We investigated the molecular dynamics of unilamellar liposomes by neutron spin echo spectroscopy. We report the first experimental evidence of a short-range motion at the length scale of the size of the headgroup of a lipid. The associated mean squared displacement shows a t dependence in the pico- to nanosecond region that indicates another process beyond the predictions of the Zilman-Granek (ZG) model ( t) and translational diffusion ( t). A comparison with theory shows that the observed low exponent is associated with a non-Gaussian transient trapping of lipid molecules in a local area and supports the continuous time random walk model. The analysis of the mean squared displacement leads to the important conclusion that the friction at the interface between water and liposomes plays a minor role. Center of mass diffusion of liposomes and transient trapping of lipids define the range in which the ZG model can be applied to analyze membrane fluctuations.

No abstract

Sodium chloride (NaCl) is a very common molecule in biotic and abiotic aqueous environments. In both cases, variation of ionic strength is inevitable. In addition to the osmotic variation posed by such perturbations, the question of whether the interactions of monovalent ions Na+ and Cl–, especially with the neutral head groups of phospholipid membranes are impactful enough to change the membrane rigidity, is still not entirely understood. We investigated the dynamics of 1,2-di-(octadecenoyl)-sn-glycero-3-phosphocholine (DOPC) vesicles with zwitterionic neutral head groups in the fluid phase with increasing external salt concentration. At higher salt concentrations, we observe an increase in bending rigidity from neutron spin echo (NSE) spectroscopy and an increase in bilayer thickness from small-angle X-ray scattering (SAXS). We compared different models to distinguish membrane undulations, lipid tail motions, and the translational diffusion of the vesicles. All of the models indicate an increase in bending rigidity by a factor of 1.3–3.6. We demonstrate that even down to t > 10 ns and for Q > 0.07 Å–1, the observed NSE relaxation spectra are influenced by translational diffusion of the vesicles. For t < 5 ns, the lipid tail motion dominates the intermediate dynamic structure factor. As the salt concentration increases, this contribution diminishes. We introduced a time-dependent analysis for the bending rigidity that highlights only a limited Zilman–Granek time window in which the rigidity is physically meaningful.

A lignin-graft-poly(lactic-co-glycolic) acid (PLGA) biopolymer was synthesized with two types of lignin (LGN), alkaline lignin (ALGN) and sodium lignosulfonate (SLGN), at different (A/S)LGN/PLGA ratios (1:2, 1:4, and 1:6 w/w). 1 H NMR and Fourier-transform infrared spectroscopy (FT-IR) confirmed the conjugation of PLGA to LGN. The (A/S)LGN-graft-PLGA biopolymers were used to form nanodelivery systems suitable for entrapment and delivery of drugs for disease treatment. The LGNgraft-PLGA NPs were generally small (100−200 nm), increased in size with the amount of PLGA added, monodisperse, and negatively charged (−48 to −60 mV). Small-angle scattering data showed that particles feature a relatively smooth surface and a compact spherical structure with a distinct core and a shell. The core size and shell thickness varied with the LGN/PLGA ratio, and at a 1:6 ratio, the particles deviated from the core−shell structure to a complex internal structure. The newly developed (A/S)LGNgraft-PLGA NPs are proposed as a potential delivery system for applications in biopharmaceutical, food, and agricultural sectors.

Amphiphilic polymers show a rich variety of self-assembly behavior in aqueous solutions. In experimental studies, statistical copolymer or block copolymer architectures are usually investigated because of their ease of synthesis or their structural analogy to surfactants. A copolymer structure that links the two architectures is an alternating copolymer, which is easily accessible by polycondensation reactions. Using alternating hydrophilic and hydrophobic building blocks with varying lengths allows a systematic variation between statistical and multiblock architectures. We synthesized alternating amphiphilic copolymers as polyesters using hydrophobic dicarboxylic acids (C4–C20) and hydrophilic poly­(ethylene glycol) (PEG) units (EG3–EG1000). Copolymers with long EG units were made accessible with the help of a newly developed esterification process. The solution properties of amphiphilic copolymers feature a lower critical solution temperature (LCST) behavior in water, which can be systematically varied over a wide range from 3 to 83 °C by adjusting the lengths of the C n and EG m units. We find that the transition temperature depends linearly on the hydrophobic unit length C m and logarithmically on the hydrophilic length EG n . In the one-phase region, PEG copolymer coils are more compact compared to the respective PEG homopolymers due to hydrophobic interactions between the hydrophobic units leading to loop formation. For shorter PEG units, the copolymers form micellar structures consisting only of a few copolymer chains. The micellar cores consist of hydrophobic regions containing only a few dicarboxylic acid units embedded in a PEG-rich and water-poor matrix. The cores are surrounded by a diluted corona of PEG chains. Further decreasing the PEG unit length leads to the formation of highly swollen gels consisting of networks of interconnected micelles. These can self-assemble to form highly ordered liquid crystalline cubic phases. The study demonstrates how the structure of alternating amphiphilic copolymers can be systematically varied to adjust the thermal solution properties such as the LCST over a wide range, as well as the self-assembly properties varying between single chains, micelles, gels, and highly ordered lyotropic liquid crystals.