Divalent Transition Metal Ions Research Articles

Protein‐transition metal ion networks

AbstractProteins obtained from agricultural sources were blended with divalent metal ions to see if binding reactions occurred between protein chains. Feather keratin, egg albumin, and wheat gluten showed elastic modulus increases of 2–3 times with addition of divalent transition metal ions Cu2+ and Zn2+. Increasing concentrations of ions resulted in increased stiffness. Birefringence experiments performed concurrently with tensile experiments showed refractive index changes indicative of network formation. Binding divalent alkaline earth metal Ca2+ ions did not result in an elastic modulus increase. Addition of Zn2+ to egg albumin resulted in a 34% decrease in water permeability but no change in oxygen permeability. FTIR spectroscopy showed that the directed valence of the transition metals was primarily binding glycerol and amide sites on the protein and secondarily carbonyl sites on the protein. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Magnetic and optical properties of single crystals of transition metal doped ZnO

AbstractConsiderable effort has been devoted to the study of transition metal doped zinc oxide following various theoretical predictions of room temperature ferromagnetism in these materials. Near equilibrium growth techniques may be suitable for the production of dilute transition metal doped ZnO because the transition metal solubility in ZnO can be relatively high. This work reports on the optical, structural, and magnetic properties of single crystals of Co‐ and Mn‐doped ZnO grown by a modified melt‐growth technique. X‐ray diffraction reveals that the as grown crystals are pure single crystals with no second phases. Mn doping up to 5% results in an increase in c‐axis lattice parameter (5.207 Å to 5.211 Å), and X‐ray linewidths (78 arcsec to 252 arcsec) at doping levels of 5% Mn. Optical transmission shows distinct absorption spectra related to the color of the Zn1–x TMx O sample resulting from interatomic transitions within the divalent transition metal ion. Electron paramagnetic resonance confirms the divalent nature of the substitutional transition metal ions. Raman spectroscopy shows the predominantly the E2 (high) peak at 407 cm–1, but with increasing doping shows additional disorder‐related modes. The magnetic behavior reveals a paramagnetic behavior at all temperatures for both Mn‐ and Co‐doped ZnO up to transition metal doping levels of 5% and 3% respectively. The dominant exchange mechanism in the Mn‐ and Co‐doped ZnO crystals is found to be antiferromagnetic superexchange. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Turn-on and ratiometric mercury sensing in water with a red-emitting probe.

The synthesis, photophysical properties, and Hg(II) binding of a red-emitting sensor for mercuric ion are presented. 2-[11-[(2-[[Bis-(2-ethylsulfanylethyl)amino]methyl]phenylamino)methyl]-3-hydroxy-10-oxo-10H-benzo[c]xanthen-7-yl]benzoic acid (MS5) is based on the seminaphthofluorescein chromophore and employs a thioether-rich metal-binding unit. This sensor affords both turn-on and single-excitation dual-emission ratiometric Hg(II) detection in aqueous solution. The fluorescence response of MS5 is Hg(II)-specific, and the probe is selective for Hg(II) over alkali and alkaline earth metals, most divalent first-row transition metal ions, and the Group 12 congeners Zn(II) and Cd(II). MS5 binds Hg(II) reversibly and can be recycled. The EC50 for 1 microM MS5 is 910 nM, and a lower detection limit of 50 nM is obtained when employing 500 nM probe. X-ray crystallographic studies using a salicylaldehyde-based model of MS5 are also presented. 2-[(2-[[Bis-(2-ethylsulfanylethyl)amine]methyl]phenylamine)methyl]phenol coordinates Hg(II) with two thioether sulfur atoms, two amino nitrogen atoms, and a phenol oxygen atom arranged in a distorted trigonal bipyramidal geometry. Studies of natural water samples spiked with mercuric salts indicate that MS5 can rapidly detect Hg(II) in such complex solutions and demonstrate its potential utility in the field.

Heterotrimetallic Oxalato-Bridged ReIV2MII Complexes (M = Mn, Co, Ni, Cu): Synthesis, Crystal Structure, and Magnetic Properties

The use of the (NBu4)2[ReIVCl4(ox)] mononuclear species as a ligand toward divalent first row transition metal ions in the presence of imidazole affords the new trinuclear compounds of formula (NBu4)2[{ReIVCl4(mu-ox)}2MII(Him)2] [NBu4+=tetra-n-butylammonium cation, ox=oxalate dianion, Him=imidazole; M=Mn (1), Co (2), Ni (3), Cu (4)] whose preparation, crystal structures, and magnetic properties are reported. 1-4 are isostructural complexes which are made up of discrete trinuclear [{ReIVCl4(mu-ox)}2MII(Him)2]2- anions and bulky NBu4+ cations. The Re and M atoms exhibit somewhat distorted octahedral surroundings which are built by four chloro and two oxalate oxygens (Re) and two imidazole nitrogen and four oxalate oxygen atoms (M), the central M atom being linked to the two peripheral Re atoms through bis-bidentate oxalate. The values of the Re...M separation across bridging oxalate vary in the range 5.646(2) (M=Ni) to 5.794(2) A (M=Mn). Magnetic susceptibility measurements on polycrystalline samples of 1-4 in the temperature range 1.9-300 K show the occurrence of significant intramolecular antiferro- (1) and ferromagnetic (2-4) interactions. The nature and magnitude of the magnetic coupling in 1-4 are qualitatively understood through orbital symmetry considerations.

Conformational studies of the manganese transport regulator (MntR) from Bacillus subtilis using deuterium exchange mass spectrometry

The manganese transport regulator (MntR) of Bacillus subtilis is a metalloregulatory protein responsible for regulation of genes involved in manganese uptake by this organism. MntR belongs to the iron-responsive DtxR family, but is allosterically regulated by manganese and cadmium ions. Having previously characterized the metal binding affinities of this protein as well as the DNA-binding activation profiles for the relevant metal ions, we have focused the current study on investigating the structural changes of MntR in solution upon binding divalent transition metal ions. Deuterium exchange mass spectrometry was utilized to investigate the deuterium exchange dynamics between apo-MntR, Co(2+)-MntR, Cd(2+)-MntR, and Mn(2+)-MntR. Comparing the rates of deuteration of each metal-bound form of MntR reveals that the N-terminal DNA-binding motif is more mobile in solution than the C-terminal dimerization domain. Furthermore, significant protection from deuterium exchange is observed in the helices that contribute metal-chelating amino acids to form the metal binding site of MntR. In contrast, the bulk of the DNA-binding winged helix-turn-helix motif shows no difference in deuterium exchange upon metal binding. Mapping of the deuteration patterns onto the crystal structures of MntR yields insight into how metal binding affects the protein structure and complements earlier studies on the mechanism of MntR. Metal binding acts to rigidify MntR, thereby limiting the mobility of the protein and reducing the entropic cost of DNA binding.

Metal complexes of cyclen and cyclam derivatives useful for medical applications: a discussion based on thermodynamic stability constants and structural data

A series of the most common chelators used in magnetic resonance imaging (MRI) and in radiopharmaceuticals for medical diagnosis and tumour therapy, H(4)dota, H(4)teta, H(8)dotp and H(8)tetp, is examined from a chemical point of view. Differences between 12- and 14-membered tetraazamacrocyclic derivatives with methylcarboxylate and methylphosphonate pendant arms and their chelates with divalent first-series transition metal and trivalent lanthanide ions are discussed on the basis of their thermodynamic stability constants, X-ray structures and theoretical studies.

Properties of a new 4-imidazolyl derivative of a 14-membered tetraazamacrocyclic chelating agent

A new bis-N,N'-(5-methylimidazol-4-ylmethyl) derivative of a 14-membered tetraazamacrocycle, L1, has been synthesized. The protonation constants of this compound and the stability constants of its complexes with divalent first-row transition metal ions and Fe3+ were determined at 298.2 K in aqueous 0.10 mol dm(-3) KNO3. Compound L1 exhibits high overall basicity, which is mainly conferred by the imidazolyl groups. The complexes of the divalent first row-transition metal ions of L1 follow the Irving-Williams order of stability with the maximum for Cu2+ as expected, but a steep fall of constants is verified for the Mn2+, Fe2+ and Co2+, in one side, and for the Zn2+ complexes, in the other side. Additionally, L1 shows a large affinity for Fe3+, and the relative stability constants for its Cd2+ and Pb2+ complexes indicate that L1 may be useful for the complexometric determination of these two toxic metal ions in solutions containing both metal ions. These studies together with NMR, UV-vis and EPR spectroscopic data indicated the presence of mononuclear complexes, which adopt distorted pyramidal or octahedral geometries depending on the metal centre. The X-ray crystal structure of [Cu(HL1)](PF6)2(NO3).H2O showed that the coordination sphere of the copper centre can be described as a distorted square pyramid with the basal plane defined by three nitrogen donors of the macrocycle backbone and one nitrogen atom from one imidazolyl pendant arm. The apical position is occupied by the nitrogen atom of the macrocycle trans to the pyridine ring. To achieve this coordination environment, the macrocycle is folded along the axis defined by the two N atoms contiguous to the pyridine ring. The free methylimidazolyl arm points away from the metal centre leading to an intramolecular Cu[dot dot dot]N distance of 5.155(1) A.

Development of Immobilized Metal Ion Affinity Gel: Adsorption and Desorption Properties of Metal Ions Onto and From Chelating Sepharose Fast Flow Gel

Immobilized metal ion affinity gel is a regenerable carrier used in separation technique on the basis of a reversible interaction between the gel and a specific transition metal ion as a ligand. An experimental investigation concerning the development of an immobilized metal ion affinity gel and the adsorption and desorption properties of metal ions was carried out by using a Chelating Sepharose Fast Flow gel and divalent transition metal ions of Co2+ and Ni2+. In order to characterize and predict metal ion adsorption and desorption completely, one seeks the information about the adsorption isotherms and the necessary physical parameters for adsorption and desorption along with their mechanisms. In this experimental investigation it is considered that the two –CH2COOH groups in the gel combine with metal ions stoichiometrically and the adsorption and desorption mechanisms of the metal ions onto and from the gel are theoretically analyzed on the basis of adsorption and desorption equilibriums and the dissociation equilibrium. Consequently, the model equations, which allow quantitative consideration of the adsorption and desorption mechanisms, can be derived as a function of the concentration of hydrogen ions at the outer aqueous phase. The values of adsorption effectiveness factor were calculated as 0.87 for Co2+ and 0.90 for Ni2+. Finally, the gel adsorption isotherm and the adsorption, desorption equilibriums of metal ions can be explained fairly well by these models.

Study by liquid secondary ion and electrospray mass spectrometry of synthesized and formed‐in‐source metallocorroles

Liquid secondary ion and electrospray mass spectrometry were used to study the complexation in-source of 5,10,15-tris(pentafluorophenyl)corrole with several divalent transition-metal ions. The metallocorrole ions formed in-source were identified by comparing their product ion mass spectra with the spectra of the same ions formed from metallocorroles obtained from classical procedures. Positive metallocorrole ion formation is accompanied by oxidation of the metal centre. Mechanisms were proposed for the oxidation processes, and data from negative-ion spectra reinforced these mechanisms.

Two distinct manganese(II) complexes with hexadentate 1,3-propanediaminetetraacetate ligand: The ability of metal(II) complexes with 1,3-pdta ligand to form solid solutions

The ability of Mn(II) ion to form two distinctly different complexes with 1,3-propanediaminetetraacetate (1,3-pdta) ligand has been demonstrated by performing X-ray analyses of their crystalline Mg(II) salts. The two types of Mn(II) complexes have been obtained by different synthetic routes and their crystals constitute, respectively, the solid solution of the composition [Mg(H 2O) 6][Mg 0.5Mn 0.5(1,3-pdta)] · 2H 2O ( 1) and the ordered crystals of the composition [Mg(H 2O) 6][Mn(1,3-pdta)(H 2O)] · 2H 2O ( 2). In both, six- 1 and seven-coordinated 2 Mn(II) complexes the 1,3-pdta ligand acts as a hexadentate. As 2 makes the second example of the seven-coordinated 1,3-pdta complex with divalent transition metal ion, the other being the [Mg(H 2O) 6][Cd(1,3-pdta)(H 2O)] · 2H 2O ( 3) complex, the paper reports the results of X-ray investigations of both of these complexes at 130 K.

Liquid Phase Deposition of Transition Metal Ferrite Thin Films: Synthesis and Magnetic Properties

We report on the synthesis of highly uniform, single phase zinc and cobalt thin films prepared by the Liquid Phase Deposition (LPD) method. X-Ray diffraction, TGA and EDX measurements support the assumption that the as deposited films are constituted by a mixture of crystallized FeOOH and amorphous M(OH)₂ (M=Co, Zn) which is converted upon heat treatment in air at 600℃ into the corresponding zinc ferrites. The films with adjustable chemical compositions are identified with a crystal structure as spinel-type and present a spherical or rod-like microstructure, depending on the both the nature and concentration of the divalent transition metal ions. Zinc ferrite thin films present a superparamagnetic behavior above blocking temperatures which decrease with increasing the Zn content and are ferromagnetic at 5 K with coercivities ranging between 797.8 and 948.5 Oe, whereas the cobalt ferrite films are ferromagnetic at room temperature with magnetic characteristics strongly dependent on the chemical composition.

Unique Keto-Enol Tautomerism in Transition Metal Complexes of Cyanoimidodithiocarbonate

A novel potential bidentate sulfur ligand, K2[S2CNHCOCH2CN] and its complexes with first row divalent transition metal ions of the type, M(phen)L, [M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Pd(II), L = S2CNHCOCH2CN and phen = 1,10-phenanthroline] have been synthesised and characterised. On the basis of IR and 1H NMR an enol form is found in the case of ligand and its complexes in the solid state whereas the complexes exist predominantly in the keto form in solution. Electronic spectra and magnetic measurement data indicate that the Ni(II), Cu(II) and Pd(II) complexes have a square-planar geometry but the others have a distorted-tetrahedral structure.

Thermodynamic studies on complexation of divalent transition metal ions with some zwitterionic buffers for biochemical and physiological research

The interaction between the zwitterionic buffers (3-[ N-bis(2-hydroxyethyl)amino]-2-hydroxy propane sulfonic acid, N-(2-actamido)-2-aminoethane sulfonic acid, and 3-[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxy propane sulfonic acid) with some divalent transition metal ions (Cu II, Ni II, Co II, Zn II, and Mn II) were studied at different temperatures (298.15 to 328.15) K at ionic strength I = 0.1 mol · dm −3 NaNO 3 and in the presence of 10%, 30%, and 50% (w/w) dioxene by using potentiometry. The thermodynamic stability constants were calculated as well as the free energy change for the 1:1 binary complexation. The protonation constants of the zwitterionic buffers were also determined potentiometrically under the above conditions.

Studies on transition metal ions recognition properties of 1-(2-benzothiazole)-3-(2-thiophene)-2-pyrazoline derivatives

Spectroscopic studies revealed that 1-(2-benzothiazole)-3-(2-thiophene)-2-pyrazoline derivatives have rather strong affinity toward divalent transition metal ions. In the case of 1-(2-benzothiazole)-3-(2-thiophene)-5-(4-dimethylamine-phenyl)-2-pyrazoline, enhancement of the fluorescence intensity was observed upon addition of the Zn 2+ ion ([Zn 2+]/L2 = 100), while most of the other transition metal ions caused complete quenching.

Nitrogenous Synergists Induced Potentiometrie Response to Metal Ions with Polymeric Liquid Membranes Containing Thenoyltrifluoroacetone as an Ionophore

The effects of nitrogenous synergists on the potentiometric responses to divalent transition metal ions were investigated concerning polymeric liquid membranes containing thenoyltrifluoroacetone (Htta) as an ionophore. The tested synergists were pyridine (py) and 4,4'-dioctyl-2,2'-bipyridyl (C8bpy). The potentiometric responses to metal ions, such as Cd2+, Co2+, Ni2+ and Zn2+, were induced by adding the synergists into the liquid membrane systems. The coexistence of Htta and a synergist was necessary for generating the membrane potential. The tta- anion adsorbed at the liquid membrane/solution interface and the complex formation between the synergist and a given metal ion appeared to participate in preferential uptake of metal ions.

Synthesis and structural studies on divalent transition metal complexes of 5-acetyl 2,4-dihydroxy acetophenone semicarbazone

The synthesis of divalent transition metal complexes of a new dibasic, bis-chelating ligand 5-acetyl 2,4-dihydroxy acetophenone semicarbazone (H 2 -ADAS) with Mn II , CO II , Ni II , Cu II and Zn II and their characterization on the basis of their elemental analyses, conductivity, magnetic moments, infrared and electronic spectral data has been studied. Metal to ligand ratio in all the chelates has been found to be 1: 1. The Schiff base behaves in a dibasic pentadentate manner with OO and ONN donor atoms. All the complexes have been assigned octahedral stereochemistry. The ligand H 2 -ADAS forms polymeric metal complexes with first row divalent transition metal ions.

Quenching of Fluorophore-Labeled DNA Oligonucleotides by Divalent Metal Ions: Implications for Selection, Design, and Applications of Signaling Aptamers and Signaling Deoxyribozymes

Recent years have seen a dramatic increase in the use of fluorescence-signaling DNA aptamers and deoxyribozymes as novel biosensing moieties. Many of these functional single-stranded DNA molecules are either engineered to function in the presence of divalent metal ion cofactors or designed as sensors for specific divalent metal ions. However, many divalent metal ions are potent fluorescence quenchers. In this study, we first set out to examine the factors that contribute to quenching of DNA-bound fluorophores by commonly used divalent metal ions, with the goal of establishing general principles that can guide future exploitation of fluorescence-signaling DNA aptamers and deoxyribozymes as biosensing probes. We then extended these studies to examine the effect of specific metals on the signaling performance of both a structure-switching signaling DNA aptamer and an RNA-cleaving and fluorescence-signaling deoxyribozyme. These studies showed extensive quenching was obtained when using divalent transition metal ions owing to direct DNA-metal ion interactions, leading to combined static and dynamic quenching. The extent of quenching was dependent on the type of metal ion and the concentration of supporting monovalent cations in the buffer, with quenching increasing with the number of unpaired electrons in the metal ion and decreasing with the concentration of monovalent ions. The extent of quenching was independent of the fluorophore, indicating that quenching cannot be alleviated simply by changing the nature of the fluorescent probe. Our results also show that the DNA sequence and the local secondary structure in the region of the fluorescent tag can dramatically influence the degree of quenching by divalent transition metal ions. In particular, the extent of quenching is predominantly determined by the fluorophore location with respect to guanine-rich and duplex regions within the strand sequence. Examination of the effect of both the type and concentration of metal ions on the performance of a fluorescence-signaling aptamer and a signaling deoxyribozyme confirms that judicious choice of divalent transition metal ions is important in maximizing signals obtained from such systems.

Interactions of an acidic cyclooctapeptide with metal ions: microcalorimetric and fluorescence analyses

Abstract: The metal‐ion binding preferences of an acidic amphipathic cyclopeptide, cyclo[d‐Leu‐Leu‐d‐Leu‐Trp‐(d‐Glu‐Glu)2] (CP), was studied by isothermal titration calorimetry and steady‐state fluorescence spectroscopy. CP adopted a partial beta structure, and variable temperature circular dichroism showed small secondary structural changes over the temperature range from 5 °C to 95 °C. The peptide did not bind alkali or alkaline earth metal ions but exhibited selectivity for some divalent transition metal ions (with association constants KCu2+ 4.5 × 104 m−1, KZn2+ 1.6 × 105 m−1, KCd2+ 1.3 × 104 m−1, KHg2+ (1) 2.2 × 106 m−1, and KHg2+ (2) 6.5 × 103 m−1), for Pb2+ (2.0 × 105 m−1), and a trivalent Group III metal, Al3+ (1.6 × 105 m−1). The thermodynamic data show that the interaction between CP and these metal ions are spontaneous and entropically driven. A large range of binding enthalpies coupled with a smaller range of binding free energies of CP for these metal ions indicate an entropy–enthalpy compensation dependent on the ionic size of participating metal ions. The interaction of Pb2+, Hg2+, and Cu2+ with CP in aqueous solution specifically modulates the fluorescence emission properties of CP. The results of this study show that CP exhibits selectivity in metal‐ion binding, which is reflected in its fluorescence spectra. The observed trends can be useful for the design of heavy‐metal sensors based on fluorophore‐tagged acidic cyclopeptides.

Adsorption of Transition Metals in Aqueous Solutions by Fluted Pumpkin (Telfairia occidentalisHook f) Waste

The adsorption of some divalent transition metal (Hg, Rh, Pt, and Pd) ions in aqueous solution onto fluted pumpkin waste biomass has been investigated. The data were discussed in terms of ionic radii, surface area, and the hard-soft acid-base (HSAB) concept. The monolayer sorption capacities as obtained by the Langmuir adsorption isotherm model were determined to be ca. 9.89 mg/g, 9.81 mg/g, 10.59 mg/g, and 6.84 mg/g for for Hg(II), Rh(II), Pt(II), and Pd(II), respectively. The results are relevant for the optimal design of a wastewater treatment plant and for prediction of model parameters of sorbate-sorbent interactions.

Speciation of Cyclo(Pro-Gly) 3 and Its Divalent Metal-Ion Complexes by Electrospray Ionization Mass Spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was used to study the binding of selected group II and divalent transition-metal ions by cyclo(Pro-Gly)3 (CPG3), a model ion carrier peptide. Metal salts (CatXn) were combined with the peptide (M) at a molar ratio of 1:10 M/Cat in aqueous solvents containing 50% vol/vol acetonitrile or methanol and 1 or 10 mM ammonium acetate (NH4Ac). Species detected include [M+H]+, [M+Cat-H]+, [M2+Cat]2+, [M+Cat+Ac]+, and [M+Cat+X]+. The relative stabilities of complexes formed with different cations (Mg2+, Ca2+, Sr2+, Mn2+, Co2+, Ni2+, Cu2+, and Zn2+) were determined from the abundance of 1:1 and 2:1 M/Cat species relative to that of the unbound peptide. The largest metal ions (Ca2+, Sr2+, and Mn2+) formed the most stable complexes. Reducing the buffer concentration increased the overall extent of metal binding. Results show that the binding specificity of CPG3 depends upon the size of the metal ion and its propensity for electrostatic interaction with oxygen atoms. Product ion tandem mass spectrometry of [M+H]+ and [M+Cu-H]+ confirmed the cyclic structure of the peptide, although the initial site(s) of metal attachment could not be determined.