Article

Revised Coordination Model and Stability Constants of Cu(II) Complexes of Tris Buffer

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Abstract

2-Amino-2-hydroxymethyl-propane-1,3-diol, or tris(hydroxymethyl)aminomethane (Tris), is probably the most common biochemical buffer used alone or in combination with other buffers because it is stable, unreactive, and compatible with most proteins and other biomolecules. Being nontoxic, it has even found applications in medicine. Tris is known, however, to coordinate transition metal ions, Cu(II) among them. Although often ignored, this feature affects interactions of Cu(II) ions with biomolecules, as Tris is usually used in high molar excess. Therefore, it is important to have precise knowledge on the stoichiometry, stability, and reactivity of cupric Tris complexes. The literature data are incoherent in this respect. We reinvestigated the complex formation in the Tris-Cu(II) system by potentiometry, UV-vis, ESI-MS, and EPR at a broad range of concentrations and ratios. We found, contrary to several previous papers, that the maximum stoichiometry of Tris to Cu(II) is 2 and at neutral pH, dimeric complexes are formed. The apparent affinity of Tris buffer for Cu(II), determined by the competitivity index (CI) approach [Krężel, A.; Wójcik, J.; Maciejczyk, M.; Bal, W. Chem. Commun. 2003, 6, 704-705] at pH 7.4 varies between 2 × 10(6) and 4 × 10(4) M(-1), depending on the Tris and Cu(II) concentrations and molar ratio.

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... 15 The use of such different supporting electrolytes may alter redox processes of Cu(II)-peptide complexes, especially when the stability complex studied is not sufficiently high to withstand the competition from a high molar excess of buffers which also can coordinate Cu(II) ions. 17 Moreover, some buffers commonly labeled as non-coordinating ones, e.g. HEPES in fact bind Cu(II) ions c Present Address: Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom. ...
... TRIS is known as a stable, nontoxic and unreactive buffer, compatible with most proteins, but it coordinates Cu(II) ions with a significant affinity, especially at a high excess. 17 The presented results revealed that TRIS also strongly influenced the redox process of the (Table I). The smallest change was observed for the strongest Cu(II)-AAH-am complex 19 since its formal potential shifted from 752 mV to 741 mV, and both oxidation and reduction peaks appeared. ...
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The present work describes the calculation of the binding constants from spectrofluorimetric data using simple graphical methods and specialized software implementing the maximum likelihood approach. The following popular cases are analyzed: 1) protein-small molecule; 2) protein-metal complex; 3) DNA-small molecule; 4) DNA-metal complex interactions. The inability of graphical plots to return the correct results except for the simplest situation (single reaction with a non-fluorescent product) is demonstrated. The possibility of determining the most probable stoichiometric model using the maximum likelihood estimation (LSQ as its special case) is discussed as well as the limitations.
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[Cu( phen ) 2 ] 2+ ( phen = 1,10‐phenanthroline) is the first and still one of most efficient artificial nucleases. In general, when the phen ligand is modified, the nucleolytic activity of its Cu(II) complex is significantly reduced. This is most likely due to higher steric bulk of such ligands and thus lower affinity to DNA. Cu(II) complexes with phen ligands having fluorinated substituents (F, CF 3 , SF 5 , SCF 3 ) surprisingly showed excellent DNA cleavage activity – in contrast to the unsubstituted [Cu( phen ) 2 ] 2+ – in the absence of the otherwise required external reducing agents. This nucleolytic activity correlates well with the half‐wave potentials E 1/2 of the complexes. Cancer cell studies show cytotoxic effects of all complexes with fluorinated ligands in the low µM range, whereas they were less toxic towards healthy cells (fibroblasts).
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Lanthanides such as cerium(III), europium(III), and gadolinium(III) are widely used for designing fluorescent probes or magnetic resonance imaging contrasting agents for biological systems. The synthesis and study of lanthanide complexes in buffer solutions imitating biological fluids are often complicated because of a lack of data on the lanthanide interactions with buffer solution components. Therefore, Ln(III) [where Ln(III) = La(III), Ce(III), Gd(III), Eu(III)] complexation with a widely used buffer agent, tris(hydroxymethyl)aminomethane (Tris), in aqueous solution is studied using potentiometry, spectrofluorimetry, and 139La NMR spectroscopy. The stoichiometric composition of complexes is determined using mass spectrometry. The thermodynamic stability constants of Ln(III)-Tris complexes are calculated from potentiometric and spectral data; the difficulties in the study of these systems, reliability, and accuracy of the obtained constants are discussed. The possible structures of free Tris and its complexes with lanthanides(III) are optimized on the density functional theory/PBE0 level; the peculiarities of metal-ligand bonds were studied by Quantum Theory Atoms in Molecules analysis.
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Easy access to radioiodinated and ²¹¹At-labelled bio(macro)molecules is essential to develop new strategies in nuclear imaging and targeted radionuclide therapy of cancers. Yet, the labelling of complex molecules with heavy radiohalogens is often poorly effective due to the multiple steps and intermediate purifications needed. Herein, we investigate the potential of arylboron chemistry as an alternative approach for the late stage labelling of antibodies. The reactivity of a model precursor, 4-chlorobenzeneboronic acid (1) with nucleophilic iodine-125 and astatine-211 was at first investigated in aqueous conditions. In the presence of a copper(II) catalyst and 1,10-phenanthroline, quantitative radiochemical yields (RCYs) were achieved within 30 minutes at room temperature. The optimum conditions were then applied to a CD138 targeting monoclonal antibody (mAb) that has previously been validated for imaging and therapy in a preclinical model of multiple myeloma. RCYs remained high (>80% for ¹²⁵I-labelling and >95% for ²¹¹At-labelling), and the whole procedure led to increased specific activities within less time in comparison with previously reported methods. Biodistribution study in mice indicated that targeting properties of the radiolabelled mAb were well preserved, leading to a high tumour uptake in a CD138 expressing tumour model. The possibility of divergent synthesis from a common modified carrier protein demonstrated herein opens facilitated perspectives in radiotheranostic applications with the radioiodine/²¹¹At pairs. Overall, the possibility to develop radiolabelling kits offered by this procedure should facilitate its translation to clinical applications.
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The interactions of divalent metal ions with several normal biological buffers, such as 2-(N-morpholino)ethane sulfonic acid (MES), 3-(N-morpholino)propane sulfonic acid (MOPS), 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid (HEPES), tris(hydroxymethyl)aminomethane (Tris) and N-[tris(hydroxymethyl)methyl]-2-aminoethanesulfonic acid (TES) have been investigated by using isothermal titration calorimetry (ITC) from the calorimetric perspective. MES at pH 6.0 does not form complexes with Zn²⁺, Cd²⁺, Ca²⁺, Co²⁺, Mg²⁺, Mn²⁺, and Ni²⁺, and shows imperceptible complexation ability to Cu²⁺ and Pb²⁺. MOPS and HEPES at pH 7.4 show no binding affinity to Ca²⁺, Co²⁺, Mg²⁺, Mn²⁺, and Ni²⁺, mild binding affinity towards Cu²⁺ and Pb²⁺, and weak binding affinity to Zn²⁺ and Cd²⁺. The metal complexation abilities of Tris are much stronger than MOPS or HEPES, especially towards Cu²⁺ and Pb²⁺. TES shows negligible binding affinity to Zn²⁺, Cd²⁺, Ca²⁺, Co²⁺, Mg²⁺, Mn²⁺, and Ni²⁺, and a moderate binding affinity towards Cu²⁺.
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Present contribution describes the UV-Vis study of the mixture of Cu(II) ions, pyridoxal 5'-phosphate nicotinoyl hydrazone and DNA. Neither free hydrazone nor its copper(II) complex interacts with DNA under the given concentration conditions. The changes in the UV-Vis spectra of the mixture containing metal complex and DNA are caused by partial dissociation of the coordination compound and complexation of the released Cu(II) ions with DNA. This result was obtained by the analysis of a number of the reactions that could occur in the solution of Cu(II) ions, buffer components (namely, Tris), ligand (hydrazone), and DNA.
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Metal ion interactions with weakly coordinating ligands, such as amino acids, are dependent on several factors, including metal ion availability, metal ion propensity for hydrolysis, ligand availability, and thermodynamic stability, as measured by stability constants. Metal ions in biological systems are often controlled by highly specific chaperone, transport, and storage proteins. Disruption in the homeostasis of redox active metal ions, such as Cu(I), Cu(II), Fe(II), and Fe(III), has been linked to increased oxidative damage and disease. Weakly binding ligands such as amino acids may play an active role in mitigating this metal-mediated damage, but a comprehensive understanding of the availability and thermodynamic likelihood of coordination must be understood to accurately predict complex formation in a competitive environment. This review presents an overview of amino acid stability constants with Cu(I), Cu(II), Fe(II), and Fe(III), the most common redox-active metal ions in biological systems. Specific attention is given to sulfur- and selenium-containing amino acids, since their interactions with Cu(I) and Fe(II) is of particular biological interest. This review also describes methods available for stability constant determination, with particular attention to specific difficulties encountered when working with weakly binding ligands and each of these four metal ions. Finally, the potential biological implications of these results are discussed based on reported stability constants as well as amino acid, copper, and iron bioavailability.
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(5-Hydroxy-6-methyl-4-{(E)-[2-oxo-2-(pyrazin-2-yl)ethyl]hydrazinylidenemethyl}pyridin-3-yl)- methyl phosphate has been synthesized via the interaction of pyridoxal-5-phosphate and pyrazin-2- carbohydrazide. Its stability constants in an aqueous solution at pH = 1.9, 6.6, 7.0, and 7.4 have been determined. The kinetics of formation and hydrolysis of the hydrazone has been studied, and rate constants of the direct and reverse reactions have been calculated from the electronic absorption spectroscopy data. The interaction of the obtained hydrazone and its Cu(II) complex with calf thymus DNA has been investigated.
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Four dicopper(II) complexes, [Cu 2 (¯-X)(bcmp)](ClO 4 ) 2 [X = OH (1a) and X = Cl (1b)], [Cu 2 (¯-OH)(Me 4 bcmp)]-(ClO 4 ) 2 (2), and [Cu 2 (bcc)](ClO 4 ) 3 (3), were synthesized with three p-cresol-derived ligands, 2,6-bis(1,4,7-triazacyclononyl-methyl)-4-meth-ylphenol (Hbcmp), 2,6-bis(1,4,7-triaza-4,7-dimethylcyclonon-ylmethyl)-4-methylphenol (HMe 4 bcmp), and 2,6-bis(1,4,7,10-tetrazacyclododecylmethyl)-4-methylphe-nol (Hbcc) to study hydrolytic DNA cleavage. Crystal structures of 1a, 1b, 2, and 3 were determined by X-ray analysis. The pH titrations and spectroscopic studies in the complex-ations of the ligands with copper(II) perchlorate revealed that the dicopper core structures of 1a, 2, and 3 in the solid state are kept at pH 59 in an aqueous solution. DNA binding abilities of 1a, 2, and 3 were examined by isothermal titration calorimetry (ITC). DNA cleavage studies were carried out by using supercoiled plasmid pUC19 DNA. 1a largely accelerated hydrolytic DNA cleavage at pH 56 but not at pH 78. This is the first example of pH-dependent DNA cleavage by a dicopper complex. Inhibition studies with specific DNA binders, 4¤,6-diamidino-2-phenylindole and methyl green, suggested that 1a accelerates the DNA cleavage via GC-specific binding. The mechanistic insights into the pH-dependent DNA cleavage are proposed on the basis of the crystal structures, structures in aqueous solutions, DNA binding modes, and DNA cleavage activities of 1a, 1b, 2, and 3.
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The specific interactions of Cu(2+) with self-complementary DNA sequences involving d[G4C4(GC)2G4C4], d[(GC)10], and d[(AT)10], as well as the chiral recognition mechanism of ofloxacin enantiomers via the Cu(II)-modulated DNAs, were investigated using characterizations of circular dichroism, gel electrophoresis, FT-IR spectroscopy, UV melting measurement, electron paramagnetic resonance, and HPLC. The Cu(II)-coordinated GC-rich DNAs exhibit amplified enantioselectivity toward the S-enantiomer of ofloxacin. Especially in the case of d[G4C4(GC)2G4C4], ofloxacin enantiomers intercalate into the two adjacent guanine bases through the minor groove mediated by Cu(2+), which leads to a more favorable binding between S-ofloxacin and DNA. The highest ee value of ofloxacin enantiomers in the permeate after being adsorbed by the Cu(II)-DNA complex is obtained as 49.2% in the R-enantiomer at the [Cu(2+)]/[base] molar ratio of 0.25, while at the [Cu(2+)]/[base] molar ratio of 0.05 the highest ee value of ofloxacin enantiomers in the retentate reaches 26.3% in the S-enantiomer. This work illustrates a novel promising route to construct DNA-based chiral selectors toward certain drug enantiomers through the programmable enantioselective recognition on the basis of DNA chirality and the specific binding of transition metal ions.
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The interaction of copper with tris(hydroxymethyl)aminomethane (TRIS) has been studied by optical and esr spectroscopic techniques. In solution, three different copper complexes are obtained as a function of pH. At pH 10 the room temperature esr parameters are g0 = 2.135, A0 = 82 G and nitrogen superhyperfine structure AN = 9.5 G, characteristic of two nitrogen ligands; at pH 6.5, g0 = 2.147, A0 = 65 G and at pH 5.0, g0 = 2.180, A0 = 44 G. The high pH complex was crystallized and its molecular structure determined by X-ray methods. Space group and cell dimensions are C2/c, a = 12.955(2) Å, b = 10.793(1) Å, c = 10.091(2) Å, β = 116.62(1)°, V = 1261.4(6) Å3, Z = 4, Dc = 1.694 g cm−3, R = 0.034 for938 reflections with I > 3σ(I). The Cu2+ ion is located on the two-fold axis and coordinated to the oxygen and nitrogen atoms of two TRIS moieties; these ligand atoms form the rectangular base of a pyramid structure in which oxygen from a water molecule acts as the fifth ligand.
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Background Copper is an essential catalytic co-factor for metabolically important cellular enzymes, such as cytochrome-c oxidase. Eukaryotic cells acquire copper through a copper transport protein and distribute intracellular copper using molecular chaperones. The copper chelator, neocuproine, inhibits Plasmodium falciparum ring-to-trophozoite transition in vitro, indicating a copper requirement for malaria parasite development. How the malaria parasite acquires or secretes copper still remains to be fully elucidated. Methods PlasmoDB was searched for sequences corresponding to candidate P. falciparum copper-requiring proteins. The amino terminal domain of a putative P. falciparum copper transport protein was cloned and expressed as a maltose binding fusion protein. The copper binding ability of this protein was examined. Copper transport protein-specific anti-peptide antibodies were generated in chickens and used to establish native protein localization in P. falciparum parasites by immunofluorescence microscopy. Results Six P. falciparum copper-requiring protein orthologs and a candidate P. falciparum copper transport protein (PF14_0369), containing characteristic copper transport protein features, were identified in PlasmoDB. The recombinant amino terminal domain of the transport protein bound reduced copper in vitro and within Escherichia coli cells during recombinant expression. Immunolocalization studies tracked the copper binding protein translocating from the erythrocyte plasma membrane in early ring stage to a parasite membrane as the parasites developed to schizonts. The protein appears to be a PEXEL-negative membrane protein. Conclusion Plasmodium falciparum parasites express a native protein with copper transporter characteristics that binds copper in vitro. Localization of the protein to the erythrocyte and parasite plasma membranes could provide a mechanism for the delivery of novel anti-malarial compounds.
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Unlabelled: The comparative study of the acid-base balance (ABB) parameters has been performed on 20 clinically healthy mature Małopolski horses. An arterial blood sample from the facial artery and a sample of venous blood from the external cervical vein were colected from each animal. In the samples tested, the blood pH, pCO2, tCO2, HCO3-, concentration of Na+, K+, Cl-, and a value of the anion gap were determined. The difference among pCO2, tCO2, and HCO3- in both samples tested was statistically significant, whereas the pH of the arterial blood and the pH of the venous blood did not differ significantly. The anion gap in both types of blood did not differ significantly. Conclusions: 1) ABB parameters such as pCO2, HCO3-, and tCO2 determined in the arterial and venous blood of the Małopolski horses differ from each other significantly. 2) In spite of the lack of the differences between pH of the arterial and venous blood, the ABB parameters in horses should be determined in the arterial blood, because the comparative study performed proves that the analysis of the ABB parameters determined for the venous blood of a healthy horse may lead to a wrong diagnosis of the compensated respiratory acidosis. 3) The mean value of anion gap in horses aged 8-12 years amounts to 20.9 mmol/l for the arterial blood and 19.93 for the venous blood; the difference between the two values is not statistically significant.
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The issue of the acid-base balance (ABB) parameters and their disorders in pets is rarely raised and analysed, though it affects almost 30% of veterinary clinics patients. Traditionally, ABB is described by the Henderson-Hasselbach equation, where blood pH is the resultant of HCO3- and pCO2 concentrations. Changes in blood pH caused by an original increase or decrease in pCO2 are called respiratory acidosis or alkalosis, respectively. Metabolic acidosis or alkalosis are characterized by an original increase or decrease in HCO3- concentration in the blood. When comparing concentration of main cations with this of main anions in the blood serum, the apparent absence of anions, i.e., anion gap (AG), is observed. The AG value is used in the diagnostics of metabolic acidosis. In 1980s Stewart noted, that the analysis of: pCO2, difference between concentrations of strong cations and anions in serum (SID) and total concentration of nonvolatile weak acids (Atot), provides a reliable insight into the body ABB. The Stewart model analyses relationships between pH change and movement of ions across membranes. Six basic types of ABB disorders are distinguished. Respiratory acidosis and alkalosis, strong ion acidosis, strong ion alkalosis, nonvolatile buffer ion acidosis and nonvolatile buffer ion alkalosis. The Stewart model provides the concept of strong ions gap (SIG), which is an apparent difference between concentrations of all strong cations and all strong anions. Its diagnostic value is greater than AG, because it includes concentration of albumin and phosphate. The therapy of ABB disorders consists, first of all, of diagnosis and treatment of the main disease. However, it is sometimes necessary to administer sodium bicarbonate (NaHCO3) or tromethamine (THAM).
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Visible-range circular dichroism titrations were used to study Cu(II) binding properties of Multimetal Binding Site (MBS) of Human Serum Albumin (HSA). The formation of ternary MBS-Cu(II)-Buffer complexes at pH 7.4 was positively verified for sodium phosphate, Tris, and Hepes, the three most common biochemical buffers. The phosphate > Hepes > Tris order of affinities, together with strong spectral changes induced specifically by Tris, indicates the presence of both Buffer-Cu(II) and Buffer-HSA interactions. All complexes are strong enough to yield a nearly 100% ternary complex formation in 0.5 mM HSA dissolved in 100 mM solutions of respective buffers. The effects of warfarin and ibuprofen, specific ligands of hydrophobic pockets I and II in HSA on the Cu(II) binding to MBS were also investigated. The effects of ibuprofen were negligible, but warfarin diminished the MBS affinity for Cu(II) by a factor of 20, as a result of indirect conformational effects. These results indicate that metal binding properties of MBS can be modulated directly and indirectly by small molecules.
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Fluorimetric Cu(ii) titrations of Alzheimer's disease (AD) Abeta40 peptide at various ammonium acetate concentrations demonstrated that ternary Cu(Abeta40)L complexes are formed with buffer components L, thereby providing a novel perspective on Cu(ii)-Abeta interactions.
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Evidence is growing to support a functional role for the prion protein (PrP) in copper metabolism. Copper ions appear to bind to the protein in a highly conserved octapeptide repeat region (sequence PHGGGWGQ) near the N terminus. To delineate the site and mode of binding of Cu(II) to the PrP, the copper-binding properties of peptides of varying lengths corresponding to 2-, 3-, and 4-octarepeat sequences have been probed by using various spectroscopic techniques. A two-octarepeat peptide binds a single Cu(II) ion with Kd approximately 6 microM whereas a four-octarepeat peptide cooperatively binds four Cu(II) ions. Circular dichroism spectra indicate a distinctive structuring of the octarepeat region on Cu(II) binding. Visible absorption, visible circular dichroism, and electron spin resonance spectra suggest that the coordination sphere of the copper is identical for 2, 3, or 4 octarepeats, consisting of a square-planar geometry with three nitrogen ligands and one oxygen ligand. Consistent with the pH dependence of Cu(II) binding, proton NMR spectroscopy indicates that the histidine residues in each octarepeat are coordinated to the Cu(II) ion. Our working model for the structure of the complex shows the histidine residues in successive octarepeats bridged between two copper ions, with both the Nepsilon2 and Ndelta1 imidazole nitrogen of each histidine residue coordinated and the remaining coordination sites occupied by a backbone amide nitrogen and a water molecule. This arrangement accounts for the cooperative nature of complex formation and for the apparent evolutionary requirement for four octarepeats in the PrP.
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The cellular prion protein is known to be a copper-binding protein. Despite the wide range of studies on the copper binding of PrP, there have been no studies to determine the affinity of the protein on both full-length prion protein and under physiological conditions. We have used two techniques, isothermal titration calorimetry and competitive metal capture analysis, to determine the affinity of copper for wild type mouse PrP and a series of mutants. High affinity copper binding by wild type PrP has been confirmed by the independent techniques indicating the presence of specific tight copper binding sites up to femtomolar affinity. Altogether, four high affinity binding sites of between femto- and nanomolar affinities are located within the octameric repeat region of the protein at physiological pH. A fifth copper binding site of lower affinity than those of the octameric repeat region has been detected in full-length protein. Binding to this site is modulated by the histidine at residue 111. Removal of the octameric repeats leads to the enhancement of affinity of this fifth site and a second binding site outside of the repeat region undetected in the wild type protein. High affinity copper binding allows PrP to compete effectively for copper in the extracellular milieu. The copper binding affinities of PrP have been compared with those of proteins of known function and are of magnitudes compatible with an extracellular copper buffer or an enzymatic function such as superoxide dismutase like activity.
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The formation of complex species between mercury(II), lead(II) and cadmium(II) and some β-amino-alcohols which are frequently employed as a pH buffer in biological studies is evidenced and discussed. The ligands considered are 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol and tris(hydroxymethyl)-aminomethane and differ from each other as regards the number of hydroxyl groups. From a comparison of the equilibrium data, while the coordination of lead(II) is to be only attributed to the amino group, the hydroxyl groups also seem to contribute to the coordination of cadmium(II). Equilibrium data related to mercury(II) systems could not be deduced from potentiometric measurements, owing to the high strength of the complexes formed.
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The synthesis of 2-amino-1,6-anhydro-2-deoxy-4-O-methyl-beta-D-mannopyranose (3) is described. Potentiometric and spectroscopic methods were used to evaluate the equilibria and the complex structures in systems containing Cu(II) ions and 3, and two other 1,6-anhydro derivatives. The results showed that no mannosamine derivative is able to form dimeric species found earlier for 1,6-anhydro-glucosamine ligands. The correlation between complex formation and sugar structure is discussed.
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The reactions of 2-amino-2(hydroxymethyl)-1,3-propanediol (TRIS, THAM) with H+, Ni2+, Cu2+, and Zn2+ ions have been studied at 298 K in aqueous solutions (0.15 mol dm−3 NaCl) using ptentiometric techniques. The protonation constant of the ligand and the formation constants of several metal complexes have been calculated with the aid of the program MIQUV. The equilibrium models are selected on the basis of a critical evaluation of the least squares results and of a statistical analysis of the wieghted residuals.
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The review describes the state of the art in the field of stability constant determination for Cu(II), Cu(I) and Zn(II) complexes of proteins and peptides involved in neurodegenerative diseases, α-synuclein (aS), prion protein (PrP), amyloid precursor protein (APP) and amyloid β peptides (Aβ). The methodologies and results are critically analyzed and recommendations are formulated about possible systematic errors in these studies. The possibility of formation of ternary complexes with titration competitors is discussed.
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Possible errors in the measurement of acid dissociation constants by potentiometric titration techniques have been considered, with particular references to nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA). Unknown junction potentials can arise when pH measurements are carried out using a glass electrode with saturated calomel reference electrode which have been previously calibrated with a standard buffer solution. The magnitude of the influence of these unknown potentials has been demonstrated and an experimental procedure recommended which gives meaningful results.
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Protonation and copper(II) co-ordination properties of amikacin (A) were studied in solution by potentiometry, and NMR, UV/VIS, CD and EPR spectroscopies. Mononuclear, tetragonal and five-co-ordinate complexes of stoichiometries ranging from Cu(H3A) to CuH–2A were found. The effects of amikacin on copper(II) binding by physiological copper(II) carriers, histidine and albumin, and facilitation of oxidation of 2′-deoxyguanosine by copper(II)–amikacin complexes were also investigated. The results indicate that complexation of CuII by amikacin should not be expected to affect copper(II) homeostasis in blood, but may contribute to the intracellular activity of the drug.
Article
Complex formation between Cu(II) and the amino sugars methylβ-L-daunosaminide (MeDauN), 6-amino-6-deoxy-D-glucose (Glc6N), 3-dimethylamino-3,4,6-trideoxy-D-xyloheksose (desosamine DSA), and methyl-3-amino-3-deoxy-α-D-mannopyranose (MeMan3N) was studied in aqueous solution by potentiometric and spectroscopic (EPR, electron absorption, and CD) techniques. The results show that Glc6N and DSA ligands, lacking the cis-oriented couples of [NH2, OH] donors, give rise only to dimeric complexes. The other two ligands, although both forming mononuclear species, exhibit different coordination abilities, depending on the assistance of donors able to yield axial interaction with the metal ion.
Article
A series of 4-aminobutanetriols and 5-aminopentanetetrols was synthesised and their co-ordination abilities towards copper(II) studied by potentiometry and spectroscopic techniques (UV/VIS, ESR and CD). The basic binding mode involves the amino nitrogen and the adjacent deprotonated hydroxyl group. The latter donor acts as a bridge between two metal ions giving stable dimeric species. No monomeric complexes were detected in the systems studied. The formation of the alkoxo-bridged complexes seems to be the most characteristic feature of the investigated ligands. Other hydroxyl donors are also involved in the metal-ion binding. The stability constants calculated from the pH-metric data showed that the chirality of the carbons in an aminoalcohol molecule may have a considerable effect on its co-ordination ability.
Article
The synthesis, optical, magnetic properties and X-ray crystal structure of [Cu(dmbipy)(OH)(CF3SO3)]2 (in which dmbipy=4,4′-dimethyl-2,2′-bipyridine) is described as a new dinuclear hydroxo bridged copper(II) compound with a Cu–O–Cu angle of 94.5(3)° and a strong ferromagnetic interaction having an exchange parameter J of 148 cm−1 (singlet above the triplet ground state). The Cu–O–Cu angle is the smallest observed so far for hydroxo-bridged compounds.
The stability constants of the 1 : 1 and 2 : 1 ligand–silver complexes of imidazole and tri(hydroxymethyl)methylamine have been determined from pH measurements at a glass electrode over the range 0–50° and 0–60°, respectively, at 10° intervals. A computer program, based on Schwarzenbach, Willi, and Bach's method for the evaluation of equilibrium constants, has been developed and used in the calculations. The program includes a statistical procedure whereby the most consistent values of the constants are selected. Some aspects of the program are discussed. The thermodynamic quantities for the formation of the complexes, together with their probable errors, have been calculated from the temperature coefficients of the stability constants.
Article
A series of diaminoalcohols (1,5-diaminotriols and 1,6-diaminotetrols) have been synthesised and their co-ordination abilities towards CuII studied by potentiometry and spectroscopic techniques (UV/VIS, EPR and CD). Both amino groups act as anchoring sites for two metal ions. Thus, two independent NH2, O– chelates are formed leading to dimeric complexes in which two metal ions are bound to two N-terminal atoms of the 1,5- or 1,6-diaminoalcohols. In all cases studied both ligand conformation and absolute configuration have a distinct impact on the stabilities of the complexes formed.
Article
For the formation of a complex of Cu2+ with the amyloid-β (Aβ) proxy N-α-dihydrourocanylhistamine (L) in unbuffered aqueous solution (pH 5.7, 25.0 °C), UV spectrophotometric measurements give a stability constant of 3.8 × 105 L mol–1. This stability constant is within the lower limit of the range of stability constants reported in the literature for complexes of Aβ with Cu2+ — as expected, in view of the smaller number of coordination sites in L. Computer modeling indicates that the Cu2+–L complex is CuL(H2O)22+, with terdentate L bound to Cu2+ via two Nπ atoms and the O atom of the peptide link. Attempts to make stability constant measurements for Cu2+ with L in aqueous solution buffered with Tris/TrisH+/ClO4– to pH near 7.2 were unsuccessful because the Tris base when in large excess over CuL2+ promoted its dissociation to Cu2+ + L by scavenging free Cu2+ as Cu(Tris)(TrisH–1)+, or when in roughly equimolar concentrations formed a ternary adduct, CuL(Tris)2+. The interactions of Cu2+ with Tris buffer were re-examined spectrophotometrically and with the aid of computations that show that the most stable Cu2+–Tris complexes are the syn- and anti-isomers of Cu(Tris)22+, but in the experimental pH ranges these are present as Cu(Tris)(TrisH–1)+. Since Cu2+(aq) is strongly complexed by almost any base capable of forming a buffer system with near-physiological pH, stability constants reported for Cu2+–Aβ complexes in any buffer solution should be regarded with skepticism unless interactions of the buffer with Cu2+ and with CuAβ2+ are taken quantitatively into account. Moreover, in vivo, biological buffers will reduce the physiological importance of Aβ–Cu2+ complexes by competing with Aβ for Cu2+.
Article
The solid compounds Cu(AOH)2SO4, Cu(AO⁻)2°H2O, and Ni(AOH)2(ClO4)2 have been prepared from 2-amino-2-(hydroxymethyl)-1,3-propanediol⁴ and the corresponding copper(II) or nickel(II) salts. In the presence of an excess of the amine salt, copper(II) and amine complexes may be formed in the ratios, in the order named, 1:1, 1:2 and 1:3. The successive formation constants are, in terms of log K, 3.98, 3.49, and 3.2. At and above pH 10 the stable species present in solution is Cu(AO⁻)2. In solution Ni(AOH)⁺² and Ni(AO⁻)⁺¹ species are formed. For Ni(AOH)⁺², log K is approximately 2.86. Above pH 9 a polynuclear species is formed.
Article
Following X-ray crystal structure studies, the products of the reaction between Cu(II) halides and tris(hydroxymethyl)methylamine (TRIS) can be formulated as [Cu(TRISH−1)(TRIS)]2X2 and [Cu(TRISH−1)X]4 (X Cl, Br). TRISH−1 is the deprotonated ligand. Initial metal-ligand stoichiometric ratios of 1:2 and 1:1 are required to obtain the former and the latter species, respectively. Relevant crystal data for the dimeric compound with X Br are: monoclinic, a = 11.39(2), b = 10.049(2), c = 12.149(2) Å, β = 95.83(2)°, space group P21/c, Z = 2. The tetramer with X Cl crystallizes in teh triclinic space group P1 with a 9.182(1), b = 9.120(2), c = 8.817(1) Å, α = 88.95(1), β = 87.01(1), γ = 84.13(1), Z = 1. In the dimer, two square planar Cu(II)-units are held together by two H-bonds of the type OH … O, which involve the O-atoms coordinated to the metals. The formation of an eight-membered cycle containing two metal ons ensues. The tetramer contains two dinuclear units formed by two metal centers, square planar in first approximation, which share one edge; the arrangement is significantly puckered at this vector. One of these bridging O-atoms has μ3 character as it serves as a weak apical donor for a Cu-atom of another binuclear unit. Thus a step-like geometry of the central core is obtained. Both compounds have constant magnetic moments at least down to the liquid N2 temperature. In this respect, they differ from other complexes of Cu(II) having comparable geometries, but temperature-dependent magnetic moments.
Article
The behaviour of solutions containing copper(II) and several β-amino alcohols was examined by potentiometric and spectrophotometric techniques. The potentiometric results at 25°C and KNO3 0.5 M, indicates in all the examined systems the formation of four main species with M:L:H stoichiometry 1:1:0, 1:1:−1, 1:2:−1 and 1:2:−2, respectively. The deprotonated species have been demonstrated to be alkoxo chelates formed by the loss of alcoholic hydrogen. No evidence of formation of ternary hydroxy or polynuclear complexes have been found in the examined experimental conditions, and the absence of dimeric alkoxo-bridged species have been confirmed by the analysis of the UV charge-transfer bands. The dependence of complex stability on the ligand structure is discussed with particular regard to the influence exherted by the number of hydroxyl groups. Also, the comparison with the behaviour of other metal ions is discussed.
Article
Copper(II) and nickel(II) complexes of 2-amino-2-(hydroxymethyl)-1,3-propanediol have been studied in aqueous solution at 25° and at an ionic strength of 0·10 M. The equilibrium constants for the various species present in solution have been determined from potentiometric measurements of hydrogen ion concentration. With both metal ions, the “ordinary” complexes of the neutral ligand, which first formed, undergo further dissociation as the pH is increased, forming polynuclear chelates in which alcoholate groups are probably involved in metal ion coordination. With copper(II), no polynuclear complexes are formed in the presence of excess ligand. On the other hand, nickel(II) forms polynuclear species even in the presence of excess ligand.
Article
One of the most complex establishments of standards in quality control is that for the measurement of acidity, the pH. Not only is this complexity linked with the environment or the matrix considered (solutions from chemical laboratories or industries, biophysiological fluids, sea waters, estuarine waters, freshwaters, acid rains, etc.) but also with the solvent type (water, nonaqueous solvents, aqueous-organic solvent mixtures). The results are distinct pH scales which, for each solvent considered, are articulated on one reference value standard (pHRVS) plus a group of primary standards (pHPS) and/or operational standards (pHos), as specified in recent IUPAC recommendations. Such specifications ensure that the above standards be determined according to the same electrochemical principles and procedures and be accurate typically to 0.002 in pH. However, the acquisition and availability of such standards, though rapidly expanding, are hitherto limited to a few nonaqueous solvents or aqueous-organic solvent mixtures. Within this context, the determination of pHRVS in ethylene glycol/water mixtures, based on electromotive force measurements of the cell Pt|H2|RVS Buffer + KCl|AgCl|Ag|Pt over a range of temperatures and solvent compositions is here described. Anyway, the comparability of pH scales in different solvent media (and even in different environments) depends on the uncertain determinability of the primary medium effect upon the H+ ion. Finally, the predictability of the above standards, whithin acceptable reliability limits, for hitherto unexplored solvent media has been recently assessed in terms of such qualifying physicochemical quantities as solvent composition, dielectric constant and temperature. Status, applications and problems related to the above points are here analysed.
Article
A new suite of 10 programs concerned with equilibrium constants and solution equilibria is described. The suite includes data preparation programs, pretreatment programs, equilibrium constant refinement and post-run analysis. Data preparation is facilitated by a customized data editor. The pretreatment programs include manual trial and error data fitting, speciation diagrams, end-point determination, absorbance error determination, spectral baseline corrections, factor analysis and determination of molar absorbance spectra. Equilibrium constants can be determined from potentiometric data and/or spectrophotometric data. A new data structure is also described in which information on the model and on experimental measurements are kept in separate files.
Article
The interaction of 2-amino-2(hydroxymethyl)-1,3-propanediol (Tris) with the metal ions (M2+) Mg2+, Ca2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ was studied by potentiometry and spectrophotometry in aqueous solution (I = 0.1 or 1.0 M, KNO3, 25 degrees C). Stability constants of the M(Tris)2+ complexes were determined; those constants which were measured by both methods agreed well. Ternary complexes containing ATP4- as a second ligand were also investigated and it is shown that in the presence of Tris, mixed-ligand complexes of the type M(ATP)(Tris)2- are formed. The values for delta log KM, where delta log KM = log KM(ATP)M(ATP)Tris--log KMM(Tris), are all negative, thus indicating that the interaction of Tris with M(ATP)2- is somewhat less pronounced than with M2+. However, it should be noted that even in mixed-ligand systems complex formation with Tris may still be considerable, hence great reservations should be exercised in employing Tris as a buffer in systems which also contain metal ions. Distributions of the complex species in dependence on pH are shown for several systems, and the structures of the binary M(Tris)2- and the ternary M(ATP)(Tris)2- complexes are discussed. The participation of a Tris-hydroxo group in complex formation is, at least for the M(Tris)2- species, quite evident.
Article
After Tris(hydroxymethyl)aminomethane[Tris buffer]-treatment cross-linking of the chloroplast thylakoid peptides of 11, 13, 18, 43, 55, and 87 kdaltons was observed on SDS-polyacrylamide gel electrophoresis. Tris-induced disulfide formation was suggested by the decrease of thiol groups of the chloroplast thylakoids in Tris medium at pHs above 8. In addition to the finding that Tris coordinates to Cu2+ in the forms of Tris-Cu2+ and Tris2-Cu2+ whose successive stability constants are 5.78 x 10(3) M-1 and 4.46 x 10(6) M-2, respectively, it was observed that Tris-Cu2+ complexes catalyze cysteine oxidation. Sinc release of copper from the chloroplast thylakoids is enhanced by increasing the concentration of Tris, oxidation of thiols by Tris-Cu2+ complexes formed in chloroplast thylakoids is a possible mechanism for the cross-linking of chloroplast thylakoid peptides.
Article
The production of formaldehyde from tris(hydroxymethyl) aminomethane(Tris) by interaction with hydroxyl radicals(.OH) was studied, since the reaction mixture from the Fenton reaction performed in Tris/HCl buffer was found to be color-developed by colorimetric determination of formaldehyde. The absorption spectrum of chromogens was identical to that of authentic formaldehyde. Color development, which required the presence of Tris, hydrogen peroxide and cupric ions in the Fenton reaction mixture, was inhibited by the addition of hydroxyl radical scavengers such as glucose or hyaluronic acid. These results indicated that formaldehyde was produced when Tris interacted with .OH. With structures similar to Tris, Good's buffers were also found to produce formaldehyde by interaction with .OH. Analysis of formaldehyde derived from these buffers may provide a simple and convenient assay for detecting .OH generation. In evaluating effects of .OH on the biological system in Tris/HCl buffer or certain Good's Buffers, .OH loss may be due to interactions of .OH with these buffers. The formaldehyde produced as a result of such interactions may affect biological systems.
Article
1-deoxynojirimycin (DNJ), a 5-imino analog of 1-deoxyglucose, is a potent inhibitor of alpha-glucosidase 1. DNJ and its derivatives have been considered as experimental drugs against human HIV-1 and hepatitis B viruses. Since amino and imino ligands have a high affinity for copper, it seems possible that biological activity of DNJ may be, at least in part, modulated by tissue copper. To test this possibility, potentiometric and spectroscopic studies of the complexation of DNJ by cupric ions were performed in order to obtain thermodynamic and structural background for further pharmacologic investigations. The effect of histidine, a major tissue copper carrier, on coordination equilibria was also studied. Results indicate that DNJ and Cu(II) form two stable complexes at physiological pH, CuH-1(DNJ)2+ and CuH-2(DNJ)2, involving Cu(II) chelation by the N-5 and O-6 donor atoms. In the presence of histidine, ternary complexes are also formed, of which the CuDNJHis+ species is stable in the physiological pH range. Binary Cu(II)-DNJ complexes are extremely effective mediators of in vitro oxidation of the guanine moiety in both 2'-deoxyguanosine (dG) and DNA to 8-oxoguanine (8-oxo-dG) and of DNA double strand scission by ambient O2 or H2O2. This mediation is suppressed by histidine in dG, but not in DNA. The results suggest that tissue Cu(II) may greatly enhance nonspecific cytotoxic effects of systemically administered DNJ through oxidative damage mechanisms, and therefore the prospective use of DNJ for therapeutic purposes must be developed with caution. On the other hand, however, the expected high genotoxic potential of synthetic Cu(II)-DNJ complexes may be used against viruses by means of targeted delivery of these complexes to the infected cells.
Article
Binding of Zn(II), Cu(II) and Fe(II) ions to A beta1-40, A beta1-42 and a single tryptophan mutant of Abeta 1-40 in solution at pH 7.4 was studied by fluorescent titration. Job plots and fitting of titration curves revealed formation of 1:1 and 1:2 peptide-metal complexes. For dimeric peptides A beta1-40 and A betaF4W the order of metal to peptide affinities is Fe < Cu > Zn, which is in agreement with the Irving-Williams series of complex stability. The affinity of A beta1-42 for Fe increases dramatically upon aggregation: K(D) changes from ca. 100 to ca. 0.2 microM.
Article
Mechanical hyperventilation of acidemic patients with acute lung injury (ALI) requires the use of high volumes and pressures that may worsen lung injury. However, permissive hypercapnia in the presence of shock, metabolic acidosis, and multi-organ system dysfunction may compromise normal cellular function. Tris-hydroxymethyl aminomethane (THAM) may be an effective method to control acidosis in this circumstance. Protonated THAM is excreted by the kidneys, so that carbon dioxide production is not raised. In an uncontrolled study, we administered THAM to 10 patients with acidosis (mean pH = 7.14) and ALI (mean lung injury score = 3.28) in whom adequate control of arterial pH could not be maintained during either eucapnic ventilation or permissive hypercapnia ventilation. THAM was given at a mean dose of 0.55 mmol/kg/h. Administration of THAM was associated with significant improvements in arterial pH and base deficit, and a decrease in arterial carbon dioxide tension that could not be fully accounted for by ventilation. Although further studies are needed to confirm these observations, THAM appears to be an effective alternative to sodium bicarbonate for treating acidosis during ALI.
Article
The binding of Ni(II) and Cu(II) to histidine, to the tripeptides GlyGlyHis and HisGlyHis, and to the protein bovine serum albumin has been studied by isothermal titration calorimetry (ITC) to determine the experimental conditions and data analysis necessary to reproduce literature values for the binding constants and thermodynamic parameters. From analysis of the ITC data, we find that there are two major considerations for the use of this method to accurately quantify metal ion interaction with biological macromolecules. First, to determine true pH-independent binding constants, ITC data must be corrected for metal ion competition with protons by accounting for the experimental pH and pKa values of the metal-binding residues. Second, metal interaction with the buffer (stability and enthalpy of formation of metal-buffer complex(es)) must be included in the analysis of the ITC data to determine the binding constants and the change in enthalpy. While it may be possible to use a buffer that forms only weak, and therefore negligible, complexes with the metal, a buffer that has a strong and well-characterized interaction has the benefit of suppressing metal ion hydrolysis and precipitation, and of allowing the quantification of high-affinity metal-binding sites on biological macromolecules. This study has also quantified the contribution of the N-terminal imidazole of HisGlyHis to the stability of the Cu(II) and Ni(II) complexes of this protein sequence and has provided new insight about Cu(II) binding to albumin.