Levothyroxine (3,5,3',5'-tetraiodothyronine), which is a L-isomer of thyroxine T4 (L-T4), is a synthetic thyroid hormone that is biochemically and physiologically indistinguishable from endogenous T4. It is used as a thyroid hormone replacement drug to treat an underactive thyroid gland. The interaction of L-T4, with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) multilamellar liposomes (MLVs) was studied in the presence (1 mol%, 3 mol%, 6 mol%, 9 mol%, 15 mol%, 24 mol% and 30 mol%) and absence of L-T4 by using two different non-invasive techniques; Fourier Transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). The results show that L-T4 does perturb the phase transition profile by either decreasing the main transition temperature (Tm) and enthalpy (ΔH) or increasing the width at half height (ΔT½). That means; it changes the physical properties of DPPC bilayers. Addition of L-T4 into pure DPPC liposomes shifts the phase transition to lower temperature, disorder the system in gel phase with opposite effect in liquid-crystalline phase and increases the dynamics of the system in both phases and also causes dehydration of the groups of lipids and the water molecules around.

中文翻译：

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左甲状腺素对DPPC脂质体结构和动力学的影响：FTIR和DSC研究。

左甲状腺素（3,5,3'，5'-四碘甲甲状腺素）是甲状腺素T4（L-T4）的L-异构体，是一种合成的甲状腺激素，在生化和生理上与内源性T4没有区别。它被用作甲状腺激素替代药物来治疗甲状腺功能低下的甲状腺。研究了L-T4与两性离子二棕榈酰磷脂酰胆碱（DPPC）多层脂质体（MLV）的相互作用（1 mol％，3 mol％，6 mol％，9 mol％，15 mol％，24 mol％和30 mol％），并且通过使用两种不同的非侵入性技术不存在L-T4；傅立叶变换红外（FTIR）光谱和差示扫描量热法（DSC）。结果表明，L-T4确实会通过降低主转变温度（Tm）和焓（ΔH）或增加半高宽度（ΔT1/ 2）来扰乱相变曲线。那意味着 它改变了DPPC双层的物理性质。在纯DPPC脂质体中添加L-T4会使相变转变为更低的温度，使凝胶相中的系统混乱，在液晶相中产生相反的作用，并增加两个相中系统的动力学，还导致脂质组脱水和周围的水分子。