The local structures of Cu(II) and Zn(II) complexes of hyaluronate

Screening of the Chemical Composition and Identification of Hyaluronic Acid in Food Supplements by Fractionation and Fourier-Transform Infrared Spectroscopy

Hyaluronic acid, together with collagen, vitamins or plant extracts, is a part of many cosmetic and food preparations. For example, this polysaccharide is used in formulation of many food supplements due to its protective effects on human health. In this work, the screening of the chemical composition of three chosen dietary supplements (powder, tablets and capsules) containing hyaluronic acid was carried out using Fourier-transform infrared spectroscopy. Because of the low amount of analyte in all these samples, it was isolated or concentrated prior to the analysis using a suitable sequential fractionation protocol. Individual isolation procedures were established for each sample based on their declared composition. Firstly, the major components such as collagen or vitamins were removed to obtain polysaccharide fractions by the enzymatic treatment and/or washing out with the appropriate solvents. In some cases, the water insoluble part was removed from the rest dissolved in water. Then, hyaluronic acid was precipitated with copper(II) cations and thus separated from the other polysaccharides. Finally, the analyte was identified in the enriched fractions by the characteristic vibrational bands. The amount of hyaluronic acid in the purified fractions was determined in three ways: gravimetrically, spectrophotometrically, and using isotachophoresis. The combination of the appropriate preparative and analytical steps led to the successful evaluation of chemical composition, finding and quantification of hyaluronic acid in all the studied samples.

The molecular basis of memory

We propose a tripartite biochemical mechanism for memory. Three physiologic components are involved, namely, the neuron (individual and circuit), the surrounding neural extracellular matrix, and the various trace metals distributed within the matrix. The binding of a metal cation affects a corresponding nanostructure (shrinking, twisting, expansion) and dielectric sensibility of the chelating node (address) within the matrix lattice, sensed by the neuron. The neural extracellular matrix serves as an electro-elastic lattice, wherein neurons manipulate multiple trace metals (n > 10) to encode, store, and decode coginive information. The proposed mechanism explains brains low energy requirements and high rates of storage capacity described in multiples of Avogadro number (N(A) = 6 × 10(23)). Supportive evidence correlates memory loss to trace metal toxicity or deficiency, or breakdown in the delivery/transport of metals to the matrix, or its degradation. Inherited diseases revolving around dysfunctional trace metal metabolism and memory dysfunction, include Alzheimer's disease (Al, Zn, Fe), Wilson's disease (Cu), thalassemia (Fe), and autism (metallothionein). The tripartite mechanism points to the electro-elastic interactions of neurons with trace metals distributed within the neural extracellular matrix, as the molecular underpinning of "synaptic plasticity" affecting short-term memory, long-term memory, and forgetting.

Protective effects of manganese(II) chloride on hyaluronan degradation by oxidative system ascorbate plus cupric chloride

The degradation of several high-molar-mass hyaluronan samples was investigated in the presence of ascorbic acid itself and further by an oxidative system composed of ascorbic acid plus transition metal ions, i.e. Fe(II) or Cu(II) ions. The latter oxidative system imitates conditions in a joint synovial fluid during early phase of acute joint inflammation and can be used as a model for monitoring oxidative degradation of hyaluronan under pathophysiological conditions. The system Cu(II) plus ascorbate (the Weissberger oxidative system) resulted in a more significant decrease of hyaluronan molar mass compared to the oxidative system Fe(II) plus ascorbate. Addition of manganese(II) chloride was found to decrease the rate of the oxidative damage of hyaluronan initiated by ascorbate itself and by the Weissberger system.

Oxidative damage to extracellular matrix and its role in human pathologies

The extracellular compartments of most biological tissues are significantly less well protected against oxidative damage than intracellular sites and there is considerable evidence for such compartments being subject to a greater oxidative stress and an altered redox balance. However, with some notable exceptions (e.g., plasma and lung lining fluid) oxidative damage within these compartments has been relatively neglected and is poorly understood. In particular information on the nature and consequences of damage to extracellular matrix is lacking despite the growing realization that changes in matrix structure can play a key role in the regulation of cellular adhesion, proliferation, migration, and cell signaling. Furthermore, the extracellular matrix is widely recognized as being a key site of cytokine and growth factor binding, and modification of matrix structure might be expected to alter such behavior. In this paper we review the potential sources of oxidative matrix damage, the changes that occur in matrix structure, and how this may affect cellular behavior. The role of such damage in the development and progression of inflammatory diseases is discussed.

The antioxidant effect exerted by TGF-1beta-stimulated hyaluronan production reduced NF-kB activation and apoptosis in human fibroblasts exposed to FeSo4 plus ascorbate

Previous studies suggest that Transforming growth factor-1beta (TGF-1beta) administration in human fibroblasts exposed to oxidative stress is able to modulate hyaluronan synthases (HASs). HAS modulation in turn increases high molecular weight (Hyaluronan) HA concentration. Nuclear factor kB (NF-kB) is a response transcription factor involved in inflammation and acts by enabling the expression of certain detrimental molecules. Caspases are specific proteases responsible for regulating and programming cell death. HA at medium molecular weight together with chondroitin-4-sulphate proved to be effective on NF-kB and caspases. We investigated whether the protective effect afforded by the high molecular weight HA produced by TGF-1beta treatment has any effect on NF-kB and apoptosis activation in fibroblast cultures exposed to oxidative stress. Generation of free radicals gives rise to cell death, increases lipid peroxidation, activates NF-kB, reduces its cytoplasmic inhibitor IkBalpha, augments caspase-3 and caspase-7 gene expression and their relative protein activity, and depletes catalase (CAT) and glutathione peroxidase (GPx). Treatment of fibroblasts with TGF-1beta 12 h before inducing oxidative stress greatly increased HA levels, ameliorated cell survival, inhibited lipid peroxidation, blunted NF-kB translocation, normalized IkBalpha protein, reduced caspase gene expression and protein levels, and restored the endogenous antioxidants CAT and GPx. Since it was previously reported that antioxidants can work as inhibitors of NF-kB and apoptosis induction we can hypothesize that endogenous HA, by inhibiting lipid peroxidation, may block a step whereby free radical activity converges in the signal transduction pathway leading to NF-kB and caspase activation.

Characterization of complexes formed between [Me2Sn(IV)]2+ and carboxymethylcelluloses

Complexes formed between carboxymethylcellulose (CMC) and the [Me(2)Sn(IV)]2+ cation have been prepared in the solid state and characterized by FTIR and Mössbauer spectroscopy. The complexes contained CMC with varying molar weight and degree of carboxylation, and the complexes were isolated both from acidic and from neutral solutions at varying metal-to-ligand ratios. The characteristic vibration bands of the ligands were identified from their pH-dependent FTIR spectra. In the organotin(IV) complexes obtained at pH approximately 2, the -COO- moieties were found to be coordinated in a monodentate manner, and the band characteristic of the protonated (unbound) -COO- group(s) was also identified. The broad -OH band can be interpreted as the sum of the contributions of the alcoholic -OH groups of the anhydroglucose units and the mixed organotin aqua complexes. In complexes obtained at pH approximately 7, the broad -OH band significantly sharpens, which is probably due to the metal-ion induced deprotonation and subsequent coordination of the alcoholic -OH groups. At the same time, -COO- groups are also involved in the coordination of the metal ions, resulting in a complicated network that forms through inter- and intramolecular bridges. Quadrupole splitting (/Delta(exp)/) values observed by Mössbauer spectroscopy revealed that the valence state of tin is four in all of the complexes. The /Delta(exp)/ values were compared with the calculated ones, obtained from the pqs theory. From these data, trigonal bipyramidal (Tbp) and octahedral (Oh) geometries have been suggested for the complexes obtained. It has also been concluded that the structure of the complexes prepared depends mainly on the pH of the solution, and it is relatively insensitive to the other parameters, like molar mass or degree of carboxylation of the ligand, or the metal-to-ligand ratio in the reaction mixture.

Purified human plasma glycosaminoglycans limit oxidative injury induced by iron plus ascorbate in skin fibroblast cultures

A number of studies in vivo and in vitro showed that high levels of glycosaminoglycans (GAGs) are found as a consequence of free radical damage. The GAG over production may represent an endogenous mechanism capable to limit oxidative damage. Based on these hypotheses, the aim of this study was to evaluate the antioxidant property of GAGs of human origin in fibroblast cultures. Purified human plasma GAGs were added to the fibroblast cultures in which oxidative stress was induced by the oxidizing system employing iron (Fe2+) plus ascorbate. We assessed cell death, lactate dehydrogenase activity, membrane lipid peroxidation, DNA damage, protein oxidation, hydroxyl radical (OH*) generation and endogenous antioxidant depletion. The exposure of fibroblasts to FeSO4 produced cell death and increased OH* production. It also caused DNA strand breaks and protein oxidation as shown by the DNA fragment analysis and protein carbonyl content, respectively. In addition, FeSO4 enhanced lactate dehydrogenase activity and lipid peroxidation while decreased antioxidant defences. Purified human GAGs, at three different doses, reduced cell death, limited DNA fragmentation and protein oxidation, decreased OH* generation and lactate dehydrogenase activity, inhibited lipid peroxidation and improved endogenous antioxidant defences. These results further support the hypothesis that these molecules may function as antioxidants.

Coordination modes between copper(II) and N-acetylneuraminic (sialic) acid from a 2D-simulation analysis of EPR spectra. Implications for copper mediation of sialoglycoconjugate chemistry relevant to human biology

The equilibrium distribution of species formed between Cu(II) and N-acetylneuraminic (sialic) acid (I, LH) at 298 K has been determined using a two-dimensional (2D) simulation analysis of electron paramagnetic resonance (EPR) spectra. In acidic solutions (pH values < 4), the major species present are Cu(2+), [CuL]+ [logbeta = 1.64(4)], and [CuL2] [logbeta = 2.77(5)]. At intermediate pH values (4.0 < pH < 7.5), [CuL2H-1]- [logbeta = -2.72(7)] and two isomers of [CuLH-1] [logbeta (overall) = -3.37(2)] are present. At alkaline pH values (7.5 < pH < 11), the major species present is [CuL2H-2]2-, modeled as three isomers with unique giso and Aiso values [logbeta (overall) = -8.68(3)]. Two further species ([CuLH-3]2- and [CuL2H-3]3-) appear at pH values > 11. It is proposed that [CuL]+ most likely features I coordinated via the deprotonated carboxylic acid group (O1) and the endocyclic oxygen atom (OR) forming a five-membered chelate ring. Select Cu(II)-I species of the form [CuLH-1] may feature I acting as a dianionic tridentate chelate, via oxygen atoms derived from O1, OR, and one deprotonated hydroxy group (O7 or O8) from the glycerol tail. Alternatively, I may coordinate Cu(II) in a bidentate fashion as the tert-2-hydroxycarboxylato (O1,O2) dianion. Spectra predicted for Cu(II)-I complexes in which I is coordinated in either a O1,OR {I1-} or O1,O2 {I2-} bidentate fashion {e.g., [CuL]+ (O1,O R), [CuL2] (bis-O1,O R), [CuLH-1] (isomer: O1, O2), [CuL2H-1]- (O1, O R; O1, O2), and [CuL2H-2]2- (isomer: bis-O1, O2)} have "irregular" EPR spectra that are ascribed to the existence of Cu(II)-I(monomer) <==> Cu(II)-I(polymer) equilibria. The formation of polymeric Cu(II)-I species will be favored in these complexes because the glycerol-derived hydroxyl groups at the complex periphery (O, 7O, 8O9) are available for further Cu(II) binding. The presence of polymeric Cu(II)-I species is supported by EPR spectral data from solutions of Cu(II) and the homopolymer of I, colominic acid (Ipoly). Conversely, spectra predicted for Cu(II)-I complexes where I is coordinated in a {I2-} tridentate {e.g., [CuLH-1] (isomer: O1, O R, O7, or O8) and [CuL2H-2]2- (isomer: bis-O1,O R,O7, or O8)} or tetradentate fashion {I3-} {e.g., [CuLH-3]2- (O1, O R, O, 8O9)} are typical for mononuclear tetragonally elongated Cu(II) octahedra. In this latter series of complexes, the tendency toward the formation of polymeric Cu(II)-I analogues is small because the polydentate I effectively wraps up the mononuclear Cu(II) center. This work shows that Cu(II) could potentially mediate the chemistry of sialoglycoconjugate-containing proteins in human biology, such as the sialylated amyloid precursor protein of relevance to Alzheimer's disease.

Hypochlorite and superoxide radicals can act synergistically to induce fragmentation of hyaluronan and chondroitin sulphates

Activated phagocytes release the haem enzyme MPO (myeloperoxidase) and also generate superoxide radicals (O2*-), and hence H2O2, via an oxidative burst. Reaction of MPO with H2O2 in the presence of chloride ions generates HOCl (the physiological mixture of hypochlorous acid and its anion present at pH 7.4). Exposure of glycosaminoglycans to a MPO-H2O2-Cl- system or reagent HOCl generates long-lived chloramides [R-NCl-C(O)-R'] derived from the glycosamine N-acetyl functions. Decomposition of these species by transition metal ions gives polymer-derived amidyl (nitrogen-centred) radicals [R-N*-C(O)-R'], polymer-derived carbon-centred radicals and site-specific strand scission. In the present study, we have shown that exposure of glycosaminoglycan chloramides to O2*- also promotes chloramide decomposition and glycosaminoglycan fragmentation. These processes are inhibited by superoxide dismutase, metal ion chelators and the metal ion-binding protein BSA, consistent with chloramide decomposition and polymer fragmentation occurring via O2*--dependent one-electron reduction, possibly catalysed by trace metal ions. Polymer fragmentation induced by O2*- [generated by the superoxide thermal source 1, di-(4-carboxybenzyl)hyponitrite] was demonstrated to be entirely chloramide dependent as no fragmentation occurred with the native polymers or when the chloramides were quenched by prior treatment with methionine. EPR spin-trapping experiments using 5,5-dimethyl1-pyrroline-N-oxide and 2-methyl-2-nitrosopropane have provided evidence for both O2*- and polymer-derived carbon-centred radicals as intermediates. The results obtained are consistent with a mechanism involving one-electron reduction of the chloramides to yield polymer-derived amidyl radicals, which subsequently undergo intramolecular hydrogen atom abstraction reactions to give carbon-centred radicals. The latter undergo fragmentation reactions in a site-specific manner. This synergistic damage to glycosaminoglycans induced by HOCl and O2*- may be of significance at sites of inflammation where both oxidants are generated concurrently.

Metal-ion environment in solid Mn(II), Co(II) and Ni(II) hyaluronates

Amorphous powders and films of some metal hyaluronate complexes of general composition (C14H20O11N)2 x xH2O (M = Mn2+, Ni2+ and Co2+) have been prepared at pH 5.5-6.0. The coordination geometry around the metal ions has been analyzed by EXAFS (extended X-ray absorption fine structure) and FTIR spectroscopy. Mn2+, Ni2+, and Co2+ ions are coordinated to carboxylate oxygen atoms and water molecules. The process of local geometry formation round the metal ions is sensitive to sample preparation.

The antioxidant and antifibrogenic effects of the glycosaminoglycans hyaluronic acid and chondroitin-4-sulphate in a subchronic rat model of carbon tetrachloride-induced liver fibrogenesis

Hepatic fibrosis involves the interplay of many factors including reactive oxygen species. Recent reports described antioxidant properties of glycosaminoglycans (GAGs). Since several findings have shown that hyaluronic acid (HYA) and chondroitin-4-sulphate (C4S) may act as antioxidant molecules, the aim of this research was to evaluate the antioxidant effects of HYA and C4S treatment in a rat model of liver fibrosis. The effect on tissue inhibitors of metalloproteinases (TIMPs) was also studied. Liver fibrosis was induced in rats by eight intraperitoneal injections of CCl4, twice a week for 6 weeks. HYA or C4S alone (25 mg/kg) or HYA and C4S in combination (12.5 + 12.5 mg/kg) were administered daily by the same route during the 6 weeks. At the end of the 6-week treatment period (24 h after the last dose of GAGs), the following parameters were evaluated: (1) serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, as index of hepatic cell disruption; (2) hepatic conjugated dienes (CD), as index of lipid peroxidation; (3) hepatic TIMPs activity and expression; (4) hepatic superoxide dismutase (SOD) and glutathione peroxidase (GPx) activity, as index of endogenous defences; (5) hepatic hydroxyproline, as index of collagen deposition. CCl4-induced liver fibrosis enhanced lipid peroxidation and TIMPs activation, increased ALT and AST, depleted antioxidants SOD and GPx, and caused collagen deposition in liver tissue. Treatment with GAGs, especially when in combination, successfully reduced ALT and AST rise, lipid peroxidation by evaluating conjugated dienes, TIMPs activation and mRNA expression, partially restored SOD and GPx activities, and limited collagen deposition in the hepatic tissue. The data obtained showed that these molecules were able to limit hepatic injury induced by chronic CCl4 intoxication and especially limited liver fibrosis. They also confirm that HYA and C4S may exert antioxidant mechanism, while reduction of TIMPs expression suggests that GAGs may influence MMPs and TIMPs imbalance in liver fibrosis.

Reduction of DNA fragmentation and hydroxyl radical production by hyaluronic acid and chondroitin-4-sulphate in iron plus ascorbate-induced oxidative stress in fibroblast cultures

Glycosaminoglycans (GAGs), components of extracellular matrix, are thought to play important roles in cell proliferation and differentiation in the repair process of injured tissue. Oxidative stress is one of the most frequent causes of tissue and cell injury and the consequent lipid peroxidation is the main manifestation of free radical damage. It has been found to play an important role in the evolution of cell death. Since several reports have shown that hyaluronic acid (HYA) and chondroitin-4-sulphate (C4S) are able to inhibit lipid peroxidation during oxidative stress, We investigated the antioxidant capacity of these GAGs in reducing oxidative damage in fibroblast cultures. Free radicals production was induced by the oxidizing system employing iron (Fe2+) plus ascorbate. We evaluated cell death, membrane lipid peroxidation, DNA damage, protein oxidation, hydroxyl radical (OH*) generation and endogenous antioxidant depletion in human skin fibroblast cultures. The exposition of fibroblasts to FeSO4 and ascorbate caused inhibition of cell growth and cell death, increased OH* production determined by the aromatic trap method; furthermore it caused DNA strand breaks and protein oxidation as shown by the DNA fragments analysis and protein carbonyl content, respectively. Moreover, it enhanced lipid peroxidation evaluated by the analysis of conjugated dienes (CD) and decreased antioxidant defenses assayed by means of measurement of superoxide dismutase (SOD) and catalase (CAT) activities. When fibroblasts were treated with two different doses of HYA or C4S a protective effect, following oxidative stress induction, was shown. In fact these GAGs were able to limit cell death, reduced DNA fragmentation and protein oxidation, decreased OH* generation, inhibited lipid peroxidation and improved antioxidant defenses. Our results confirm the antioxidant activity of HYA and C4S and this could represent a useful step in the understanding of the exact role played by GAGs in living organisms.

Hyaluronate tetrasaccharide- Cu(II) interaction: a NMR study

The coordination of Cu(II) to a hyaluronate tetrasaccharide (HAt) was investigated in aqueous solution by 13C and 1H relaxation measurements at two magnetic fields, 9 and 14 T. The HAt interaction with the metal ion was monitored following the nuclear paramagnetic relaxation enhancements R1p and R2p produced by the copper addition. The data analysis shows that the paramagnetic effect is differently experienced by the nuclei in different monosaccharide residues. A molecular model for the complex HAt-Cu(II) was built taking into account the experimental data. The model shows the presence of two binding sites, both involving the carboxylate groups of the two glucuronic acid units. The first site, that best simulates the HA binding site, is located on the ligand core, while the second one is located on the terminal glucuronic acid residue. Both binding sites involve, in addition to the carboxylate groups, the O4 oxygens of the glucuronic acid residues.

XAFS Studies of Anti-Inflammatory Dinuclear and Mononuclear Zn(II) Complexes of Indomethacin

Zinc K-edge X-ray absorption fine structure (XAFS) experiments were performed in the solid and solution states at low temperature (10 K), on dimeric and monomeric anti-inflammatory Zn(II) complexes of indomethacin [1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid=IndoH] of the formula [Zn2(Indo)4L2] [L=pyridine (Py), N,N-dimethylacetamide (DMA)], [Zn(Indo)2L2] [L=ethanol (EtOH), methanol (MeOH)], and Zn(II) acetate dihydrate [Zn(OAc)2(OH2)2]. The bond distances and angles obtained from multiple-scattering fits to the XAFS data of the Zn(II) dimeric complexes in the solid and solution states exhibit excellent correspondence with those obtained from single crystal diffraction studies. The Zn...Zn separations of 2.97 and 2.96 A and carboxylate group O-C-O angles of 125 degrees for powdered [Zn2(Indo)4(Py)2] and [Zn2(Indo)4(DMA)2] agree well with the XRD values of 2.969(1) and 2.9686(6) A and 125.8(4) degrees and 126.1(2) degrees, respectively. The calculated Zn-O(RCOO) and Zn-L bond distances of 2.03 and 2.04 A, or 2.02 and 1.98 A for Py or DMA complexes, respectively, also agree well with crystallographic data. The X-ray powder diffraction data on samples of the monomers exhibited additional reflections apart from those due to the crystallographically characterized cis-[Zn(eta2-O,O'-Indo)2L2], but microanalyses were consistent with this formulation. Therefore, mixed models that contained the cis complex and a second component consisting of a trans-six-coordinate complex, a five-coordinate complex, or a four-coordinate complex were used to model the XAFS. The best fits to the XAFS data were obtained with a mixture of the cis-six-coordinate complex and a four-coordinate complex containing two monodentate Indo ligands. The bond lengths for the six-coordinate structure were consistent with those determined on a single crystal, and those for the four-coordinate complexes were consistent with related four-coordinate structures with two monodentate carboxylate ligands. Dissolution of the dimer (DMA adduct) in DMF resulted in a mixture of dimer and monomer species as shown by MS XAFS fitting. This is the first time that solution structures have been determined for anti-inflammatory Zn(II) complexes, and this is an important first step in understanding the pharmacology of the complexes.

Mechanism of the transition-metal-catalyzed mutarotation reaction of N-(p-chlorophenyl)-beta-D-glucopyranosylamine in methanol

Rate constants for the mutarotation reaction of N-(p-chlorophenyl)-beta-D-glucopyranosylamine (NGlc) in methanol have been determined in the presence of transition metal chlorides (MCl(2)), at 25 degrees C. The activity of the metal ions catalyzing the alpha-pyranoside<-->beta-pyranoside interconversion has been found to increase in the following series: Mn(2+)<Co(2+)<Ni(2+)<Zn(2+)<Cu(2+). The pHs of the methanolic solutions of the chlorides were measured and acidity constants of the [MCl(CH(3)OH)(5)](+) ions and NGlc were determined in this solvent. Addition of NGlc to the salt solutions resulted in lowering their pH. Raising the methyloxonium ion concentration in the solutions resulted in rapid increase in the rate of mutarotation in the presence of MCl(2). It is suggested that in solutions of NGlc and MCl(2), the CH(3)OH(2)(+) ions are generated by solvolysis of the salts and additionally by dissociation of the hydroxyl group at C-6 of the glucosylamine molecule taking place during complexation of the metal ions. A scheme has been derived for interaction of deprotonated NGlc molecules with the transition metal ions.

Effect of different metal ions on the oxidative damage and antioxidant capacity of hyaluronic acid

Degradation and the antioxidative effect of Na-, Zn-, Co-, Cu-, and Mn-hyaluronic acid (HA) associates were studied. Our findings revealed the protective effect of certain counterions against ROS-induced HA degradation. We could also separate the antioxidative effect of certain counterions from that of the HA by examining the effect of the counterions in their free ionic forms. The result showed that metal ions with altering oxidative status (Co(2+), Cu(2+), Mn(2+)) proved to be effective in themselves or their effect added to that of HA when HA was also effective. Moreover, the effects of Co-HA against z.rad;O(2)(-) and of Mn-HA against ONOO(-) as well as the synergic effect of Zn-HA associates where Zn(2+) is of fixed oxidative status were attributed to the structure-stabilizing complex formed between certain counterions and HA. Our examination also concerned the influence of HA associates on the indirect antioxidation related to Fe(2+) chelating. The individual effects of Zn(2+), Co(2+), and Cu(2+) were only detectable, which could be explained by the competitive displacement of ferrous from its binding site.

Equilibrium and structural studies on metal complexes of carbohyrates and their derivatives

A summary is presented of the studies of our group on metal complexes of carbohydrates (aldoses, ketoses, mono-, di- and polysaccharides) and their derivatives (aldonic, alduronic acids, polyalcohols, amino sugars, amino acid sugar adducts, AMP, ATP, etc.). The results are reported of equilibrium, electrochemical, solution and solid-state structural studies of complexes of transition metals [Cu(II), Fe(III), Ni(II), Zn(II), Co(II), Ag(I), Mn in different oxidation states and organotin(IV)]. The structural parameters (coordination number, bond distance, and Debye-Waller factor) obtained by extended X-ray absorption fine structure spectroscopic (EXAFS) spectroscopy are discussed in detail. The general rules concerning the formation and structure of such complexes are emphasized.

23Na NMR study of the interaction between hyaluronan and the bications Ca(++), Mg(++) and Cu(++)

The relaxation rate R = pi Delta nu(1/2) of the quadrupolar (23)Na nucleus was measured at pH approximately 7 using a 200 MHz NMR spectrometer with a view to observe the interaction between hyaluronan and its natural counterion Na(+) and the bications Ca(++), Mg(++) and Cu(++). An interpretation of our results, by means of the "entropy of fluctuations" concept of Na(+), is presented. We show that Cu(++) ions are more effective than Ca(++) and Mg(++). A possible model of complexation of Cu(++) in a cage formed by the 1-4 glycosidic bond, the carboxylate side-chain and the acetoamide side-chain is proposed, according to electrostatic potential computations using the ZINDO1 quantum semi empirical method.

Binding ability of sialic acid towards biological and toxic metal ions. NMR, potentiometric and spectroscopic study

The binary complexes of 5-amino-3,5-dideoxy-D-glycero-D-galactononulosic acid (NANA), commonly called N-acetyl neuraminic acid, formed with biological metal ions such as Co(II) and Cu(II) and toxic metal ions such as Cd(II) and Pb(II) were investigated in aqueous solution by means of potentiometry, UV and NMR spectroscopy. The corresponding ternary systems with 2,2'-bipyridine were studied in aqueous solution by potentiometry and UV spectroscopy. NANA co-ordinates all metal ions, in both binary and ternary systems through the carboxylic group (protonated or deprotonated according to pH), pyranosidic ring oxygen and glycerol chain alcoholic hydroxy groups. The prevailing species in the pH range 2-7 are of [M(NANA)(2)] type, and their stability constants are greater than those of simple carboxylate complexes. Above pH 7, the species [M(NANA)(2)OH](-) are also formed, but they do not prevent the precipitation of metal hydroxides. This work provides information on the solution state chemistry of NANA in the presence of bivalent metal ions; its great affinity for the toxic metals Cd(II) and Pb(II), near physiological conditions, and the relatively high stability of the complex species found may also account for the mechanism of toxicity.

Sugar complexes with metal(2+) ions: thermodynamic parameters of associations of Ca(2+), Mg(2+) and Zn(2+) with galactaric acid

A solution study on the complex ability of galactaric acid (GalaH(2)) for complexation with Ca(2+), Mg(2+) and Zn(2+) ions is reported. The stability constants of the complex species are determined by means of potentiometric measurements. From the dependence of stability constants on temperature, the DeltaH degrees and DeltaS degrees values are also determined. The formation of the complex species is an endothermic process and DeltaH degrees and DeltaS degrees values suggest a chelate coordination mode of galactaric acid involving carboxylic oxygen and alpha-hydroxylic group. The prevailing species at acidic or neutral pH is [MGala] (M=Ca(2+), Mg(2+), Zn(2+)) which is also isolated in the solid state and characterised by means of IR spectroscopy. On increasing pH, the [MGalaH(-1)](-) species is also formed, where the coordinated OH group undergoes deprotonation.

Metal ion coordination of macromolecular bioligands: formation of zinc(II) complex of hyaluronic acid

The coordination of zinc(II) ion to hyaluronate (Hya), a natural copolymer, in aqueous solution at pH 6 was investigated by potentiometric and circular dichroism (CD) spectroscopic methods, and by monitoring the changes in macroscopic properties by high-precision measurements. The zinc(II)-selective electrode, and CD measurements proved the binding of zinc(II) by Hya. A number of Hya fragments (Mr approximately 3.3 x 10(3)-1.4 x 10(6)) were studied to estimate the contributions of the polyelectrolyte effect, the solvation and host-guest interactions to the extra stabilization of the macromolecular zinc(II) complexes as compared with the monomeric unit. The zinc(II) ion activity increase reflected a stability decrease for the fragments with Mr < 4 x 10(4). This molecular weight differs from that where cleavage of the Hya skeleton starts (approximately 5 x 10(5), according to the size-exclusion gel, and anion-exchange chromatographic behavior of the Hya fragments) and from that where the polyelectrolyte effect stops (approximately 6 x 10(3)). The excess volumes and Bingham shear yield values of the solutions revealed the transformation of the coherent random coil structure stabilized by intermolecular association in the NaHya to an intramolecular association producing the globular structure of the ZnHya molecule, with a smaller but more strongly bound solvate water sheet.

Preparation and characterisation of copper(II) hyaluronate

Amorphous copper complexes of the general composition Cu(C14H20O11N)2 x xH2O have been prepared with high- and low-molecular-weight hyaluronic acid (HA). Optimal conditions for preparation are obtained at pH values from 5.0 to 5.5, with a molar ratio of HA versus Cu2+ of 1:1, and at a mass concentration of 5 and 10 mg/mL for high- (Mw = 1.8 x 10(6) Da) and low-molecular-weight sodium hyaluronate (Mw = 2 x 10(5) Da), respectively. The coordination polyhedron of the copper ion has been elucidated by EXAFS and XANES spectroscopy. Copper atoms are octahedrally coordinated in both cases with four equatorial Cu-O bond lengths of 1.95 A, and two axial Cu-O bonds of 2.46 A. Visible spectra of acidic aqueous solution suggest that substitution of axial oxygens by NH groups occurs at pH 6.5 or higher. If the pH value of the copper(II) hyaluronate solution increases above 6.5, the coordination of copper(II) changes. It is very likely that the N atom coming from the acetamido group enters into the coordination sphere of the copper(II) ion.

Control of enzymatic degradation of hyaluronan by divalent cations

Enzymatic degradation of hyaluronan (HA) by testicular hyaluronidase (HAase, hyaluronate 4-glucanohydrolase) requires inclusion of mono- or divalent cations in the reaction mixture. Most divalent cations activated HAase with equal potency; however, Cu2+ suppressed degradation, and Ca2+ showed a concentration-dependent regulation of size of the oligosaccharide products. Careful selection of HAase assay parameters is critical for discovery of novel HAase inhibitors and for preparation of controlled-size oligosaccharide fragments.