分子层次的金纳米棒-表面活性剂-磷脂自组装复合体形貌

Morphologies of self-assembled gold nanorod-surfactantlipid complexes at molecular level

金纳米粒子表面修饰剂的组分和形貌影响其物理化学性质.本文采用隐式溶剂耗散粒子动力学模拟的方法,研究了金纳米棒、溴化十六烷基三甲基铵和二肉豆蔻酰磷脂酰胆碱的自组装形貌.结果表明,复合体组装形貌主要与溴化十六烷基三甲基铵和二肉豆蔻酰磷脂酰胆碱这两种修饰剂的摩尔比有关,而金纳米棒与修饰剂的相互作用强度以及金纳米棒的直径对形貌的影响不明显.当作用强度和直径一定时,随着摩尔比增加,修饰剂在金纳米棒表面会形成完整的双层膜、有裂痕的双层膜、长片状胶束、以及以螺旋形式缠绕在金纳米棒上的蠕虫状胶束.进一步分析发现,金纳米棒直径越小、摩尔比越大、或作用强度越大时,金纳米棒两端的覆盖程度越高,同时修饰剂吸附层的厚度越薄.这些结果直接表征了溴化十六烷基三甲基铵和二肉豆蔻酰磷脂酰胆碱混合物在金纳米棒表面的形态,在分子水平上加深了对金纳米棒自组装行为的理解,有助于实现金纳米棒的可控自组装.

Gold nanorods(GNRs)have aroused the extensive interest of many researchers in recent years due to their unique physicochemical properties.However,the toxic cetyltrimethylammonium bromide(CTAB)is often introduced into the process of synthesizing GNRs,which hinders the wide-range applications of GNRs in clinical practice.To reduce the toxicity,the CTAB molecules coated on the surface of GNRs should be replaced by nontoxic and biocompatible agents such as phospholipid.Thus the component and morphology of the mixed coating agents on the surface of GNRs affect the physicochemical properties of GNRs.To study the morphology and properties of the coated GNRs at a molecular level,we investigate the self-assembly of GNRs,CTAB,and dimyristoyl phosphatidylcholine(DMPC)by using solvent-free dissipative particle dynamics simulations.Our results show that the morphology of the assembled complex mainly depends on the CTAB/DMPC molar ratio,while neither of the interaction strength between GNRs and the coating agents nor the diameter of GNRs has significant effect on the morphology.At a certain combination of GNRs-coating agent interaction strength with GNRs diameter,the mixture of CTAB and DMPC on the surface of GNRs undergoes a gradual change in morphology as the CTAB/DMPC molar ratio increases,including the forming of intact bilayer membrane,cracked bilayer membrane,long patches of micelles,and short wormlike micelles winding GNRs in spiral shape.The morphology of intact bilayer membrane verifies the experimental guess,while the other three morphologies are brand-new discoveries.We also find that when the GNR’s diameter becomes smaller,or the CTAB/DMPC molar ratio is larger,or the interaction strength is greater,the agents cap the ends of GNRs,meanwhile the membrane thickness becomes thinner.The multiple morphologies of the assembled complexes can be qualitatively explained by the shape energy of a membrane adsorbed on a solid surface.When the surface tension of the membrane(which is proportional to the spontaneous curvature of the membrane)exceeds a critical value(which is equal to the adhesion energy density of the membrane),the membrane dissociates from the solid surface and its shape changes.The change trend is related to the spontaneous curvature of the free membrane.As a result of the synergy and competition among the inherent curvatures of GNRs,the spontaneous curvature of CTAB/DMPC membrane or micelle,as well as the adhesion energy,various interesting morphologies are produced.Our simulations and analyses directly characterize the morphological structures of CTAB and lipid coated GNRs,which allow us to in depth understand the self-assembling behaviors of GNRs at a molecular level.This is also conductive to achieving the controlled assemblies of GNRs.