Influence of assembling pH on the stability of poly(L-glutamic acid) and poly(L-lysine) multilayers against urea treatment.
Polyelectrolyte multilayers of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) were built up using the layer-by-layer (LbL) technique in low pH (3.6, PM3.6) and in neutral pH (7.4, PM7.4) solutions. The multilayers were then treated with a concentrated urea (one kind of denaturant for proteins and polypeptides) solution (8M) and rinsed with corresponding buffer. The buildup and treatment processes were investigated by ultraviolet visible spectroscopy and ellipsometry. The surface morphology was observed by scanning force microscopy (SFM). The inner structures were determined by X-ray reflectometry and circular dichroism spectroscopy (CD). An exponential growth of the optical mass and the layer thickness was observed for both PM3.6 and PM7.4. After urea treatment, a significant mass loss for PM3.6 was found, while no mass change was recorded for PM7.4. The dominant driving force for PM7.4 is electrostatic interaction, resulting in multilayers with an abundant beta-sheet structure, which has higher stability against urea treatment. By contrast, the dominant driving force for PM3.6 is hydrogen bonding and hydrophobic interaction, which are sensitive to the urea treatment. The mechanism is substantiated by molecular mechanics calculation. This has offered a convenient pathway to mediate the multilayer properties, which is of great importance for potential applications.
Zhou
Jie
J
Key Laboratory of Macromolecular Synthesis and Functionalization, Ministry of Education, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China.
Wang
Bo
B
Tong
Weijun
W
Maltseva
Elena
E
Zhang
Gang
G
Krastev
Rumen
R
Gao
Changyou
C
Möhwald
Helmuth
H
Shen
Jiacong
J
D002942:Circular Dichroism; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D011099:Polyglutamic Acid / Q000737:chemistry*; D011107:Polylysine / Q000737:chemistry*; D017433:Protein Structure, Secondary; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D014508:Urea / Q000737:chemistry*; D014961:X-Ray Diffraction
D012996:Solutions; D011107:Polylysine; D011099:Polyglutamic Acid; D014508:Urea