Mechanical properties of multi-walled beryllium-oxide nanotubes: a molecular dynamics simulation study.

Molecular dynamic (MD) simulation was employed to take the molecular fingerprint of mechanical properties of beryllium-oxide nanotubes (BeONTs). In this regard, the effect of the radius, the number of walls (single-, double-, and triple-walled), and the interlayer distance, as well as the temperature on the Young's modulus, failure stress, and failure strain, are visualized and discussed. It was unveiled that larger single-walled BeONTs have lower Young's modulus in zigzag and armchair direction, and the highest Young's modulus was obtained for the (8,0) zigzag and (4,4) armchair SWBeONTs as of 645.71 GPa and 624.81 GPa, respectively. Unlike Young's modulus, however, the failure properties of the armchair structures were higher than those of zigzag ones. Furthermore, similar to SWBEONTs, an increase in the interlayer distance of double-walled BeONTs (DWBeONTs) led to a slight reduction in Young's modulus value, while no meaningful trend was found among failure behavior. For double-walled BeONTs (TWBeONTs), the elastic modulus was obviously higher in both armchair and zigzag directions compared to DWBeONTs.

Thermal rectification in polytelescopic Ge nanowires.

Herein we served non-equilibrium molecular dynamics (NEMD) approach to simulate thermal rectification in the mono- and polytelescopic Ge nanowires (GeNWs). We considered mono-telescopic structures with different Fat-Thin configurations (15-10 nm-nm or Type (I); 15-5 nm-nm or Type (II); and 10-5 or Type (III) nm-nm) as generic models. We simulated the variation of thermal conductivity against interfacial cross-sectional temperature as well as the direction of heat transfer, where a higher thermal conductivity correlating to thicker nanowires, and a more significant drop (or discontinuity) in the average interface temperature in the positive (or negative) direction were detected. Noticeably, interfacial thermal resistance followed the order of Type (II) (48 K/µW, maximal) ˃ Type (III) ˃ Type (I) (5 K/µW, minimal). In the second stage, a series of polytelescopic nanostructures of GeNWs were born with consecutive cross-sectional interfaces. Surprisingly, larger interfacial cross-sectional areas equivalent to smaller diameter changes along the GeNWs were responsible for higher temperature rectification. This led to a very limited thermal conductivity loss or a very high unidirectional heat transfer along the polytelescopic structures - the key for manufacturing next generation high-performance thermal diodes.

Dynamics of Antimicrobial Peptide Encapsulation in Carbon Nanotubes: The Role of Hydroxylation.

INTRODUCTION: Carbon nanotubes (CNTs) have been widely employed as biomolecule carriers, but there is a need for further functionalization to broaden their therapeutic application in aqueous environments. A few reports have unraveled biomolecule-CNT interactions as a measure of response of the nanocarrier to drug-encapsulation dynamics. METHODS: Herein, the dynamics of encapsulation of the antimicrobial peptide HA-FD-13 (accession code 2L24) into CNTs and hydroxylated CNTs (HCNTs) is discussed. RESULTS: The van der Waals (vdW) interaction energy of CNT-peptide and HCNT-peptide complexes decreased, reaching -110.6 and -176.8 kcal.Mol-1, respectively, once encapsulation of the peptide inside the CNTs had been completed within 15 ns. The free energy of the two systems decreased to -43.91 and -69.2 kcal.Mol-1 in the same order. DISCUSSION: The peptide was encased in the HCNTs comparatively more rapidly, due to the presence of both electrostatic and vdW interactions between the peptide and HCNTs. However, the peptide remained encapsulated throughout the vdW interaction in both systems. The negative values of the free energy of the two systems showed that the encapsulation process had occurred spontaneously. Of note, the lower free energy in the HCNT system suggested more stable peptide encapsulation.

Thermal conductivity of random polycrystalline BC3 nanosheets: A step towards realistic simulation of 2D structures.

Boron carbide nanosheets (BC3NSs) are semiconductors possessing non-zero bandgap. Nevertheless, there is no estimation of their thermal conductivity for practical circumstances, mainly because of difficulties in simulation of random polycrystalline structures. In the real physics world, BC3NS with perfect monocrystalline is rare, for the nature produces structures with disordered grain regions. Therefore, it is of crucial importance to capture a more realistic picture of thermal conductivity of these nanosheets. Polycrystalline BC3NS (PCBC3NSs are herein simulated by Molecular Dynamics simulation to take their thermal conductivity fingerprint applying ΔT of 40 K. A series of PCBC3NSs were evaluated for thermal conductivity varying the number of grains (3, 5, and 10). The effect of grain rotation was also modeled in terms of Kapitza thermal resistance per grain, varying the rotation angle (θ/2 = 14.5, 16, 19, and 25°). Overall, a non-linear temperature variation was observed for PCBC3NS, particularly by increasing grain number, possibly because of more phonon scattering (shorter phonon relaxation time) arising from more structural defects. By contrast, the heat current passing across the slab decreased. The thermal conductivity of nanosheet dwindled from 149 W m-1 K-1 for monocrystalline BC3NS to the values of 129.67, 121.32, 115.04, and 102.78 W m-1 K-1 for PCBC3NSs having 2, 3, 5, and 10 grains, respectively. The increase of the grain̛s rotation angle (randomness) from 14.5° to 16°, 19° and 25° led to a rise in Kapitza thermal resistance from 2⨯10-10 m2 K·W-1 to the values of 2.3⨯ 10-10, 2.9⨯10-10, and 4.7⨯ 10-10 m2 K·W-1, respectively. Thus, natural 2D structure would facilitate phonon scattering rate at the grain boundaries, which limits heat transfer across polycrystalline nanosheets.

α-Helical Antimicrobial Peptide Encapsulation and Release from Boron Nitride Nanotubes: A Computational Study.

INTRODUCTION: Antimicrobial peptides are potential therapeutics as anti-bacteria, anti-viruses, anti-fungi, or anticancers. However, they suffer from a short half-life and drug resistance which limit their long-term clinical usage. METHODS: Herein, we captured the encapsulation of antimicrobial peptide HA-FD-13 into boron nitride nanotube (BNNT) (20,20) and its release due to subsequent insertion of BNNT (14,14) with molecular dynamics simulation. RESULTS: The peptide-BNNT (20,20) van der Waals (vdW) interaction energy decreased to -270 kcal·mol-1 at the end of the simulation (15 ns). However, during the period of 0.2-1.8 ns, when half of the peptide was inside the nanotube, the encapsulation was paused due to an energy barrier in the vicinity of BNNT and subsequently the external intervention, such that the self-adjustment of the peptide allowed full insertion. The free energy of the encapsulation process was -200.12 kcal·mol-1, suggesting that the insertion procedure occurred spontaneously. DISCUSSION: Once the BNNT (14,14) entered into the BNNT (20,20), the peptide was completely released after 83.8 ps. This revealed that the vdW interaction between the BNNT (14,14) and BNNT (20,20) was stronger than between BNNT (20,20) and the peptide; therefore, the BNNT (14,14) could act as a piston pushing the peptide outside the BNNT (20,20). Moreover, the sudden drop in the vdW energy between nanotubes to the value of the -1300 Kcal·mol-1 confirmed the self-insertion of the BNNT (14,14) into the BNNT (20,20) and correspondingly the release of the peptide.

Theory for designing mechanically stable single- and double-walled SiGe nanopeapods.

Herein, we utilized molecular dynamic (MD) simulations using LAMMPS software and selecting Tersoff and Lennard-Jones potentials to design and investigate mechanical properties of (8,8), (9,9), (10,10), and (11,11) single-walled and (8,8)@(11,11) double-walled silicon-germanium (SiGe) armchair nanopeapods. The number of encapsulated fullerenes and the working temperature were changed as variables to evaluate the mechanical properties. The larger nanopeapods had lower Young's modulus and failure strain, but, surprisingly enough, no significant variation was found in failure strain values by increasing the number of Si30Ge30 cages and the temperature (300-900 K). Overall, higher mechanical properties were the case for double-walled SiGe nanopeapods and that the more the number of encapsulated cages, the lower the mechanical properties whatever the nanopeapod. Amazingly, fullerenes remained undamaged even after the SiGe nanopeapods ruptured. Thus, thermally/mechanically stable nanopeapods developed theoretically herein can be considered potential super-carriers for drug and gene encapsulation.

Fracture fingerprint of polycrystalline C3N nanosheets: Theoretical basis.

Polycrystalline carbon nanosheets are composed of several randomly rotated monocrystalline regions facing each other in grain boundaries-the cause of stress concentration-that affects the mechanics of 2D carbon nanostructures. They have been widely used in different fields, particularly in electronic devices. Herein, heterogeneous graphitic carbon nitride (C3N) was considered as typical of polycrystalline carbon nanosheets for modelling its fracture behavior. The number of grains with random configuration, temperature, and crack length were systematically changed to track the mode and the intensity of failure of model nanosheets. Molecular dynamics simulations predictions unraveled the interatomic interaction in the C-C and C-N bonds. An increase in the number of grain boundaries from 3 to 25 as well as the length of crack led to more than 70% fall in the Young's modulus of polycrystalline carbon platelets. Stress intensity factor decreased against temperature, but increased by crack length enlargement demonstrating higher fracture toughness of small cracks. This theoretical approach can be generalized to capture the unique fracture fingerprint of polycrystalline carbon structures of different types.

Boron Nitride Nanotube as an Antimicrobial Peptide Carrier: A Theoretical Insight.

INTRODUCTION: Nanotube-based drug delivery systems have received considerable attention because of their large internal volume to encapsulate the drug and the ability to penetrate tissues, cells, and bacteria. In this regard, understanding the interaction between the drug and the nanotube to evaluate the encapsulation behavior of the drug in the nanotube is of crucial importance. METHODS: In this work, the encapsulation process of the cationic antimicrobial peptide named cRW3 in the biocompatible boron nitride nanotube (BNNT) was investigated under the Canonical ensemble (NVT) by molecular dynamics (MD) simulation. RESULTS: The peptide was absorbed into the BNNT by van der Waals (vdW) interaction between cRW3 and the BNNT, in which the vdW interaction decreased during the simulation process and reached the value of -142.7 kcal·mol-1 at 4 ns. DISCUSSION: The increase in the potential mean force profile of the encapsulated peptide during the pulling process of cRW3 out of the nanotube showed that its insertion into the BNNT occurred spontaneously and that the inserted peptide had the desired stability. The energy barrier at the entrance of the BNNT caused a pause of 0.45 ns when half of the peptide was inside the BNNT during the encapsulation process. Therefore, during this period, the peptide experienced the weakest movement and the smallest conformational changes.

Atomic simulation of adsorption of SO2 pollutant by metal (Zn, Be)-oxide and Ni-decorated graphene: a first-principles study.

Due to the impact of toxic gases on human health, considerable interest has been shown in detecting noxious air pollutants, particularly sulfur dioxide (SO2), both experimentally and theoretically. This work provides new insights into the adsorbing (SO2) molecules on the surface of metal-oxide graphitic structures, i.e., Beryllium-Oxide (BeO), Zinc-Oxide (ZnO), and Ni-decorated graphene applying a first-principles study. Computational analyses suggest that the type of binding of SO2 molecule on BeO and ZnO sheets is physisorption so that binding energies of -0.405 and -0.154 eV were assigned to ZnO and BeO nanosheets in that order. The adsorption energy of SO2 on metal oxide sheets was much higher than the pristine graphene. Taking pristine graphene as an adsorbent for SO2 molecule, it was found that such nanomaterial is not an efficient adsorbent due to the weak interactions (-0.157 eV) and low electron charge transfer (0.042 e) present in SO2/graphene complex. To overcome this issue, graphene nanosheets decorated with nickel atoms were studied for interaction with SO2 molecules; the results indicate that the SO2 molecules were chemisorbed on Ni-decorated graphene sheets with an adsorption energy of -2.297 eV. Chemisorption of SO2 molecules on Ni-decorated graphene sheets was proven by the strong orbital hybridization between Ni 3d and sulfur 3p orbitals in the Projected Density of States (PDOS) plot. This work provides useful information about SO2 adsorption on Ni-decorated graphene sheets in order to develop a new class of gas sensing devices. Superior chemisorption of SO2 on Ni-decorated graphene sheets compared to the physical adsorption on BeO and ZnO sheets makes Ni-decorated graphene a potential candidate for detecting SO2 molecules.

Adsorption of hazardous atoms on the surface of TON zeolite and bilayer silica: a DFT study.

In the present study, the adsorption of two types of hazardous atoms including arsenic and lead with TON zeolite and bilayer silica (2D-SiO2) have been investigated by employing Ab initio-based density functional theory (DFT) calculations. To reach a full structural optimization and the most stable configuration, four sites were considered for TON zeolite as well as five sites for 2D-SiO2, and adsorption energy along with equilibrium geometry was determined. The adsorption energies of arsenic atom on the surface of 2D-SiO2 absorbents and TON zeolite have obtained equal to and - 1.25 eV and - 2.76 eV, respectively, which both of them are chemisorption type. We also found that the adsorption of lead on the surface of 2D-SiO2 was physisorption type with the adsorption energy accounting for - 0.13 eV, while the adsorption energy between lead and TON was calculated equal to - 2.32 eV which was chemisorption type. Furthermore, our results demonstrate that the TON zeolite was more capable of adsorbing hazardous atoms compared with 2D-SiO2 due to having greater adsorption energy. The adsorption of arsenic on the 2D-SiO2 and TON adsorbents is also stronger than those of lead atom. Furthermore, we modeled and considered graphene, as a common adsorbent nanostructure, to compare and validate the accuracy of our simulations and obtained results. Finally, the electronic density of states (DOS) calculations and charge analysis were done by the use of Mulliken method, and the results confirmed those results that had already been obtained from adsorption energies. Graphical abstract.

Mechanical, electronic and stability properties of multi-walled beryllium oxide nanotubes and nanopeapods: a density functional theory study.

Single-, double-, and triple-walled beryllium oxide nanotubes (BeONTs) along with BeO nanopeapods were simulated and geometrically optimized under the density functional theory (DFT) framework to investigate their Young's modulus, electronic properties, and stability. We found better properties in single-walled nanotubes, either their electronic or mechanical properties, than other mentioned nanotubes. Increase in the radius and inter-wall distance made an overall decrease in the Young's modulus of SW and DW BeONTs. The highest obtained modulus of SWBeONTs and DWBeONTS was calculated for structures (14,0) and (8,0)@(14,0) with the magnitudes of 700.12 Gpa and 712.24 Gpa, respectively. In addition, increasing the wall number from one to two resulted to significant growth in Young's modulus of DWBeONTs while created no significant difference between DWBeONTs and TWBeONTs. Bandgap energy of single-walled nanotubes was higher than those of double- and triple-walled nanotubes, and the bandgap showed consistent soar in both SW and DW BeONTs via increase in the radius and inter-wall distance, respectively. Furthermore, considering nanopeapods with various interlayer distances revealed that the Young's modulus and energy gap behavior of these structures were similar to what we observed in SWBeONTs. However, nanopeapods showed weaker mechanical and semiconducting properties compared with SWBeONTs. Moreover, calculating the formation energies of all under consideration structures revealed a reduction of formation energy via an increase in the dimension of single-walled nanotubes, an increase in the dimension of nanotubes via adding more walls, and an increase in the dimension of peapod structures as well, and the bigger structures are more stable than smaller ones.