Simplified current decoupler for microchip capillary electrophoresis with electrochemical and pulsed amperometric detection

There is a need to develop broadly applicable, highly sensitive detection methods for microchip CE that do not require analyte derivatization. LIF is highly sensitive but typically requires analyte derivatization. Electrochemistry provides an alternative method for direct analyte detection; however, in its most common form, direct current (DC) amperometry, it is limited to a small number of easily oxidizable or reducible analytes. Pulsed amperometric detection (PAD) is an alternative waveform that can increase the number of electrochemically detectable analytes. Increasing sensitivity for electrochemical detection (EC) and PAD requires the isolation of detection current (nA) from the separation current (muA) in a process generally referred to as current decoupling. Here, we present the development of a simple integrated decoupler to improve sensitivity and its coupling with PAD. A Pd microwire is used as the cathode for decoupling and a second Au or Pt wire is used as the working electrode for either EC or PAD. The electrode system is easy to make, requiring no clean-room facilities or specialized metallization systems. Sensitive detection of a wide range of analytes is shown to be possible using this system. Using this system we were able to achieve detection limits as low as 5 nM for dopamine, 74 nM for glutathione, and 100 nM for glucose.     

Triazene proton affinities: A comparison between density functional,Hartree–Fock,and post-Hartree–Fock methods

The consistency of three density functional computational implementations (DMol, DGauss, and deMon) are compared with high-level Hartree–Fock and Møller–Plesset (MP) calculations for triazene (HN?NNH₂) and formyl triazene (HN?NNHCOH). Proton affinities on all electronegative sites are investigated as well as the geometries of the neutral and protonated species. Density functional calculations employing the nonlocal gradient corrections show agreement with MP calculations for both proton affinities and geometries of neutral and protonated triazenes. Local spin density approximation DMol calculations using numerical basis sets must employ an extended basis to agree with other density functional codes using analytic Gaussian basis sets. The lowest energy conformation of triazene was found to be nonplanar; however, the degree of nonplanarity, as well as some bond lengths, is dependent on the basis set, electron correlation treatment, and methods used for the calculation. © 1994 by John Wiley & Sons, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America.

     

Exact solution (within a double-zeta basis set) of the schrodinger electronic equation for water

Using recently developed theoretical techniques it has been possible to achieve an exact variational solution of the Schrödinger equation within a modest basis set or one-eleltron functions. The full configuration interaction for this system included a total of 256473 ¹A₁ spin-and space-adapted configurations. Comparison with many-body perturbation theory proves to be quite interesting.     

Single-run analysis of retinal isomers, retinol and photooxidation products by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) procedure was developed to allow the rapid separation, in a single run, of a mixture of the main retinal isomers (all-trans, 13-cis, 9-cis), all-trans-retinol, and of the two major photooxygenated photoproducts (5,8-peroxyretinal and 5,6-epoxyretinal). The mixture was separated by HPLC on an octadecyl (ODS) column with 16% (v/v) diethyl ether in hexane as mobile phase and anthracene as the internal standard. A commercial type cosmetic formulation containing 0.05% all-trans-retinal was analyzed successfully for this analyte.     

Synthesis of β-tosylethylhydrazine and its use in preparation of N-protected pyrazoles and 5-aminopyrazoles

β-Tosylethylhydrazine (6) can be prepared efficiently in one step from commercially available p-tolyl vinyl sulfone (7) and hydrazine hydrate. This hydrazine reacts with both 1,3-diketones and conjugated ynones in glacial acetic acid to provide a variety of N-tosylethyl-protected (TSE) pyrazoles in good yields. The TSE group can be removed from the pyrazoles using potassium t-butoxide in THF at −30 °C-rt. In addition, hydrazine 6 condenses with β-ketonitriles and β-aminoacrylonitriles to afford 5-aminopyrazoles, which can be deprotected by brief treatment with NaOEt in EtOH/DMSO at 45 °C.     

Enzymatic and electrochemical oxidation of uric acid: A mechanism for the peroxidase catalyzed oxidation of uric acid

The oxidation of uric acid has been studied by thin-layer spectroelectrochemistry using an optically transparent gold minigrid electrode and enzymatically using peroxidase. Under both enzymatic and electrochemical conditions a u.v.-absorbing intermediate (λ_max=302–304 nm between pH 7–9.3) is observed. This intermediate is proposed to be an imine-alcohol species formed by rapid hydration of the primary reaction product which is a diimine. Under the conditions employed in both the enzymatic electrochemical studies the imine-alcohol intermediate is hydrated in a first order reaction with an observed rate constant of 3.5×10^?3s^?1 between pH 7–9.3. This study establishes the similarity between the electrochemical and enzymatic oxidation of uric acid and indicates that electrochemical investigations of the redox behavior of purines can provide unique insights into their biological redox properties.