Reaktivität und Toxizität homologer Brom- und Dibromalkane

Reactivity and Toxicity of Homologous Bromo- and Dibromoalkanes The rate constants of the reactions of 4-(4-nitrobenzyl)-pyridine (NBP) with ω,ω′-dibromoalkanes Br (CH₂)_n Br (n = 2–4), alkyl bromides C_nH_2+n1Br (N = 2–4) and allyl bromide in acetophenone were measured and compared with the LD₅₀-values of these compounds estimated on mice. The tested dibromoalkanes show a contrary graduation of reactivity and acute toxicity.     

Die kristallinität von äthylen-vinylacetat-copolymeren

Copolymers of ethylene and vinyl acetate of different composition were investigated by differential thermal and x-ray analysis in the temperature range of ?80 to 140°C. Compounds with more than 60 weight-% of vinyl acetate are amorphous. In the partially crystalline copolymers with lower contents of vinyl acetate the glass transition temperature is independent of composition and lies below that in amorphous copolymers. The melting points of the partially crystalline compounds increase with ethylene contents and can be described with the aid of a modified FLORY equation. The increase of the degree of crystallinity with ethylene content is demonstrated. The influence of thermal pre-treatment on the melting behaviour is discussed.     

Zur Essentialität der Polyenfettsäuren

On the Essential Nature of Polyunsaturated Fatty Acids Several plant oils contain polyunsaturated fatty acids which cannot be synthesized by the human body. They have been recognized as essential nutrients, as characteristic symptoms are caused by deficient intake. The LCP-fatty acids are incorporated into structural lipids and cell membrans and influence directly their properties. LCP-fatty acids are precursors of prostaglandins, lencotrienes and eicosanoid mediators, which intern regulate numerous cell functions. The effects of LCP-fatty acids on pre- and postnatal growth and the nervous system are discussed in detail.     

Fettgewebsbildung und Fleischqualität

Formation of Fatty Tissue and the Quality of Meat The formation of depot fat and intramuscular fat in slaughter animals during growth follows specific patterns. The effects of race, type, sex, age, weight, castration, housing, feeding and growth rhythm on the formation of fatty tissues at various parts and their structure were studied within individual species of animals. The influence of the formation of fatty tissues on the structure of the muscle can be measured either directly or in conjunction with the aforesaid variable factors.     

Hitzestabilität der Tocopherole

Heat Stability of Tocopherole The tocopherols are very important biological and nutritive components of our food. Furthermore, they are also antioxidants. The tocopherols are not volatile substances (such as e.g. BHA and BHT) and they don't cause off-flavour (TBHQ) or colour (lecithin) at higher temperatures, therefore, they can be used for stabilisation of frying fats. They stability of tocopherols at 180°C is relatively good and it depends on the kind of fat. The heat stability of tocopherols is mostly higher in fats with higher iodine value.     

Pufferkapazität mikrofiltrierter Magermilchkonzentrate

The buffering capacity β of skim milk, of microfiltration concentrates made thereof, and of an evaporated concentrate was analyzed using a titrimetric method and the well‐known van Slyke equation. The contribution of the different active buffer pairs was calculated based on their apparent dissociation constants (pK_a) and their individual buffering curves. β was found to be correlated with their casein contents, and also with their whey protein‐ and ash content. Higher concentrations of dry matter, e.g., due to microfiltration or evaporation, result in a higher measured buffering capacity.     

Affinität an Molekularsieben

Affinity on Molecular Sieves The affinity on molecular sieves in dependent on various physical factors and intermolecular forces, which, however, can not be measured quantitatively. This led to the use of the so called polarity series. Since these forces have also an effect on boiling point, a simple formula is presented, which enables the calculation of affinity from data that are easily obtained. This enables the technologist to compare different adsorbates.     

Taktizität bei Polykondensaten

The concept of tacticity, originally established for vinyl polymers, is shown to be valid also for condensation polymers if extended to include some particularities. From this point of view the preparation and properties of exclusively isotactic polyesters from lactic acid and substituted β-hydroxy propionic acid are described. Ditactic polyurethanes were prepared from tartaric acid esters. In contrast to tactic vinyl polymers, the condensation polymers obtained show optical activity. A special kind of steric regularity was found to be possible in polyesters and polyamides having built-in single bonds with hindered rotation. Thermal isomerisation of these polyesters may result in removal of their tacticity. The kinetics of this reaction were investigated. Cis-tacticity and trans-tacticity was observed to occur in condensation polymers having CC or NN double bonds in the backbone chain. The preparation of some of these polymers is reported, including experiments based on a photolytic polyreaction. The application of catalysts or light led to isomerisation at the double bonds.     

Basizität von Ketonen

Basicity of Ketones The determination of the protonation ratios of weak organic bases e. g. ketones in strong acidic solutions by means of NMR and UV spectroscopy is described. Different extrapolation procedures which allow to obtain the basicity and solvation parameters are presented and compared. Literature data for aliphatic, cyclic and aromatic ketones as well as diketones are collected and discussed in terms of structural and solvation effects on basicity.     

Stabilität von Dispersionen

Stability of Dispersions The importance of production and application of disperse systems in the industry is steadily growing. On the other site colloidale systems surround us every day (for example foodstuffs, pharmaceutica, and so on). With the knowledge about the mechanism of interaction forces we are able to develope new materials and improve available systems. The stability of such systems is one of the central point of research. One of the well known physical models of colloid stability is given by DLVO‐Theory. With this theory we have a tool to influence the stability of such dispersion systems. In this paper electrokinetic methods are used to investigate interaction forces in disperse systems. The influence of pH‐value, electrolyte concentration, and valency is shown. But, not in all cases the DLVO‐model works satisfactoryly. Some reasons of this behavior will be discussed.     

Funktionalität von Lecithinen

Functionality of lecithins. In industry the functional emulsifying power of soya lecithin has a great technical and commercial importance, while egg lecithin has taken an interesting market niche. The requirements on consistent emulsifying, stabilizing and nutritional properties can be achieved by adjustment of standard qualities and a range of lecithin modifications: Enzymatic hydrolysis, acetylation and hydroxylation give lecithins with increased hydrophilicity and subsequently improved oil-in-water emulsifying properties. Alcohol fractionation, sometimes combined with chromatographic isolation, divides crude lecithin in specific phospholipid fractions, yielding an optimal functionality in specific product applications. Oil free “pure” lecithins in powder and granular form are used because of convenient dosage, neutral taste and enhanced O/W emulsifying performance. Combinations of the processes give a vaste range of tailor made special lecithins with different hydrophilic-lipophilic balance properties in food, feed, pharmaceutical, cosmetic and technical industries.     

Zur Stabilität Stationärer Elektrischer Zweipolzustände

In connection with the work of U. F. Franck on the stability of electrode conditions equivalent circuits are presented for dipoles, the characteristics of which can be described by capacity and inductivity effects. Equations are derived for the variation of current and potential with time. From these equations conclusions can be made regarding the stability of the system and the occurrence of periodic phenomena. The latter are possible only if the dipole has duplicate storage properties.

The results obtained are checked with known electrical circuits and applied to experimental data taken from the literature pertaining to electrodes with surface layers.

Résumé

Analyse du rôle de la formation de dipoles stationnaires dans la stabilité des électordes, compte tenu des effets capacitifs et inductifs dûs au passage du courant. Dans les cas d'accumulation simple et d'accumulation double de ces dipoles, les lois de variation horaires de l'intensité et de la tension, après ouverture ou fermeture du circuit, peuvent être établies. Des critères de stabilité, dont on précise les modalités d'applications, en sont déduits.     

Rasche Ermittlung von Lösungsinhomogenität neben molekularer Polydispersität bei Polymer-Lösungen

By measuring the light scattering curve up to very small angles it is possible to derive, with polymer solutions containing supermolecular gels a total molecular weight M and a molecular weight of the gelfree portion, M_w. It is suggested to use the ratio of both these figures as a measure for the gel fraction and to characterize thereby the homogeneity of the solution.