Understanding the relative binding ability of hydroxyfullerene to divalent and trivalent metals.

Metal contamination of water is a serious challenge faced by environmental chemists, but there is also economic value in the removal of metals for recycling or extraction. Our prior observation that hydroxyfullerenes [C60O(x)(OH)y](n-) act as chelate agents to Fe(3+) suggests that these material, or derivatives, may be used for co-precipitation. We report the removal of main group (Al(3+), Ag(+), Ca(2+), and Zn(2+)) as well transition metal (Fe(3+), Co(2+), Cu(2+), Mn(2+), and Ni(2+)) and lanthanide (La(3+) and Nd(3+)) ions from solution. The resulting complexes have been characterized by XPS, SEM, TEM, and DLS. The competitive binding with Fe(3+) shows that the binding affinity with hydroxyfullerenes follows the order: Zn(2+) > Co(2+) > Mn(2+) > Ni(2+) > La(3+) > Nd(3+) > Cd(2+) > Cu(2+) > Ag(+) > Ca(2+) > Fe(3+) > Al(3+). The relative binding ability is dependent on ionic radius; however, divergent trends are observed for M(2+) and M(3+), i.e., for divalent ions the binding is stronger for smaller ions, while the opposite trend is observed for trivalent ions. Previously the coordination of hydroxyfullerene to metals was assumed to be analogous to a 1,2-diol or catechol. However, while ab initio calculations using [M(catecholate)n](n-) (n = 2, 3) provide an explanation of the observed trend for M(2+), the use of cis-cis-1,3,5-cyclohexanetriol and cis-1,3-cyclohexanediol as model ligands provides insight into the relative binding efficiency for M(3+).

Catalytic epoxidation of C60 using Mo(O)2(acac)2/(t)BuOOH.

Highly oxygenated fullerenes, C(60)O(n) with 1 ≤ n ≤ 13, have been prepared by the Mo(O)(2)(acac)(2) catalysed oxidation of C(60) with (t)BuOOH. Increasing the catalyst : C(60) ratio or increasing the reaction temperature increases the yield as well shifting the product distribution to higher oxygenated products, in contrast, increasing the (t)BuOOH concentration shifts the product distribution in the opposite manner. The MALDI mass spectra of reactions containing the highest oxygenated products (n > 5) show additional peaks (not observed for C(60) under the same MS conditions) due to the cage-opened products C(x) (x = 54, 56, 58) along with their oxygenated derivatives, C(x)O(n) (x = 54, 56, 58; n = 1-3).

In vivo quantum-dot toxicity assessment.

Quantum dots have potential in biomedical applications, but concerns persist about their safety. Most toxicology data is derived from in vitro studies and may not reflect in vivo responses. Here, an initial systematic animal toxicity study of CdSe-ZnS core-shell quantum dots in healthy Sprague-Dawley rats is presented. Biodistribution, animal survival, animal mass, hematology, clinical biochemistry, and organ histology are characterized at different concentrations (2.5-15.0 nmol) over short-term (<7 days) and long-term (>80 days) periods. The results show that the quantum dot formulations do not cause appreciable toxicity even after their breakdown in vivo over time. To generalize the toxicity of quantum dots in vivo, further investigations are still required. Some of these investigations include the evaluation of quantum dot composition (e.g., PbS versus CdS), surface chemistry (e.g., functionalization with amines versus carboxylic acids), size (e.g., 2 versus 6 nm), and shape (e.g., spheres versus rods), as well as the effect of contaminants and their byproducts on biodistribution behavior and toxicity. Combining the results from all of these studies will eventually lead to a conclusion regarding the issue of quantum dot toxicity.

Systematic investigation of preparing biocompatible, single, and small ZnS-Capped CdSe quantum dots with amphiphilic polymers.

The successful transfer of nanoparticles between solvents is critical for many applications. We evaluated the impact of amphiphilic polymer composition on the size, transfer efficiency, and biocompatibility of tri-n-octylphosphine oxide/hexadecylamine-stabilized semiconductor ZnS-capped CdSe and CdS-capped CdTe(x)Se(1-x) quantum dots (QDs). We also investigated the adsorption of various proteins onto the surface of these QDs and studied the effect of surface chemistry on non-specific protein binding. The results from these studies will have implications in the design of QDs and other nanoparticles for biological and biomedical applications.

Solubilization of single-wall carbon nanotubes in Organic solvents without sidewall functionalization.

Single walled carbon nanotubes (SWNTs) may be made soluble in a range of organic solvents without sidewall functionalization via their reduction by Na/Hg amalgam in the presence of dibenzo-18-crown-6. The [Na(dibenzo-18-crown-6)]n[SWNT] complex has been characterized by UV-Visible, Raman, and AFM and is consistent with no additional sidewall functionalization as compared with raw SWNTs, while MALDI-MS shows the presence of the [Na(dibenzo-18-crown-6)]+ ion. Solubility is greatest in CH2Cl2 and DMF being comparable to surfactant dispersed SWNTs, however, measurable solubilities are also observed in hexane, toluene, and alcohols. Reaction with alkyl halides (bromohexane, 1-iodododecane) yields alkyl functionalized SWNTs (i.e., C6H11-SWNTs and C12H25-SWNTs) with an C(SWNT):alkyl ratio (ca. 40:1) significantly lower than that observed by the analogous reaction of alkyl halides with reduced SWNTs formed by the Billups method in liquid ammonia.

A study of the formation, purification and application as a SWNT growth catalyst of the nanocluster [HxPMo12O40[subset]H4Mo72Fe30(O2CMe)15O254(H2O)98].

The synthetic conditions for the isolation of the iron-molybdenum nanocluster FeMoC [HxPMo12O40 [subset]H4Mo72Fe30(O2CMe)15O254(H2O)98], along with its application as a catalyst precursor for VLS growth of SWNTs have been studied. As-prepared FeMoC is contaminated with the Keplerate cage [H4Mo72Fe30(O2CMe)15O254(H2O)98] without the Keggin [HxPMo12O40]n- template, however, isolation of pure FeMoC may be accomplished by Soxhlet extraction with EtOH. The resulting EtOH solvate is consistent with the replacement of the water ligands coordinated to Fe being substituted by EtOH. FeMoC-EtOH has been characterized by IR, UV-vis spectroscopy, MS, XPS and 31P NMR. The solid-state 31P NMR spectrum for FeMoC-EtOH (delta-5.3 ppm) suggests little effect of the paramagnetic Fe3+ centers in the Keplerate cage on the Keggin ion's phosphorous. The high chemical shift anisotropy, and calculated T1 (35 ms) and T2 (8 ms) values are consistent with a weak magnetic interaction between the Keggin ion's phosphorus symmetrically located within the Keplerate cage. Increasing the FeCl2 concentration and decreasing the pH of the reaction mixture optimizes the yield of FeMoC. The solubility and stability of FeMoC in H2O and MeOH-H2O is investigated. The TGA of FeMoC-EtOH under air, Ar and H2 (in combination with XPS) shows that upon thermolysis the resulting Fe : Mo ratio is highly dependent on the reaction atmosphere: thermolysis in air results in significant loss of volatile molybdenum components. Pure FeMoC-EtOH is found to be essentially inactive as a pre-catalyst for the VLS growth of single-walled carbon nanotubes (SWNTs) irrespective of the substrate or reaction conditions. However, reaction of FeMoC with pyrazine (pyz) results in the formation of aggregates that are found to be active catalysts for the growth of SWNTs. Activation of FeMoC may also be accomplished by the addition of excess iron. The observation of prior work's reported growth of SWNTs from FeMoC is discussed with respect to these results.