Synthesis and Molecular Structures of CuII15-Metallacrown-5 Complexes with Encapsulated CaII, PrIIIand NdIIIIons

Praseodymium Metallacrown-Based NMR Probe for Enantioselective Discrimination of Mandelate Anions in Water

Recently, the enhanced interest in water-soluble aminohydroximate Ln(III)-Cu(II) metallacrowns (MC) is largely due to their fascinating structural chemistry, diverse properties and ease of synthesis. We examined the water-soluble praseodymium(III) alaninehydroximate complex Pr(H₂O)₄[15-MC_Cu(II)Alaha-5]·3Cl (1) as a highly effective chiral lanthanide shift reagent for NMR analysis of the biologically relevant (R/S)-mandelate (MA) anions in aqueous media. The R-MA and S-MA enantiomers can be easily discriminated in the presence of small (1.2-6.2 mol %) amounts of MC 1 by the ¹H NMR signals of multiple protons exhibiting an enantiomeric shift difference (ΔΔδ) of 0.06 ppm up to 0.31 ppm. Additionally, a possibility of coordination of MA to the metallacrown was investigated by the ESI-MS technique and a Density Functional Theory modeling of the molecular electrostatic potential and noncovalent interactions.

The first water-soluble polynuclear metallamacrocyclic Sr(ii)-Cu(ii) complex based on simple glycinehydroximate ligands

Recently, aminohydroximate ligands have found wide applications in the fascinating class of polynuclear metallamacrocyclic compounds named 15-MC-5 metallacrowns. The enhanced interest in water-soluble aminohydroximate Ln(iii)-Cu(ii) complexes is largely due to their rich coordination chemistry, diverse properties and ease of synthesis. We examined glycinehydroxamic acid as a simple ligand for the preparation of the first water-soluble polynuclear metallamacrocyclic Sr(ii)-Cu(ii) compound. The complex Sr(H2O)3[15-MCCuGlyha-5](Cl)2 was synthesized and characterized structurally and spectroscopically. The single-crystal structure reveals the classic metallamacrocyclic 15-MC-5 configuration. The Sr(ii) ion is located at the center of the 15-MCCu(II)Glyha-5 ring and coordinated by five oxygen atoms of the cycle in the equatorial plane and an additional three oxygen atoms of the water molecules at apical positions. Detailed DFT and QT AIM studies were carried out for the hydrated isoelectronic Sr[15-MCCuGlyha-5]2+ and Y[15-MCCuGlyha-5]3+ systems. The ionic contribution to the metal-ligand interactions appears to be higher for the Sr(ii) derivative despite the smaller charge separation. DFT calculations suggest a thermodynamically favorable substitution of the Sr(ii) central ion with Y(iii). Indeed, it was shown experimentally that the strontium ion can be easily replaced by yttrium. Preliminary cytotoxic studies revealed the low toxicity of the strontium complex and its yttrium analogue, so the water-soluble Sr(ii) and Y(iii) metallacrowns can be further investigated as possible platforms for the development of new 90Sr and 90Y radiotherapy drugs.

Complexes in aqueous cobalt(II)-2-picolinehydroxamic acid system: Formation equilibria, DNA-binding ability, antimicrobial and cytotoxic properties

The coordination properties of 2-picolinehydroxamic acid towards cobalt(II) in aqueous solution were determined by a pH-metric method and confirmed by spectroscopic (UV-Vis and ESI-MS) studies. The results show the formation of mononuclear complexes, as well as of metallacrowns (MC). All methods indicate a high tendency of 2-picolinehydroxamic acid to form cobalt(II) metallacrown 12-MC-4. ESI-MS additionally confirms 15-MC-5 and 18-MC-6, stabilized by a sodium ion and methanol. The complexes observed in the speciation model at a pH about 7.2 were studied for their DNA-binding ability. The decrease of absorbance in the range of ca 310-400 nm indicates effective binding to calf thymus DNA by 2-picolinehydroxamic acid complexes, via intercalative mode. The antimicrobial properties of 2-picolinehydroxamic acid, cobalt(II) ions and of the complexes formed in the Co(II) - ligand system were determined against Gram-positive bacteria (Enterococcus faecalis, Enterococcus faecium, Staphylococcus aureus, Bacillus subtilis), Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, Helicobacter pylori) and fungal strains (Candida, Aspergillus niger). The results indicate that the complexes demonstrate greater antibacterial and antifungal activity for most strains than the ligand. Both the complexes and the ligand induce a slight decrease in the metabolic activity of cells, while the complexes do not damage the cell nuclei. The 2-picolinehydroxamic acid complexes activate the human monocytic cells, suggesting they have immunomodulating properties, which are particularly important in combating infections caused by strains resistant to other drugs.

Crystal structure of N-hy-droxy-quinoline-2-carboxamide monohydrate

The title compound, C10H8N2O2·H2O, consists of an N-hy-droxy-quinoline-2-carboxamide mol-ecule in the keto tautomeric form and a water mol-ecule connected through an O-H⋯O hydrogen bond. The N-hy-droxy-quinoline-2-carboxamide mol-ecule has a nearly planar structure [maximum deviation = 0.062 (1) Å] and only the hy-droxy H atom deviates significantly from the mol-ecule plane. In the crystal, π-π stacking between the aromatic rings [inter-centroid distance = 3.887 (1) Å] and inter-molecular O-H⋯O hydrogen bonds organize the crystal components into columns extending along the b-axis direction.

Crystal structure of bis-(μ-N-hy-droxy-picolin-amid-ato)bis-[bis-(N-hy-droxy-picolinamide)-sodium]

The title compound, [Na2(C6H5N2O2)2(C6H6N2O2)4], is a centrosymmetric coordination dimer based on the sodium(I) salt of N-hy-droxy-picolinamide. The mol-ecule has an {Na2O6(μ-O)2} core with two bridging carbonyl O atoms and two hydroxamate O atoms of two mono-deprotonated residues of N-hy-droxy-picolinamide, while two neutral N-hy-droxy-picolinamide mol-ecules are coordinated in a monodentate manner to each sodium ion via the carbonyl O atoms [the Na-O distances range from 2.3044 (2) to 2.3716 (2) Å]. The penta-coordinated sodium ion exhibits a distorted trigonal-pyramidal coordination polyhedron. In the crystal, the coordination dimers are linked into chains along the c axis via N-H⋯O and N-H⋯N hydrogen bonds; the chains are linked into a two-dimensional framework parallel to (100) via weak C-H⋯O and π-π stacking inter-actions.

Crystal structure of μ-oxalodi-hydroxamato-bis-[(2,2'-bipyrid-yl)(di-methyl sulfoxide-κO)copper(II)] bis-(perchlorate)

The centrosymmetric binuclear complex, [Cu2(C2H2N2O4)(C10H8N2)2(C2H6OS)2](ClO4)2, contains two copper(II) ions, connected through an N-deprotonated oxalodi-hydroxamic acid dianion, two terminal 2,2'-bi-pyridine ligands, and two apically coordinating dimethylsulfoxide mol-ecules. Two non-coordinating perchlorate anions assure electrical neutrality. The copper(II) ions in the complex dication [Cu2(C10H8N2)2(μ-C2H2N2O4)(C2H6SO)2](2+) are in an O2N3 square-pyramidal donor environment, the Cu-Cu separation being 5.2949 (4) Å. Two hydroxamate groups in the deprotonated oxalodi-hydroxamic acid are located trans to one each other. In the crystal, O-H⋯O and C-H⋯O hydrogen bonds link the complex cations to the perchlorate anions. Further C-H⋯O hydrogen bonds combine with π-π contacts with a centroid-to-centroid separation of 3.6371 (12) Å to stack the mol-ecules along the a-axis direction.

Crystal structure of N-hy-droxy-picolinamide monohydrate

The crystal structure of the title compound, C6H6N2O2·H2O, consists of N-hy-droxy-picolinamide and water mol-ecules connected through O-H⋯O and N-H⋯N hydrogen bonds. The O-H⋯O inter-actions and π-π stacking inter-actions between the pyridine rings [centroid-centroid distance = 3.427 (1) Å] organize the components into columns extending along the b axis and the N-H⋯N hydrogen bonds link these columns into a two-dimensional framework parallel to (100). The N-hy-droxy-picolinamide mol-ecule adopts a strongly flattened conformation and only the O-H group H atom deviates significantly from the mol-ecule best plane. The dihedral angle between the hydroxamic group and the pyridine ring is 5.6 (2)°. The conformation about the hydroxamic group C-N bond is Z and that about the C-C bond between the pyridine and hydroxamic groups is E.