Conformations of Poly-l-lysine Molecules in Electrolyte Solutions: Modeling and Experimental Measurements

Abstract

Physicochemical properties of poly-L-lysine (PLL) hydrobromide were determined by Molecular Dynamics (MD) modeling and a variety of experimental techniques. Primarily, the density, the chain diameter, the monomer length and PLL molecule conformations were theoretically calculated. These results were applied for the interpretation of experimental data acquired for 2 PLL sample of the average molar mass equal to 122 kg/mol. They comprised the diffusion coefficient, the hydrodynamic diameter and the electrophoretic mobility of molecules determined for ionic strength range 2×10 -5 to 0.15 M and pH 5.6. Using these data, the electrokinetic charge and the effective ionization degree of PLL molecules were determined as a function of ionic strength. Additionally, precise dynamic viscosity measurements for dilute PLL solutions were performed yielding the intrinsic viscosity, which decreased from 2420 to 120, for ionic strength of 2×10 -5 and 0.15 M, respectively. This confirmed that PLL molecules assume extended conformations in accordance with theoretical modeling. These data enabled to determine the molecule length, the chain diameter and its effective molecule cross-section area for various ionic strengths. Therefore, it was concluded that the combined dynamic light scattering and viscosity measurements supplemented by MD modeling furnish reliable information about PLL macromolecule conformations in electrolyte solution. Beside significance for basic science, the results obtained in this work can be exploited for precisely determining molar mass of macroions.

Effect of the Anchoring Layer and Transport Type on the Adsorption Kinetics of Lambda Carrageenan

“…The increase in the adsorbed mass with the initial bulk concentration of poly- l -lysine, having an elongated shape, 74 was also observed in studies by Kosior et al ( 75 ) Similar to the results obtained from the OWLS, no desorption of λ-car molecules from both bilayer types was observed.…”

pH-Induced Changes in Polypeptide Conformation: Force-Field Comparison with Experimental Validation

“…Recently, viscosity measurements have showed that the PLL has an extremely extended conformation at pH 5.6. 16 …”

“…The finite-size effects rising from the peptide chain length should be negligible for the highly charged polypeptides at low ionic strength, because the electrostatic repulsions make the peptide end-to-end distance then linearly dependent on the molar mass. 16 On the other hand, for the low ionization degrees, it is very likely that longer peptides would fold onto themselves more than these short segments. However, examining this would need a significantly longer equilibration and larger box size, which makes such simulations computationally very demanding.…”

“…Typical choices for PGA MD modeling in recent years have been the different variants of the AMBER force field 13 , 35 , 36 , 60 and the OPLS-AA force field. 31 , 61 For PLL, the most frequent force-field choice in recent years has been AMBER, 8 , 16 , 60 , 62 − 68 but also OPLS-AA, 31 , 61 , 69 , 70 CHARMM, 71 and GROMOS 72 have been used. Also, coarse-grained MD approaches using the MARTINI force field 73 exist for PLL.…”

Deposition of Polymer Particles with Fibrinogen Corona at Abiotic Surfaces under Flow Conditions

“…Poly-L-lysine hydrobromide (PLL), a synthetic polypeptide having a molar mass of 75-189 kg mol −1 (determined by MALS), was purchased from Sigma Aldrich Merck KGaA, Darmstadt, Germany. The average molar mass of the PLL sample of 120 kg mol −1 was more precisely determined by dynamic viscosity measurements [43].…”