Self-Assembled Molecules – New Kind of Protein Ligands: Supramolecular Ligands

immunotargeting techniques; ligands; intramolecular immunological signals; congo red amyloid

Dispersibility of and adsorption on functionalized carbon nanotubes

As the applications of carbon nanotubes (CNTs) proliferate, mass production and widespread use of these nanocarbons will continue to rise. While raw, unrefined, and hydrophobic carbon nanotubes tend to settle out of aqueous media/environments, water dispersible, functionalized CNTs (F-CNTs) will contaminate water resources and will also be highly bioavailable on exposure. Therefore, there is a need to develop an understanding of the fate of F-CNTs in aqueous media. The colloidal behavior of aqueous dispersions of F-CNTs formed via carboxylation and polymer wrapping with polyvinyl pyrrolidone (PVP) is investigated. The presence of polymer on the nanotube surface provides steric stabilization, and the aggregation behavior of the colloidal system is quite different from its covalently functionalized analog. Based on hydrophobicity index (HI), particle size distribution, zeta potential as well as the aggregation kinetics studies using time-resolved dynamic light scattering, the PVP wrapped CNT is less prone to agglomeration, It is however, less stable in the long term, which is attributed to the partial unwrapping of the polyvinyl pyrrolidone layer on the CNT surface. CNTs represent a diverse group of nanotubes that vary in size, shape and chirality. Since size alters many of the properties of CNTs, it may also affect their fate and transport and is an important parameter when CNTs are in consideration as pollutants. Size dependent colloidal behavior of aqueous dispersions of carboxylated multiwall carbon nanotubes (c-MWCNTs) is presented. While the aspect ratio does not show any definite correlation, the HI, zeta potential and aggregation kinetics show dependence on the length of the c-MWCNTs. The shorter c-MWCNTs show significantly lower HI values, smaller particle aggregates, higher absolute zeta potential values and higher critical coagulation concentrations (ccc) in the presence of electrolytes. The diameter of the short c-MWCNTs does not appear to influence their aggregation behavior. The longer c-MWCNTs however, show a dependence on diameter where stability decreases with increasing CNT diameter. The potential for contaminant specific functionalization of CNTs for water purification is explored. The adsorptive removal of arsenic from water using multiwall carbon nanotube-metal oxide hybrids (MWCNT-ZrO2 and Fe-MWCNT) is presented. The synthesis of the sorbent was facilitated by the high degree of nanotube functi onal ization using a microwave assisted process, and controlled assemblies of iron oxide and zi rconi a are possible where the MWCNT serve as an effective support for the oxides. Metal oxide loadings of up to 11% per carbon atom are achieved and the hybrids are effective in arsenic removal to below drinking water standard levels of 10 μg L-1. Equilibrium and kinetic modeling indicate a pseudo-second order sorption process fitting both the Langmuir and Freundlich isotherms. Regeneration data show that both sorbent materials can be used for effective arsenic removal in a cycl able fashion

Evaluation of the purity and dispersion of single walled carbon nanotubes as potential pharmaceutical excipients

Single walled carbon nanotubes (SWNTs) are considered potential biomedical materials because of their flexible structure, hollow interior for fluidic transport, propensity for functionalization of the exterior walls, and biocompatibility. Research into exploiting these properties has focused on SWNTs as building blocks for novel drug-delivery systems, dosage forms, and biomedical substrates. However, the use of the internal nanochannels as conduits for trans-membrane drug delivery has not been explored. This research was initially designed to explore the latter. It is postulated that due to their mechanical strength and the presence of an internal conduit, SWNTs can be used for nanofluidic transport. Using a magnetic field, the magnetically responsive SWNT are driven into intact stratum corneum, creating nanochannels, for trans-membrane drug delivery. Initial studies showed however that a bottleneck is the aggregation of SWNTs on the surface of stratum corneum. To achieve trans-membrane nanofluidic delivery, the SWNTs have to be well dispersed in an appropriate pharmaceutical medium, and the SWNT have to be of high purity. Similarly, the presence of impurities in SWNTs, and the dispersion state of these materials in pharmaceutical solvents may give an insight into the discrepancies in toxicity that is reported. The purity of five commercially available SWNTs (AP-SWNT and P2-SWNT, from Carbon Solutions Inc, HMS-SWNT from Helix Materials, and NA-SWNT from Nanostructured and Amorphous Materials Inc. and CT-SWNT from ChepTubes Inc.) were analyzed by raman and electron dispersive x-ray spectroscopy (EDS) spectroscopy. Secondly, the dispersion states of SWNTs in various pharmaceutical solvents were evaluated by ultraviolet (UV) spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), zeta potential, and Raman spectroscopy to identify potential agents for exfoliation of SWNTs in selected pharmaceutical solution. SWNTs were dispersed in various solvents (water, propylene glycol [PG], dimethylsulfoxide [DMSO], and ethanol) as well as in 0.1% w/v aqueous solutions of anionic, cationic and neutral surfactants at a SWNT concentration of 0.1 mg/mL. SWNT suspensions described as dispersed yielded an evenly coloured suspension with no visible precipitate. The most stable dispersions were obtained with the gemini surfactants, which were confirmed by SEM observation of exfoliated SWNTs. Zeta (î) potential measurements of the fully dispersed SWNTs showed typical values of greater than +30 mV, while non-dispersed samples were less than +20 mV. SEM images of the dispersed solution showed the presence of exfoliated SWNTs compared to the aggregated SWNT clusters observed in non-dispersed systems. Raman spectra of dispersed SWNTs showed G-band peak shifts (to higher wavelengths), confirming the presence of exfoliated SWNTs. Even though the purity of SWNT did not correlate with amount of SWNT in dispersion, exfoliation of bundled SWNTs was accompanied by an increase in UV absorbance of the dispersion, with maximum exfoliation determined by a relatively stable UV absorbance. As pharmaceutical excipients, we have demonstrated that gemini surfactants are suitable dispersing agents for SWNTs, and shown that the dispersion of SWNT for gemini surfactants (12-3-12) is achieved below the critical micelle concentration. The dispersion of SWNT bundles into individual strands is the first crucial step towards their use in biological systems as drug carriers

Surfactant Assisted Dispersion of Single-Walled Carbon Nanotubes in Polyvinylpyrrolidone Solutions

Obtaining stable aqueous dispersions is one of the main challenges hindering a widespread and effective use of single-walled carbon nanotubes (SWNT) in many applications. Although it has been recognized that their versatility makes them an extremely attractive material, the unique molecular structure that gives SWNTs their unmatched electronic, mechanical, and thermal properties is also responsible for strong van der Waals interactions. This, combined with extremely high aspect ratios and flexibility, causes SWNTs to adhere strongly into tightly bundled ropes. In these bundles, SWNTs are not as useful as their linearized unbundled equivalents. Thus, in order to take advantage of their properties effectively, SWNTs must be debundled. In this contribution we will report the characterization of a novel non-covalent system using the surfactant, cetyltrimethylammonium bromide (CTAB) and the polymer, polyvinylpyrrolidone (PVP) at different molecular weights. Initial tests using Vis-NIR spectroscopy showed that although individually these molecules are poor dispersers of SWNTs, they show a synergic effect when combined for all cases. We have probed for a mechanism using a battery of characterization techniques including Vis-NIR, atomic force microscopy (AFM), viscosity, dynamic light scattering (DLS), surface tension, and pH. Our data suggests that CTAB binds normally to nanotubes while PVP is augmenting dispersion through a physical mechanism specifically linked to its hydrodynamic radius. We propose our approach as a facile way of augmenting current nanotube dispersion techniques, potentially allowing for increased usage in the world today

Fonctionnalisations de nanotubes de carbone : étude expérimentale et théorique

Dans ce travail nous avons exploré des nouvelles voies pour synthétiser et fonctionnaliser des nanotubes de carbone. des tube de diamètreet de longueur bien définie ont été obtenu en utlisant une approche "Template" pour la synthèse. Par la suite, des nanotubes ont été solubilisés en utlisant une approche à la fois simple et originale. Enfin, nous avons pu mettre au point une technique permettant de fonctionnaliser sélectivement une extrémité de ces nanotubes avec une couche métallique en utilisant le concept d'électrochimie bipolaire. Le travail a été complété par une étude théorique de la réactivité des objet

Hydrogen Bonding Donor–Acceptor Carbon Nanostructure

The natural process of photosynthesis is paradigmatic in converting sunlight into energy. This complicated process requires a cascade of energy- and electron-transfer events in a highly organised matrix of electron–donor, electron–acceptor and antennae units and has prompted researchers to emulate it. In fact, energy- and electron-transfer processes play a pivotal role in molecular-scale optoelectronics. In this chapter we compile a number of remarkable examples of noncovalent aggregates formed by the combination of carbon-based electroactive species (fullerenes and carbon nanotubes) hydrogen bonded with a variety of moieties. We will show that: (a) the connection of complementary electroactive species by means of H bonds in C60-based donor–acceptor ensembles is at least as efficient as that found in covalently connected systems; (b) hydrogen-bonding fullerene chemistry is a versatile concept to construct supramolecular polymers, and (c) H-bonding interactions is contributing to create very appealing carbon-nanotube-based donor–acceptor supramolecular architectures

Carbon Nanotubes: Functionalisation And Their Application In Chemical Sensors

Carbon nanotubes (CNTs) have been recognised as a promising material in a wide range of applications, from safety to energy-related devices. However, poor solubility in aqueous and organic solvents has hindered the utilisation and applications of carbon nanotubes. As studies progressed, the methodology for CNTs dispersion was established. The current state of research in CNTs either single wall or multiwall/polymer nanocomposites has been reviewed in context with the various types of functionalisation presently employed. Functionalised CNTs have been playing an increasingly central role in the research, development, and application of carbon nanotube-based nanomaterials and systems. The extremely high surface-to-volume ratio, geometry, and hollow structure of nanomaterials are ideal for the adsorption of gas molecules. This offers great potential applications, such as in gas sensor devices working at room temperature. Particularly, the advent of CNTs has fuelled the invention of CNTbased gas sensors which are very sensitive to the surrounding environment. The presence of O2, NH3, NO2 gases and many other chemicals and molecules can either donate or accept electrons, resulting in an alteration of the overall conductivity. Such properties make CNTs ideal for nano-scale gas-sensing materials. Conductive-based devices have already been demonstrated as gas sensors. However, CNTs still have certain limitations for gas sensor application, such as a long recovery time, limited gas detection, and weakness to humidity and other gases. Therefore, the nanocomposites of interest consisting of polymer and CNTs have received a great deal of attention for gas-sensing application due to higher sensitivity over a wide range of gas concentrations at room temperature compared to only using CNTs and the polymer of interest separatel