Acid Complexes In Solution Research Articles

Metal coating combining metal-ethylenediaminetetraacetic acid complex solutions and high-heat treatment via hydrogen/oxygen coupled flame

Metal coating combining metal-ethylenediaminetetraacetic acid complex solutions and high-heat treatment via hydrogen/oxygen coupled flame

Tetraaza macrocyclic complexes of Cu(II), Co(III) and Ni(II) derived from template condensation of 2,6-pyridinedicarbohydrazide and 2,6-diacetylpyridine: Stability investigation and coloring properties on plastics

Completely conjugated 14-membered ring hexaaza ligand complexes of Cu(II), Co(III) and Ni(II) were synthesized by the template cyclo-condensation reaction of 2,6-diacetylpyridine and 2,6-pyridinedicarbohydrazide: [Cu(HL)Cl]·1.35H2O (1), [Cu(HL)Br]·CH3OH (2), [Cu(L)(H2O)]·4H2O (3), [Co(HL)Cl2]·CH3OH (4), (H3O)[Co(H2L)Cl2][Co(HL)Cl2]Cl2·H2O (5), [Co(HL)(SCN)2]·CH3OH (6), [Ni(L)]·3H2O (7) and (H3O)[Ni(L)]Cl·H2O (8). The structure of all complexes derived from this novel diprotic macrocyclic ligand H2L (5,7-dimethyl-3,4,8,9-tetraaza-1,6(2,6)-dipyridinacyclodecaphane-4,7-diene-2,10-dione) were determined by single crystal X-ray diffraction method. The tetraaza 14-membered conjugated macrocycle is N4-tetracoordinated to metal, adopts an essentially planar configuration and forms four fused metallocycles rings, two five-membered and two six-membered chelates. The structures of the studied complexes reveal three isomers out of three possible: with a 5-6-5-6 order of alternation of metallocycles for 1–6, the 5-5-6-6 isomer in 8 and the coexistence of two different isomers with 5-5-6-6 and 6-6-5-5 alternation of metallocycles in 7. Based on the protonation state of the macrocyclic ligand, four forms of the ligand have been registered: bis-deprotonated L2− (compounds 3, 7 and 8), monodeprotonated HL− (1, 2 and 4), neutral H2L (5) and for compound 6 tautomeric (amide → imidic acid) HL− form. The organisation of crystal structures 1–8 depends on the nature of the metal and the composition of the solvents and outer-sphere ions, but shows clear common features for the same type of metal. The hydrolytic study demonstrated a high stability of the Co(III) and Ni(II) complexes in acidic solutions and the most thermally stable are the complexes 3 and 7 with the limit of 350 °C for Ni(II) complex. Testing of the coloring properties of the [Ni(L)] (8) complex on plastics indicates a high coloring efficiency, especially for polyamide polymers.

Metal-Fluoride Complex Stability Constant in Acid Solution as an Indicator to Identify the Corrosion Behavior of Metal Cations on Titanium

The Ti was immersed in 0.058 mol/L NaF containing 1.68 mol/L H2SO4 solution with different metal cations (Ca2+, Cu2+, Fe2+, Mg2+, Mn2+, Ni2+, Zn2+, Al3+, and Fe3+) for 7 d to identify the role of metal cations on corrosion behavior of titanium. To elucidate the role of metal cations on the corrosion behavior of Ti in acid solution, the standard electrode potential, E0, hardness of metal cations, X, and metal-fluoride complex stability constant, Kn, were chosen as the potential indicator. It is found that the mass loss fraction obtained from the immersion tests as a function of the metal-fluoride complex stability constant, Kn, has the highest correlation coefficient (0.92). The metal cations (Al3+ and Fe3+) with higher stability constant of the metal-fluoride complex in acid solution, (Kn > 3.27), show corrosion inhibition effect on Ti in acid solution. The Kn could be a suitable indicator to understand the role of metal cations on the Ti corrosion mechanism.

Science in a cup of coffee: A structural study of a trigonelline aqueous solution

Bioactive trigonelline is one of the important components of coffee, contributing to its characteristic undue bitterness. In this report we looked at the structure of an aqueous solution of trigonelline by means of Neutron Diffraction with Isotopic Substitution (NDIS). This experimental approach has been coupled with a Monte Carlo simulation to get an atom-level description of the solution. The rationale behind the present study is to investigate the solvent-solute and the solute-solute interactions; these have implications relevant also to other bioactive molecules and, in addition, can provide basic information on the extraction efficiency and on the solubility of important molecules in coffee. Results indicate a limited short-ranged involvement of the solute trigonelline with the water solvent and a not negligible clustering of trigonelline molecules. The investigated solution contains both positively charged and zwitterionic trigonelline, along with Cl− and H+, with this latter ion involved in hydronium ion formation. Here it is found that the observed structures are compatible with a Zundel-like cation, thus contributing to the still on-going debate on the presence of either Zundel or Eigen complexes in acidic solution. The role of a Zundel-like cation, along with its interaction with the chloride ion, might be related to the extraction and solubility of important molecules in coffee, in order to define the best water composition resulting in the best coffee.

Contrast variation SAXS: Sample preparation protocols, experimental procedures, and data analysis.

Proteins and nucleic acids, alone and in complex are among the essential building blocks of living organisms. Obtaining a molecular level understanding of their structures, and the changes that occur as they interact, is critical for expanding our knowledge of life processes or disease progression. Here, we motivate and describe an application of solution small angle X-ray scattering (SAXS) which provides valuable information about the structures, ensembles, compositions and dynamics of protein-nucleic acid complexes in solution, in equilibrium and time-resolved studies. Contrast variation (CV-) SAXS permits the visualization of the distinct molecular constituents (protein and/or nucleic acid) within a complex. CV-SAXS can be implemented in two modes. In the simplest, the protein within the complex is effectively rendered invisible by the addition of an inert contrast agent at an appropriate concentration. Under these conditions, the structure, or structural changes of only the nucleic acid component of the complex can be studied in detail. The second mode permits observation of both components of the complex: the protein and the nucleic acid. This approach requires the acquisition of SAXS profiles on the complex at different concentrations of a contrast agent. Here, we review CV-SAXS as applied to protein-nucleic acid complexes in both modes. We provide some theoretical framework for CV-SAXS but focus primarily on providing the necessary information required to implement a successful experiment including experimental design, sample quality assessment, and data analysis.

Sealing of near-surface voids on cement concretes by combined application of metal-ethylenediaminetetraacetic acid complex solutions and high-heat treatment via hydrogen/oxygen coupled flame

Near-surface voids on a cement concrete sample were successfully sealed by applying a metal-ethylenediaminetetraacetic (EDTA) acid complex solution, followed by treatment with high-heat hydrogen/oxygen (H2-O2) coupled flame. The calcium aluminates used for sealing were fabricated on cement substrates using calcium-aluminate (Ca,Al)-EDTA solutions prepared at various elemental ratios. The sealing effects were investigated through crystal & pore structure analysis and water permeability tests, using X-ray computed tomography (X-CT). Existence of the calcium aluminates were confirmed. From X-CT analysis, the average void diameter was changed from 16 μm to 10 μm with the calcium aluminate’s sealing. A sealing process model combining metal-EDTA complex solutions and high-heat treatment, intended for the surface sealing of cement concretes used in construction, was comprehensively proposed.

Characterization of Protein-Nucleic Acid Complexes by Size-Exclusion Chromatography Coupled with Light Scattering, Absorbance, and Refractive Index Detectors.

Size-exclusion chromatography (SEC) coupled with multiangle light scattering detection (SEC/MALS) enables determination of the molecular weight, oligomeric state, and stoichiometry of protein-nucleic acid complexes in solution. Often such complexes show anomalous behavior on SEC, thus presenting a challenge in determination of molecular weight and stoichiometry based solely on the elution position from SEC. In contrast to analytical ultracentrifugation, the SEC/MALS analysis is not affected by the shape of the complex. Here we describe the use of SEC/MALS for characterization of the stoichiometry of the complex between thereverse transcriptase (RT) domain from group II intron-maturase from Eubacterium rectale and intron RNA, and for monitoring protein dimerization that is driven by interaction between single-stranded DNA upstream of the P1 promoter, known as FUSE and FUSE binding protein-interacting repressor (FIR).

A novel acid-responsive HNTs-based corrosion inhibitor for protection of carbon steel

In this work, a novel Cu-BTA-Na2MoO4-HNTs corrosion inhibitor was reported by loading Na2MoO4 and benzotriazole (BTA) into halloysite nanotubes (HNTs), followed by incorporated insoluble Cu-BTA complex stoppers at the end of tubes through the interaction between BTA and Cu2+. For Cu-BTA-Na2MoO4-HNTs, BTA can not only participate in the stoppers preparation of Cu-BTA complex extending the release time of Na2MoO4, but also act as another corrosion inhibitor similar with Na2MoO4. Very importantly, the obtained Cu-BTA-Na2MoO4-HNTs is also responsive to acid medium, owing to the decomposition of the insoluble Cu-BTA complex in acid solution. In addition, the Q235 steel in 3.5% NaCl + 1.0 g/L Cu-BTA-Na2MoO4-HNTs shows higher inhibition efficiency than Q235 steel in 3.5% NaCl, such as the inhibition efficiency can be improved to 60.39% at 48 h by the synergistic effect between Na2MoO4 and BTA. Therefore, Cu-BTA-Na2MoO4-HNTs is a promising efficient and acid-response corrosion inhibitor for carbon steel.

Dynamic light scattering and electrophoretic mobility studies of starch-fatty acid complexes in solution

Electrophoretic mobility and dynamic light scattering measurements were carried out to investigate the physical characteristics of amylose inclusion complexes with a series of long chain fatty acids, in alkaline solution (0.1 N or 0.01 N KOH). Amylose molecules exhibited lower values of electrophoretic mobility compared to those of the amylose-fatty acid complexes. The presence of amylopectin affected the electrophoretic mobility of starch–fatty acid complexes. Particle size distribution measurements of amylose-fatty acid complexes in aqueous suspension (pH 4.6) were performed employing the laser light scattering technique. The size of the diameter of the complexes in alkaline solution was found to be much smaller than that of the size of the complexes in aqueous suspension. The results are discussed in the light of solvent contribution to the conformational changes of the complexes occurred in the environments employed.

Intrinsic37/35Cl and18/16O isotope shifts in195Pt and103Rh NMR of purely inorganic Pt and Rh complexes as unique spectroscopic fingerprints for unambiguous assignment of structure

Well-resolved intrinsic 1ΔM(37/35Cl) and 1ΔM(18/16O) isotope shifts (where M = 195Pt or 103Rh) are visible in the 195Pt NMR peak profiles of relatively kinetically inert [PtCln(H2O)6-n]4-n (n = 1-6) complexes, their corresponding hydroxido [PtCl6-n(OH)n]2- (n = 1-5/6) anions, and [RhCln(H2O)6-n]3-n (n = 3-6) complexes in aqueous solutions at ca. 293 K. Although some such isotope effects have been previously reported, there are very limited published data in the open literature, and the first systematic studies of such intrinsic 1ΔM(37/35Cl) and 1ΔM(18/16O) isotope effects are reviewed in this perspective. In high magnetic-field NMR spectrometers, the 195Pt and 103Rh NMR peak profiles acquired within a relatively narrow temperature range (288-300 K) constitute unique 'spectroscopic fingerprints', which allow unambiguous structural assignment in solution. Available data for Pt(iv) and Rh(iii) complexes give rise to intrinsic isotope 1Δδ195Pt/103Rh(37/35Cl) profiles, which are extraordinarily sensitive to the structure of a particular complex or its geometric isomer. The profiles of aquated Pt(iv) and Rh(iii) complexes in acidic solutions may be resolved at either an isotopologue level only or at both an isotopologue and an isotopomer level depending on the structure. By contrast, in the series of [PtCl6-n(OH)n]2- (n = 1-6) anions, 1Δδ195Pt(37/35Cl) isotope shifts are resolved only at an isotopologue level. Relatively larger 1Δ195Pt(18/16O) isotope shifts obtained by the partial 18O enrichment of both the [PtCln(H2O)6-n]4-n (n = 1-6) and [PtCl6-n(OH)n]2- (n = 1-6) series give rise to remarkable 195Pt NMR peak profiles showing both 37/35Cl and 18/16O shifts. In the [PtCl6-n(OH)n]2- (n = 1-5/6) anions a typical NMR peak profile spanning ∼2 ppm only may be resolved at both the isotopologue and isotopomer levels, depending on whether 18/16OH- ions are coordinated trans to chloride ions or not. The potential utility of such 1Δ195Pt(37/35Cl) and 1Δ195Pt(18/16O) isotope shifts in selected practical applications involving such complexes is briefly illustrated.

Protolytic dissociation mechanisms and comparative acid stabilities of palladium(II), zinc(II), copper(II), and nickel(II) complexes of alkylated dipyrrins

Complexes of Pd(II), Cu(II), Ni(II), and Zn(II) with alkylated dipyrrins (Hdpm) were synthesized and characterized by physicochemical and spectroscopic methods. Protolytic dissociation kinetics of these complexes in benzene in the presence of acetic and trichloroacetic acid was studied. A protonated dipyrrin is the reaction product of protolytic dissociation of the complexes in acid solutions. The observed and true dissociation rate constants, as well as activation reaction parameters, were calculated. Kinetic models of the processes are proposed, and the patterns of influence of the ligand nature on dissociation kinetics were determined. The Pd(II) complexes proved to be much more stable than other those of the other metals, according to the results of the kinetic studies. The lability of the complexes strongly depends on the length and position of the alkyl substituent of the ligand. The dissociation of the Ni(II) complex gives a heteroligand complex at low concentrations of acid, but the complex undergoes full protolytic dissociation at higher concentrations of acid. The dissociation of the complex of Cu(II) is an equilibrium process, involving formation of the protonated form of the ligand.

Study of structural and dynamic characteristics of copper(II) amino acid complexes in solutions by combined EPR and NMR relaxation methods.

Structural features and dynamical behaviour of the copper(ii) bis-complexes with glycine, d-alanine, d-valine, l-serine, l-aspartic acid, l-glutamic acid, l-lysine, l-proline, and sarcosine were studied by combined EPR and NMR relaxation methods. The cis and trans isomers were unambiguously assigned and characterized by EPR data. It was found that addition of a salt background has an influence on the cis-trans isomer equilibrium in favour of the formation of the cis isomer. By comparison of NMRD, DFT computations, and structural data it was shown that only one water molecule is coordinated in the axial position of these complexes. The increased exchange rates of this molecule found for Cu(l-Asp)2(2-), Cu(l-Glu)2(2-), Cu(l-LysH)2(2+), and Cu(l-Pro)2 were attributed to its pushing out by side chain groups of the ligands. By simulation of NMRD profiles an increase of lifetimes of the copper(ii) 2nd coordination sphere water molecules was revealed in the presence of additional carboxylic, alcoholic, or ammonium groups of the ligands, as well as the pyrrolidine ring of proline. The very short lifetimes of the 2nd coordination sphere water molecules (4-13 ps at 298 K) were explained in terms of the Frank-Wen structural model by the existence of cavities which draw in quickly enough water molecules from the 2nd coordination sphere.

Small-angle scattering contrast calculator for protein and nucleic acid complexes in solution

Small-angle neutron scattering (SANS) with contrast variation can provide useful information about the structure and disposition of two or more chemically distinct components within a complex. TheSASSIE Contrast Calculator(SCC) is a new software tool designed to assist in planning SANS experiments with contrast variation on protein and nucleic acid complexes. On the basis of the primary sequence and deuteration level of each protein or nucleic acid component, theSCCcalculates and plotsI(0), contrast and scattering length densities; since SANS experiments often complement small-angle X-ray scattering studies, the program provides both neutron and X-ray parameters. TheSCCis run as an integrated component ofSASSIE[Curtis, Raghunandan, Nanda & Krueger (2012).Comput. Phys. Commun.183, 382–389], a software suite for atomistic modeling of ensembles of structures consistent with scattering data.

Influence of Ligand Structure on the Hydrolysis and Stability of NAMI Derivatives Containing 2-Methyl imidazole andN-Ethyl imidazole

Two NAMI (new antitumor metastasis inhibitor; trans-[RuCl4(DMSO)(imidazole)]Na•2DMSO) derivatives, trans-[RuCl4(DMSO)(2-MeIm)Na•2DMSO (2-MeIm=2-methyl imidazole, Compd. 1) and trans-[RuCl4(DMSO)(N-EtIm)]Na•2DMSO (N-EtIm=N-ethyl imidazole, Compd. 2) were prepared. Their hydrolytic mechanism-kinetics in pH 7.40/5.00 buffer solution and stability in physiological condition were investigated by UV, cyclic voltammetry (CV) and NMR. Similar to NAMI, both compounds undergo two well separated steps chloro-hydrolysis in pH 7.40 buffer solution; while dimethyl sulfoxide (DMSO) hydrolyze in pH 5.00 acetic buffer solution. The kobs and t1/2 for each reaction were determined. In conclusion, the stability of the complex in acidic solution is much more stable. The stability of the complex formed by introducing ethyl group at N position of imidazole ring would be much better than that of complex formed by introducing methyl group at 2 position of imidazole. The NAMI-A (new antitumuor metastasis inhibitor, A: this is the first of a series; trans-[RuCl4(DMSO)(imidazole)][Himidazole]) derivatives are somewhat more No. 7 梁曜华等: 配体结构对含 2-甲基咪唑及 N-乙基咪唑的 NAMI 衍生物水解及溶液稳定性的影响 865 stable than the relative NAMI derivatives.

Electronic structure calculation study of metal complexes with a phytosiderophore mugineic acid

Structural and thermodynamic properties of biologically important metal–mugineic acid complexes have been studied from the theoretical side in order to understand the metal-chelating mechanism of phytosiderophore mugineic acid at an atomic level. Density-functional theory methods combined with the polarizable continuum model (PCM) have been employed to obtain free energies of complex formation and redox potentials for metal–mugineic acid complexes in solution. It has been found that the free energies of complex formation calculated at the B3LYP/PCM level of theory are in moderate agreement with available experimental results. The inclusion of explicit water molecules interacting with the carboxylic groups in deprotonated mugineic acid through strong hydrogen-bonds is found to further improve the calculated free energies of complex formation.

Structure of polymer–acid complexes in solution and crystal-solvate phases of rigid-rod heterocyclic polymer - poly(p-phenylene benzobisoxasole)

Investigations of the structures of the complexes formed by di-protonated oligomer molecules of poly (p-phenylene benzobisoxasole) (PBO) with charged and neutral molecules of orthophosphoric acid (OPA) by quantum-chemical and molecular mechanics methods are described. The complexes with partially compensated, fully compensated, and overcompensated PBO molecular charges as models of the polymer–acid complexes in solution and in crystal-solvate phases (Phase I and Phase II) are considered. It is shown that the structures with one anion associated with two heterocycles are most energetically favorable for the complexes with a partially compensated polycation charge. The polymer molecule bending resulting from this association can contribute to an enhanced PBO chain flexibility in solution. The PBO chains in Phase I are protonated due to the presence of neutral acid molecules. The protonated state of the PBO molecules in Phase II can be explained by the presence of excess anions.

Determination of hydroxamic acids by direct spectrophotometry of colored complex in acidic solution

An improved spectrophotometry of hydroxamic acids was evaluated. A synthetic aromatic hydroxamic acid for flotation was directly determined without any extraction in the solution of appropriate acidity. The introduction of ethanol made the process more stable. The characteristic absorption peak of the soluble complex at the wavelength of 525 nm was sensitive to being detected. The relationship between the absorbance and the concentration was in accordance with Lambert–Beer’s law in the range 0–120 mg/L, with a related coefficient of 0.9997. Compared with other determinations, this method considerably reduces the period and manipulation under the precondition of accuracy, so that it could be an available determination for hydroxamic acids.

Gas-phase IR spectra of intact α-helical coiled coil protein complexes

Electrospray ionization (ESI) is the softest ionization method that is currently available and it is widely accepted, that ESI generated ions of proteins and protein assemblies at certain conditions retain characteristic aspects of their solution-state conformation. ESI mass spectrometry (MS) therefore evolved as a useful tool to obtain information on composition, stoichiometry, and dynamics of non-covalently associated protein complexes. While tertiary structure information of proteins can be obtained from ion mobility spectrometry (IMS), only a few techniques yield direct information on the secondary structure of gas-phase peptides and proteins. We present here the mid-IR spectroscopic secondary structural analysis of three de novo designed α-helical coiled coil model peptides and their non-covalently associated complexes in the gas-phase. The conformational stability of such coiled coil peptides in solution is primarily driven by aggregation. Isolated monomers usually remain unfolded. Two of the investigated peptides were designed to assemble into stable α-helical complexes in acidic solution, while the third one remains monomeric and unfolded at these conditions. Monomer ions of all three peptides show comparable photodissociation IR spectra and therefore suggest an unfolded conformation in the gas phase. In contrast, considerable C O stretch (amide-I) and N–H bend (amide-II) band shifts have been observed for the dimers which is consistent with an elevated H-bond content. These findings provide evidence that at least a fraction of the condensed phase α-helical structure is retained in the gas-phase coiled coil complexes.

Simultaneous determination of Pt and Rh by catalytic adsorptive stripping voltammetry, using hexamethylene tetramine (HMTA) as complexing agent

Characteristics of the adsorption/electro-reduction of Pt/Rh hexamethylene tetramine (HMTA) complex on static mercury drop electrode surface were studied. Cyclic voltammetry was carried out to get the insight about the mechanistic behaviour of the catalytic current obtained in the voltammetric scan of Pt/Rh HMTA complex in acidic solution. Adsorptive stripping voltammetry using HMTA as the complexing agent was found to be highly sensitive method for the determination of Pt/Rh. Voltammetric measurements were carried out using hanging mercury drop electrode (HMDE) as the working electrode, a glassy carbon rod as the counter and an Ag/AgCl/KCl saturated as the reference electrode. Various electrochemical parameters like deposition potential, deposition time, concentration of the ligand, supporting electrolyte etc. were optimized. The detection limit of Pt and Rh was found to be 4.38 pML −1 and 2.80 pML −1, respectively for the deposition time of 30 s. Simultaneous determination of Pt(II) and Rh(III) in water samples was possible. The method was found to be free from the commonly occurring interfering ions such as Cu(II), Cd(II), Zn(II), Pb(II), Cr(III), Cr(VI), Fe(III), Fe(II), Ni(II) and Co(II). Spike recovery tests for both Pt and Rh in tap water and sea water samples were also carried out. The method has been verified by analyzing certified reference material (WMG-1).

Peculiarities of the Formation of Supramolecular Structures of Copper- and Lead-Humic Acid Complexes in Aqueous Solutions

Mechanisms are proposed for the formation of metal-humic acid complexes in solutions with a high content of heavy metal salts. Specific features of complex formation are considered with the reference to copper and lead.