CHEMILUMINESCENCE FROM THE OXIDATION OF AUXIN DERIVATIVES

Abstract— The thiophenyl ester of indole-3-acetic acid and indole-3-acetonitrile produce chemiluminescence in aerated dimethylsulfoxide in the presence of potassium t -butoxide. The emitter is the aromatic aldehyde. In the case of acetonitrile, the other product expected from the cleavage of an intermediate dioxetane, cyanate/isocyanate, has also been identified. Other auxins also chemiluminesce under similar conditions, but the emitters have not been properly identified.
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route.     

Spirophostins: conformationally restricted analogues of adenophostin A

The synthesis, biological evaluation, and molecular modeling of two conformationally restricted analogues of adenophostinA (1), denominated as spirophostin (3R)-10 and (3S)-11, as novel ligands for the D-myo-inositol 1,4,5-trisphosphate receptor (IP3R), is presented. These diastereoisomeric spiroketals are synthesized by spiroketalization of D-glucose derivatives (2S)-15 and (2R)-16, separation of the protected isomers (3R)-19 and (3S)-20, followed by phosphorylation and deprotection. The spirophostins (3R)-10 and (3S)-11 display comparable biological activity, with a 3H-IP3-displacing and Ca2+-releasing potency less than IP3 and adenophostin A.     

Energy dependence of the epithermal neutron spectrum shape parameter α with respect to application of comparator-type NAA

The epithermal neutron spectrum shape parameter in nuclear reactors is explained from a theoretical point of view in terms of the neutron slowing down density function. The latter is approximated by Fermi's age theory. Values for are calculated for a simple approximation of a nuclear reactor: a disk shaped fission neutron source in an infinite graphite moderator. The model produces -values with the correct sign and magnitude, compared to experimental values from the literature, determined in a real reactor. It is shown that varies strongly with distance to the neutron source and less strongly with neutron energy. The inappropriateness of average -values, obtained from the slope of quasi-straight lines produced by log-log plots of E^– versus E, for the correction of non-ideal epithermal neutron activation is discussed. Conclusions are formulated concerning the impact of an energy dependent on comparator type NAA.     

Defect concentration in Ti-substituted YIG from TG curves

The article discusses theory and experiment about the measurement of defect concentration in Ti-substituted yttrium iron garnet by means of thermogravimetry techniques. The two possible cases arising from oxygen interchange with atmosphere, oxygen vacancies and interstitial cations, may be analyzed quantitatively from the derived expressions. The possibility of another type of defects being present in the samples, not associated to oxygen evolution, is not excluded. Measurements were carried out in air and CO₂ for different Ti contents. The substitution tends to increase slightly the defect parameter θ in YIG, while a CO₂ reducing atmosphere is much more effective than the Ti substitution for increasing θ. Calculations for a given single-phased sample sintered in air show two possibilities: a deficit of one oxygen atom for every 2.5 unit cells of 96 atoms, or one excess cation for every 3.5 cells. Other samples show very similar results. The accuracy involved in the measurements is about 2–3%.     

Local dynamic mechanical properties in model free-standing polymer thin films

High-frequency sinusoidal oscillations of a coarse-grained polymer model are used to calculate the local dynamic mechanical properties (DMPs) of free-standing polymer thin films. The storage modulus G(') and loss modulus G(") are examined as a function of position normal to the free surfaces. It is found that mechanically soft layers arise near the free surfaces of glassy thin films, and that their thickness becomes comparable to the entire film thickness as the temperature approaches the glass transition T(g). As a result, the overall stiffness of glassy thin films decreases with film thickness. It is also shown that two regions coexist in thin films just at the bulk T(g); a melt-like region (G(')G(")) in the middle of the film. Our findings on the existence of a heterogeneous distribution of DMPs in free-standing polymer thin films provide insights into recent experimental measurements of the mechanical properties of glassy polymer thin films.     

Hydride generation atomic fluorescence spectrometric determination of ultratraces of selenium and tellurium in cow milk

A sensitive procedure has been developed for selenium and tellurium determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS) after microwave-assisted sample digestion. The method provides sensitivity values of 1591 and 997 fluorescence units ng⁻¹ ml⁻¹ with detection limits of 0.005 and 0.015 ng ml⁻¹ for Se and Te, respectively. The application of the developed methodology to the analysis of cow milk samples of the Spanish market evidenced the presence of concentration ranges from 11.1 to 26.0 ng ml⁻¹ for Se, and from 1.04 to 9.7 ng ml⁻¹ for Te having found a good comparability with data obtained after dry-ashing of samples.     

Attenuated Total Reflection-Fourier transform infrared analysis of the fermentation process of pineapple

A direct and reagent free procedure has been developed to monitor the fermentation process of pine apple nectar using Attenuated Total Reflectance Fourier-transform mid-infrared spectrometry (FT-IR) and multivariate analysis. A classical 4² design for standards was employed for calibration using the information in the spectral range from 907 to 1531 cm⁻¹ of the first order derivative spectra after mean centering of infrared data. The root mean square error of calibration (RMSEC) of 0.040, 0.021, 0.063 and 0.074% w/w were obtained for glucose, fructose, saccharose and ethanol, respectively, and a mean relative validation error of 2.9, 2.1, 2.6 and 3.6% was achieved for glucose, fructose, saccharose and ethanol. Results obtained by the proposed procedure for the alcohol content at different fermentation levels were statistically comparable with those obtained by a reference spectrometric method. So, FT-IR spectrometry provides a fast alternative to long and tedious classical procedures to ethanol determination and sugar enzymatic analysis.