Birgül Zümreoglu-Karan

Layered double hydroxides — multifunctional nanomaterials

Layered double hydroxides (LDH’s), also known as anionic clays, are lamellar inorganic solids. The structure of most of them corresponds to that of mineral hydrotalcite, consisting of brucite-like hydroxide sheets, where partial substitution of trivalent or divalent cations results in a positive sheet charge compensated by reversibly exchangeable anions within interlayer galleries. These layered materials have good intercalation properties capturing inorganic and organic ions and they are promising materials for a large number of practical applications, both for direct preparation and for after thermal treatment.Over the past decade, significant interest has been devoted to the synthesis of LDHs with new compositions allowing improved applications in many areas. This contribution reviews the recent advances in water treatment, nuclear waste treatment/storage, catalytic, industrial, and advanced applications and biomedical applications of LDH-based nanomaterials.

Bioinorganic Magnetic Core−Shell Nanocomposites Carrying Antiarthritic Agents: Intercalation of Ibuprofen and Glucuronic Acid into Mg−Al−Layered Double Hydroxides Supported on Magnesium Ferrite

This paper describes the synthesis and characterization of a composite constituted by an antiarthritic agent (AA) intercalated into a layered double hydroxide (LDH) supported on magnesium ferrite. Core-shell nanocomposites were prepared by depositing Mg-Al-NO(3)-LDH on a MgFe(2)O(4) core prepared by calcination of a nonstoichiometric Mg-Fe-CO(3)-LDH. Intercalation of ibuprofen and glucuronate anions was performed by ion-exchange with nitrate ions. The structural characteristics of the obtained products were investigated by powder X-ray diffraction, element chemical analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Morphologies of the nanocomposite particles were examined by scanning electron microscopy and transmission electron microscopy. The products were shown to intercalate substantial amounts of AA with enhanced thermal stabilities. Room-temperature magnetic measurements by vibrating sample magnetometry revealed that the products show soft ferromagnetic properties suitable for potential utilization in magnetic arthritis therapy.

Water oxidation catalysis by birnessite@iron oxide core-shell nanocomposites.

In this work, magnetic nanocomposite particles were prepared for water oxidation reactions. The studied catalysts consist of maghemite (γ-Fe2O3), magnetite (Fe3O4), and manganese ferrite (MnFe2O4) nanoparticles as cores coated in situ with birnessite-type manganese oxide shells and were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermal, chemical, and surface analyses, and magnetic measurements. The particles were found to be of nearly spherical core-shell architectures with average diameter of 150 nm. Water oxidation catalysis was examined using Ce(4+) as the sacrificial oxidant. All core-shell particles were found to be active water oxidation catalysts. However, the activity was found to depend on a variety of factors like the type of iron oxide core, the structure and composition of the shell, the coating characteristics, and the surface properties. Catalysts containing magnetite and manganese ferrite as core materials displayed higher catalytic activities per manganese ion (2650 or 3150 mmolO2 molMn(-1) h(-1)) or per mass than nanoiron oxides (no activity) or birnessite alone (1850 mmolO2 molMn(-1) h(-1)). This indicates synergistic effects between the MnOx shell and the FeOx core of the composites and proves the potential of the presented core-shell approach for further catalyst optimization. Additionally, the FeOx cores of the particles allow magnetic recovery of the catalyst and might also be beneficial for applications in water-oxidizing anodes because the incorporation of iron might enhance the overall conductivity of the material.

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, 13C NMR, API-ES and thermogravimetric measurements. Theoretical calculations have been performed to propose a structure in accord with results obtained.

Water oxidation catalysis by using nano-manganese ferrite supported 1D-(tunnelled), 2D-(layered) and 3D-(spinel) manganese oxides

We report a new series of core–shell composite catalysts obtained by supporting 1D-(tunnelled), 2D-(layered) and 3D-(spinel) manganese oxides on nano-manganese ferrite. All other factors being equal, magnetic 2D-MnOx structures carried out the chemical water oxidation reaction with Ce4+ at a higher efficiency than their 1D-, 3D- and non-magnetic counterparts. Ca-birnessite, when supported on a ferrite core, produced the highest amount of O2 [3900 mmol (O2) per mol (Mn) per h] normalized per mol of manganese in the catalysts. The composition and morphology parameters of the magnetic core–shell structures appeared to be important in determining the observed activity while no direct correlation was noted with the surface area.

5-Fluorouracil intercalated iron oxide@layered double hydroxide core-shell nano-composites with isotropic and anisotropic architectures for shape-selective drug delivery applications.

We report the synthesis, characterization and in vitro release behavior of anti-cancer drug carrying iron oxide@layered double hydroxide core-shell nanocomposites with sizes ranging from 40 to 300 nm, good drug loading capacities and soft ferromagnetic properties. HRTEM analyses verified that nearly spherical isotropic carriers were obtained by coating spherical magnetite particles while anisotropic carriers were obtained by coating spindle-shaped hematite particles. They both displayed a fluctuating in vitro release profile with a higher release percentage for the anisotropic carrier.

SYNTHESIS AND CHARACTERIZATION OF COPPER ASCORBATE

The preparation of copper ascorbate in CH2Cl2 is described. The reaction between copper(II) methoxide and L-ascorbic acid in the presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA) and under strictly anaerobic conditions leads to the formation of a stable Cu(II)-ascorbate complex. No redox reaction takes place. Spectroscopic evidence suggest that the compound is polymeric where Cu(II) is chelated by the enolic oxygens of one ascorbate unit and the side chain alcoholic oxygens of another.

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.

Prolate spheroidal hematite particles equatorially belt with drug-carrying layered double hydroxide disks: Ring Nebula-like nanocomposites

A new nanocomposite architecture is reported which combines prolate spheroidal hematite nanoparticles with drug-carrying layered double hydroxide [LDH] disks in a single structure. Spindle-shaped hematite nanoparticles with average length of 225 nm and width of 75 nm were obtained by thermal decomposition of hydrothermally synthesized hematite. The particles were first coated with Mg-Al-NO3-LDH shell and then subjected to anion exchange with salicylate ions. The resulting bio-nanohybrid displayed a close structural resemblance to that of the Ring Nebula. Scanning electron microscope and transmission electron microscopy images showed that the LDH disks are stacked around the equatorial part of the ellipsoid extending along the main axis. This geometry possesses great structural tunability as the composition of the LDH and the nature of the interlayer region can be tailored and lead to novel applications in areas ranging from functional materials to medicine by encapsulating various guest molecules.