Carbon Nanotubes and Graphene Promote Pyrolysis of Free-Base Phthalocyanine

Unsubstituted phthalocyanines (including free-base H₂Pc and many of its metal complexes) are among the most stable organic compounds. They can sublime without decomposition under reduced pressure and temperatures of up to 550 °C. This property was previously employed to design a novel approach to noncovalent functionalization of pristine single-walled carbon nanotubes (SWNTs) with 3d metal(II) phthalocyanine complexes. However, when we attempted to use the same sublimation protocol to prepare a SWNTs-H₂Pc hybrid, an unexpected side effect of partial H₂Pc pyrolysis was detected, phthalonitrile being a main decomposition product, under the conditions when H₂Pc is supposed to be totally stable. By using density functional theory calculations, we offer an explanation for the thermal behavior of H₂Pc based on its covalent attachment to the pentagonal-ring topological defects, which are very common in all graphene-derived carbon nanomaterials and capable of reacting with amines via nucleophilic addition process.

One-step nondestructive functionalization of graphene oxide paper with amines

Direct functionalization of prefabricated free-standing graphene oxide paper (GOP) is the only approach suitable for systematic tuning of its mechanical, thermal and electronic characteristics. However, the traditional liquid-phase functionalization can compromise physical integrity of the paper-like material up to its total disintegration. In the present paper, we attempted to apply an alternative, solvent-free strategy for facile and nondestructive functionalization of GOP with 1-octadecylamine (ODA) and 1,12-diaminododecane (DAD) as representatives of aliphatic amines, and with 1-aminopyrene (AP) and 1,5-diaminonaphthalene (DAN) as examples of aromatic amines. The functionalization can be carried out under moderate heating at 150–180 °C for 2 h in vacuum, and proceeds through both amidation and epoxy ring opening reactions. Comparative characterization of pristine and amine-modified GOP samples was carried out by means of Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopy, thermogravimetric and differential thermal analysis, scanning electron and atomic force microscopy. In addition, we compared stability in water, wettability, electrical conductivity and elastic (Young's) modulus of GOP samples before and after functionalization. The highest content of amine species was obtained in the case of GOP-ODA, followed by GOP-DAD, GOP-AP and GOP-DAN. The functionalization increased mechanical and thermal stability, as well as the electrical conductivity of GOP. The magnitude of each effect depends on the structure of amine employed, which allows for tuning a given GOP characteristic. Morphological characterization showed that, compared to pristine graphene oxide paper, amine-modified mats become relatively ordered layered structures, in which individual GO sheets are organized in a near-parallel fashion.

Solvent-free functionalization of graphene oxide paper with amines is facile, nondestructive, and attractive from economic and environmental points of view.

Interactions of the innate immune system with carbon nanotubes

The therapeutic application of nanomaterials requires that they are biocompatible and can reach the desired target. The innate immune system is likely to be the first defence machinery that would recognise the nanomaterials as 'non-self'. A number of studies have addressed the issue of how carbon nanotubes (CNTs) interact with phagocytic cells and their surface receptors that can impact on their intracellular processing and subsequent immune response. In addition, soluble innate immune factors also get involved in the recognition and clearance of CNTs. The interaction of CNTs with the complement system, the most potent and versatile innate immune mechanism, has shed interesting light on how complement activation on the surface of CNTs can modulate their phagocytosis and effector cytokine response. The charge or altered molecular pattern on the surface of CNTs due to functionalization and derivatization can also dictate the level of complement activation and subsequent inflammatory response. It is becoming evident that complement deposition may facilitate phagocytic uptake of CNTs through receptor routes that leads to dampening of pro-inflammatory response by complement-receptor bearing macrophages and B cells. Thus, recombinant complement regulators decorated on the CNT surface can constructively influence the therapeutic strategies involving CNTs and other nanoparticles.

Spectroscopic studies on covalent functionalization of single-walled carbon nanotubes with glycine

Single-walled carbon nanotubes (SWCNTs) have a great potential in a wide range of applications, but faces limitation in terms of dispersion feasibility. The functionalization process of SWCNTs with the amino acid, glycine involves oxidation reaction using a mild aqueous acid mixture of HNO3 and H2SO4 (1:3), via ultrasonication technique and the resulted oxidized SWCNTs were again treated with the amino acid glycine suspension. The resulted glycine functionalized carbon nanotubes have been characterized by XRD, UV-Vis, FTIR, EPR, SEM, and EDX, spectroscopic techniques. The enhanced XRD peak (002) intensity was observed for glycine functionalized SWCNTs compared with oxidized SWCNTs, which is likely due to sample purification by acid washing. The red shift was observed in the UV-Vis spectra of glycine functionalized SWCNTs, which reveals that the covalent bond formation between glycine molecule and SWCNTs. The functional groups of oxidized SWCNTs and glycine functionalized SWCNTs were identified and assigned. EPR results indicate that the unpaired electron undergoes reduction process in glycine functionalized SWCNTs. SEM images show that the increase in the diameter of the SWCNTs was observed for glycine functionalized SWCNTs, which indicates that the adsorption of glycine molecule on the sidewalls of oxidized SWCNTs. EDX elemental micro analysis confirms that the nitrogen element exists in glycine functionalized SWCNTs. The functionalization has been chosen due to CONH bioactive sites in glycine functionalized SWCNTs for future applications.

Complement activation by carbon nanotubes

Carbon nanotube interaction with an important part of the innate immune system, complement, needs to be taken into account when envisaging their use in biomedical applications. Carbon nanotubes (CNTs) and other synthetic materials are recognized by various components of the complement system in human or mammalian blood and also collectins in the lungs. Modification of the surface chemistry of CNTs alters their interactions with complement proteins and collectins. Functionalizations of CNTs which have been tested so far do not completely prevent complement activation or plasma protein binding. The interaction of the functionalized CNTs with the complement system proteins in blood may influence the adhesion of CNTs to phagocytic cells and red blood cells. Excessive activation of complement can have a harmful effect on human tissues and therefore significantly limit CNT applications in biomedicine.