Potentiometric pH Titrations Research Articles

Synthesis, crystal structures, spectroscopic, thermal analysis, electrochemical and solution studies of two new mixed metal coordination polymers based on dipicolinic acid and 3,4-diaminopyridine

Two new 2D heteronuclear coordination polymers with Ni(II), Zn(II) and Ca(II), namely {(dapH)2[CaM2(pydc)4(H2O)2]·2H2O}n (M=Ni (1) and M=Zn (2)) where [pydcH2=pyridine-2,6-dicarboxylic acid (dipicolinic acid), dap=3,4-diaminopyridine] have been synthesized and characterized by elemental analysis, infrared spectroscopy, thermal (TG/DTG/DTA) analysis, electrochemical as well as X-ray single crystal diffraction. The compounds 1 and 2 display isostructural features and crystallized in the monoclinic P21/n space group. Both of the compounds contain cationic and anionic fragments and two uncoordinated water molecules. In 1 and 2 (pydc)2− acts as tridentate ligands and connected to calcium ions through carboxylate bridging. Then each dipicolinate ligand bridges one calcium to a M(II) atom.The equilibrium constants of the binary, ternary and quaternary complexes of ligands or proton transfer system with metal ions in an aqueous solution were investigated by a potentiometric pH titration method.

Separation and Determination of Quinolone Antibacterials by Capillary Electrophoresis

The migration behavior and separation of 13 quinolone antibacterials were investigated by capillary electrophoresis (CE). In order to predict the electrophoretic mobility, the protonation macroconstants of all the compounds were determined by pH-potentiometric titrations. We proved that the electrophoretic mobility of ionized quinolones (QNs) can be described with Offord's equation, and the migration order depends on their charge-to-mass ratios. A buffer of 25 mM sodium tetraborate adjusted to pH 9.3 was an efficient electrophoresis system for the separation of 12 QNs by capillary zone electrophoresis. This method can be considered a general method to separate quinolone derivatives. Ciprofloxacin, norfloxacin and ofloxacin, fluoroquinoles with very similar structural characteristics, were separated by micellar electrokinetic chromatography. Validation parameters, including linearity and detection and quantification limits, were also determined. Our results prove the applicability of CE for the simultaneous determination of QNs from complex mixtures. Our methods are environment-friendly replacement and improvement of a common high-performance liquid chromatography determination with rapid analysis time without using any organic solvents.

Potentiometric and spectroscopic studies of three new mixed inorganic–organic hybrid materials based on Preyssler and Wells–Dawson heteropolyoxometalates containing proline, leucine, and asparagine

Three new organic–inorganic hybrid materials based on two important heteropolyoxometalates namely Preyssler (=K12.5H1.5[Na(H2O)P5W30O110]·35H2O) and Wells–Dawson (=K6[P2W18O62]·10H2O) anions, namely, (Hpro)9(Hleu)3K2[Na(H2O)P5W30O110]·25H2O (1), (Hpro)4(Hasp)[HP2W18O62]·20H2O (2), and (Hpro)11K3[Na(H2O)P5W30O110]·18H2O (3) where pro, leu, and asp are proline, leucine, and asparagine, respectively, were prepared and identified by elemental analysis, infrared and proton nuclear magnetic resonance spectroscopies, and thermogravimetric analysis. The hybrid materials are made up of positively charged amino acids, [Na(H2O)P5W30O110]14− and [P2W18O62]6− anions, and H2O molecules of crystallization. These constituents’ fragments held together into a three-dimensional supermolecular network through non-covalent interactions. The protonation constants of the amino acids used, and Preyssler and Wells–Dawson species in all possible protonated forms, the equilibrium constants for binary systems of proline–asparagine and proline–leucine, and the stoichiometry and stability constants of the corresponding binary and ternary hybrids with Preyssler and Wells–Dawson heteropolyoxometalates in aqueous solution were investigated by potentiometric pH titration method. The stoichiometries of the most hybrid species in solution were compared with the corresponding hybrids in the solid phase, in detail.

Competition of zinc(II) with cadmium(II) or mercury(II) in binding to a 12-mer peptide

Speciation of the complexes of zinc(II) with a dodecapeptide (Ac-SCPGDQGSDCSI-NH2), inspired by the metal binding domain of MerR metalloregulatory proteins, have been studied by pH-potentiometric titrations, UV, SRCD (synchrotron radiation circular dichroism) and 1H NMR experiments. (MerR is a family of transcriptional regulators the archetype of which is the Hg2+-responsive transcriptional repressor-activator MerR protein.) The aim of the ligand-design was to retain the advantageous metal binding features of MerR proteins in a model peptide for the efficient capture of toxic metal ions. The peptide binds zinc(II) via two deprotonated Cys-thiol groups and one of the Asp-carboxylates in the ZnL parent complex, possessing a remarkably high stability (logK=9.93). In spite of the relatively long peptide loop, bis-complexes are also formed with the metal ion under basic conditions. In a competition with cadmium(II) or mercury(II), zinc(II) cannot prevent the binding of toxic metal ions by the thiolate donor groups of the ligand. Around neutral pH one equivalent of mercury(II) was shown to fully replace zinc(II) from the ZnL species. Partial replacement of zinc(II) from the peptide by one equivalent of cadmium(II), relative to zinc(II) and the ligand, is also presumable, nevertheless, spectroscopic data may suggest the formation of mixed metal ion complexes, as well. Based on the obtained results the investigated dodecapeptide can be a promising candidate for capturing toxic metal ions in practical applications.

Extent of Intramolecular π Stacks in Aqueous Solution in Mixed‐Ligand Copper(II) Complexes Formed by Heteroaromatic Amines and 1‐[2‐(Phosphonomethoxy)ethyl]cytosine (PMEC), a Relative of Antivirally Active Acyclic Nucleotide Analogues (Part 72)[1, 2]

AbstractStability constants of the ternary Cu(Arm)(H;PMEC)+ and Cu(Arm)(PMEC) complexes {PMEC2– = dianion of 1‐[2‐(phosphonomethoxy)ethyl]cytosine, Arm = 2, 2′‐bipyridine (Bpy) or 1, 10‐phenanthroline (Phen)} were measured by potentiometric pH titrations (aq. sol.; 25 °C; I = 0.1 M, NaNO3) and compared with those of Cu(Arm)(H;PMEA)+ and Cu(Arm)(PMEA) {PMEA2– = dianion of 9‐[2‐(phosphonomethoxy)ethyl]adenine}, and related species. The basicity of the terminal phosphonate group is similar in PMEC2– and PMEA2–. Stability‐constant comparisons reveal, that in the monoprotonated ternary Cu(Arm)(H;PMEC)+ complexes H+ is at the phosphonate group, that the ether oxygen atom of the –CH2–O–CH2–P(O)–2(OH) residue participates, next to the P(O)–2(OH) group, in Cu(Arm)2+ coordination, and that π–π stacking between the aromatic rings of Cu(Arm)2+ and the pyrimidine moiety is important. The Cu(Arm)(PMEC) complexes are considerably more stable than the corresponding Cu(Arm)(R–PO3) species, where R–PO2–3 is a phosph(on)ate with a group R unable to interact intramolecularly. The stability enhancements are mainly attributed to intramolecular stacks and, to a smaller extent, to the formation of five‐membered chelates involving the ether oxygen atom of the –CH2–O–CH2–P(O)2–3 residue of PMEC2–. Analysis of the intramolecular equilibria reveals that ca. 10 % of the isomeric ternary complexes exist with Cu(Arm)2+ solely coordinated to the phosphonate group, ca. 25 % as a five‐membered chelate involving the ether oxygen, and ca. 65 % with an intramolecular π–π stack between the pyrimidine moiety of PMEC2– and the rings of Bpy or Phen. For a given Cu(Arm)2+ the stacking intensity increases from PMEC2– to PMEA2–. It seems feasible that the reduced stacking intensity of PMEC2–, together with a different hydrogen bonding pattern, leads to a different orientation of the cytosine residue (compared to the adenine moiety) in the active site of the nucleic acid polymerases, thus resulting in a reduced antiviral activity of PMEC compared to PMEA.

Solution and solid state studies of three new supramolecular compounds of zinc(II), nickel(II) and uranium(VI) with chelidamic acid and 9-aminoacridine

Three new supramolecular compounds, (aacrH)2[Zn(hypydc)2]·4H2O 1, (aacrH)2[UO2(hypydc)2]·2DMSO 2, and (aacrH)2[Ni(hypydc)2]·4H2O 3, [where hypydcH2=4-hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid), aacr=9-aminoacridine and DMSO=dimethyl sulfoxide] have been synthesized and characterized by elemental analysis, spectral (IR, UV–Vis, fluorescence), 1H NMR spectroscopy, thermal (TG/DTG/DTA) analysis and single crystal X-ray diffraction. All three compounds are proton transfer salts of the aminoacridinium cation and transition metal complex anions that crystallized from a solution of the dicarboxylic acid, aminoacridine, and metal nitrates as starting materials. The coordinating dicarboxylic acid is deprotonated at the carboxyl rather than the hydroxyl group, and the aminoacridine is selectively protonated at the pyridyl nitrogen but not at the amino group. In the crystal structures of 1–3 complex hydrogen bonding arrangements and π–π stacking play important roles. Water clusters (H2O)n [n=2–4] are formed in compounds 1 and 3. The complexes are strongly luminescent at room temperature, exhibiting a sharp emission at 400nm. The equilibrium constants of chelidamic acid (hypydc), 9-aminoacridine (aacr), proton transfer system as well as those of the complexes, were investigated by a potentiometric pH titration method.

Synthesis, X-ray crystal structure, and solution studies of two novel supramolecular coordination polymers of barium(II) and copper(II) based on chelidamic acid

Two homometal–organic coordination polymers, [Ba(C7H3NO5)2(H2O)4Ba(H2O)3]n·(2H2O)n and [[Cu(C7H2NO5)(C5H6N2)2]2Cu(C5H6N2)2(H2O)2]n·(6H2O)n, have been synthesized and characterized by X-ray single-crystal diffraction. In the barium compound (the first example of chelidamic acid introduced into the alkaline earth metal organic framework), two independent barium ions are coordinated by water and chelidamic acid molecules in monocapped and bicapped square anti-prismatic geometries. The two independent chelidamic acid molecules bridge several alkaline earth metal ions assembling a layered metal organic structure. In the copper compound, chelidamic acid shows its versatility as a ligand since it bridges three copper ions, with the carboxylate O atoms, the hydroxyl O atom, and the pyridine N atom coordinating the 3D metal ions. 4-Aminopyridine and water as ligands complete the coordinating sphere of the two independent Cu ions in distorted octahedral geometries. The equilibrium constants for the chelidamic acid-4-aminopyridine proton transfer system and the stoichiometry and stability of complexation of this system with Cu(II) and Ba(II) ions in aqueous solution were investigated by potentiometric pH titration method. The stoichiometry of some complex species in solution was found to be similar to the cited crystalline metal ion complexes.

Comparative study on MnII, NiII and CuII supramolecular complexes obtained from a proton transfer methodology: solid- and solution-state studies

In this study, the solution chemistry and solid-state structures of a novel proton transfer compound, (pipzH2)(pyc)2·H2O 1, and three metal–organic complexes of [Mn(pyc)2(H2O)2]2·2H2O 2, [Ni(pyc)2(H2O)2]·H2O 3 and [Cu(pyc)2H2O] n 4, (pyc = pyridine-2-carboxylate, pipz = piperazine) were investigated. On the basis of crystallographic data, each MII ion is coordinated to pyridine-2-carboxylate as bidentate ligand. Furthermore, these complexes form a three-dimensional structure by a variety of noncovalent interactions such as extensive O–H···O, O–H···N, N–H···O, N–H···N, C–H···O hydrogen bonds, C–H···π and C–O···π interactions. The equilibrium constants for the binary pyc-pipz proton transfer system, the stoichiometry and stability of complexation of this system with Mn2+, Ni2+ and Cu2+ ions in aqueous solution were investigated by potentiometric pH titration method. In each case, the stoichiometry of the dominant metal complex species in solution was compared with that obtained from the crystal structure.

Complex Bilding Behavior of 2 ((4-Methyl-5-Nitro-6- (Pyrolidine-1-yl)Pyrimidine-2-yl)Amino)Propionic Acid in Aqueous Solution

The acidity constants of MNPPAP1 were determined by potentiometric pH titration. The stability constants of the 1:1 complexes formed between M2+: Ca2+, Mg2+, Mn2+, Co2+, Ni2+, Cu2+ or Zn2+ and MNPPAP2-, were determined by potentiometric pH titration in aqueous solution (I =0.1 M, NaNO3, 25℃). The order of the stability constants was reported. It is shown that the stability of the binary M(MNPPAP) complexes is determined by the basicity of the carboxyl or amino group. All the stability constants reported in this work show the usual trend. The obtained order is Ca2+ 2+ > Mn2+ Co2+ Ni2+ Cu2+ > Zn2+. The observed stability order for MNPPAP follows approximately the Irving-Williams sequence. It is shown that regarding to M ion-binding properties vital differences on complex bilding were considered. It is demonstrated, that in M-MNPPAP complexes, M ion is coordinated to the carboxyl group, M ion is also able to bild macrochelate over pyrimidine group. The up mentioned results demonstrate that for M-MNPPAP complex the stability constants is also largely determined by the affinity of M2+ for carboxyl group. It is shown that MNPPAP can exert a direct influence on reaction mechanism through different kinds of metal ions and donor groups of MNPPAP.

Effect of surface site interactions on potentiometric titration of hematite (α-Fe2O3) crystal faces

Time dependent potentiometric pH titrations were used to study the effect of atomic scale surface structure on the protonation behavior of the structurally well-defined hematite/electrolyte interfaces. Our recently proposed thermodynamic model [1,25] was applied to measured acidimetric and alkalimetric titration hysteresis loops, collected from highly organized (001), (012), and (113) crystal face terminations using pH equilibration times ranging from 15 to 30min. Hysteresis loop areas indicate that (001) faces equilibrate faster than the (012) and (113) faces, consistent with the different expected ensembles of singly-, doubly-, and triply-coordinated surface sites on each face. Strongly non-linear hysteretic pH-potential relationships were found, with slopes exceeding Nernstian, collectively indicating that protonation and deprotonation is much more complex than embodied in present day surface complexation models. The asymmetrical shape of the acidimetric and alkalimetric titration branches were used to illustrate a proposed steric “leaky screen” repulsion/trapping interaction mechanism that stems from high affinity singly-coordinated sites electrostatically and sterically screening lower affinity doubly- and triply-coordinated sites. Our data indicate that site interaction is the dominant phenomenon defining surface potential accumulation behavior on single crystal faces of metal oxide minerals.

Lanthanide Complexes Based on a Diazapyridinophane Platform Containing Picolinate Pendants

A new macrocyclic ligand, N,N'-bis[(6-carboxy-2-pyridyl)methyl]-2,11-diaza[3.3](2,6)pyridinophane (H(2)BPDPA), was prepared, and its coordination properties toward the Ln(III) ions were investigated. The hydration numbers (q) obtained from luminescence lifetime measurements in aqueous solution of the Eu(III) and Tb(III) complexes indicate that they contain one inner-sphere water molecule. The structure of the complexes in solution has been investigated by (1)H and (13)C NMR spectroscopy, as well as by theoretical calculations performed at the density functional theory (B3LYP) level. The minimum-energy conformation calculated for the Yb(III) complex is in excellent agreement with the experimental structure in solution, as demonstrated by analysis of the Yb(III)-induced paramagnetic (1)H shifts. Nuclear magnetic relaxation dispersion (NMRD) profiles and (17)O NMR measurements recorded on solutions of the Gd(III) complex were used to determine the parameters governing the relaxivity. The results show that this system is endowed with a relatively fast water-exchange rate k(ex)(298) = 63 × 10(6) s(-1). Thermodynamic stability constants were determined by pH-potentiometric titration at 25 °C in 0.1 M KCl. The stability constants, which fall within the range logK(LnL) = 12.5-14.2, point to a relatively low stability of the complexes primarily as a consequence of the low basicity of the ligand.

Coordinating properties of uridine 5′-monophosphate with selected Ln3+ ions in ionic micellar media

Coordinating properties of uridine 5'-monophosphate (UMP) towards trivalent La, Pr, Nd, Sm, Eu and Gd ions in presence of cationic and anionic micelles have been investigated by potentiometric pH-titration and spectroscopic methods. Stability constants of the 2:1 complexes have been determined and the change in free energy, enthalpy and entropy associated with the complexation are also calculated. Nd(III) complexes isolated from aqueous and aqueous-micellar media do not show any significant structural difference. Formation of Ln(III) complexes in all cases completes below pH 7.5 showing that UMP best interacts with Ln(3+) ions at the physiological pH range 7.3-7.5. The nucleobase is not involved in the complexation and the metal ion coordination of UMP is through the phosphate moiety only. Coordinating tendency of UMP with lanthanides, Nd(III) ion in particular, at different pH is also discussed. Luminescent properties of Eu(III) complex and its decay lifetime are also presented. This information may prove helpful regarding the use of lanthanides as biological probes for calcium/magnesium ions.

Synthesis and AcidBase Properties of an Imidazole‐Containing Nucleotide Analog, 1‐(2′‐Deoxy‐β‐D‐ribofuranosyl)imidazole 5′‐Monophosphate (dImMP2−)

Deletion of the substituted pyrimidine ring in purine-2'-deoxynucleoside 5'-monophosphates leads to the artificial nucleotide analog dImMP(2-). This analog can be incorporated into DNA to yield, upon addition of Ag(+) ions, a molecular wire. Here, we measured the acidity constants of H(2)(dImMP)(±) having one proton at N(3) and one at the PO(3)(2-) group by potentiometric pH titrations in aqueous solution. The micro acidity constants show that N(3) is somewhat more basic than PO(3)(2-) and, consequently, the (H·dImMP)(-) tautomer with the proton at N(3) dominates to ca. 75%. The calculated micro acidity constants are confirmed by (31)P- and (1)H-NMR chemical shifts. The assembled data allow many quantitative comparisons, e.g., the N(3)-protonated and thus positively charged imidazole residue facilitates deprotonation of the P(O)(2)(OH)(-) group by 0.3 pK units. Information on the intrinsic site basicities also allows predictions about metal-ion binding; e.g., Mg(2+) and Mn(2+) will primarily coordinate to the phosphate group, whereas Ni(2+) and Cu(2+) will preferably bind to N(3). Macrochelate formation for these metal ions is also predicted. The micro acidity constant for N(3)H(+) deprotonation in the (H·dImMP·H)(±) species (pk(a) 6.46) and the M(n+)-binding properties are of relevance for understanding the behavior of dImMP units present in DNA hairpins and metalated duplexes.

Extent of Intramolecular π‐Stacks in Aqueous Solution in Mixed‐Ligand Copper(II) Complexes Formed by Heteroaromatic Amines and Several 2‐Aminopurine Derivatives of the Antivirally Active Nucleotide Analog 9‐[2‐(Phosphonomethoxy)ethyl]adenine (PMEA)

The acidity constants of twofold protonated, antivirally active, acyclic nucleoside phosphonates (ANPs), H(2)(PE)(±), where PE(2-)=9-[2-(phosphonomethoxy)ethyl]adenine (PMEA(2-)), 2-amino-9-[2-(phosphonomethoxy)ethyl]purine (PME2AP(2-)), 2,6-diamino-9-[2-(phosphonomethoxy)ethyl]purine (PMEDAP(2-)), or 2-amino-6-(dimethylamino)-9-[2-(phosphonomethoxy)ethyl]purine (PME(2A6DMAP)(2-)), as well as the stability constants of the corresponding ternary Cu(Arm)(H;PE)(+) and Cu(Arm)(PE) complexes, where Arm=2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen), are compared. The constants for the systems containing PE(2-)=PMEDAP(2-) and PME(2A6DMAP)(2-) have been determined now by potentiometric pH titrations in aqueous solution at I=0.1M (NaNO(3)) and 25°; the corresponding results for the other ANPs were taken from our earlier work. The basicity of the terminal phosphonate group is very similar for all the ANP(2-) species, whereas the addition of a second amino substituent at the pyrimidine ring of the purine moiety significantly increases the basicity of the N(1) site. Detailed stability-constant comparisons reveal that, in the monoprotonated ternary Cu(Arm)(H;PE)(+) complexes, the proton is at the phosphonate group, that the ether O-atom of the -CH(2)-O-CH(2)-P(O)(2)(-)(OH) residue participates, next to the P(O)(2)(-)(OH) group, to some extent in Cu(Arm)(2+) coordination, and that π-π stacking between the aromatic rings of Cu(Arm)(2+) and the purine moiety is rather important, especially for the H·PMEDAP(-) and H·PME(2A6DMAP)(-) ligands. There are indications that ternary Cu(Arm)(2+)-bridged stacks as well as unbridged (binary) stacks are formed. The ternary Cu(Arm)(PE) complexes are considerably more stable than the corresponding Cu(Arm)(R-PO(3)) species, where R-PO(3)(2-) represents a phosph(on)ate ligand with a group R that is unable to participate in any kind of intramolecular interaction within the complexes. The observed stability enhancements are mainly attributed to intramolecular-stack formation in the Cu(Arm)(PE) complexes and also, to a smaller extent, to the formation of five-membered chelates involving the ether O-atom present in the -CH(2)-O-CH(2)-PO(3)(2-) residue of the PE(2-) species. The quantitative analysis of the intramolecular equilibria involving three structurally different Cu(Arm)(PE) isomers shows that, e.g., ca. 1.5% of the Cu(phen)(PMEDAP) system exist with Cu(phen)(2+) solely coordinated to the phosphonate group, 4.5% as a five-membered chelate involving the ether O-atom of the -CH(2)-O-CH(2)-PO(3)(2-) residue, and 94% with an intramolecular π-π stack between the purine moiety of PMEDAP(2-) and the aromatic rings of phen. Comparison of the various formation degrees of the species formed reveals that, in the Cu(phen)(PE) complexes, intramolecular-stack formation is more pronounced than in the Cu(bpy)(PE) species. Within a given Cu(Arm)(2+) series the stacking intensity increases in the order PME2AP(2-) <PMEA(2-) <PMEDAP(2-) <PME(2A6DMAP)(2-). One could speculate that the reduced stacking intensity of PME2AP(2-), together with a different H-bonding pattern, could well lead to a different orientation of the 2-aminopurine moiety (compared to the adenine residue) in the active site of nucleic acid polymerases and thus be responsible for the reduced antiviral activity of PME2AP compared with that of PMEA and the other ANPs containing a 6-amino substituent.

Complex Bilding Behavior of L-Tryptophan and Related Amino Acids, a Comparative Investigation

The acidity constants of Tryptophan1 were determined by potentiometric pH titration. The stability constants of the 1:1 complexes formed between M2+: Ca2+, Mg2+, Mn2+, Co2+, Ni2+, Cu2+ or Zn2+ and Trp2−, were determined by potentiometric pH titration in aqueous solution (I = 0.1 M, NaNO3, 25°C). The order of the stability constants was reported. It is shown that the stability of the binary M(Trp) complexes is solely determined by the basicity of the carboxyl or amino group. All the stability constants reported in this work show the usual trend. The obtained order is Ca2+ Zn2+. The observed stability order for Tryptophan follows the Irving-Williams sequence. It is shown that regarding to M ion–binding properties vital differences on complex bilding were considered. It is demonstrated, that in M−Trp complexes, M ion is coordinated to the carboxyl group, M ion is also able to bild macrochelate over amino group. The up mentioned results demonstrate that for M−Trp complex the stability constants is also largely determined by the affinity of Cu2+ for amino group. It is shown that Trp can exert a direct influence on reaction mechanism through different kinds of metal ions and donor groups of Trp.

L-Tryptophan, a Study on Interactions in Cu(II) Binary and Ternary Complexes in Aqueous Solution

The acidity and stability constants of M(Trp)1 M: Cu2+, Cu(Bpy2)2+, and Cu(Phen3)2+ complexes, were determined by potentiometric pH titration. It is shown that the stability of the binary Cu(Trp) complexes is determined by the basicity of the carboxylate group on one side and amino group on the other side. It is demonstrated that the equilibrium, Cu(Har4)2+ + Cu(Trp) Cu(Har)(Trp) + Cu2+, is displacement due to the well known experience that mixed ligand complexes formed by a divalent 3d ion, a heteroaromatic N base and an O donor ligand possess increased stability. The other part of this displacement, which amount on average to an increased stability of the mixed ligand Cu(Bpy)(Trp) and Cu(Phen)(Trp) complexes of about 0.97 or 1.31 log unit. The stability constants of the 1:1 complexes formed between Cu2+, Cu(Bpy)2+ or Cu(Phen)2+ and Trp2−, were determined by potentiometric pH titration in aqueous solution (I = 0.1 M, NaNO3, 25℃). The order of the stability constants was reported.

Potentiometric Study of Complexation Between Three Oxime Derivatives and Some Metal Ions in Water-Dioxane Mixed Solvent

The complexation equilibria of oximes including 1-phenyl-2-(quinodin-2-yl) ethanoneoxime (pqeo), 2-acetophenone oxime (apo) and 3-nitro benzaldoxime (nbo) with some transition and heavy metal ions such as Cu 2+ , Co 2+ , Ni 2+ , Zn 2+ , UO 2 2+ and La 3+ were studied by potentiometric method in water-dioxane mixed solution. All of the titration steps were carried out at 25.0±0.1 uC and ionic strength (µ) of 0.1 M supported by KNO 3. The overall stability constants logof respective species were evaluated by computer refinement of the corresponding potentiometric pH titration data using BEST computer program. The corresponding distribution diagrams were depicted as a function of pH by using HySS2009 program. The most likely species were obtained from distribution diagrams and the effect of the oximes structures on the stability constant values were investigated.

New Approaches in Modeling Carbonate Alkalinity and Total Alkalinity

Alkaline measurements (carbonate alkalinity and total alkalinity) are of great importance in analyses of ocean, marine, lake and river waters, and other samples. Carbonate alkalinity (CA) refers to the cases in which only bicarbonate and carbonate species are considered. Total alkalinity (Alk) implies additional species having acid-base properties. Biochemical processes give rise to the organic alkalinity (OA) in natural waters. The value of these topics is obvious if we refer to the plethora of publications in this field. As a matter of fact, the approaches towards Alk provide ambiguous results and those for CA arouse some reservations as well. Having this in mind, a new approach for alkalinity determination, presented in recent review paper published in this journal (Crit. Rev. Anal. Chem. 2011, 41, 151), was developed in a more systematic and complete way, and new acronyms, TAL for total alkalinity and CAM for carbonate alkalinity, were introduced in that article. The methods proposed there and here are based on potentiometric pH titration, as the most common method applied for studying acid-base properties of humic substances (humic and fulvic acids). The parameters involved with CAM are resolved with the use of an Excel spreadsheet for the resolution of linear equations, whereas the parameters of a nonlinear regression equation referring to the TAL method are obtainable according to a more advanced, iterative computer program. A compact approach to CAM, based on the modified Gran II method, is carried out, but in a manner quite different and more thorough than the ones presented hitherto. Except for equivalence volumes, the CAM method enables evaluating the activity coefficient of hydrogen ions and values for (hybrid and concentration) dissociation constants of carbonic acid and ionic product of water. The possibilities and limitations of this method are tested by using a simulation procedure. The results obtained from simulated titrations provide the reference level related to error-free V and pH values at the points of titration curve ph = ph(V), ph = – log h, h – activity of hydrogen ions. The TAL model with Simms constants involved allows “homogenizing” the treatment of mono- and polyprotic acids and bases, especially those of undefined composition, i.e., carbonate species, fulvic acids, and their soluble complexes with metal ions. The TAL model may also be extended to the option where an approach based on a pre-dose addition is applied. pH and acid-base equilibria are very important topics and some aspects of them have been treated in this journal. Alkalinity determinations are of value in anaerobic digesters and anaerobic wastewater treatment, mine drainage and associated water, coastal seawater, marine aquaculture, estuarine water, and food and beverages, to point out a few recent examples.

Unusual Absence of Head-to-Tail Chains in the Crystal Structure of Glycyl-l-glutamyl-l-phosphoseryl-l-leucine

The structure of glycyl-l-glutamyl-l-phosphoseryl-l-leucine, (C16H29N4O11P)2·3H2O is reported. The dimeric structure is characterized by an unusual absence of head-to-tail chains in connection with an extended intermolecular hydrogen bonding network. Two of the three H2O molecules included in the network are disordered. The protonation constants of the tetrapeptide were determined as log K1 = 1.50, log K2 = 3.63, log K3 = 4.32, log K4 = 6.08 and log K5 = 8.65 by potentiometric pH titration. The dimeric structure of glycyl-l-glutamyl-l-phosphoseryl-l-leucine, (C16H29N4O11P)2·3H2O is characterized by the unusual absence of head-to-tail chains in connection with an extended intermolecular hydrogen bonding network.

Three new supramolecular compounds of copper (II), cobalt (II) and zirconium (IV) with pyridine-2,6-dicarboxylate and 3,4-diaminopyridine: Solid and solution states studies

Three new Cu(II), Co(II) and Zr(IV) compounds, [Cu(pydcH)(pydcH2)]·OH−·2H2O (1), (dapH2)[Co(pydc)2]·pydcH2·4H2O (2) and (dapH)2[Zr(pydc)3]·0.5H2O (3) [pydcH2=pyridine-2,6-dicarboxylic acid, dap=3,4-diaminopyridine] have been synthesized and characterized by elemental analysis, spectral (IR, UV–Vis), thermal (TG/DTG/DTA) analysis, electrochemical and X-ray single crystal diffraction. Compound 1 consists of a cationic complex and in 1 the acid is coordinated to metal ion in the neutral form, which is quite rare, whereas 2 and 3 are anionic complexes with dianionic ligands. In all the compounds, the acid is coordinated to the metal center in a tridentate fashion. The coordination polyhedron in 1 and 2 is a distorted octahedron, however for 3 it is a distorted tricapped trigonal prism. These compounds are stabilized in the solid state by a complicated network of hydrogen bonds between crystallization water molecules, anionic and cationic fragments, which form 3D-supramolecular arrays. Furthermore hydrogen bonds, π–π and C–O⋯π stacking interactions seem to be effective in stabilizing the crystal structures. The complexes and dap ligand were additionally tested for their antibacterial properties. The protonation constants of pydc and dap, the equilibrium constants for the pydc-dap proton transfer system, the stoichiometry and stability of complexation of this system with Co2+, Cu2+ and Zr4+ ions in aqueous solution were investigated by the potentiometric pH titration method. The stoichiometries of most of the complex species in solution were found to be very similar to the cited crystalline metal ion complexes.