Structure Of LDH Research Articles

Thermo-oxidative stabilization of poly(lactic acid) with antioxidant intercalated layered double hydroxides

Two antioxidant modified layered double hydroxides (AO-LDHs) were successfully prepared by the intercalation of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (IrganoxCOOH) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) in the layered structure of LDH. It was found that by anchoring the phenolic moieties to the LDH layers the antioxidant power is retained in the case of Trolox, and even amplified in the case of IrganoxCOOH. A small amount of the two AO-LDHs was incorporated into poly(lactic acid), PLA, by solution mixing and melt extrusion. The thermo-oxidative stability of the composites was compared with that of the neat PLA and PLA containing free AOs. SEC analysis indicates that, after a controlled period of ageing, both the AO-LDHs protect the PLA from chain scission. The oxidation induction time (OIT, DSC) at 230 °C shows also the beneficial effects of the presence of the functional filler in the polymer matrix. Further, results from a preliminary migration test suggest that the AO species have a low tendency to migrate away from the AO-LDHs embedded in the polymer matrix thus keeping the AO protected inside the nanofiller layers thereby remaining active for a longer time.

Controlled synthesis and enhanced electrochemical performance of self-assembled rosette-type Ni-Al layered double hydroxide

We report the synthesis of a rosette-type three-dimensional Ni-Al layered double hydroxide (Ni-Al LDH) positive electrode material for energy storage devices using a template-free, simple, self-assembling hydrothermal synthesis method. Poly (sodium-p-styrene-sulfonate) (PSS) plays a key role in efficiently controlling the morphology. Moreover a model that explains the formation mechanism of rosette-type Ni-Al LDH is proposed. The model is verified by a series of experiments. SEM images reveal that the three-dimensional (3D) structure of Ni-Al LDH consists of individual nanosheets that form a rosette-type morphology thus improving its mechanical stability. The electrochemical properties of the material were studied by means of cyclic voltammetry (CV), galvanostatic charge/discharge measurements, and by electrochemical impedance spectroscopy (EIS). Owing to the greatly improved faradaic redox reaction and mass transfer, the 3D Ni-Al LDH structure exhibits excellent energy storage performance. This positive electrode material shows a high specific capacity of 788C/g (the corresponding area-normalized capacity is 23.64C/cm2) at a charge/discharge current density of 1A/g and retains 82.9% of its capacity after 1000 cycles at current densities of 2A/g. These results illustrate that the rosette-type Ni-Al LDH is a highly promising active material for energy storage application. Using our methodology, it can be synthesized in a simple, controllable low cost way.

Preparation and inhibition properties of molybdate intercalated ZnAlCe layered double hydroxide

ZnAlCe layered double hydroxide intercalated by molybdate (ZnAlCeMoO4 LDH) was successfully synthesized by using co-precipitation method, and the morphology, structure of ZnAlCeMoO4 LDH were observed and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) techniques. The inhibition behavior of ZnAlCeMoO4 LDH for Q235 steel in 3.5%NaCl solution was determined by polarization curves, electrochemical impedance spectroscopy (EIS), inductively coupled plasma mass spectrometer (ICP-MS) and X-ray photoelectron spectrometer (XPS) methods. The results shows that the synthesized ZnAlCeMoO4 LDH has a lamellar structure with a particle size of 0.1–2.0 μm, an average thickness of 30 nm, and a basal plane spacing of 0.898 nm. Compared with the addition of ZnAl layered double hydroxide intercalated by nitrate (ZnAlNO3 LDH) and ZnAl layered double hydroxide intercalated by molybdate (ZnAlMoO4 LDH) in 3.5% NaCl solution, Q235 steel in 3.5%NaCl + ZnAlCeMoO4 LDH solution has a lower corrosion current density, larger polarization resistance and a higher inhibition efficiency. The addition of ZnAlCeMoO4 LDH will reduce the chloride concentration in 3.5% NaCl solution by the anion exchanged with molybdate, and improve the corrosion resistance of Q235 steel owing to the formation of passive film with the composition of ferrous or iron molybdate and deposition film with zinc and cerium hydroxides.

Adsorption behavior of phosphate on Mg–Al layered double hydroxide/montmorillonite composite

In this study, Mg–Al-layered double hydroxide (LDH) and montmorillonite (M) were mixed (mass ratio = 1:1) with high-shear action to prepare a mineral composite (LDH–M). The structure, morphology, and textural properties of LDH and LDH–M were investigated via X-ray diffraction, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, and nitrogen physisorption. The phosphate adsorption performances of LDH and LDH–M were assessed and compared by conducting batch experiments. The effects of initial adsorbate concentration and contact time on phosphate uptake were examined. The adsorption kinetics and isothermal adsorption of both adsorbents showed that the pseudo-second-order model and the Langmuir isotherm fitted well with the experimental data. The maximum adsorption capacity of 127.8 mg g−1 of phosphate onto LDH–M improved by ~21% compared with that onto pure LDH. Hence, the composite exhibited better affinity toward phosphate adsorption than pure LDH. The enhanced adsorption of phosphate by LDH–M probably resulted from the textural changes of the composite compared with those of its precursors. The adsorption process mainly follows ion-exchange mechanism. The results revealed a synergic effect between LDH and M during phosphate removal.

Characterization of a dextran–coated layered double hydroxide acetylsalicylic acid delivery system and its pharmacokinetics in rabbit

The aim of this study was to prepare a dextran–coated layered double hydroxide acetylsalicylic acid (DEX–LDH–ASA) delivery system by co-precipitation of LDH–ASA and its in-situ compositing with DEX. The structure of the system was investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry (TG). Its in vitro drug release properties and in vivo pharmacokinetics in rabbit were also determined. The results show that the DEX–LDH–ASA system retained the crystal structure of LDH–ASA and gave a marked improvement in its dispersion. It also prolonged the release of ASA and shifted the release pattern from first-order to zero-order kinetics. The pharmacokinetics of ASA administered in the DEX–LDH–ASA system to rabbits produced two absorption peaks with a Cmax of 14.8±1.7mg/L at 2.11±0.69h and an elimination half-life of 2.25±0.84h for the first peak. The fact that delivery of ASA in the DEX–LDH–ASA system was sustained with improved bioavailability indicates the potential of the system as a controlled release formulation with application to other drugs.

One-pot in situ synthesized TiO2/layered double hydroxides (LDHs) composites toward environmental remediation

In this paper, a novel approach to synthesize nanostructural composite materials of TiO2/ZnAl LDH is reported for the first time. By simply mixing precursor solutions, TiO2/ZnAl LDH composite materials can be readily synthesized. The deposition of TiO2 nanoparticles on the basal face of ZnAl LDH had maintained the original layered structure of ZnAl LDH. TiO2/LDH composites exhibited a typical IV isotherm type indicating a mesopore structure. The specific surface area of TiO2/LDH composites was four times that of pristine LDH. Furthermore, the adsorption test using the typical dye (methylene blue: MB) indicated that the adsorption ability of LDH had been significantly enhanced after the incorporation of TiO2 by this strategy. Therefore, the developed TiO2/LDH composite materials with unique adsorption characteristics have great potential for diverse applications.

Structural characteristics and flammability of fire retarding EPDM/layered double hydroxide (LDH) nanocomposites

A high performance elastomeric flame retardant nanocomposite was prepared which was based on maleic anhydride grafted ethylene-propylene-diene terpolymer (mEPDM), a one-step synthesised organo-layered double hydroxide (LDH), and an intumescent flame retardant (FR) comprised of pentaerythritol (PER), ammonium polyphosphate (APP) and methyl cyanoacetate (MCA). The morphology, fire behavior and mechanical properties of the flame-retarded mEPDM/LDH nanocomposite have been studied in detail. Wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS) and TEM observation confirmed an exfoliated structure of LDH in a particular composite containing 2 phr (parts per hundred) LDH and 38 phr FR. As an effective flame retardant synergistic agent, MgAl–LDH shows a significant decrease in the heat release rate (HRR), low mass loss (ML) and low fire growth rate (FIGRA) of the nanocomposite. The flame retardant mechanism has been proposed, which is mainly due to the condensed phase flame retardant mechanism to form reinforced char layers during combustion, leading to the low volatiles produced. Moreover, as far as the mechanical properties of the vulcanizates are concerned, in all cases of flame retardant mEPDM and flame retarded mEPDM/LDH nanocomposites, they exhibit superior values compared to the gum compound.

Design of a Multifunctional Nanohybrid System of the Phytohormone Gibberellic Acid Using an Inorganic Layered Double-Hydroxide Material

To offer a multifunctional and applicable system of the high-value biotechnological phytohormone gibberellic acid (GA), a nanohybrid system of GA using the inorganic Mg-Al layered double-hydroxide material (LDH) was formulated. The ion-exchange technique of LDH was applied to synthesize the GA-LDH hybrid. The hybrid structure of GA-LDH was confirmed by different spectroscopic techniques. The nanohybrid size was described by SEM to be ∼0.1 μm. The GA-LDH nanohybrid structure was the key parameter that controlled GA properties. The layered molecular structure of LDH limited the interaction of GA molecules in two-dimensional directions. Accordingly, GA molecules did not crystallize and were released in an amorphous form suitable for dissolution. At various simulated soil solutions, the nanohybrids showed a sustained release process following Higuchi kinetics. The biodegradation process of the intercalated GA showed an extended period of soil preservation as well as a slow rate of degradation.

The Effects of Lanthanoid on the Structure–Function of Lactate Dehydrogenase from Mice Heart

The activity of lactate dehydrogenase (LDH, EC1.1.1.27) is often changed upon inflammatory responses in animals. Lanthanoid (Ln) was shown to provoke various inflammatory responses both in rats and mice; however, the molecular mechanism by which Ln3+ exert its toxicity has not been completely understood, especially that we know little about the mechanism of the interaction between Ln with 4f electron shell and alternation valence and LDH. In this report, we investigated the mechanisms of LaCl3, CeCl3, and NdCl3 on LDH activity in vivo and in vitro. Our results showed that La3+, Ce3+, and Nd3+ could significantly activate LDH in vivo and in vitro; the order of activation was Ce3+>Nd3+> La3+>control. The affinity of LDH for Ce3+ was higher than Nd3+ and La3+; the saturated binding sites for Ce3+ on the LDH protein were 1.2 and for La3+ and Nd3+ 1.55. Ln3+ caused the reduction of exposure degree of cysteine or tryptophan/tyrosine of LDH, the increase of space resistance, and the enhancement of α-helix in secondary structure of LDH, which was greatest in Ce3+ treatment, medium in Nd3+ treatment, and least in La3+ treatment. It implied that the changes of structure-function on LDH caused by Ln3+ were closely related to the characteristics of 4f electron shell and alternation valence in Ln.

The Effects of Nano-anatase TiO2 on the Activation of Lactate Dehydrogenase from Rat Heart

Lactate dehydrogenase (LDH, EC1.1.1.27), widely expressed in the heart, liver, and other tissues, plays an important role in glycolysis and glyconeogenesis. The activity of LDH is often altered upon inflammatory responses in animals. Nano-TiO(2) was shown to provoke various inflammatory responses both in rats and mice; however, the molecular mechanism by which TiO(2) exerts its toxicity has not been completely understood. In this report, we investigated the mechanisms of nano-anatase TiO(2) (5 nm) on LDH activity in vitro. Our results showed that LDH activity was greatly increased by low concentration of nano-anatase TiO(2), while it was decreased by high concentration of nano-anatase TiO(2). The spectroscopic assays revealed that the nano-anatase TiO(2) particles were directly bound to LDH with mole ratio of [nano-anatase TiO(2)] to [LDH] was 0.12, indicating that each Ti atom was coordinated with five oxygen/nitrogen atoms and a sulfur atoms of amino acid residues with the Ti-O(N) and Ti-S bond lengths of 1.79 and 2.41 A. We postulated that the bound nano-anatase TiO(2) altered the secondary structure of LDH, created a new metal ion-active site for LDH, and thereby enhanced LDH activity.

In Situ Polymerization of the 4-Vinylbenzenesulfonic Anion in Ni−Al−Layered Double Hydroxide and Its Molecular Dynamic Simulation

This paper describes a systematic study on the thermal polymerization of both pristine 4-vinylbenzenesulfonic anion (VBS) and intercalated VBS in the two-dimensional (2D) gallery of Ni-Al layered double hydroxide (VBS/Ni-Al-LDH), by virtue of combining experimental and theoretical investigations. In situ FT-IR, in situ high-temperature X-ray diffraction (HT-XRD), UV-vis absorption spectroscopy, TG-DTA and elemental analysis were used to study the polymerization process, and it was found that the polymerization of VBS/Ni-Al-LDH occurs at ca. 150-170 degrees C, at least 40 degrees C lower than that of the pristine VBS, indicating that the layered structure of LDH is favorable for thermal polymerization of VBS. Therefore, this layered inorganic material may have potential application as a "molecular reactor" for enhancing the efficiency of polymerization reaction. Furthermore, the sheet-like polymerization product was obtained with the LDHs lamella as template. For better understanding the structure and arrangement of intercalated VBS and the polymerization product between the layers of Ni-Al-LDH, molecular dynamics (MD) simulation method was employed. The simulation results of hydration energies show that there are two relatively stable stages upon the increase of the number of interlayer water molecules. VBS molecules exhibit a tendency from tilted to vertical orientation with respect to the layers as the interlayer water content increases. Compared with the experimental results, the calculated interlayer spacing is more severely affected by interlayer water content. Finally, a typical tetramer product of VBS intercalated LDH was studied and the simulated equilibrium interlayer spacing is consistent with the experimental result of in situ HT-XRD. Based on the combination of experimental and theoretical studies on the interlayer polymerization system, the aim of this work is to deeply investigate the differences in thermal polymerization process between pristine monomers and intercalated ones in the gallery of LDHs, and to give detailed information of the arrangement and swelling behavior of guest molecules confined between the sheets of host layers.

Anion-exchange and thermal change of layered zinc hydroxides formed in the presence of Al(III)

Zinc hydroxide chloride particles of ZHC (simonkolleite, Zn 5(OH) 8Cl 2·H 2O) and layered double hydroxides (LDH, Zn–Al–Cl) were prepared by hydrolysis of ZnCl 2 solutions dissolving AlCl 3 at Al/Zn = 0.1 and 0.6 in atomic ratio, respectively. The anion-exchange and thermal change of ZHC and LDH were investigated by XRD, TEM, FTIR, analysis of Zn, Al, and Cl and gas adsorption of N 2, H 2O, and CCl 4. The formed ZHC and LDH particles were hexagonal thin plates and irregularly shaped thin plates, respectively. LDH was more easily ion-exchanged with CO 3 2− and SO 4 2− compared to ZHC. The layered structure of LDH was damaged by the ion-exchange with SO 4 2− but not CO 3 2−, whereas that of ZHC was kept after the ion-exchange with both the anions. The TEM observation of the ZHC and LDH particles outgassed at different temperatures of 75–400 °C revealed that exfoliation takes place on outgassing ZHC at 100–150 °C but not occurs in LDH. ZHC showed a high H 2O adsorption selectivity when outgassed below 100 °C, however the adsorption selectivity completely disappeared above 125 °C where the exfoliation took place. On the other hand, LDH exhibited less adsorption selectivity than ZHC though the selectivity was held after outgassed at 400 °C. The facilitated delamination of ZHC indicates that ZHC exhibits weaker interlalyer attractive force than LDH in vacuo.

Neutron Scattering Reveals the Dynamic Basis of Protein Adaptation to Extreme Temperature

To explore protein adaptation to extremely high temperatures, two parameters related to macromolecular dynamics, the mean square atomic fluctuation and structural resilience, expressed as a mean force constant, were measured by neutron scattering for hyperthermophilic malate dehydrogenase from Methanococcus jannaschii and a mesophilic homologue, lactate dehydrogenase from Oryctolagus cunniculus (rabbit) muscle. The root mean square fluctuations, defining flexibility, were found to be similar for both enzymes (1.5 A) at their optimal activity temperature. Resilience values, defining structural rigidity, are higher by an order of magnitude for the high temperature-adapted protein (0.15 Newtons/meter for O. cunniculus lactate dehydrogenase and 1.5 Newtons/meter for M. jannaschii malate dehydrogenase). Thermoadaptation appears to have been achieved by evolution through selection of appropriate structural rigidity in order to preserve specific protein structure while allowing the conformational flexibility required for activity.

Thermal behaviour of a heterothermic enzyme: A 4 lactate dehydrogenase from Triturus cristatus

The behaviour of T. cristatus A 4 lactate dehydrogenase at different temperatures was studied on the pure isoenzyme. The molecule displays a number of properties which do not conform to any current model of biochemical adaptation to temperature. Our hypothesis is that the structure of newt LDH evolved is such a way to become able to sustain its physiological action over the entire thermal range of the species, and thus no adjustment in kinetic features is needed when temperature varies.

Polymorphisms, linkage and mapping of four enzyme loci in the fish genus Xiphophorus (Poeciliidae).

Electrophoretic variants at four additional enzyme loci--two esterases (Est-2, Est-3), retinal lactate dehydrogenase (LDH-1) and mannose phosphate isomerase (MPI)--among three species and four subspecies of fish of the genus Xiphophorus were observed. Electrophoretic patterns in F1 hybrid heterozygotes confirmed the monomeric structures of MPI and the esterase and the tetrametric structure of LDH in these fishes. Variant alleles of all four loci displayed normal Mendelian segregation in backcross and F2 hybrids. Recombination data from backcross hybrids mapped with Haldane's mapping function indicate the four loci to be linked as Est-2--0.43--Est3--0.26--LDH-1--0.19--MPI. Significant interference was detected and apparently concentrated in the Est-3 to MPI region. No significant sex-specific differences in recombination were observed. This group (designated linkage group II) was shown to assort independently from the three loci of linkage group I (adenosine deaminase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase) and from glyceraldehyde-3-phosphate dehydrogenase and two isocitrate dehydrogenase loci. Evidence for conservation of the linkage group, at least in part, in other vertebrate species is presented.