Chachaj-Brekiesz Anna, Kobierski Jan, Wnętrzak Anita, Dynarowicz-Latka Patrycja
Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Kraków, Poland.
Department of Pharmaceutical Biophysics, Faculty of Pharmacy, Jagiellonian University Medical College, Medyczna 9, 30-688 Kraków, Poland.
Membranes (Basel). 2021 Jan 13;11(1):53. doi: 10.3390/membranes11010053.
Experimental surface pressure (π) and electric surface potential (ΔV) isotherms were measured for membrane lipids, including the following phosphatidylcholines (PCs)-1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC); 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC); 1,2-diarachidoyl-sn-glycero-3-phosphocholine (DAPC); and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). In addition, other phospholipids, such as phosphatidylethanolamines (represented by 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE)) and sphingolipids (represented by N-(hexadecanoyl)-sphing-4-enine-1-phosphocholine (SM)) were also studied. The experimental apparent dipole moments (μAexp) of the abovementioned lipids were determined using the Helmholtz equation. The particular contributions to the apparent dipole moments of the investigated molecules connected with their polar (μ⟂p) and apolar parts (μ⟂a) were theoretically calculated for geometrically optimized systems. Using a three-layer capacitor model, introducing the group's apparent dipole moments (calculated herein) and adopting values from other papers to account for the reorientation of water molecules (μ⟂w/εw), as well as the for the local dielectric permittivity in the vicinity of the polar (εp) and apolar (εa) groups, the apparent dipole moments of the investigated molecules were calculated (μAcalc). Since the comparison of the two values (experimental and calculated) resulted in large discrepancies, we developed a new methodology that correlates the results from density functional theory (DFT) molecular modeling with experimentally determined values using multiple linear regression. From the fitted model, the following contributions to the apparent dipole moments were determined: μ⟂w/εw=-1.8±1.4 D; εp=10.2±7.0 and εa=0.95±0.52). Local dielectric permittivity in the vicinity of apolar groups (εa) is much lower compared to that in the vicinity of polar moieties (εp), which is in line with the tendency observed by other authors studying simple molecules with small polar groups. A much higher value for the contributions from the reorientation of water molecules (μ⟂w/εw) has been interpreted as resulting from bulky and strongly hydrated polar groups of phospholipids.
测量了膜脂的实验表面压力（π）和表面电势能（ΔV）等温线，其中包括以下磷脂酰胆碱（PC）：1,2-二棕榈酰-sn-甘油-3-磷酸胆碱（DPPC）；1,2-二硬脂酰-sn-甘油-3-磷酸胆碱（DSPC）；1,2-二花生四烯酰-sn-甘油-3-磷酸胆碱（DAPC）；以及1,2-二油酰-sn-甘油-3-磷酸胆碱（DOPC）。此外，还研究了其他磷脂，如磷脂酰乙醇胺（以1,2-二棕榈酰-sn-甘油-3-磷酸乙醇胺（DPPE）为代表）和鞘脂（以N-（十六烷酰基）-鞘氨醇-4-烯-1-磷酸胆碱（SM）为代表）。上述脂质的实验表观偶极矩（μAexp）使用亥姆霍兹方程测定。对于几何优化系统，从理论上计算了与所研究分子的极性部分（μ⟂p）和非极性部分（μ⟂a）相关的表观偶极矩的特定贡献。使用三层电容器模型，引入基团的表观偶极矩（在此计算）并采用其他论文中的值来考虑水分子的重新取向（μ⟂w/εw），以及极性基团（εp）和非极性基团（εa）附近的局部介电常数，计算了所研究分子的表观偶极矩（μAcalc）。由于比较这两个值（实验值和计算值）导致了很大差异，我们开发了一种新方法，该方法使用多元线性回归将密度泛函理论（DFT）分子建模的结果与实验测定值相关联。从拟合模型中，确定了对表观偶极矩的以下贡献：μ⟂w/εw = -1.8±1.4 D；εp = 10.2±7.0和εa = 0.95±0.52）。与极性部分附近的局部介电常数（εp）相比，非极性基团附近的局部介电常数（εa）要低得多，这与其他研究具有小极性基团的简单分子的作者所观察到的趋势一致。水分子重新取向的贡献（μ⟂w/εw）的值要高得多，这被解释为是由磷脂的庞大且高度水合的极性基团导致的。
