Multipumping Nitrite Determination in Exhaled Breath Condensate

Abstract

A flow system based on multicommutation is proposed for the rapid, clean, and inexpensive determination of nitrites in small volumes of breath condensates. The procedure exploits the colorimetric detection of nitrite with the Griess reagent [0.03% naphthylethylene diamine dihydrochloride (NED), 0.5% sulpfhanilamide, and 3.0% phosphoric acid] in acidic medium at 540 nm correcting the variations of the baseline with measurements at 424 nm. The flow system was designed with a set of solenoid micropumps to minimize sample and reagent consumption and waste generation. The detection limit was estimated as 3.8 ng mL^?1 (99.7% confidence level) with a linear response ranging up to 500 ng mL^?1. The coefficient of variation was estimated as 0.7% for a solution containing 300 ng mL^?1 nitrite (n=9). Approximately 144 determinations can be carried out per hour, consuming only 678.4 µg Griess reagent and generating 1.184 mL of effluent per determination, thus providing an environmentally friendly alternative and a nonexpensive method. The procedure was successfully applied to determine nitrite in breath condensates.     

The madelung constant for the tetragonal distortion of the cscl lattice

The Madelung constant is calculated for the tetragonal distortion of the CsCl lattice using Ewald's method over a large $\text{c}\text{a}$ range. The results deviate considerably from the analytical expressions for the Madelung constant in the literature. As a checkpoint for our calculation, the Madelung constant for the ideal cubic AuCuI structure $\text{(}\text{c}\text{a}\text{= √2)}$ is also computed by direct lattice summation using Evjen's method.     

One-Pot synthesis of unsymmetrically substituted 2,4-dialkylisoflavenes

The trimethylsilyl derivative of formonometine reacts sequentially with two different organometallic derivatives to afford regiospecifically and with good yield 2,4-dialkylisoflavenes unsymmetrically substituted.     

1,6- and 1,7-naphthyridines. I. Rearrangement of quinolinimidoacetic acid derivatives

The reaction of N-substituted quinolinimides 1a-d with sodium alkoxides afforded a mixture of 1,6-naphthyridines 2 and 1,7-naphthyridines 3 which were isolated by chromatographic methods. Structure assignment for each pair of isomers was made by comparison of their ¹H nmr spectra with those of picolinamide and nicotinamide. When esters 1a -c were treated with alkoxides from primary alcohols, other than that of the ester, total transesterification took place. Experimental results suggest that transesterification occurs in open intermediary species.     

Effective Hamiltonians for Atoms in Very Strong Magnetic Fields

 We propose rigorous statements for several properties of atoms in intense homogeneous magnetic fields. Received October 30, 2001; accepted for publication November 9, 2001     

Inhibition of amyloid beta protein fibrillation by polymeric nanoparticles

Copolymeric NiPAM:BAM nanoparticles of varying hydrophobicity were found to retard fibrillation of the Alzheimer's disease-associated amyloid beta protein (Abeta). We found that these nanoparticles affect mainly the nucleation step of Abeta fibrillation. The elongation step is largely unaffected by the particles, and once the Abeta is nucleated, the fibrillation process occurs with the same rate as in the absence of nanoparticles. The extension of the lag phase for fibrillation of Abeta is strongly dependent on both the amount and surface character of the nanoparticles. Surface plasmon resonance studies show that Abeta binds to the nanoparticles and provide rate and equilibrium constants for the interaction. Numerical analysis of the kinetic data for fibrillation suggests that binding of monomeric Abeta and prefibrillar oligomers to the nanoparticles prevents fibrillation. Moreover, we find that fibrillation of Abeta initiated in the absence of nanoparticles can be reversed by addition of nanoparticles up to a particular time point before mature fibrils appear.     

Diffusion NMR for determining the homogeneous length-scale in lamellar phases

The size of the anisotropic domains in a lyotropic liquid crystal is estimated using a new protocol for diffusion NMR. Echo attenuation decays are recorded for different durations of the displacement-encoding gradient pulses, while keeping the effective diffusion time and the range of the wave vectors constant. Deviations between the sets of data appear if there are non-Gaussian diffusion processes occurring on the time-scale defined by the gradient pulse duration and the length-scale defined by the wave vector. The homogeneous length-scale is defined as the minimum length-scale for which the diffusion appears to be Gaussian. Simulations are performed to show that spatial variation of the director orientation in an otherwise homogeneous system is sufficient to induce non-Gaussian diffusion. The method is demonstrated by numerical solutions of the Bloch-Torrey equation and experiments on a range of lamellar liquid crystals with different domain sizes.     

Quantum-Mechanical and Solvatochromic Characterization of Quercetin

ABSTRACT

Quercetin was subjected to a quantum-mechanical analysis and energetic and electro-optic parameters were evaluated. A solvatochromic study was used to estimate the dipole moment of quercetin in the excited state and to determine the angle between the dipole moments of this molecule in the electronic states responsible for the visible absorption band. The contribution of each type of intermolecular interactions to the total spectral shift experimentally recorded in quercetin solution was also established in this study.