Crystallization during polymerization of L‐alanine N‐carboxy anhydride initiated by diamines

Abstract

Polymerization of L-alanine N-carboxy anhydride (4-methyl-2,5-dioxo-l-oxa-3-azacyclopentane) was carried out in acetonitrile using hexamethylene diamine (HM), ethylene diamine (ED) and bis(4-aminophenyl) ether (AP) as initiators, in order to investigate the effect of diamines on the crystallization mechanism during polymerization in comparison with that for butylamine already reported.The resultant polymers obtained here had wider molecular weight distributions than those obtained with butylamine, indicating the occlusion of some active growing chain ends into the precipitate during polymerization. The relative width of the molecular weight distribution of the polymers formed in the later stages of the polymerization was larger in the following order as compared among the initiators: HM<ED<AP. The oligomer chains formed in the beginning of the polymerization crystallized into the antiparallel p-structure and thereafter the a-helical chains grew from the active sites of the P-chains. However, it is likely that, in the later stages of the polymerization, the cc-helical chains grew from one of the amino groups of a diamine molecule but most of the other amino groups were inactive, since the ends of the p-chains were occluded into the precipitate due to the antiparallel nature of the D-chains precipitated. The morphologies of the resultant polymer crystals were in good agreement with the results obtained from the intrinsic viscosities (molecular weights), conformations, and structures. ZUSAMMENFASSUNG:Es wurde die Polymerisation des Leuchs'schen Anhydrids von L-Alanin (4-Methyl-2,Sdioxo-I-oxa-3-azacyclopentan) in Acetonitril unter Verwendung von Hexamethylendiamin (HM), Athylendiamin (ED) und Bis(4-aminopheny1)ather (AP) als Initiatoren durchgefuhrt, um die Wirkung der Diamine auf den Kristallisationsmechanismus wahrend der Polymerisation im Vergleich zu der Wirkung des Butylamins, iiber die bereits berichtet wurde, zu untersuchen.Die hier erhaltenen Polymere wiesen breitere Molekulargewichtsverteilungen als die mit Butylamin erhaltenen auf, was auf eine Okklusion einiger aktiver wachsender Kettenenden im ausfallenden Polymer wahrend der Polymerisation hinweist. Die relative Breite der Molekulargewichtsverteilung der in spateren Phasen der Polymerisation gebildeten Polymere stieg beziiglich der Initiatoren in der folgenden Reihenfolge an : HM < ED < AP. Die Oligomer-Ketten, die sich am Anfang der Polymerisation bildeten, kristallisierten in der antiparallelen P-Struktur und danach wuchsen die a-Helix-Ketten, ausgehend von den aktiven Stellen der rJ-Ketten. Es ist jedoch wahrscheinlich, daI3 in den spateren Polymerisationsphasen die a-Helix Ketten ausgehend von einer der Aminogruppen eines Diamin-Molekiils wuchsen, daI3 aber die meisten der anderen Aminogruppen inaktiv waren, da die Enden der P-Ketten wegen deren antiparalleler Natur im ausgefallenen Polymer okkludiert waren. Die Morphologie der erhaltenen Polymerkristalle befand sich in guter Ubereinstimmung mit den Ergebnissen, die aus den Staudingerindices (Molekul...

Synthesis and characterization of novel poly(γ‐benzyl‐L‐glutamate) derivatives tailored for the preparation of nanoparticles of pharmaceutical interest

“…Indeed, for a polypeptide in an α‐helix conformation, the amide I band and the amide II band are located at 1656 and 1548 cm −1 , respectively, while for a polypeptide in a β conformation, the amide I band and the amide II band are located at 1630 and 1536 cm −1 , respectively 20. Moreover, an absorption band at 1260 cm −1 corresponding to the amide III band was observed in the FTIR spectrum of α‐helix conformation polypeptide 26. In the present case, FTIR spectra of all polymers presented a peak at 1650 cm −1 which is characteristic of the amide I band of the α‐helix conformation.…”

“…However, β‐sheet structures are predominant for peptides with low degrees of polymerization (<10) 24. Moreover, the α‐helix of PBLG can exist either in a 7/2 conformation (7 residues for 2 turns) or an 18/5 conformation (18 residues for 5 turns), which is a more usual conformation for peptides 23, 25, 26. The 7/2 helix conformations caused by the cooperative stacking of benzyl groups at the end of side chains27 is transformed to 18/5 helix conformations by a broad first‐order transformation when heating.…”