Low molecular weight adds

The lower fatty acid most frequently bound in esters is acetic acid, while formic, propionic, butyric and isobutyric adds occur less often. The common alcohol bound in esters is ethanol. However, esters of methanol, aUyl alcohol, butan-l-ol higher alcohols and very often esters of monoterpenic and aromatic alcohols also occur in foods, and esters of sulfur-containing alcohols are also common. Esters of low molecular weight acids and alcohols usually have a fruity odour esters of terpenic alcohols with low molecular weight adds tend to have fragrant odours resembling flowers. Esters of aromatic adds and aromatic alcohols generally have heavy balsamic odours. 

Addition polymerization requires a chain reaction in which one monomer molecule adds to a second, then a third and so on to form a macromolecule. Addition polymerization monomers are mainly low molecular-weight olefinic compounds (e.g., ethylene or styrene) or conjugated diolefins (e.g., hutadiene or isoprene). 

When catalyzed by acids, low molecular weight aldehydes add to each other to give cyclic acetals, the most common product being the trimer. The cyclic trimer of formaldehyde is called trioxane, and that of acetaldehyde is known as paraldehyde. Under certain conditions, it is possible to get tetramers or dimers. Aldehydes can also polymerize to linear polymers, but here a small amount of water is required to form hemiacetal groups at the ends of the chains. The linear polymer formed from formaldehyde is called paraformaldehyde. Since trimers and polymers of aldehydes are acetals, they are stable to bases but can be hydrolyzed by acids. Because formaldehyde and acetaldehyde have low boiling points, it is often convenient to use them in the form of their trimers or polymers. 

That the relatively inert CC14 adds in this way may seem a little surprising, but the AH values for both steps of the reaction chain are exothermic — 75( — 18), and -17( — 4)kJ (kcal)mol-. The first formed radical (74) may, however, compete with -CC13 in adding to RCH=CH2, so that low molecular weight polymers are formed under some conditions, as well as the normal addition product (75). 

The hydroxyl radicals may abstract hydrogen from the substrate (which initiates grafting) (16) or add to a vinyl monomer (which gives homopolymer). The decomposition rate of persulfate ions is enhanced by the presence of a low-molecular weight alcohol. A high-molecular weight alcohol like cellulose can react in the same way. 

The variety of control mechanisms of xylanase synthesis is demonstrated by examples of the synthesis of xylanase induced by xylose (38,74,75). To a list of low-molecular weight xylanase inducers one can add 4-thioxylobiose (80,81) and 4-O-p-D-xylopyranosyl-L-arabinopyranose (73,77). 

WOF is a problem associated with the use of precooked meat products such as roasts and steaks. The term WOF was first used by Tims and Watts (2) to describe the rapid development of oxidized flavors in refiigerated cooked meats. Published evidence indicates that the predominant oxidation catalyst is iron from ntyoglobin and hemoglobin, which becomes available following heat denaturation of the protein moiety of these complexes. The oxidation of the lipids results in the formation of low molecular weight components such as aldehydes, adds, ketones and hydrocarbons which may contribute to undesirable flavor. 

The most practical method for preventing WOF in meat products is to add antioxidants prepared from natural precursors such as sugars and amino adds by heating them to produce constituents that not only act as antioxidants but serve to enhance meaty flavor as well. The resulting Maillard products have been known to have antioxidant activity in lipid systems (6-8). It is assumed that the antioxidative property of the Maillard reaction is assodated with the formation of low molecular weight reductones and high molecular weight melanoidins (6, 7, 9-13). 

PB has a specific gravity of 0.91 and a Tm of 226 C. Like PP. it is readily oxidized because of the tertiary carbon atoms present. Since its solubility parameter is about 8.0 H, it is not soluble in polar solvents nor in low-molecular-weight alkanes such as pentane, but is soluble in hot alkanes with slightly higher molecular weights. PB is not attacked by nonoxidizing adds, alkalis, or salts. 

Low molecular weight lignin model compounds (synthetic phenyl-tetramers and Igepals ) were found to fit universal calibration. Fractions from preparative GPC, when analyzed by universal calibration, yield molecular weight distributions which add to a similar value to that found for the unfractionated parent sample. 

As mentioned above, in metal ion-catalyzed oxidations many polymer-metal complexes have been found to exhibit high catalytic efficiency in comparison with their low-molecular-weight analogs. Table 12 summarizes the catalytic activity of the Cu complexes of synthetic polymers. It is noteworthy that high efficiency is observed for complexes composed of simple synthetic polymers arch as poly-(ethyleneimine), poly(vinylpyridine) and poly(acrylic add). 

All known flavodoxins have low molecular weights (14,500-23,000 g mole" ) and contain a single polypeptide chain and a single bound FMN. Upon the addition of one reducing equivalent, the FMN adds one electron and one proton to form the neutral semiquinone. This species is blue in color (as contrasted to the yellow color of the oxidized form) and has broad absorption bands in the visible between 400 and 700 nm. Addition of a second equivalent leads to a one-electron reduction to the hydroquinone, which is pale yellow in color and has weak bands at around 450 and 365 nm. 

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