Conformational Impact on Amino Acid-Surface π–π Interactions on a (7,7) Single-Walled Carbon Nanotube: A Molecular Mechanics Approach

On the chirality-dependent adsorption behavior of volatile organic compounds on carbon nanotubes

The capture and removal of volatile organic compounds (VOCs) have received extensive attention due to their toxicity and carcinogenicity. In order to extend the applications of carbon nanotubes (CNTs) in this field, a deep understanding of the interaction mechanism between VOCs and CNTs is crucial. In this article, molecular dynamics simulations are performed to systematically investigate the multi-molecule adsorption behavior of four representative VOC species on CNTs with a variety of chirality indices. Simulation results reveal that different VOC species exhibit significantly different adsorption preferences on CNTs. For both zigzag and armchair CNTs, the adsorption affinity is positively correlated with the hydrophobicity of VOC molecules and follows the order of toluene > ether > acetone > methanol. This adsorption preference is supported by the binding free energy calculations resulting from the umbrella sampling algorithm. Moreover, the adsorption affinity increases with the diameter of both zigzag and armchair CNTs. Furthermore, the effects of diameter become more significant for those VOC species possessing higher hydrophobicity. As for the effects of chirality, zigzag CNTs show greater adsorption affinity than armchair ones with similar diameters. However, simulation results also indicate that the adsorption affinity does not vary monotonically from zigzag to armchair orientations, leading to additional complexities of harvesting and elimination of VOC molecules in terms of CNTs. Results and data analysis presented in this work suggest that CNT chirality is an important factor for controlling the adsorption of harmful VOC molecules on CNT surfaces.

Noncovalent Pyrene-Polyethylene Glycol Coatings of Carbon Nanotubes Achieve in Vitro Biocompatibility

Single-walled carbon nanotubes (SWNTs) have become increasingly exploited in biological applications, such as imaging and drug delivery. The application of SWNTs in biological settings requires the surface chemistry to remain through the low solubility in aqueous media. In this research, a facile approach for the preparation of a polyethylene glycol (PEG)-coated SWNT-based nanocarrier was reported. We focused on the effect of PEG chain length and SWNT size on the cytotoxicity of PEG-coated SWNTs as a superior drug delivery nanovector. First, all-atom molecular dynamics (MD) simulations were employed to explore the stability and behavior of SWNT/pyrene-PEG (SWNT/Pyr-PEG) structures at a molecular level that is not attainable with experiments. The MD studies revealed that (i) π-π stacking interactions between the pyrene bearing PEG molecules and SWNTs are maintained in bulky situations, regardless of PEG molecular weight or SWNT size; (ii) pyrene molecules diffuse over the SWNT surface without detaching; and (iii) both short and long dynamic Pyr-PEG chains have the capability of effectively coating the SWNT surface. In light of the simulations, noncovalent (π-π stacking) assemblies of SWNT/Pyr-PEG with different molecular weights of PEG ( M_w = 2000, 5000, and 12000) were successfully fabricated and characterized. For longer PEG chains, more effective coating of SWNTs was obtained, resulting in more biocompatible SWNT/Pyr-PEG nanomaterials. The number of SWNTs coated by Pyr-PEG was highly dependent on the length of pyrene bearing PEG polymers. Moreover, the short SWNTs showed a higher amount of PEG coating with respect to the long SWNTs. Cell viability results demonstrated a dose-dependent cytotoxicity of coated SWNTs. Short SWNTs coated with longer PEG chains have low cytotoxicity to be used in in vivo studies.