Effects of organic ligands, electrostatic and magnetic interactions in formation of colloidal and interfacial inorganic nanostructures

Spherical Assembly of Halloysite Clay Nanotubes as a General Reservoir of Hydrophobic Pesticides for pH-Responsive Management of Pests and Weeds

The development of smart systems for pesticidal delivery presents a significant advancement in enhancing the utilization efficiency of pesticides and mitigating environmental risks. Here an acid-responsive pesticidal delivery system using microspheres formed by the self-assembly of halloysite clay nanotubes (HNTs) is proposed. Insecticide avermectin (AVM) and herbicide prometryn (PMT) are used as two models of hydrophobic pesticide and encapsulated within the porous microspheres, followed by a coating of tannic acid/iron (TA/FeIII) complex films to generate two controlled-release pesticides, named as HCEAT and HCEPT, resulting in the loading capacity of AVM and PMT being 113.3 and 120.3 mg g-1, respectively. Both HCEAT and HCEPT exhibit responsiveness to weak acid, achieving 24 h-release ratios of 85.8% and 80.5% at a pH of 5.5. The experiment and simulation results indicate that the coordination interaction between EDTA2- and Ca2+ facilitates the spherical aggregation of HNTs. Furthermore, these novel pesticide formulations demonstrate better resistance against ultraviolet (UV) irradiation, higher foliar affinity, and less leaching effect, with negligible impact of the carrier material on plants and terrestrial organisms. This work presents a promising approach toward the development of efficient and eco-friendly pesticide formulations, greatly contributing to the sustainable advancement of agriculture.

Effect of colloidal magnetite (Fe3O4) nanoparticles on the electrical characteristics of the azolectin bilayer in a static inhomogeneous magnetic field

This work is devoted to the study of the combined effects of applied magnetic field and MNPs on the electrical characteristics of bilayer lipid membranes. We present results of the study of electrical parameters of azolectin membranes in a static inhomogeneous magnetic field at the one-sided addition of positively charged quasi-spherical superparamagnetic magnetite nanoparticles with a diameter of about 4 nm. The magnet was located at different distances from the membrane, and the magnetic field attracted the nanoparticles to the membrane surface with different strengths. We observed three pronounced effects that depended on the external magnetic field. Firstly, after addition of nanoparticles in a magnetic field, the conductance of the membranes increased. A smooth increase in conductance was accompanied in some cases by the appearance of current jumps, which can be associated with the formation of through pores with a radius of no more than 1 nm. The conductance increased with increasing magnetic field gradient. Secondly, at zero command voltage, a negative current through the membrane was observed. Although our experiments did not allow us to unambiguously determine which particles create this current, we believe that this current is associated with the penetration of particles through the membrane. This effect intensified with increasing magnetic field gradient. Thirdly, we observed a sharp change in the nonlinear dependence of capacitance on voltage associated both with the change in the surface potential of the azolectin membrane and with the effect of MNP binding to the membrane surface on the apparent membrane capacitance.

Shaping Magnetite by Hydroxyl Group Numbers of Small Molecules

Despite numerous reports on magnetite formation with the assistance of various additives, the role of hydroxyl group (-OH) numbers in small polyol molecules has not yet been understood well. We selected small molecules containing different -OH numbers, such as ethanol, ethylene glycol, propanetriol, butanetetrol, pentitol, hexanehexol, and cyclohexanehexol, as additives in coprecipitation. By increasing the -OH number in these small polyol molecules, the formation of crystallization was slowed, and the size and shape of magnetite were regulated as well possibly due to the changed complexation strength and the stability of the precursor. The increase in temperature and the Fe²⁺/Fe³⁺ ratio can reduce the complexation strength. The nucleation and growth of magnetite proceed possibly through the aggregation of polyol-stabilized amorphous complexes and two-line ferrihydrite with low crystallinity based on the -OH numbers, suggesting a nonclassical pathway. The as-prepared magnetite showed a r₂/r₁ ratio after in vitro MRI measurement as follows: Fe₃O₄@He-6OH rod < Fe₃O₄@Pr-3OH sheet < Fe₃O₄@Pe-5OH cube. The Fe₃O₄@He-6OH rod and Fe₃O₄@Pr-3OH sheet displayed T₁-T₂ dual modal contrast ability, while the Fe₃O₄@Pe-5OH cube can be T₂-dominated. This research provides a simple but an essential approach for designing MRI contrast agents.

The effect of magnetically induced linear aggregates on proton transverse relaxation rates of aqueous suspensions of polymer coated magnetic nanoparticles

It has been recently reported that for some suspensions of magnetic nanoparticles the transverse proton relaxation rate, R(2), is dependent on the time that the sample is exposed to an applied magnetic field. This time dependence has been linked to the formation of linear aggregates or chains in an applied magnetic field via numerical modeling. It is widely known that chain formation occurs in more concentrated ferrofluids systems and that this has an affect on the ferrofluid properties. In this work we examine the relationships between colloidal stability, the formation of these linear structures, and changes observed in the proton transverse relaxation rate of aqueous suspensions of magnetic particles. A series of iron oxide nanoparticles with varying stabilizing ligand brush lengths were synthesized. These systems were characterized with dynamic light scattering, transmission electron microscopy, dark-field optical microscopy, and proton transverse relaxation rate measurements. The dark field optical microscopy and R(2) measurements were made in similar magnetic fields over the same time scale so as to correlate the reduction of the transverse relaxivity with the formation of linear aggregates. Our results indicate that varying the ligand length has a direct effect on the colloidal arrangement of the system in a magnetic field, producing differences in the rate and size of chain formation, and hence systematic changes in transverse relaxation rates over time. With increasing ligand brush length, attractive inter-particle interactions are reduced, which results in slower aggregate formation and shorter linear aggregate length. These results have implications for the stabilization, characterization and potentially the toxicity of magnetic nanoparticle systems used in biomedical applications.

DNA-assisted "double-templating" approach for the construction of hollow meshed inorganic nanoshells

A "double-templating" approach was elaborated to produce meshed nanoshells made of semiconductor material in a two-step process. First, DNA adsorption is templated by spherical nanobeads, and second, DNA is mineralized by an inorganic material (CdS). Dissolution of the core beads leaves nanometer-size shells, the surface structure of which represents a mineralized network of DNAs. This method demonstrates the opportunity to metalize an arbitrary three-dimensional template by depositing a network of nanowires.

Kinetic approach for the study of noncovalent interaction between [Ru(NH3)5pz]2+ and gold nanoparticles

Gold nanoparticles (AuNPs) capped with N-(2-mercaptopropionyl)glycine have been used to study the strength and character of the binding of a cationic metal complex, [Ru(NH3)5pz]2+ (pz = pyrazine), at pH = 8, to these nanoparticles. The strength of the binding has been studied using a kinetic approach consisting of the study of the kinetics of the oxidation of this ruthenium complex by S2O82- at different NaCl concentrations. When the ionic strength increases, the strength of the binding decreases, as a consequence of the partial neutralization of the charge on the AuNPs which, at pH = 8, has the tiopronin residue negatively charged. The increase of the ionic strength also produces a change in the character of the binding, which changes from anticooperative to noncooperative when the ionic strength increases. The nonelectrostatic and electrostatic components of the free energy of binding are determined. From the latter, we have obtained the values of the electrostatic potential differences at the AuNPs/solutions interface.