Systems with Branched Side Chains

If further branched side chains are present it must be remembered that side chains are always connected through their position I with the main 

Identical side chains are indicated by the multiplicative prefixes di, tri, tetra,penta, etc. If side chains with identical further substituents are present the multiplicative prefix forms bis, tris, tetrakis, pentakis, etc. are employed. (The prefix forms bi, ter, quater, quinque, sexi, septi, etc. are reserved for direct linking of identical units see the following Sections.) 

If such a complex hydrocarbon system is present as a substituent group, the free valence must again be assigned locant 1, only then are the usual prority rules applied accordingly. 

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Aliphatic ethers with branched side chains such as MTBE (methyl t-butyl ether), especially, deactivate enzymes only to a very small degree in incubation experiments for example, the BAL mentioned above has a half-life h/2 of up to 500 h in aqueous-organic two-phase systems (see Fig. 3.1.6) [21]. This may not hold true for a special enzyme/solvent combination under process conditions. When incubated at higher temperatures or even in the presence of the substrate benzaldehyde the deactivation of the enzyme is much higher (see Table 3.1.2)... 

NAD+ serves as the oxidant. The reaction is catalyzed by a complex of enzymes whose molecular mass varies from 4 to 10 x 106, depending on the species and exact substrate.297 Separate oxoacid dehydrogenase systems are known for pyruvate,298-300 2-oxoglut-arate,301 and the 2-oxoacids with branched side chains derived metabolically from leucine, isoleucine, and... 

Turos and Ping found that two (3-lactam analogs (73 and 74), both containing a branched-chain system at C3 of the ring, exhibited potent apoptosis-inducing activity. However, 73 exhibited superior in vitro activity over 74. (Fig. 3) The (3-lactams with these side chains were able to inhibit the growth of mice bearing... 

For polymers containing branched side chains Fig. 2.67 show the variation of the modulus E , E and the loss tangent for PDIPI and PDIBI in the temperature range under study. Two relaxations can be observed where the most prominent is the a relaxation associated to the glass transition as in the systems previously reported. Tg increases as the volume of the side chain increases. This result is in good agreement with that observed for the corresponding family of poly(methacrylate)s [242],... 

The side chain can also affect electronic events of the tricyclic ring system. Electron spin resonance experiments allowed Fenner S to suggest that the influence of the side chain of phenothiazine on the formation of free radicals showed a correlation between the redox activity of the phenothiazine nucleus and dynamic aspects of stereochemistry. For example, there was a difference in the formation of cationic free radicals between promazine and alimemazine. The latter has a branched side chain, and forms cationic free radicals only under irradiation. It differs from promazine in pharmacodynamic properties, reported s to result in considerably shifted ion exchange equilibria. A kinetic study of the oxidation of dopamine by dialkylaminoalkyl phenothiazine cationic free radicals showed that a strong correlation existed between side-chain structures and oxidation rates phenothiazine free radicals with two carbon side chains had faster rates than those with three carbon side diains, albeit both were very rapid at physiological pH. 

To reveal a better understanding of the reaction mechanism, the effect of the amino group on the formation of 2,3-dihydrobenzo[/] isoindoles was studied including the importance of the structure of the amino acid side branch. The results showed that amino acids with different side chains alter considerably the reactivity of the very unstable enediyne system, as seen from the comparison of the data of DSC. 

Fluorosilicones consist of PDMS backbones with some degree of fluoro-aliphatic side chains. The fluorinated group can be trifluoropropyl, nonafluorohexylmethyl, or fluorinated ether side group [78,28,79]. These polymers differ not only in substituent group, but also in the amount of fluoro-substitution relative to PDMS, the overall molecular weight and crosslink density, and the amount of branching. In most commercially available cases, these polymers are addition cure systems and the reactions are those discussed previously for silicone networks. 

In the systems that I have examined, I can satisfy the dynamic requirements with a ten second pulse delay. The longest methyl T] may be 3 seconds. In general, the longer the side chain, the longer will be the methyl Tj. We will hear more about this subject later on. We need not be too concerned about NOE factors because they are usually full under the experimental conditions (T = 120-130°C) used for polymer quantitative measurements. The Tj problem can be handled, even under non-equilibrium conditions, by utilizing resonances from the same types of carbon atoms in a quantitative treatment. Such an approach can sometimes lead to more efficient quantitative NMR measurements. Adequate pulse spaclngs will have to be used whenever one wishes to utilize all of the observed resonances. Quantitative measurements in branched polyethylenes are very desirable because this is one of the best applications of analytical polymer C-13 NMR. 

The aliphatic amino acids (class 1) include glycine, alanine, valine, leucine, and isoleucine. These amino acids do not contain heteroatoms (N, 0, or S) in their side chains and do not contain a ring system. Their side chains are markedly apolar. Together with threonine (see below), valine, leucine, and isoleucine form the group of branched-chain amino acids. The sulfurcontaining amino acids cysteine and methionine (class 11), are also apolar. However, in the case of cysteine, this only applies to the undissociated state. Due to its ability to form disulfide bonds, cysteine plays an important role in the stabilization of proteins (see p. 72). Two cysteine residues linked by a disulfide bridge are referred to as cystine (not shown). 

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