Association of poly-(L-lysine) homologues in sodium carbonate solution

Abstract

The molecular weights of isopoly(L-lysine), poly(L-ornithine), and poly(L-a, }~diaminobutylic acid), the homologues of poly (L-lysine), were determined by the sedimentation equilibrium method in aqueous solutions of 1.0 M NaC1 or 0.1 M Na2CO3. In every sample the molecular weights in the presence of carbonate ions was twice that in NaC1 solution. In a previous paper we reported that poly(L-lysine) behaved as a dimer at concentrations higher than 0.4 g/dl in the presence of carbonate ions and as a monomer in dilute solution, and these two forms were related by a monomer-dimer equilibrium. The homologues did not have a monomer-dimer equilibrium relationship under the conditions of the measurements that we carried out. The CD spectrum of isopoly(L-lysine) in water showed a uniform increase with a decrease in the wave length in the presence of carbonate ions. However, in the alkaline region in NaOH solution, the spectrum changed and a small minimum at 212 nm was found. When additional carbonate ions were added a large minimum at 205 nm was observed. This result can be explained by a change in the conformation from a random coil to a regular structure. We could not compare isopoly(L-lysine) with other polypeptides, because it does not have peptide bonds. The CD spectra of poly(L-ornithine) and poly(L-a, ~-diaminobutylic acid) in NaOH or Na2CO3 solutions showed only slightly regular structures. It was also confirmed that the dimer-structures of the poly(L-lysine) homologues do not have regular structures.

Computational Study on the Conformation and Vibration Frequencies of β-Sheet of ε-Polylysine in Vacuum

“…This kind of cationic homopolymer can be used as emulsifying or delivery agents [ 1 , 2 ], anti-obese regents [ 3 ], hydrogels [ 4 ], biodegradable materials [ 5 ], food preservatives [ 6 ] and so on. Because α-PLL can take on different conformations such as α-helix, β-sheet, β-turn and random coil, there are many publications using it as a model to examine the structure of proteins [ 7 – 10 ]. The investigating methods, consisting of Fourier Transfer Infrared Spectra (FT-IR), Raman Spectra, Circular Dichroism (CD) and Nuclear Magnetic Resonance (NMR), etc, are usually used.…”