Vulcanization and antioxidation effects of accelerator modified antioxidant in styrene-butadiene rubber: Experimental and computational studies

Effect of PVP and HPMC on production of indomethacin amorphous nanoparticles: experiments and molecular dynamics simulations

OBJECTIVE

This study investigated the effect of molecular interactions between drug and polymers on preparation of nanoamorphous indomethacin (IND) through milling of solid dispersions (SDs).

SIGNIFICANCE

The polymer selection (molecular interaction) emerged as a critical factor in the dynamic milling process for achieving nanoamorphous drug.

METHODS

Polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose (HPMC) were selected as models. Amorphous dispersions were used to prepare nanoamorphous drugs by applying wet milling. Molecular simulations were employed to elucidate the molecular mechanisms of drug-polymer miscibility, interaction energy, and molecular migration.

RESULTS

Both PVP and HPMC related SDs could be nanosized after milling. The rate of size reduction might be related to the solid state of the dispersions. The combination of amorphous PVP SDs with reduced particle size significantly improved the dissolution rate of IND. However, HPMC-based samples exhibited recrystallization during milling. Molecular simulation indicated that PVP formed strong molecular interaction with the drug to maintain the amorphous form, which contributed to avoid recrystallization induced by the external milling forces. The radial distribution function of hydrated IND/HPMC amorphous cells demonstrated the absence of hydrogen bonding interactions between IND and HPMC.

CONCLUSION

PVP contributed to maintain the amorphous state during the milling process, which resulted from the higher molecular binding energy compared to HPMC. Controlled milling of amorphous SD with optimized polymer selection could simultaneously achieve nanoamorphous particle and enhanced dissolution rate.

Crystallization and intermolecular hydrogen bonding in carbamazepine-polyvinyl pyrrolidone solid dispersions: An experiment and molecular simulation study on drug content variation

The choice of drug content is a critical factor as far as the solid dispersion is concerned. This investigation aims to build the relationship between the drug content, intermolecular hydrogen bonding and the crystalline of the carbamazepine-polyvinyl pyrrolidone solid dispersion. In this work, the microstructural changes of solid dispersions were investigated using experimental characterization combined with molecular simulation. Experimental investigations demonstrated that increasing the drug content enhances the intermolecular hydrogen bonding between drugs, resulting in the crystalline phase of the drug emerged in the solid dispersion. This negatively affects the solubility and stability of solid dispersions. Molecular simulations were then used to analyze the changes of intermolecular hydrogen bonding at different drug content in the system. It revealed a tenfold increase in drug-drug hydrogen bonding concentration as drug content elevated from 10% to 50%, while the drug-excipient hydrogen bonding concentration decreased by 45%. The correlation analysis proves the significant relationships among the drug content, intermolecular hydrogen bonding, and crystallinity of solid dispersion. Using polynomial fitting analysis, the quantitative relationships between the drug content and crystalline properties were investigated. This study will offer valuable insights into the impact of drug content on the performance of solid dispersion.

Synthesis and Properties of a Novel Reactive and Low-Migration-Resistant Antioxidant and Its Application in Rubber Composites

The addition of antioxidants to rubber is one of the most economical and effective methods for delaying rubber aging. However, antioxidant migration can cause environmental pollution. To address this issue, a new reactive antioxidant was synthesized via the chemical bonding of glycidyl methacrylate (GMA) and p-aminodiphenylamine (PPDA). The product was characterized by Fourier-transform infrared spectroscopy, which confirmed the successful reaction between GMA and PPDA, resulting in a compound with the expected structure. The mixture was then combined with a composite of styrene-butadiene rubber and carbon black. The tensile strength, antioxidant properties, migration, and RPA of the resulting materials were tested and compared with those of the commercial antioxidants N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-1,4-phenylenediamine, and poly(1,2-dihydro-2,2,4-trimethylquinoline). After the glycidyl methacrylate antioxidant was grafted onto p-aminodiphenylamine, it became highly compatible with and dispersed in the rubber matrix. The antiaging and antimigration properties of the rubber antioxidants were enhanced without damaging the mechanical properties of the rubber matrix. The short-term and long-term antiaging and antimigration properties of this antioxidant are superior to those of commercially available antioxidants.

Screening of Organic Small Molecule Excipients on Ternary Solid Dispersions Based on Miscibility and Hydrogen Bonding Analysis: Experiments and Molecular Simulation

The preparation of solid dispersions by mixing insoluble drugs with polymers is the main way to improve the aqueous solubility of drugs. The introduction of organic small molecule excipients into binary solid dispersions is expected to further enhance drug solubility by regulating intermolecular hydrogen bonding within the system at the microscopic level. In this study, we used carbamazepine (CBZ) as the target drug and polyvinylpyrrolidone as the solid dispersion matrix and screened the third component from 13 organic small molecules with good miscibility in the solid dispersion based on the principle of similarity of solubility parameters. The hydrogen bonding parameters and dissociation Gibbs free energy of the 13 organic small molecule-CBZ dimer were calculated by quantum mechanical simulation, and the tryptophan (Try) was identified as the optimal third component of organic small molecule. The migration of CBZ in binary and ternary systems was also analyzed by molecular dynamics simulation. On this theoretical basis, the corresponding solid dispersions were prepared, characterized, and tested for solubility analysis, which verified that the drug solubility was stronger for the system with the addition of polar fractions and the Try was indeed the best third component of organic small molecule compound, which was consistent with the simulation predictions. This screening method may provide theoretical guidance for drug modification design and clinical studies.

Study on micromolecular mechanical properties of C-atom reinforced SBR polymer composites

A three-layer microscopic model with Fe atoms as the top and bottom layer and SBR polymer composites as the middle layer and SBR polymer composite was established and studied. By adding C atoms as reinforcement, the stability and elastic modulus and frictional coefficient changes of SBR polymer composites before and after adding C atoms were studied. In this study, the molecular dynamics method was used to change of elastic modulus was observed by stretching, compression and shear of the SBR polymer composite; The simulation shows that after adding C atom the elastic modulus of SBR polymer composite increased, the friction coefficient of polymer composite upper and lower decreases and the relative atomsic concentration, temperature, velocity, overall temperature average, kinetic energy, total energy and MSD in the thickness direction are reduced after adding C atoms. The stability of SBR polymer composites is enhanced, and the deformation under shear is weakened. In addition, it is found that the binding energy between SBR polymer composites and Fe atoms is reduced after adding C atoms.The stability of SBR polymer composites is improved during use. This work provides a method for studying the properties of rubber composites by studying the enhancement of the stability of SBR polymer composites from the microscopic point of view.

Preparation, Characterization and Molecular Dynamics Simulation of Rutin-Cyclodextrin Inclusion Complexes

Rutin is a natural flavonoid that carries out a variety of biological activities, but its application in medicine and food is limited by its water solubility. One of the classical methods used to enhance drug solubility is encapsulation with cyclodextrins. In this paper, the encapsulation of different cyclodextrins with rutin was investigated using a combination of experimental and simulation methods. Three inclusions of rutin/beta-cyclodextrin (β-CD), rutin/2-hydroxypropyl beta-cyclodextrin (HP-β-CD) and rutin/2,6-dimethyl beta-cyclodextrin (DM-β-CD) were prepared by the freeze-drying method, and the inclusions were analyzed using Fourier infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC) and ultraviolet-visible spectroscopy (UV) to characterize and demonstrate the formation of the inclusion complexes. Phase solubility studies showed that rutin formed a 1:1 stoichiometric inclusion complex and significantly increased its solubility. β-CD, HP-β-CD, DM-β-CD, rutin and the three inclusion complexes were modeled by using MS2018 and AutoDock 4.0, and molecular dynamics simulations were performed to calculate the solubility parameters, binding energies, mean square displacement (MSD), hydrogen bonding and radial distribution functions (RDF) after the equilibration of the systems. The results of simulation and experiment showed that rutin/DM-β-CD had the best encapsulation effect among the three cyclodextrin inclusion complexes.

Study on the Effect of Polymer Excipients on the Dispersibility, Interaction, Solubility, and Scavenging Reactive Oxygen Species of Myricetin Solid Dispersion: Experiment and Molecular Simulation

Although the preparation of amorphous solid dispersions can improve the solubility of crystalline drugs, there is still a lack of guidance on the micromechanism in the screening and evaluation of polymer excipients. In this study, a particular method of experimental characterization combined with molecular simulation was attempted on solubilization of myricetin (MYR) by solid dispersion. According to the analysis of the dispersibility and hydrogen-bond interaction, the effectiveness of the solid dispersion and the predicted sequence of poly(vinyl pyrrolidone) (PVP) > hypromellose (HPMC) > poly(ethylene glycol) (PEG) as the polymer excipient were verified. Through the dissolution, cell viability, and reactive oxygen species (ROS)-level detection, the reliability of simulation and micromechanism analysis was further confirmed. This work not only provided the theoretical guidance and screening basis for the miscibility of solid dispersions from the microscopic level but also served as a reference for the modification of new drugs.