Functionalization of SWNTs to facilitate the coordination of metal ions, compounds and clusters.

The carboxylate residues of the open ends of aryl-tert-butyl and arylsulfonic acid side-walled functionalized single walled carbon nanotubes (SWNTs) have been investigated for the complexation conditions of the iron-molybdenum cluster [H(x)PMo(12)O(40)CH(4)Mo(72)Fe(30)(O(2)CMe)(15)O(254)(H(2)O)(98)] ("FeMoC"). A range of alternative donor groups for the attachment of FeMoC have been investigated for piranha etched SWNTs, dodecyl side-walled functionalized SWNTs (DD-SWNTs) and ultra-short SWNTs (US-SWNTs), including include pyridines, thiols and phosphines, using coupling reactions to either the carboxylate or hydroxide residues of the SWNTs' open ends. The functionalized SWNTs have been characterized by XPS, uptake of Fe(3+) and, where appropriate, MAS (31)P NMR. The efficacy of binding is dependent on the presence and identity of the ligand moiety. TEM and AFM of the SWNT-FeMoC conjugates show the presence of a 2-3 nm spherical feature on the tip of individual SWNTs.

Epoxidation and deoxygenation of single-walled carbon nanotubes: quantification of epoxide defects.

Epoxidation of single-walled carbon nanotubes (SWNTs) may be carried out by the reaction of SWNTs with either trifluorodimethyldioxirane or 3-chloroperoxybenzoic acid; the resulting O-SWNTs are spectroscopically similar to those formed by ozonolysis. Quantification of the epoxide substituents is possible through the catalytic de-epoxidation reaction using MeReO3/PPh3 and the 31P NMR spectroscopy. The de-epoxidation methodology may be used to determine that wet air oxidation is preferable to either acid or O2/SF6 purification. We have demonstrated that previously assumed "pure" SWNTs are actually "doped" to a level of at least 1 oxygen per 250 carbon atoms.

Single-walled carbon nanotube growth using [Fe(3)(mu(3)-O)(mu-O(2)CR)(6)(L)(3)](n+) complexes as catalyst precursors.

We present herein the VLS growth of SWNTs from oxo-hexacarboxylate-triron precursors, [Fe(3)O(O(2)CCH(3))(6)(EtOH)(3)] and [Fe(3)O(O(2)CCH(2)OMe)(6)(H(2)O)(3)][FeCl(4)], on spin-on-glass surfaces, using C(2)H(4)/H(2) (750 degrees C) and CH(4)/H(2) (800 and 900 degrees C) growth conditions. The SWNTs have been characterized by AFM, SEM and Raman spectroscopy. The characteristics of the SWNTs are found to be independent of the identity of the precursor complex or the solvent from which it is spin-coated. The as grown SWNTs show a low level of side-wall defects and have an average diameter of 1.2-1.4 nm with a narrow distribution of diameters. At 750 and 800 degrees C the SWNTs are grown with a range of lengths (300 nm-9 microm), but at 900 degrees C only the longer SWNTs are observed (6-8 microm). The yield of SWNTs per unit area of catalyst nanoparticle decreases with the growth temperature. We have demonstrated that spin coating of molecular precursors allows for the formation of catalyst nanoparticles suitable for growth of SWNTs with a high degree of uniformity in the diameter, without the formation of preformed clusters of a set diameter.

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.

An efficient synthesis of the constrained peptidomimetic 2-oxo-3-(N-9-fluorenyloxycarbonylamino)-1-azabicyclo[4.3.0]nonane-9-carboxylic acid from pyroglutamic acid.

[reaction: see text] Azabicyclo[X.Y.0]alkane amino acids are rigid dipeptide mimetics that are useful tools for structure-activity studies in peptide-based drug discovery. Herein, we report an efficient synthesis of three diastereomers of 9-tert-butoxycarbonyl-2-oxo-3-(N-tert-butoxycarbonylamino)-1-azabicyclo[4.3.0]nonane (3S,6S,9S, 3S,6R,9R, and 3S,6R,9S). Methyl N-Boc-pyroglutamate is cleaved with vinylmagnesium bromide to produce an acyclic gamma-vinyl ketone. Michael addition of N-diphenylmethyleneglycine tert-butyl ester produces the N-Boc-delta-oxo-alpha,omega-diaminoazelate intermediate, which, on hydrogenloysis, gives the fused ring system. Acidolytic deprotection followed by Fmoc-protection provided building blocks suitable for solid-phase synthesis.