Dursun Ali Köse

Complexation of boric acid with vitamin C

Mono-chelate (1 : 1) and bis-chelate (1 : 2) anionic complexes of boric acid with vitamin C (L-ascorbic acid, H2A) were isolated from aqueous solutions in salt form with Li+, Na+ and Ca2+ ions. The complexes were characterized by FTIR, 13C and 11B MAS (magic angle spinning) NMR techniques. The spectral data agreed with the calculated structures that H2A complexes with boric acid through its cis-enediol groups by forming five-membered chelate rings. Side-chain OH groups do not participate in complexation as corroborated by the results of the test experiments conducted with iso-propylideneascorbic acid (i-H2A) where the side chain is blocked. Empirical relations, that can be used as diagnostics for the 1 : 1 and 1 : 2 ascorbatoborate complexes, were derived from the observed chemical shift values. Bis-chelate complexes were found to have higher thermal and hydrolytic stabilities than their mono-chelate homologs. The effect of the cation on the stabilization of the complexes was also investigated. The observed relative stability of the 1 : 1 Na–ascorbatoborate complex with respect to the analogous Ca complex, correlated with the recent reports about the role of alkali metal ions in the stabilization of ribose in the prebiotic world.

Synthesis and characterization of transition metal-vitamin B13 complexes mixed with a co-vitamin

The synthesis and structural characterization of mixed vitamin-metal complexes are reported. A complex bearing two vitamins (B3 and B13) on the same metal centre, nicotinamide(orotato)nickel(II) pentahydrate, has been prepared and characterised by single-crystal X-ray diffraction methods. A complex of Cr(III) with vitamins C and B13, bis(ascorbato)orotatochromium(III) dihydrate, has been isolated and its nature investigated by means IR, 13Cu2009NMR, API-ES and thermogravimetric measurements. Theoretical calculations have been performed to propose a structure in accord with results obtained.

Synthesis and characterization of N,N-diethylnicotinamide-acetylsalicylato complexes of Co(II), Ni(II), Cu(II), and Zn(II)

N,N-diethylnicotinamide-acetylsalicylato complexes of Co(II), Ni(II), Cu(II), and Zn(II) were synthesized and investigated by elemental analysis, magnetic susceptibility, solid state UV–Vis, direct injection probe mass spectra, FTIR spectra and thermoanalytic TG-DTG methods. The complexes contain two waters, two acetylsalicylate (asa) and two N,N-diethylnicotinamide (dena) ligands per formula unit. The acetylsalicylate and N,N-diethylnicotinamide are monodentate through acidic oxygen and nitrogen of pyridine ring. Decomposition of each complex starts with dehydration then decomposition of N,N-diethylnicotinamide and acetylsalicylate, respectively. The thermal dehydration of the complexes takes place in one or two steps. The decomposition mechanism and thermal stability of the investigated complexes are interpreted in terms of their structures. The final decomposition products are found to be metal oxides.

Mixed-ligand complexes of boric acid with organic biomolecules

Boric acid forms meta-stable complexes with biomolecules like amino and hydroxy acids and stable complexes with the diol group containing carbohydrates, vitamins, and nucleotides, yielding mono-chelate (1: 1 complex) or bis-chelate (1: 2 complex) structures with negatively charged tetrahedral borate anions. Here we report water-soluble, bio-available mixed-ligand boron adducts for potential nutritional and/or pharmaceutical applications. The complexes were prepared by complete esterification of boric acid with a number of acyclic- and cyclic hydroxy-functionalized biomolecules employing sodium as the counter ion. Structural and thermal properties of the complexes were investigated using chemical analysis, 11B NMR, FTIR, and TGA-DTA techniques. Complexes containing salicylic acid as one of the ligands displayed higher thermal and hydrolytic stabilities.

catena-Poly[[[triaqua­cobalt(II)]-μ-2,6-dioxo-1,2,3,6-tetra­hydro­pyrimidine-4-carboxyl­ato(2–)] 1.72-hydrate]

The Co(II) ion in the title complex {[Co(C5H2N2O4)(H2O)3].1.72H2O}n, has a distorted octahedral coordination geometry comprised of three water ligands, one deprotonated pyrimidine N atom and an adjacent carboxylate O atom of one orotate ligand. The sixth coordination site is occupied by an exocyclic O atom from a neighbouring orotate moiety, and through this interaction a helicoidal chain is formed. The molecules are linked by intramolecular Owater-H...O and intermolecular N-H...O and Owater-H...O hydrogen bonds, forming a three-dimensional network.

Boric acid: a simple molecule of physiologic, therapeutic and prebiotic significance

Abstract Boric acid, H3BO3, is a weak acid and at physiological pH is in the form of an uncharged small molecule. Behaving as a Lewis acid, it forms complexes with amino- and hydroxy acids, carbohydrates, nucleotides and vitamins through electron donor-acceptor interactions. These interactions are believed to be beneficial for human health. Synthetic bis-chelate complexes of boric acid with organic biomolecules are therefore considered for nutritional and/or pharmaceutical applications. The use of boric acid for BNCT has gained attention due to the short biological half-life, solubility, plasma circulation and the non-selective soft tissue accumulation properties of this simple molecule. Complexation of boric acid with sugars is of particular importance in understanding the role of boron as a carrier for nucleotides and carbohydrates. A potential and catalytic role of boric acid in peptide and nucleic acid synthesis and in the stabilization of sugar molecules by acting as a complexing agent have been demonstrated. Its possible role as a phosphorylation chaperone in a prebiotic world has been recently suggested. This contribution reviews the highlights in the physiologic, therapeutic and prebiotic significance of boric acid in the last decade.

Diaquabis(4-fluorobenzoato-κO)bis(nicotinamide-κN)cobalt(II)

The title compound, [Co(C7H4FO2)2(C6H6N2O)2(H2O)2], is a three-dimensional hydrogen-bonded supraxadmolecular comxadplex. The CoII ion resides on a centre of symmetry and is in an octaxadhedral coordination environment comprising two pyridyl N atoms, two carboxylxadate O atoms and two O atoms from water molxadecules. Interxadmolecular N—H⋯O and O—H⋯O hydrogen bonds produce R32(6), R22(12) and R22(16) rings, which lead to two-dimensional chains. An extensive three-dimensional network of C—H⋯F, N—H⋯O and O—H⋯O hydrogen bonds and π–π interxadactions are responsible for crystal stabilization.

Synthesis and characterization of bis(nicotinamide) m-hydroxybenzoate complexes of Co(II), Ni(II), Cu(II), and Zn(II)

Mixed-ligand m-hydroxybenzoate complexes of Co(II), Ni(II), Cu(II), and Zn(II) with nicotinamide were synthesized and characterized by elemental analysis, FT-IR spectrometry, solid state UV-vis spectrometry, and magnetic susceptibility measurements. The thermal behavior of the complexes was studied by simultaneous TG-DTA methods in static air atmosphere. The infrared spectral characteristics of the complexes are discussed and the mass spectra data are recorded. The complexes contain two water molecules, two m-hydroxybenzoato (m-hba), and two nicotinamide (na) ligands per formula unit. In these complexes, the m-hydroxybenzoate and nicotinamide behave as a monodentate ligand through acidic oxygen and nitrogen of the pyridine ring. The decomposition pathways and the stability of the complexes are interpreted in terms of the structural data. The final decomposition products were found to be the respective metal oxides.

Magnetic nanocomposites of boron and vitamin C

Magnetic nanocomposites comprising elemental boron and vitamin C in the form of mono or bis(ascorbatoborate) complexes have been synthesized for targeted delivery/therapy applications. These nanocomposites were characterized by chemical analysis, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and magnetic measurements. Structural motifs were proposed to justify the arrangement of the complexes around the magnetic core. The nanocomposite particles showed a quasi-spherical morphology with an average size of around 10–15 nm and exhibited a superparamagnetic behavior at 300 K to qualify for potential targeted biomedical applications. The data of chemical analysis suggested that the nanocomposites contain ca. 1015 boron atoms per microgram of sample.

trans‐Diaquabis(nicotinamide‐κN)bis(salicylato‐κO)cobalt(II)

The title compound, [Co(C(7)H(5)O(3))(2)(C(6)H(6)N(2)O)(2)(H(2)O)(2)], forms a three-dimensional hydrogen-bonded supramolecular structure. The Co(II) ion is in an octahedral coordination environment comprising two pyridyl N atoms, two carboxylate O atoms and two O atoms from water molecules. Intermolecular N-H...O and O-H...O hydrogen bonds produce R(2)(2)(8), R(2)(2)(12) and R(2)(2)(14) rings, which lead to two-dimensional chains. An extensive three-dimensional supramolecular network of C-H...O, N-H...O and O-H...O hydrogen bonds and C-H...pi interactions is responsible for crystal structure stabilization. This study is an example of the construction of a supramolecular assembly based on hydrogen bonds in mixed-ligand metal complexes.