Layered double hydroxide-based antioxidant dispersions with high colloidal and functional stability

Molecular Antioxidants Maintain Synergistic Radical Scavenging Activity upon Co-Immobilization on Clay Nanoplatelets

Unbalanced levels of reactive oxygen species (ROS) result in oxidative stress, affecting both biomedical and industrial processes. Antioxidants can prevent ROS overproduction and thus delay or inhibit their harmful effects. Herein, activities of two molecular antioxidants (gallic acid (GA), a well-known phenolic compound, and nicotinamide adenine dinucleotide (NADH), a vital biological cofactor) were tested individually and in combination to assess possible synergistic, additive, or antagonistic effects in free radical scavenging and in redox capacity assays. GA was a remarkable radical scavenger, and NADH exhibited moderate antioxidant activity, while their combination at different molar ratios led to a synergistic effect since the resulting activity was superior to the sum of the individual GA and NADH activities. Their coimmobilization was performed on the surface of delaminated layered double hydroxide clay nanoplatelets by electrostatic interactions, and the synergistic effect was maintained upon such a heterogenization of these molecular antioxidants. The coimmobilization of GA and NADH expands the range of their potential applications, in which separation of antioxidant additives is important during treatments or manufacturing processes.

The Influence of Solvents and Colloidal Particles on the Efficiency of Molecular Antioxidants

The radical scavenging activity of three molecular antioxidants (trolox, rutin and ellagic acid) was investigated in different solvents with and without added polymer-based colloidal particles (SL-IP-2). Rutin and ellagic acid showed poor solubility in water, preventing the accurate measurement of the effective antioxidant concentration values, which were determined in ethanol/water (EtOH/H₂O) mixtures. The presence of trolox and rutin changed neither the surface charge properties nor the size of SL-IP-2 in these solvents, while significant adsorption on SL-IP-2 was observed for ellagic acid leading to overcharging and rapid particle aggregation at appropriately high antioxidant concentrations in EtOH/H₂O. The differences in the radical scavenging capacity of trolox and ellagic acid that was observed in homogeneous solutions using water or EtOH/H₂O as solvents vanished in the presence of the particles. Rutin lost its activity after addition of SL-IP-2 due to the larger molecular size and lower exposure of the functional groups to the substrate upon interaction with the particles. The obtained results shed light on the importance of the type of solvent and particle-antioxidant interfacial effects on the radical decomposition ability of molecular antioxidants, which is of crucial importance in industrial processes involving heterogeneous systems.

Topology dependent modification of layered double hydroxide for therapeutic and diagnostic platform

Layered double hydroxide is a family of two-dimensional materials with wide range of compositions. Recently, its ability to accommodate various chemical species and biocompatibility have been attracted in the biomedical applications to develop drug delivery system and nanodiagnostics. In this review, we categorized biomedical approaches of layered double hydroxide with respect to the three topologies of, namely, interlayer space, outer surface with particle edge, and the lattice points. There have been extensive researches on the intercalation of drug or tracing to make use of interlayer space of layered double hydroxide for drug stabilization, sustained release, cellular delivery and etc. Outer surface or edge has been utilized to immobilization of large therapeutic moieties and to attach tracing moiety. Lattice points consisting of various metal species could be utilized for the specific metal species like paramagnetic elements or radioisotopes. Based on these topologies in layered double hydroxide, both the synthetic routes and the achieved functionalities in terms of biomedical application will be discussed.

A nanohybrid layered double hydroxide as an effective carrier for delivery and application of the phytohormone indole acetic acid

The increasing need for agricultural production on the one hand, and requirements for greener and more sustainable agricultural practices on the other, have led to a growing demand for efficient and eco-friendly materials for the delivery of agrochemicals. Here we describe, the use of layered double hydroxide (LDH) particles as a carrier for a plant hormone. Magnesium-aluminum LDH intercalated with indole-3-acetic acid (IAA) was synthesized by co-precipitation method, characterized, and examined for real-life applications. Scanning electron microscopy revealed that both pristine and IAA-intercalated LDH particles exhibit hexagonal platelet morphology. X-ray diffraction showed a hydrotalcite-like structure and, together with Fourier transform infrared spectroscopy, verified the efficacious intercalation of IAA anions. The intercalation protected the IAA from enzymatic degradation and allowed its sustained release, as demonstrated by enzymatic stability and release tests, correspondingly. In-vivo assay revealed that intercalation inside LDH significantly increases the biological activity of IAA in promoting adventitious root development in plant cuttings. Results demonstrate the applicability of LDH as an advanced, effective, and sustainable carrier that overcomes the practical limitations of agrochemicals and significantly enhances their efficiency.

Complex Coacervation and Overcharging during Interaction between Hydrophobic Zein and Hydrophilic Laponite in Aqueous Ethanol Solution

In this paper, for the first time, we have reported the formation of complex coacervate during interaction between hydrophobic protein, zein, and hydrophilic nanoclay, Laponite, in a 60% v/v ethanol solution at pH 4. Dynamic light scattering and viscosity measurements revealed the formation of zein-Laponite complexes during the interaction between zein at fixed concentration, C Z = 1 mg/mL, and varying concentrations of Laponite, C L (7.8 × 10-4 - 0.25% w/v). Further investigation of the zein-Laponite complexes using turbidity and zeta potential data showed that these complexes could be demarcated in three different regions: Region I, below the charge neutralization region (C Z = 1 mg/mL, C L ≤ 0.00625% w/v) where soluble complexes was formed during interaction between oppositely charged zein and Laponite; Region II, the charge neutralization region (C Z = 1 mg/mL, 0.00625 < C L ≤ 0.05% w/v) where zein-Laponite complexes form neutral coacervates; and Region III, the interesting overcharged coacervates region (C Z = 1 mg/mL, C L > 0.05% w/v). Investigation of coacervates using a fluorescence imaging technique showed that the size of neutral coacervates in region II was large (mean size = 1223.7 nm) owing to aggregation as compared to the small size of coacervates (mean size = 464.7 nm) in region III owing to repulsion between overcharged coacervates. Differential scanning calorimeter, DSC, revealed the presence of an ample amount of bound water in region III. The presence of bound water was evident from the presence of an additional peak at 107 °C in region III apart from normal enthalpy of evaporation of water from coacervates.