Noncovalent Interaction of Methylene Blue with Carbon Nanotubes: Theoretical and Mass Spectrometry Characterization

Abstract

Noncovalent interaction of methylene blue dye cation (MB + ) with single walled carbon nanotubes (CNT) is characterized by molecular dynamics (MD) simulation, quantum chemical calculations, and laser desorption/ionization (LDI) mass spectrometry. The MD simulation of the (MB + ) n −CNT (n = 1−10) complexes in water demonstrates that the MB + cations are adsorbed on the nanotube surface in the monomeric form. MD reveals both parallel and perpendicular orientations of the MB + tricyclic plane in relation to the long axis of CNT when placed in the water environment. The interaction energy between the components of the complex in the perpendicular conformation, as determined by quantum chemical calculations at the DFT/M05-2X/6-31++G(d,p) level of theory, explains why the bending of the MB + cation at the sulfur atom weakens the π-system of bonds and allows for the perpendicular orientation to occur. It is also found that the adsorbed MB + induces positive electrostatic potential around the adjacent semicylindrical segment of the nanotube. The mainly monomolecular adsorption of the MB + cations at the CNT surface leads to the absence in the LDI mass spectra of (MB + ) n −CNT of features corresponding to products of the reduction of MB + commonly observed in the LDI mass spectra of crystalline dyes.

Complexation of aromatic drugs with single-walled carbon nanotubes

“…Close packing of the DOX/ PF/EB molecules on the surface was achieved when the longitudinal axes of the ligand and SWCNT were parallel, whereas for MB, they were perpendicular (a consequence of the MB chromophore being bent along the N-S atoms so that the shape mimics the curvature of the surface of SWCNT). The obtained structure of the MB-SWCNT complex is similar to that reported (Chagovets et al 2012). In addition, MD simulation was employed to verify the stability of such complexes by means of controlling the stability of geometry of the complex during the course of system evolution.…”

“…The hypochromic effect seen in the titration curves, as well as literature data (Chagovets et al 2012;Cheng and Adronov 2006;Gupta et al 2013;Ji et al 2009;Koh et al 2012;Nakashima 2006;Pan and Xing 2008;Rajendra et al 2004), also support the view that the main mode of ligand binding is stacking on the surface of SWCNT. It is suggested that the minimum site for ligand binding is a portion of SWCNT surface containing n carbon atoms.…”

“…Such effect has recently been demonstrated for the binding of charged ligands with neutral or negatively charged surface of C 60 molecule (Evstigneev et al 2013). The lowering of electrostatic energies in water was also reported in MD simulation of MB binding with CNT (Chagovets et al 2012). The compensatory nature of the intermolecular and to water interactions for the case of ligand-SWCNT complexation is most clearly seen in Table 2 with respect to the components of the VDW energy, viz.…”

“…Let L 0 be the total molar concentration of the ligand, bound to the SWCNT surface in the non-cooperative mode; indirect justification of this assumption comes from MD simulation (Chagovets et al 2012), which reports the random monomolecular adsorption of MB on the surface of CNT. In addition the fraction of agglomerated SWCNTs in solution was found to be small as evidenced from AFM measurements (see above).…”

“…Nowadays, several novel CNT-based tumortargeted drug delivery systems have been developed demonstrating ability to suppress proliferation of cancer cells, thus providing a new promising approach in antitumor therapy (Adeli et al 2013;Chen et al 2008). As a consequence, investigations of CNT complexation with antibiotics (Ji et al 2009(Ji et al , 2010Wang et al 2009), dyes (Chagovets et al 2012;Gupta et al 2013;Koh et al 2012;Kuo et al 2008;Liu et al 2008;Machado et al 2012;Yao et al 2010), and other types of ligands (Pan and Xing 2008;Yan et al 2008;Yang and Xing 2010), have been undertaken with an aim to determine the binding parameters in solution.…”