Microwave-assisted polycondensation of aliphatic diols of isosorbide with aliphatic disulphonylesters via phase-transfer catalysis

Numerous polycondensations of aliphatic diol of isosorbide and 1,8-dimesyloctane or other aliphatic dibromo and disulphonated alkylating agent was performed under phase-transfer catalytic conditions. In order to check the possible specific non-thermal microwave (MW) effects, reactions were comparatively performed inside a thermostated oil bath (Δ) under similar conditions. The reactions conditions were varied to optimize both, the fraction insoluble in methanol (FP MeOH) and the molecular weight of polyethers. In all cases, it was found that microwave-assisted polycondensations proceeded more efficiently compared with conventional heating (the reaction time was reduced from 24 h to 30 min: ratio 1/50). The polycondensation under microwave yields 63% of polyethers precipitating in methanol with relatively high average-weight molecular weights (M_w up to approximately 7000). The polyethers were characterized by NMR (¹H, ¹³C) and FT-IR spectroscopy and SEC measurement and MALDI-TOF mass spectrometry.     

Development and validation of a routine multiresidue method for determining 140 pesticides in fruits and vegetables by gas chromatography/tandem quadrupole mass spectrometry

A GC/tandem quadrupole MS/MS method was developed and validated for the determination of the residues of 140 pesticides in fruits and vegetables. Pesticides were extracted from samples by using a miniaturized acetonitrile-based extraction technique known as the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. Validation studies were carried out on carrots, tomatoes, and strawberries. In order to reduce systematic errors due to a matrix-induced effect, quantification was carried out using matrix-matched standard calibration curves. The recovery and precision results satisfied the European Union criteria (i.e., average recoveries were in the range 70-120% with RSDs < or = 20%) for 125 of the 140 pesticides at a spiking level of 0.01 mg/kg. At the higher spiking levels, there were just two instances of overall average recovery < 70% (chlorothalonil and captan). The measurement uncertainty was estimated following a "top down" approach as being 21 and 35%, on average, based on validation and ongoing recovery data, respectively (coverage factor k = 2, confidence level 95%). Practical application to 541 samples of apples, tomatoes, strawberries, cucumbers, currants, mushrooms, carrots, peppers, pears, onions, and gooseberries under strict QC conditions demonstrated the ruggedness of the total procedure.     

57Fe Mössbauer Study of One-Hour Annealing in Argon of Radiation Damage in Metamict Gadolinite from Ytterby

Hyperfine Interactions - Gadolinite, REE2FeBe2Si2O10, belongs to the group of metamict minerals. Metamict minerals incorporate uranium and thorium in their structures. Alpha-decays of uranium and...     

Representing homology classes by locally flat 2-spheres

We prove an existence result for topologically locally flat embeddings of 2-spheres in simply connected 4-manifolds. This topological result is deduced from a splitting theorem for pointed Hermitian modules over a cyclic group ring. A stability result for such modules is also proved. This applies to the isotopy classification of locally flat embeddings.Partially supported by the NSF.     

Solutions with constant sign at infinity of a linear functional equation of infinite order

We investigate how the existence and behaviour of solutions φ with a constant sign of the equation

     

Properties of an equilibrium hadron gas subjected to the adiabatic longitudinal expansion

We consider an ideal gas of massive hadrons in thermal and chemical equilibrium. The gas expands longitudinally in an adiabatic way. This evolution for a baryonless gas reduces to a hydrodynamic expansion. Cooling process is parametrized by the sound velocity. The sound velocity is temperature dependent and is strongly influenced by hadron mass spectrum.Work partially supported by the Polish Committee for Scientific Research under contract KBN-200579101     

Femtosecond time-resolved transient absorption spectroscopy of xanthophylls

Xanthophylls are a major class of photosynthetic pigments that participate in an adaptation mechanism by which higher plants protect themselves from high light stress. In the present work, an ultrafast time-resolved spectroscopic investigation of all the major xanthophyll pigments from spinach has been performed. The molecules are zeaxanthin, lutein, violaxanthin, and neoxanthin. beta-Carotene was also studied. The experimental data reveal the inherent spectral properties and ultrafast dynamics including the S(1) state lifetimes of each of the pigments. In conjunction with quantum mechanical computations the results address the molecular features of xanthophylls that control the formation and decay of the S* state in solution. The findings provide compelling evidence that S* is an excited state with a conformational geometry twisted relative to the ground state. The data indicate that S* is formed via a branched pathway from higher excited singlet states and that its yield depends critically on the presence of beta-ionylidene rings in the polyene system of pi-electron conjugated double bonds. The data are expected to be beneficial to researchers employing ultrafast time-resolved spectroscopic methods to investigate the mechanisms of both energy transfer and nonphotochemical quenching in higher plant preparations.