COMPONENTS OF THE CARBONYL STRETCHING BAND IN THE INFRARED-SPECTRA OF HYDRATED 1,2-DIACYLGLYCEROLIPID BILAYERS - A REEVALUATION
COMPONENTS OF THE CARBONYL STRETCHING BAND IN THE INFRARED-SPECTRA OF HYDRATED 1,2-DIACYLGLYCEROLIPID BILAYERS - A REEVALUATION
复制标题
DOI：
10.1016/s0006-3495(94)80723-4
复制
发表时间：
1994-12-01
影响因子：
3.4
通讯作者：
MANTSCH, HH
中科院分区：
文献类型：
--
作者：
LEWIS, RNAH;MCELHANEY, RN;MANTSCH, HH
以往对固体酰基-烷基和二酰基磷脂酰胆碱的振动光谱研究表明，1,2-二酰基甘油脂的sn1-和sn2-羰基拉伸模式具有不同的吸收最大值。为了确定水合1,2-二酰基甘油脂的sn1-和sn2-羰基拉伸模式，采用傅里叶变换红外光谱对1-棕榈酰-2-十六烷基磷脂酰胆碱（PHPC）、1-十六烷基-2-棕榈酰磷脂酰胆碱（HPPC）、1,2-二棕榈酰磷脂酰胆碱（DPPC）以及未标记、sn1-C-13= o标记、sn2-C-13= o标记和双C-13= o标记的二myristoyl磷脂酰胆碱（DMPC）的水合样品进行了表征。HPPC和PHPC的酯羰基拉伸带（nu(C=O)）均在1726 cm（-1）附近出现最大值，并且似乎是三个子组分的总和，其中最大值在1740 cm(-1)， 1725和1705-1711 cm（-1）附近。相比之下，DPPC的nu（C=O）波段在1733 cm（-1）附近最大，似乎是在1742和1727 cm（-1）附近两个分量的总和。因此，酰基-烷基pc的酯羰基似乎比它们的二酰基类似物的酯羰基驻留在更极性的环境中。这一观察结果表明，PHPC和HPPC形成的水合双层的极性/极性界面与DPPC有显著不同，并提出了酰基-烷基pc是否适合作为二酰基类似物的模型的问题。双C-13=O标记的DMPC的nu（C=O）波段的吸收最大值出现在1691 cm（-1）附近，其子组分的吸收最大值出现在1699和1685 cm（-1）附近。这些频率与C-12=O/C-13=O的42-43 cm（-1）的“同位素位移”一致。sn1-和sn2-C-13=O标记的DMPC均表现出良好的C-12和C-13 nu（C=O）波段，吸收最大值分别在1734和1692 cm（-1）附近。对于这两种特定的C-13=O标记的脂质，C-12和C-13 nu（C=O）波段似乎都是吸收最大值在1742和1727 cm(-1) （C-12 nu(C=O)）和1699和1685 cm(-1) （C-13 nu(C=O)）附近的子组分的总和，而不管C-13=O标记的脂肪酰基链是在甘油主链的sn1-或sn2-位置酯化。我们得出结论，在水合1,2-二酰基PC双分子层中，位于甘油主链一级和二级位置的酯羰基所表现出的红外吸收模式是相似的。此外，它们的nu（C=O）波段的可分解子组分是两个酯羰基的可比较贡献的总和，因此不能归因于两个酯羰基的不相等位置。这个结果不同于上面提到的振动光谱研究，并提出了一个问题，即在干燥（或缺水）脂质研究中获得的数据是否适用于完全水合的脂质双分子层。为了解释为什么这两项研究的结果不同，我们还研究了DPPG、HPPC和PHPC固体样品的nu（C=O）波段。我们发现所研究的所有固体脂类的nu（C=O）带都与水合样品不同。此外，对于固体脂类，nu（C=O）谱带随对映体构型、对映体纯度、热历史以及样品制备方式的不同而变化。此外，尽管固体HPPC和PHPC的nu（C=O）带随样品制备方法的不同而有显著差异，但相同方法制备的PHPC和HPPC样品的nu（C=O）吸收带非常相似。我们得出结论，就脂质极性/极性界面的组织而言，固体脂质不是水合脂质双层的良好模型，这可能是本工作和先前发表的研究得出不同结论的主要原因。
Previous vibrational spectroscopic studies of solid acyl-alkyl and diacyl phosphatidylcholines suggested that the sn1- and sn2-carbonyl stretching modes of 1,2-diacylglycerolipids have different absorption maxima. To address the assignment of sn1- and sn2-carbonyl stretching modes of hydrated 1,2-diacylglycerolipids, aqueous dispersions of 1-palmitoyl-2-hexadecyl phosphatidylcholine (PHPC), 1-hexadecyl-2-palmitoyl phosphatidylcholine (HPPC), 1,2-dipalmitoylphosphatidylcholine (DPPC), as well as hydrated samples of unlabeled, sn1-C-13=O-labeled, sn2-C-13=O-labeled, and doubly C-13=O-labeled dimyristoylphosphatidylcholine (DMPC) were examined by Fourier transform infrared spectroscopy. The ester carbonyl stretching (nu(C=O)) bands of HPPC and PHPC each exhibit maxima near 1726 cm(-1) and appear to be a summation of three subcomponents with maxima near 1740 cm(-1), 1725 and 1705-1711 cm(-1). In contrast, the nu(C=O) band of DPPC exhibits its maximum near 1733 cm(-1) and appears to be a summation of two components centered near 1742 and 1727 cm(-1). Thus the ester carbonyl group of the acyl-alkyl PCs appears to reside in a more polar environment than the ester carbonyl groups of their diacyl analogue. This observation implies that the polar/apolar interfaces of hydrated bilayers formed by PHPC and by HPPC are significantly different from that of DPPC and raises the question of whether the acyl-alkyl PCs are suitable models of their diacyl analogue. The absorption maximum of the nu(C=O) band of the doubly C-13=O-labeled DMPC occurs near 1691 cm(-1) and those of its subcomponents occur near 1699 and 1685 cm(-1).These frequencies are consistent with a C-12=O/C-13=O 'isotopic shift' of 42-43 cm(-1). sn1- and sn2-C-13=O-labeled DMPC each exhibit well resolved C-12 and C-13 nu(C=O) bands with absorption maxima near 1734 and 1692 cm(-1), respectively. With both specifically C-13=O-labeled lipids, the C-12 and C-13 nu(C=O) bands each seem to be a summation of subcomponents with absorption maxima near 1742 and 1727 cm(-1) (C-12 nu(C=O)) and 1699 and 1685 cm(-1) (C-13 nu(C=O)), regardless of whether the C-13=O-labeled fatty acyl chain is esterified at the sn1- or sn2- positions of the glycerol backbone. We conclude that in hydrated 1,2-diacyl PC bilayers, the patterns of infrared absorption exhibited by ester carbonyl groups located at the primary and secondary positions of the glycerol backbone are similar. Also, the resolvable subcomponents of their nu(C=O) bands are each a summation of comparable contributions from both ester carbonyl groups and therefore cannot be attributed to the inequivalent locations of the two ester carbonyl groups. This result differs from that of the vibrational spectroscopic studies alluded to above and raises the question of whether data obtained in studies of dry (or poorly hydrated) lipids are applicable to fully hydrated lipid bilayers. To address questions of why the results of the two studies differ, we have also examined the nu(C=O) bands of solid samples of DPPG, HPPC, and PHPC. We find that the nu(C=O) bands of all solid lipids studied differ from those of the hydrated samples. Moreover, with solid lipids the nu(C=O) bands vary with the enantiomeric configuration, enantiomeric purity and thermal thermal history as well as with the way in which the sample was prepared. Also, although the nu(C=O) bands of solid HPPC and PHPC vary significantly with sample preparation methodology, samples of PHPC and HPPC prepared by the same method exhibit very similar nu(C=O) absorption bands. We conclude as far as the organization of lipid polar/apolar interfaces is concerned, solid lipids are not good models of hydrated lipid bilayers and suggest that this may be largely responsible for the different conclusions drawn in this work and in previously published studies.