Water soluble polyamino acids

The synthetic polyamino acids are convenient models for chemical studies of proteins since they have the extended polypeptide structure of the proteins but are free from the complications which arise in the proteins from the large number of different side chains. The work described here has been confined to the water-soluble polyamino acids poly-D,L-alanine (PDLA), poly-a,L-glutamic acid (PGA), poly-a,D-glutamic acid, and poly-a,L-lysine, and the polyimino acid, poly-L-proline. 

The work presented in the next section concerns the immobilization of retinoic acid by three polyamino acids poly(-L-lysine), poly(-L-arginine) and poly(-L-histidine). The mesomorphous structure of these complexes, which are prepared as nano-particles, has been examined. Then we will report on the physicochemical characteristics of water-soluble complexes formed between PEO-PLL block copolymers and retinoic acid. The structure in the solid-state and solution are discussed. Further the dissociation of the complex when changing the pH is reported. Finally, the immobilization of retinoic acid by PEI with different molecular weights is presented. 

Most of the thermodynamic studies have been performed in aqueous solutions as the cycles and their derivatives are first of all ligands for complexation of water-soluble metal ions. Numerous compounds have been studied and, therefore, only a general overview of trends is given. More information can be find in commercial databases such as NIST Standard Reference Database 46 (Critically Selected Stability Constants of Metal Complexes) or The IUPAC Stability Constants Database (SC-Database) or in reviews <2005PAC1445> (critically evaluated data for DOTA 3 and TETA 4), <1999CCR97> (protonation constants of polyamines) and <2000CCR309> (protonation constants of polyamino-polycarboxylic acids). Overall basicity of the ligands is mostly the main determinant for values of stability constants of metal complexes. 

---