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.

Theoretical Encapsulation of Fluorouracil (5-FU) Anti-Cancer Chemotherapy Drug into Carbon Nanotubes (CNT) and Boron Nitride Nanotubes (BNNT).

INTRODUCTION: Chemotherapy with anti-cancer drugs is considered the most common approach for killing cancer cells in the human body. However, some barriers such as toxicity and side effects would limit its usage. In this regard, nano-based drug delivery systems have emerged as cost-effective and efficient for sustained and targeted drug delivery. Nanotubes such as carbon nanotubes (CNT) and boron nitride nanotubes (BNNT) are promising nanocarriers that provide the cargo with a large inner volume for encapsulation. However, understanding the insertion process of the anti-cancer drugs into the nanotubes and demonstrating drug-nanotube interactions starts with theoretical analysis. METHODS: First, interactions parameters of the atoms of 5-FU were quantified from the DREIDING force field. Second, the storage capacity of BNNT (8,8) was simulated to count the number of drugs 5-FU encapsulated inside the cavity of the nanotubes. In terms of the encapsulation process of the one drug 5-FU into nanotubes, it was clarified that the drug 5-FU was more rapidly adsorbed into the cavity of the BNNT compared with the CNT due to the higher van der Waals (vdW) interaction energy between the drug and the BNNT. RESULTS: The obtained values of free energy confirmed that the encapsulation process of the drug inside the CNT and BNNT occurred spontaneously with the free energies of -14 and -25 kcal·mol-1, respectively. DISCUSSION: However, the lower value of the free energy in the system containing the BNNT unraveled more stability of the encapsulated drug inside the cavity of the BNNT comparing the system having CNT. The encapsulation of Fluorouracil (5-FU) anti-cancer chemotherapy drug (commercial name: Adrucil®) into CNT (8,8) and BNNT (8,8) with the length of 20 Å in an aqueous solution was discussed herein applying molecular dynamics (MD) simulation.

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.

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.

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.

Insight into the Self-Insertion of a Protein Inside the Boron Nitride Nanotube.

Nanotubes have been considered as promising candidates for protein delivery purposes due to distinct features such as their large enough volume of cavity to encapsulate the protein, providing the sustain and target release. Moreover, possessing the properties of suitable cell viabilities, and biocompatibility on the wide range of cell lines as a result of structural stability, chemical inertness, and noncovalent wrapping ability, boron nitride nanotubes (BNNTs) have caught further attention as protein nanocarriers. However, to assess the encapsulation process of the protein into the BNNT, it is vital to comprehend the protein-BNNT interaction. In the present work, the self-insertion process of the protein SmtA, metallothionein, into the BNNT has been verified by means of the molecular dynamics (MD) simulation under NPT ensemble. It was revealed that the protein was self-inserted into the BNNT through the protein-BNNT van der Waals (vdW) interaction, which descended and reached the average value of -189.63 kcal·mol-1 at 15 ns of the simulation time. The potential mean force (PMF) profile of the encapsulated protein with increasing trend, which was obtained via the pulling process unraveled that the encapsulation of the protein into the BNNT cavity proceeded spontaneously and the self-inserted protein had reasonable stability. Moreover, due to the strong hydrogen interactions between the nitrogen atoms of BNNT and hydrogen atoms of SmtA, there was no evidence of an energy barrier in the vicinity of the BNNT entrance, which resulted in the rapid adsorption of this protein into the BNNT.

Kinetics of Cross-Linking Reaction of Epoxy Resin with Hydroxyapatite-Functionalized Layered Double Hydroxides.

The cure kinetics analysis of thermoset polymer composites gives useful information about their properties. In this work, two types of layered double hydroxide (LDH) consisting of Mg2+ and Zn2+ as divalent metal ions and CO32- as an anion intercalating agent were synthesized and functionalized with hydroxyapatite (HA) to make a potential thermal resistant nanocomposite. The curing potential of the synthesized nanoplatelets in the epoxy resin was then studied, both qualitatively and quantitatively, in terms of the Cure Index as well as using isoconversional methods, working on the basis of nonisothermal differential scanning calorimetry (DSC) data. Fourier transform infrared spectroscopy (FTIR) was used along with X-ray diffraction (XRD) and thermogravimetric analysis (TGA) to characterize the obtained LDH structures. The FTIR band at 3542 cm-1 corresponded to the O-H stretching vibration of the interlayer water molecules, while the weak band observed at 1640 cm-1 was attributed to the bending vibration of the H-O of the interlayer water. The characteristic band of carbonated hydroxyapatite was observed at 1456 cm-1. In the XRD patterns, the well-defined (00l) reflections, i.e., (003), (006), and (110), supported LDH basal reflections. Nanocomposites prepared at 0.1 wt % were examined for curing potential by the Cure Index as a qualitative criterion that elucidated a Poor cure state for epoxy/LDH nanocomposites. Moreover, the curing kinetics parameters including the activation energy (Eα), reaction order, and the frequency factor were computed using the Friedman and Kissinger-Akahira-Sunose (KAS) isoconversional methods. The evolution of Eα confirmed the inhibitory role of the LDH in the crosslinking reactions. The average value of Eα for the neat epoxy was 54.37 kJ/mol based on the KAS method, whereas the average values were 59.94 and 59.05 kJ/mol for the epoxy containing Zn-Al-CO3-HA and Mg Zn-Al-CO3-HA, respectively. Overall, it was concluded that the developed LDH structures hindered the epoxy curing reactions.