Using a laser tweezers method, we have determined the long-range repulsive force as a function of separation between two charged, spherical polystyrene particles (2.7 microm diameter) present at a nonpolar oil-water interface. At large separations (6 to 12 microm between particle centers) the force is found to decay with distance to the power -4 and is insensitive to the ionic strength of the aqueous phase. The results are consistent with a model in which the repulsion arises primarily from the presence of a very small residual electric charge at the particle-oil interface. This charge corresponds to a fractional dissociation of the total ionizable (sulfate) groups present at the particle-oil surface of approximately 3 x 10(-4).

A new synthetic route to functionalized single walled carbon nanotubes (SWNTs) via supramolecular interactions using a specifically designed naphthalenediimide (NDI) nanoreceptor is demonstrated. The tendency of the NDI to spontaneously form composites with carbon nanomaterials leads to fluorescent amino acid tagged SWNTs, which are dispersible in widely accessible organic solvents (CHCl 3 , DMSO) as well as in biocompatible cell medium (EMEM, Eagle's modified essential medium). The X-ray crystal structure of the first iodine-tagged and amino acid-functionalized NDI molecule, designed especially to facilitate the high resolution transmission electron microscopy (HR TEM) imaging whilst retaining its ability to self-assemble into a nanodimensional receptor in weakly polar solvents, is also described. A new hybrid material, NDI@SWNT, was prepared and characterized as dispersed in organic solvents and aqueous media and in the solid state by HR TEM, tapping mode atomic force microscopy (TM AFM), scanning electron microscopy (SEM), circular dichroism, Raman and fluorescence spectroscopies (steady-state single and two-photon techniques). We have been interested in the design and spectroscopic investigation of new nanomaterials with light emitting properties.[67] The NDI nanotubular receptor recently developed [55] should have the ability to bind via donor-acceptor interactions to carbon nanomaterials, in an analogous manner to that found in the exciting new hybrids containing perylenes in SWNTselectron acceptor composites for photovoltaic applications, reported by the groups of Hirsch [12][13][14] and Guldi.[14]We report our investigations at the formation of a new nanohybrid, denoted NDI@SWNT, in solution and on a preparative scale. We report here for the first time, the recognition and coating of the aromatic surface of ultra-purified SWNTs (provided by Thomas Swan Ltd, Elicarb SWNTs, and further steampuriffied to ensure they are free of catalytic impurities or carbonaceous materials from the nanotube synthesis, Supplementary Information) by a new iodine-and amino acid-derivatized NDI. Investigations into the properties of the new material synthesized (in bulk and in dispersions in CHCl 3 , EtOH, DMSO and serum free aqueous cell culture media such as EMEM) have been carried out by Raman, circular dichroism, FT IR, UV-vis-NIR and fluorescence spectroscopies and imaged at the nanoscale by HR TEM, SEM, EDS and TM AFM. The cellular translocation of the resulting NDI@SWNT complex was investigated by a combination of fluorescence microscopy techniques including fluorescence lifetime imaging and cytotoxicity assays (MTT) in cancerous and non-cancerous cell lines. Here we have used such techniques to probe the integrity of a new nanocomposite denoted NDI@SWNT in vitro. Such an approach could aid the future understanding of the mechanism of action of supramolecular materials at the cellular level and improve the synthetic design of nanohybrids for biomedical imaging and therapeutic applications. Results and Discussions Synthe...

The Golgi-associated Arabidopsis thaliana protein AtCASP may form part of a golgin-mediated tethering complex involved in anchoring plant Golgi stacks to the endoplasmic reticulum (ER).