Effects of divalent cations on the ultrasonic absorption coefficient of negatively charged liposomes (LUV) near their phase transition temperature.
Effects of divalent cations on the ultrasonic absorption coefficient of negatively charged liposomes (LUV) near their phase transition temperature.
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二价阳离子对带负电的脂质体（LUV）在相变温度附近超声吸收系数的影响。
DOI：
10.1016/0005-2736(87)90294-x
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Dunn,F
中科院分区：
文献类型：
--
作者：
Ma,LD;Magin,RL;Dunn,F
用双晶体声学干涉仪测定了大单层囊泡（LUV）在磷脂相变温度附近的单位波长超声吸收系数（αλ），它是温度和频率的函数。(The囊泡由二棕榈酰磷脂酰胆碱（DPPC）和二棕榈酰磷脂酰甘油（DPPG）的4：1（w/w）混合物组成。在超声弛豫频率为2.1MHz时，αλ在磷脂的相变温度（tm）处达到最大值（αλ）max。二价阳离子（Ca ~（2+）和Mg ~（2+））加入到LUV悬浮液中，使（αλ）max向高温移动，这取决于二价阳离子的浓度。还发现αλ versust曲线的形状发生了显著变化，这代表了转变的Van 't霍夫焓的变化，因此，转变的合作单位。这表明，二价阳离子个别地与DPPG的带负电荷的磷脂头基和DPPC头基相互作用，从而减少了过渡的合作单位。所观察到的向上移位intm表明增加活化能的相互作用，因此，相变的温度。然而，作为频率的函数的αλ不随二价阳离子的添加而改变，因此，负责超声吸收的事件的弛豫时间不因二价阳离子的添加而改变。
The ultrasonic absorption coefficient per wavelength (αλ), as a function of temperature and frequency, was determined for large unilamellar vesicles (LUV) in the vicinity of their phospholipid phase transition temperature, using a double crystal acoustic interferometer. (The vesicles were composed of a 4:1 (w/w) mixture of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG)). It has been found that αλ reaches a maximum (αλ)maxat the phase transition temperature (tm) of the phospholipids in the bilayer, at an ultrasonic relaxation frequency of 2.1 MHz. Divalent cations (Ca2+and Mg2+), added to LUV suspensions, shifted (αλ)maxto higher temperatures, dependent upon the concentration of divalent cation. It was also found that the shape of the αλ versustcurve was significantly changed, representing changes in the Van't Hoff enthalpy of the transition, and therefore, the cooperative unit of the transition. This suggests that divalent cations interact individually with the negatively charged phospholipid headgroups of DPPG and with DPPC headgroups, thus decreasing the cooperative unit of the transition. The observed upward shift intmsuggests an interaction that increases the activation energy and, therefore, the temperature of the phase transition. However, αλ as a function of frequency did not change with the addition of divalent cations and, thus, the relaxation time of the event responsible for the absorption of ultrasound is not changed by the addition of divalent cations.
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DOI：
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