High surface area carbon aerogel monoliths with hierarchical porosity

This letter describes the synthesis and structural characterization of monolithic carbon aerogel (CA) materials that possess both high surface areas and hierarchical porosity. Thermal activation of a macroporous CA structure, one that was derived from an acetic acid-catalyzed sol-gel polymerization reaction, yields monolithic materials with large pore volumes and surface areas exceeding 3000 m²/g. Given the flexibility of CA synthesis, this approach offers viability to engineer new materials for use as catalyst supports, electrodes, capacitors and sorbent systems.     

Transport properties of copper-doped carbon aerogels

The magnetic susceptibility, conductivity, magnetoresistance (MR) and Hall effect of copper-doped carbon aerogels are measured and compared with corresponding results from the original carbon aerogels. The experimental results indicate that the temperature-dependent magnetic susceptibility of the copper-doped and of the original carbon aerogels is well fit by a Curie function at low temperatures. The copper-doped carbon aerogels show a higher susceptibility and spin concentration than the original carbon aerogel. After doping by copper, the materials exhibit a more linear current-voltage curve than the original carbon aerogel under the same measurement conditions. The electrical resistance of the copper-doped carbon aerogels is strikingly lower than that of the original carbon aerogels, and decreases with increasing copper content in the samples. The temperature-dependent resistivity ρ(T) of all of the copper-doped and original carbon aerogels can be fitted by an exp(T^−1/2) dependence for T<100 K. The copper-doped and pristine carbon aerogels follow a quadratic MR behavior Δρ/ρ=AB² in the magnetic field range B investigated (up to 5 T), except at very low temperatures (T<4 K).     

A simple and cost effective method for the quantification of 8-hydroxy-2'-deoxyguanosine from urine using liquid chromatography tandem mass spectrometry

A rapid and high-throughput method for the determination of urinary levels of the oxidative stress biomarker, 8-hydroxy-2'-deoxyguanosine (8-OH-dG), has been developed and validated using liquid chromatography combined with electrospray ionization tandem mass spectrometry (LC-MS/MS). The assay features a cheap and readily available non-isotopic internal standard, a single-step filtration sample preparation, and a total analysis time of 6 min including column re-equilibration. The method was validated based on linearity, accuracy (100-106%), precision (CV < 7%), sample preparation stability (< or =5%, 72 h). Intra-laboratory patient ranges were established comparing children and adults (n = 345).     

A scalable synthesis of an azabicyclooctanyl derivative, a novel DPP-4 inhibitor

A practical synthetic strategy to a chiral azabicycclooctanyl derivative (1), a potent DPP-4 inhibitor, starting from a commercially available nortropine is described. The stereogenic center of 1 was established employing a modified protocol of Ellman's diastereoselective addition of a benzylic nucleophile to tert-butanesulfinimine. Other key steps include Corey-Chaykovsky reaction, Meinwald rearrangement, and CDMT-promoted amide bond formation involving a sterically hindered amine 2.     

Diffusion-influenced reversible geminate ABCD reaction in the presence of an external field

We investigate a diffusion-influenced ground-state reversible geminate ABCD reaction in the presence of a constant external field in one dimension. In the Laplace domain, we first obtain the nonreactive Green function from which the reactive Green function is derived. Analytic asymptotic expressions of the survival probability are obtained in the time domain for both short and long time regions. There exist four regimes for the equilibrium survival probability according to the signs of the field intensities a1 and a2 that reactant and product states feel, respectively. Analysis of the long-time asymptotic behavior of the survival probability shows two regimes depending on the sign of a parameter K( identical with a(2)(2)D(2) -a(2)(1)D(1)), where D(1) and D(2) are the relative diffusion constants of corresponding states, respectively. Combining these two results, we predict a total of eight regimes for the long-time asymptotic behavior of the survival probability. We find that the long-time asymptotic behavior of the deviation of the effective survival probability shows the t(-3/2) power law when m( identical with min {a(2)(1)D(1), a(2)(2)D(2)}) not equal 0, whereas it shows t(-1/2) power law when m = 0. When one of the fields is turned off, the long-time asymptotic behavior of the survival probability shows a kinetic transition as the sign of the remaining field changes.     

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays--a step toward light harvesting antenna and multibit information storage

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays have been prepared using coordination of the axial position of the metal ion onto 4-aminopyridine preassembled single-walled carbon nanotubes directly anchored to a silicon(100) surface (SWCNTs-Si). The formation of these ruthenium porphyrin functionalized single-walled carbon nanotube array electrodes (RuTPP-SWCNTs-Si) has been monitored using infrared spectroscopy (IR), differential pulse voltammetry (DPV), atomic force microscopy (AFM), laser desorption time-of-flight mass spectroscopy (LDI-TOF-MS), UV-vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Electrochemical results show two successive one-electron reversible redox waves. The surface concentration of the ruthenium porphyrin molecules is 3.44 x 10 (-8) mol cm (-2). Optical results indicate that the immobilization of ruthenium porphyrin enhances the light absorption of SWCNTs-Si surfaces in the visible light region. Moreover mixed assembly of ferrocene/porphyrin onto carbon nanotube arrays has been achieved by altering the ratio of two redox-active species in the deposition solution. These results suggest the ruthenium porphyrin modified electrodes are excellent candidates for molecular memory devices and light harvesting antennae.     

Transition-state analysis of the DNA repair enzyme MutY

The transition state (TS) structure of MutY-catalyzed DNA hydrolysis was solved using multiple kinetic isotope effect (KIE) measurements. MutY is a base excision repair enzyme which cleaves adenine from 8-oxo-G:A mismatches in vivo, and also from G:A mismatches in vitro. TS analysis of G:A-DNA hydrolysis revealed a stepwise S(N)1 (D(N)*A(N)(double dagger)) mechanism proceeding through a highly reactive oxacarbenium ion intermediate which would have a lifetime in solution of <10(-10) s. C-N bond cleavage is reversible; the N-glycoside bond breaks and reforms repeatedly before irreversible water attack on the oxacarbenium ion. KIEs demonstrated that MutY uses general acid catalysis by protonating N7. It enforces a 3'-exo sugar ring conformation and other sugar ring distortions to stabilize the oxacarbenium ion. Combining the experimental TS structure with the previously reported crystal structure of an abortive Michaelis complex elucidates the step-by-step catalytic sequence.