Comparison of analytical techniques to quantify malondialdehyde in milk powders

Several analytical methods were compared to quantify malondialdehyde (MDA) in milk powders. Modified thiobarbituric acid (TBA) methods, using either visible spectrophotometry (direct absorbance reading or after third derivative transformation of the spectrum) or HPLC, required derivatisation at elevated temperature, which appeared to catalyse artefactual MDA formation and thus overestimate the MDA content. In contrast to the TBA derivatisation method, the measurement of MDA as the dinitrophenylhydrazone derivative by HPLC or as the phenylhydrazone product by GC-MS with a deuterated internal standard resulted in lower estimates in the ranges of 2-17- and 3-30-fold, respectively; apparently due to the milder derivatisation conditions. The estimates of MDA determined by both HPLC-UV and GC-MS techniques result in lower values which are similar in magnitude even though the GC-MS technique is more sensitive.     

Vergleich der Elektronendichteverteilungen des Hydrido-Interstitialkomplexes HNb6I11 und des Interstitalhydrids HNb Ein Beitrag zur Cluster-bulk-Analogie

Comparison of Electron Density Distributions in the Hydrido-interstitial Complex HNb₆I₁₁ and in the Interstital Hydride HNb: A Contribution to Cluster-Bulk-Analogy The SW? Xα? SCF method has been used to compare changes of the electronic distributions in Nb₆I₁₁ and in Nb-metal caused by hydrogen at the octahedrally coordinated interstitial sites. Density maps of clusters Nb₆, Nb₆, Nb₆I₈³⁺, and HNb₆I₈³⁺ show: 1. The influence of the iodine ligands on the electronic distribution at the interstitial site is slight. 2. The spherically symmetric electron density of hydrogen at the interstitial sites is only deformed by the bonds to the neighbouring niobium atoms in both cases. Difference electron density maps illustrate that the interstitial hydrogen is weakly polarized in HNb₆I₁₁ as well as in HNb.     

Alkylation of ethyl bromomalonate by alkylcobaloximes

Allylcobaloximes react under very mild conditions with ethyl bromomalonate to yield allyl-substituted ethylmalonates in good yield. In the case of crotyl-, 3,3 dimethyl, allyl- and cinnamyl-cobaloximes, the substitution occurs with total rearrangement of the allyl groups. Similar rearrangements are observed during the reactions of propargyl- and allenylcobaloximes with BrCH(CO₂Et)₂ yielding allenyl- and propargyl-malonic esters respectively.     

Tritium in Lebensmitteln

In order to test the method of tritium determination and to determine the tritium activity, foods of known origin were investigated. The accuracy of the method over a prolonged period of time is confirmed by the statistical evaluation of the background values and of the counting efficiency. An average value of 600–800 pCi of tritium in one litre of water was found in milk, potatoes and apples. Drinking water contained very different activities of tritium, depending on its origin as ground or surface water. Food samples from the environment of nuclear reactors were not different in their tritium content when compared to those of other origin.     

Investigations in the field of vinyl ethers and esters of the furan series

Vinyl-furancarboxylate has been synthesized by the reaction of-furancarboxylic acid with acetylene and with vinyl acetate in the presence of various catalysts. The structure of the vinyl ester has been confirmed by IR spectra and by catalytic hydrogenation. The acid and alkaline hydrolyses of vinyl-furancarboxylate have been studied.     

Kettenlängeneffekte in Paraffinen, 4. Mitt.: Synthese von primären Carbonsäuren neben Alkylmalonsäuren aus n-Paraffinen durch Ummetallierung und anschließende Carboxylierung

Zusammenfassung Ausn-Paraffinen lassen sich mit Hilfe des Systems Quecksilberdialkyl/Kalium und nachfolgender Carboxylierung mit CO₂ primäre Monocarbonsäuren neben alkylierten Malonsäuren darstellen. Sekundäre Monocarbonsäuren bilden sich aus Paraffinen dabei höchstens in Spuren. Verzweigte Paraffine reagieren unter den beschriebenen Versuchsbedingungen schwer und stören als Verunreinigungen inn-Paraffinen nicht.Herrn ProfessorAsinger zu seinem 60. Geburtstag herzlichst zugeeignet. F. Korte, W. Klein undE. J. Schmid, Tetrahedron1966, Suppl.8, 93 (1966).     

A convenient synthesis of (2-styrylchromon-8-yl)acetic acids

(2-Styrylchromon-8-yl)acetic acids, structural analogs of (flavon-8-yl)acetic acid (FAA) have been synthesized with satisfactory yields according to two different methods. The ¹H and ¹³C nmr data fovor the S-trans stereoisomers.     

Electrical conductivity of liquid and film polymer composites filled with anion-radical salts in the presence of crown ethers

In the example of alkali metal tetracyanoquinodimethanides (M⁺TCQDM), a study has been made of the influence of resonance charge exchange on the conductivity () of polymer composites filled with anion-radical salts. When neutral molecules TCQDM⁰ are introduced into such systems, this leads to an increase in as a result of the lower activation energy of jumps between states TCQDM and TCQDM⁰. The addition of molecules of crown ethers has an analogous effect: They favor the appearance in the polymer matrix (the same as in solution) of TCQDM molecules in different charge states (TCQDM⁰, TCQDM) with migration of the cation within the limits of ternary associates (CE...M⁺...A) that are formed in systems for which the ratio of the crown ether cavity diameter to the cation diameter 1.4. Symbaticity has been found in the dependences of the electrical conductivity of films and the limiting mobility of solutions with the same composition on the parameter .Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 446–452, July–August, 1989.     

Initiation of polymerization of alkyl 2-cyanoacrylates in aqueous solutions of glycine and its derivatives

The polymerization of methyl 2-cyanoacrylate and heptyl 2-cyanoacrylate was carried out with the use of aqueous solutions of ¹⁴C-tagged glycine, methyl glycine, and acetyl glycine as initiators. When glycine and methyl glycine were used, radioactive polymers were formed. When acetyl glycine was used, the polymer formed was not radioactive. The data seem to indicate that free NH₂ groups appear to be necessary for the incorporation of the glycine initiator in the polymer. A possible mechanism for the polymerization is presented.     

Molecular spectra and molecular structure of heterocyclic compounds. Infrared and near ultraviolet absorption spectra of pyridine N-oxide derivatives

The infrared and ultraviolet spectra of many pyridine N-oxide derivatives have been studied. Ultraviolet spectra show a strong solvent effect in going from aprotic to hydroxylic solvents due to strong hydrogen bonding. Values of δ H° for several systems CH₃OH/XPyNO in tetra-chloroethylene solution were evaluated by infrared techniques and a linear correlation δ H° vs. δ v OH has been found. Features of the infrared and ultraviolet characteristic absorption bands were also investigated.