Modeling the IR Spectra of Aqueous Metal Carboxylate Complexes: Correlation between Bonding Geometry and Stretching Mode Wavenumber Shifts

A widely used principle is that shifts in the wavenumber of carboxylate stretching modes upon bonding with a metal center can be used to infer if the geometry of the bonding is monodentate or bidentate. We have tested this principle with ab initio modeling for aqueous metal carboxylate complexes and have shown that it does indeed hold. Modeling of the bonding of acetate and formate in aqueous solution to a range of cations was used to predict the infrared spectra of the metal‐carboxylate complexes, and the wavenumbers of the symmetric and antisymmetric vibrational modes are reported. Furthermore, we have shown that these shifts in wavenumber occur primarily due to how bonding with the metal changes the carboxylate C?O bond lengths and O‐C‐O angle.     

Structural characteristics of different types of nanoparticles synthesised in mesomorphic metal alkanoates

The class of thermotropic ionic liquid crystals (LCs) of the metal alkanoates possesses a number of unique properties, such as intrinsic ionic conductivity, high dissolving ability and ability to form time-stable mesomorphic glasses. These ionic LCs can be used as nanoreactors for the synthesis and stabilisation of different types of nanoparticles (NPs). Thus, some semiconductors, metals and core/shell NPs were chemically synthesised in the thermotropic ionic liquid crystalline phase (smectic A) of the cadmium octanoate (CdC₈) and of the cobalt octanoate (CoC₈). By applying the scanning electron microscopy, the cadmium and cobalt octanoate composites containing CdS, Au, Ag and core/shell Au/CdS NPs have been studied. NPs’ sizes and dispersion distribution of the NPs’ size in the nanocomposites have been obtained.     

Single laboratory validation of a microsatellite marker-based method in tomato variety identification

The objective of this study was to develop a systematic and flexible method for assembling multiplex simple sequence repeat marker panels for high-throughput genome analysis in the tomato, Solanum lycopersicum, for varietal identification and to demonstrate the technical viability of these genetic markers for use in the enforcement of U.S. Department of Agriculture marketing order-based identity preservation programs. GeneMapper, a semiautomated software tool, was used for designing multiplex panels, allele identification, and polymorphism pattern evaluation of diverse tomato cultivars. Semiautomated genotyping was performed on a set of 12 microsatellite markers providing genome-wide coverage of the tomato chromosomes. Microsatellites were detected with fluorescently labeled primers grouped into five multiplex panels, and each primer pair was assessed in replicated trials for reliability of allele size estimates. Allele sizes for each locus were compared, and a database for 34 tomato varieties was developed. The microsatellite marker set identified distinct allelic peaks and unique genetic fingerprints for each of the studied tomato varieties. A "blind testing" exercise with UglyRipe and Vintage Ripe tomato varieties, using the above set of markers and database, further established the usefulness of these microsatellite markers for tomato commodity marketing order enforcement.     

Super strong effect of surface impurities on the resistance and Hall effect of quench condensed Cs films

Thin films of Cs, quench condensed onto a He cold quartz plate, possess electronic mean free paths which considerably exceed the film thicknesses. When theses films are covered in situ with sub monolayers of Au, Ag, In, Rh and Pb in the range between 0.01 and 1 monolayers the film resistance and the Hall constant increase dramatically. This corresponds to a scattering cross section of the surface impurities which is larger than 1 in units of Various models are explored to explain these unusual behavior. None yields a satisfactory explanation for this extremely strong effect of surface impurities on the resistance and the Hall effect. Received: 8 January 1998 / Accepted: 17 March 1998     

Electron spin exchange in isoviscous solvent mixtures

Electron spin exchange rate constants and hyperfine coupling constants have been measured for two nitroxide spin probes in a number of isoviscous mixed solvents. Collision rate constants, normalized to 1 cP, are lower for solvents in which the major component is water. Further anomalies in the coupling constant for the systemtert-butanol-water are explained in terms of the marked concentration fluctuations known to occur in this solvent mixture. Substitution of a hydrophobic spin probe by one containing an –OH group leads to lowering of the spin exchange rate, possibly due to solvation of the probe.     

Interlaboratory comparison for the measurement of particle size and zeta potential of silica nanoparticles in an aqueous suspension

The Institute for Reference Materials and Measurements has organised an interlaboratory comparison (ILC) to allow the participating laboratories to demonstrate their proficiency in particle size and zeta potential measurements on monomodal aqueous suspensions of silica nanoparticles in the 10–100 nm size range. The main goal of this ILC was to identify competent collaborators for the production of certified nanoparticle reference materials. 38 laboratories from four different continents participated in the ILC with different methods for particle sizing and determination of zeta potential. Most of the laboratories submitted particle size results obtained with centrifugal liquid sedimentation (CLS), dynamic light scattering (DLS) or electron microscopy (EM), or zeta potential values obtained via electrophoretic light scattering (ELS). The results of the laboratories were evaluated using method-specific z scores, calculated on the basis of consensus values from the ILC. For CLS (13 results) and EM (13 results), all reported values were within the ±2 |z| interval. For DLS, 25 of the 27 results reported were within the ±2 |z| interval, the two other results were within the ±3 |z| interval. The standard deviations of the corresponding laboratory mean values varied between 3.7 and 6.5%, which demonstrates satisfactory interlaboratory comparability of CLS, DLS and EM particle size values. From the received test reports, a large discrepancy was observed in terms of the laboratory’s quality assurance systems, which are equally important for the selection of collaborators in reference material certification projects. Only a minority of the participating laboratories is aware of all the items that are mandatory in test reports compliant to ISO/IEC 17025 (ISO General requirements for the competence of testing and calibration laboratories. International Organisation for Standardization, Geneva, 2005b). The absence of measurement uncertainty values in the reports, for example, hindered the calculation of zeta scores.     

The size of particle aggregates produced by flocculation with PNIPAM, as a function of temperature

This work investigates the effect of temperature on the size of alumina aggregates formed by flocculation with temperature responsive Poly(N-Isopropylacrylamide)(PNIPAM). The results are discussed in terms of the effects of temperature on particle collision, particle adhesion and aggregate breakage. It was found that the size of alumina aggregates increases with increasing solution temperature. Particle/particle collision and aggregate breakage are largely unaffected by increasing solution temperature and therefore could not account for the change in aggregate size. The dominant factor in aggregate growth with increasing temperature was found to be the increase in the force of adhesion between alumina particles. The appearance of the adhesive force is triggered by the increase in temperature above the lower critical solution temperature of PNIPAM.