【作者】 丁元华； 王晓彤； 谢礼霞； 孟芳； 郭荣；

【Author】 Yuanhua Ding;Xiaotong Wang;Lixia Xie;Fang Meng;Rong Guo;School of Chemistry and Chemical Engineering, Yangzhou University;

【机构】 扬州大学胶体与界面化学研究所；

【摘要】 手性生物相容表面活性剂能通过自组装形成各种结构的手性自组装体,在生物医药领域具有重要的应用价值,可以用于生物、药物的识别,制备靶向性的DNA纳米载体材料等。因此,研究该类表面活性剂手性自组装行为和缔合机理,以及其与DNA的缔合模式,不仅可从分子的水平理解手性自组装体的缔合特性,更有望拓展手性表面活性剂的应用,发展更多功能性的手性自组装体材料。本文设计合成了三种不同链长的手性嘧啶型表面活性剂（8-（1-胸腺嘧啶基）辛基）三甲基溴化铵,（10-（1-胸腺嘧啶基）癸基）三甲基溴化铵和（12-（1-胸腺嘧啶基）十二烷基）三甲基溴化铵,简称为T-C_n-TAB （n=8, 10, 12）,以及N-（2-羟基十二烷基）丙氨酸(C₁₂Ala)、N-（2-羟基辛基）丙氨酸（C₈Ala）和N-（2-羟基丁基）丙氨酸（C4Ala）等系列氨基酸型手性生物相容表面活性剂。通过电导率法、圆二色谱法、等温滴定微量热法、¹HNMR、2DNOESY、动态光散射、负染透射电镜和密度泛函理论计算等一系列手段探讨其缔合行为,并研究了这类手性表面活性剂与DNA相互作用特性和分子间的缔合机理。研究发现,手性嘧啶型表面活性剂在水中的缔合是一个焓驱动的自组装行为,反应的热效应△H_mic⁰在-10.7kJ/mol,且随温度升高,反应的热效应逐步增加。动态光散射表明手性聚集体的水合流体力学半径在0.7nm左右,透射电镜表明这种手性聚集体为尺寸均一,分散性良好的球形聚集体。¹HNMR和2D NOESY表明在形成手性胶束的过程中,胸腺嘧啶基的嘧啶环处于胶核内部并且相邻的嘧啶环之间形成π-π堆积,平行排列于其中,得到结构紧密的胶束聚集体。密度泛函理论计算进一步证实上述的聚集体中分子的紧密排列方式。并且,升高温度,聚集体的尺寸与手性信号都发生了改变,这可能由于温度的改变使得氢键发生断裂,从而改变了聚集体的构型。另一方面,当手性丙氨酸型表面活性剂的浓度小于0.1mmol/L时,其呈单分子状态,当浓度在0.1mmol/L-1.0 mmol/L时,手性聚集体呈球形状态,直径约为20 nm,当浓度超过1.0 mmol/L时,得到了一维螺旋状结构,长度为1.5μm左右,宽度为50 nm左右。在固定C₁₂Ala浓度为8.0 mmol/L时,升高温度,螺旋状结构变短,并收缩;改变pH,螺旋状结构逐渐被破坏,向中空状结构转变,动态光散射进一步验证了上述结果（图1）。圆二色谱表明,随着浓度的增加,正吸收峰强度增加,但峰位置不变,表明手性自组装体的结构不变,但其空间堆积方式发生变化。根据对¹H NMR和2D NOESY的谱图分析,表明溶液中分子在聚集过程中发生了分子的扭曲和折叠,进而导致不对称螺旋结构的出现。因此,通过调节C12Ala的浓度、温度、pH值可以调控手性聚集体的结构和性能。与通常加入离子液体表面活性剂和传统表面活性剂与DNA的作用行为正好相反,手性嘧啶型表面活性剂与DNA具有独特的缔合特性。动态光散射测定表明DNA/T-C12-TAB复合物的流体力学半径从220 nm增加为360 nm左右,进一步表明尽管手性表面活性剂与DNA之间有电荷吸引作用,但手性嘧啶型表面活性剂与DNA存在着独特的空间缔合作用,也验证了其荧光特性。圆二色谱表明在作用的过程中,B-型DNA的结构基本保持不变,但其碱基堆积部分发生转变,进一步验证了上述结果。研究发现胸腺嘧啶环与DNA的碱基对之间有较强的氢键作用和疏水作用,使得表面活性剂处于DNA双螺旋结构的沟槽中,使其尺寸变大,相应地,其与DNA形成的手性结构也在发生变化。更多还原

【Abstract】 Chiral biosurfactants can form various chiral aggragates via their self-assembling behavior in aqueous solution, which have potential application in biochemical technology, such as the recognition of drugs and the preparation of targeting DNA nanocarriers. Thus, great attention have been paid to the binding behavior and self-assembling mechanism of this kind of surfactants, which not only can explore the applications of chiral biosurfactants, but also can be used to develop functional chiral materials. In the present work, the chiral nucleobase-type surfactants T-C_n-TAB(n=8, 10, 16) and the amino acid surfactants C_nAla(n=4, 8, 12) were synthesized. The conductivity method, dynamic light scattering(DLS), transmission electron microscopy(TEM), ~1H nuclear magnetic resonance(NMR), circular dichroism spectroscopy(CD) and DFT calculation were used to investigate the binding behaviors and their interaction with DNA. It is found that the association of chiral nucleobase-type surfactants is an entropy-driven process with the thermal effect being-10.7 kJ/mol. In the chiral aggregates, pyimidine rings lie in the colloidal nucleus, in which adjacenting thymine is located parallelly due to π-π stacking, thus leading to the formation of dense aggragets. Also, temperature can change the size and chiral signal of self-assemblies, which is due to the breakage of hydrogen bonding resulting from the change of temperature, consequently altering configuration of self-assemblies. On the other hand, it is also found that N-(2-Hydroxydodecyl)alanine in aqueous solution can form various chiral aggregates form spherical micelles with the diameter of about 20 nm to the one-dimensional helical structure with the length of about 7μm and the width of about 17 nm. Furthermore, the binding of the chiral surfactants on DNA show unique binding mode, which is different from those for ionic liquid surfactants. Owing to chiral recognition and the strong H-bond between the thymine ring and DNA base pairs, the chiral molecules lie in the grooves of DNA, resulting in the larger chiral complexes.更多还原