Tamás Gajda

University of Szeged, Algyő, Csongrád, Hungary

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Publications (74)188.55 Total impact

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    ABSTRACT: The mobility and bioavailability of metal ions in natural waters depend on their chemical speciation, which involves a distribution of the metal ions between different complex (metal-ligand) species, colloid-adsorbed species and insoluble phases, each of which may be kinetically labile or inert. For example, in fresh water the metal ions are distributed among organic complexes (e.g., humates), colloids (e.g., as surface-adsorbed species on colloidal phases such as FeOOH), solid phases (e.g., hydroxide, oxide, carbonate mineral phases), and labile complexes with the simple inorganic anionic ligands commonly present in natural waters (e.g., for Zn
    Full-text · Article · Feb 2015
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    ABSTRACT: The numerical modeling of Zn-II speciation amongst the environmental inorganic ligands Cl-, OH-, CO32-, SO42-, and PO43- requires reliable values for the relevant stability (formation) constants. This paper compiles and provides a critical review of these constants and related thermodynamic data. It recommends values of log(10) beta(p,q,r)degrees valid at I-m = 0 mol.kg(-1) and 25 degrees C (298.15 K), and reports the empirical reaction ion interaction coefficients,Delta epsilon, required to calculate log(10) beta(p,q,r) values at higher ionic strengths using the Bronsted-Guggenheim-Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies Delta H-r, are reported where available. There is scope for additional high-quality measurements for the Zn2+ + H+ + CO32- system and for the Zn2+ + OH- and Zn2+ + SO42- systems at I > 0. In acidic and weakly alkaline fresh water systems (pH < 8), in the absence of organic ligands (e. g., humic substances), ZnII speciation is dominated by Zn2+(aq). In this respect, ZnII contrasts with Cu-II and Pb-II (the subjects of earlier reviews in this series) for which carbonato- and hydroxido- complex formation become important at pH > 7. The speciation of Zn-II is dominated by ZnCO3(aq) only at pH > 8.4. In seawater systems, the speciation at pH = 8.2 is dominated by Zn2+(aq) with ZnCl+, Zn(Cl)(2)(aq), ZnCO3(aq), and ZnSO4(aq) as minor species. This behaviour contrasts with that for CuII and PbII for which at the pH of seawater in equilibrium with the atmosphere at 25 degrees C (log(10) {[H+]/c degrees} approximate to 8.2) the MCO3(aq) complex dominates over the MCln(2-n)+ species. The lower stability of the different complexes of ZnII compared with those of CuII, PbII, and Cd-II is also illustrated by the percentage of uncomplexed M2+ in seawater, which is ca. 55, 3, 2, and 3.3 % of [M-II](T), respectively.
    Full-text · Article · Nov 2013 · Pure and Applied Chemistry

  • No preview · Article · Nov 2013 · Pure and Applied Chemistry
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    ABSTRACT: The brain specific zinc transporter protein ZnT3 can be related to the amyloid neuropathology of Alzheimer's disease. In order to analyze the metal binding ability of human ZnT3 protein, here we report a potentiometric and solution structural (UV-Vis, CD, EPR, NMR) study of nickel(ii), copper(ii) and zinc(ii) complexes of three peptides mimicking the possible metal binding sequences of this protein. The peptide (Ac-RHQAGPPHSHR-NH2) is a minimalist, the cyclic peptide (cyclo(Ac-CKLHQAGPPHSHGSRGAEYAPLEEGPEEKC-NH2) is a more complete model of the intracellular His-rich loop, which is widely accepted as a putative metal binding site. The peptide (Ac-PFHHCHRD-NH2) is the model of the conserved cytoplasmic N-terminal -HHCH- sequence. In the physiological pH-range, the Zn, ZnH3 and Zn complexes are the major species in the corresponding binary systems, with {3Nim}, {3Nim,2/3Oamide} and {3Nim,S(-)} coordination environments, respectively. The species Zn has 3-4 orders of magnitude higher stability than the other two complexes, indicating the presence of a high-affinity zinc-binding site at the N-terminal tail of the human ZnT3 transporter. Moreover, shows preferred zinc binding as compared to nickel (log β(Zn) - log β(Ni) = 2.3), probably due to the higher preference of zinc(ii) for tetrahedral geometry. These facts suggest that zinc binding to the N-terminal -HHCH- sequence of human ZnT3 may be involved in the biological activity of this zinc transporter protein in zinc sensing, binding or translocation processes.
    No preview · Article · Jul 2013 · Dalton Transactions
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    ABSTRACT: In order to mimic the active center of matrix metalloproteinases (MMPs), we synthesized a pentadecapeptide (Ac-KAHEFGHSLGLDHSK-NH2) corresponding to the catalytic zinc(II) binding site of human MMP-13. The multi-domain structural organization of MMPs fundamentally determines their metal binding affinity, catalytic activity and selectivity. Our potentiometric, UV-visible, CD, EPR, NMR, mass spectrometric and kinetic studies are aimed to explore the usefulness of such flexible peptides to mimic the more rigid metal binding sites of proteins, to examine the intrinsic metal binding properties of this naked sequence, as well as to contribute to the development of a minimalist, peptide-based chemical model of MMPs, including the catalytic properties. Since the multiimidazole environment is also characteristic for copper(II), and recently copper(II) containing variants of MMPs have been identified, we also studied the copper(II) complexes of the above peptide. Around pH6-7 the peptide, similarly to MMPs, offers a {3Nim} coordination binding site for both zinc(II) and copper(II). In the case of copper(II), the formation of amide coordinated species at higher pH abolished the analogy with the copper(II) containing MMP variant. On the other hand, the zinc(II)-peptide system mimics some basic features of the MMP active sites: the main species around pH7 (ZnH2L) possesses a {3Nim,H2O} coordination environment, the deprotonation of the zinc-bound water takes place near the physiological pH, it forms relatively stable ternary complexes with hydroxamic acids, and the species ZnH2L(OH) and ZnH2L(OH)2 have notable hydrolytic activity between pH7 and 9.
    No preview · Article · Jun 2013 · Journal of inorganic biochemistry
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    ABSTRACT: Available online at: http://www.oecd-nea.org/dbtdb/pubs/tin.pdf. No.: 122 Preface This volume is the 12th in the “Chemical Thermodynamics” series edited and produced by the OECD Nuclear Energy Agency (NEA). It is a critical review of the thermodynamic properties of tin, its compounds and aqueous complexes, initiated by the Management Board of the NEA Thermochemical Database Project Phase III (NEA TDB III). The European members of the TDB Sn Review Team − Wolfgang Voigt (Freiberg University of Mining and Technology, Germany), Tamás Gajda (University of Szeged, Hungary) and Heinz Gamsjäger as Chairman (Montanuniversität Leoben, Austria) − first met at the NEA in Issy-les-Moulineaux (France) in September 2004. The overseas members − Surendra K. Saxena (Florida International University, Miami, United States) and James Sangster (Sangster Research Laboratories, Montreal, Canada) participated in this kickoff meeting via phone and video link. Four subsequent plenary meetings took place at the NEA in March 2005, October 2005, March 2006 and October 2006. The latter was held in conjunction with the TDB III Executive Group Meeting on 25 October and the TDB III Management Board Meeting on 26-27 October 2006. In these meetings the Review Team reported that key values on Sn4+ formation and the redox couple Sn4+/Sn2+ were lacking. Moreover, essential formation data on Sn(IV) chlorido and hydroxido complexes were also lacking. Therefore the Review Team submitted a proposal to the Management Board requesting to fund an experimental programme to obtain values for the most important critical data, while the already completed sections dealing with solids and gases were sent to peer review. The Management Board agreed and the experimental investigation was carried out under the leadership of Tamás Gajda at the University of Szeged Department of Inorganic and Analytical Chemistry. From 7 to 10 August 2008 the solution chemistry group comprising Wolfgang Voigt, Tamás Gajda and Heinz Gamsjäger met at Montanuniversität Leoben to include the results of the experimental study in the tin draft. The publication of these results, mandatory by NEA standards for including new data in chemical thermodynamics volumes, appeared in 2009. Heinz Gamsjäger presented these results at the meeting of the TDB IV Executive Group on 19 May 2010 in Karlsruhe. Hans Wanner participated in meetings of the Review Team as the designated member of the Executive Group until he retired from this position in 2007. At the NEA Data Bank the responsibility for the overall co-ordination of the project was placed with Federico Mompean (from its initiation in 2004 to 2007), with Mireille Defranceschi (2008 to 2010) and Jane Perrone (2011). Jane Perrone was in charge of the preparation of the successive drafts, updating the NEA Thermodynamic Database and editing the book in its present final form. Primary responsibility for the different chapters was divided as follows. James Sangster and Surendra Saxena assessed the thermodynamic properties of solid and gaseous compounds, while Wolfgang Voigt, Tamás Gajda and Heinz Gamsjäger were in charge of the aqueous chemistry. Surendra Saxena drafted the sections on solid oxides, hydrides, halides, pnictides and selected minerals. James Sangster prepared the sections on elemental tin, gaseous compounds of all groups and solid compounds not treated by Surendra Saxena. Tamás Gajda drafted the sections on hydrolysis of Sn(II) and Sn(IV) and the sections on aqueous Sn(II) and Sn(IV) complexes. Wolfgang Voigt prepared the sections on solubilities of all groups. The chairman drafted the sections on simple aqua ions and those on solubilities of Sn(II) as well as Sn(IV) oxides and hydroxides. The key values for Sn(IV) which were lacking prompted close co-operation of the solution chemistry group. This contributed favourably to the final solution of the problem and to the quality of the solution chemistry section. It is worth noting that the selection of key values, e.g., for Sn2+, revealed gaps in our knowledge which may stimulate rewarding projects on the experimental thermodynamics of tin compounds. Leoben, Austria, May 2012 Heinz Gamsjäger, Chairman
    Full-text · Book · Jan 2013
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    ABSTRACT: For elucidating the mechanism of the general acid/base catalysis of the hydrolysis of RNA phosphodiester bonds, a number of cleaving agents having two cyclen moieties tethered to a 1,3,5-triazine core have been prepared and their ability to bind and cleave uridylyl-3',5'-uridine (UpU) studied over a wide pH range. Around neutral pH, the cleaving agents form a highly stable ternary complex with UpU and Zn(II) through coordination of the uracil N3 and the cyclen nitrogen atoms to the Zn(II) ions. Under conditions where the triazine core exists in the deprotonated neutral form, hydrolysis of UpU, but not of adenylyl-3',5'-adenosine (ApA), is accelerated by approximately two orders of magnitude in the presence of the cleaving agents, suggesting general base rather than metal ion catalysis. The probable mechanism of the observed catalysis and implications to understanding the general acid/base-catalyzed phosphodiester hydrolysis by ribozymes are discussed.
    No preview · Article · Feb 2012 · Dalton Transactions
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    ABSTRACT: Reaction of 1,3-bis(2′-Ar-imino)isoindolines (HLn, n = 1–7, Ar = benzimidazolyl, N-methylbenzimidazolyl, thiazolyl, pyridyl, 3-methylpyridyl, 4-methylpyridyl, and benzthiazolyl, respectively) with Cu(OCH3)2 yields mononuclear hexacoordinate complexes with Cu(Ln)2 composition. With cupric perchlorate square-pyramidal [CuII(HLn)(NCCH3)(OClO3)]ClO4 complexes (n = 1, 3, 4) were isolated as perchlorate salts, whereas with chloride CuII(HLn)Cl2 (n = 1, 4), or square-planar CuIICl2(HLn) (n = 2, 3, 7) complexes are formed. The X-ray crystal structures of Cu(L3)2, Cu(L5)2, [CuII(HL4)(NCCH3)(OClO3)]ClO4, CuIICl(L2) and CuIICl(L7) are presented along with electrochemical and spectral (UV–Vis, FT-IR and X-band EPR) characterization for each compound. When combined with base, the isoindoline ligands in the [CuII(HLn)(NCCH3)(OClO3)]ClO4 complexes undergo deprotonation in solution that is reversible and induces UV–Vis spectral changes. Equilibrium constants for the dissociation are calculated. X-band EPR measurements in frozen solution show that the geometry of the complexes is similar to the corresponding X-ray crystallographic structures. The superoxide scavenging activity of the compounds determined from the McCord–Fridovich experiment show dependence on structural features and reduction potentials.
    No preview · Article · Oct 2011 · Inorganica Chimica Acta
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    ABSTRACT: The Cu,Zn superoxide dismutases (Cu,Zn SOD) isolated from some Gram-negative bacteria possess a His-rich N-terminal metal binding extension. The N-terminal domain of Haemophilus ducreyi Cu,Zn SOD has been previously proposed to play a copper(II)-, and may be a zinc(II)-chaperoning role under metal ion starvation, and to behave as a temporary (low activity) superoxide dismutating center if copper(II) is available. The N-terminal extension of Cu,Zn SOD from Actinobacillus pleuropneumoniae starts with an analogous sequence (HxDHxH), but contains considerably fewer metal binding sites. In order to study the possibility of the generalization of the above mentioned functions over all Gram-negative bacteria possessing His-rich N-terminal extension, here we report thermodynamic and solution structural analysis of the copper(II) and zinc(II) complexes of a peptide corresponding to the first eight amino acids (HADHDHKK-NH(2), L) of the enzyme isolated from A. pleuropneumoniae. In equimolar solutions of Cu(II)/Zn(II) and the peptide the MH(2)L complexes are dominant in the neutral pH-range. L has extraordinary copper(II) sequestering capacity (K(D,Cu)=7.4×10(-13)M at pH 7.4), which is provided only by non-amide (side chain) donors. The central ion in CuH(2)L is coordinated by four nitrogens {NH(2),3N(im)} in the equatorial plane. In ZnH(2)L the peptide binds to zinc(II) through a {NH(2),2N(im),COO(-)} donor set, and its zinc binding affinity is relatively modest (K(D,Zn)=4.8×10(-7)M at pH 7.4). Consequently, the presented data do support a general chaperoning role of the N-terminal His-rich region of Gram-negative bacteria in copper(II) uptake, but do not confirm similar function for zinc(II). Interestingly, the complex CuH(2)L has very high SOD-like activity, which may further support the multifunctional role of the copper(II)-bound N-terminal His-rich domain of Cu,Zn SODs of Gram-negative bacteria. The proposed structure for the MH(2)L complexes has been verified by semiempirical quantum chemical calculations (PM6), too.
    No preview · Article · Sep 2011 · Journal of inorganic biochemistry
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    ABSTRACT: The numerical modeling of CdII speciation amongst the environmental inorganic ligands Cl-, OH-, CO32-, SO42-, and PO43- requires reliable values for the relevant stability (formation) constants. This paper compiles and provides a critical review of these constants and related thermodynamic data. It recommends values of log10 βp,q,r° valid at Im = 0 mol kg-1 and 25 °C (298.15 K), along with the equations and empirical reaction ion interaction coefficients, Δε, required to calculate log10 βp,q,r values at higher ionic strengths using the Brønsted-Guggenheim-Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies, ΔrH, are reported where available. Unfortunately, with the exception of the CdII-chlorido system and (at low ionic strengths) the CdII-sulfato system, the equilibrium reactions for the title systems are relatively poorly characterized.
    No preview · Article · Mar 2011 · Pure and Applied Chemistry
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    ABSTRACT: Copper(II) and nickel(II) binding properties of two pseudo tetrapeptides, N-Boc-Gly-Gly-Gly-Histamine (BGGGHa) and Gly-Gly-Gly-Histamine (GGGHa) have been investigated by pH-potentiometric titrations, UV-visible-, EPR-, NMR- and ESI-HRMS (electrospray ionization high resolution MS) spectroscopies, in order to compare the role of N-terminal amino group and imidazole moiety at the fourth position in the complex formation processes. Substantially higher stabilities were determined for the ML complexes of GGGHa, compared to those of BGGGHa, supporting the coordination of the terminal amino group and the histamine imidazole of the non-protected ligand. A dimeric Cu(2)H(-2)L(2) species, formed through the deprotonation of peptide groups of the ligands, was found in the GGGHa-copper(II) system. Deprotonation and coordination of further amide nitrogens led to CuH(-2)L and, above pH~10, CuH(-3)L. Experimental data supports a {NH(2), 2 × N(amide),N(im)} macrochelate structure in CuH(-2)L whereas a {NH(2), 3 × N(amide)} coordination environment in CuH(-3)L. The first two amide deprotonation processes were found to be strongly cooperative with nickel(II) and spectroscopic studies proved the transformation of the octahedral parent complexes to square planar, yellow, diamagnetic species, NiH(-2)L and above pH~9, NiH(-3)L. In the basic pH-range deprotonation and coordination of the amide groups also took place in the BGGGHa containing systems, leading to complexes with a {3 × N(amide),N(im)} donor set, and in parallel the re-dissolving of precipitate. Above pH~11, a further proton release from the pyrrolic NH group of the imidazole ring of BGGGHa occurred providing an additional proof for the different binding modes of the two ligands.
    No preview · Article · Jan 2011 · Journal of inorganic biochemistry
  • Tamás Gajda · Attila Jancsó
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    ABSTRACT: The speciation of organotin(IV) cations in natural waters, in sewage or in biofluids is strongly influenced by the complex formation with the available metal-binding compounds, i.e., both high and low molecular weight ligands of biological and environmental interest. The primary intention of this chapter is to discuss the aquatic solution chemistry of organotin cations and their complexes formed with low and high molecular weight bioligands. Besides, some synthetic aspects, applications and sources of organotin pollution, their destinations in the environment, and toxicology will be also shortly discussed.
    No preview · Article · Jan 2010 · Metal ions in life sciences
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    Tamás Gajda · Pál Sipos · Heinz Gamsjäger
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    ABSTRACT: No.: 118 The Sn4+/Sn2+ redox couple is, thermodynamically, the connecting link between aqueous tin(IV) and tin(II) chemistry. Because the equilibrium potential E�(Sn4+/Sn2+) was not known with sufficient accuracy, we were prompted to attempt its determination by means of a potentiometric study. The equilibrium potential of the redox couple Sn4?/Sn2? has been determined in x M HClO4 + 1 M HCl media (x = 3, 4, 5). The formal potentials determined for different electrolyte mixtures were extrapolated to zero ionic strength by the extended specific ion interaction theory approach (E�(Sn4+/Sn2+) = 0.384 ± 0.020 V). The evaluation of the data required knowledge of the formation constants of tin(IV) chloro complexes; these were determined spectrophotometrically at five different HClO4 concentrations (4.5–8.0 M), and were extrapolated to zero ionic strength. Keywords: Aqueous tin(IV) chemistry, �Standard redox potential � Sn4+/Sn2+ couple, �Tin(IV) chloro complexes, � Formation constant
    Full-text · Article · Nov 2009 · Monatshefte fuer Chemie/Chemical Monthly
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    ABSTRACT: The zinc(II) and copper(II) binding ability of two oligopeptide fragments, Ac-HHPHG-NH(2) and Ac-HHPHGHHPHG-NH(2), derived from the repeat-region of the His-Pro-rich domain of histidine-rich glycoprotein (HRG) and the structure of the formed complexes have been investigated by potentiometry, NMR-, UV-visible-, CD-, SRCD- and EPR spectroscopy. Exclusive coordination of the side-chain imidazoles of the peptides has been observed with both metal ions in the acidic and neutral pH range. While the three His units of the pentapeptide resulted in a modest stability of the ML complexes, the decapeptide with its increased number of His residues offered a high-affinity metal binding site for both metal ions with the participation of at least four nitrogen donors. Due to the high number of potential donor groups, the formation of binding isomers of the protonated and parent complexes is very likely. Both peptides show a synchrotron radiation (SR) CD-pattern resembling to that of the polyproline II structure, similarly to that of the His-Pro-rich domain of the HRG protein. The longer sequence was shown to bind a second metal ion in the slightly acidic pH-range. The determined stability data suggest a remarkable extra stabilization emerging in the decapeptide for the coordination of the second metal ions, as compared to the ML complexes of the pentapeptide. Whether the observed cooperativity has similarities to the cooperative metal binding feature of HRG or the two phenomena have different sources is a question yet to be clarified.
    No preview · Article · Sep 2009 · Journal of inorganic biochemistry
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    ABSTRACT: A histidine-rich peptide HSHRDFQPVLHL-NH(2) (L), identical with the N-terminal fragment of the anti-angiogenic human endostatin has been synthesized. Endostatin is a recently identified broad spectrum angiogenesis inhibitor, which inhibits 65 different tumor types. The N-terminal 25-mer peptide fragment of human endostatin has the same antitumor effect as the entire protein. The zinc(II) binding is crucial for the antitumor effect in both cases. Our peptide may provide all critical interactions for zinc(II) binding present in the N-terminal 25-mer peptide fragment. In addition, the N-terminus of human endostatin has a supposedly high affinity binding site for copper(II), similar to human serum albumin. Since copper(II) is intimately involved in angiogenesis, this may have biological relevance. In order to determine the metal binding properties of the N-terminal fragment of endostatin, we performed equilibrium, UV-visible (UV-vis), CD, EPR and NMR studies on the zinc(II) and copper(II) complexes of L. In the presence of zinc(II) the formation of a stable [NH(2),3N(im),COO(-)] coordinated complex was detected in the neutral pH-range. This coordination mode is probably identical to that present in the zinc(II) complex of the above mentioned N-terminal 25-mer peptide fragment of human endostatin. Moreover, L has extremely high copper(II) binding affinity, close to those of copper-containing metalloenzymes, and forms albumin-like [NH(2),N(-),N(-),N(im)] coordinated copper(II) complex in the neutral pH-range, which may suggest that copper(II) binding is involved in the biological activity of endostatin.
    No preview · Article · May 2009 · Journal of inorganic biochemistry
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    ABSTRACT: Complex formation between PbII and the common environmental inorganic ligands, Cl–, OH–, CO32–, SO42–, and PO43–, can be significant in natural waters with low concentrations of organic matter. Numerical modeling of the speciation of PbII amongst these inorganic ligands requires reliable values for the relevant stability (formation) constants. This paper provides a critical review of such constants and related thermodynamic data. It recommends values of log10 βp,q,r° valid at Im = 0 mol kg–1 and 25 °C (298.15 K), along with the equations and empirical coefficients required to calculate log10 βp,q,r values at higher ionic strengths using the Brønsted–Guggenheim–Scatchard specific ion interaction theory (SIT). Some values for reaction enthalpies, ΔrH, are also reported. In weakly acidic fresh water systems (–log10 {[H+]/c°} < 6), the speciation of PbII is similar to that of CuII. In the absence of organic ligands, PbII speciation is dominated by Pb2+(aq), with PbSO4(aq) as a minor species. In weakly alkaline solutions, 8.0 < –log10 {[H+]/c°} < 9.0, the speciation is dominated by the carbonato species PbCO3(aq) and Pb(CO3)2 2–. In weakly acidic saline systems (–log10 {[H+]/c°} < 6), the speciation is dominated by PbCln (2–n)+ complexes, (n = 0–3), with Pb2+(aq) as a minor species. In this medium (and in seawater), the speciation contrasts with that of CuII because of the higher stability of the Pb2+-chlorido- complexes. In seawater at –log10 {[H+]/c°} = 8.2, the calculated speciation is less well defined, although it is clearly dominated by the uncharged species PbCO3(aq) (41 % of [Pb]T) with a significant contribution (16 %) from Pb(CO3)Cl– and minor contributions (5–10 %) from PbCln (2–n)+ , (n = 0–3) and Pb(CO3)2 2–. The uncertainty in calculations of PbII speciation in seawater arises from (a) the large uncertainty in the stability constant for the apparently dominant species PbCO3(aq), (b) the reliance on statistical predictions for stability constants of the ternary species Pb(CO3)Cl– and Pb(CO3)OH–, and (c) the uncertainty in the stability constant for PbCl4 2–, the available value being considered “indicative” only. There is scope for additional detailed high-quality measurements in the Pb2+ + CO3 2– + Cl– system.
    Full-text · Article · Jan 2009 · Pure and Applied Chemistry
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    ABSTRACT: The aim of this work was to construct chemical models for selective hydrolysis of phosphate monoesters in order to elucidate the role of metal ions in the hydrolytic mechanisms and to develop artificial enzymes for practical applications. A dinuclear copper(II) complex of a cyclohexane-based polyamino polyalcohol provided a selective and by far the highest rate acceleration among the transition metal complexes containing divalent metal ions for the hydrolysis of a phosphate monoester.
    No preview · Article · Jan 2009
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    ABSTRACT: The peptides Ac-His-Pro-His-Pro-His-NH(2) (L1) and Ac-Lys-His-Pro-His-Pro-His-Gln-NH(2) (L2) have been prepared and the equilibria of their proton, copper(II) and zinc(II) complexes in aqueous solution have been studied by the combination of pH-potentiometric titrations, UV/visible and circular dichroism (CD) spectroscopy. The latter methods also provided information on solution structure of the complexes formed under different conditions. Both ligands formed complexes with three imidazole nitrogens around the metal ion at pH ~7. In the L1 containing system precipitation of either copper(II) or zinc(II) complexes occurred upon slight increase of the pH. The re-titration of the filtered and acidified precipitates revealed that the insoluble materials were neutral complexes rather than metal-hydroxides. Indeed, by attaching amino acids with polar side-chains to the His-Pro-His-Pro-His template in L2 we could prevent any precipitation, and the soluble complexes around pH ~7 exerted three imidazole nitrogens and a (deprotonated) water molecule around the metal ions. To our knowledge L2 provides the first example of a short peptide preventing both the amide nitrogen coordination in copper(II) and the formation of copper(II) and zinc(II) hydroxides. The zinc(II) and copper(II) complexes at pH ~7 having similar structure to the natural hydrolytic and redox enzymes, respectively, showed considerable activity in hydrolytic cleavage assays with a model substrate (2-hydroxypropyl-4-nitrophenyl phosphate), as well as with native plasmid DNA, and in a superoxide dismutase-like reaction.
    No preview · Article · Jan 2009 · Dalton Transactions
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    ABSTRACT: The copper(II), nickel(II) and zinc(II) binding ability of the multi-histidine peptide N-acetyl-His-Pro-His-His-NH(2) has been studied by combined pH-potentiometry and visible, CD and EPR spectroscopies. The internal proline residue, preventing the metal ion induced successive amide deprotonations, resulted in the shift of this process toward higher pH values as compared to other peptides. The metal ions in the parent [ML](2+) complexes are exclusively bound by the three imidazole side chains. In [CuH(-1)L](+), formed between pH 6-8, the side chains of the two adjacent histidines and the peptide nitrogen between them are involved in metal ion binding. The next deprotonation results in the proton loss of the coordinated water molecule (CuH(-1)L(OH)). The latter two species exert polyfunctional catalytic activity, since they possess superoxide dismutase-, catecholase- (the oxidation of 3,5-di-tert-butylcatechol) and phosphatase-like (transesterification of the activated phosphoester 2-hydroxypropyl-4-nitrophenyl phosphate) properties. On further increase of the pH rearrangement of the coordination sphere takes place leading to the [CuH(-3)L](-) species, the deprotonated amide nitrogen displaces a coordinated imidazole nitrogen from the equatorial position of the metal ion. The shapes of the visible and CD spectra reflect a distorted arrangement of the donor atoms around the metal ion. In presence of zinc(II) the species [ZnL](2+) forms only above pH 6, which is shortly followed by precipitation. On the other hand, the [NiL](2+) complex is stable over a wide pH range, its deprotonation takes place only above pH 8. At pH 10 an octahedral NiH(-2)L species is present at first, which transforms slowly to a yellow square planar complex.
    Full-text · Article · Aug 2008 · Journal of inorganic biochemistry
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    ABSTRACT: The ability of the dinuclear Zn2+ complex of 1,4-bis[(1,5,9-triazacyclododecan-3-yloxy)methyl]benzene (L(1)) to promote the cleavage of the phosphodiester bond of dinucleoside-3',5'-monophosphates that contain a guanine base has been studied over a narrow pH range from pH 5.8 to 7.2 at 90 degrees C. Comparative measurements have been carried out by using the trinuclear Zn2+ complex of 1,3,5-tris[(1,5,9-triazacyclododecan-3-yloxy)methyl]benzene (L(2)) as a cleaving agent and guanylyl-3',5'-guanosine (5'-GpG-3') as a substrate. The strength of the interaction between the cleaving agent and the starting material has been elucidated by UV spectrophotometric titrations. The speciation and binding mode have been clarified by potentiometric titrations with hydrolytically stable 2'-O-methylguanylyl-3',5'-guanosine and 1H NMR spectroscopic measurements with guanylyl-3',5'-guanosine. The results show that the guanine base is able to serve as a site for anchoring for the Zn2+-azacrown moieties of the cleaving agents L(1) and L(2), analogously to uracil base. The interaction is, however, weaker than with the uracil base and, hence, only the 5'-GpG-3' site (in addition to 5'-GpU-3' and 5'-UpG-3' sites) is able to markedly modulate the phosphodiester cleavage by the Zn2+ complexes of di- and trinucleating azacrown ligands containing an ether oxygen as a potential H-bond-acceptor site.
    Full-text · Article · Aug 2008 · ChemBioChem

Publication Stats

1k Citations
188.55 Total Impact Points


  • 1990-2013
    • University of Szeged
      • Department of Inorganic and Analytical Chemistry
      Algyő, Csongrád, Hungary
  • 2007
    • University of Canterbury
      • Department of Chemistry
      Christchurch, Canterbury Region, New Zealand
  • 2000
    • University of Münster
      Muenster, North Rhine-Westphalia, Germany