HEAT CAPACITY EFFECTS IN LIPIDS DURING UNICELLULAR/MULTICELLULAR PHASE CHANGES

单细胞/多细胞相变期间脂质的热容量效应

• 批准号: 3852960
• 负责人: C P MUDD
• 金额: --
• 依托单位: NATIONAL CENTER FOR RESEARCH RESOURCES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/3852960
• 关键词: biomedical equipment development; calorimetry; lipid bilayer membrane; liposomes; membrane activity; membrane model; method development; phase change; phospholipids; temperature; thermodynamics

Recent studies of the properties of phospholipid dispersions in water indicate that a higher-order phase transition occurs involving a spontaneous transformation from a unilamellar liquid-crystal state to a suspension of large, unilamellar vesicles upon increasing the ambient temperature; it has been suggested that the unilamellar vesicles that form are a critical state. The thermodynamic properties of this transformation have been inferred primarily from the properties of air-water surface films in equilibrium with the dispersed phospholipid phase. A more direct, and conceptually simpler, analysis of the thermodynamic properties of this higher-order transition may be attained by measurements of the temperature dependence of the heat capacity of the lipid dispersions. Since transformations of this type are believed to be intimately involved in the assembly of cell membranes, we have developed an extremely sensitive differential heat conduction calorimeter for measuring heat capacities of aqueous membrane lipid dispersions. (It should be noted that attempts to measure this transformation in commercial calorimeters have not been successful.) This instrument has certain obvious advantages over the commercial differential scanning calorimeters, notably baseline repeatability and resolution. In this transformation, to measure the heat capacity change sensibly requires a calorimeter with a sensitivity of 0.0001 cal/deg-g. We estimated the sensitivity for the energetics of unilamellar vesicle formation from multilamellar liquid crystals using the intrabilayer cohesive energy of approximately 0.01 ergs/cm2. Assuming a one-degree temperature interval for the transition, this translates into a change of heat capacity on the order of 0.001 cal/deg-g. To assure reasonable precision, we required an instrument with a sensitivity of at least one percent of the calculated transition energy. Moreover, since only mg quantities of membrane lipids are available, we are restricted to small sample sizes (1 cc).

磷脂在水中分散体特性的最新研究 表明发生高阶相变涉及 从单层液晶态到单层液晶态的自发转变 增加环境温度后，大的单层囊泡悬浮 温度;有人认为单层囊泡 形式是临界状态。 该物质的热力学性质 变换主要是从以下性质推断出来的 空气-水表面膜与分散的磷脂保持平衡 阶段。 更直接、概念上更简单的分析 可以获得这种高阶转变的热力学性质 通过测量热容量的温度依赖性 脂质分散体。 由于这种类型的变换被认为是 密切参与细胞膜的组装，我们开发了 极其灵敏的差热传导量热计 测量水膜脂质分散体的热容量。 （它 应该指出的是，试图衡量这种转变 商业热量计尚未成功。）该仪器已 与商业差示扫描相比有一些明显的优势 量热计，特别是基线重复性和分辨率。 在这个 变换，为了合理地测量热容变化需要 热量计，灵敏度为 0.0001 cal/deg-g。 我们估计了 对单层囊泡形成的能量学的敏感性 利用双层内聚能的多层液晶 约 0.01 ergs/cm2。 假设温度间隔为一度 对于转变，这转化为热容量的变化 0.001 cal/deg-g 量级。 为了确保合理的精度，我们需要 仪器的灵敏度至少为计算值的百分之一 跃迁能量。 此外，由于只有毫克量的膜脂 可用，但我们仅限于小样本量（1 cc）。