Chen H, Mendelsohn R, Rerek M E, Moore D J
Rutgers University, Department of Chemistry, 73 Warren Street, Newark, NJ 07102, USA.
Biochim Biophys Acta. 2000 Sep 29;1468(1-2):293-303. doi: 10.1016/s0005-2736(00)00271-6.
Ceramides provide a major component of the barrier function of skin. An understanding of barrier organization requires a detailed characterization of ceramide phase behavior and molecular interactions. Toward this end, Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) studies of ceramide 2 analogues (non-hydroxylated fatty acid N-acyl sphingosines) of specific chain lengths (C(14), C(16), C(18), C(20)) are presented. In addition, the molecular interactions of the individual chains in each molecule are elucidated through thermotropic FTIR studies of derivatives possessing perdeuterated fatty acid chains. DSC data showed a much smaller chain length variation (for the C(16), C(18), C(20) derivatives) in the main order-disorder transition temperature (approx. 93+/-1 degrees C) than is observed in the corresponding series of phosphatidylcholines, consistent with minimal ceramide hydration. The temperature dependence of the methylene stretching and scissoring modes revealed a solid-solid phase transition at 20-25 degrees C below the main order-disorder transition accompanied by chain packing alterations from orthorhombic-->hexagonal subcells. The chain packing transition was accompanied by enhanced penetration of water into the polar region. This was deduced from the temperature dependence of the amide I and II modes, which provide direct evidence for H-->D exchange. The CD(2) scissoring mode splitting of the deuterated fatty acid constituent of the C(16), C(18), C(20) chains revealed preferential segregation of microdomains (3-5 chains) of this species within the orthorhombic phase. In contrast, the sphingosine base chains appeared to be sufficiently separated so as to inhibit interchain vibrational coupling between them. FTIR spectroscopy provides a convenient means for characterizing domain formation, chain packing, and hydration sites of these phases, which are highly ordered under physiological conditions.
神经酰胺是皮肤屏障功能的主要组成部分。要了解屏障组织，需要详细表征神经酰胺的相行为和分子相互作用。为此，本文介绍了对特定链长（C(14)、C(16)、C(18)、C(20)）的神经酰胺2类似物（非羟基化脂肪酸N-酰基鞘氨醇）进行的傅里叶变换红外光谱（FTIR）和差示扫描量热法（DSC）研究。此外，通过对具有全氘代脂肪酸链的衍生物进行热致FTIR研究，阐明了每个分子中各个链的分子相互作用。DSC数据显示，在主要的有序-无序转变温度（约93±1℃）下，链长变化（对于C(16)、C(18)、C(20)衍生物）比在相应的磷脂酰胆碱系列中观察到的要小得多，这与神经酰胺的最小水合作用一致。亚甲基伸缩和剪式振动模式的温度依赖性揭示了在主要的有序-无序转变以下20-25℃处存在固-固相变，同时链堆积从正交晶胞转变为六方亚晶胞。链堆积转变伴随着水向极性区域的渗透增强。这是从酰胺I和II模式的温度依赖性推导出来的，它们为H→D交换提供了直接证据。C(16)、C(18)、C(20)链的氘代脂肪酸成分的CD(2)剪式振动模式分裂揭示了该物种的微区（3-5条链）在正交相中优先分离。相比之下，鞘氨醇碱基链似乎充分分离，从而抑制了它们之间的链间振动耦合。FTIR光谱为表征这些在生理条件下高度有序的相的域形成、链堆积和水合位点提供了一种方便的手段。
