Co-ordination of transition metal ions by galactaric acid: a potentiometric and spectroscopic study

A solution study on the ability of galactaric acid [GalaH(2), HOOC(CH)(4)COOH] in the complexation of biological metal ions such as Co(II) and Ni(II) and toxic metal ions such as Cd(II), Pb(II) and Hg(II), is reported. The stability constants of the complex species are determined by means of potentiometric measurements. Galactaric acid behaves as chelate ligand through carboxylic oxygen and alpha-hydroxy group towards Co(II) and Ni(II), while in the Pb(II) and Cd(II) containing system it co-ordinates the metal ion with carboxylic oxygen and two alcoholic hydroxy groups. The prevailing species at acidic or neutral pH is [MGala] which is also isolated in the solid state and characterized by means of IR spectroscopy. On increasing pH, the [MGalaH(-1)](-) species is also formed where the co-ordinated OH group undergoes deprotonation in all metal ion complexes except those with Hg(II), where the co-ordination of hydroxide ion is suggested as the precipitation of the metal hydroxide occurs at pH 7.     

Solution and solid state behavior of Co2+, Ni2+ and Zn2+ tosylaminoacidate systems: Crystal and molecular structure of bis(N-tosylglycinato)tetraaquocobalt(II) and bis(N-tosyl-β-alaninato)tetraaquozinc(II) complexes

The interactions between N-tosylamino acids and cobalt(II), nickel(II) and zinc(II) ions in aqueous solution and in the solid state have been investigated. From concentrated aqueous solutions, compounds of general formula [M(II)(N-tosylaminoacidato)₂(H₂O)₄](M = Co(II), Ni(II) and N-tosylaminoacidato = N-tosylglycinate (Tsgly^?), N-tosyl-α- and -β-alaninate (Ts-α- and Ts-β-ala^?); M = Zn(II) and N-tosylaminoacidate = Tsgly^?, Ts-β-ala^?) and [Zn(II)(N- tosylaminoacidato)₂(H₂O)₂] were isolated and characterized by means of thermogravimetric, electronic and infrared spectra. For two of them: [Co(Tsgly)₂(H₂O)₄](I) and [Zn(Ts-β-ala)₂(H₂O)₄](II) the crystal and molecular structures were also determined. Both compounds crystallize in the monoclinic space group P2₁/c, with two formula units in a cell of dimensions: a = 13.007(6), b = 5.036(2), c = 18.925(7) Å, β = 102.33(3)° for (I) and a = 14.173(6), b = 5.469(2), c = 17.701(7) Å, β = 106.63(3)° for (II). The structures were solved by the heavy-atom method and refined by least-squares calculations to R = 0.031 and 0.064 for (I) and (II) respectively. The cobalt and zinc atoms lie in the centers of symmetry, each bonded to two amino- acid molecules through a carboxylic oxygen atom and four water molecules in a slightly tetragonally distorted octahedral geometry. The second carboxylic oxygen atom is not involved in metal coordination. Electronic and X ray-powder spectra suggest that the tetrahydrate complexes of Co²⁺, Ni²⁺ and Zn²⁺ ions of the same amino acids are isomorphous and isostructural. No coordinative interactions between ligand and metal ions were found in aqueous solution on varying the pH values before hydroxide precipitation.     

Spectroscopic and structural investigation of two (2,2′-bipyridyl)bis(N-protected-aminoacidato)copper(II) complexes,two compounds containing truly CuN2O2 chromophore

The compounds of formula [Cu(bipy)(acleuO)₂] (1) and [Cu(bipy)(ts-β-alaO)₂] (2) (bipy = 2,2′-bipyridil, acleuO = N-acetyl-DL-leucinate anion, ts-β-alaO = N-tosyl-β-alaninate anion) were synthesized and characterized by means of spectroscopic and structural measurements. Complex (1) crystallizes in the monoclinic space group C2/c with cell parameters a = 17.465(4), b = 19.740(5), c = 9.080(2) Å, β = 115.0(1)° with Z = 4; complex (2) crystallizes in the triclinic space group P$\text{1}$, with cell parameters a = 14.489(3), b = 14.308(3), c = 8.659(1) Å, α = 75.0(1), β = 74.6(1), γ = 66.6(1)°, Z = 2. Both structures were solved by conventional Patterson and Fourier methods and refined to R factors of 4.10 and 3.8% respectively. In both crystals the Cu atom is four-coordinated by the nitrogen atoms of a bipy molecule and two carboxylate oxygens of two N-protected aminoacid anions acting as unidentate ligands. The only significant difference between the coordination geometry of (1) and (2) is in the tetrahedral distortion of the coordination plane. Complex (2) is strictly planar, while in complex (1) the distortion expressed by the dihedral angle between the (N)(1)CuN(1′) and O(1)CuO(1′) planes is 20.8°. The electronic and EPR results agree with these different coordination geometries. The infra-red data are consistent with a truly monodentate carboxylate group. The spectroscopic results on a series of previously investigated [Cu(bipy)(N-protected aminoacidato)²] complexes of unknown structures are discussed again in the light of the present structural reports.     

Metal(II) binding ability of a novel N-protected amino acid. A solution-state investigation on binary and ternary complexes with 2,2'-bipyridine

The binary and ternary systems 2,2'-bipyridine (bpy)-M(II)-NO2psglyH2 (M(II) = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II); NO2psglyH2 = N-(2-nitrophenylsulfonyl)glycine) were investigated in aqueous solution by means of potentiometry and electron spectroscopy in order to identify the type, number and stability of the complex species as a function of pH and metal-to-ligand molar ratio. The aim is to evaluate the effect of a substituent on the phenyl ring of the N-sulfonyl amino acids on their coordination properties. The prevailing species in the binary systems is the [ML] (M = Co(II), Ni(II), Cu(II), Cd(II), Pb(II)) where the amino acid molecule is in the dianionic form and coordinates the metal ion through both carboxylic oxygen and deprotonated sulfonamidic nitrogen, while in the Mn(II)- and Zn(II)-containing binary system the only complex species found are those with the amino acid in the monoanionic form. In the ternary 2,2'-bipyridine-containing systems the chelating coordination mode of the dianionic amino acid is maintained with M(II) = Co(II), Ni(II), Cu(II), Cd(II), Pb(II) and the addition of the aromatic base also enables the Zn(II) ion to substitute for the sulfonamide nitrogen-bound hydrogen of NO2psglyH2.     

Imidazole-containing ternary complexes of N-benzyloxycarbonyl-aminoacids. Crystal and molecular structure of bis(N-benzyloxycarbonyl-alaninato)bis-(N-methylimidazole)copper(II) ethanol solvate

Mixed ligand complexes of the type Cu(Z-aminoacidato)₂(B₂) (Z = benzyloxycarbonyl group, Z-aminoacidate = Z-glycinate (Zgly), Z-alaninate (Zala); Z-valinate (Zval), Z-leucinate (Zleu) ion, B = imidazole (Im), N-methylimidazole (MeIm)) were synthesized and characterized by means of electronic, infrared and EPR spectroscopies. For one of them, bis(Z-alaninato)bis(N-methylimidazole)copper(II) ethanol solvate, the crystal and molecular structure was also determined by the single crystal X-ray diffraction method. The complex crystallizes in the monoclinic space group P2₁/c, with cell dimensions a = 11.1119(6), b = 18.8398(7), c = 8.9652(5) Å, β = 105.380(2)° and Z = 2. The structure was solved by conventional Patterson and Fourier methods and refined by full-matrix least-squares to an R value of 0.045. The complex has square-planar coordination via two centrosymmetric carboxylic oxygens and two N-methylimidazole nitrogens. The second carboxylate oxygen is 2.731(5) Å from the copper atom in an ‘out of plane’ position. Packing is mainly determined by hydrogen bondings between amide nitrogen and amide carboxyl oxygen. Electronic, infrared and EPR spectra are consistent with this type of coordination geometry for anhydrous complexes, while for hydrate complexes are suggestive of tetragonal bipyramidal geometry.     

Physical predictors,behavioural/emotional attributes and neurochemical determinants of dominant behaviour

Significant differences in physical and behavioural/emotional/cognitive predictors and attributes, as well as of neurochemical inducers of behaviour, between dominant and subordinate animals are discussed. It is still unknown whether these factors are the causes of differences between dominants and subordinates, or vice versa whether the differences between dominants and subordinates are the origin of differences in these factors. The possibility is discussed that no differences exist among juveniles in the concentrations of neurochemical agents (known in the literature as determinants of dominance) between the brains of future dominants and future subordinates. We describe a study design that makes the assessment of the ‘original’ neurochemical profile of the brain possible.     

Conjunctival amelanotic melanoma--a case report

Conjunctival melanoma is a relatively rare malignancy. It is presented as pigmented nodule in any area of conjunctiva, amelanotic tumors are pink with smooth appearance. The authors describe an amelanotic melanoma of the conjunctiva in an 82-year-old female patient. Cytological, histopathological and immunohistochemical studies revealed an invasive amelanotic melanoma exhibiting S-100 and MART-1 positivity. The patient undervent surgical and chemotherapy treatment and three years after the initial treatment is in the terminal stage of metastatic disease. Absence of pigmentation delayed early clinical detection and treatment. Awareness of this nonpigmented melanoma is crucial for early recognition and appropriate management.     

Testosterone dynamics during encounter: role of emotional factors

This study attempts to develop a new theory to explain the varying dynamics of testosterone levels in dominant (winners) and subordinate (losers) males, both pre- and post-encounter. The crux of our new theory consists of the following four theses: (1) the strengthening of testosterone synthesis is a result of not only the existence of challenges, but also of a positive mood before an encounter that is associated with the anticipation of a victory; (2) in situations where the anticipation of victory is present but the positive mood is absent, no rise in testosterone levels will occur; (3) testosterone acts as a "pleasure" hormone and usually releases in situations where the individual achieves or anticipates possible satisfaction; (4) an increased release of testosterone to the blood not only decreases anxiety but also elevates the mood, which increases animal's/human's assertiveness and consequently aggressiveness.     

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.     

Cytotoxicity of zinc-containing bioactive glasses in contact with human osteoblasts

Bioactive glasses such as Hench's 45S5 have applications to tissue engineering and bone repair: the insertion of zinc has been proposed to improve their bone-bonding ability and to slacken their dissolution in extracellular body fluids. In view of a potential clinical application, we have investigated whether zinc-containing 45S5 (HZ) glasses might be cytotoxic for human MG-63 osteoblasts. In our experimental conditions, after 24h of incubation HZ glasses released significant amounts of Zn(2+) and induced in MG-63 cells release of lactate dehydrogenase (index of cytotoxicity) and the following indexes of oxidative stress: (i) accumulation of intracellular malonyldialdehyde, (ii) increased activity of pentose phosphate pathway, (iii) increased expression of heme oxygenase-1, (iv) increased activity of Cu,Zn-superoxide dismutase, (v) decreased level of intracellular thiols. These effects were inversely related to the zinc content of glass powders, were mimicked by ZnCl(2) solutions and were prevented by either metal chelators (EDTA, NTA) or the antioxidant ascorbate, suggesting that Zn(2+) released fastly from HZ glasses can cause MG-63 cell damage via an oxidative stress. This work highlights the importance of designing Zn-containing bioactive glasses without cytotoxic effects and gives supplementary information about the prooxidant role of zinc in living systems.