Amino acid chain polymers

Uchegbu and coworkers have studied the complexation and delivery of DNA using a unique poly(amino acid)-based polymer vesicle. A polymer of either poly (L-lysine) or poly(L-omithine) was functionalized with methoxy-poly(ethylene glycol) (mPEG) and hydrophobic palmitic acid chains to synthesize an amphiphilic triblock of either mPEG-6-poly(L-lysine)-6-palmitoyl or mPEG-Z>-poly(L-omithine)-6-palmitoyl. Vesicles formed from these polymers were complexed with DNA and showed improved transfection in vitro over poly(amino acid) complexed with DNA or DNA alone [82]. 

All proteins are polymers of amino acids. The polymers, or polypeptides, consist of a sequence of up to 20 different L-a-amino acids (residues). For chains under 40 residues the term peptide is frequently used instead of protein. The term protein is generally used to refer to the complete biological molecule in a stable conformation. 

Another area of active research is the synthesis of main-chain and side-chain amino acid-containing polymers for various biological apphcations. These chiral polymers are novel structures and represent the fusion of polyolefins and peptides [55, 56[ (Scheme 6.13). 

Proteins are polymers of amino acids. These polymers are chains, each containing him-dreds or thousands of amino acids, that fold up into a three-dimensional structure. 

The starting materials were chosen partly for their simplicity and cheapness and partly for their possible application in the final polymer— as either chelating groups (for example, V and VII) or polymeric drugs (VI). Structures such as the nitro compound (I) offer a simple method for obtaining primary amino groups on a polymer chain. This may have applications in the attachment of amino acid chains in protein synthesis. 

A further class of synthetic gene vectors that has received attention in past years is cationic polymers, which condense and package DNA with high efficiency. Polymerized or oligomerized branched or nonbranched amino acid chains composed of lysine or arginine are common [59, 60]. Polyethylenimine, however, developed in 1995 by Boussif]61] and already used for... 

Peptides are also amphiphilic polymers, i.e., mostly positively charged molecules with short amino acid chains, and are a key component of the innate immune system. The focus on amphiphilic polymers is due to some reports suggesting that the current global drug pipeline is woefully inadequate due to bacterial resistance to antibiotics [3]. The application of amphiphilic polymers and their block polymers to stop the microbial growth of infected tissue has been reported in the literature [4]. 

Peptides exhibit the highest antimicrobial activities of amphiphilic polymers and also possess antibacterial, antiviral, antifungi and anticancer activities [30-32]. In view of the potential applications of peptides, we will now discuss the synthesis of some important antibacterial peptides. Gad-1 and Gad-2 are peptides with amino acid chains and are prepared using O-fluorenylmethyloxycarbonyl (Fmoc) chemistry. 

Polymers imprinted for amino acids with larger side groups generally displayed a higher, yet relatively modest, enantioselectivity. Also, polymers are able to separate amino acids with functional groups that are similar to the imprint amino acid. For example, polymers imprinted for L-phenylalanine displayed a selectivity of 1.45 for L-phenylalanine 1.36 for L-tyrosine and 0.99-1.08 for alanine, valine, leucine, and isoleucine. This indicates that the larger cavity created by phenylalanine does not have the ability to differentiate the smaller side chains of the smaller amino acids. Likewise, polymers imprinted with smaller amino acid side chains showed moderate selectivity for similar amino acids, but could not differentiate the larger amino acids. 

Pseudopoly(amino acids) are polymers derived fi om amino acids with nonamide linkages these are represented by the wavy line in Structures 20,21, and 22. This is usually done by the polymerization of trifunctional amino acids by reaction with side chain functional groups. Three important categories include serine derived polyesters [88] hydroxy-proline derived polyesters, and tyrosine-derived polymers. The first has not been widely used as a biomaterial [89]. The second group consists of poly(A-acyl-hydroxyproline esters) from A-protected hydroxyproline. These polyesters are soluble in benzene, toluene, chloroform, di-chloromethane, carbon tetrachloride, tetrahydrofuran, and dime thy Iformamide. They are thermally stable up to 300 °C, have glass transition temperatures ranging firom 71 °C to 157 °C, and are easily processed [89]. 

Proteins are made of amino acids thus, since 1970, scientists have been evaluating these materials for biomedical applications. However, because of their immunoge-nicity responses and poor mechanical properties, only a small number of poly(y-substituted glutamates) possess interesting performances. Several efforts were made to obtain amino acid—derived polymers with modified backbone to achieve adequate physicomechanical properties. On the basis of structural configuration, these materials can be classified into different subcategories synthetic polymers with amino acid side chains, copolymers of amino acid and non—amino acid monomer, block... 

Although the steps just shown can be repeated to add one amino acid at a time to a growing chain, the synthesis of a large peptide by this sequential addition is long and arduous. An immense simplification is possible, however, using the Merrifield solid-phase method. In the Merrifield method, peptide synthesis is carried out with the growing amino acid chain covalently bonded to small beads of a polymer resin rather than in solution. In the original Merrifield procedure, polystyrene resin was used, prepared so that 1 of... 

By certain physical factors like thermal, ultraviolet irradiation, high pressure and other chemical parameters like organic solvents the helical pol5mers are easily denaturalized. A variety of helical polymers are synthesized, which include polyisocyanates, polyisocyanides, polychloral, polymethacrylates, polysilanes, polythiophenes, poly (p-phenylene)s, poly(l-methylpropargyl-ester)s, poly(phenylacetylene)s and poly (-unsaturated ketone) [18-24] (Fig. 1). Other polymers are whose optical activity is main chain or side chain chirality dependent e.g. amino-acid-based polymers are nontoxic, biocompatible and biodegradable. 

Polymers are, by definition, molecules composed by a large number of small chemical units, the monomers. Above, we have discussed A- and B-homopolymers, assuming that all A-polymers are composed of the same single A-monomer, and B-polymers by another specific B-monomer. Such chemical equality is often the situation in synthetic polymers, as for example polyethylene purely composed of -CH2- ethylene monomers. Many natural polymers, on the other hand, are composed of several different monomers example of these include proteins, which are polymeric chains composed of different amino acids such polymers are termed copolymers. 

Proteins are naturally occurring polymers in animals, plants, bugs, fungi, and other living organisms. These are made up of long-chain amino acids. A polymer protein with an amide group as the backbone is called polyamide, and artificial polyamides are known as nylon. 

A polymer is a macromolecule that is constructed by chemically linking together a sequent of molecular fragments. In simple synthetic polymers such as polyethylene or polystyrer all of the molecular fragments comprise the same basic unit (or monomer). Other poly me contain mixtures of monomers. Proteins, for example, are polypeptide chains in which eac unit is one of the twenty amino acids. Cross-linking between different chains gives rise to j-further variations in the constitution and structure of a polymer. All of these features me affect the overall properties of the molecule, sometimes in a dramatic way. Moreover, or... 

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