Charge-Transfer Reinforced Folding of Novel Ionenes
Charge-Transfer Reinforced Folding of Novel Ionenes
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DOI：
10.1021/ma901954x
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发表时间：
2009-11-24
期刊：
影响因子：
5.5
通讯作者：
Ramakrishnan, S.
中科院分区：
文献类型：
--
作者：
De, Swati;Ramakrishnan, S.
离子烯1可以被解释为通过以头对尾的方式连接表面活性剂分子以产生长链而形成的聚合物。迄今为止研究的大多数紫罗烯是阳离子的并且带有季铵基团。它们通常通过二叔胺与二卤化物在标准孟舒特金反应2条件下反应以生成带有周期性季铵基团的聚合物来制备，所述周期性季铵基团根据两种单体的选择是等间隔的（对称的）或不等间隔的（不对称的）。自Rembaum及其同事的早期研究以来，3种紫罗烯引起了研究人员的兴趣，因为它们代表了一类聚电解质，其中电荷直接驻留在聚合物主链上，重要的是，电荷的周期性可以非常容易地控制。各种紫罗烯，对称和不对称的，已被调查，和一个相当全面的了解他们的属性方面的长度，刚度，和疏水性的亚烷基间隔段，这是铵基团之间，已经获得。4 Kunitake等人5的早期研究表明，在带有长亚烷基间隔基（> 12个碳）的对称紫罗烯中，聚合物链在水溶液中可以采用手风琴型构象（方案1）。这一想法后来被Hinze等人利用。6使用长链紫罗烯开发用于改进分离和化学分析的胶束模拟系统。刚性偶氮苯单元内的亚烷基链段的掺入也被证明诱导类似的过渡到折叠的手风琴式结构中的溶剂中的适当的极性。7将半氟烷基侧基并入紫罗烯中导致在薄固体膜中形成层状结构域。8荧光探针，共价连接的悬垂单元，已被用来研究的构象变化，在紫罗烯作为各种参数的函数，如间隔段，盐浓度，等。9另一个有趣的功能紫罗烯的是，他们的溶液性质也可以调制的简单交换的counterweight，这通常是一个卤化物，可以交换各种有机阴离子。离子烯的卤化物与表面活性剂如月桂基硫酸盐的交换使这些系统具有有趣的胶束性质，其精确性质强烈依赖于离子交换的程度。10.最近，人们研究了阳离子带电的聚电解质，包括紫罗烯，因为它们能够与带相反电荷的DNA形成复合物，因此有可能作为基因传递载体。[11]从本质上讲，很明显，紫罗烯形成了一类有趣的易于合成的聚合物，其溶液构象和固态性质可以通过简单的结构操作来调节，包括电荷的周期性或反离子的性质。近年来，由于研究人员的动机是模仿生物大分子系统中精细的构象控制以实现所需的功能，因此溶液中聚合物构象的控制引起了大量的关注。折叠体12形成一类有趣的大分子，其响应于外部刺激（例如溶剂极性、温度、离子强度、添加的金属离子等）以预定方式改变其构象，而这些研究的主要焦点一直是定义明确的低聚物，相对较少的报道探索了具有更大构象自由度的柔性高分子量聚合物。13几年前…
Ionenes1 may be construed as polymers that are built-up by linking surfactant molecules in a head-to-tail fashion to generate long chains. The majority of the ionenes studied so far are cationic and carry quaternary ammonium groups. They are generally prepared by the reaction of a di-tert-amine with a dihalide under standard Menschutkin reaction2 conditions to generate a polymer bearing periodic quaternary ammonium groups, either equally spaced (symmetric) or unequally spaced (unsymmetric) depending on the choice of the two monomers. Since the early studies by Rembaum and coworkers, 3 ionenes have fascinated researchers because they represent a class of polyelectrolytes wherein the charges reside directly on the polymer backbone and, importantly, the periodicity of the charges can be very easily controlled. A variety of ionenes, both symmetrical and unsymmetrical, have been investigated, and a fairly comprehensive understanding of their properties with regard to the length, stiffness, and hydrophobicity of the alkylene spacer segment, which lies between the ammonium groups, has been gained. 4 Early studies by Kunitake et al. 5 suggested that in symmetric ionenes bearing long alkylene spacers (> 12 carbons), the polymer chain could adopt an accordion-type conformation (Scheme 1) in aqueous solutions. This idea was later exploited by Hinze et al. 6 using long chain ionenes to develop micelle-mimetic systems that were utilized for improved separation and chemical analysis. The incorporation of a rigid azobenzene unit within the alkylene segment was also shown to induce a similar transition to a folded accordiontype structure in a solvent of suitable polarity. 7 Incorporation of pendant semifluoroalkyl groups into ionenes led to the formation of layered domains in thin solid films. 8 Fluorescent probes, covalently linked as pendant units, have been used to study the conformational changes in ionenes as a function of various parameters, such as spacer segment, salt concentration, and so on. 9 One other interesting feature of ionenes is that their solution properties can also be modulated by the simple exchange of the counterion, which typically is a halide that can be exchanged for a variety of organic anions. The exchange of the halide counterion of ionenes with surfactants, such as lauryl sulfate, renders interesting micellar properties to these systems, the precise nature of which strongly depends on the extent of counterion exchange. 10 In recent times, cationically charged polyelectrolytes, including ionenes, have been investigated for their potential to serve as gene-delivery vehicles because of their ability to form complexes with oppositely charged DNA. 11 In essence, it is clear that ionenes form an interesting class of easily synthesizable polymers whose solution conformation and solid-state properties can be modulated by simple structural manipulations involving either the periodicity of the charges or the nature of the counterions. Control of polymer conformation in solution has attracted a great deal of attention in recent times because of the motivation of researchers to emulate the exquisite conformational control exercised in biomacromolecular systems to achieve a desired function. Foldamers12 form an interesting class of macromolecules that change their conformation in a predetermined manner in response to external stimuli, such as solvent polarity, temperature, ionic strength, added metal ion, and so on. Whereas the major focus of these studies has been well-defined oligomers, relatively fewer reports have explored flexible high-molecular-weight polymers that possess greater conformational freedom. 13 Some years ago …