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Biocompatible Cu(II)-doped layered double hydroxide (CMA) nanoparticles were developed to combat reactive oxygen species. The 2-dimensional nanozymes showed both superoxide dismutase- and catalase-like activities in chemical assays, while proving as efficient antioxidants in the reduction of intracellular oxidative stress. The results indicate the great promise of CMA in antioxidant therapies. [ABSTRACT FROM AUTHOR]

The detection and quantification of antioxidant molecules is an important task in food science, the fine chemical industry and healthcare. Antioxidants help in preventing the deterioration of nutrition and healthcare products, while eliminating over-the-limit exogenic reactive species, which may lead to illnesses. In our contribution, an inexpensive and rapid method to determine the concentration of various molecular antioxidants was developed. The principle of the analysis relies on the cupric ion reducing antioxidant capacity (CuPRAC) method, which is based on the color-changing reduction of chelated Cu2+ ions. This complex was successfully immobilized on an alginate-functionalized layered double hydroxide (dLDH) nanosheet via electrostatic interactions. The synthesis conditions of alginate (NaAlg) and the cupric complex were optimized, and the optimized composite was fabricated on cellulose paper to obtain a sensing platform. The paper-based sensor was superior to the ones prepared without the dLDH support, as the limit of detection (LOD) values decreased, and the linearity ranges broadened. The results offer a single-point measurement to evaluate the antioxidant efficiency in a cuvette-based method. The superior ability of the sensor was assigned to the presence of solid dLDH particles, as they offer adsorption sites for the dissolved antioxidant molecules, which contributes significantly to the decrease of the diffusion limitation during the detection process. [ABSTRACT FROM AUTHOR]

An efficient synthetic route was developed to prepare hierarchically ordered mesoporous layered double hydroxide (LDH) materials. Sodium dodecyl sulfate (SDS) was used as a sacrificial template to tune the interfacial properties of the LDH materials during the synthetic process. The SDS dose was optimized to obtain stable dispersions of the SDS-LDH composites, which were calcined, then rehydrated to prepare the desired LDH structures. Results of various characterization studies revealed a clear relationship between the colloidal stability of the SDS-LDH precursors and the structural features of the final materials, which was entirely SDS-free. A comparison to the reference LDH prepared by the traditional co-precipitation-calcination-rehydration method in the absence of SDS shed light on a remarkable increase in the specific surface area (one of the highest within the previously reported LDH materials) and pore volume as well as on the formation of a beneficial pore size distribution. As a proof of concept, the mesoporous LDH was applied as adsorbent for removal of nitrate and dichromate anions from aqueous samples, and excellent efficiency was observed in both sorption capacity and recyclability. These results make the obtained LDH a promising candidate as adsorbent in various industrial and environmental processes, wherever the use of mesoporous and organic content-free materials is required. [ABSTRACT FROM AUTHOR]

It has been generally accepted for long that water molecules are integral parts of layered double hydroxides (LDHs). It is even thought that in the absence of water molecules, there is no LDH structure. It is shown in this contribution that via the solvolysis of Mg- or Ca-alkoxides and Al-alkoxide with methanol or propanol and co-precipitated in methanolic methoxide, water-free LDH-like structures could be constructed. These novel LDH-like materials proved to be more active and selective catalysts in a Knoevenagel condensation than the corresponding 'classical' LDHs. Synthesis, thought to be not possible to prepare, characterization and a catalytic application of water-free LDHs are described. Water molecules are replaced by small alcohol molecules in the interlayer space. [ABSTRACT FROM AUTHOR]

Ni(II)-containing layered double hydroxides (LDHs) were synthesized with various methods with the intention of placing the Ni(II) ions in different positions in/on the LDH. Ni(II) was introduced as a lattice-modifier into CaAl-, CaFe- and MgAl-LDHs or in the interlayer space in form of a complex anion or as the divalent component of NiAl-LDH or as surface dopant. The materials were structurally characterized by various instrumental methods; however, the final proof of lattice modification was proven by the Suzuki–Miyaura and the Heck coupling reactions. Each as-prepared catalyst was active and selective towards the coupling products with or without various additives. They could be recycled except the surface-doped material, in which intense leaching of the Ni(II) content was observed on reuse. Ni(II)-containing LDHs are active and recyclable catalysts in the Suzuki and Heck coupling reactions—this is the final proof that the Ni(II) ions are constituents of the lattice. [ABSTRACT FROM AUTHOR]

Abstract The construction of Co(II)-amino acid complexes (l -histidine, l -cysteine, l -tyrosine) among the layers of CaAl-layered double hydroxide was attempted. The stepwise intercalation (introducing the anionic form of the amino acid first, then constructing the Co(II) complex) proved to be unsuccessful, while the direct ion exchange of the anionic form of the separately prepared complex provided with the Co(II) complex intercalated substances. The success of the intercalation was verified by X-ray diffractometry. The resulting composite materials were structurally characterized by a range of instrumental methods like UV–vis, inductively coupled plasma–optical emission, mid-range as well as far infrared spectroscopies and scanning electron microscopy. Highlights • Attempted intercalation of Co(II)-amino acid complexes among the layers of CaAl-LDH. • Successful intercalation was achieved using the anionic forms of the separately prepared complexes. • Verification by powder X-ray diffractometry. • Mapping the possible coordination sites with classical and instrumental methods. [ABSTRACT FROM AUTHOR]

Photocatalytic decomposition of methylene blue was attempted over as-prepared Mn(II)Cr(III)-layered double hydroxide (LDH) containing Mn(II) and Cr(III) in 2:1 molar ratio. The LDH was prepared by the co-precipitation method, and was found to form at pH = 10 and at 80 °C following 24 h hydrothermal treatment. The Mn 2 Cr-LDH thus obtained was structurally characterized by X-ray diffractometry, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The Mn 2 Cr-LDH displayed significant photocatalytic activity in the degradation of methylene blue under illumination with UV–vis light. The photocatalytic performance of the phase-pure and uncalcined Mn 2 Cr-LDH is practically identical to that of the commercially available Degussa P25 TiO 2 , and it was found to remain unaltered over five consecutive photocatalytic runs. The presence of the LDH structure in the composite is the prerequisite of the photocatalytic activity. Applying increasing calcination temperature, the LDH structure gradually collapses, and the Mn 2 Cr-LDH transforms to photocatalytically inactive double oxide. [ABSTRACT FROM AUTHOR]

Intercalated composite materials were prepared with CaAl-layered double hydroxide as host and Cu(II)-amino acid ( l -cysteine, l -histidine and l -tyrosine) complex anions as guests. Two methods (intercalation of the ligand first followed by constructing the complex; preforming the complex first, then introducing it among the layers of the host) and optimization of the synthesis conditions were performed to obtain composites having the complex exclusively among the layers. The composite materials were structurally characterized by powder X-ray diffractometry, mid infrared (IR) spectroscopy with ATR (attenuated total reflectance) or photoacoustic detections, transmission and scanning electron microscopies and X-ray photoelectron spectroscopy. Structural features of the intercalant (coordination number, coordination sites) were elucidated by classical chemical and energy dispersive X-ray analyses, EPR (electron paramagnetic spectroscopy), X-ray absorption and far IR spectroscopies. Structural models based on these methods are also given. Catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants in the liquid phase. The catalysts were active in the Ullmann coupling reaction as well. The intercalated substances were found to be efficient and highly selective catalysts with very good recycling abilities. [ABSTRACT FROM AUTHOR]

Intercalated composite materials were prepared with CaAl-layered double hydroxide as the host and Mn(II)–amino acid ( l -cysteine, l -histidine and l -tyrosine) complex anions as the guest. Two methods (intercalation of the ligand first followed by constructing the complex; preforming the complex first, then introducing it among the layers of the host) and optimization of the auxiliary conditions were performed to arrive at composites having the complex exclusively among the layers. The obtained substances were structurally characterized by powder X-ray diffractometry, mid IR spectroscopy in diffuse reflectance mode and with ATR or photoacoustic detections, and scanning electron microscopy. The structural features of the intercalant (coordination number, coordination sites) were elucidated by classical chemical and energy dispersive X-ray analyses, EPR, X-ray absorption and far IR spectroscopies. Structural models are also given. The catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants and allylic alcohol with peracetic acid, in the liquid phase. The intercalated substances proved to be efficient and highly selective (with peracetic acid: outstanding epoxide, with iodosylbenzene superior diol selectivities) catalysts with very good recycling abilities. [ABSTRACT FROM AUTHOR]

Hybrid E-cinnamate- and Z-cinnamate-intercalated layered double hydroxides (Mg 2 Al- E- or Z-Cin LDH and Zn 2 Al- E- or Z - Cin LDH) were prepared by the co-precipitation method, and structurally characterised by powder X-ray diffractometry, UV–Vis, FT-IR and 13C CP MAS solid-state NMR spectroscopies to gain further insights on the arrangement of the organic anions in the interlamellar domain. UV light irradiation induced E–Z isomerisation reaction was subsequently attempted in the solid state and in methanolic suspension. Although reaction was observed in the solid state; however, E–Z isomerisation mainly occurred in the slurry phase. The fact that there was no isomerisation when E-Cin was solely adsorbed on the surfaces of pristine LDHs highlights that the reaction took place in the interlayer region. Similar behaviour was observed for the two LDH compositions proving that the LDH structures acted as nanoreactors confining the photoinduced isomerisation. • Intercalation and structural description of cinnamate isomers intercalated in MgAl and ZnAl LDHs. • E-Z isomerisation in the solid state and in slurry. • Isomerisation is followed and verified by various spectroscopic methods (FT-IR, UV–Vis, 13C CP MAS NMR). [ABSTRACT FROM AUTHOR]

Abstract Layered double hydroxides (LDHs) consist of layers with two or three positively charged metal ions surrounded by hydroxide ions, water molecules and partially or fully hydrated exchangeable charge-compensating anions between the layers. These materials have many application possibilities. In this work, CaAl-LDH samples were synthesized and used as catalysts. The esterification reactions of acetate and benzoate ions were studied with benzyl bromide under solvent-free conditions over CaAl-LDH samples. The as-prepared as well as the used LDH samples were characterized with X-ray diffractometry, and the reaction products were identified by ATR-IR spectroscopy. Highlights • Acetate- and benzoate-containing CaAl-LDH samples were prepared ions by co-precipitation. • The organic anion-containing samples could be used successfully in the esterification with benzyl bromide. • The reaction and changes in the LDH structure were followed by XRD, ATR-IR and SEM–EDX. [ABSTRACT FROM AUTHOR]

[Display omitted] • LDH-biopolymer interactions must be understood to design hybrid materials. • Biopolymer adsorption changes the surface charge and aggregation properties. • Colloidal stability of the composites must be tuned to avoid particle aggregation. • Biopolymers proved to stabilize delivery particle systems during medical uses. • Quantitative dispersion studies on LDH-biopolymer systems are still needed. Layered double hydroxides (LDHs) are appealing nanomaterials for (bio)medical applications and their potential is threefold. One can gain advantage of the structure of LDH frame (i.e., layered morphology), anion exchanging property towards drugs with acidic character and tendency for facile surface modification with biopolymers. This review focuses on the third aspect, as it is necessary to evaluate the advantages of polymer adsorption on LDH surfaces. Beside the short discussion on fundamental and structural features of LDHs, LDH-biopolymer interactions will be classified in terms of the effect on the colloidal stability of the dispersions. Thereafter, an overview on the biocompatibility and biomedical applications of LDH-biopolymer composite materials will be given. Finally, the advances made in the field will be summarized and future research directions will be suggested. [ABSTRACT FROM AUTHOR]

• Catalytic activity of niacin has been proven by using it in a Betti reaction as actual catalyst. • An efficient protocol for anchoring niacin was designed and developed, using anion exchanger hydrocalumite as host. • In a Betti reaction, the catalytic activity and selectivity of the heterogenized niacin was fine-tuned. By carrying out a three component Mannich-type Betti reaction, the catalytic ability of niacin and its heterogenized counterpart were tested in. Both homogeneous niacin and layered double hydroxide (LDH) supported heterogeneous catalysts enabled selective Betti reaction with notable yield of the desired product under remarkably mild reaction conditions. The heterogenized nicotinate showed higher selectivity toward desired product, which was coupled with outstanding recyclability. The success of the immobilization was proven by combining XRD and comparative IR analysis, which was initialized at the first time. [ABSTRACT FROM AUTHOR]