Model reactions on roast aroma formation

Summary After reaction of serine with glucose, fructose, diacetyl or cyclotene in an autoclave at 120° C, 150° C, or 180° C 338 volatile compounds (aliphatic and carbocyclic carbonyls, furans, furanones, pyranones, phenols, pyridines, pyrazines and pyrroles) were identified. The total amounts of some of these compound classes were determined and compared. Serine forms, beside glycolic aldehyde, also aminoethanol and some aliphatic aldehydes which lead to the formation of a great many compounds. Fructose obviously forms, under same conditions, more methylglyoxal than glucose, but generally the degradation products are identical. With rising temperature the number and amounts of reaction products increased some of which, like furylpyrazine and furfurylpyrazine, additionally required special intermolecular condensations. Diacetyl at 180° C obviously forms dimeric condensation products which, by further reactions, yield benzene compounds, 3-hydroxy-2,5,6-trimethylpyridine, 2-acetyl-4,5-furan and 2-acetyl-4,5-pyrrole. Cyclotene itself forms during heating numerous derivatives by condensation-, dehydration- or hydrogentransfer reactions. By reaction with NH₃ from serine, these derivatives formed imines which, by further reactions, yielded cyclopentapyrazines and dicyclopentapyrazines. Some mechanisms are proposed for the formation of pyrrolylalkanols, pyrrolopyrazines and products mentioned here.

---

Modellreaktionen zur Röstaroma-Bildung XI. Erhitzen von Serin mit ausgewählten Zuckern und Zuckerabbauprodukten im Autoklaven

Zusammenfassung Die Umsetzung von Serin mit Glucose oder Fructose bzw. mit Diacetyl oder Cycloten im Autoklaven bei 120 °C, 150 °C bzw. 180 °C führte insgesamt zur Identifizierung von 338 flüchtigen Verbindungen wie aliphatische und carbocyclische Carbonyle, Furane, Furanone, Pyranone, Phenole, Pyridine, Pyrazine und Pyrrole. Die Gehalte dieser Substanzklassen wurden bestimmt und verglichen. Serin bildet neben Glykolaldehyd auch Aminoethanol sowie einige aliphatische Aldehyde und ermöglicht so die Entstehung zahlreicher Reaktionsprodukte. Fructose setzt bei Erhitzen offenbar mehr Methylglyoxal frei als Glucose, bildet im übrigen aber gleiche Abbauprodukte. Allgemein bilden sich mit steigender Temperatur steigende Anzahlen und Mengen von Reaktionsprodukten, von denen einige wie z.B. Furyl- und Furfurylpyrazine bestimmte, zusätzliche intermolekulare Kondensationen voraussetzen. Diacetyl bildet offensichtlich bei 180 °C dimere Kondensationsprodukte, die dann zu benzolaromatischen Verbindungen bzw. 3-Hydroxy-2,5,6-trimethylpyridin, 2-Acetyl-4,5-dimethylfuran bzw. -pyrrol weiterreagieren. Cycloten bildet schon allein durch Kondensation, Wasserabspaltung bzw. Wasserstofftransfer zahlreiche Derivate. In Gegenwart von Serin bilden sie mit NH₃ Amine, die zu Cyclopentapyrazinen bzw. Dicyclopentapyrazinen weiter reagieren. Es werden Mechanismen für die Bildung einer Reihe von Röstaromaprodukten wie Pyrrolalkanole, Pyrrolopyrazine sowie den bereits genannten Verbindungen vorgeschlagen.

     

Fast frequency sweep computations using a multi‐point Padé‐based reconstruction method and an efficient iterative solver

Problems of the form Z (σ) u (σ)= f (σ), where Z is a given matrix, f is a given vector, and σ is a circular frequency or circular frequency‐related parameter arise in many applications including computational structural and fluid dynamics, and computational acoustics and electromagnetics. The straightforward solution of such problems for fine increments of σ is computationally prohibitive, particularly when Z is a large‐scale matrix. This paper discusses an alternative solution approach based on the efficient computation of u and its successive derivatives with respect to σ at a few sample values of this parameter, and the reconstruction of the solution u (σ) in the frequency band of interest using multi‐point Padé approximants. This computational methodology is illustrated with applications from structural dynamics and underwater acoustic scattering. In each case, it is shown to reduce the CPU time required by the straightforward approach to frequency sweep computations by two orders of magnitude. Copyright © 2006 John Wiley & Sons, Ltd.     

Photonic crystal optrode sensor for detection of Pb2+ in high ionic strength environments

We developed an optrode sensing device that utilizes a polymerized colloidal array (PCCA) photonic crystal material. This array diffracts light in the visible spectral region due to the periodic spacing of colloidal particles. The PCCA changes diffraction wavelength due to binding of Pb2+ to an 18-crown-6 ether molecular recognition agent. This optrode consists of a probe assembly that contains the PCCA Pb2+ sensing film. An inexpensive, commercial diode array spectrometer and a fiber-optic reflectance probe monitors the wavelength of light back diffracted by the PCCA. Liquid inlet and outlet connections are provided to introduce the sample solution and to exchange out nonbinding ions. In low ionic strength solutions, diffraction wavelength shifts are actuated by the binding of the Pb2+ to the crown ether to immobilize the Pb2+ counterions. In these low ionic strength solutions, a Donnan potential forms to cause an osmotic pressure, which swells the PCCA in proportion to the number density of bound Pb2+. This Donnan potential disappears at high ionic strengths. Thus, no response of the PCCA occurs. Our optrode design allows for the fast removal of nonbound ions from the PCCA by washing with pure water. Since the bound Pb2+ ions have a slow off rate from the crown ether, the bound Pb2+ PCCA diffraction transiently red shifts during washing, directly in proportion to the sample Pb2+ concentration. This transient diffraction red-shift can be used to quantitatively determine Pb2+ concentrations in high ionic strength solutions such as bodily fluids.     

Finite element modelling of rubber-like materials — a comparison between simulation and experiment

In this work finite element simulations are used based on the micro structure of polymers in order to transfer the information of the micro level to the macro level. The microscopic structure of polymers is characterized by a three-dimensional network consisting of randomly oriented chain-like macromolecules linked together at certain points. Different techniques are used to simulate the rubber-like material behaviour of such networks. These techniques range from molecular dynamics to the finite element method.The proposed approach is based on a so-called unit cell. This unit cell consists of one tetrahedral element and six truss elements. To each edge of the tetrahedron one truss element is attached which models the force-stretch behaviour of a bundle of polymer chains. The proposed method provides the possibility to observe how changes at the microscopic level influence the macroscopic material behaviour. Such observations were carried out in [1]. The main focus of this work is the validation of the proposed approach. Therefore the model is compared to different experimental data and other statistically-based network models describing rubber-like material behaviour.     

Aphid feeding deterrents in sorghum

Improvements in a synthetic diet for use in a bioassay to screen for feeding deterrents againstSchizaphis graminum, greenbug, are reported. Feeding on the synthetic diet was highly pH dependent with maximum feeding occurring at about pH 8.0. The bioassay was used as a guide in the isolation of feeding deterrent substances from aphid-resistant lines of sorghum (Sorghum bicolor). The major greenbug feeding deterrents isolated from sorghum leaves wereP-hydroxybenzaldehyde (ED₅₀ 0.13%), dhurrin (ED₅₀ 0.16%), and procyanidin (ED₅₀ 0.08%).Reference to a company and/or product named by the department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable.     

Mutiple Ionization of Rare Gases by Electron Impact

Electron impact studies of multiple ionization processes in helium, neon, argon, and xenon appear to support theoretical conclusions that the threshold probability for n-fold ionization is proportional to the nth power of the electron energy in excess of the threshold energy. The probability law applies, for the cases studied, over a considerable energy range that, for all but He²⁺, includes the possible onset of more than one mode of ionization. The presence of a Boltzmann spread in the energy of the electron beam or specific focusing effects due to ion source geometry are found to affect only the foot of the probability curve. By the use of certain assumptions, an estimate is also made of the departure from a ³P ionization probability curve resulting from onset of ionization to the ¹D and ¹S states.     

The thermal decomposition of some tolylene bis-carbamates

In fires, flexible polyurethane foams can decompose to give smokes which are subsequently degraded with the generation of hydrogen cyanide. In order to understand the general nature of this hazard it is first necessary to obtain information about the decomposition mechanism of the polyurethane foams and the structures of the intermediate smokes. The complexity of this problem has required the use of suitable model compounds. The preparation is described of (i) the four bis-carbamates based on pure tolylene 2, 4-diisocyanate and pure tolylene 2,6-di-isocyanate, each in combination with 2-ethoxyethanol and with triethylene glycol monomethyl ether, and (ii) a urethane-carbodi-imide-urethane and a urethane-urea-urethane based on pure tolylene 2,6-di-isocyanate and 2-ethoxyethanol. All were decomposed by heating under nitrogen at temperatures near 300°C. The two di-2-ethoxyethyl bis-carbamates ( la and IIa ) gave volatile monoisocyanate-monourethanes and 2-ethoxyethanol. The two di-2-[2-(2-methoxyethoxy)ethoxy] ethyl bis-carbamates ( Ib and IIb ) gave corresponding products and residue which contained carbodi-imide functions. The urethane-carbodi-imide-urethane ( Va ) gave a volatile urethane-carbodi-imide-isocyanate ( Via ) and 2-ethoxyethanol. The urethane-urea-urethane ( VIIIa ) decomposed through isocyanate- and carbodi-imide-containing materials to a volatile polymeric urea, which was obtained as a smoke and appeared to be virtually identical with the smoke obtained in earlier work from a commercial polyurethane. These results suggest that poly-urethanes based on tolylene di-isocyanate and polyether polyols decompose, when heated under nitrogen at 300°C, by cleavage of urethane groups to regenerate isocyanate groups and liberate alcohols. The isocyanato groups may react either with other isocyanato groups to give carbodi-imides, which are then rapidly hydrated to ureas, or with water to give amines, which react with other isocyanato groups again to give ureas. Whether these processes occur separately or together, the ultimate product at 300°C, i.e. the smoke, will be a polymeric urea.     

Verbal mediation as a function of age level.

A variety of experimental paradigms (reversal-nonreversal learning, transposition learning, etc.) indicate that young children evidence less mediational behavior than older children. Many variables have been shown to influence mediation, but it is not yet clear whether the emergence of mediational behavior is a voluntary or involuntary process, i.e., modifiable or unmodifiable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)