Valtierrez-Gaytan Cain, Barakat Joseph M, Kohler Mitchell, Kieu Khanh, Stottrup Benjamin L, Zasadzinski Joseph A
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA.
Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.
Sci Adv. 2022 Apr 8;8(14):eabl9152. doi: 10.1126/sciadv.abl9152. Epub 2022 Apr 6.
Competition between intradomain electrostatic repulsions and interdomain line tension leads to domain shape transitions in phase-separating lipid monolayers. The question remains if these morphologies are energy minima or are kinetically trapped metastable states. We show the reversible evolution of uniform width stripe domains from polydisperse semicircular domains in monolayers of dipalmitoylphosphatidylcholine (DPPC), hexadecanol (HD) or palmitic acid (PA), and dihydrocholesterol (DChol). The initial semicircular domains grow at a fixed 2:1 DPPC:HD (or PA) stoichiometry, depleting the liquid phase of HD, leaving behind a liquid enriched in DPPC and DChol. At higher surface pressures, the remaining DPPC precipitates onto existing domains, decreasing the ratio of line tension to the square of the dipole density difference, λ/μ. Theory predicts that, as λ/μ decreases, circular domains reversibly transform to uniform width stripes as the minimum energy structure. Measuring the stripe width provides the first estimates of λ/μ at liquid condensed-liquid expanded phase coexistence.
域内静电排斥与域间线张力之间的竞争导致相分离脂质单层中的域形状转变。这些形态是能量最小值还是动力学捕获的亚稳态，这个问题仍然存在。我们展示了在二棕榈酰磷脂酰胆碱（DPPC）、十六醇（HD）或棕榈酸（PA）以及二氢胆固醇（DChol）的单层中，从多分散半圆形域到均匀宽度条纹域的可逆演变。最初的半圆形域以固定的2:1 DPPC:HD（或PA）化学计量比生长，耗尽HD的液相，留下富含DPPC和DChol的液相。在较高表面压力下，剩余的DPPC沉淀到现有域上，降低了线张力与偶极密度差平方的比值，即λ/μ。理论预测，随着λ/μ降低，圆形域作为最低能量结构可逆地转变为均匀宽度条纹。测量条纹宽度提供了在液-凝聚相-液-膨胀相共存时λ/μ的首次估计值。
