Simultaneous Determination of Tyrosine and Histidine by Differential Pulse Cathodic Stripping Voltammetry Using H‐point Standard Addition Method in Tap and Seawater

H‐point standard addition method (HPSAM) has been applied for simultaneous determination of tyrosine and histidine in trace levels using copper ions by adsorptive cathodic stripping voltammetry. The amino acids‐Cu(II) complexes were accumulated onto the surface of a hanging mercury drop electrode for 40 s. The reduction peaks of preconcentrated complexes were used for simultaneous determination of amino acids in the range 8.0–180 and 30–1100 nM for tyrosine and histidine respectively. The effect of various parameters such as pH, concentration of copper, accumulation time and scan rate on the selectivity were studied. Under the optimized conditions the method was successfully applied for determination of tyrosine and histidine in synthetic and real samples.     

Selective determination of amino acids using flow injection analysis coupled with chemiluminescence detection

The determination of the amino acids proline, histidine, tyrosine, arginine, phenylalanine and tryptophan using flow injection analysis (FIA) with chemiluminescence detection is described. Proline was the only amino acid to exhibit chemiluminescence with the tris(2,2-bipyridyl)ruthenium(III) reaction at pH 10. While, histidine was found to selectively enhance the reaction of luminol with Mn(II) salts in a basic medium. Acidic potassium permanganate chemiluminescence was able to selectively determine tyrosine at pH 6.75. Low pressure separations using a C18 guard column allowed the simultaneous determination of tyrosine and tryptophan or phenylalanine and tryptophan with acidic potassium permanganate and copper(II)-amino acid-hydrogen peroxide chemiluminescence, respectively. Precision for each method was less than 3.9% (R.S.D.) for five replicates of a standard (1×10⁻⁵ M) and the detection limits ranged between 4×10⁻⁹ and 7×10⁻⁶ M. Preliminary investigations revealed that the methodology developed was able to selectively determine the individual amino acids in an equimolar mixture of the 20 naturally occurring amino acids.     

The effect of Cu(II) ions on dopaquinone cyclization

The kinetics of the dopaquinone cyclization in the absence and presence of Cu(II) ions at pHs from 6 to 7.4 has been studied by cyclic, normal and reverse pulse voltammetry. Distinct inhibition of the dopaquinone ring closure reaction was observed in the. presence of Cu(II) ions. At pHs below 6 this effect is attributed to the formation of amino acid type complexes. At pH 7.4 the amino acid type and the catechol type Cu(II)-DOPA chelates coexist, and simultaneous interactions of copper ions with both ends of the DOPA molecule result in the association of the Cu(II)-DOPA complexes. These effects, observed at physiological pH, suggest that the rate of melanin formation is affected by the presence of Cu(II) ions.     

Products of Cu(II)-catalyzed oxidation of alpha-synuclein fragments containing M1-D2 and H50 residues in the presence of hydrogen peroxide

Metal-catalyzed oxidation (MCO) of proteins is mainly a site-specific process in which one or a few amino acids at metal-binding sites on the protein are preferentially oxidized. The oxidation of proteins by MCO can lead to oxidation of amino acid residue side chains, cleavage of the peptide bonds and formation of covalent protein-protein cross-linked derivatives. In an attempt to elucidate the products of the copper(II)-catalyzed oxidation of the 29-56, M29-D30-56 and Ac-M29-D30-56 fragments of alpha-synuclein, high performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) methods and Cu(II)/hydrogen peroxide as a model oxidizing system were employed. The peptide solution (0.50 mM) was incubated at 37 degrees C for 24 h with metal : peptide : hydrogen peroxide 1 : 1 : 4 molar ratio in phosphate buffer, pH 7.4. Oxidation targets for all studied peptides are the histidine residues coordinated to the metal ions. For the M29-D30-56 and Ac-M29-D30-56 peptides the oxidation of the methionine residue to methionine sulfoxide and sulfone is observed. The cleavage of the peptide bond M29-D30 for the M29-D30-56 peptide was detected as metal binding residues. The fragmentations of the M29-D30-56 peptide near the Lys residues were observed supporting the participation of this (Lys) residue in the coordination of the copper(II) ions.     

Effects of transition metal ion coordination on the collision-induced dissociation of polyalanines

Transition metal-polyalanine complexes were analyzed in a high-capacity quadrupole ion trap after electrospray ionization. Polyalanines have no polar amino acid side chains to coordinate metal ions, thus allowing the effects metal ion interaction with the peptide backbone to be explored. Positive mode mass spectra produced from peptides mixed with salts of the first row transition metals Cr(III), Fe(II), Fe(III), Co(II), Ni(II), Cu(I), and Cu(II) yield singly and doubly charged metallated ions. These precursor ions undergo collision-induced dissociation (CID) to give almost exclusively metallated N-terminal product ions whose types and relative abundances depend on the identity of the transition metal. For example, Cr(III)-cationized peptides yield CID spectra that are complex and have several neutral losses, whereas Fe(III)-cationized peptides dissociate to give intense non-metallated products. The addition of Cu(II) shows the most promise for sequencing. Spectra obtained from the CID of singly and doubly charged Cu-heptaalanine ions, [M + Cu - H](+) and [M + Cu](2+) , are complimentary and together provide cleavage at every residue and no neutral losses. (This contrasts with [M + H](+) of heptaalanine, where CID does not provide backbone ions to sequence the first three residues.) Transition metal cationization produces abundant metallated a-ions by CID, unlike protonated peptides that produce primarily b- and y-ions. The prominence of metallated a-ions is interesting because they do not always form from b-ions. Tandem mass spectrometry on metallated (Met = metal) a- and b-ions indicate that [b(n) + Met - H](2+) lose CO to form [a(n) + Met - H](2+), mimicking protonated structures. In contrast, [a(n) + Met - H](2+) eliminate an amino acid residue to form [a(n-1) + Met - H](2+), which may be useful in sequencing.     

Substantial contribution of the two imidazole rings of the His13-His14 dyad to Cu(II) binding in amyloid-β(1-16) at physiological pH and its significance

The interaction of amyloid-β (Aβ) peptide with Cu(II) appears to play an important role in the etiology of Alzheimer's disease. At physiological pH, the Cu(II) coordination in Aβ is heterogeneous, and there exist at least two binding modes in which Cu(II) is coordinated by histidine residues. Electron spin resonance studies have revealed a picture of the Cu(II) binding at a higher or lower pH, where only one of the two binding modes is almost exclusively present. We describe a procedure to directly examine the coordination of Cu(II) to each histidine residue in the dominant binding mode at physiological pH. We use nonlabeled and residue-specifically (15)N-labeled Aβ(1-16). For quantitative analysis, the intensities of three-pulse electron spin-echo envelope modulation (ESEEM) spectra are analyzed. Spectral simulations show that ESEEM intensities provide information about the contribution of each histidine residue. Indeed, the ESEEM experiments at pH 6.0 confirm the dominant contribution of His6 to the Cu(II) coordination as expected from the work of other researchers. Interestingly, however, the ESEEM data obtained at pH 7.4 reveal that the contributions of the three residues to the Cu(II) coordination are in the order of His14 ≈ His6 > His13 in the dominant binding mode. The order indicates a significant contribution from the simultaneous coordination by His13 and His14 at physiological pH, which has been underappreciated. These findings are supported by hyperfine sublevel correlation spectroscopy experiments. The simultaneous coordination by the two adjacent residues is likely to be present in a non-β-sheet structure. The coexistence of different secondary structures is possibly the molecular origin for the formation of amorphous aggregates rather than fibrils at relatively high concentrations of Cu(II). Through our approach, precise and useful information about Cu(II) binding in Aβ(1-16) at physiological pH is obtained without any side-chain modification, amino acid residue replacement, or pH change, each of which might lead to an alteration in the peptide structure or the coordination environment.     

Characterisation by immobilised metal ion affinity chromatographic procedures of the binding behaviour of several synthetic peptides designed to have high affinity for Cu(II) ions.

In this investigation, several peptides containing an increasing number of histidine residues have been designed and synthesised. The peptides involved repeat units of either the pentameric EAEHA or the tetrameric HLLH sequence motifs. Adsorption isotherms for these synthetic peptides and hexahistidine (hexa-His) as a control substance were measured under batch equilibrium binding conditions with an immobilised Cu(II)-iminodiacetic acid (IDA) sorbent. The experimental data were analysed in terms of Langmuirean binding behaviour. In common with previous studies with synthetic peptides, these investigations have demonstrate that the sequential organisation of the histidine side chains in these peptides can affect the selectivity of the coordination interactions with borderline metal ions in immobilised metal ion affinity chromatographic systems. The results also confirm that peptides selected on the basis of their potential to form amphipathic secondary structures with their histidine residues presented on one face of the molecule can exhibit equivalent or higher affinity constants towards copper ions than hexa-His, although they contain fewer histidine residues. These findings are thus relevant to the selection of peptides produced inter alia by combinatorial synthetic procedures to have enhanced binding properties for Cu(II) or Ni(II) ions, or intended for use as peptide tags in the fusion handle approach for the affinity chromatographic purification of recombinant proteins.     

Syntheses, structures, and properties of high-nuclear 3d-4f clusters with amino acid as ligand: {Gd6Cu24}, {Tb6Cu26}, and {(Ln6Cu24)2Cu} (Ln = Sm, Gd)

Four novel high-nuclear 3d-4f heterometallic clusters were obtained through the self-assembly of Ln(III), Cu(II), and amino acid ligands (2-methylalanine (mAla), glycine (Gly), and L-proline (Pro), respectively). The metal skeleton of cluster 1, [Gd6Cu24(mu3-OH)30(mAla)16(ClO4)(H2O)22].(ClO4)17.(OH)2.(H2O)2(0), may be described as a huge {Gd6Cu12} octahedron connected with 12 additional Cu(II) ions. The structure of cluster 2, Na4[Tb6Cu26(mu3-OH)30(Gly)18(ClO4)(H2O)22].(ClO4)25.(H2O)42, may be described as a {Tb6Cu24} main structure connected with two [Cu(Gly)(H2O)2]+ groups. Compounds {[Ln6Cu24(mu3-OH)30(Pro)12(Ac)6(ClO4)(H2O)13]2Cu(Pro)2}.(ClO4)18.(OH)16.(H2O)55 (Ln= Sm (3), Gd (4)) are 61-nuclear clusters, which represent the largest known 3d-4f clusters so far, the structure can be described as two {Ln6Cu24} octahedral units connected by a trans-Cu(proline)2 bridge. The electrical conductivity measurements reveal that they are temperature-sensitive semiconductors. The magnetic susceptibility measurements display that compound 4 is ferromagnetic.     

Selective isolation-detection of two different positively charged peptides groups by strong cation exchange chromatography and matrix-assisted laser desorption/ionization mass spectrometry: application to proteomics studies

We report here a procedure for the independent analysis of two groups of peptides by liquid chromatography-matrix-assisted laser desorption/ionization mass spectrometry (LC-MALDI MS/MS), using a selective isolation-detection procedure. In this procedure all primary amino groups of tryptic peptides derived from mouse liver proteins are blocked, restricting their positive charge, at acidic pH, to the presence of histidine and arginine residues. After strong cation exchange chromatography, multiply charged peptides (R + H > 1) are retained on the column and separated with high selectivity from singly (R + H = 1) and neutral peptides (R + H = 0) which are together collected in the flow-through. Using LC-MALDI-MS/MS analysis, the retained fraction displayed a 94% of enrichment of multiply charged peptides while in the flow-through; peptides with at least one arginine or histidine residue were exclusively identified, which suggests that MS detection in this fraction is restricted only to those peptides with ionizable side chains, arginine and histidine amino acids.     

Synthesis and magnetic properties of heterometal cyclic tetranuclear complexes [Cu(II)LM(II)(hfac)]2 (M(II) = Zn,Cu, Ni,Co, Fe,Mn; H3L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane; Hhfac = hexafluoroacetylacetone)

A series of heterometal cyclic tetranuclear complexes [Cu(II)LM(II)(hfac)](2) (M(II) = Zn (1), Cu (2), Ni (3), Co (4), Fe(5), and Mn (6)) have been synthesized by the assembly reaction of K[CuL] and [M(II)(hfac)(2)(H(2)O)(2)] with a 1:1 mole ratio in methanol, where H(3)L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane and Hhfac = hexafluoroacetylacetone. The crystal structures of 2, 4, and [Cu(II)LMn(II)(acac)](2) (6a) (Hacac = acetylacetone) were determined by single-crystal X-ray analyses. Each complex has a cyclic tetranuclear Cu(II)(2)M(II)(2) structure, in which the Cu(II) complex functions as a "bridging ligand complex", and the Cu(II) and M(II) ions are alternately arrayed. One side of the planar Cu(II) complex coordinates to one M(II) ion at the two phenoxo and the methoxy oxygen atoms, and the opposite side of the Cu(II) complex coordinates to another M(II) ion at the amido oxygen atom. The temperature-dependent magnetic susceptibilities revealed spin states of S(M) = 0, 1/2, 1, 3/2, 2, and 5/2 for the Zn(II), Cu(II), Ni(II), Co(II), Fe(II), and Mn(II) ions, respectively. Satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a rectangular arrangement with two different g-factors for the Cu(II) and M(II) ions, two different isotropic magnetic exchange interactions, J(1) and J(2), between the Cu(II) and M(II) ions, and a zero-field splitting term for the M(II) ion. In all cases, the antiferromagnetic coupling constants were found for both exchange interactions suggesting nonzero spin ground states with S(T) = 2/S(M) - S(Cu)/, which were confirmed by the analysis of the field-dependent magnetization measurements.     

Study of peptide-ligand interactions in open-tubular capillary columns covalently modified with porphyrins

The inner surface of fused silica capillaries has been covalently modified with different porphyrins (deuteroporphyrin, complexes of deuteroporphyrin with metal ions Fe(III), Cu(II), Zn(II), Ni(II), and Cu(II)-meso-tetra (carboxyphenyl) porphyrin) and it was applied for the separation of biologically active peptides by open-tubular capillary electrochromatography. Separations were performed in a mobile phase composed of 25?mM potassium phosphate, pH 4.0, 5%?v/v ACN and 10?mM hydroquinone. Changes in the effective electrophoretic mobility of peptides were studied concerning porphyrin central metal atom, attachment geometry, and the presence of coordinating or aromatic amino acid residues in the peptide sequence. The results showed that differences in metal core on the porphyrin and the spatial conformation of attached porphyrin result in changes in the analyte interaction with the stationary phase.     

Molecular and multidimensional polyoxotungstates functionalized by {Cu(bpy)}2+ groups

Five new materials built from polyoxotungstates and Cu(ii) ions as linkers have been synthesized by hydrothermal reactions from a mixture of sodium tungstate, copper chloride and bipyridine. The value of the initial pH, the nature of the heteroelement (P or Si) and of the ligand (2,2'- and/or 4,4'-bipyridine) permit the control of the nature of the polyoxotungstate clusters and their connectivity via the copper ions, and hence the dimensionality of the framework. A single phase has been obtained with silicon as heteroelement at an initial pH of 5, namely the 2D material [SiW(12)O(40)][Cu(2,2'-bpy)(2)](2).10H(2)O (1) with saturated Keggin polyoxotungstates linked by {Cu(2,2'-bpy)(2)}(2+) groups. With phosphorous as heteroelement and at the same initial pH, three different structures have been isolated according to the nature of the ligand. Indeed, the two 1D materials [{Cu(5)(2,2'-bpy)(5)(H(2)O)(HPO(4))(PO(4))}PW(11)CuO(39)].6H(2)O (2) with 2,2'-bpy and [4,4'-Hbpy][{Cu(2)(2,2'-bpy)(2)(4,4'-bpy)(2.5)}PW(11)CuO(39)].16H(2)O (3) with a mixture of 2,2'- and 4,4'-bpy have been characterized, and a coordination polymer with polyoxometalate guests Na(3)[4,4'-Hbpy]{Cu(4)(4,4'-bpy)(8)(H(2)O)(8)}[PW(11)CuO(39)(H(2)O)][PW(10)Cu(2)O(38)(H(2)O)(2)].38H(2)O (4) with 4,4'-bpy has been obtained. Finally, in basic medium (pH = 10) the unprecedented molecular cluster Na(2)[{Cu(8)(2,2'-bpy)(8)}(PW(8)O(31))(2)].15H(2)O (5) has been evidenced. Magnetic studies of compound 2 revealed that the predominant interactions involve only 4 paramagnetic centers, which are interacting within pairs, among the 6 Cu(ii) centers. The chi(M)T=f(T) curve can be fitted using the dinuclear expression appropriate to the HDVV isotropic exchange Hamiltonian H=-JS(1)xS(2), with S(1)=S(2)=(1/2) and J=-105.4 cm(-1), showing strong antiferromagnetic interactions within the two Cu(ii) pairs.     

Template-assisted solvothermal synthesis of five copper(I)-thioantimonate(III) composites: crystal structures and optical and thermal properties of (C6N2H18)0.5Cu2SbS3, (C4N3H15)0.5Cu2SbS3, (C8N4H22)0.5Cu2SbS3, (C4N3H14)Cu3Sb2S5, and (C6)N4H20)0.5Cu3Sb2S5

The novel copper(I)-thioantimonates(III) (C(6)N(2)H(18))(0.5)Cu(2)SbS(3) (I) (C(6)N(2)H(16) = 1,6-diaminohexane), (C(4)N(3)H(15))(0.5)Cu(2)SbS(3) (II) (C(4)N(3)H(13) = diethylenetriamine), (C(8)N(4)H(22))(0.5)Cu(2)SbS(3) (III) (C(8)N(4)H(20) = 1,4-bis(2-aminoethyl)piperazine), (C(4)N(3)H(14))Cu(3)Sb(2)S(5) (IV) (C(4)N(3)H(13) = diethylenetriamine), and (C(6)N(4)H(20))(0.5)Cu(3)Sb(2)S(5) (V) (C(6)N(4)H(18) = triethylenetetramine) were synthesized under solvothermal conditions reacting Sb, Cu, and S with the amines. The compounds I-III belong to the RCu(2)SbS(3) structure family (R = amine) and are built up of trigonal SbS(3) pyramids and two CuS(3) moieties forming 6-membered (6 MR) and 10-membered (10 MR) rings. The rings are condensed yielding single layers which are joined into [Cu(2)SbS(3)](-) double layers via Cu-S bonds. The organic ions are located between the anionic layers, and the shortest interlayer distances are 7.8 Angstroms (I), 7.4 Angstroms (II), and 8.8 Angstroms (III). The structure of the novel inorganic-organic hybrid compound IV contains one SbS(3) group, one SbS(4) unit, two CuS(3) triangles, and one CuS(4) tetrahedron. These units are joined into four-membered (4 MR) and six-membered rings (6 MR) forming a hitherto unknown strong undulated layered (Cu(3)Sb(2)S(5))(-) anion. Anions and cations are arranged in a sandwichlike manner with an interlayer distance of 6.184 A. The new composite V contains an anion with the same chemical composition as compound IV, but the structure exhibits a unique and different network topology which is constructed by two SbS(3) pyramids, two CuS(3) triangles, and one CuS(4) tetrahedron. These units are joined into 6 MR which may be described as an inorganic graphene-like layer or as a 6(3) net. Two such layers are connected via Cu-S bonds into the final double layer. The interlayer distance amounts to 6.44 Angstroms. All compounds decompose in a more or less complex manner when heated in an inert atmosphere.     

Extraction and preconcentration of toxic metal ions from aqueous solution using benzothiazole-based chelating resins

Polystyrene-divinylbenzene resin (PS-DVB) was functionalized with a benzothiazole group. PS-DVB with amino group was initially prepared by nitration and reduction reactions and subsequently treated with ethyl 2-benzothiazolylacetate (BA) to obtain the chelating resin with an amide linkage (BA-PS-DVB). Meanwhile, the amino-PS-DVB was diazotized and coupled with BA to obtain the chelating resin with an azo linkage (azo-BA-PS-DVB). The resins were characterized by elemental analysis and infrared spectroscopy and evaluated for their extraction of Cd(II), Cu(II) and Pb(II) ions in water before their determinations by flame atomic absorption spectrometry (FAAS). Extraction conditions were optimized for batch method such as the pH of the solution, the extraction time and the adsorption isotherm. The optimum pH for the extraction of Cd(II), Cu(II) and Pb(II) are 8.0, 7.0 and 6.0, respectively, while the equilibrium time of all ions was reached within 10-20 min. The adsorption behavior of all the metal ions followed the Langmuir adsorption isotherm. In the column method, the optimum flow rates of metal sorption onto BA-PS-DVB and azo-BA-PS-DVB columns were 2.5 and 4.0 mL min^− 1. Metal ions sorbed onto columns were eluted by 0.5 to 2.0 M HNO₃. The preconcentration factors of Cd(II) and Cu(II) on azo-BA-PS-DVB and Cu(II) on BA-PS-DVB were 50, 50, and 20, respectively. The present column method gave acceptable validation results: 71.2 and 74.0% recovery for Cd(II) and Cu(II) and an overall relative standard deviation (R.S.D) less than 10% (n = 15). The proposed method was applicable for determining Cu(II) in drinking water.     

pH-Dependent Cu(II) coordination to amyloid-β peptide: impact of sequence alterations, including the H6R and D7N familial mutations

Copper ions have been proposed to intervene in deleterious processes linked to the development of Alzheimer's disease (AD). As a direct consequence, delineating how Cu(II) can be bound to amyloid-β (Aβ) peptide, the amyloidogenic peptide encountered in AD, is of paramount importance. Two different forms of [Cu(II)(Aβ)] complexes are present near physiological pH, usually noted components I and II, the nature of which is still widely debated in the literature, especially for II. In the present report, the phenomenological pH-dependent study of Cu(II) coordination to Aβ and to ten mutants by EPR, CD, and NMR techniques is described. Although only indirect insights can be obtained from the study of Cu(II) binding to mutated peptides, they reveal very useful for better defining Cu(II) coordination sites in the native Aβ peptide. Four components were identified between pH 6 and 12, namely, components I, II, III and IV, in which the predominant Cu(II) equatorial sites are {-NH(2), CO (Asp1-Ala2), N(im) (His6), N(im) (His13 or His14)}, {-NH(2), N(-) (Asp1-Ala2), CO (Ala2-Glu3), N(im)}, {-NH(2), N(-) (Asp1-Ala2), N(-) (Ala2-Glu3), N(im)} and {-NH(2), N(-) (Asp1-Ala2), N(-) (Ala2-Glu3), N(-) (Glu3-Phe4)}, respectively, in line with classical pH-induced deprotonation of the peptide backbone encountered in Cu(II) peptidic complexes formation. The structure proposed for component II is discussed with respect to another coordination model reported in the literature, that is, {CO (Ala2-Glu3), 3 N(im)}. Cu(II) binding to the H6R-Aβ and D7N-Aβ peptides, where the familial H6R and D7N mutations have been linked to early onset of AD, has also been investigated. In case of the H6R mutation, some different structural features (compared to those encountered in the native [Cu(II)(Aβ)] species) have been evidenced and are anticipated to be important for the aggregating properties of the H6R-Aβ peptide in presence of Cu(II).     

Insights into the N-terminal Cu(II) and Cu(I) binding sites of the human copper transporter CTR1

Abstract

Copper transporter 1 (CTR1) is the main copper transporter in the eukaryotic system. CTR1 has several important roles: It binds Cu(II) ions that are present in the blood; it reduces those Cu(II) ions to Cu(I); and it subsequently transfers Cu(I) to the cytoplasmic domain, where the ion is delivered to various cellular pathways. Here, we seek to identify CTR1 binding sites for Cu(II) and Cu(I) and to shed light on the Cu(II)-to-Cu(I) reduction process. We focus on the first 14 amino acids of CTR1. This N-terminal segment is rich with histidine and methionine residues, which are known to bind Cu(II) and Cu(I), respectively; thus, this region has been suggested to have an important function in recruiting Cu(II) and reducing it to Cu(I). We utilize electron paramagnetic resonance (EPR) spectroscopy together with nuclear magnetic resonance (NMR) and UV-VIS spectroscopy and alanine substitution to reveal Cu(II) and Cu(I) binding sites in the focal 14-amino-acid segment. We show that H5 and H6 directly coordinate to Cu(II), whereas M7, M9, and M12 are involved in Cu(I) binding. This research is another step on the way to a complete understanding of the cellular copper regulation mechanism in humans.     

Coordination of copper(II) ions by the fragments of neuropeptide gamma containing D1, H9, H12 residues and products of copper-catalyzed oxidation

A potentiometric, spectroscopic (UV-Vis, CD and EPR) and mass spectrometric (ESI-MS) study of Cu(II) binding to the (1-2,7-21)NPG, Asp(1)-Ala-Ile(7)-Ser-His(9)-Lys-Arg-His(12)-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met(21)-NH(2), and Ac-(1-2,7-21)NPG, Ac-Asp(1)-Ala-Ile(7)-Ser-His(9)-Lys-Arg-His(12)-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met(21)-NH(2), fragments of neuropeptide gamma were carried out. The results clearly indicate the stabilization of the 1 N {NH(2), β-COO(-)}, 2 N {NH(2), β-COO(-), N(Im)} and 3 N {NH(2), β-COO(-), 2N(Im)} complexes by the coordination of the β-carboxylate group of the D(1) residue. For the (1-2,7-21)NPG the CuH(2)L complex with 3 N {NH(2), β-COO(-), 2N(Im)}, the binding mode dominates in a wide pH range of 4-8.5. With the sequential increase of pH, deprotonated amide nitrogens are involved in copper coordination. For the Ac-(1-2,7-21)NPG peptide the imidazole nitrogen atoms are the primary metal binding sites forming macrochelates in the pH range 4 to 7. The CuHL complex with 4 N {N(Im), N(-), N(-), N(Im)} coordination mode is formed in pH range 6-9. Deprotonation and co-ordination of the third amide nitrogen were detected at pH ～8.6. Metal-catalyzed oxidation (MCO) of proteins is mainly a site-specific process in which one or a few amino acids at metal-binding sites on the protein are preferentially oxidized. To elucidate the products of the copper(II)-catalyzed oxidation of the (1-2,7-21)NPG and Ac-(1-2,7-21)NPG, the liquid chromatography-mass spectrometry (LC-MS) method and Cu(II)/hydrogen peroxide as a model oxidizing system were employed. In the presence of hydrogen peroxide with 1?:?4 peptide-H(2)O(2) molar ratio for the Ac-(1-2,7-21)NPG peptide the oxidation of the methionine residue to methionine sulfoxide and for (1-2,7-21)NPG to sulfone was observed. For the Cu(II)-peptide-hydrogen peroxide in 1?:?1?:?4 molar ratio systems, oxidation of the histidine residues to 2-oxohistidines was detected. Under experimental conditions the (1-2,7-21)NPG and Ac-(1-2,7-21)NPG undergo fragmentations by cleavage of the S(8)-H(9), H(9)-K(10), R(11)-H(12) and H(12)-K(13) peptide bonds supporting the participation of the H(9) and H(12) residues in the coordination of copper(II) ions. For the (1-2,7-21)NPG peptide chain the involvement of the D(1) residue in the coordination of metal ions is supported by the alkoxyl radical modification of this amino acid residue.     

Coordination properties of Cu(II) and Ni(II) ions towards the C-terminal peptide fragment -TYTEHA- of histone H4

In order to reveal more information about the toxicity caused by metals and furthermore their influence to the physiological metabolism of the cell, the hexapeptide model Ac-ThrTyrThrGluHisAla-am representing the C-terminal 71-76 fragment of histone H4 which lies into the nucleosome core, was synthesized. A combined pH-metric and spectroscopic UV-VIS, EPR, CD and NMR study of Ni(II) and Cu(II) binding to the blocked hexapeptide, revealed the formation of octahedral complexes involving imidazole nitrogen of histidine, at pH 5 and pH 7 for Cu(II) and Ni(II) ions respectively. In basic solutions a major square-planar 4 N Ni(II)-complex, adopting a {N(Im), 3N(-)} coordination mode, was formed. In the case of Cu(II) ions, a 3 N complex, involving the imidazole nitrogen of histidine and two deprotonated amide nitrogens of the backbone of the peptide, at pH 7 and a series of 4 N complexes starting at pH 6.5, were suggested. In addition Ni(II)-mediated hydrolysis of the peptide bond-Tyr-Thr was evident following our experimental data.     

Synthesis and Structural Characterization of Cu（pic）2[CO（NH2）2]2 and （picH2）2[Cu（pic）2（SCN）2]

1 INTRODUCTION The picolinic acid (picH), also called pyridine- 2-carboxylic acid, has a broad spectrum of physio- logical effects on the activity functions of both ani- mal and plant organisms. It is attributed increasing interest due to its ability to …     

Solid phase extraction and determination of metal ions in aqueous samples using Quercetin modified Amberlite XAD-16 chelating polymer as metal extractant

A new chelating polymer has been developed using Amberlite XAD-16 anchored with Quercetin. The modified polymer was characterised by Fourier Transform Infra Red (FTIR) spectroscopy, thermogravimetric analysis, surface area analysis and elemental analysis. The Quercetin anchored polymer showed superior binding affinity for Cr(III), Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) with greater than 95% adsorption under optimum conditions. The optimum pH conditions for the quantitative sorption of metal ions were studied. The developed method showed superior extraction qualities with high metal loading capacities of 387, 313, 195, 473, 210 and 320 µmol g^?1 for Cu(II), Co(II), Cr(III), Fe(III), Mn(II) and Ni(II), respectively. The rate of metal ion uptake i.e. kinetics studies performed under optimum levels, showed t _1/2 for Co(II), Cu(II), Cr(III), Fe(III), Mn(II) and Ni(II) is 20, 15, 25, 10, 30 and 15 min, respectively. Desorption of metal ions was effective with 10 mL of 2 M HCl prior to analysis using flame atomic absorption spectrophotometer. The chelating polymer was highly ion selective in nature even in the presence of interferent ions, with a high preconcentrating ability for the metal ions of interest. The developed chelating polymer was tested on its utility with synthetic and real samples like river, tap water samples and also with multivitamin tablets. It showed relative standard deviation (R.S.D.) values of/less than 3.0% reflecting on the accuracy and reproducibility of data using the newly developed chelating polymer.