Branched side chains

The synthesis involves the nickel-catalyzed coupling of the mono-Grignard reagent derived from 3-alkyl-2,5-diiodothiophene (82,83). Also in that year, transition-metal hahdes, ie, FeCl, MoCl, and RuCl, were used for the chemical oxidative polymerization of 3-substituted thiophenes (84). Substantial decreases in conductivity were noted when branched side chains were present in the polymer stmcture (85). 

Polyolefins with branched side chains other than P4MP1 have been prepared Figure 11.14). Because of their increased cohesive energy, ability for the molecules to pack and the effect of increasing chain stiffness some of these polymers have very high melting points. For example, poly-(3-methylbut-l-ene) melts at about 240°C and poly-(4,4-dimethylpent-l-ene) is reported to have a melting point of between 300 C and 350°C. Certain cyclic side chains can also... 

As is the case in the polyolefins, the polymethacrylates with branched side chains have higher softening points and are harder than their unbranched isomers. The effect of branching of Vicat Softening point is shown in Table 75.5.> ... 

The conductivity obtained for the polymers bearing branched side chains (Table 14) are similar to those obtained with the hnear oligoethyleneoxy ana-... 

Polyacetylenes are the most important class of synthetic polymers containing conjugated carbon-carbon double bonds. Some optically active monomers have been used with the following conclusions. Polymers of 1-alkynes having a branched side-chain assume in solution a helical conformation. A chiral side-chain induces a predominant screw sense in these helices. In particular, for alkyl branching, it has been shown that (S) monomers lead to a left-handed screw sense. 

As noted by the original authors (Dorovska et al., 1972), and cited by Fersht (1985), there is an excellent linear correlation between log/ccat/KM and the Hansch hydrophobicity parameters (v) of the side chains (Fig. 9, A), except for the two branched side chains (valine and isoleucine residues). However, since the ku values for the esters do vary somewhat (Table A6.8), the values of pKrs do not correlate as strongly with ir (Fig. 9, B). Moreover, the plot shows distinct curvature which probably indicates the onset of a saturation effect due to the physical limits of the Sj binding pocket, adjacent to the enzyme s active site. Still, the points for valine and isoleucine deviate below the others, suggesting that the pocket has a relatively narrow opening. 

The superscript br refers to the branches (side chains). h Apparent values for the graft polymers, from SEC analysis. 

Protein ALBP-PX was the first pyridoxamine-conjugated protein to be synthesized and structurally characterized. Under single-turnover conditions, this protein demonstrated amino acid production rates of only 56% of the free cofactor. However, depending on the nature of the a-keto acid, ALBP-PX did show a range of optical inductions for the amino acid product. Notably, enantiomeric excesses in the order of 94% were observed for the production of valine. Additionally, several trends were noted. All amino acid products that showed optical induction favored the 1-enantiomer, except alanine, which favored the d-enantiomer. Furthermore, a-keto acids with branched side chains... 

Methyl-branched side chain with 8 carbons... 

No investigation has been published where substituted ferrocenes are used. Highly branched side chains should make the so-called unsaturated groups less labile for quenching since close contact would be impossible. 

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)... 

The more conventional approach used for the synthesis of the analogue incorporating a branched side chain involves additional steps, which are not shown but are required for... 

This hypothesis suggests that drug-resistant mutations would be of the type that destabilize protein structures. Such mutations are typically from larger to smaller side chains or from highly branched to less branched side chains [43-45]. Four of five observed compensation mutants are of this type (Table... 

The dimensions of protein random coils are calculated for a variety of proteins of known amino acid sequence. Glycine and proline contribute to reducing the dimensions of random coil proteins. Branched side chains expand the chain only slightly more than unbranched side chains. Side chains represented as structured to the y position are compared with structureless representations. It is demonstrated that the two approaches give comparable chain dimensions. The effect of sequence is investigated. 

Peptides with C-terminal amino acids with aromatic or bulky, branched side chains are best substrates... 

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... 

After Ala, residues with long side chains exhibit higher tendencies to form helices due to possible position-dependent, side-chain interactions that are helix stabilizing, such as salt bridges and hydrogen bonding. However, aromatic or ((-branched side chains act as helix breakers in monomeric peptides due to constraints on side-chain rotational entropy when in an a-helical conformation/11,14 201... 

The presence of bulky, (3-branched side chains can be helix promoting or destabilizing depending on the environment. 100 The role of hydrophobic residues in helix stabilization has been studied in Ala-based peptides 106 as well as through Monte Carlo calculations. 107 The positioning of hydrophobic residues is also important. In amphiphilic helices, hydrophobic residues repeat approximately every three to four residues, such that one side of the helix is hydrophilic and one side hydrophobic. The amphiphilicity makes the peptide susceptible to helix formation in the presence of lipid-water interfaces. 108 109 ... 

Stability constants for Cu11 complexation of Gly—X and X—Gly dipeptides show that even relatively small alkyl side chains can influence coordination. 3 At low pH, for example, the bidentate chelates N(amino),0(peptide) of L-Leu-Gly and L-Ile-Gly are the thermodynamically less stable, presumably due to steric hindrance from the branched side chains. Similar coordination by Gly—X is virtually independent of the nature of X. This latter result is not unexpected since only the Gly moiety is coordinating. However, on raising the solution pH (> 4) the peptide deprotonation that occurs to give tridentate N(amino),N(peptide),0(carboxyl) chelation is slightly inhibited by the Leu and lie residues (by 0.7-0.8 log units). 

Compound 114d possesses significantly lower transition temperatures (Scheme 60) due to the branched side chains [126]. A columnar phase is present even below room temperature. At 14 °C, anew chiral columnar phase was observed while above 111 °C, an achiral columnar rectangular phase was observed. The spiral-pattern texture of 114d in the chiral Col mesophase is shown in Fig. 17. 

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