Effect of60Co radiation on some chemical changes in potato starch pastes and gels

The effect of ionizing radiation /-⁶⁰Co/ on some chemical changes in potato starch pastes stored for 14 d at 4–5 °C and prepared from the starch irradiated in the range of doses 1.5–15 kGy has been studied. It was found that along with the increase in the doses used, the viscosity of pastes as well as the pH of solutions decreased. On the other hand, the increase in the concentration of reducing sugars was observed. The retrogradation of pastes was found to be inhibited by increasing doses of radiation pointing out that ionizing radiation has a favourable effect on their stability during the time of storage.     

EPR and Raman investigations into anionic redox chemistry of nanoporous 12CaO·7Al2O3 interacting with O2, H2 and N2O

EPR and Raman spectroscopy jointed with temperature-programmed reduction (TPR) and oxidation (TPO) were used to elucidate of the anionic redox processes occurring during the interaction of dioxygen, nitrous oxide and dihydrogen with nanoporous 12CaO·7Al₂O₃. The results showed that hydrogen and oxygen enter the mayenite cages following a dissociative pathway involving hydride, hydroxyl and peroxide intermediates, respectively. Generation and annihilation of the cage O ₂ ⁻ and O⁻ radicals upon oxidative and reductive treatments, confined to the near to the surface region, were found to be reversible. The key intermediates of this process were identified and a detailed mechanism of the surface and cage reactions was proposed.     

Adsorption of phenylacetylene on Si(100)-2 x 1: kinetics and structure of the adlayer

Direct adsorption of phenylacetylene on clean silicon surface Si(100)-2 x 1 is studied in ultrahigh vacuum (UHV). The combination of scanning tunnel microscopy (STM) and surface differential reflectance spectroscopy (SDRS) with Monte Carlo calculations are put together to draw a realistic kinetic model of the evolution of the surface coverage as a function of the molecular exposure. STM images of weakly covered surfaces provide evidence of two very distinct adsorption geometries for phenylacetylene, with slightly different initial sticking probabilities. One configuration is detected with STM as a bright spot that occupies two dangling bonds of a single dimer, whereas the other configuration occupies three dangling bonds of adjacent dimers. These data are used to implement a Monte Carlo model which further serves to design an accurate kinetic model. The resulting evolution toward saturation is compared to the optical data from surface differential reflectance spectroscopy (SDRS). SDRS is an in situ technique that monitors the exact proportion of affected adsorption sites and therefore gives access to the surface coverage which is evaluated at 0.65. We investigate the effect of surface temperature on this adsorption mechanism and show that it has no major effect either on kinetics or on structure, unless it passes the threshold of dissociation measured at ca. 200 degrees C. This offers a comprehensive image of the whole adsorption process of phenylacetylene from initial up to complete saturation.     

Structural Studies of Aluminated form of Zeolites—EXAFS and XRD Experiment,STEM Micrography,and DFT Modelling

In this article, the results of computational structural studies on Al-containing zeolites, via periodic DFT + D modelling and FDM (Finite Difference Method) to solve the Schrödinger equation (FDMNES) for XAS simulations, corroborated by EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy and PXRD (powder X-ray diffractometry), are presented. The applicability of Radial Distribution Function (RDF) to screen out the postulated zeolite structure is also discussed. The structural conclusions are further verified by HR-TEM imaging.     

Decoupling conditions for the vibronic equation in dimers

The analytical conditions are obtained and discussed under which the vibronic equations for dimers can be decoupled.     

Analysis of α‐acyloxyhydroperoxy aldehydes with electrospray ionization–tandem mass spectrometry (ESI‐MSn)

A series of α‐acyloxyhydroperoxy aldehydes was analyzed with direct infusion electrospray ionization tandem mass spectrometry (ESI/MSⁿ) as well as liquid chromatography coupled with the mass spectrometry (LC/MS). Standards of α‐acyloxyhydroperoxy aldehydes were prepared by liquid‐phase ozonolysis of cyclohexene in the presence of carboxylic acids. Stabilized Criegee intermediate (SCI), a by‐product of the ozone attack on the cyclohexene double bond, reacted with the selected carboxylic acids (SCI scavengers) leading to the formation of α‐acyloxyhydroperoxy aldehydes. Ionization conditions were optimized. [M + H]⁺ ions were not formed in ESI; consequently, α‐acyloxyhydroperoxy aldehydes were identified as their ammonia adducts for the first time. On the other hand, atmospheric‐pressure chemical ionization has led to decomposition of the compounds of interest. Analysis of the mass spectra (MS² and MS³) of the [M + NH₄]⁺ ions allowed recognizing the fragmentation pathways, common for all of the compounds under study. In order to get detailed insights into the fragmentation mechanism, a number of isotopically labeled analogs were also studied. To confirm that the fragmentation mechanism allows predicting the mass spectrum of different α‐acyloxyhydroperoxy aldehydes, ozonolysis of α‐pinene, a very important secondary organic aerosol precursor, was carried out. Spectra of the two ammonium cationized α‐acyloxyhydroperoxy aldehydes prepared with α‐pinene, cis‐pinonic acid as well as pinic acid were predicted very accurately. Possible applications of the method developed for the analysis of α‐acyloxyhydroperoxy aldehydes in SOA samples, as well as other compounds containing hydroperoxide moiety are discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Testing the 1,1,3,3-tetramethyldisiloxane linker in olefin metathesis

Compounds 12-15, possessing two styrenes connected by a silicon linker [1,1,3,3 tetramethyl-di-siloxane], were synthesized, characterized and used as model compounds for the ring-closing metathesis (RCM) catalyzed by commercially available ruthenium catalysts 1, 2 and 3. The RCM reactions of 12 and 15 in the presence of catalysts 1 or 2 resulted exclusively in the formation of (E)-stilbenes. The RCM reactions of 13 and 14, compounds possessing alkoxide substituents in the ortho position to styrene functionality, were not observed in the presence of 2, presumably due to the formation of inactive Hoveyda type ruthenium complexes. The RCM of mixture of 12 and 15, with 2, was used for the detailed examination of the mechanism of metathesis reactions investigated in this work. They revealed that both inter- and intramolecular metathesis is possible, in this case, despite the use of siloxane linker.