Comparison of extraction techniques for gas chromatographic determination of volatile carbonyl compounds in alcohols

Two extraction procedures, i.e. conventional liquid-liquid extraction (LLE) and liquid solid-phase microextraction (SPME) for extraction of the oximes formed after derivatization of carbonyl compounds with o-(2,3, 4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) in alcoholic solutions have been compared. The limit of detection for LLE followed by GC-ECD determination of C₁–C₆ was in the range of 0.23–3.3 μg/L, whereas for liquid SPME 0.005–0.33 μg/L. Both methods elaborated can be applied to the determination of carbonyl compounds present in spirits and alcoholic beverages. Received: 26 September 2000 / Revised: 14 January 2001 / Accepted: 16 January 2001     

Synthesis and Structural Studies of New (Triphenylphosphine)(trialkoxysilanethiolato)gold(I) Complexes

Compounds of general formula Au{SSi(OR)₃}(PPh₃), R = Prⁱ ( 1 ), Bu^s ( 2 ) or Bu^t ( 3 ), have been obtained by reaction of AuCl(PPh₃) with triethylammonium salts of respective silanethiols, (RO)₃SiSH. Molecular and crystal structures of 1 , 2 , and 3 have been determined by the single crystal X‐ray structural analysis. Compounds 1 and 2 are the first structurally characterized metal derivatives of hydrolytically unstable trialkoxysilanethiols (PrⁱO)₃SiSH and (Bu^sO)₃SiSH.     

Synthesis of 1,4‐phenylene‐bis‐aminomethanephosphonates: The stereochemical aspect

The synthesis of new 1,4‐phenylene‐bis‐(N‐alkylaminomethane)‐bis‐phosphonates 3Aa–3Da by the addition of dialkyl or diaryl phosphites to the azomethine bond of 1,4‐phenylene Schiff bases is reported. Some NMR studies on the stereochemistry of dialkyl phosphite addition to terephthalic bis‐imines showing the exclusive formation of the meso‐form are presented. The mechanism and the origin of such a high stereoselectivity are discussed. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:144–151, 2000     

The role of polymers in random lasing

In this review article, we describe the basic principles of random laser operation with particular emphasis on π‐conjugated, dye‐doped and biologically inspired polymers. Random lasers are unusual types of lasers that use disorder in the light amplifying medium to provide positive feedback for laser operation. Organic systems like polymers are affected with disorder resulting both from their molecular structure and fabrication techniques. Due to this fact polymers seem to fit to role of random lasers and now are being extensively studied in this direction. Despite multiline and multidirectional operation polymeric random lasers have potential for several interesting applications. Here we show that they can be successfully applied to sensing in biology and medicine, encoding of information, display technology and search and rescue. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 951–974     

Temperature dependence of the linewidths of shallow impurity spectral lines

A pronounced broadening of shallow donor transition linewidths in GaAs and CdTe by a factor of 2-2·5 on raising the sample temperature from 4 K to 10 K is reported. At low temperatures such impurity lines are inhomogeneously broadened by the Stark effect due to random electric fields arising from the ionized impurities in the crystal. The experimental observation is analysed and explained in terms of the temperature dependent spatial correlation between ionized donors and acceptors in the crystal.     

Mass spectrometry of some methyl esters of N-4-pyrimidinylamino acids: Rearrangements of the ions occurring on electron-impact ionization

The electron-impact-induced mass fragmentations of methyl esters of N-(1H-2-oxo-4-pyrimidinyl)ainino acids are reported. The loss of a ·COOCH₃ radical and the elimination of a methanol molecule were observed and possible mechanisms of these processes are proposed. The loss of a ·COOH radical and elimination of water were established, which suggests the rearrangement of the investigated esters into isomeric N-4-pyrimidinylamino acids.     

On the Brownian motion of a massive sphere suspended in a hard-sphere fluid. II. Molecular dynamics estimates of the friction coefficient

The friction coefficient exerted by a hard-sphere fluid on an infinitely massive Brownian sphere is calculated for several size ratios , where and are the diameters of the Brownian and fluid spheres, respectively. The exact microscopic expression derived in part I of this work from kinetic theory is transformed and shown to be proportional to the time integral of the autocorrelation function of the momentum transferred from the fluid to the Brownian sphere during instantaneous collisions. Three different methods are described to extract the friction coefficient from molecular dynamics simulations carried out onfinite systems. The three independent methods lead to estimates of which agree within statisticalerrors (typically 5%). The results are compared to the predictions of Enskog theory and of the hydrodynamic Stokes law. The former breaks down as the size ratio and/or the packing fraction of the fluid increase. Somewhat surprisingly, Stokes' law is found to hold withstick boundary conditions, in the range 1/4.5 explored in the present simulations, with a hydrodynamic diameterd=. The analysis of the moleuclar dynamics data on the basis of Stokes' law withslip boundary conditions is less conclusive, although the right trend is found as / increases.     

Pictet-Spengler reaction of biogenic amines with (2R)-N-Glyoxyloylbornane-10,2-sultam. Enantioselective synthesis of (S)-(+)-N-methylcalycotomine

(2R)-N-Glyoxyloylbornane-10,2-sultam reacted with dopamine hydrochloride, forming the Pictet-Spengler condensation product, which was further converted into (S)-(+)-N)-methylcalycotomine of high enantiomeric purity. The same kind of reaction with tryptamine hydrochloride gave the condensation product with 100% d.e.     

Synthesis and characterization of amphiphilic fullerenes and their Langmuir-Blodgett films

We report here the synthesis and characterization of three amphiphilic fullerene derivatives and their Langmuir-Blodgett thin films. Two of the C(60) amphiphiles are mono-derivatives with a long alkyl chain terminated with either -COOH (2) or NH(2) (3) as the hydrophilic headgroup, and the third one (5) is designed to bear the same NH(2) group as 3 but with 10 additional hydrophobic alkyl chains grafted on the C(60) sphere (Scheme 1). These amphiphiles form stable, ordered monolayers at the air-water interface. The molecular packing at the air-water interface and the mean area per molecule are determined by pressure isotherms at room temperature. Hysteresis of pressure isotherms of side chain C(60) (5) shows complete reversibility upon compression and decompression, which suggests that side chains on the C(60) sphere inhibit formation of aggregates at the air-water interface. Comparative studies of all three amphiphiles allow us to better determine the interaction between C(60)'s and their self-assembly kinetics at the air-water interface. Monolayers of monoderivatized amphiphiles (2 and 3) were transferred successfully onto quartz substrates as Z-type multilayered Langmuir-Blodgett films, and monolayers of 5 were transferred as Y-type films. Detailed characterization of the multilayer films (Z-type deposition) prepared from amine-terminated C(60) (3) using X-ray and neutron reflectometry reveals staggering of C(60) spheres and a head-to-head (Y-type) structure presumably due to flipping and reattaching of C(60) amphiphiles to the previous underlying C(60) layer.