Altunayar-Unsalan Cisem, Unsalan Ozan
Graduate School of Natural and Applied Sciences, Ege University, 35100, Bornova, Izmir, Turkey.
Faculty of Science, Department of Physics, Ege University, 35100, Bornova, Izmir, Turkey.
J Membr Biol. 2025 Feb;258(1):47-61. doi: 10.1007/s00232-024-00329-w. Epub 2024 Dec 7.
The purpose of this work is to examine how triterpenoids betulin (BE) and betulinic acid (BA) affect the thermotropic phase behaviour and bilayer packing in pulmonary surfactant membranes. Therefore, the interaction of these triterpenoids with dipalmitoylphosphatidylcholine (DPPC) bilayers is studied by differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and quantum chemical computations with density functional theory (DFT). From DSC data, the effects are more pronounced with BE compared to BA. At BE concentration of 20 mol%, the pretransition does not completely disappear and the lamellar phase transition broadens further. There are two indistinguishable peaks in the main phase transition, which may indicate the start of inhomogeneous mixing or phase separation in the gel phase. BA reduces the main transition temperature and almost completely eliminates the pretransition at concentrations of 1-10 mol%. Endotherms continue to have a symmetric, broad form that suggests perfect mixing. From ATR-FTIR data, both triterpenoids display the CH antisymmetric stretching, C = O stretching, PO asymmetric stretching to higher wavenumber in DPPC system. These results indicate an increase in the lateral mobility and dehydration in the polar head group and glycerol-acyl chain interface of DPPC liposomes. From microscopic results, it is found that the addition of high concentration (20 mol%) of BE and BA into pure DPPC membranes, single and double planar layers are formed, and the size of the liposomes increases. According to computational studies, the O-H OH group of BE and the P-O head group of DPPC formed a hydrogen bonding of 1.805 Å between BE and DPPC in gas phase. This hydrogen bonding is observed between BA and DPPC via the P-O head group of DPPC and the O-H OH group of BA.
这项工作的目的是研究三萜类化合物桦木醇（BE）和桦木酸（BA）如何影响肺表面活性物质膜的热致相行为和双层堆积。因此，通过差示扫描量热法（DSC）、衰减全反射傅里叶变换红外光谱（ATR-FTIR）、原子力显微镜（AFM）、场发射扫描电子显微镜（FE-SEM）以及密度泛函理论（DFT）的量子化学计算，研究了这些三萜类化合物与二棕榈酰磷脂酰胆碱（DPPC）双层的相互作用。从DSC数据来看，与BA相比，BE的影响更为显著。在BE浓度为20 mol%时，预转变并未完全消失，层状相转变进一步变宽。在主相转变中有两个无法区分的峰，这可能表明凝胶相中开始出现不均匀混合或相分离。在1 - 10 mol%的浓度下，BA降低了主转变温度并几乎完全消除了预转变。吸热峰继续呈现对称、宽阔的形式，表明混合良好。从ATR-FTIR数据可知，在DPPC体系中，两种三萜类化合物都使CH反对称伸缩振动、C = O伸缩振动、PO不对称伸缩振动向更高波数移动。这些结果表明DPPC脂质体极性头部基团和甘油 - 酰基链界面处的横向流动性增加以及脱水。从微观结果发现，向纯DPPC膜中添加高浓度（20 mol%）的BE和BA时，会形成单层和双层平面层，并且脂质体尺寸增大。根据计算研究，在气相中，BE的O - H OH基团与DPPC的P - O头部基团在BE和DPPC之间形成了1.805 Å的氢键。通过DPPC的P - O头部基团和BA的O - H OH基团在BA和DPPC之间也观察到了这种氢键。
