Molecular Dynamics Study of Stability and Diffusion of Graphene-Based Drug Delivery Systems

Graphene, a two-dimensional nanomaterial with unique biomedical properties, has attracted great attention due to its potential applications in graphene-based drug delivery systems (DDS). In this work graphene sheets with various sizes and graphene oxide functionalized with polyethylene glycol (GO-PEG) are utilized as nanocarriers to load anticancer drug molecules including CE6, DOX, MTX, and SN38. We carried out molecular dynamics calculations to explore the energetic stabilities and diffusion behaviors of the complex systems with focuses on the effects of the sizes and functionalization of graphene sheets as well as the number and types of drug molecules. Our study shows that the binding of graphene-drug complex is favorable when the drug molecules and finite graphene sheets become comparable in sizes. The boundaries of finite sized graphene sheets restrict the movement of drug molecules. The double-side loading often slows down the diffusion of drug molecules compared with the single-side loading. The drug molecules bind more strongly with GO-PEG than with pristine graphene sheets, demonstrating the advantages of functionalization in improving the stability and biocompatibility of graphene-based DDS

Multiwalled carbon nanotubes grown in hydrogen atmosphere : An x-ray diffraction study

X-ray diffraction study of multiwalled carbon nanotube (MWNT) grown by arc discharge in hydrogen atmosphere is presented. It is found that the thermal-expansion coefficient along the radial direction of MWNT is widely distributed in a range from 1.6×10-5 K-1 to 2.6×10-5 K-1, indicating the existence of both of Russian doll MWNT and highly defective MWNT. Russian doll MWNT is suggested to have the outer diameter less than ∼100  Å . Thicker MWNT's are typically highly defective, and may have the jelly roll (scroll) or defective polygonal structure consisting of flat graphite domains

Electrochemical detection of norepinephrine based on Ag/Fe decorated single walled carbon nanotubes

547-553A sensitive norepinephrine (NE) sensor using silver and iron nanoparticles decorated single walled carbon nanotubes modified glassy carbon electrode (Ag-Fe/SWCNTs/GCE) for electrochemical detection of trace NE, has been developed. The Ag-Fe/SWCNTs have been prepared using DC arc discharge evaporation and characterized by transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The oxidation peak current of NE at Ag-Fe/SWCNTs modified GCE has been greatly increased than that of SWCNTs modified GCE and unmodified GCE. The designed sensor successfully detected NE with good reproducibility and stability, indicating its promising practical applicability. Impressively, the detection limit of NE on Ag-Fe/SWCNTs/GCE has been found to be 5 μM. Owing to the Ag-Fe/SWCNTs specific catalysis of the NE oxidation, NE can be detected selectively in the presence of high concentrations of ascorbic acid (AA). Consequently, this strategy offers a potential, convenient, low-cost, and sensitive sensor for NE diagnosis

Changing the Phosphorus Allotrope from a Square Columnar Structure to a Planar Zigzag Nanoribbon by Increasing the Diameter of Carbon Nanotube Nanoreactors

Elemental phosphorus nanostructures are notorious for a large number of allotropes, which limits their usefulness as semiconductors. To limit this structural diversity, we synthesize selectively quasi-1D phosphorus nanostructures inside carbon nanotubes (CNTs) that act both as stable templates and nanoreactors. Whereas zigzag phosphorus nanoribbons form preferably in CNTs with an inner diameter exceeding 1.4 nm, a previously unknown square columnar structure of phosphorus is observed to form inside narrower nanotubes. Our findings are supported by electron microscopy and Raman spectroscopy observations as well as ab initio density functional theory calculations. Our computational results suggest that square columnar structures form preferably in CNTs with an inner diameter around 1.0 nm, whereas black phosphorus nanoribbons form preferably inside CNTs with a 4.1 nm inner diameter, with zigzag nanoribbons energetically favored over armchair nanoribbons. Our theoretical predictions agree with the experimental finding

Origin of Dirac Cones in SiC Silagraphene: A Combined Density Functional and Tight-Binding Study

The formation of Dirac cones in electronic band structures via isomorphous transformation is demonstrated in 2D planar SiC sheets. Our combined density functional and tight-binding calculations show that 2D SiC featuring C–C and Si–Si atom pairs possesses Dirac cones (DCs), whereas an alternative arrangement of C and Si leads to a finite band gap. The origin of Dirac points is attributed to bare interactions between Si–Si bonding states (valence bands, VBs) and C–C antibonding states (conduction bands, CBs), while the VB–CB coupling opens up band gaps elsewhere. A mechanism of atom pair coupling is proposed, and the conditions required for DC formation are discussed, enabling one to design a class of 2D binary Dirac fermion systems on the basis of DF calculations solely for pure and alternative binary structures