Radiation-Induced Synthesis and Superparamagnetic Properties of Ferrite Fe3O4 Nanoparticles.

Ultra-small magnetic Fe3O4 nanoparticles are successfully synthesized in basic solutions by using the radiolytic method of the partial reduction in FeIII in the presence of poly-acrylate (PA), or by using the coprecipitation method of FeIII and FeII salts in the presence of PA. The optical, structural, and magnetic properties of the nanoparticles were examined using UV-Vis absorption spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and SQUID magnetization measurements. The HRTEM and XRD analysis confirmed the formation of ultra-small magnetite nanoparticles in a spinel structure, with a smaller size for radiation-induced particles coated by PA (5.2 nm) than for coprecipitated PA-coated nanoparticles (11 nm). From magnetization measurements, it is shown that the nanoparticles are superparamagnetic at room temperature. The magnetization saturation value Ms = 50.1 A m2 kg-1 of radiation-induced nanoparticles at 60 kGy is higher than Ms = 18.2 A m2 kg-1 for coprecipitated nanoparticles. Both values are compared with nanoparticles coated with other stabilizers in the literature.

Anomalous Light-Induced Spin-State Switching for Iron(II) Spin-Crossover Molecules in Direct Contact with Metal Surfaces.

Light-induced spin-state switching is one of the most attractive properties of spin-crossover materials. In bulk, low-spin (LS) to high-spin (HS) conversion via the light-induced excited spin-state trapping (LIESST) effect may be achieved with a visible light, while the HS-to-LS one (reverse-LIESST) requires an excitation in the near-infrared range. Now, it is shown that those phenomena are strongly modified at the interface with a metal. Indeed, an anomalous spin conversion is presented from HS state to LS state under blue light illumination for FeII spin-crossover molecules that are in direct contact with metallic (111) single-crystal surfaces (copper, silver, and gold). To interpret this anomalous spin-state switching, a new mechanism is proposed for the spin conversion based on the light absorption by the substrate that can generate low energy valence photoelectrons promoting molecular vibrational excitations and subsequent spin-state switching at the molecule-metal interface.

Anticancer Activity of Polyoxometalate-Bisphosphonate Complexes: Synthesis, Characterization, In Vitro and In Vivo Results.

We synthesized a series of polyoxometalate-bisphosphonate complexes containing MoVIO6 octahedra, zoledronate, or an N-alkyl (n-C6 or n-C8) zoledronate analogue, and in two cases, Mn as a heterometal. Mo6L2 (L = Zol, ZolC6, ZolC8) and Mo4L2Mn (L = Zol, ZolC8) were characterized by using single-crystal X-ray crystallography and/or IR spectroscopy, elemental and energy dispersive X-ray analysis and 31P NMR. We found promising activity against human nonsmall cell lung cancer (NCI-H460) cells with IC50 values for growth inhibition of ∼5 µM per bisphosphonate ligand. The effects of bisphosphonate complexation on IC50 decreased with increasing bisphosphonate chain length: C0 ≈ 6.1×, C6 ≈ 3.4×, and C8 ≈ 1.1×. We then determined the activity of one of the most potent compounds in the series, Mo4Zol2Mn(III), against SK-ES-1 sarcoma cells in a mouse xenograft system finding a ∼5× decrease in tumor volume than found with the parent compound zoledronate at the same compound dosing (5 µg/mouse). Overall, the results are of interest since we show for the first time that heteropolyoxomolybdate-bisphosphonate hybrids kill tumor cells in vitro and significantly decrease tumor growth, in vivo, opening up new possibilities for targeting both Ras as well as epidermal growth factor receptor driven cancers.

Polyoxomolybdate Bisphosphonate Heterometallic Complexes: Synthesis, Structure, and Activity on a Breast Cancer Cell Line.

Six polyoxometalates containing Mn(II) , Mn(III) , or Fe(III) as the heteroelement were synthesized in water by treating Mo(VI) precursors with biologically active bisphosphonates (alendronate (Ale), zoledronate (Zol), an n-alkyl bisphosphonate (BPC9 ), an aminoalkyl bisphosphonate (BPC8 NH2 )) in the presence of additional metal ions. The Pt complex was synthesized from a polyoxomolybdate bisphosphonate precursor with Mo(VI) ions linked by the 2-pyridyl analogue of alendronate (AlePy). The complexes Mo4 Ale2 Mn, Mo4 Zol2 Mn, Mo4 Ale2 Fe, Mo4 Zol2 Fe, Mo4 (BPC8 NH2 )2 Fe, and Mo4 (BPC9 )2 Fe contain two dinuclear Mo(VI) cores bound to a central heterometallic ion. The oxidation state of manganese was determined by magnetic measurements. Complexes Mo12 (AlePy)4 and Mo12 (AlePy)4 Pt4 were studied by solid-state NMR spectroscopy and the photochromic properties were investigated in the solid state; both methods confirmed the complexation of Pt. Activity against the human breast adenocarcinoma cell line MCF-7 was determined and the most potent compound was Mn(III) -containing Mo4 Zol2 Mn (IC50 ≈1.3 µM). Unlike results obtained with vanadium-containing polyoxometalate bisphosphonates, cell growth inhibition was rescued by the addition of geranylgeraniol, which reverses the effects of bisphosphonates on isoprenoid biosynthesis/protein prenylation. The results indicate an important role for both the heterometallic element and the bisphosphonate ligand in the mechanism of action of the most active compounds.

Mn(II)-containing coordination nanoparticles as highly efficient T(1) contrast agents for magnetic resonance imaging.

Large longitudinal relaxivities were observed in Mn(II)-containing Prussian blue analogue nanoparticles. At low concentrations and high field (7 T), a remarkable positive contrast enhancement was seen which exceeded that of clinical contrast agents and was attributed to the very large proportion of surface atoms of these coordination nanoparticles.

Trinuclear manganese complexes of unsymmetrical polypodal diamino N3O3 ligands with an unusual [Mn3(µ-OR)4]5+ triangular core: synthesis, characterization, and catalase activity.

Two new tri-Mn(III) complexes of general formula [Mn3L2(µ-OH)(OAc)]ClO4 (H3L = 1-[N-(2-pyridylmethyl),N-(2-hydroxybenzyl)amino]-3-[N'-(2-hydroxybenzyl),N'-(4-X-benzyl)amino]propan-2-ol; 1ClO4, X = Me; 2ClO4, X = H) have been prepared and characterized. X-ray diffraction analysis of 1ClO4 reveals that the complex cation possesses a Mn3(µ-alkoxo)2(µ-hydroxo)(µ-phenoxo)(4+) core, with the three Mn atoms bound to two fully deprotonated N3O3 chelating L(3-), one exogenous acetato ligand, and one hydroxo bridge, the structure of which is retained upon dissolution in acetonitrile or methanol. The three Mn atoms occupy the vertices of a nearly isosceles triangle (Mn1···Mn3 = 3.6374(12) Å, Mn2···Mn3 3.5583(13) Å, and Mn1···Mn2 3.2400(12) Å), with one substitution-labile site on the apical Mn ion occupied by terminally bound monodentate acetate. Temperature-dependent magnetic susceptibility studies indicate the presence of predominant antiferromagnetic intramolecular interactions between Mn(III) ions in 1ClO4. Complexes 1ClO4 and 2ClO4 decompose H2O2 at comparable rates upon initial binding of peroxide through acetate substitution, with retention of core structure during catalysis. Kinetic and spectroscopic studies suggest that these complexes employ the [Mn-(µ-oxo/aquo)-Mn](4+) moiety to activate peroxide, with the additional (µ-alkoxo)(µ-phenoxo)Mn(µ-alkoxo) metallobridge carrying out a structural function.

Hydrophilic chlorin-conjugated magnetic nanoparticles--potential anticancer agent for the treatment of melanoma by PDT.

This Letter reports the synthesis and the characterization of two new water-stable and soluble photosensitizer-conjugated magnetic nanoparticles (PS-MNPs) composed of an iron oxide magnetic core coated with a biocompatible dextran shell bearing polyaminated chlorin p6. Designed to improve cancer cell targeting, these photosensitizers were assayed for their antitumour activity against two variants of B16 mouse melanoma cell line (B16F10 and B16G4F, with or without melanin, respectively). Cell viability measurements demonstrated that PS-MNPs were more phototoxic than PEI-chlorin p6 making these photosensitizers promising for further in vitro and in vivo investigations.

Properties of a tunable multinuclear nickel polyoxotungstate platform.

A series of hybrid nickel bisphosphonate (BP) polyoxometalates (POMs) has been isolated. The complexes NaK-Ni7-Ale2 (Ale = [H2O3PC(C3H6NH2)(OH)PO3H2]) and NaNH4-Ni7-Ale2 are both made of two {PW9O34} fragments enclosing a heptanuclear Ni(II) core connected to two alendronate ligands. By pre-functionalising the alendronate moiety through the amino group, the naphthalene (napht) derivative Ni7-(AleNapht)2 and the compounds Ni7-(AlePy2 Ni)2 (py = pyridyl) and Ni7-(AleAc2Ni)2 (Ac = acyl) have been obtained. Compared with the NaK-Ni7-Ale2 species, these last two complexes contain two additional Ni(II) centres connected through two bis(2-pyridylmethyl)amine or two iminodiacetate groups, respectively. This results show that it is possible to functionalise the heptanuclear POM in a controlled manner. Quantification of the magnetic interactions in NaK-Ni7-Ale2 revealed that in the {Ni7} core, ferromagnetic interactions are predominant, with a S = 5 ground state. Magnetisation versus dc field sweeps on a single crystal of NaK-Ni7-Ale2 exhibited hysteresis at low temperature. (1)H and (31)P NMR studies in aqueous solution performed on NaK-Ni7-Ale2 and Ni7-(AleNapht)2 evidenced that the PW9/Ni7/bisphosphonate assembly is stable in solution. This was completed by (31)P magic angle spinning (MAS) investigations and confirmed by (1)H DOSY experiments. The electrochemistry of these compounds proceeds through two well-defined four-electron chemically reversible waves in a medium at pH 6. NaK-Ni7-Ale2 proved to be efficient for the electrocatalytic reduction of nitrate, nitrite and nitrous oxide. Remarkably, its electrocatalytic efficiency for nitrate reduction is approximately three times higher than those previously reported for POMs in a medium at pH >4 under the same potential. The catalytic properties of two representatives of the hybrid family were also examined. It is shown that these nickel bisphosphonate polyoxotungstates are pre-catalysts for the oxidation of alcohols into ketones or carboxylic acids, depending on the classes of alcohols considered, the stoichiometric oxidant used being H2O2. Noticeably, it has been found that an analogous cobalt bisphosphonate polyoxotungstate complex does not present any related activity, highlighting the crucial role of the 3d cations on the catalytic process.

Polyoxometalates functionalized by bisphosphonate ligands: synthesis, structural, magnetic, and spectroscopic characterizations and activity on tumor cell lines.

We report the synthesis and characterization of eight new Mo, W, or V-containing polyoxometalate (POM) bisphosphonate complexes with metal nuclearities ranging from 1 to 6. The compounds were synthesized in water by treating Mo(VI), W(VI), V(IV), or V(V) precursors with biologically active bisphosphonates H(2)O(3)PC(R)(OH)PO(3)H(2) (R = C(3)H(6)NH(2), Ale; R = CH(2)S(CH(3))(2), Sul and R = C(4)H(5)N(2), Zol, where Ale = alendronate, Sul = (2-Hydroxy-2,2-bis-phosphono-ethyl)-dimethyl-sulfonium and Zol = zoledronate). Mo(6)(Sul)(2) and Mo(6)(Zol)(2) contain two trinuclear Mo(VI) cores which can rotate around a central oxo group while Mo(Ale)(2) and W(Ale)(2) are mononuclear species. In V(5)(Ale)(2) and V(5)(Zol)(2) a central V(IV) ion is surrounded by two V(V) dimers bound to bisphosphonate ligands. V(6)(Ale)(4) can be viewed as the condensation of one V(5)(Ale)(2) with one additional V(IV) ion and two Ale ligands, while V(3)(Zol)(3) is a triangular V(IV) POM. These new POM bisphosphonates complexes were all characterized by single-crystal X-ray diffraction. The stability of the Mo and W POMs was studied by (31)P NMR spectroscopy and showed that all compounds except the mononuclear Mo(Ale)(2) and W(Ale)(2) were stable in solution. EPR measurements performed on the vanadium derivatives confirmed the oxidation state of the V ions and evidenced their stability in aqueous solution. Electrochemical studies on V(5)(Ale)(2) and V(5)(Zol)(2) showed reduction of V(V) to V(IV), and magnetic susceptibility investigations on V(3)(Zol)(3) enabled a detailed analysis of the magnetic interactions. The presence of zoledronate or vanadium correlated with the most potent activity (IC(50)~1-5 µM) against three human tumor cell lines.

Thermo- and photoswitchable spin-crossover nanoparticles of an iron(II) complex trapped in transparent silica thin films.

The elaboration and study of hybrid nanocomposites based on photoswitchable spin-crossover nanoparticles is reported. A silica polymeric gel is used as the confining medium to control the kinetics of nucleation and growth of a molecular spin-crossover prototype [Fe((mepy)(3)tren)](PF(6))(2). The precipitation of nanoparticles in the matrix is triggered by spin-coating of the doped gel on a convenient substrate. This process leads to spherical particles of controlled size from 730 (+/- 80) to 47 (+/- 10) nm homogeneously dispersed in transparent silica thin films. The chemical integrity of the coordination compound is checked by EDS and Raman spectroscopies. UV-Vis measurements confirm the persistence of a spin-crossover regime for these nanocomposites. Indeed, the MLCT absorption features are typical of the molecules being in the high-spin state at high temperature and in the low-spin state at low temperature. With respect to the microcrystalline parent compound, the spin-crossover curves afforded by the nanoparticles do not significantly vary over the explored size range. In addition, they are strongly shifted toward lower temperatures. This feature is accounted for by the in-silica formation of a quenched product which behaves like a new phase generated by sudden precipitation of [Fe((mepy)(3)tren)](PF(6))(2). Indeed the precipitated bulk phase, characterized by powder XRD, exhibits both magnetic and optical characteristics very close to those of the nanoparticles. The photoswitching properties based on light-induced excited spin-state trapping (LIESST) are probed by UV-Vis and magnetic measurements. The complexes embedded in silica thin films can be efficiently photoexcited and evidences are provided for the formation of a metastable HS state.

Iron polyoxometalate single-molecule magnets.

Iron sandwich on a tungstate bun: Two new polyoxotungstates with paramagnetic iron(III) heteroatoms (see structure, W blue, Fe yellow, O red) possess S=15/2 and S=5 ground states. Both compounds are single-molecule magnets, and the hexairon species shows large hysteresis (see picture) and quantum tunneling effects at low temperature. Electrochemical studies indicate that these species are stable in solution for a wide range of pH values.

Octa- and nonanuclear nickel(II) polyoxometalate clusters: synthesis and electrochemical and magnetic characterizations.

Three high-nuclearity NiII-substituted polyoxometalate compounds functionalized by exogenous ligands have been synthesized and characterized. The octanuclear complexes in Na15[Na{(A-R-SiW9O34)Ni4(CH3COO)3(OH)3}2] . 4NaCl . 36H2O (1) and Na15[Na{(A-R-SiW9O34)Ni4(CH3COO)3(OH)2(N3)}2] . 32H2O (2) can be described as two {Ni4} subunits connected via a {Na(CH3COO)6} group, with the acetato ligands also ensuring in each subunit the connection between the paramagnetic centers. In 2, two azido groups replace two of the six mu-hydroxo ligands present in 1. The nonanuclear complex K7Na7[(A-R-SiW9O34)2Ni9(OH)6(H2O)6(CO3)3] . 42H2O (3) exhibits a double cubanestructure with two [(A-R-SiW9O34)Ni4(OH)3]5- subunits linked by three carbonato ligands. A ninth NiII center connected to one subunit via a carbonato ligand and a O=W group completes this asymmetric polyoxometalate.Electronic spectroscopy and electrochemical studies indicate that, while compounds 1-3 decompose in a pure aqueous medium, these complexes are very stable in a pH 6 acetate medium. The cyclic voltammetry pattern of each complex is constituted by a first eight-electron reduction wave followed by a second large-current intensity wave. The characteristics of the first waves of the complexes are clearly distinct from those obtained for their lacunary precursor [A-R-SiW9O34]10-, a feature that is due to the Ni centers in the complexes. Such observations of electroactive, stable, and highly nickel-rich polyoxometalates are not common. Measurements of the magnetic susceptibility revealed the occurrence of concomitant ferromagnetic and antiferromagnetic interactions in 1 and 3.For both of these compounds, the extension of the magnetic exchange has been determined by means of a spin Hamiltonian with three and four J constants, respectively.

Square versus tetrahedral iron clusters with polyoxometalate ligands.

Two new insoluble transition metal substituted phosphotungstates, (C2N2H10)11[{(B-alpha-PW9O34)Fe3(OH)3}4(PO4)4Fe].38H2O(1) and K4(C2N2H10)12[(alpha-PW10Fe2O39)4].30H2O(2), have been isolated by the hydrothermal reaction of [A-alpha-PW9O34]9-, Fe(III) ions and ethylenediamine. Compound 1 has a tetrahedral symmetry and contains a Fe13 core built from the assembly of four Fe(III) trisubstituted [B-alpha-PW9O34]9- anions around a central disordered iron ion via four phosphato ligands. The anion in 2 can be described as a square of disubstituted [PW10O37]9- anions linked by Fe(III)-O-Fe(III) bridges. Magnetic measurements performed on 1 and 2 have shown the occurrence of antiferromagnetic interactions between the iron ions and have allowed the coupling constants between the magnetic centers to be determined.

Water substitution on iron centers: from 0D to 1D sandwich type polyoxotungstates.

Four novel polyoxotungstates have been synthesized by reaction of the sandwich type compound [Fe (III) 4(H 2O) 10(B-beta-SbW 9O 33) 2] (6-) (noted Fe 4(H 2O) 10Sb 2W 18) with ethylenediamine (en) and/or oxalate (ox) ligands under various conditions. The one-dimensional (1D) compound [enH 2] 3[Fe (III) 4(H 2O) 8(SbW 9O 33) 2].20H 2O ( 1) is isolated at 130 degrees C and results from the elimination of two water molecules and the condensation of the polyoxotungstate precursor. The reaction of Fe 4(H 2O) 10Sb 2W 18 with oxalate ligands affords the molecular complex Na 14[Fe (III) 4(ox) 4(H 2O) 2(SbW 9O 33) 2].60H 2O ( 2) where two organic ligands substitute four water molecules, while the same reaction in the presence of en molecules at 130 degrees C leads to the formation of the functionalized 1D chain [enH 2] 7[Fe (III) 4(ox) 4(SbW 9O 33) 2].14H 2O ( 3) with protonated ethylenediamine counterions. Finally, at 160 degrees C a rearrangement of the Fe 4(H 2O) 10Sb 2W 18 polyoxotungstate is observed, and the sandwich type compound [enH 2] 5[Fe (II) 2Fe (II) 2(enH) 2(Fe (III)W 9O 34) 2].24H 2O ( 4) crystallizes. In 4, the heteroelement is a Fe (III) ion, and the water molecules on the two outer Fe (II) centers are bound to pendant monoprotonated en ligands. The four compounds have been characterized by IR spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. A detailed study of the magnetic properties of the mixed-valent hexanuclear iron complex in 4 shows evidence of an S = 5 ground-state because of spin frustration effects. A quantification of the electronic parameters characterizing the ground state ( D = +1.12 cm (-1), E/ D = 0.15) confirms that polyoxotungstate ligands induce large magnetic anisotropy.

A new two-dimensional molybdenum(V) nickel phosphate built up of [H18(Mo16O32)Ni16(PO4)26(OH)6(H2O)8]18- wheels.

The new molybdenum(V) nickel phosphate Na(6)Ni(6)[(Mo(2)O(4))(8)Ni(16)(H(2)PO(4))(4)(HPO(4))(10)(PO(4))(12)(OH)(6)(H(2)O)(8)].66H(2)O (1) was synthesized hydrothermally. The structure (orthorhombic, space group Cccm; a = 23.999(4), b = 36.595(6), c = 20.445(4) A) was solved from single-crystal data. The framework structure of 1 consists of anionic inorganic sheets formed by the linkages of large polyoxomolybdate rings via nickel(II) octahedra. Charge-compensating sodium atoms are interleaved between the sheets. Magnetic studies of compound 1 revealed that among the 22 nickel(II) centers, 10 are interacting. The chi(M)T = f(T) curve can be fitted using the dinuclear expression appropriate to the HDVV isotropic exchange Hamiltonian H = -2JS(1).S(2), with S(1) = S(2) = 1 and J = -24.1 cm(-)(1), showing that nickel is antiferromagnetically coupled within Ni(2) pairs.