Synthesis, structure and magnetic properties of a new family of chiral metal(II) citramalates

A new series of chiral carboxylate-bridged complexes of Mn(II), Co(II), and Ni(II) has been synthesized by reaction of M(II) salts with (S)-2-hydroxy-2-methyl-butanedioic acid ((S)-citramalic acid) under solvothermal conditions. The Mn(II) compound 1 is obtained as a crystalline powder, whereas the Co(II) and Ni(II) compounds (2 and 3 respectively) are obtained as single crystals. All the compounds crystallize in orthorhombic chiral space group P2₁2₁2₁. Compounds 2 and 3 are isostructural, and their structure consists in helicoïdal chains of M(II) centres linked by carboxylate bridges. The magnetic data indicate a rather weak coupling interaction between paramagnetic centres. The Mn(II) compound 1 exhibits antiferromagnetic ordering at T_N = 2.64 K. The Co(II) and Ni(II) compounds show ferromagnetic interactions within the chains. For 3, the chains couple antiferromagnetically, which leads to a metamagnetic behaviour with T_N = 1.69 K.     

Synthesis, crystal structure and magnetic properties of a 1D mixed-metal-mixed-ligand Ni(II)/Fe(II) coordination polymer built on the nitroprusside anion

A new complex [Ni(L)Fe(CN)₅NO] · 2H₂O (L = 4,6,6-trimethyl-1,9-diamino-3,7-di-aza-nona-3-ene) has been obtained and characterized by means of X-ray crystallographic analysis and magnetochemistry. The Fe(CN)₅NO²⁻ anion links to the Ni(L)²⁺ cation through two bridging cyanide groups in a bent fashion. The intrachain Ni?Ni and interchain Ni?Ni distances are equal to 9.81(8) and 7.75(1) Å, respectively. The magnetic behaviour of the complex indicates the zero field splitting parameter D higher than 3 cm⁻¹ and the average exchange parameter (intra- and interchain) corresponding to direct Ni-Ni magnetic interaction in the crystal lattice equals ∼−0.2 cm⁻¹.     

BEHAB, a new member of the proteoglycan tandem repeat family of hyaluronan-binding proteins that is restricted to the brain [published erratum appears in J Cell Biol 1997 Apr 21;137(2):521]

Hyaluronan (HA) is a ubiquitous component of the extracellular matrix of all tissues. In the mammalian central nervous system (CNS) HA is present throughout development and into adulthood. While the functions of HA are likely to be mediated by HA-binding proteins, no cell or tissue specific HA-binding proteins have been reported. In an effort to characterize the composition of the extracellular matrix of the CNS, we sought to identify neural HA-binding proteins. We report here the isolation and characterization of a cDNA with a high degree of sequence homology to members of the proteoglycan tandem repeat (PTR) family of HA-binding proteins. Unlike other HA-binding proteins, the expression of this cDNA is restricted to the CNS. We propose the name BEHAB, Brain Enriched HyAluronan Binding protein, for this gene. The expression of BEHAB mRNA is developmentally regulated; expression is first detected in the late embryonic period and peaks during the first two postnatal weeks. In the embryo, BEHAB is expressed at highest levels in mitotically active cells. The sequence of BEHAB has long stretches of identity between rat and cat, suggesting that the encoded protein is functionally important. The size and sequence of BEHAB are consistent with the possibility that it could serve a function like link protein, stabilizing interactions between HA and brain proteoglycans. These observations suggest that existence of other tissue specific HA-binding proteins.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.     

Assembly of metal coordination framework, [M(C5O5)(dpe)], with a 2D bi-layer architecture: Thermal stability and magnetic properties (M = Mn, Fe, Cd and Co; dpe = 1,2-bis(4-pyridyl)ethane)

A series of coordination polymers, [M(C₅O₅)(dpe)] (M = Mn 1, Fe 2, Cd 3 and Co 4; dpe = 1,2-bis(4-pyridyl)ethane) with a 2D metal-organic framework (MOF) has been synthesized and characterized by single-crystal X-ray diffraction studies. Structural determination reveals that compounds 1-4 are isostructural and possess a 2D brick-wall-like layered framework with a rectangle grid as the basic building unit through the connectivity of metal ions with μ₃-, μ₄-croconates and anti-dpe ligands. Two 2D layers are then cross-linkaged by gauche-dpe ligands to complete a 2D bi-layered MOF and then extended to a 3D supramolecular architecture through π-π and C-H?O interactions between the croconate and pyridyl rings of dpe, which exhibit high thermo-stability and keep their crystalline forms up to 350 °C. The magnetic exchange coupling between the metal centers for compounds 1, 2 and 4 was analyzed and based on the Curie-Weiss expression and a binuclear magnetic model. The negative values of the Weiss constant and the magnetic exchange coupling constant indicate the antiferromagnetic nature between the metal ions via the bridges of bis-bidentate adjacent μ₃-croconate ligands.