Hydro-amino-addition

Addition of Ammonia and Amines Hydro-amino-addition... 

When chromatographic resolution of species based on modifications located at the protein surface is desired, it may be advisable to use conditions that favor retention of native conformation.17 Here, the standard acidic conditions described in the preceding text may be inappropriate, and mobile phases buffered near neutrality may be required. Buffers based on ammonium acetate, ammonium bicarbonate, and triethylammonium phosphate may prove more useful in resolving polypeptide variants with differing posttranslational modifications, amino acid substitutions, or oxidation and deamidation products. The addition of more hydro-phobic ion-pairing agents may be needed to obtain polypeptide retention, and a variety of alkyl sulfonates and alkyl amines have been described for specific applications.17... 

The Addition of Ammonia or Amines to Nitriles /V-Hydro-C-amino-addftion... 

The collagen superfamily of proteins includes more than twenty colla gen types, as well as additional proteins that have collagen-like domains. The three polypeptide a-chains are held together by hydro gen bonds between the chains. Variations in the amino acid sequence of the a-chains result in structural components that are about the same size (approximately 1000 amino acids long), but with slightly dif ferent properties. These a-chains are combined to form the various types of collagen found in the tissues. For example, the most common collagen, type I, contains two chains called a1 and one chain called... 

Further discussion and additional references to the synthesis of peptides containing dide-hydro-a-amino acids, reduced peptide isosteres, TV-hydroxy amides and hydrazides, and Ca-tetrasubstituted amino acids including 2,3-methano amino acids can be found in Sections 11.1,10.7,10.8, and 10.3, respectively. 

Addition of an alcohol to the amino-substituted disilene 18 proceeds with an even higher regioselectivity than that to the methoxy-substituted disilene 17. Thus, the addition of t-BuOH to 18 is completely regioselective, where only l-diethylamino-l-t-butoxy-2-hydro-l,2,2-trimethyldisilane 33a is obtained. 

Murakami et al. [19] developed an additional vitamin B6 model system with a binding site. They synthesized an octopus cyclophane (27) as a functional model of the protein matrix of transaminase. This cyclophane formed a hydrophobic cavity in water where PLP could be noncovalendy incorporated. Alkylamines having various hydro-phobic chains were employed as substrates, in place of a-amino adds, to evaluate the hydrophobic effect on the Schiff base-forming equilibrium. The Schiff base formation constant was found to depend markedly on the chain length of a substrate in the presence of 27, indicating that the octopus cyclophane can be utilized as an effective ho-loenzyme model capable of forming a ternary complex. 

The O-amino-a-hydro xyalkyl radicals shown in Table 4 are produced by addition of an electron to the corresponding amides. The dissociation constants are also affected by electron-withdrawing groups similarly to the previous cases. No parent compounds are available in this case for comparison. 

Cosolvents and Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO2. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-w-butyl phosphate (TBP) to CO2 increases the solubility of hydro-quinone by a factor of 250 due to Lewis acid-base interactions. Very recently surfactants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO2. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO2 include fluoroethers, fluoroaciylates, fluoroalkanes, propylene oxides, and siloxanes. 

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