(n,m) Abundance evaluation of single-walled carbon nanotubes by fluorescence and absorption spectroscopy

A methodology that takes into account the (n,m) structure of single-walled carbon nanotubes (SWNTs), through an exciton-exciton resonance model and an electron-phonon interaction model, was employed in order to evaluate the semiconducting (n,m) abundance of two SWNT samples (i.e., Co-MCM-41 and HiPco). This was based on photoluminescence and near-infrared absorption data obtained on aqueous suspensions of individually dispersed SWNTs. In the absence of known (n,m) abundance SWNT samples, we resorted to determining the diameter distribution curves for both samples, which were found to obey an unsymmetrical log-normal distribution, typical for vapor-phase particle growth. Using this log-normal function, we reconstructed the near-infrared E S11 absorption spectrum of the narrow diameter distribution Co-MCM-41 SWNT sample, which in turn enabled us to assess the predictions of these two theoretical models. High spectral reconstruction accuracy was obtained from the electron-phonon interaction model when considering (11,0) and (10,0) zigzag nanotubes, along with (n,m) line widths inversely proportional to their extinction coefficients.     

DNA-directed assembly of polyanilines: modified cytosine nucleotides transfer sequence programmability to a conjoined polymer

A series of polyaniline (PANI) oligomers was constructed from monomer units covalently linked to duplex DNA through N-(2-aminoethyl) groups bonded through cytosines. DNA oligomers containing the aniline monomers were treated with horseradish peroxidase (HRP) and H2O2 under conditions known to cause polymerization of aniline. No change in the absorption spectrum of the DNA was observed for samples containing fewer than four contiguous aniline groups. However, for oligomers containing four, five, or six aniline units, treatment with HRP and H2O2 led to the appearance of absorption features characteristic of the conducting "proton doped" emeraldine oxidation state of PANI. Molecular modeling shows that the DNA is distorted in the region of the PANI, but flanking regions of the DNA maintain their B-form structure. These findings provide a method to exploit the self-recognition, self-assembly, and sequence programmability of DNA for the formation of conducting polymers.     

Carbon nanotube amplification strategies for highly sensitive immunodetection of cancer biomarkers

We describe herein the combination of electrochemical immunosensors using single-wall carbon nanotube (SWNT) forest platforms with multi-label secondary antibody-nanotube bioconjugates for highly sensitive detection of a cancer biomarker in serum and tissue lysates. Greatly amplified sensitivity was attained by using bioconjugates featuring horseradish peroxidase (HRP) labels and secondary antibodies (Ab(2)) linked to carbon nanotubes (CNT) at high HRP/Ab(2) ratio. This approach provided a detection limit of 4 pg mL(-)(1) (100 amol mL(-)(1)), for prostate specific antigen (PSA) in 10 microL of undiluted calf serum, a mass detection limit of 40 fg. Accurate detection of PSA in human serum samples was demonstrated by comparison to standard ELISA assays. PSA was quantitatively measured in prostate tissue samples for which PSA could not be differentiated by the gold standard immunohistochemical staining method. These easily fabricated SWNT immunosensors show excellent promise for clinical screening of cancer biomarkers and point-of-care diagnostics.     

New palladium(II)-(eta(3/5)- or eta1-indenyl) and dipalladium(I)-(mu,eta3-indenyl) complexes

Reaction of the dimeric species [(eta3-Ind)Pd(mu-Cl)]2 (1) (Ind = indenyl) with NEt3 gives the complex (eta(3-5)-Ind)Pd(NEt3)Cl (3), whereas the analogous reactions with BnNH2 (Bn = PhCH2) or pyridine (py) afford the complexes trans-L2Pd(eta1-Ind)Cl (L = BnNH2 (4), py (5)). Similarly, the one-pot reaction of 1 with a mixture of BnNH2 and the phosphine ligands PR3 gives the mixed-ligand, amino and phosphine species (PR3)(BnNH2)Pd(eta1-Ind)Cl (R = Cy (6a), Ph (6b)); the latter complexes can also be prepared by addition of BnNH2 to (eta(3-5)-Ind)Pd(PR3)Cl (R = Cy (2a), Ph (2b)). Complexes 6 undergo a gradual decomposition in solution to generate the dinuclear Pd(I) compounds (mu,eta3-Ind)(mu-Cl)Pd2(PR3)2 (R = Cy (7a), Ph (7b)) and the Pd(II) compounds (BnNH2)(PR3)PdCl2 (R = Cy (8a), Ph (8b)), along with 1,1'-biindene. The formation of 7 is proposed to proceed by a comproportionation reaction between in situ-generated Pd(II) and Pd0 intermediates. Interestingly, the reverse of this reaction, disproportionation, also occurs spontaneously to give 2. All new compounds have been characterized by NMR spectroscopy and, in the case of 3, 4, 5, 6a, 7a, 7b, and 8a, by X-ray crystallography.     

On-line monitoring of microg/L levels of haloacetic acids using ion chromatography with post-column nicotinamide reaction and fluorescence detection

A method for measuring the concentrations of the five regulated haloacetic acids (HAA5) in drinking water is reported. This method uses ion chromatography to separate HAA5 species, followed by post-column reaction with nicotinamide and detection of the fluorescent products. The result of method detection limit, accuracy, precision, linearity and interference studies are reported. The on-line monitoring method is compared directly to USEPA 552.3 in Memphis drinking water. Though not meant to replace the USEPA 552.3 for compliance monitoring, the proposed method does offer attractive alternatives considering the ease of automation and application of on-line monitoring directly from drinking water distribution systems.     

Models of the cytochromes: crystal structures and EPR spectral characterization of low-spin bis-imidazole complexes of (OETPP)Fe(III) having intermediate ligand plane dihedral angles

The preparation, EPR spectra, and crystal structures of octaethyltetraphenylporphyrinatoiron(III) having two imidazole, N-benzylimidazole, and N-methylimidazole axial ligands are reported, [(OETPP)Fe(HIm)2]Cl, [(OETPP)Fe(N-BzIm)2]Cl, and [(OETPP)Fe(N-MeIm)2]Cl. Despite large variation in axial ligand size, the unit cell parameters for all complexes are very similar; each structure has the same basic motif, with large voids formed by the extended porphyrin framework (filled by ordered or disordered axial ligands and disordered solvent), which allows differently sized ligands to fit within the same cell dimensions. Each porphyrin core adopts a saddled conformation with absolute value(deltaC(beta)) = 1.13-1.15 A. The dihedral angles between axial ligand planes, delta phi, are far from being either ideal parallel or perpendicular: 30.1 degrees, 57.2 degrees for [(OETPP)Fe(HIm)2]Cl (molecules 1 and 2), 56.8 degrees for [(OETPP)Fe(N-BzIm)(2)]Cl, and 16.0 degrees, 44.6 degrees, 59.6 degrees, and 88.1 degrees for [(OETPP)Fe(N-MeIm)2]Cl, which has disordered axial ligands. Among the complexes of this study, an axial ligand delta phi of 56.8 degrees is found to be the largest "parallel" angle (as defined by the observation of a normal rhombic or Type II EPR signal (N-BzIm, g = 3.08, 2.19, 1.31)), while 57.2 degrees is found to be the smallest "perpendicular" delta phi (as defined by the observation of a "large gmax" or Type I EPR signal (HIm, gmax = 3.24)). From the results of this study, it is clear that the size of the largest g for Types I and II complexes varies continuously, with no break between the two. While the switch in EPR signal type, from Type II to Type I, appears to be very sharp in this study, this may be somewhat artificial based upon limited numbers of examples and the required saddle distortion of the (OETPP)Fe(III) complexes. However, in comparison to several proteins with dihedral angles near 60 degrees and Type II EPR spectra, we may conclude that the switch in EPR signal type occurs near 57 degrees +/- 3-5 degrees.     

A low-spin alkylperoxo-iron(III) complex with weak Fe-O and O-O bonds: implications for the mechanism of superoxide reductase

The synthesis of a mononuclear, five-coordinate ferrous complex [([15]aneN4)FeII(SPh)](BF4) (1) is reported. This complex is a new model of the reduced active site of the enzyme superoxide reductase (SOR), which is comprised of a [(NHis)4(Scys)FeII] center. Complex 1 reacts with alkylhydroperoxides (tBuOOH, cumenylOOH) at low temperature to give a metastable, dark red intermediate (2a: R = tBu; 2b: R = cumenyl) that has been characterized by UV-vis, EPR, and resonance Raman spectroscopy. The UV-vis spectrum (-80 degrees C) reveals a 526 nm absorbance (epsilon = 2150 M-1 cm-1) for 2a and a 527 nm absorbance (epsilon = 1650 M-1 cm-1) for 2b, indicative of alkylperoxo-to-iron(III) LMCT transitions, and the EPR data (77 K) show that both intermediates are low-spin iron(III) complexes (g = 2.20 and 1.97). Definitive identification of the Fe(III)-OOR species comes from RR spectra, which give nu(Fe-O) = 612 (2a) and 615 (2b) cm-1, and nu(O-O) = 803 (2a) and 795 (2b) cm-1. The assignments for 2a were confirmed by 18O substitution (tBu18O18OH), resulting in a 28 cm-1 downshift for nu(Fe-18O), and a 46 cm-1 downshift for nu(18O-18O). These data show that 2a and 2b are low-spin FeIII-OOR species with weak Fe-O bonds and suggest that a low-spin intermediate may occur in SOR, as opposed to previous proposals invoking high-spin intermediates.     

A second generation mesoscopic lipid bilayer model: connections to field-theory descriptions of membranes and nonlocal hydrodynamics

A new mesoscopic membrane model is developed in order to examine long-wavelength structural and dynamical membrane phenomena. Two different explicit mesoscopic solvent models are employed. The first mesoscopic solvent is denoted the big liquid oscillating blob system, which is parametrized to model water at a coarse-grained level and is motivated by a Langevin-like approach; the resulting membrane dynamics predict a solvent viscosity dependence consistent with the known viscosity of water. The second mesoscopic solvent is a Weeks-Chandler-Anderson model. Here, it is found that the correct mesoscopic hydrodynamic scaling of the membrane undulation dynamics is still preserved, although accelerated. When the behavior of the two membranes in close proximity to one another is examined, very little correlated motion is observed. However, the theoretically predicted scaling of the entropic undulation energy is confirmed, demonstrating that the entropic interaction between two membranes becomes increasingly repulsive with decreasing separation.     

Synthesis of functionalized organotrifluoroborates via the 1,3-dipolar cycloaddition of azides

[reaction: see text] We have successfully prepared potassium azidoalkyltrifluoroborates from the corresponding halogen compounds in 94-98% yields through a nucleophilic substitution reaction with NaN(3). In the presence of various alkynes and Cu(I) as a catalyst, these azidotrifluoroborates easily formed 1,4-disubstituted organo-[1,2,3]-triazol-1-yl-trifluoroborates in 85-98% yields. This method was then developed into a facile one-pot synthesis for the preparation of various organo-[1,2,3]-triazol-1-yl-trifluoroborates using haloalkyltrifluoroborates as the starting materials.     

Mode-locked Yb:KGW laser longitudinally pumped by polarization-coupled diode bars

Mode-locked operation of a simple Yb:KGW (potassium gadolinium tungstate) oscillator is described, providing 10 W at 1039 nm with a 290 fs pulse width. A polarization-coupled scheme is used for efficient longitudinal pumping by a pair of reshaped laser diode bars. With changes in cavity dispersion, the pulse width is adjustable from 134 to 433 fs, in a high-quality circular mode. A saturable absorber mirror provides self-starting operation, and the cavity is stabilized by the Kerr-lens effect.