when using a 0-20mM NaOH gradient elution profile. However, the phytosiderophore complexes of Cu2+ and Fe3+ were also detected when using NH4NO3 as the mobile phase at pH 7. Base-assisted hydrolysis of the latter two complexes is proposed to explain their apparent 'instability' in the high pH NaOH mobile phase. The absolute detection limits of the developed methodologies for these metal complexes ranged from 0.1 to 2.8pmol. As phytosiderophore complexes with Cd2+ and Zn2+ were not detected, it was concluded that the dissociation kinetics of these metal-phytosiderophore complexes were too rapid for these complexes to be observed in the present chromatographic conditions.     

Fluorescence and viscometry study of complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide)

Interpolymer complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide) was studied by fluorescence spectroscopy and viscometry in dilute aqueous solutions. Changes in chain conformation and flexibility due to the interpolymer association are reflected in the intramolecular excimer fluorescence of pyrene groups covalently attached to the polymer chain. Both poly(acrylamide) and hydrolysed poly(acrylamide) form stable complexes with poly(acrylic acid) at low pH. The molecular weight of poly(acrylic acid) and solution properties such as pH and ionic strength were found to influence the stability and the structure of the complexes. In addition, the polymer solutions mixing time showed an effect on the mean stoichiometry of the complex. The intrinsic viscosity of the solutions of mixed polymers at low pH suggested a compact polymer structure for the complex.     

Effect of buffer,electric field,and separation time on detection of aptamer-ligand complexes for affinity probe capillary electrophoresis

The separation and detection of complexes of aptamers and protein targets by capillary electrophoresis (CE) with laser-induced fluorescence was examined. Aptamer-thrombin and aptamer-immunoglobulin E (IgE) were used as model systems. Phosphate, 3-(N-morpholino)propanesulfonic acid with phosphate, and tris(hydroxyamino)methane-glycine-potassium (TGK) buffer at pH 8.4 were tested as electrophoresis media. Buffer had a large effect with TGK providing the most stable complexes for both protein-aptamer complexes. Conditions that suppressed electroosmotic flow, such as addition of hydroxypropylmethylcellulose to the media or modification of the capillary inner wall with polyacrylamide, were found to prevent detection of complexes. The effect of separation time and electric field were evaluated by monitoring complexes with electric field varied from 150-2850 V/cm and effective column lengths of 3.5 and 7.0 cm. As expected, shorter times on the column greatly increased peak heights for the complexes due to a combination of less dilution by diffusion and less dissociation on the column. High fields were found to have a detrimental effect on detection of complexes. It is concluded that the best conditions for detection of noncovalent complexes involve use of the minimal column length and electric field necessary to achieve separation. The results will be of interest in developing affinity probe CE assays wherein aptamers are used as affinity ligands.     

Structural analysis of electrolyte solutions for rechargeable Mg batteries by stereoscopic means and DFT calculations

We present a rigorous analysis of unique, wide electrochemical window solutions for rechargeable magnesium batteries, based on aromatic ligands containing organometallic complexes. These solutions are comprised of the transmetalation reaction products of Ph(x)MgCl(2-x) and Ph(y)AlCl(3-y) in different proportions, in THF. In principle, these reactions involve the exchange of ligands between the magnesium and the aluminum based compounds, forming ionic species and neutral molecules, such as Mg(2)Cl(3)(+)·6THF, MgCl(2)·4THF, and Ph(y)AlCl(4-y)(-) (y = 0-4). The identification of the equilibrium species in the solutions is carried out by a combination of Raman spectroscopy, multinuclear NMR, and single-crystal XRD analyses. The association of the spectroscopic results with explicit identifiable species is supported by spectral analyses of specially synthesized reference compounds and DFT quantum-mechanical calculations. The correlation between the identified solution equilibrium species and the electrochemical anodic stability window is investigated. This study advances both development of new nonaqueous solution chemistry and possible development of high-energy density rechargeable Mg batteries.     

A Model for Simultaneous Homogeneous and Heterogeneous Nucleation in the Case of Slow Reaction Rate

(Gd(x)Y(1-x))(2)O(3):Eu [x=0, 0.25, 0.5, 0.75, 1.0] phosphor particles with 6 at.% Eu dopant of total concentration were prepared using spray pyrolysis. The effects of composition on the morphology, crystallinity, and photoluminescence characteristics of composite particles were investigated. The morphological control of (Gd(x)Y(1-x))(2)O(3):Eu particles in spray pyrolysis was also attempted by using colloidal and aqueous solutions. The particles prepared from colloidal solutions containing small amounts of Gd or Y hydroxy carbonate sol as seed material had spherical and filled morphology after the post-treatment at high temperature. On the other hand, the (Gd(x)Y(1-x))(2)O(3):Eu particles prepared from aqueous solutions were hollow and porous after post-treatment in all compositions. Particles prepared from colloidal solutions had photoluminescence emission intensities higher than those of particles prepared from aqueous solutions. Copyright 2000 Academic Press.     

多孔二元过渡金属纳米片阵列电极制备及电催化析氢研究

碱性电解液中,电解水析氢的H2O解离过程非常缓慢,造成析氢反应较高的过电位和Tafel效率。选择具有本征高析氢活性的合金催化剂与水解离中心-过渡金属氧化物复合,并进一步优化复合物形貌结构,被证明是解决这个科学问题的重要策略。本文报道一例新颖的二元过渡金属纳米片阵列自支撑电极（MoO3-x-MoNi4@NF）, 多孔MoO3-x纳米片阵列均匀生长在泡沫镍电极表面,纳米片表面镶嵌着MoNi4合金纳米颗粒,多孔的纳米片阵列使得催化剂具有高的比表面积（57 m2/g）和丰富的活性位点。在碱性电解液中（1 M KOH）,MoO3-x-MoNi4@NF仅需要过电位30mV就能达到10 mA cm-2电流密度,如此低的过电位超过了贵金属催化剂20% Pt/C (32 mV)。同时,MoO3-x-MoNi4@NF具有超低的Tafel斜率,仅为31 mV dec-1,如此低的Tafel斜率得益于Ni-Mo合金与MoO3-x之间的协同催化剂作用的发挥,MoO3-x可以有效促进H2O解离并释放Hads,MoNi4纳米颗粒作为Hads吸脱附位点可以促进H2生成,这使得该催化剂有望替代贵金属铂用作碱性电催化析氢领域。