Synthesis, crystal structure and properties of a 2-D Cd(II) coordination polymer based on ferrocenecarboxylate and 4,4′-bipyridine ligands

A new cadmium(II)-based coordination polymer [Cd3(FcCOO)6(4,4′-bipy)(H2O)2] n (FcCOO = ferrocenecarboxylato and 4,4′-bipy = 4,4′-bipyridine) has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. The results of a crystal structural analysis has revealed that the title compound consists of two crystallographically unique CdII centers, one in a general position with a five-coordinated and one on an inversion center with a six-coordinated environment. The CdII centers are connected by FcCOO− units to form a metal carboxylate oxygen chain extending parallel to the [100] direction while the 4,4′-bipy ligands further act as bridging linkers of the CdII centers resulting in a layered polymer. In addition, an X-ray powder diffraction and thermal gravimetric analysis and a cyclo-voltammetric characterization of the complex have also been carried out.

Structural and Functional Characterization of OXA-48: Insight into Mechanism and Structural Basis of Substrate Recognition and Specificity

Class D β-lactamase OXA-48 is widely distributed among Gram-negative bacteria and is an important determinant of resistance to the last-resort carbapenems. Nevertheless, the detailed mechanism by which this β-lactamase hydrolyzes its substrates remains poorly understood. In this study, the complex structures of OXA-48 and various β-lactams were modeled and the potential active site residues that may interact with various β-lactams were identified and characterized to elucidate their roles in OXA-48 substrate recognition. Four residues, namely S70, K73, S118, and K208 were found to be essential for OXA-48 to undergo catalytic hydrolysis of various penicillins and carbapenems both in vivo and in vitro. T209 was found to be important for hydrolysis of imipenem, whereas R250 played a major role in hydrolyzing ampicillin, imipenem, and meropenem most likely by forming a H-bond or salt-bridge between the side chain of these two residues and the carboxylate oxygen ions of the substrates. Analysis of the effect of substitution of alanine in two residues, W105 and L158, revealed their roles in mediating the activity of OXA-48. Our data show that these residues most likely undergo hydrophobic interaction with the R groups and the core structure of the β-lactam ring in penicillins and the carbapenems, respectively. Unlike OXA-58, mass spectrometry suggested a loss of the C6-hydroxyethyl group during hydrolysis of meropenem by OXA-48, which has never been demonstrated in Class D carbapenemases. Findings in this study provide comprehensive knowledge of the mechanism of the substrate recognition and catalysis of OXA-type β-lactamases.

Slow Magnetic Relaxation in {[CoCxAPy)] 2.15 H2O}n MOF Built from Ladder-Structured 2D Layers with Dimeric SMM Rungs

We present the magnetic properties of the metal-organic framework {[CoCxAPy]·2.15 H2O}n (Cx = bis(carboxypropyl)tetramethyldisiloxane; APy = 4,4`-azopyridine) (1) that builds up from the stacking of 2D coordination polymers. The 2D-coordination polymer in the bc plane is formed by the adjacent bonding of [CoCxAPy] 1D two-leg ladders with Co dimer rungs, running parallel to the c-axis. The crystal packing of 2D layers shows the presence of infinite channels running along the c crystallographic axis, which accommodate the disordered solvate molecules. The Co(II) is six-coordinated in a distorted octahedral geometry, where the equatorial plane is occupied by four carboxylate oxygen atoms. Two nitrogen atoms from APy ligands are coordinated in apical positions. The single-ion magnetic anisotropy has been determined by low temperature EPR and magnetization measurements on an isostructural compound {[Zn0.8Co0.2CxAPy]·1.5 CH3OH}n (2). The results show that the Co(II) ion has orthorhombic anisotropy with the hard-axis direction in the C2V main axis, lying the easy axis in the distorted octahedron equatorial plane, as predicted by the ab initio calculations of the g-tensor. Magnetic and heat capacity properties at very low temperatures are rationalized within a S* = 1/2 magnetic dimer model with anisotropic antiferromagnetic interaction. The magnetic dimer exhibits slow relaxation of the magnetization (SMM) below 6 K in applied field, with a tlf ≈ 2 s direct process at low frequencies, and an Orbach process at higher frequencies with U/kB = 6.7 ± 0.5 K. This compound represents a singular SMM MOF built-up of Co-dimers with an anisotropic exchange interaction.

Tribarium dicitrate pentahydrate, [Ba3(C6H5O7)2(H2O)4]·H2O

The crystal structure of tribarium dicitrate pentahydrate, [Ba3(C6H5O7)2(H2O)4]·H2O, has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. The BaO9 and BaO10 coordination polyhedra share edges and corners to form a three-dimensional network. All of the active hydrogen atoms act as donors in O—H...O hydrogen bonds. Most of the acceptors are carboxylate oxygen atoms, but there are also water...water hydrogen bonds. Both of the citrate hydroxyl groups form intramolecular O—H...O hydrogen bonds to terminal carboxyl groups.

Water as a reactant in the first step of triosephosphate isomerase catalysis

ABSTRACTThe enzyme triosephosphate isomerase (TIM) performs a crucial role in the extraction of energy from glucose, doing so by converting dihydroxyacetone phosphate (DHAP) into glyceraldehyde phosphate, thereby doubling the yield of ATP molecules during glycolysis. The initial step of the mechanism is the seemingly unlikely abstraction of the pro-R methylene hydrogen from C1 by a conserved glutamate (Glu165), an assignment that has been both universally accepted yet a much-studied phenomenon for decades. In this work we introduce an alternative mechanism in which water as a strong general base abstracts the carbon proton acting effectively as hydroxide. We posit that strong electric fields associated with the substrate phosphate promote facile autoionization of water trapped near the phosphate dianion of DHAP and Glu165, an example of substrate assisted catalysis. Classical molecular dynamics simulations assert that the closest water oxygen atom is consistently closer to the pro-R H than the carboxylate oxygen atoms of the accepted base Glu165. Our proposal is further supported by quantum computations that confirm the implausibility of abstraction of the methylene hydrogen by glutamate and the ease with which it is abstracted by hydroxide. The necessity of Glu165 for efficient catalysis is attributed to its crucial involvement in trapping the vital water in an environment of high electric fields which promote ionization far more rapidly than in bulk solvent.

Toxicological assessment of synthesized and characterized transition metal(II) complexes of eflornithine hydrochloride hydrate on albino rats

Transition metal complexes of Cu(II), Co(II) and Ni(II) with eflornithine hydrochloride hydrate (EFN), an antitrypanosomiasis drug, as ligand have been synthesized and characterized by melting point, elemental analysis, Fourier transform infrared (FTIR), electronic spectra, magnetic susceptibility and electrospray ionization mass spectrometry (ESI-MS). The FTIR spectral data suggested the coordination modes of the ligand to be bidentate, coordinated to the metal ions through its carboxylate oxygen atom and an amino nitrogen atom. From the microanalytical data, the stoichiometry of the metal complexes is 1:2 (metal to ligand). The electronic absorption and magnetic susceptibility studies generally suggested octahedral geometry for the metal complexes. Toxicological evaluation of the ligand (EFN) and complexes were carried out using albino rats. Twenty-five albino rats that were used for the experiment were randomly divided into five groups and animals in group 1 served as a control. All the animals were sacrificed twenty-four hours after completion of their doses. The results revealed a high level of toxicity of EFN than the synthesized metal complexes. KEY WORDS: Eflornithine hydrochloride hydrate, Carboxylate moiety, Antitrypanosomiasis drug, Toxicological evaluation, Albino rats Bull. Chem. Soc. Ethiop. 2020, 34(3), 489-500. DOI: https://dx.doi.org/10.4314/bcse.v34i3.6

Synthesis, Characterization and Biocidal Activity of Some Schiff Base Metal(II) Complexes

A Schiff base, 2-[4-(N,N-dimethylamino)benzylidene]benzoic acid has been synthesized by the condensation of 4-(N,N-dimethylamino)benzaldehyde and 2-amino-benzoic acid in 1:1 molar stoichiometry. The Schiff base complexes were synthesized from the chloride salts of Fe(II), Cu(II) and Zn(II) in ethanolic medium and elucidated by infrared spectroscopy, CHN elemental analysis, atomic absorption spectroscopy as well as conductivity and magnetic susceptibility measurements. The solubility and thermal stability were also determined. The metal(II) complexes are coloured solids that are soluble in DMF and DMSO. The melting point of the Schiff base was found to be 177 oC, while the complexes decompose within a temperature range of 202–261 oC suggestive of rather good thermal stability. The molar conductance values were low, indicating non-electrolytic nature of the complexes. Elemental analysis revealed that the stoichiometries of the synthesized complexes are of 1:2 metal-to-ligand ratio. All complexes were hydrated. The spectroscopic and magnetic susceptibility data revealed that the complexes possess four- coordinate distorted square planar stereochemistry, whereas the Schiff base behaves as monoanionic bidentate ligand with the nitrogen atom of the azomethine (C=N) and carboxylate oxygen (COO-) as donor sites. The Schiff base and its corresponding metal(II) complexes were assayed against a number of bacterial and fungal strains to evaluate their inhibitory potentials. All the complexes showed significant bactericidal and fungicidal activities against the tested organisms.

Synthesis and characterization of novel four heterodimetallic mixed metal complexes of 2,6-pyridinedicarboxylic acid

Four novel hetero dimetallic mixed metal complexes of 2,6-pyridinedicarboxylic acid (H2dipic), [Ni(H2O)5Co(dipic)2] (1), [Co(H2O)5Co(dipic)2][Ni(H2O)5Ni(dipic)2][Co(dipic)(H2O)3] (2), [Cu(H2O)5Ni(dipic)2]2[Co(dipic)(H2O)] (3) and [Ni(H2O)5Cu(dipic)2]2[Co(dipic)(H2O)] (4) have been prepared and characterized by elemental, AAS, spectral (IR and UV-Vis), and thermal analyses, as well as by using magnetic measurement and molar conductivity techniques. The results indicate that metal ions coordinate with 2,6-pyridinedicarboxylate ions (dipic2-) nitrogen atoms and carboxylate oxygen atoms of ligands. The mole ratio of dipic2- and metal ions in the complexes have been determined to be 2:2 (Co, Ni) for 1, 5:5 (3Co, 2Ni) for 2, 5:5 (Co, 2Ni and 2Cu) for 3 and 5:5 (Co, 2Ni and 2Cu) for 4 according to the results of elemental analysis. The structures of 1-4 might be proposed as octahedral ([Cu(dipic)(H2O)] unit for 2 square plane) according to results of spectroscopic analysis. The TG and DTA properties of compounds have been studied. KEY WORDS: 2,6-Pyridinedicarboxylic acid, Mixed metal, Metal complex Bull. Chem. Soc. Ethiop. 2020, 34(2), 313-321 DOI: https://dx.doi.org/10.4314/bcse.v34i2.9

Structures of dipotassium rubidium citrate monohydrate, K2RbC6H5O7(H2O), and potassium dirubidium citrate monohydrate, KRb2C6H5O7(H2O), from laboratory X-ray powder diffraction data and DFT calculations

The crystal structures of the isostructural compounds dipotassium rubidium citrate monohydrate, K2RbC6H5O7(H2O), and potassium dirubidium citrate monohydrate, KRb2C6H5O7(H2O), have been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The compounds are isostructural to K3C6H5O7(H2O) and Rb3C6H5O7(H2O), but exhibit different degrees of ordering of the K and Rb cations over the three metal-ion sites. The K and Rb site occupancies correlate well to both the bond-valence sums and the DFT energies of ordered cation systems. The MO6 and MO7 coordination polyhedra share edges to form a three-dimensional framework. The water molecule acts as a donor in two strong charge-assisted O—H...O hydrogen bonds to carboxylate groups. The hydroxyl group of the citrate anion forms an intramolecular hydrogen bond to one of the central carboxylate oxygen atoms.

Structures of disodium hydrogen citrate monohydrate, Na2HC6H5O7(H2O), and diammonium sodium citrate, (NH4)2NaC6H5O7, from powder diffraction data

The crystal structures of disodium hydrogen citrate monohydrate, Na2HC6H5O7(H2O), and diammonium sodium citrate, (NH4)2NaC6H5O7, have been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. In NaHC6H5O7(H2O), the NaO6 coordination polyhedra share edges, forming zigzag layers lying parallel to the bc plane. The hydrophobic methylene groups occupy the interlayer spaces. The carboxylic acid group makes a strong charge-assisted hydrogen bond to the central carboxylate group. The hydroxyl group makes an intramolecular hydrogen bond to an ionized terminal carboxylate oxygen atom. Each hydrogen atom of the water molecule acts as a donor, to a terminal carboxylate and the hydroxyl group. Both the Na substructure and the hydrogen bonding differ from those of the known phase Na2HC6H5O7(H2O)1.5. In (NH4)2NaC6H5O7, the NaO6 coordination octahedra share corners, making double zigzag chains propagating along the b-axis direction. Each hydrogen atom of the ammonium ions acts as a donor in a discrete N—H...O hydrogen bond. The hydroxyl group forms an intramolecular O—H...O hydrogen bond to a terminal carboxylate oxygen atom.