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PubMed2001

The system VO2+ +oxidized glutathione: a potentiometric and spectroscopic study.

The equilibria in the system VO2+ +oxidized glutathione in aqueous solution have been studied in the pH range 2-11 by a combination of pH potentiometry and spectroscopy (EPR, visible absorption and circular dichroism). The results of the various methods are self-consistent and the equilibrium model includes the species MLH4, MLH3, MLH2, MLH, ML, MLH(-1), MLH(-2) and several hydrolysis products (where H4L denotes oxidized glutathione); individual formation constants and spectra are given. Plausible structures for each stoichiometry are discussed.

Circular Dichroism↗
PubMed1979

A comparative study of Zn(II) and Co(II) binding to glycyl-L-tyrosine, a pseudosubstrate for carboxypeptidase A.

A comprehensive investigation of the interaction of Zn(II) and Co(II) with the dipeptide glycyl-L-tyrosine has been carried out. The carboxyl, amino, and tyrosyl pKa values, as well as the distribution of solution complexes, have been determined by analytical potentiometry. The amide pKa value was determined by relating the proton magnetic resonance (PMR) titration behavior of the tyrosyl alpha-hydrogen resonance to an H2-acidity function for concentrated solutions of aqueous base. Both metals behave in a qualitatively similar manner, yielding equivalent species as a function of pH. Both metals formed bis-peptide complexes, involving amino and peptide carbonyl coordination near pH = 8, with Zn(II) demonstrating a substantially higher affinity for the ligand. No evidence could be found for direct, metal-promoted phenolic dissociation, although the tyrosyl pKa value was sensitive to metal binding at other loci on the dipeptide molecule. At high pH, both systems ionized two additional protons. In the Co(II) system, these correspond to amide protons. However, it is not entirely clear whether the protons in the Zn(II) system originate from the peptide linkage or metal-bound water molecules.

Carboxypeptidases↗
PubMed2001

Copper(II)-lincomycin: complexation pattern and oxidative activity.

Coordination of Cu(II) to lincomycin was studied by potentiometry, UV-Vis, circular dichroism (CD), EPR, NMR, cyclic voltammetry (CV) and ESI-MS. Only mononuclear complexes of stoichiometries ranging from CuL to CuH(-3)L were found. In the main species present at neutral pH, CuH(-2)L, lincomycin bonds Cu(II) through both of its nitrogen donors, and a deprotonated oxygen donor at C4 of the sugar moiety. High pressure liquid chromatography (HPLC) of products of 2'-deoxyguanosine (dG) oxidation and agarose gel electrophoresis of plasmid DNA confirmed that lincomycin complexes effectively facilitate dG oxidation by H2O2, but are not able to cleave double-stranded plasmid DNA.

Anti-Bacterial Agents↗
PubMed2002

Synthesis, molecular structure, solution equilibrium, and antiproliferative activity of thioxotriazoline and thioxotriazole complexes of copper II and palladium II.

Preparations of copper(II) and palladium(II) complexes of 4-amino-5-methylthio-3-(2-pyridyl)-1,2,4-triazole (L(1)) and the copper(II) complex of 1,4-dihydro-4-amino-3-(2-pyridyl)-5-thioxo-1,2,4-triazole (HL) are described. These complexes have been characterized by means of spectroscopy and microanalysis. Molecular structures of HL (1), [CuCl(2)(H(2)L)]Cl.2H(2)O (2a), cis-[CuCl(2)(L(1))] (3), and cis-[PdCl(2)(L(1))] (4) have been determined by single-crystal X-ray diffraction. The HL ligand acts as a N,S bidentate through the thioxo moiety and the exo-amino group whilst the ligand L(1) forms N,N coordination complexes through the pyridine and triazole nitrogen atoms. Speciation in solution of the systems Cu/HL and Cu/L(1) have been determined by means of potentiometry and spectrophotometry as well as for the Cu/L(1)/A (HA=glycine) system in order to determine species present at physiological pH. Antiproliferative activity of these complexes and their ligands was evaluated, using the AlamarBlue Assay, on normal human fibroblasts (HF) and human fibrosarcoma tumor (HT1080) cells. The copper compounds cis-[CuCl(2)(H(2)L)]Cl and cis-[CuCl(2)(L(1))] exerted significant antiproliferative activity of both normal and neoplastic cells; although dose-response experiments revealed that the HT1080 cell line was more sensitive to the tested drugs than normal fibroblasts.

Antineoplastic Agents↗
PubMed2003

Pentacopper(II) 12-metallacrown-4 complexes with alpha- and beta-aminohydroxamic acids in aqueous solution: a reinvestigation.

A reinvestigation of the equilibria of (S)-alpha-alaninehydroxamic acid (alpha-Alaha) and (R)-aspartic-beta-hydroxamic acid (Asp-beta-ha) with copper(II) was performed in aqueous solution in order to clarify some contradictory literature reports regarding the stoichiometry of the polynuclear complexes formed. beta-Alaninehydroxamic acid (beta-Alaha, HL), for which the formation of a planar 12-metallacrown-4, [Cu(5)L(4)H(-4)](2+), was already reported, was also re-examined for comparison. Among the different techniques used (potentiometry, absorption spectrophotometry, spectropolarimetry and electrospray ionization mass spectrometry), ES data allowed to define unambiguously that all these three ligands form the same pentanuclear species. Therefore it can be concluded that in aqueous solution the hydroxamates of both alpha- and beta-amino acids form 12-metallacrown-4 complexes, and that the formers are less stable.

Alanine↗
PubMed2003

Synthesis and DNA binding properties of a cationic 2,2':6',2"-terpyridine cobalt(II) complex containing an oligopeptide.

The first example of DNA metallointercalator containing an oligopeptide moiety is presented. The ternary cobalt(II) complex [(DOTA)Co(II)(TPY)](ClO(4))(2) (DOTA=1,4,7,10-tetraaza-cyclododecane-2,9-dione, TPY=2, 2':6',2"-terpyridine) was found to be efficient in binding ct-DNA. The binding constant was determined by spectrophotometric titration. In vitro antitumor studies shows that this complex has significant antitumor activity. The single-crystal of a six coordinated oligopeptide cobalt(II) complex [Co(II)(DOTA)(2)](ClO(4))(2) is also reported. The stabilities and species distributions of Co(II)-DOTA (1:1) and DOTA-Co(II)-TPY (1:1:1) systems were investigated by potentiometry titration.

Animals↗
PubMed2003

Interaction of Al(III) with the peptides AspAsp and AspAspAsp.

The interactions of Al(III) with the dipeptide AspAsp and the tripeptide AspAspAsp in aqueous solutions were studied by pH-potentiometry and multinuclear 1H- and 13C- nuclear magnetic resonance (NMR) spectroscopy. Their numerous negatively charged COO(-) functions allow these ligands to bind Al(III) even in weakly acidic solutions. Various mononuclear 1:1 complexes are formed in different protonation states. 13C-NMR spectroscopy unambiguously proved participation of the COO(-) functions in a monodentate or chelating mode in Al(III) binding, however, the terminal-NH(2) group seems to be excluded from the coordination. Depending on the metal ion to ligand ratio precipitation occurs at pH approximately 5 to 6. This indicates that the COO(-) groups at the low level of preorganization in such small peptides are not sufficient to keep the Al(III) ion in solution and to prevent the precipitation of Al(OH)(3) at physiological pH. To achieve this, a more specific arrangement of the side-chain donors seems necessary.

Aluminum↗
PubMed1997

Binding ability of Cu2+ ions by opiate-like fragments of bovine casein.

The coordination modes of Cu(II) to alpha-casein (90-95) and alpha-casein (90-96) peptides with opioid activity isolated from pepsin hydrolisates of alpha-casein were investigated by means of electron paramagnetic resonance, absorption, and circular dichroism spectroscopy and potentiometry. The results allow the identification of the complex species involved and the attribution of the spectral data set to the various complex structures. According to the spectroscopic data, a phenolate side-chain of Tyr residue belonging to the Gly-Tyr-Leu or Gly-Tyr-Leu-Gln fragment of the peptides is involved in the metal coordination in a complex which is a minor species at neutral pH range.

Amino Acid Sequence↗
PubMed1998

Specific interactions of bovine and human beta-casomorphin-7 with Cu(II) ions.

Complex formation between Cu(II) and human and bovine beta-casomorphin heptapeptides, Tyr-Pro-Phe-Val-Glu-Pro-Ile and Tyr-Pro-Phe-Pro-Gly-Pro-Ile, respectively, was investigated by pH potentiometry and spectroscopic (CD, EPR and electronic absorption) techniques. The results showed the critical impact of Pro residues on the complex equilibria formed. The presence of the Pro residue at the second position leads to formation of very stable dimeric species in which two metal ions co-ordinate to N-terminal ¿NH2, C=O¿ binding sites of one peptide molecule and the deprotonated phenolic oxygen of the second ligand molecule. The presence of two additional hydrophobic residues on the C-terminal makes heptapeptide molecule much more effective ligand than its pentapeptide N-terminal fragment.

Animals↗
PubMed1997

Experimental measurement of the effective dielectric in the hydrophobic core of a protein.

The dielectric inside a protein is a key physical determinant of the magnitude of electrostatic interactions in proteins. We have measured this dielectric phenomenologically, in terms of the dielectric that needs to be used with the Born equation in order to reproduce the observed pKa shifts induced by burial of an ionizable group in the hydrophobic core of a protein. Mutants of staphylococcal nuclease with a buried lysine residue at position 66 were engineered for this purpose. The pKa values of buried lysines were measured by difference potentiometry. The extent of coupling between the pKa and the global stability of the protein was evaluated by measuring pKa values in hyperstable forms of nuclease engineered to be 3.3 or 6.5 kcal mol-1 more stable than the wild type. The crystallographic structure of one mutant was determined to describe the environment of the buried lysine. The dielectrics that were measured range from 10 to 12. Published pKa values of buried ionizable residues in other proteins were analyzed in a similar fashion and the dielectrics obtained from these values are consistent with the ones measured in nuclease. These results argue strongly against the prevalent use of dielectrics of 4 or lower to describe the dielectric effect inside a protein in structure-based calculations of electrostatic energies with continuum dielectric models.

Proteins↗
PubMed2002

Effect of humic substances on Cu(II) solubility in kaolin-sand soil.

The type and amount of organic matter present in industrially contaminated soils will influence the risk they pose. Previous studies have shown the importance of humic and fulvic acids (FAs) (important components of soil organic matter) in increasing the solubility of toxic metals but were not carried out using toxic metal levels and the pH range typical of industrially contaminated soils. This study investigated the influence of three humic substances (HSs: humates, fulvates and humins) on the solubility of copper(II) ions in kaolinitic soil spiked with Cu at levels representative of industrially contaminated soil. Humates, fulvates and humin were extracted from Irish moss peat, and controlled pH batch leaching tests were conducted on an artificial kaolin-sand soil that was spiked with each. Further leaching tests were conducted on soil spiked with each HS and copper nitrate. Dissolved organic contents were determined by titration and total and free aqueous copper concentrations in the leachate were measured using AAS and ion selective electrode (ISE) potentiometry respectively (dissolved complexed copper levels were determined by difference). It was found that humates and fulvates are partially sorbed by the soil, probably by chemisorption on positively charged gibbsite (Al-hydroxide) sites in the kaolinite. The addition of 340 mg/kg Cu(II) ions did not significantly affect the amount of humate or fulvate sorbed. Dissolved humates and fulvates form soluble complexes with copper over the pH range 3-11. However, in the presence of kaolinite, soluble copper humates and fulvates are unable to compete with the kaolinite for Cu ions at pH 6-7. Above pH 8, humate and fulvate complexes are the only forms of dissolved Cu. Humin is largely insoluble and has little effect on Cu mobility between pH 2 and 12. The implication of this study is that measurement of total soil organic content and water leaching tests should be a standard part of contaminated site investigation.

Adsorption↗
PubMed2001

Copper complexes of glycyl-histidyl-lysine and two of its synthetic analogues: chemical behaviour and biological activity.

Copper complex formation equilibria of glycyl-L-histidyl-L-lysine (Gly-His-Lys, GHK) and of two synthetic analogues, where the histidine residue was replaced with a synthetic amino acid (L-spinacine or L-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid), have been carefully investigated using different experimental techniques: potentiometry, solution calorimetry, UV-VIS spectrophotometry, circular dichroism and electron paramagnetic resonance spectroscopies. All the ligands formed complexes having different stoichiometries and stabilities; evidence for the formation of binuclear species is also shown. The structures of the main complexes are discussed. It is suggested that the lateral lysine amino group participates in complex formation, but only at alkaline pH values: at physiological pH this group is protonated and available for possible interactions with cellular receptors. The above tripeptides have been tested for their enzymatic stability in human serum: the synthetic compounds showed no significant degradation for at least 3 h. Finally, their activity as growth factor has been studied in vitro. The two synthetic analogues showed an activity comparable to or even higher than that of GHK, thus suggesting their possible use as additives in cell culture media, even in the presence of serum. Relevant information on the GHK action mechanism as cell growth factor has been obtained: the formation of copper complexes, driven by the first (Gly) residue, appears necessary while the second residue (His) does not appear to play a specific role; the presence of the free side chain of the third residue (Lys) appears to be of fundamental importance.

Circular Dichroism↗
PubMed1999

Characterization of potential NMDA and cholecystokinin antagonists I. acid-base properties of 2-methyl-4-oxo-3H-quinazoline-3-alkyl-carboxylic acids at the molecular and submolecular levels.

The protonation macroconstants (log K) of 4(3H)-quinazolone (1) and two 2-methyl-4-oxo-3H-alkyl-quinazoline-3-carboxylic acid derivatives (2,3) were determined by pH-potentiometry. The acid-base chemistry of compounds 2 and 3, where proton-bindings take place in an overlapping fashion, was described in terms of protonation microconstants as well. Microspeciation was carried out by two means: UV-pH titration (selective, pH-dependent monitoring of the N1-binding site), and deductively (using a derivative compound as covalently fixed model of one of the protonation isomers). The microconstant values obtained by the two different methods are in agreement within 0.05 log K units. Microspeciation revealed remarkable differences between the two homologue compounds (2 and 3). The microconstant values show that insertion of a second methylene moiety into the aliphatic acid side-chain (1) increases the electron-density and most basicity parameters of both functional groups; (2) significantly modifies the extent of site-site interactions in the molecule; (3) opens new conformational preferences by N1 ring nitrogen-carboxylic group intramolecular hydrogen bond formation and (4) reverses the predominantly zwitterion-involved protonation pathway into a neutral form-involved pathway. These molecules exemplify that microconstant values allow the comparative prediction and quantitative evaluation of pharmacokinetic behaviour, and signify the fact that microspeciation is a powerful tool in the process of drug development.

Cholecystokinin↗
PubMed2002

Drug-selective electrode for ketamine determination in pharmaceutical preparations and electrochemical study of drug with BSA.

Ion-selective membrane electrode to the drug ketamine hydrochloride has been constructed using a modified PVC membrane which has ionic end-groups as ion-exchanger sites and which was cast using plasticized with ortho-nitrophenyloctyl ether (o-NPOE) as plastisizer. This drug electrode show excellent Nernstian responses (59 mV per decade) in the concentration range 1 x 10(-5)-1 x 10(-2) M with a detection limit of 5 x 10(-6) M. Response time was about 10 s for ketamine concentrations between 1 x 10(-5) and 1 x 10(-2) M. The response is not affected by pH between 4 and 8.5. Selectivity coefficients against various organic and inorganic cations were evaluated. The electrode was applied for determination of ketamine hydrochloride in pharmaceutical preparations using direct potentiometry. The drug electrode has also been used to study the interaction of bovine serum albumin (BSA) with ketamine in buffer solution (phosphate, pH 7). The saturated quantities of ketamine binding were 114, 32 and 25 mol/mol in 0.01, 0.02 and 0.1% of protein, respectively. The Hill equations were applied to obtain co-operative drug bindings to BSA at 27 degrees C.

Animals↗
PubMed2003

Determination of dissociation constants of labile drug compounds by capillary electrophoresis.

The utility of capillary electrophoresis (CE) for determination of the negative logarithm of dissociation constants (pK(a)) of labile compounds was investigated. In this study pyridinyl-methyl-sulfinyl-benzimidazoles (PMSB's), which have both an acidic and a basic pK(a), were selected as a first set of model drug compounds. This is a group of compounds that are known to degrade in aqueous solutions under neutral and acidic conditions which thus may impair their pK(a) determination when using common batch techniques based on spectrophotometry or potentiometry. An additional set of model drug compounds, benzenesulfonic acid phenethyloxy-phenyl esters (BSAP's), which are labile at high pH, were also studied. It is demonstrated that pK(a) values can be determined with high precision and accuracy by CE for both these sets of model compounds because decomposition products and impurities can be sufficiently separated from the main component. Based on the results in this study, a general strategy is proposed and discussed for determination of pK(a) for labile compounds. Key steps comprise use of a stabilizing sample diluent, injection by electromigration, short analysis time, and characterization of the main component by UV-Vis spectra.

Benzimidazoles↗
PubMed1998

Copper(II) increases bile acid binding to asparagine.

Interactions of two bile acids (cholic and glycocholic acids) with asparagine have been studied by potentiometry in aqueous solutions under conditions similar to those observed in biological fluids (37 degrees C and I = 0.15 M NaCl), and in the absence and presence of copper(II). To characterize the equilibria for the systems copper(II)/bile acid/asparagine, specifically to assess cooperative binding between bile acids and asparagine, the acidity constant of asparagine and formation constants for copper(II)/bile acid and copper(II)/asparagine were also obtained under the same conditions. The results obtained suggest cooperativity in the binding of bile acid to asparagine in the presence of copper(II).

Asparagine↗
PubMed2001

Solution chemistry and DNA binding properties of MEN 10755, a novel disaccharide analogue of doxorubicin.

The behavior under physiological conditions of MEN 10755, a novel disaccharide analogue of doxorubicin, was investigated in detail by a variety of spectroscopic techniques including spectrophotometry, fluorescence, and (1)H NMR. The pH dependent properties of MEN 10755 were also analysed by spectrophotometry and potentiometry within the pH range 5--11. It is found that MEN 10755 behaves very similarly to doxorubicin and reproduces closely its pH dependent pattern. Like doxorubicin, MEN 10755 undergoes dimerization with a significantly smaller association constant. The interaction of MEN 10755 with calf thymus DNA was studied in detail. Spectrophotometric and fluorescence titrations of MEN 10755 with calf thymus DNA show spectral patterns almost identical to those obtained with doxorubicin implying that the binding mechanism and the stability of the resulting adducts are very similar. An apparent affinity constant of 1.2 x 10(6) was determined for the interaction of MEN 10755 with calf thymus DNA to be compared with the value of 3.3 x 10(6) measured for doxorubicin, under the same conditions. The effects of both anthracyclines on the thermal denaturation profiles of calf thymus DNA were also analyzed; both compounds turned out to stabilize to a similar extent the DNA double helix and to give rise to a characteristic two-step melting profile. The implications of the present results for the pharmacological activity and the mechanism of action of this novel and promising antitumor compound are discussed.

Animals↗
PubMed2002

Assay methods and biological roles of labile sulfur in animal tissues.

Sulfur is a chemically and biologically active element. Sulfur compounds in animal tissues can be present in two forms, namely stable and labile forms. Compounds such as methionine, cysteine, taurine and sulfuric acid are stable sulfur compounds. On the other hand, acid-labile sulfur and sulfane sulfur compounds are labile sulfur compounds. The sulfur atoms of labile sulfur compounds are liberated as inorganic sulfide by acid treatment or reduction. Therefore, the determination of sulfide is the basis for the determination of labile sulfur. Determination of sulfide has been performed by various methods, including spectrophotometry after derivatization, ion chromatography, high-performance liquid chromatography after derivatization, gas chromatography, and potentiometry with a sulfide ion-specific electrode. These methods were originally developed for the determination of sulfide in air and water samples and were then applied to biological samples. The metabolic origin of labile sulfur in animal tissues is cysteine. The pathways of cysteine metabolism leading to the formation of sulfane sulfur are discussed. Finally, reports on the physiological roles and pathological considerations of labile sulfur are reviewed.

Animals↗