Sequence-controlled polymers approaches

Today we routinely use the 3-nitrophthalic anhydride blocker It is applicated in a single dose of a ten- to twenty fold excess on estimated amounts of remaining amino functions and added as a 0.1 niolar solution in pure pyridine with ten minutes reaction time at the end of each peptide synthesis stage, in which all chemical operations are monitored by photometric control and forced to approach completion. We have no indications to date that the acidically marked, blocked sequences on polymer cause undesired side reactions in subsequent stages of the synthesis, particularly in further peptide coupUngs, probably because of the acidity of the blocker functions (pK 2), which in their anionic salt form possess only a very diminished nucleophilicity. 

Block copolymers are an attractive approach to the preparation of DMFC membranes, because their highly controlled polymer architecture means that the ionic and nonionic domains can be on the same polymer backbone in a defined sequence. Furthermore, through careful control of the block lengths, the microphase separation can also be controlled to a certain extent. Kim et al. prepared partially sulfonated polystyrene-block-poly(ethylene-ran-... 

Unambiguous determination of monomer sequence in copolymers 3 is a requisite for evaluation of various synthetic approaches in controlling their microstructure. Knowledge of microstructure, especially monomer sequence information, is vital to detailed understanding of structure-property relationships. All well established spectroscopic methods, e.g. IR, UV-VIS, and NMR, are severely limited by the structural similarity of these monomers. All contain the N-alkyl-4-vinylpyridinium chromophone. A new method for sequencing synthetic polymers based on pyrolysis/tandem mass spectrometry has been developed by Cooks and associates [66] and applied to analysis of copolymer 3. Desorption chemical ionization (DCI) and desorption electron... 

In the synthesis of polypeptides with biological activity on a crosslinked polymer support as pioneered by Merrifield (1 2) a strict control of the amino acid sequence requires that each of the consecutive reactions should go virtually to completion. Thus, for the preparation of a polypeptide with 60 amino acid residues, even an average conversion of 99% would contaminate the product with an unacceptable amount of "defect chains". Yet, it has been observed (13) that with a large excess of an amino acid reagent —Tn the solution reacting with a polymer-bound polypeptide, the reaction kinetics deviate significantly from the expected exponential approach to quantitative conversion, indicating that the reactive sites on the polymer are not equally reactive. 

The investigations directed at the synthesis of thymine-substituted polymers demonstrate that the type of functional groups displayed by nucleic acid bases are compatible with ROMP. Moreover, the application of MALDI-TOF mass spectrometry to the analysis of these polymers adds to the battery of tools available for the characterization of ROMP and its products. The utility of this approach for the creation of molecules with the desired biological properties, however, is still undetermined. It is unknown whether these thymine-substituted polymers can hybridize with nucleic acids. Moreover, ROMP does not provide a simple solution to the controlled synthesis of materials that display specific sequences composed of all five common nucleic acid bases. Nevertheless, the demonstration that metathesis reactions can be conducted with such substrates suggests that perhaps neobiopolymers that function as nucleic acid analogs can be synthesized by such processes. 

Protein polymers based on Lys-25 were prepared by recombinant DNA (rDNA) technology and bacterial protein expression. The main advantage of this approach is the ability to directly produce high molecular weight polypeptides of exact amino acid sequence with high fidelity as required for this investigation. In contrast to conventional polymer synthesis, protein biosynthesis proceeds with near-absolute control of macromolecular architecture, i.e., size, composition, sequence, topology, and stereochemistry. Biosynthetic polyfa-amino acids) can be considered as model uniform polymers and may possess unique structures and, hence, materials properties, as a consequence of their sequence specificity [11]. Protein biosynthesis affords an opportunity to completely specify the primary structure of the polypeptide repeat and analyze the effect of sequence and structural uniformity on the properties of the protein network. 

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