Tuning Properties of Iron Oxide Nanoparticles in Aqueous Synthesis without Ligands to Improve MRI Relaxivity and SAR.

Aqueous synthesis without ligands of iron oxide nanoparticles (IONPs) with exceptional properties still remains an open issue, because of the challenge to control simultaneously numerous properties of the IONPs in these rigorous settings. To solve this, it is necessary to correlate the synthesis process with their properties, but this correlation is until now not well understood. Here, we study and correlate the structure, crystallinity, morphology, as well as magnetic, relaxometric and heating properties of IONPs obtained for different durations of the hydrothermal treatment that correspond to the different growth stages of IONPs upon initial co-precipitation in aqueous environment without ligands. We find that their properties were different for IONPs with comparable diameters. Specifically, by controlling the growth of IONPs from primary to secondary particles firstly by colloidal and then also by magnetic interactions, we control their crystallinity from monocrystalline to polycrystalline IONPs, respectively. Surface energy minimization in the aqueous environment along with low temperature treatment is used to favor nearly defect-free IONPs featuring superior properties, such as high saturation magnetization, magnetic volume, surface crystallinity, the transversal magnetic resonance imaging (MRI) relaxivity (up to r2 = 1189 mM-1·s-1 and r2/r1 = 195) and specific absorption rate, SAR (up to 1225.1 W·gFe-1).

{2,2'-[1,1'-(3-Aza-pentane-1,5-diyl-dinitrilo)diethyl-idyne]diphenolato}(piperidine)cobalt(III) tetra-phenyl-borate.

The title compound, [Co(C(20)H(23)N(3)O(2))(C(5)H(11)N)](C(24)H(20)B) or [Co{(Me-sal)(2)dien}(pprdn)]BPh(4), where (Me-sal)(2)dien is 2,2'-[1,1'-(3-aza-pentane-1,5-diyldinitrilo)diethyl-idyne]diphenolate and pprdn is piperidine, contains a penta-dentate (Me-sal)(2)dien ligand furnishing an N(3)O(2) set, such that two of the N and one of the O atoms of the salicyl-idene rings define three positions of an equatorial plane, whereas the secondary amine N atom and the other O atom of the salicyl-idene lie in axial positions. The piperidine ligand occupies an equatorial position trans to one of the imine N atoms of the salicyl-idene. In the observed conformation of the penta-dentate ligand, the salicyl-idene rings attain asymmetrical positions owing to the structural demands. The geometry of the resulting CoN(4)O(2) coordination can be described as distorted octa-hedral. The asymetric unit contains two formula units.

Potassium gallium hydrogenphosphate fluoride, K(2)Ga[H(HPO(4))(2)]F(2).

Hydrothermally synthesized dipotassium gallium {hydrogen bis[hydrogenphosphate(V)]} difluoride, K(2)Ga[H(HPO(4))(2)]F(2), is isotypic with K(2)Fe[H(HPO(4))(2)]F(2). The main features of the structure are ([Ga{H(HPO(4))(2)}F(2)](2-))(n) columns consisting of centrosymmetric Ga(F(2)O(4)) octahedra [average Ga-O = 1.966 (3) Angstrom and Ga-F = 1.9076 (6) Angstrom] stacked above two HPO(4) tetrahedra [average P-O = 1.54 (2) Angstrom] sharing two O-atom vertices. The charge-balancing seven-coordinate K(+) cations [average K-O,F = 2.76 (2) Angstrom] lie in the intercolumn space, stabilizing a three-dimensional structure. Strong [O...O = 2.4184 (11) Angstrom] and medium [O...F = 2.6151 (10) Angstrom] hydrogen bonds further reinforce the connections between adjacent columns.

Electrochemically triggered open and closed Pacman bis-metalloporphyrins.

A new type of very compact Pacman bis-porphyrin scaffold has been obtained in which a calix[4]arene spacer provides both cofacial preorganization and flexibility. Changes in the distance between the two tetrapyrrolic macrocycles can be triggered by electrochemistry, where closed and open conformers can be interconverted in a handclapping motion.

{2,2'-[1,1'-(4-Azaheptane-1,7-diyldinitrilo)diethylidyne]diphenolato}copper(II).

The quinquedentate ligand 2,2'-[1,1'-(4-azaheptane-1,7-diyldinitrilo)diethylidyne]diphenol in the title compound, [Cu(C22H27N3O2)], furnishes an N3O2 donor set, which results in a distorted square-pyramidal coordination; the two O and two imine N atoms lie in the basal plane, while the secondary amine N atom of the ligand occupies the axial position. The axial Cu-N bond is 0.33 A longer than the average of the equatorial bonds, and the O atoms are trans. The symmetry of the molecule is lowered by the twist-boat and chair conformations adopted by the two CuNN chelate rings. The complex contains two intramolecular C-H...O interactions, and two molecules of the complex are linked into a dimer by means of moderate N-H...O hydrogen bonds. Spectroscopic evidence supports the presence of hydrogen bonds.

Structural and binding features of cofacial bis-porphyrins with calixarene spacers: pac-man porphyrins that can chew.

Based on the efficient combination of calixarene spacers and acetylenic porphyrin derivatives, a new generation of cofacial bis-porphyrins has been synthesized. The first crystal structure of a cofacial bis-porphyrin-calixarene conjugate is reported. Their unique architectural features, analogous to those of pac-man-type bis-porphyrins, allow these calixarene-porphyrin conjugates to adapt their shape to the size of bidentate guests, such as diazabicyclo[2.2.2]octane (dabco) and 1,4-pyrazine. The predefined, cofacial arrangement of the porphyrin moieties observed in the solid state and in solution results in extremely high affinities (in the range of 10(9) M(-1)) for these guests. The 1,3-alternate calixarene conformations afford "open-mouth" pac-man structures whose ability to bite on nitrogen bidentates depends on their functionalization. A cone conformer provides a much more flexible structure that exhibits the highest affinity for dabco and pyrazine.

3-[2,6-Bis(diethylcarbamoyl)pyridin-4-yl]-N-(tert-butoxycarbonyl)alanine methyl ester: a chiral tridentate ligand that causes a diastereomeric excess of its lanthanide complexes in solution.

L(4), or 3-[2,6-bis(diethylcarbamoyl)pyridin-4-yl]-N-(tert-butoxycarbonyl)alanine methyl ester, C(24)H(38)N(4)O(6), crystallizes in neat [010] laths stabilized by abundant intra- and intermolecular hydrogen bonds. The strongest of these form [010] chains of molecules, thus rationalizing the fastest growth direction, while the slowest direction coincides with the normal to the (110) layers, which are linked by very weak hydrogen bonds. There exist two independent molecules, the distances and bond angles of which differ in a random manner only. The torsion and dihedral angles, however, differ so as to achieve optimal packing. The influence of the chiral group in the 4-position of the pyridine ring on the helical wrapping and on the ensuing diastereomeric induction is briefly discussed.

Taxiphyllin from Henriettella fascicularis.

(2R)-alpha-(beta-D-Glucopyranosyloxy)-4-hydroxybenzeneacetonitrile (taxiphyllin) dihydrate, C(14)H(17)NO(7) x 2H(2)O, is a naturally occurring cyanogenetic glycoside which has been isolated from Henriettella fascicularis (Sw.) C. Wright (Melastomataceae). Its structure is stabilized by a wealth of intermolecular O-H...O and O-H...N hydrogen bonds spun into a three-dimensional network. Further stabilization arises from an intramolecular O-H...O bond and weak intermolecular C-H...O interactions. The very anisotropic growth speeds of the basal pinacoids from methanol mirror a certain structural inhomogeneity.

Urotropin azelate: a rather unwilling co-crystal.

Urotropin (U) and azelaic acid (AA) form 1:1 co-crystals (UA) that give rise to a rather complex diffraction pattern, the main features of which are diffuse rods and bands in addition to the Bragg reflections. UA is characterized by solvent inclusions, parasite phases, and high vacancy and dislocation densities. These defects compounded with the pronounced tendency of U to escape from the crystal edifice lead to at least seven exotic phase transitions (many of which barely manifest themselves in a differential scanning calorimetry trace). These involve different incommensurate phases and a peritectoid reaction in the recrystallization regime (T(h) > 0.6). The system may be understood as an OD (order-disorder) structure based on a layer with layer group P(c)c2 and cell a(o) approximately 4.7, b approximately 26.1 and c approximately 14.4 A. At 338 K the layer stacking is random, but with decreasing temperature the build-up of an orthorhombic MDO (maximal degree of order) structure with cell a(1) = 2a(o), b(1) = b, c(1) = c and space group Pcc2 is begun (at approximately 301 K). The superposition structure of the OD system at T = 286 (1) K with space group Bmmb and cell â = 2a(o), b = b and c = c/2 owes its cohesion to van der Waals interactions between the AA chains and to three types of hydrogen bonds of varied strength between U-U and U-AA. Before reaching completion, this MDO structure is transformed, at 282 K, into a monoclinic one with cell a(m) = -a(o) + c/4, b(m) = b, c(m) = -2(a(o) + c/2), space group P2(1)/c, spontaneous deformation approximately 2 degrees, and ferroelastic domains. This transformation is achieved in two steps: first a furtive triggering transition, which is not yet fully understood, and second an improper ferroelastic transition. At approximately 233 K, the system reaches its ground state (cell a(M) = a(m), b(M) = b, c(M) = c(m) and space group P2(1)/c) via an irreversible transition. The phase transitions below 338 K are described by a model based on the interaction of two thermally activated slip systems. The OD structure is described in terms of a three-dimensional Monte Carlo model that involves first- and second-neighbour interactions along the a axis and first-neighbour interactions along the b and c axes. This model includes random shifts of the chains along their axes and satisfactorily accounts for most features that are seen in the observed diffraction pattern.

Luminescent Properties of Lanthanide Nitrato Complexes with Substituted Bis(benzimidazolyl)pyridines.

The protonated form of the ligand 2,6-bis(1'-methylbenzimidazol-2'-yl)pyridine crystallizes as its perchlorate salt (HL(1))ClO(4) (1) in the orthorhombic system Pbca, with a = 13.976(3) Å, b = 14.423(3) Å, c = 19.529(4) Å, Z = 8. The proton is located on one benzimidazole N-atom, and the two N-methyl substituents lie on the same side of the pyridine N-atom (cisoid conformation). New 1:1 nitrato complexes of composition [Eu(NO(3))(3)(L(i)())](solv')(y)() have been isolated with L(4) (4), L(6) (5), L(7) (6), and L(8) (7), and their structural and photophysical properties are compared with those of the previously reported complexes [Eu(NO(3))(3)(L(1))(MeOH)] (2) and [Eu(NO(3))(3)(L(3))] (3). The crystal and molecular structure of [Eu(NO(3))(3)(L(7))(MeCN)].2.5MeCN at 180 K (6a, triclinic, P&onemacr;, a = 12.137(2) Å, b = 14.988(3) Å, c = 16.926(3) Å, alpha = 114.52(3) degrees, beta = 98.28(3) degrees, gamma = 103.99(3) degrees, Z = 2) shows a decacoordinated Eu(III) ion to six O-atoms from the nitrates, three N-atoms from L(7), and one N-atom from a coordinated MeCN. The metal-centered luminescence arising upon ligand excitation in the solid state is analyzed in terms of nephelauxetic effects of the ligand and crystal field splitting of the (7)F(1) level. Quantum yields of 10(-3) and 10(-)(4) M solutions in MeCN are substituent dependent and may be rationalized by taking into account several factors, including the energy of the ligand singlet and triplet levels and the arrangement of the ligands in the first coordination sphere. We also show that the quantum yield of the ligand-centered luminescence decreases in the order L(1) > [La(NO(3))(3)(L(1))]MeOH > [La(L(1))(3)](ClO(4))(3).

Stability and Size-Discriminating Effects in Mononuclear Lanthanide Triple-Helical Building Blocks with Tridentate Aromatic Ligands.

The planar aromatic tridentate ligand 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (L(1)) reacts with Ln(III) (Ln = La-Lu) in acetonitrile to give the successive complexes [Ln(L(1))(n)()](3+) (n = 1-3). Stability constants determined by spectrophotometry and potentiometric competitive titrations with Ag(I) show that the 1:1 and the 1:2 complexes display the usual thermodynamic behavior associated with electrostatic effects while the 1:3 complexes exhibit an unusual selectivity for the midrange Ln(III) ions (Delta log K(3)(Gd-Lu) approximately 4). A detailed investigation of the solution structure of [Ln(L(1))(3)](3+) (Ln = La-Dy) reveals that the closely packed triple-helical structure found in the crystal structure of [Eu(L(1))(3)](3+) is retained in acetonitrile for the complete series. A sharp control of the coordination cavity results from the interstrand pi-stacking interactions which appear to be optimum for Gd(III). For Yb(III), for instance, a 1:2 complex only could be isolated, which crystallizes as a hydroxo-bridged dimer [Yb(OH)(L(1))(2)](2)(ClO(4))(4)(HClO(4))(0.5)(CH(3)CN)(7.32)(L(1))(0.5) (triclinic, P&onemacr;, a = 13.250(2) Å, b = 16.329(2) Å, c = 27.653(3) Å, alpha = 99.941(9) degrees, beta = 93.394(9) degrees, gamma = 108.114(9) degrees, Z = 2). The binding of bulky substituents to the nitrogen atoms of the benzimidazole side arms in L(4) (i) severely affects the wrapping process, (ii) leads to less stable triple-helical building blocks, and (iii) removes the size-discriminating effect. The last can however be restored if a strong electron-donor group is connected to the central pyridine ring in L(8). Stability and solution structure data for [Ag(2)(L(i)())(2)](2+) (i = 1, 4, 8) are also reported and discussed.