Surface Potentials in Langmuir Monolayers of Unidirectionally Oriented α-Helical Diblock Copolypeptides

Abstract

The surface potentials and effective dipole moments of alpha-helical amphiphilic diblock copolypeptides during monolayer compression at the air-water interface are reported. Amphiphilic diblock copolypeptides (PLGA-b-PMLGSLGs) of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) of various block lengths were studied during the double-brush formation process at the water surface. Upon monolayer spreading of PLGA-b-PMLGSLGs, surface potentials of hundreds of millivolts were recorded, attributed to the dipole moments of water molecules reorienting due to interactions with the monolayers. Upon compression, the effective dipole moments derived from the surface potentials of the PLGA-b-PMLGSLG monolayers decrease gradually, most likely as a result of the immersion of the hydrophilic block in water and cancellation of the interactions between the hydrophobic block and the underlying water molecules. The polypeptide macrodipole moment immersed in water was apparently effectively screened out. The remaining effective dipole moment of the monolayer contributes mainly to the hydrophobic block, and upon tilting away from the water surface toward the surface normal, it was found to increase with the hydrophobic block length, indicating the gradual formation of unidirectional aligned polypeptide molecules in the double-brush monolayer.

Chain length dependence of the helix orientation in Langmuir–Blodgett monolayers of α-helical diblock copolypeptides

“…21 The compression-decompression of these monolayers is a reversible process with a large hysteresis upon monolayer compression to a pressure above the second transition and no hysteresis before this transition. 30 The linear increment in surface pressure following the first transition in the isotherms of PLGA-b-PMLGSLGs corresponds to the packing and tilting of the PMLGSLG block segments away from the water surface after the PLGA block is immersed. Assuming the same maximum compression of the PMLGSLG blocks for all of the PLGA-b-PMLGSLGs (i.e.…”

“…We have measured the surface potentials of the PLGA-b-PMLGSLG monolayers during compression at the air-water interface. 30 The results showed that the polypeptide macrodipole moment immersed in water was effectively screened out. However, the effective dipoles of the a-helices of the hydrophobic block tilted away from the water surface were largely maintained and related increasingly to DP PMLGSLG .…”

Dipping-Induced Azimuthal Helix Orientation in Langmuir−Blodgett Monolayers of α-Helical Amphiphilic Diblock Copolypeptides

“…Besides the high mobility provided by the amorphous side chain mantle of the hairy-rod polypeptide block, monolayers of these diblock copolypeptides exhibit a brush structure composed of densely packed parallel R-helices, which are tilted at an angle with respect to the water surface normal. [30][31][32] Interestingly, we observed strong effects of in-plane anisotropy produced by the transfer process in the LB monolayers of these diblock copolypeptides. Particularly, a dipping-induced helix orientation oblique by an angle with respect to the dipping direction was observed for the first time.…”

Poly(L-glutamic acid) via catalytical hydrogenation for the fabrication of carbon nanotube nanocomposites

“…(BG-NCA) 11.85 g of BG (0.05 mol) was dissolved in 100 mL of dry THF. 19.0 mL of α-pinene (0.12 mol, 1.2 eq.)…”

“…Alternatively, PG has been chemically prepared via amine-initiated ring-opening polymerization of a γ-R-L-glutamate N-carboxyanhydride (NCA) monomer, with R is an acid labile blocking group such as the tert-butyl or piperonyl protecting group 9,10 . However, the ring-opening polymerization of glutamate NCA monomers bearing these substituents often resulted in polyamides with relatively low molecular weights low yields 9,11 . Moreover, although these carboxylic protected polyglutamates can be in the α-helix conformation, the PGs resulted after removal of the protected groups have low molecular weights and hence a high propensity for forming β-sheet aggregates.…”