Department of Physics, University of Nevada, Reno, NV 89557, USA.
Spectrochim Acta A Mol Biomol Spectrosc. 2011 Oct 15;81(1):583-9. doi: 10.1016/j.saa.2011.06.055. Epub 2011 Jun 30.
The thermotropic phase behavior of a suite of newly developed self-forming synthetic biopolymers has been investigated by variable-temperature Fourier transform infrared (FT-IR) absorption spectroscopy. The temperature-induced infrared spectra of these artificial biopolymers (lipids) composed of 1,2-dimyristoyl-rac-glycerol-3-dodecaethylene glycol (GDM-12), 1,2-dioleoyl-rac-glycerol-3-dodecaethylene glycol (GDO-12) and 1,2-distearoyl-rac-glycerol-3-triicosaethylene glycol (GDS-23) in the spectral range of 4000-500 cm(-1) have been acquired by using a thin layered FT-IR spectrometer in conjunction with a custom built temperature-controlled demountable liquid cell having a pathlength of ∼15 μm. The lipids under consideration have long hydrophobic acyl chains and contain various units of hydrophilic polyethylene glycol (PEG) headgroups. In contrast to conventional phospholipids, this new kind of lipids forms liposomes or nanovesicles spontaneously upon hydration, without requiring external activation energy. We have found that the thermal stability of the PEGylated lipids differs greatly depending upon the acyl chain-lengths as well as the nature of the associated bonds and the number of PEG headgroup units. In particular, GDM-12 (saturated 14 hydrocarbon chains with 12 units of PEG headgroup) exhibits one sharp order-disorder phase transition over a temperature range increasing from 3°C to 5°C. Similarly, GDS-23 (saturated 18 hydrocarbon chains with 23 units of PEG headgroup) displays comparatively broad order-disorder phase transition profiles between temperature 17°C and 22°C. In contrast, GDO-12 (monounsaturated 18 hydrocarbon chains with 12 units of PEG headgroup) does not reveal any order-disorder transition phenomena demonstrating a highly disordered behavior for the entire temperature range. To confirm these observations, differential scanning calorimetry (DSC) was applied to the samples and revealed good agreement with the infrared spectroscopy results. Finally, the investigation of thermal properties of lipids is extremely critical for numerous purposes and the result obtained in this work may find application in various studies including the development of PEGylated lipid based novel drug and substances delivery vehicles.
通过变温傅里叶变换红外（FT-IR）吸收光谱法研究了一系列新开发的自形成合成生物聚合物的热致相行为。使用配备有定制的可拆式液体池的薄层 FT-IR 光谱仪，在 4000-500 cm(-1) 的光谱范围内获得了由 1,2-二肉豆蔻酰基-rac-甘油-3-十二烷撑乙二醇（GDM-12）、1,2-二油酰基-rac-甘油-3-十二烷撑乙二醇（GDO-12）和 1,2-二硬脂酰基-rac-甘油-3-二十三烷撑乙二醇（GDS-23）组成的这些人工生物聚合物（脂质）的温度诱导红外光谱。考虑到的脂质具有长疏水酰基链，并含有各种亲水聚乙二醇（PEG）头基单元。与传统的磷脂不同，这种新型脂质在水合时会自发形成脂质体或纳米囊泡，而不需要外部激活能。我们发现，PEG 化脂质的热稳定性很大程度上取决于酰链长度以及相关键的性质和 PEG 头基单元的数量。特别是，GDM-12（具有 12 个 PEG 头基单元的 14 个饱和烃链）在从 3°C 增加到 5°C 的温度范围内显示出一个尖锐的有序-无序相变。同样，GDS-23（具有 23 个 PEG 头基单元的 18 个饱和烃链）在 17°C 和 22°C 之间显示出相对较宽的有序-无序相变谱。相比之下，GDO-12（具有 12 个 PEG 头基单元的单不饱和 18 个烃链）没有显示出任何有序-无序转变现象，表明在整个温度范围内呈现出高度无序的行为。为了证实这些观察结果，应用差示扫描量热法（DSC）对样品进行了研究，结果与红外光谱结果吻合良好。最后，脂质热性质的研究对于许多目的都是至关重要的，本工作的结果可能会在各种研究中得到应用，包括基于 PEG 化脂质的新型药物和物质传递载体的开发。
