Screen-printed electrochemical hybridization biosensor for the detection of DNA sequences from the Escherichia coli pathogen

An electrochemical biosensor for the specific detection of short DNA sequences from the E. coli pathogen is described. This hybridization device relies on the immobilization of a 25-mer oligonucleotide probe, from the E. coli lacZ gene, onto a screen-printed carbon electrode. Chronopotentiometric detection of the Co(bpy)₃⁺³ indicator is used for monitoring the hybridization event. Numerous variables of the assay protocol, including those of the probe immobilization step, the hybridization event, and the indicator association/detection, are characterized and optimized. Hybridization times of 2- and 30-min are sufficient for detecting 300- and 50 ng/mL, respectively, of the E. coli DNA target. Applicability to analysis of untreated environmental water samples is illustrated. Such single-use electrochemical sensors hold great promise for decentralized environmental and food testing for the E. coli pathogen.     

Synthesis and characterization of trifluoromethyl fluoroformyl peroxycarbonate,CF3OC(O)OOC(O)F

The synthesis of CF(3)OC(O)OOC(O)F is accomplished by the photolysis of a mixture of (CF(3)CO)(2)O, FC(O)C(O)F, CO, and O(2) at -15 degrees C using a low-pressure mercury lamp. The new peroxide is obtained in pure form in low yield after repeated trap-to-trap condensation and is characterized by NMR, IR, Raman, and UV spectroscopy. Geometrical parameters were studied by ab initio methods [B3LYP/6-311+G(d)]. At room temperature, CF(3)OC(O)OOC(O)F is stable for many days in the liquid or gaseous state. The melting point is -87 degrees C, and the boiling point is extrapolated to 45 degrees C from the vapor pressure curve log p = 8.384 - 1715/T (p/mbar, T/K). A possible mechanism for the formation of CF(3)OC(O)OOC(O)F is discussed, and its properties are compared with those of related compounds.     

Trifluoromethoxycarbonyl peroxynitrate, CF3OCOOONO2

The trioxide, CF(3)OC(O)OOOC(O)OCF(3), reacts with NO(2) at 0 degrees C to yield the new peroxynitrate, CF(3)OC(O)OONO(2), which is stable for hours at room temperature. It is spectroscopically characterized and some thermal properties are reported. From the vapor pressure, ln(p/p(0)) = 14.06 - 4565/T, of the liquid above the melting point of -89 degrees C, the extrapolated boiling point is 52 degrees C. CF(3)OC(O)OONO(2) dissociates at higher temperatures and low pressures into the radicals CF(3)OC(O)OO and NO(2) as demonstrated by matrix isolation experiments. The matrix-isolated peroxy radicals consist in a rotameric mixture of trans,trans,trans-CF(3)OC(O)OO and trans,trans,cis-CF(3)OC(O)OO, where trans and cis denote dihedral angles of ca. 180 degrees and 0 degree, respectively, around beta F-C-O-C, beta C-O-C-O, and beta O-C-O-O, with an equilibrium composition dependent on the thermolysis temperature. The radical trans,trans,cis-CF(3)OC(O)OO is found to be ca. 3 kJ mol(-1) higher in enthalpy than trans,trans,trans-CF(3)OC(O)OO. DFT calculations are performed to support the vibrational assignments and to provide structural information about CF(3)OC(O)OONO(2).     

Estimation of the uncertainty of mass measurements from in-house calibrated analytical balances

The uncertainty evaluation of mass measurements when using “in-house” calibrated analytical balances is revisited according to the Guide to the expression of Uncertainty Measurement (GUM). The calibration of analytical balances is discussed according to the guidelines of several bodies such as ASTM, UKAS and DKD/PTB. The remainder components of uncertainty can be estimated from the balance data sheet specifications.     

Importance of chain-chain interactions on the band gap of trans-polyacetylene as predicted by second-order perturbation theory

We employ the Laplace-transformed second-order Moller-Plesset perturbation theory for periodic systems in its atomic orbital basis formulation to determine the geometric structure and band gap of interacting polyacetylene chains. We have studied single, double, and triple chains, and also two-dimensional crystals. We estimate from first principles the equilibrium interchain distance and setting angle, along with binding energy between trans-polyacetylene chains due to dispersion interactions. The dependence of the correlation corrected quasiparticle band gap on the intrachain and interchain geometric parameters is studied, obtaining that the gap of the compound structures is substantially reduced with respect to the single chain polymer.     

Synthesis and characterization of cobalt(II) and copper(II) complexes with 5-amino-3,4-dimethylisoxazole

Summary Complexes of cobalt(II) and copper(II) with 5-amino-3,4-dimethylisoxazole (5-ADI) have been prepared and studied by means of magnetic susceptibility measurements, near and far i.r. spectra, electronic spectroscopy and, when possible, conductivity measurements. The 5-ADI generally behaves as bridging (N_ring-, O- or N_ring-, -NH₂) ligand. All the complexes have an octahedral sterochemistry, except Co(5-ADI)₂X₂ (X = Cl, Br), Co₂(5-ADI)₇I₄ which are tetrahedral and Cu(5-ADI)₂ (ClO₄)₂ · 4 H₂O which is square planar.     

Estimation of third virial coefficients at low reduced temperatures

We use the Clausius–Clapeyron equation to calculate third virial coefficients at low reduced temperatures. This procedure gives an alternative to predict third virial coefficients in a region where the third virial coefficient is difficult to measure. We compare the results of this method with published third virial coefficient data. Calculated third virial coefficients have average percentage deviations within 5% of the experimental values at reduced temperatures between 0.8 and 1.0.     

Molecular dynamics studies of melting and solid-state transitions of ammonium nitrate

Molecular dynamics simulations are used to calculate the melting point and some aspects of high-temperature solid-state phase transitions of ammonium nitrate (AN). The force field used in the simulations is that developed by Sorescu and Thompson [J. Phys. Chem. A 105, 720 (2001)] to describe the solid-state properties of the low-temperature phase-V AN. Simulations at various temperatures were performed with this force field for a 4 x 4 x 5 supercell of phase-II AN. The melting point of AN was determined from calculations on this supercell with voids introduced in the solid structure to eliminate superheating effects. The melting temperature was determined by calculating the density and the nitrogen-nitrogen radial distribution functions as functions of temperature. The melting point was predicted to be in the range 445 +/- 10 K, in excellent agreement with the experimental value of 442 K. The computed temperature dependences of the density, diffusion, and viscosity coefficient for the liquid are in good agreement with experiment. Structural changes in the perfect crystal at various temperatures were also investigated. The ammonium ions in the phase-II structure are rotationally disordered at 400 K. At higher temperatures, beginning at 530 K, the nitrate ions are essentially rotationally unhindered. The density and radial distribution functions in this temperature range show that the AN solid is superheated. The rotational disorder is qualitatively similar to that observed in the experimental phase-II to phase-I solid-state transition.     

Scaling laws in simple and complex proteins: size scaling effects associated with domain number and folding class

The native states of the most compact globular proteins have been described as being in the so-called “collapsed-polymer regime,” characterized by the scaling law R _g ~ n ^ν, where R _g is radius of gyration, n is the number of residues, and ν ≈ 1/3. However, the diversity of folds and the plasticity of native states suggest that this law may not be universal. In this work, we study the scaling regimes of: (i) one to four-domain protein chains, and (ii) their constituent domains, in terms of the four major folding classes. In the case of complete chains, we show that size scaling is influenced by the number of domains. For the set of domains belonging to the all-α, all-β, α/β, and α?+?β folding classes, we find that size-scaling exponents vary between 0.3?≤?ν?≤?0.4. Interestingly, even domains in the same folding class show scaling regimes that are sensitive to domain provenance, i.e., the number of domains present in the original intact chain. We demonstrate that the level of compactness, as measured by monomer density, decreases when domains originate from increasingly complex proteins.