Mixed layers of DPPC and a linear poly(ethylene glycol)-b-hyperbranched poly(glycerol) block copolymer having a cholesteryl end group

Abstract

Interactions of the phospholipid 1,2-dipalmitoylsn-glycero-3-phosphocholine (DPPC) with the amphiphilic diblock copolymer Ch-lPEG 30 -b-hbPG 24 (ChP) are studied at the air-water interface by surface pressure-mean molecular area (π-mmA) measurements of mixed Langmuir films and adsorption measurements of ChP to the air-water interface covered with DPPC monolayers at different initial surface pressure values π 0 . ChP is composed of a single hydrophobic cholesteryl (Ch) moiety covalently bound to a diblock copolymer consisting of a hydrophilic linear poly (ethylene glycol) (lPEG) block and a hydrophilic hyperbranched poly(glycerol) (hbPG) block. Langmuir isotherms and compression moduli of the mixed Langmuir films of different molar ratios reveal distinct interactions between DPPC and ChP during compression. It is demonstrated that the behavior of the DPPC/ChP mixtures is dominated by DPPC up to a molar ratio of 10:1, whereas the behavior is predominantly governed by ChP in mixtures with lower DPPC content (molar ratios of 5:1, 2:1, and 1:1). In adsorption measurements, a strong affinity of ChP to DPPC is observed after injection into the water subphase. The surface pressure value π in up to which ChP is able to penetrate into DPPC monolayers is determined to the remarkably high value of 48.2 mN/m which attests the favorable interactions between DPPC and the Ch moiety of ChP. Atomic force microscopy on LB films of DPPC/ChP mixtures of different molar ratios transferred onto hydrophilic substrates confirms the presence of two different phases, a DPPC-rich phase and a ChP-rich phase.

Block copolymers in giant unilamellar vesicles with proteins or with phospholipids

“…Previous detailed studies of the molecular interactions between these block copolymers and phospholipids in Langmuir monolayers suggested their strong affinity. [23][24][25][26] In interactions with GUV phospholipid bilayers we observed clear differences assumed to arise from the different copolymer conformations in water. Moreover, it was found that the studied copolymers are able to cross articial and natural phospholipid membranes.…”

“…Cholesterol, by itself a weak amphiphile and a component of natural membranes, is known for its strong interaction with phospholipids 34 and acts as an anchor in phospholipid layers. 26,29 The PPO-chain, as the weak hydrophobic middle block, is very exible and can interact with phospholipid layers in different ways. 23,24 Furthermore, the different architectures of the hydrophilic blocks, linear or hyperbranched, are expected to show different spatial molecular conformations in dilute aqueous solutions.…”

Unusual triskelion patterns and dye-labelled GUVs: consequences of the interaction of cholesterol-containing linear-hyperbranched block copolymers with phospholipids

“…9b). 25,26,55 Small membrane pieces are released inside and outside the bilayer, but nevertheless these GUVs remained stable for more than 24 h (see Fig.…”

“…Furthermore, the LE/LC transition has much in common with the liquid-crystalline to gel phase transition in bilayer systems. [24][25][26] Monolayer experiments were combined with epi-fluorescence microscopy, and interactions of the fluorescent labelled block copolymer with phospholipid bilayers were studied by confocal laser scanning microscopy (CLSM) employing giant unilamellar vesicles (GUVs). 1,14,15 Cholesterol exhibits a so-called ''condensing effect'' on liquid-crystalline bilayers, 1,7,10 which can be understood as the induction of an intermediate state of the lipid acyl chains between the ordered and the liquid crystalline state.…”

Polyphilic Interactions as Structural Driving Force Investigated by Molecular Dynamics Simulation (Project 7)

“…There exist numerous lipid bilayer-forming agents. Dipalmitoylphosphatidylcholine (DPPC) is a typical example; on the one hand, it is extensively studied experimentally [ 14 , 21 , 22 , 23 , 24 , 25 ], while, on the other hand, it is well-covered in force-field support [ 26 , 27 , 28 ].…”