Investigation of nanoparticle-polymer interaction in bio-based nanosilica-filled PLA/NR nanocomposites: molecular dynamics simulation.

Molecular dynamics (MD) simulation, by employing the COMPASS force field, was utilized to investigate structural and thermal characteristics as well as interfacial interactions between components of nanocomposite consisting of poly(lactic acid) (PLA)/natural rubber (NR)/nanosilica, abbreviated as PSxN, where 1 ≤ x ≤ 7 and it represents the parts of SiO2 nanoparticles added to the PLA/NR (PN) blend. Analysis of the obtained results including density (ρ), fractional free volume (FFV), glass transition temperature (Tg), interaction energy (Einteraction), and radial distribution function (RDF) of these nanocomposites was performed. Comparing Einteraction of nanocomposites with that of the PN blend showed that the interactions between the chains of the two polymers are highly dependent on the added amounts of silica nanoparticles, so that by adding silica to the PN blend to obtain PS1N and PS3N nanocomposites, the amount of Einteraction was reduced to a smaller positive value, which indicates the tendency of the nanocomposite's components to interact with each other. By further addition of silica nanoparticles to have PS5N and PS7N nanocomposites and then by analysis of the RDF results, it was found that the nanoparticles were not well dispersed in these two nanocomposites and they were accumulated in the NR rubbery phase. Therefore, the percolation threshold for silica loading on the PN blend is at most 3 parts (x = 3). These results as well as the other obtained simulation results were compared with the available experimental data, and the agreement observed between them approved the simulation procedure and validated the obtained results.

Removal of Acid Blue 62 textile dye from aqueous solutions by cerium reagents.

The removal of Acid Blue 62 (AB62) dye which is known as a pollutant agent and contains in wastewater of textile industry has been studied in this work by using five various cerium compounds as the oxidizing agents. The parameters involved in the oxidation reaction such as pH, initial dye concentration and the oxidizing agent dosage have been investigated using both batch and semi-batch reactors at ambient temperature. The results indicated that the rate of oxidation for various cerium reagents is in the following order: CeF4 > (NH4)2Ce (NO3)6 > Ce (SO4)2 > CeCl3 > Ce (CH3COO)3, where cerium fluoride (CeF4) had the highest removal yields, 99.9% and 95%, for dye de-colouration and COD (chemical oxygen demand), respectively. The analysis of the dye removal was done by using UV-VIS spectrometry, GC-MS and HPLC methods which indicated the aromatic ring cleavage of AB62 dye by CeF4. The half-life measurement was employed to evaluate the reaction rate model for decomposition of AB62 dye by CeF4.

Adsorption and encapsulation of the drug doxorubicin on covalent functionalized carbon nanotubes: A scrutinized study by using molecular dynamics simulation and quantum mechanics calculation.

Adsorption of the drug doxorubicin (DOX) onto covalent functionalized carbon nanotubes (CNTs) as drug carriers was studied by employing molecular dynamics (MD) simulation. CNT was covalently functionalized by the chemical groups: amine, carboxyl and hydroxyl and the change in the electrostatic charge of CNT as a result of functionalization was investigated by quantum mechanics calculations. The drug adsorption onto the functionalized CNTs (f-CNT) was examined by analyzing the evaluated radial probability of the drug by MD simulation. Overall consideration of the results demonstrated that surface functionalization enhances the loading capacity of CNT for the drug encapsulation, also agglomeration of unprotonated drug molecules has increased encapsulation capacity. Analysis of the obtained results indicated that carboxyl and amine f-CNTs can act as a pH sensitive drug carrier where their protonation in acidic condition can decrease the electrostatic interactions of the loaded drug with the f-CNT and as a result can promote the drug release.

Molecular Perspective Mechanism for Drug Loading on Carbon Nanotube-Dendrimer: A Coarse-Grained Molecular Dynamics Study.

The loading mechanism of the protein ubiquitin and the drug pyrene, as a representatives of large and small molecules, onto the drug carrier carbon nanotube-polyamidoamine (PAMAM) was studied by using coarse-grained molecular dynamics simulation. The results indicated that the optimum and stable drug delivery system for protein loading can be obtained by inserting the molecules in the sequence of: (i) PAMAM, (ii) protein, and (iii) PAMAM. Also, it was found that properly adjusting the weight ratio of PAMAM to the protein, defined as MwPAMAM/ Mwprotein (where Mw is the molecular weight) can lead to achieve a stable system for loading the protein. However, for pyrene loading, it was found that the insertion sequence has no significant effect and only encapsulation of the pyrene molecules into PAMAM and adjustment of the weight ratio of PAMAM to pyrene ( MwPAMAM/ Mwpyrene) can affect the stability of the drug delivery system.

Effect of drug amlodipine on the charged lipid bilayer cell membranes DMPS and DMPS + DMPC: a molecular dynamics simulation study.

In this work, the effects of the anti-hypertensive drug amlodipine in native and PEGylated forms on the malfunctioning of negatively charged lipid bilayer cell membranes constructed from DMPS or DMPS + DMPC were studied by molecular dynamics simulation. The obtained results indicate that amlodipine alone aggregates and as a result its diffusion into the membrane is retarded. In addition, due to their large size aggregates of the drug can damage the cell, rupturing the cell membrane. It is shown that PEGylation of amlodipine prevents this aggregation and facilitates its diffusion into the lipid membrane. The interaction of the drug with negatively charged membranes in the presence of an aqueous solution of NaCl, as the medium, is investigated and its effects on the membrane are considered by evaluating the structural properties of the membrane such as area per lipid, thickness, lipid chain order and electrostatic potential difference between bulk solution and lipid bilayer surface. The effect of these parameters on the diffusion of the drug into the cell is critically examined and discussed.

A coarse grained molecular dynamics simulation study on the structural properties of carbon nanotube-dendrimer composites.

By employing coarse grained (CG) molecular dynamics (MD) simulation, the effect of the size and hydrophilic/hydrophobic properties of the interior/exterior structures of the dendrimers in carbon nanotube (CNT)-dendrimer composites has been studied, to find a stable composite with high solubility in water and the capability to be used in drug delivery applications. For this purpose, composites consisting of core-shell dendrimer complexes including: [PPI{core}-PAMAM{shell}], [PAMAM{core}-polyethyleneglycol (PEG){shell}] and [PAMAM{core}-fattyacid (FTA){shell}] were constructed. A new CG model for the fatty acid (FTA) molecules as functionalized to the dendrimer was developed, which, unlike the previous models, could generate the structural conformations of the FTA properly. The obtained results indicated that the dendrimer complexes with short FTA chains can form stable composites with the CNT. Also, it was found that the pristine PAMAM and PPI-PAMAM with small PPI, and PAMAM-PEG dendrimers with short PEG chains, can distribute their chains into the water medium and interact with the CNT efficiently, to form a stable water-soluble CNT-dendrimer composite. The results demonstrated that the structural difference between the interior and exterior of a core-shell dendrimer complex can prevent the core and the interior layers of the dendrimer complex from interacting with the CNT. An overall analysis of the results manifested that the CNT-PAMAM:4-PEG:4 is the most stable composite, due to strong binding of the dendrimer with the CNT while also having high solubility in water, and its core retains its structure properly and unchanged, suitable for encapsulating drugs in the targeted delivery applications.

Interaction of drugs amlodipine and paroxetine with the metabolizing enzyme CYP2B4: a molecular dynamics simulation study.

The interactions of the drugs amlodipine and paroxetine, which are prescribed respectively for treatment of hypertension and depression, with the metabolizing enzyme cytochrome CYP2B4 as the drug target, have been studied by molecular dynamics (MD) simulation. Poly ethylene glycol was used to control the drugs' interactions with each other and with the target CYP2B4. Thirteen simulation systems were carefully designed, and the results obtained from MD simulations indicated that amlodipine in the PEGylated form prescribed with paroxetine in the nonPEGylated form promotes higher cytochrome stability and causes fewer fluctuations as the drugs approach the target CYP2B4 and interact with it. The simulation results led us to hypothesize that the combination of the drugs with a specific drug ratio, as proposed in this work, manifests more effective diffusivity and less instability while metabolizing with enzyme CYP2B4. Also, the active residues in the CYP2B4 enzyme that interact with the drugs were determined by MD simulation, which were consistent with the reported experimental results. Graphical Abstract Efficient drug-enzyme interactions, as a result of PEGylation.

Effect of pristine and functionalized single- and multi-walled carbon nanotubes on CO2 separation of mixed matrix membranes based on polymers of intrinsic microporosity (PIM-1): a molecular dynamics simulation study.

Molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations were conducted to investigate the transport properties of carbon dioxide, methane, nitrogen, and oxygen through pure and mixed matrix membranes (MMMs) based on polymers of intrinsic microporosity (PIM-1). For this purpose, first, 0.5 to 3 wt% of pristine single-walled carbon nanotube (p-SWCNT) and multi-walled carbon nanotube (p-MWCNT) were embedded into the pure PIM-1, and then for better dispersion of CNT particles into the polymer matrix and to improve the performance of the resulting MMMs, polyethylene glycol (PEG) functionalized SWCNT and MWCNT (f-SWCNT and f-MWCNT, respectively) were loaded. The characterization of the obtained MMMs was carried out by using density, glass transition temperature, X-ray pattern, and fractional free volume calculations. Comparing the obtained results with the available reported experimental data, indicate the authenticity of the applied simulation approach. The simulation results exhibit that the pristine and PEG-functionalized CNT particles improve the transport properties such as diffusivity, solubility, and permeability of the PIM-1 membranes, without sacrificing their selectivity. Also, the MMMs incorporated with 2 wt% of the functionalized CNT particles indicate better performance for the CO2 separation from other gases. According to the calculated results, the highest permeability and diffusivity for CO2 are observed in the [PIM-1/f-SWCNT] MMM among the other membranes which represent that the loading of the f-SWCNTs can enhance the CO2 separation performance of PIM-1 more than other CNTs studied in this work.

Combination of anti-hypertensive drugs: a molecular dynamics simulation study.

The anti-hypertensive drugs amlodipine, atenolol and lisinopril, in ordinary and PEGylated forms, with different combined-ratios, were studied by molecular dynamics simulations using GROMACS software. Twenty simulation systems were designed to evaluate the interactions of drug mixtures with a dimyristoylphosphatidylcholine (DMPC) lipid bilayer membrane, in the presence of water molecules. In the course of simulations, various properties of the systems were investigated, including drug location, diffusion and mass distribution in the membrane; drug orientation; the lipid chain disorder as a result of drug penetration into the DMPC membrane; the number of hydrogen bonds; and drug surface area. According to the results obtained, combined drugs penetrate deeper into the DMPC lipid bilayer membrane, and the lipid chains remain ordered. Also, the combined PEGylated drugs, at a combination ratio of 1:1:1, enhance drug penetration into the DMPC membrane, reduce drug agglomeration, orient the drug in a proper angle for easy penetration into the membrane, and decrease undesirable lipotoxicity due to distorted membrane self-assembly and thickness. Graphical abstract ᅟ.

Hybrid Dendrimers of PPI(core)-PAMAM(shell): A Molecular Dynamics Simulation Study.

The structural properties of hybrid dendrimers PPI(core)-PAMAM(shell) for application in drug delivery are studied by coarse-grained molecular dynamics simulation, and their capacity to encapsulate drug guest molecules such as pyrene is investigated by changing the core (PPI) in the PPI-PAMAM hybrids. For this purpose, a coarse-grained model for PPI dendrimer is developed and is used to predict the structural properties as a function of PPI core size, such as the size of hybrid dendrimers, the depth of water penetration, the extent of back-folding of their chain terminals, the size and distribution of created cavities, and asphericity. The results show that the location of pyrene in the interior structure of the hybrids is independent of PPI core size and the branching chains create a barrier against the penetrating molecules in the shell of PPI. Then, by adding the PAMAM to the surface of PPI, this barrier is removed, and this will enhance the encapsulation capacity of the hybrid.

Molecular dynamics simulation of coarse-grained poly(L-lysine) dendrimers.

Poly(L-lysine) (PLL) dendrimer are amino acid based macromolecules and can be used as drug delivery agents. Their branched structure allows them to be functionalized by various groups to encapsulate drug agents into their structure. In this work, at first, an attempt was made on all-atom simulation of PLL dendrimer of different generations. Based on all-atom results, a course-grained model of this dendrimer was designed and its parameters were determined, to be used for simulation of three generations of PLL dendrimer, at two pHs. Similar to the all-atom, the coarse-grained results indicated that by increasing the generation, the dendrimer becomes more spherical. At pH 7, the dendrimer had larger size, whereas at pH 12, due to back folding of branching chains, they had the tendency to penetrate into the inner layers. The calculated radial probability and radial distribution functions confirm that at pH 7, the PLL dendrimer has more cavities and as a result it can encapsulate more water molecules into its inner structure. By calculating the moment of inertia and the aspect ratio, the formation of spherical structure for PLL dendrimer was confirmed.

Molecular dynamics simulation study of chitosan and gemcitabine as a drug delivery system.

By using molecular dynamics (MD) simulation, biodegradable biopolymer chitosan as a carrier for the drug gemcitabine was investigated and the effect of three initial drug concentrations (10, 40, and 80%) on its loading efficiency was studied. Then water was added to the systems of drug and biopolymer and the effects of water on the interactions of drug and chitosan and on the drug loading efficiency were examined. From the results it was found that the maximum loading of the drug occurred at 40% of the drug concentration. The radial distribution function calculations indicated that in the absence of water molecules, the drug molecules were located at shorter distance from chitosan and the loading efficiency of the drug in these systems was higher.

Interaction of PEGylated anti-hypertensive drugs, amlodipine, atenolol and lisinopril with lipid bilayer membrane: A molecular dynamics simulation study.

The interaction of PEGylated anti-hypertensive drugs, amlodipine, atenolol and lisinopril with lipid bilayer membrane dimyristoylphosphatidylcholine (DMPC) has been studied in nine different simulation systems consisting of 128 lipid molecules and appropriate number of water molecules by molecular dynamics method and by utilizing GROMACS software. The influences of PEGylation on the mentioned drugs and the differences in application of two types of spacer molecules on the performance of drugs and DMPC membrane have been evaluated and mass density of the components in the simulation box, mean square displacement (MSD), electrostatic potential, hydrogen bonding, radial distribution function (RDF), area per lipid, order parameter, and angle distribution of the component molecules including drug, DMPC and PEG has been investigated. Furthermore, umbrella sampling analysis indicated that, PEGylation of the drugs made amlodipine to behave more hydrophilic, whereas in case of lisinopril and atenolol, PEGylation made these drugs to behave more hydrophobic. In almost all of the simulated systems, PEGylation increased the diffusion coefficient of the drugs.

The influence of cholesterol on interactions and dynamics of ibuprofen in a lipid bilayer.

In this work, molecular dynamics (MD) simulations with atomistic details were performed to examine the influence of the cholesterol on the interactions and the partitioning of the hydrophobic drug ibuprofen in a fully hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayer. Analysis of MD simulations indicated that ibuprofen molecules prefer to be located in the hydrophobic acyl chain region of DMPC/cholesterol bilayers. This distribution decreases the lateral motion of lipid molecules. The presence of ibuprofen molecules in the bilayers with 0 and 25mol% cholesterol increases the ordering of hydrocarbon tails of lipids whereas for the bilayers with 50mol% cholesterol, ibuprofen molecules perturb the flexible chains of DMPC lipids which leads to the reduction of the acyl chain order parameter. The potential of the mean force (PMF) method was used to calculate the free energy profile for the transferring of an ibuprofen molecule from the bulk water into the DMPC/cholesterol membranes. The PMF studies indicated that the presence of 50mol% cholesterol in the bilayers increases the free energy barrier and slows down the permeation of the ibuprofen drug across the DMPC bilayer. This can be due to the condensing and ordering effects of the cholesterol on the bilayer.

Effect of cholesterol on behavior of 5-fluorouracil (5-FU) in a DMPC lipid bilayer, a molecular dynamics study.

In this work, molecular dynamics (MD) simulations were performed to investigate the effects of cholesterol on the interaction between the hydrophilic anticancer drug, 5-FU, and fully hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayer. Several structural and dynamical parameters of DMPC bilayers with varying amounts of cholesterol (0, 25, and 50mol%) in the presence and absence of drug molecules were calculated. Moreover, the free energy barriers for translocation of one 5-FU molecule from water to the lipid bilayer were determined by using the potential of mean force (PMF). PMF studies indicated that the location of the maximum free energy barrier was in the hydrophobic middle region of bilayer, while the minimums of the barrier were located at the hydrophilic part of bilayer at the interface with water. The minimum and maximum of the free energy profiles were independent of cholesterol concentration and suggested that the drug molecules 5-FU were accumulated in the vicinity of the polar head group of lipid bilayers. Moreover, the results showed that with increasing cholesterol concentration in the bilayer, the free energy barrier for translocation of 5-FU across the bilayer also increases which can be attributed to the condensing effect of the cholesterol on the bilayer.

Aqueous poly(amidoamine) dendrimer G3 and G4 generations with several interior cores at pHs 5 and 7: a molecular dynamics simulation study.

Poly(amidoamine) (PAMAM) dendrimers play an important role in drug delivery systems, because the dendrimers are susceptible to gain unique features with modification of their structure such as changing their terminals or improving their interior core. To investigate the core improvement and the effect of core nature on PAMAM dendrimers, we studied two generations G3 and G4 PAMAM dendrimers with the interior cores of commonly used ethylendiamine (EDA), 1,5-diaminohexane (DAH), and bis(3-aminopropyl) ether (BAPE) solvated in water, as an aqueous dendrimer system, by using molecular dynamics simulation and applying a coarse-grained (CG) dendrimer force field. To consider the electrostatic interactions, the simulations were performed at two protonation states, pHs 5 and 7. The results indicated that the core improvement of PAMAM dendrimers with DAH produces the largest size for G3 and G4 dendrimers at both pHs 5 and 7. The increase in the size was also observed for BAPE core but it was not so significant as that for DAH core. By considering the internal structure of dendrimers, it was found that PAMAM dendrimer shell with DAH core had more cavities than with BAPE core at both pHs 5 and 7. Also the moment of inertia calculations showed that the generation G3 is more open-shaped and has higher structural asymmetry than the generation G4. Possessing these properties by G3, specially due to its structural asymmetry, make penetration of water beads into the dendrimer feasible. But for higher generation G4 with its relatively structural symmetry, the encapsulation efficiency for water molecules can be enhanced by changing its core to DAH or BAPE. It is also observed that for the higher generation G4 the effect of core modification is more profound than G3 because the core modification promotes the structural asymmetry development of G4 more significantly. Comparing the number of water beads that penetrate into the PAMAM dendrimers for EDA, DAH, and BAPE cores indicates a significant increase when their cores have been modified with DAH or BAPE and substantiates the effective influence of the core nature in the dendrimer encapsulation efficiency.

Molecular simulation study of PAMAM dendrimer composite membranes.

Pure polysulfone (PSF) and its composites with chitosan (CST), hyaluronic acid (HA), conventional poly(amidoamine), and hydroxyl poly(amidoamine) dendrimers as the membranes for separation of the gases, methane, carbon dioxide, hydrogen sulfide, nitrogen, and oxygen have been studied by molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The transport properties (solubility, diffusivity, and permeability) of pure and gas mixtures in the membranes were calculated and the results of the simulations were compared with the available experimental data. The simulated structural properties of the pure and composite PSF membranes including occupied volume, free volume, surface area, fractional free volume (FFV), and radius of gyration (R g ) were evaluated and their effects on the separability of the gases by the membranes were analyzed and interpreted by the obtained results.

Kinetic modeling of low density lipoprotein oxidation in arterial wall and its application in atherosclerotic lesions prediction.

Oxidation of low-density lipoprotein (LDL) is one of the major factors in atherogenic process. Trapped oxidized LDL (Ox-LDL) in the subendothelial matrix is taken up by macrophage and leads to foam cell generation creating the first step in atherosclerosis development. Many researchers have studied LDL oxidation using in vitro cell-induced LDL oxidation model. The present study provides a kinetic model for LDL oxidation in intima layer that can be used in modeling of atherosclerotic lesions development. This is accomplished by considering lipid peroxidation kinetic in LDL through a system of elementary reactions. In comparison, characteristics of our proposed kinetic model are consistent with the results of previous experimental models from other researches. Furthermore, our proposed LDL oxidation model is added to the mass transfer equation in order to predict the LDL concentration distribution in intima layer which is usually difficult to measure experimentally. According to the results, LDL oxidation kinetic constant is an important parameter that affects LDL concentration in intima layer so that existence of antioxidants that is responsible for the reduction of initiating rates and prevention of radical formations, have increased the concentration of LDL in intima by reducing the LDL oxidation rate.

Carbon nanotube-encapsulated drug penetration through the cell membrane: an investigation based on steered molecular dynamics simulation.

Understanding the penetration mechanisms of carbon nanotube (CNTs)-encapsulated drugs through the phospholipid bilayer cell membrane is an important issue for the development of intracellular drug delivery systems. In the present work, steered molecular dynamics (SMD) simulation was used to explore the possibility of penetration of a polar drug, paclitaxel (PTX), encapsulated inside the CNT, through a dipalmitoylphosphatidylcholine bilayer membrane. The interactions between PTX and CNT and between PTX and the confined water molecules inside the CNT had a significant effect on the penetration process of PTX. The results reveal that the presence of a PTX molecule increases the magnitude of the pulling force. The effect of pulling velocity on the penetration mechanism was also investigated by a series of SMD simulations, and it is shown that the pulling velocity had a significant effect on pulling force and the interaction between lipid bilayer and drug molecule.

Effects of protein binding on a lipid bilayer containing local anesthetic articaine, and the potential of mean force calculation: a molecular dynamics simulation approach.

Articaine, as a local anesthetic drug has been simulated in neutral and charged forms, and its interaction with the dimyristoylphosphatidylcholine (DMPC) lipid bilayer membrane is investigated by molecular dynamics simulation using GROMACS software. In order to obtain the optimum location of the drug molecules, as they penetrate into the membrane, umbrella sampling is applied and the free energy is calculated. The effect of protein binding to DMPC membrane on the process of drug diffusion through the membrane is considered. Five simulation systems are designed and by applying the potential of mean force, the molecular dynamics simulation on the system is performed. In light of the obtained results, the electrostatic potential, variation of lipid bilayer's order parameter and the diffusion coefficient of drug are discussed.