Hirst Andrew R, Smith David K
Department of Chemistry, University of York, UK.
Org Biomol Chem. 2004 Oct 21;2(20):2965-71. doi: 10.1039/B409272D. Epub 2004 Sep 16.
The self-assembly of diaminododecane solubilised by different dendritic peptides, possessing increasing levels of dendritic branching, was investigated. The dendritic peptides were based on l-lysine building blocks and were of first, second and third generation, containing one, three and seven amino acid repeat units respectively. By applying these structures as potential gelator units, the dendritic effect on gelation was investigated. The degree of structuring was modulated, with the dendritic peptide controlling the aggregate morphology and the ability of the self-assembled state to manifest itself macroscopically as gelation. First generation gelator units (G1) did not induce macroscopic gelation with diaminododecane under any conditions, whilst those self-assemblies based on second (G2) and third (G3) generation branches did form gel-phase materials. Furthermore, gel-phase materials based on G2 exhibited optimum gelation behaviour compared to those based on G3(in terms of the thermal strength of the materials). Circular dichroism showed that the dendritic effect, programmed in at the molecular level, is directly related to the degree of chiral organisation within the self-assembled state. The dendritic generation of the peptide controls the pattern of amide-amide hydrogen bonding in terms of binding strength and alignment as determined using NMR methods. The mode of self-assembly can be qualitatively rationalised in terms of an attractive enthalpic interaction (i.e., amide-amide hydrogen bonding), a repulsive interaction (i.e., steric interactions between dendritic peptides) and an entropic term related to the hierarchical organisation of the gelator building blocks. It is argued that the balance between these factors determines the nature of the dendritic effect.
研究了由具有不同树枝状分支水平的树枝状肽增溶的二氨基十二烷的自组装。这些树枝状肽基于L-赖氨酸构建块，分别为第一代、第二代和第三代，分别包含一个、三个和七个氨基酸重复单元。通过将这些结构用作潜在的凝胶剂单元，研究了树枝状结构对凝胶化的影响。结构程度得到调节，树枝状肽控制聚集体形态以及自组装状态宏观表现为凝胶化的能力。第一代凝胶剂单元（G1）在任何条件下都不会与二氨基十二烷诱导宏观凝胶化，而基于第二代（G2）和第三代（G3）分支的自组装确实形成了凝胶相材料。此外，与基于G3的材料相比，基于G2的凝胶相材料表现出最佳的凝胶化行为（就材料的热强度而言）。圆二色性表明，在分子水平上设计的树枝状效应与自组装状态内的手性组织程度直接相关。肽的树枝状代数根据使用NMR方法确定的结合强度和排列控制酰胺-酰胺氢键的模式。自组装模式可以根据有吸引力的焓相互作用（即酰胺-酰胺氢键）、排斥相互作用（即树枝状肽之间的空间相互作用）和与凝胶剂构建块的层次组织相关的熵项进行定性合理化。有人认为，这些因素之间的平衡决定了树枝状效应的性质。
