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Mn2+ complexes represent an alternative to Gd3+ chelates which are widely used contrast agents in magnetic resonance imaging. In this perspective, we investigated the Mn2+ complexes of two 12-membered, pyridine-containing macrocyclic ligands bearing one pendant arm with a carboxylic acid (HL1, 6-carboxymethyl-3,6,9,15-tetraazabicyclo[9.3.1] pentadeca-1(15),11,13-triene) or a phosphonic acid function (H2L2, 6-dihydroxyphosphorylmethyl-3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene). Both ligands were synthesized using nosyl or tosyl amino-protecting groups (starting from diethylenetriamine or tosylaziridine). The X-ray crystal structures confirmed a coordination number of 6 for Mn2+ in their complexes. In aqueous solution, these pentadentate ligands allow one free coordination site for a water molecule. Potentiometric titration data indicated a higher basicity for H2L2 than that for HL1, related to the electron-donating effect of the negatively charged phosphonate group. According to the protonation sequence determined by 1H and 31P pH-NMR titrations, the first two protons are attached to macrocyclic amino groups whereas the subsequent protonation steps occur on the pendant arm. Both ligands form thermodynamically stable complexes with Mn2+, with full complexation at physiological pH and 1:1 metal to ligand ratio. The kinetic inertness was studied via reaction with excess of Zn2+ under various pHs. The dissociation of MnL2 is instantaneous (at pH 6). For MnL1, the dissociation is very fast (kobs = 1-12 × 103 s-1), much faster than that for MnDOTA, MnNOTA, or the Mn2+ complex of the 15-membered analogue. It proceeds exclusively via the dissociation of the monoprotonated complex, without any influence of Zn2+. In aqueous solution, both complexes are air-sensitive leading to Mn3+ species, as evidenced by UV-vis and 1H NMRD measurements and X-ray crystallography. Cyclic voltammetry gave low oxidation peak potentials (Eox = 0.73 V for MnL1 and Eox = 0.68 V for MnL2), in accordance with air-oxidation. The parameters governing the relaxivity of the Mn2+ complexes were determined from variable-temperature 17O NMR and 1H NMRD data. The water exchange is extremely fast, kex = 3.03 and 1.77 × 109 s-1 for MnL1 and MnL2, respectively. Variable-pressure 17O NMR measurements have been performed to assess the water exchange mechanism on MnL1 and MnL2 as well as on other Mn2+ complexes. The negative activation volumes for both MnL1 and MnL2 complexes confirmed an associative mechanism of the water exchange as expected for a hexacoordinated Mn2+ ion. The hydration number of q = 1 was confirmed for both complexes by 17O chemical shifts. A relaxometric titration with phosphate, carbonate or citrate excluded the replacement of the coordinated water molecule by these small endogenous anions. [ABSTRACT FROM AUTHOR]

A new class of macrocyclic ligands based on 1-oxa-4,7-diazacyclononane was synthesized and their Mn2+complexes were investigated with respect to stability and relaxation properties. Each ligand has two pendant arms involving carboxylic (H2L1— 1-oxa-4,7-diazacyclononane-4,7-diacetic acid), phosphonic (H4L2— 1-oxa-4,7-diazacyclononane-4,7-bis(methylenephosphonic acid)), phosphinic (H2L3— 1-oxa-4,7-diazacyclononane-4,7-bis(methylenephosphinic acid)) or phenylphosphinic (H2L4— 1-oxa-4,7-diazacyclononane-4,7-bis[methylene(phenyl)phosphinic acid]) acid moieties. H2L3and H2L4were synthesized for the first time. The crystal structure of the Mn2+complex with H2L4confirmed a coordination number of 6 for Mn2+. The protonation constants of all ligands and the stability constants of their complexes with Mn2+and some biologically or biomedically relevant metal ions were determined by potentiometry. The protonation sequence of H2L3was followed by 1H and 31P NMR titration and the second protonation step was attributed to the second macrocyclic nitrogen atom. The potentiometric data revealed a relatively low thermodynamic stability of the Mn2+complexes with all ligands investigated. For H2L3and H2L4, full Mn2+complexation cannot be achieved even with 100% ligand excess. The transmetallation of MnL1and MnL2with Zn2+was too fast to be followed at pH 6. Variable temperature 1H NMRD and 17O NMR measurements have been performed on MnL1and MnL2to provide information on water exchange and rotational dynamics. The 17O chemical shifts indicate hydration equilibrium between mono- and bishydrated species for MnL1, while MnL2is monohydrated. The water exchange is considerably faster on MnL1(kex298= 1.2 × 109s−1) than on MnL2(kex298= 1.2 × 107s−1). Small endogenous anions (phosphate, carbonate, citrate) do not replace the coordinated water in either of the complexes, but they induce their slow decomposition. All Mn2+complexes are stable toward air-oxidation. [ABSTRACT FROM AUTHOR]

A novel positively charged surfactant N-dodecyl- N, N-dimethyl-(1,2-propandiol) ammonium chloride was used for the dynamic coating of the inner wall of a silica capillary. This paper covers the evaluation of dynamic coating and study of the influence of the analysis conditions for the magnitude and direction of electroosmotic flow as well as for the effective and selective separation of chosen proteins (ribonuclease A, cytochrome c, lysozyme, and myoglobin). The concentration of 0.1 mM of N-dodecyl- N, N-dimethyl-(1,2-propandiol) ammonium chloride enabled the reversal of the electro-osmotic flow, however, to separate basic as well as neutral proteins the higher concentration of the studied surfactant was necessary. The final conditions for the separation of studied proteins were set at 100 mM sodium acetate pH 5.5 with 10.0 mM of the studied surfactant. The results were also compared with those of two commercially available cationic surfactants, cetyltrimethylammonium bromide and dodecyltrimethylammonium bromide. Additionally, the developed method for protein separation was applied for the determination of lysozyme in a cheese sample. The limits of detection and quantification of lysozyme were 0.9 and 3.0 mg/L, respectively. The mean concentration of lysozyme found in the cheese sample was 167.3 ± 10.3 mg/kg. [ABSTRACT FROM AUTHOR]

Abstract: A series of square-planar nickel(II) benzylpiperazine–dithiocarbamato (bpdtc; 1–4) and thiomorpholine–dithiocarbamato (tmdtc; 5–8) complexes of the composition [NiX(ndtc)(PPh3)] (X symbolizes Cl for 1 and 5, Br for 2 and 6, I for 3 and 7, or NCS for 4 and 8) was prepared and thoroughly characterized by elemental analysis, UV–Vis, IR and NMR spectroscopy, mass spectrometry, molar conductivity and magnetochemical measurements, and by single-crystal X-ray analysis (for complex 1). The solution behaviour study of selected representatives (1, 4, 5 and 8) in various solvents (acetone, acetonitrile, methanol (MeOH), N,N′-dimethylformamide (DMF), chloroform, nitromethane, dimethyl sulfoxide (DMSO), MeOH/water mixture (1:1 v/v)) by a combination of NMR and UV–Vis spectroscopy, mass spectrometry and single-crystal X-ray analysis showed that the complexes decompose back to the synthetic precursors, involving the [Ni(ndtc)2] species, in DMF and DMSO, while they dissolve without a change in their composition in the remaining solvents. [Copyright &y& Elsevier]

Large uniaxial magnetic anisotropy, expressed by a negative value of the axial zero-field splitting parameter D , has been achieved in a series of trigonal prismatic Co(II) complexes with the general formula [Co(L)X]Y, where L = 1,5,13,17,22-pentaazatricyclo[15.2.2.17,11]docosa-7,9,11(22)-triene, X = Cl - (1a,b), Br - (2), N 3 - (3), NCO - (4), NCS - (5), NCSe - (6), and Y = Cl - (1), Br - (2), NCS - (4), NCSe - (5), ClO 4 - (3,6). Complexes 1-6 are six-coordinate with the distorted trigonal prismatic geometry imparted by the pentadentate pyridine-/piperazine-based macrocyclic ligand L and by one monovalent coligand X - . Based on magnetic studies, all complexes 1-6 exhibit strong magnetic anisotropy with negative D -values ranging from about -20 to -41 cm -1 . This variation in D ( i.e. the increase of magnetic anisotropy) parallels the trend obtained by theoretical calculations and the lesser distortion of the coordination sphere with respect to the trigonal prismatic reference geometry. AC magnetic susceptibility investigations revealed field-induced single-molecule magnet behaviour for all complexes except Cl - derivative 1. The series investigated represents a rare example of Co(II) complexes with a robust trigonal prismatic geometry.

A new 15-membered pyridine-based macrocyclic ligand containing one acetate pendant arm ( N -carboxymethyl-3,12,18-triaza-6,9-dioxabicyclo[12.3.1]octadeca-1(18),14,16-triene, L1) was synthesized and its Mn(II) complex MnL1 was investigated in the context of MRI contrast agent development. The X-ray molecular structure of MnL1 confirmed a coordination number of seven with an axially compressed pentagonal bipyramidal geometry and one coordination site available for an inner-sphere water molecule. The protonation constants of L1 and the stability constants of Mn(II), Zn(II), Cu(II) and Ca(II) complexes were determined by potentiometry, and revealed higher thermodynamic stabilities in comparison with complexes of 15-pyN 3 O 2 , the parent macrocycle without an acetate pendant arm. The MnL1 complex is fully formed at physiological pH 7.4, but it shows fast dissociation kinetics, as followed by relaxometry in the presence of an excess of Zn(II). The short dissociation half-life estimated for physiological pH ( ca. 3 minutes) is related to fast spontaneous dissociation of the non-protonated complex. At lower pH values, the proton-assisted dissociation pathway becomes important, while the Zn(II) concentration has no effect on the dissociation rate. 17 O NMR and 1 H NMRD data indicated the presence of one inner-sphere water molecule with a rather slow exchange ( k 298ex = 4.5 × 10 6 s -1 ) and provided information about other microscopic parameters governing relaxation. The relaxivity ( r 1 = 2.45 mM -1 s -1 at 20 MHz, 25 °C) corresponds to typical values for monohydrated Mn(II) chelates. Overall, the acetate pendant arm in L1 has a beneficial effect with respect to 15-pyN 3 O 2 in increasing the thermodynamic stability and kinetic inertness of its Mn(II) complex, but leads to a reduced number of inner-sphere water molecules and thus lower relaxivity.

Three mononuclear lanthanide complexes of a 2-pyridylmethyl pendant-armed 15-membered ligand {(3,12-bis(2-pyridylmethyl)-3,12,18-triaza-6,9-dioxabicyclo-[12.3.1]octadeca-1,14,16-triene); L} with general formula [Ln(L)(H 2 O)(NO 3 )](NO 3 ) 2 (Ln = Tb (1), Dy (2), and Er (3)) are reported. Based on X-ray diffraction analysis of 1 and 2, the central lanthanide atoms are nine-coordinated with the N 5 O 4 donor set originating from the ligand L and one coordinated water molecule and one monodentate-bonded nitrato ligand. The coordination geometry of the [LnN 5 O 4 ] cores can be described as a muffin-like shape. Magnetic measurements revealed that all three compounds show field-induced single-molecule magnet behaviour, with estimated energy barriers U ≈ 44-82 K. The experimental study was complemented by CASSCF calculations showing a trend of an increasing first excited energy gap (Tb → Dy → Er) within the muffin-like geometry with the lowest magnetization tunnelling probability for the Dy III complex 2.

This paper presents solid state synthesis and characterization of tetra-oxy iron(iv) and iron(v) species in their salt forms (Na4FeO4-Fe(IV) and K3FeO4-Fe(V)). Stability of the synthesized salts, commonly called ferrates, in water was determined by applying the (57)Fe Mössbauer spectroscopy technique. Within 2 s in water, Fe(IV) converted into Fe(III) while Fe(V) transformed into Fe(VI) and Fe(III) at pH = 8.2. Comparatively, Fe(VI) (bought as K2FeO4) remained stable in aqueous solution during the short time period. The oxidative removal efficiency of the high-valent iron species was then tested against five environmentally important estrogenic hormones (estron (E1), 17-β-estradiol (E2), estriol (E3), 17-α-ethinylestradiol (EE2), and diethylstibestrol (DES)) in effluent water of a wastewater treatment plant. Three dosages of iron species (1, 10, and 100 mg L(-1)) were applied to the effluent water. An increase in the concentration of dosages enhanced the removal of estrogens. Both Fe(V) and Fe(VI) were effective in degrading estrogens, but Fe(IV) showed limited oxidation capacity to transform estrogens. The oxidized products of the estrogens were analyzed using Raman spectroscopy and high-performance liquid chromatography-mass spectrometry (HPLC-MS) techniques. Results demonstrated the transformation of estrogens into low molecular weight oxygenated compounds such as quinone-like and opened-aromatic ring species. A detailed study on E1 by using excess Fe(VI) showed the mineralization of the parent compound. The results demonstrate great potential of high-valent iron species in the degradation of endocrine disruptor chemicals like estrogens with several superior aspects including fast reactions, complete degradation and/or formation of benign organic species, and environmentally-acceptable iron oxide by-products.

A series of novel triazole derivative pyridine-based polyamino-polycarboxylate ligands has been synthesized for lanthanide complexation. This versatile platform of chelating agents combines advantageous properties for both magnetic resonance (MR) and optical imaging applications of the corresponding Gd(3+) and near-infrared luminescent lanthanide complexes. The thermodynamic stability constants of the Ln(3+) complexes, as assessed by pH potentiometric measurements, are in the range log K(LnL)=17-19, with a high selectivity for lanthanides over Ca(2+), Cu(2+), and Zn(2+). The complexes are bishydrated, an important advantage to obtain high relaxivities for the Gd(3+) chelates. The water exchange of the Gd(3+) complexes (k(ex)(298)=7.7-9.3×10(6) s(-1)) is faster than that of clinically used magnetic resonance imaging (MRI) contrast agents and proceeds through a dissociatively activated mechanism, as evidenced by the positive activation volumes (ΔV(≠)=7.2-8.8 cm(3) mol(-1)). The new triazole ligands allow a considerable shift towards lower excitation energies of the luminescent lanthanide complexes as compared to the parent pyridinic complex, which is a significant advantage in the perspective of biological applications. In addition, they provide increased epsilon values resulting in a larger number of emitted photons and better detection sensitivity. The most conjugated system PheTPy, bearing a phenyl-triazole pendant on the pyridine ring, is particularly promising as it displays the lowest excitation and triplet-state energies associated with good quantum yields for both Nd(3+) and Yb(3+) complexes. Cellular and in vivo toxicity studies in mice evidenced the non-toxicity and the safe use of such bishydrated complexes in animal experiments. Overall, these pyridinic ligands constitute a highly versatile platform for the simultaneous optimization of both MRI and optical properties of the Gd(3+) and the luminescent lanthanide complexes, respectively., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)