Superoxide dismutase mimetic properties exhibited by vacancy engineered ceria nanoparticles

In this report ceria nanoparticles are shown to act as catalysts that mimic superoxide dismutase (SOD) with the catalytic rate constant exceeding that determined for the enzyme SOD.     

The control of turbulent end-wall boundary layers using surface suction

An experimental evaluation of the effects of spatially-limited (i.e. localized) surface suction on a turbulent junction flow was performed using Particle Image Velocimetry (PIV). The results indicate that surface suction can (1) weaken both the instantaneous turbulent vortex and its associated surface interactions in the symmetry plane, (2) effectively eliminate the presence of the average turbulent necklace vortex in the symmetry plane, and (3) weaken the average downstream extensions of the vortex. It was also established that suction effectively reduces the low frequency component of the Reynolds-stress in both the symmetry plane and trailing-edge cross-stream planes, and stabilizes the behavior of the trailing vortex legs. Received: 18 May 1998/Accepted: 26 March 1999     

An unusual seven-bond H-H spin coupling

A through-space, seven-bond (1)H-(1)H coupling has been observed in tiliacorinine (1) caused by the close spacial proximity of two aromatic protons that are located in different benzene rings which are separated by two sp(3) carbons. Results from DQF-COSY and NOESY NMR experiments, as well as molecular modeling, reveal that the two protons are unusually close to one another in space.     

The chemical behavior and degradation mitigation effect of cerium oxide nanoparticles in perfluorosulfonic acid polymer electrolyte membranes

Perfluorosulfonic acid membranes are susceptible to degradation during hydrogen fuel cell operation due to radical attack on the polymer chains. Mitigation of this attack by cerium-based radical scavengers is an approach that has shown promise. In this work, two formulations of crystalline cerium oxide nanoparticles, with an order of magnitude difference in particle size, are incorporated into said membranes and subjected to proton conductivity measurements and ex-situ durability tests. We found that ceria is reduced to Ce(III) ions in the acidic environment of a heated, humidified membrane which negatively impacts proton conductivity. In liquid and gas Fenton testing, fluoride emission is reduced by an order of magnitude, drastically increasing membrane longevity. Sideproduct analysis demonstrated that in the liquid Fenton test, the main point of attack is weak polymer end groups, while in the gas Fenton test, there is additional side-chain attack. Both mechanisms are mitigated by the addition of the ceria nanoparticles, whereby the extent of the concentration-dependent durability improvement is found to be independent of particle size.     

Viscosity B -coefficients of sodium salts of some orthosubstituted benzoic acids in relation to hydrogen bonding and electronegativity

ViscosityB-coefficients of sodium salts of salicylic, thiosalicylic, anthranilic, 2,6-dihydroxy benzoic and ito-anisic acids have been measured at 298, 303 and 308 K respectively. Temperature dependence ofB-values suggest that the salts as well as their anions excepto-anisate behave as structure breakers. This is further supported by energy of activation data. The observedB-coefficients suggest probable involvement of simultaneous intra- and intermolecular hydrogen bonding between an ortho-substituent and the carboxylate group on the one hand and between the ortho-substituent and solvent water on the other. A good correlation betweenB-coefficients and the electronegativities of oxygen, nitrogen and sulphur atoms has been noted. The probable involvement of ringπ-electrons in depolymerising the water structure has been conjectured.     

The optical activity of cobalt(III) chelate diamine complexes

The optical activity of the tris-diamine complexes of cobalt (III) in the visible region is accounted for quantitatively by a coulombic correlation between the components of the electric hexadecapole moment of the ¹ A ₁→¹ T ₁ d-electron transition of the cobalt(III) ion in the [CoN₆] chromophore and a transient electric dipole induced in each ligand group. The correlated electric dipole of the ligand group forms a non-zero scalar product with a component of the magnetic dipole moment of the cobalt(III) ion d-electron transition in the first order employing either an O or a D ₃ effective chromophoric symmetry. The calculated first-order rotational strengths account largely for the observed optical activity due to the chiral puckered conformation of the chelate rings and for the axial single-crystal circular dichroism of a cobalt(III) tris-diamine complex in a uniaxial crystal. The second-order rotational strengths improve the agreement and accommodate the observed circular dichroism of randomly-oriented cobalt(III) tris-diamine complexes. The increase in the dipole strength of the ¹ A ₁→¹ T ₁ transition in a tris-diamine complex, relative to [Co(NH₃)₆]³⁺, is explained by the model in the first order.     

Multiple scattering calculation of double and single differential cross sections for ionization of hydrogen atoms by electrons at intermediate energies

The multiple scattering approach of Das and Seal, which was applied earlier to calculate the triple differential cross section for the ionization of atomic hydrogen by electrons is now used to calculate the double and the single differential cross sections for the same system. The range of the incident electron energy is taken to be 100–250 eV. The present results are compared with the measured results of Shyn and with the available distorted wave Born approximation results.     

Statistical thermodynamics of 1-butanol, 2-methyl-1-propanol, and butanal

The purpose of the present investigation is to calculate partition functions and thermodynamic quantities, viz., entropy, enthalpy, heat capacity, and Gibbs free energies, for 1-butanol, 2-methyl-1-propanol, and butanal in the vapor phase. We employed the multi-structural (MS) anharmonicity method and electronic structure calculations including both explicitly correlated coupled cluster theory and density functional theory. The calculations are performed using all structures for each molecule and employing both the local harmonic approximation (MS-LH) and the inclusion of torsional anharmonicity (MS-T). The results obtained from the MS-T calculations are in excellent agreement with experimental data taken from the Thermodynamics Research Center data series and the CRC Handbook of Chemistry and Physics, where available. They are also compared with Benson's empirical group additivity values, where available; in most cases, the present results are more accurate than the group additivity values. In other cases, where experimental data (but not group additivity values) are available, we also obtain good agreement with experiment. This validates the accuracy of the electronic structure calculations when combined with the MS-T method for estimating the thermodynamic properties of systems with multiple torsions, and it increases our confidence in the predictions made with this method for molecules and temperatures where experimental or empirical data are not available.     

Up conversion luminescence of Yb3+–Er3+ codoped CeO2 nanocrystals with imaging applications

The effects of Yb³⁺ doping on up conversion in Yb³⁺–Er³⁺ co-doped cerium oxide nanocrystals are reported. Green emission around 545 and 560 nm attributed to the ²H_11/2, ⁴S_3/2→⁴I_15/2 transitions and red emission around 660 and 680 nm due to ⁴F_9/2→ ⁴I_15/2 transitions under 975 nm excitation were studied at room temperature. Both green and red emission intensities increase as the Yb³⁺ concentration increases from 0%. Emission strength starts to decrease after the Yb³⁺ concentration exceeds a critical amount. The green emission strength peaks around 1% Yb³⁺ concentration while the red emission strength peaks around 4%. An explanation of competition between different decay mechanisms is presented to account for the luminescence dependence on Yb³⁺ concentration. Also, the application of up converting nanoparticles in biomedical imaging is demonstrated.