Reaction of Epichlorhydrin with Carbohydrate Polymers. Part I. Starch Reaction Kinetics

The starch-epichlorohydrin (ECH) reaction follows second order kinetics, first order with respect to ECH as well as starch. The activation energy for the reaction is of the order of 38 kJ/mole and the temperature coefficient K323/K303 is of the order of 2.     

Nonenzymic browning. XIV. Reaction of phospholipids with 1,4-benzoquinone.

Phosphatidylethanolamine reacts with 1,4-benzoquinone with the formation of a red unstable intermediary product consisting of one phosphatidylethanolamine residue and one 1,4-benzoquinone residue. The secondary reaction products are purple, violet, and reddish brown. Consequently, the absorption maximum shifts from 430 nm to 490 nm during the reaction. Finally, brown macromolecular end-products are formed. Phospholipids derived from choline, such as phosphatidylcholine, lysophosphatidylcholine, sphingomyelin, contribute only a little to the browning reactions, in comparison with phospholipids containing a primary amino-group (phosphatidylethanolamine, lysophosphatidylethanolamine, phosphatidylserine). The browning of a natural mixture of egg phospholipids depends on the content of derivatives containing a primary amino-group.     

Interaction of malonaldehyde with collagen. I. The Reaction Conditions

Summary The demonstration was carried out of the crosslinking ability of malonaldehyde whereby the optimum conditions were determined for the reaction of malonaldehyde with collagen both indirectly by studying the changes the temperature of shrinkage of collagen tendons, and directly by means of discontinual electrophoresis of soluble native and denaturated collagen.

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Zusammenfassung Optimale Bedingungen für die Reaktionen zwischen Malonaldehyd und Collagen wurden bestimmt. Die Vernetzungsfähigkeit wurde indirekt von den Temperaturveränderungen bei der Kontraktion der Collagensehne und direkt mittels der diskontinuierten Elektrophorese des löslichen, nativen und denaturierten Collagens nachgewiesen.

     

Reaction of Epichlorhydrin with Carbohydrate Polymers. Part II. Starch Reaction Mechanism and Physicochemical Properties of Modified Starch

Detailed mechanistic pathways are described for starch-epichlorohydrin (ECH) reaction. The mature and extent of side reactions accompanying the cross-linking reaction as well as the influence of reaction conditions on these have been demonstrated. The influence of degree of crosslinking of starch on its various physicochemical properties such as swelling, solubility, gelatinization, viscosity, iodine complex, crystallinity and granular structure are discussed.     

Crosslinking of Starch Xanthate III. Reaction with Low-Molecular-Weight Polyamines

Starch xanthates of 0.11-0.55 degree of substitution (D.S.) were reacted with low-molecularweight polyamines – hydrazine, diaminoalkanes, stearylpolyamines, polyethylenamines, and polyethylenimines – to produce thiourethans. The progress of the reaction was followed by observing spectral absorption and viscosity changes. In many cases the reaction produced a gel with viscosity of 10,000-60,000 cP. The magnitude of the viscosity varied directly with increasing xanthate D.S. Increased amino- to xanthate-group ratios were necessary in the reactions with xanthates at the low end of the D.S. range to achieve much viscosity development as compared to the xanthates of highest D.S. The basicity of the amines was a factor in the rate and extent of reaction, the stronger amines being less reactive than the weaker ones. Solid products were precipitated from the gels by ethanol. Nitrogen and sulfur analyses and infrared and ultraviolet spectra were made with these solids. From those data the D.S. and amount of crosslinking in the products were calculated. The thiourethans had a D.S. that was approximately one-half of the D.S. of the starting starch xanthate.     

Reaction of D-arabino-hexosulose with L-lysine

D-arabino-hexosulose, a product of oxidative degradation of hexoses, reacts with L-lysine forming light coloured intermediary products (premelanoidins) which are further converted into brown macromolecular pigments. The reaction of D-arabino-hexosulose is not autocatalytic contrary to that of sugars. The browning proceeds after a zeroth order reaction mechanism. The induction period was observed neither in premelanoidin formation, nor in browning reaction. Both the hexosulose-lysine interaction and the browning consisted of two steps, possessing different kinetic characteristics and reaction mechanisms. The two steps of reactions are isokinetic only at lower temperatures. The activation energies and the activation enthalpies of premelanoidin formation and of browning reactions are temperature-dependent and are lower than those of the formation of intermediary compounds and of browning reactions of sugars.     

Reaction of sorbic acid in wheat flour doughs: reaction with thiols.

The general characteristics of the reaction between sorbic acid and thiols are reviewed. Cysteine adds to the conjugated diene in position 5 to form the substituted 3-hexenoic acid. This is labile in acid solution, yielding a quantitative amount of sorbic acid. When wheat flour doughs are treated with sorbic acid and heated, a significant amount of the sorbic acid is not recovered on extraction with methanol. The use of acidified methanol leads to a quantitative recovery of the preservation and evidence is presented to suggest that sorbic acid-thiol adducts are formed. This is the first report of 'reversibly bound' sorbic acid in a food.     

Reaction of apple pectin with ammonia

Amidated apple pectins were prepared in aqueous and aqueous-alcoholic media, and the factors influencing both ammonolysis and hydrolysis of the ester groups of apple pectin by ammonia were studied.
In aqueous solution, the extent of ammonolysis and hydrolysis was very dependent upon ammonia concentration. In aqueous alcohol, the products were also dependent upon the particular alcohol and its concentration, increasing concentrations suppressing hydrolysis; the overall rate of reaction is much slower than in the absence of alcohol. The product balance between amonolysis and hydrolysis of the ester groups is influenced by the polarity of the medium, and by the concentration of NH⁺₄ and OH⁻.
It was shown that the extents of ammonolysis and hydrolysis of the ester groups are significantly affected by the polarity of the medium and the acid-base equilibrium of the interaction of ammonia with water, i.e. NH₃+H₂O ↔ NH⁺₄+OH⁻. The content of free ester and amidated carboxyl groups in the pectin can be regulated by varying the concentration of ammonia, temperature, reaction time and the polarity of the medium. The rate of enzymic hydrolysis of amidated pectins decreases with increasing amide content. A mechanism for the reaction is proposed.     

Reaction of wood with inorganic salts

Wood samples and veneers of Hevea brasiliensis (Rubber wood) and Acacia auriculaeformis treated with aqueous solutions of chromium trioxide, ferric chloride and ferric nitrate were studied for water repellency and their reaction with wood constituents. FTIR spectra obtained from wood surface treated with chromium trioxide indicate the formation of a water insoluble complex between chromium trioxide and aromatic ring of lignin, whereas no reaction takes place with ferric salts. Treatment of wood by chromium trioxide was found to be effective in imparting water repellency in wood.     

The Reaction of Myosin with Malonaldehyde

SUMMARY— The protein malonaldehyde reaction was studied as a potential mechanism of protein denaturation in muscle, especially during frozen storage. Myosin, a structural protein of muscle, was reacted at pH 6.8 and ionic strength 0.5 with malonaldehyde, an oxidation product of polyunsaturated fatty acids. The rate of reaction with the s-amino groups of myosin was greater at -20° than at 0° and was almost as great as that at +20°. The same relationship was observed when the decreasing malonaldehyde concentration was measured in the protein-malonaldehyde reaction mixture. Amino acid analyses before and after reaction at 100° for 60 set showed that malonaldehyde reacted preferentially with histidine, arginine, tyrosine, and methionine. In frozen solution, malonaldehyde reacted with lysine, tyrosine, methionine, and arginine in decreasing order of intensity, but it did not react with histidine. The increased rate of reaction in the frozen system is explained as a concentration effect and as a catalytic effect involving the ice structure.     

Reaction of nonaqueous phase TCE with permanganate

Oxidative treatment of trichloroethylene (TCE) in the form of dense nonaqueous-phase liquid (DNAPL) by potassium permanganate (KMnO4) was investigated in a series of batch tests. The study focused on understanding the fundamental mechanisms of oxidative removal of DNAPL TCE by permanganate oxidation. Dissolution experiment for DNAPL TCE has been performed as a control experiment in the absence of KMnO4. DNAPL TCE dissolved into the aqueous phase until it reached the saturation concentration of 1200 mg/L (9.16 x 10(-3) M) at 20 degrees C. The rate of dissolution of DNAPL TCE was proportional to the volume of the DNAPL. In the presence of KMnO4, the experimental results showed that the amount of TCE oxidized during the reaction was increased continuously as [MnO4-] decreased even though the rate decreased as [MnO4-] decreased. It was apparent that more DNAPL TCE was removed with a faster rate for higher initial permanganate concentration. At high permanganate concentration, the aqueous concentration of TCE was kept low and practically constant by the chemical reaction between aqueous TCE and MnO4-. However, as MnO4- was consumed in the system, the aqueous concentration started to increase until it reached solubility. From experimental observation, 1.56-1.78 mol of MnO4- was consumed per mole of TCE oxidized. Furthermore, 2.85-2.98 mol of Cl- was released to the solution per mole of TCE oxidized. Since the complete mineralization of TCE requires 2.0 mol of MnO4- and releases 3 mol of Cl- per mol of TCE oxidized, the observed stoichiometric factors indicated incomplete mineralization of TCE, but nearly complete dechlorination. Enhancement factor due to chemical reaction was quantified experimentally. The enhancement factor was shown to be a function of the molar ratio of MnO4- to TCE in the system, and hence varied during the reaction period.     

Reaction of hydrogen sulphide with 2-alkenals

Summary Depending on the types of solvent and catalyst, different products are formed in the reaction of hydrogen sulphide with 2-alkenals. The structures of many of these products have been elucidated, and the reaction sequences leading to them are proposed.

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Reaktion von Schwefelwasserstoff mit 2-Alkenalen

Zusammenfassung In Abhängigkeit von der Art des Lösungsmittels und des Katalysators bilden sich verschiedene Produkte bei der Reaktion von Schwefelwasserstoff mit 2-Alkenalen. Die Strukturen vieler dieser Verbindungen wurden aufgeklärt, und die Reaktionsstufen, die dazu führten, wurden vorgeschlagen.

     

Reaction of starch with α-amino acids

 Thermogravimetric analysis and differential scanning calorimetric measurements of 10 : 1 w/w starch/α-amino acid blends were carried out in air, and from room temperature to 450  °C. Admixtures of each of the 17 tested amino acids depressed the point of starch glassy transition and point of starch decomposition. Only decomposition products of proline reacted with starch in the blend of starch with proline. Other amino acids reacted prior to their decomposition. Among them alanine, isoleucine, and valine most readily reacted with starch. The reactions were assumed to be esterifications of amino acids by starch and/or the dextrins produced from starch. Arginine, histidine and lysine being basic amino acids reacted as bifunctional reagents with involvement of carboxylic and amino groups. Received: 30 October 1998 / Revised version: 4 February 1999     

Reaction of Oxidized Lipids with Protein. Part 10. Effect of Protein on the Autoxidation of Phospholipids

Phospholipids are oxidized at 25 °C and at 60 °C under the formation of brown pigments significantly more rapidly in mixtures with cellulose than in mixtures with casein of egg albumin. The extent of browning and the difference of reactivities are more pronounced in case of phosphatidylethanolamine, lysophosphatidylethanolamine and phosphatidylserine in mixtures with a low water content than in those containing a higher percentage of water. Oxidized phospholipids are partially combined with protein in unextractable insoluble lipoprotein complexes.