Over the course of the past decade, there has been growing interest in the development of different types of membranes composed of carbon nanotubes (CNTs), including buckypapers and composite materials, for an ever-widening range of filtration applications. This article provides an overview of how different types of CNT membranes are prepared and the results obtained from investigations into their suitability for different applications. The latter involve the removal of small particles from air samples, the filtration of aqueous solutions containing organic compounds and/or bacteria, and the separation of individual liquids present in mixtures. A growing number of reports have demonstrated that the incorporation of CNTs into composite membranes confers an improved resistance to fouling caused by biomacromolecules and bacteria. These results are discussed, along with evidence that demonstrates it is possible to further reduce fouling by taking advantage of the inherent conductivity of composite membranes containing CNTs, as well as by using different types of electrochemical stimuli.

As part of a program of preparing metal complexes which exhibit unique affinities towards different DNA structures, we have synthesised the novel Schiff base complex N,N′-bis-4-(hydroxysalicylidine)meso-diphenylethylenediaminenickel(II) (4), via the reaction of meso-1,2-diphenylethylenediamine and 2,4-dihydroxybenzaldehyde. This compound was subsequently reacted with 1-(2-chloroethyl)piperidine or 1-(2-chloropropyl)piperidine, to afford the alkylated complexes N,N′-bis-(4-((1-(2-ethyl)piperidine)oxy)salicylidine)meso-1,2-diphenylethylenediaminenickel(II) (5) and N,N′-bis-(4-((1-(3-propyl)piperidine)oxy)-salicylidine)meso-1,2-diphenylethylenediaminenickel(II) (6), respectively. These complexes were characterised by microanalysis and X-ray crystallography in the solid state, and in solution by ¹H and ¹³C NMR spectroscopy. Electrospray ionisation mass spectrometry (ESI-MS) was used to confirm the identity of (5) and (6). The affinities of (5) and (6) towards a discrete 16 mer duplex DNA molecule, and examples of both tetramolecular and unimolecular DNA quadruplexes, was explored using a variety of techniques. In addition, the affinity of two other complexes (2) and (3), towards the same DNA molecules was examined. Complexes (2) and (3) were prepared by methods analogous to those which afforded (5) and (6), however 1,2-phenylenediamine was used instead of meso-1,2-diphenylethylenediamine in the initial step of the synthetic procedure. The results of ESI-MS and DNA melting temperature measurements suggest that (5) and (6) exhibit a lower affinity than (2) and (3) towards the 16 mer duplex DNA molecule, while circular dichroism (CD) spectroscopy suggested that none of the four complexes had a major effect on the conformation of the nucleic acid. In contrast, ESI-MS and CD spectroscopy suggested that both (5) and (6) show significant binding to a tetramolecular DNA quadruplex. The results of ESI-MS and Fluorescence Resonance Energy Transfer (FRET) assays indicated that (5) and (6) did not bind as tightly to a unimolecular DNA quadruplex, although both complexes had a major effect on the CD spectrum of the latter. These results highlight that the presence of the meso-1,2-diphenylethylenediamine moiety in metal complexes of this type may provide a general method for instilling selectivity for some DNA quadruplexes over dsDNA.

The effect of varying preparation conditions on the properties of buckypapers made using single-walled carbon nanotubes (SWNTs) was systematically investigated. Changing the sonication time, final dispersion volume or membrane filter used to prepare SWNT–Triton X-100 buckypapers all generally had only a small influence on the density, thickness, contact angle and electrical conductivity of the resulting material. More significant changes were noted when the effects of variations in the above preparation conditions on the mechanical properties and surface morphology of SWNT–Triton X-100 buckypapers were investigated. However, the largest changes in properties were found when various biopolymers (bovine serum albumin, lysozyme, gellan gum and chitosan) were used instead of Triton X-100 to prepare dispersions from which the buckypapers were made. It was observed that the electrical conductivity of the buckypapers decreased as the molecular mass of the biopolymer dispersant used increased, whereas the mechanical properties of the materials showed significant improvements.

The ability of macrocyclic ligands to facilitate formation of dispersions of single-walled carbon nanotubes (SWNTs) was investigated using a combination of absorption spectrophotometry and optical microscopy. Vacuum filtration of aqueous dispersions containing SWNTs and various macrocyclic ligands (derivatised porphyrin, phthalocyanine, cyclodextrin and calixarene) afforded self-supporting membranes known as buckypapers. Microanalytical data and energy dispersive X-ray spectra were obtained for these buckypapers and provided evidence for retention of the macrocyclic ligands within the structure of the membranes. The electrical conductivities of the membranes varied between 30 ± 20 and 220 ± 60 S cm⁻¹, while contact angle analysis revealed they all possessed hydrophilic surfaces. The mechanical properties of buckypapers prepared using macrocyclic ligands as dispersants were shown to be comparable to that of a benchmark material prepared using the surfactant Triton X-100 (Trix). Incorporation of the macrocyclic ligands into SWNT buckypapers was found to increase their permeability up to ten-fold compared to buckypapers prepared using Trix. No correlation was observed between the water permeability of the membranes and the average size of either their surface or internal pores. However, the water permeability of the membranes was found to be inversely dependent on their surface area.

Compounds that can bind to and stabilize quadruplex DNA structures in telomeres, or induce formation of such structures from ssDNA, represent an attractive general approach to the treatment of cancer. Until recently most effort in this area has been directed towards the synthesis of organic compounds for this purpose. More recently there has been growing recognition that metal complexes offer a number of potential advantages for the preparation of lead complexes that bind with high affinity and selectivity for quadruplex DNA. This review seeks to discuss the work that has been reported in this area to date. While most early studies focused on metal complexes of porphyrin ligands, during the past 4 years there has been a dramatic increase in the number of papers in the literature examining the potential of mononuclear complexes of a variety of other ligands, particularly Schiff base ligands and those based on phenanthroline, as quadruplex DNA binders and telomerase inhibitors. In addition, there has been growing interest in exploiting supramolecular chemistry to prepare novel multinuclear complexes that bind to this new drug target.