232nd American Chemical Society Meeting & Exposition
September 10 - 14, 2006
San Francisco, CA USA

Barron Research Group Abstracts


Transition metal ion quenching of single walled carbon nanotube fluorescence

Jonathan J. Brege, Department of Chemistry, Rice University, 6100 Main St., Houston, TX 77005, jb5001@rice.edu, Ryan Loscutova, Department of Chemistry, Rice University, and Andrew R. Barron, Department of Chemistry, Smalley Institute for Nanoscale Science and Technology, Rice University

The fluorescent properties of semiconducting single walled carbon nanotubes (SWNTs) are of great interest because specific chirality nanotubes can be assigned to characteristic peaks of the emission spectra. The fluorescence quenching of various surfacted SWNTs in aqueous solutions by transition metals has been observed. Particularly, Cd(II), Zn(II) and Cu(I) selectively quench the fluorescence of some chirality tubes, while they have no effect on others. Other metals quench all chirality tubes with varying efficiencies and exhibit no selective properties. The bimolecular quenching rate constants have been calculated for the different metal/surfactant systems. A quenching mechanism has been postulated and there is evidence that the direction of electron transfer is from the excited nanotube to the metal d-orbitals.


Bimetallic nanoparticles as catalysts for the growth of single walled carbon nanotubes

Christopher Crouse - Department of Chemistry, Rice University, Houston, TX 77005, Ramon Colorado, Jr., Department of Chemistry, Rice University, and Andrew R. Barron, Department of Chemistry, Smalley Institute for Nanoscale Science and Technology

Bimetallic (Fe, Ni, Co, Pt, Mg, Al) nanoparticles have been prepared in varying atomic ratios from the solution phase decomposition of their acac salts. The nanoparticles serve as catalysts for the vapor-liquid-solid (VLS) growth of single walled carbon nanotubes (SWNTs) on silica and alumina surfaces. The study compares the kinetic rates and overall efficiencies of the different nanoparticles to determine the optimal particle size, composition, and growth conditions necessary to obtain SWNTs in high yield. The particles were prepared with narrow dispersities in sizes ranging from 2-10 nm. Surface and chemical characterization of the particles was achieved using X-ray photoelectron spectroscopy and particle size and morphology were determined by TEM and AFM. A discussion of the factors effecting catalyst efficiency will be discussed.


Comparison of iron complexes, clusters, and colloids as catalyst precursors for
single-walled carbon nanotube (SWNT) growth

Ramon Colorado, Jr., Christopher Crouse, Douglas Ogrin, Robin E. Anderson, Benji Maruyama, Mark J. Pender, Richard E. Smalley, and Andrew R. Barron

Recent studies of the vapor-solid-liquid (VLS) growth of single-walled carbon nanotubes (SWNTs) from metallic catalysts on solid substrates (e.g. iron nanoparticles on silicon wafers) have suggested that there is a correlation between the size of the catalyst precursor and the diameter of the resultant SWNTs. Understanding how the initial catalyst properties influence the characteristics of the grown nanotubes is a crucial step toward furthering attempts to prepare SWNTs with controlled dimensions and chiralities. To this end, we have studied the VLS growth of SWNTs using the following catalyst precursors that contain increasing amounts of iron atoms and exhibit three distinct dimensions: (1) an oxo-hexacarboxylate–iron trimer complex, which contains 3 iron atoms, [Fe3O(O2CCH3)6(EtOH)3] (d < 1 nm), (2) a molecular cluster, FeMoC, which contains 30 iron atoms, [HxPMo12O40⊂H4Mo72Fe30(O2CCH3)15O254(H2O)98] (d = 2 nm), and (3) a magnetite (Fe3O4) nanoparticle, which contains 1,300 iron atoms (d = 4 nm). We will discuss how factors such as the initial iron content, catalyst size, and catalyst aggregation influence the characteristics and growth rates of the SWNTs on various substrates (Si, SOG, HOPG, Al2O3) under different growth conditions (i.e. varying growth temperatures and gases). Characterization of the SWNTs by AFM, SEM, and Raman spectroscopy will be presented.  PDF version


Polyethylenimine sidewall functionalization of fluorinated single walled carbon nanotubes

Eoghan Dillon 1 , Christopher A. Crouse 1 , and Andrew R. Barron 2 . (1) Department of Chemistry, Rice University, 6100 Main Street, Houston, TX 77005, eoghan.dillon@gmail.com, (2) Richard E. Smalley Institute for Nanoscale Science and Technology, Energy & Environmental Systems Institute, Rice University

Covalent attachment of polyamines to the sidewalls of fluorinated single walled carbon nanotubes (F-SWNTs) was explored. The covalent attachment of various diamines to F-SWNTs has been previously published along with PEI functionalization at the carboxylic acid moieties found at the end of SWNTs. It was our hope to prepare highly functionalized SWNTs with direct covalent attachment to the sidewalls providing a more stable material with increased solubility and biological compatibility. Branched polyethylenimine (B-PEI), of varying molecular weights, was chosen as a test polymer due to its commercial availability, low biological activity and solubility properties. B-PEI coated SWNTs display good solubility in water at physiological pH and may have possible applications in medicinal biotechnology as drug carriers and contrast agents.

Metal complexation with pyridine and phosphine functionalized single walled carbon nanotubes

Christopher E. Hamilton1, Doug Ogrin2, and Andrew R. Barron2. (1) Department of Chemistry- MS 60, Rice University, 6100 Main St., Houston, TX 77005, chamilton@rice.edu, (2) Department of Chemistry, Smalley Institute for Nanoscale Science and Technology, Rice University

Much attention has been paid to the ‘amplification' of single walled carbon nanotubes (SWNTs) by seeded growth. Analogous to the polymerase chain reaction (PCR) used to amplify DNA samples; seeded SWNT growth will allow the production of specific diameter and chirality tubes. Seeded growth has been demonstrated by the attachment of a metallic catalyst particle to the cut end of a SWNT. We herein report improvement of catalyst-SWNT docking by functionalizing tube ends with nitrogen and phosphorus. The ends of SWNTs have been coupled via esterification reactions to 4-hydroxypyridine and 4-hydroxyphenyl-diphenylphospine. Complexation of iron (III), cobalt (II), and nickel (II) with N- and P-SWNTs has been shown by UV-visible spectroscopy and 31P NMR.

Electrical conductance of a dispersed carbon nanotube within a polyurethane matrix

Huma R. Jafry1 Eoghan Dillon1, Divya Chakravarthi2, E. V. Barrera2, and Andrew R. Barron3. (1) Department of Chemistry, Rice University, 6100 Main Street, Houston, TX 77005, huma@rice.edu, (2) Mechanical Engineering and Materials Science, Rice University, (3) Department of Chemistry, Smalley Institute for Nanoscale Science and Technology, Rice University

Single walled carbon nanotubes (SWNT) are mixed with a polyurethane solution using various dispersion techniques including homogenization, probe sonication, and blending. The addition of solvents and surfactants has been explored to aid in the suspension of the SWNT in the polyurethane matrix. Solvents and surfactants studied include THF, Pluronic F108, and DMF. The resulting SWNT/polyurethane dispersion was sprayed onto a glass substrate, using a spray gun to provide a smooth coating. Electrical conductivity measurements were made using a four-point electrical conductivity probe. Studies were performed to determine optimal coating thickness and dispersion effects on electrical conductivity of the matrix.


The effect of fullerene amino acids with flexible linkage unit on peptide's cell transport
and peptide's secondary structure

Nadjmeh Doostdar, Jianzhong Yang, and Andrew R. Barron, Department of Chemistry, Rice University, Houston, TX 77005

In previous investigations, we synthesized a series of fullerene amino acids derived from phenylalanine, lysine, and Bucky amino acid (Baa). Our studies show that phenylalanine based fullerene amino acids are stable under conditions of SPPS and facilitate the transport of peptides into cell.   The phenylalanine provides a rigid spacer between the fullerene and peptide backbone while lysine offers a flexible linkage between the fullerene and peptide chain.   In addition, preliminary studies show that the position of phenylalanine based fullerene within the peptide sequence affects the structure and relative stability of the peptide. Currently, we are investigating the effect of fullerene with lysine linkage unit on peptide's cell transport and also the effect of its position on peptides secondary structures and stability.


Synthesis of aminoacylated dinucleotide, pdCpA-Baa, for ribosome-mediated biosynthesis
of peptide sequence including Bucky amino acid (Baa)

Amanda Strom and Andrew Barron, epartment of Chemistry, Rice University, Houston, TX 77005

Solid phase peptide synthesis (SPPS) is the standard method of peptide synthesis and is necessary when incorporating unnatural amino acids to a peptide sequence.   However, SPPS is limited by significant errors and low yield occurring in peptide sequences of more than 20-30 amino acid residues.   For this reason we are exploring a ribosome-mediated biosynthetic pathway which will incorporate the synthetic bucky-amino acid (Baa) to a peptide sequence.   Initially, the hybrid dinucleotide pdCpA was chemically synthesized and aminoacylated with the synthetic bucky-amino acid.   Misacylation is used to ligate pdCpA-Baa to a truncated suppressor tRNA CUA (-CA) to make a chemically aminoacylated suppressor tRNA capable of translation. This process attempts to afford site-specific incorporation of a synthetic amino acid to a peptide sequence through ribosome-mediated biosynthesis of a synthetic peptide including bucky-amino acid in the sequence.  

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