Periodic change in absorption maxima due to different chain packing between the bilayers of amphiphiles possessing even and odd numbers of carbons in the hydrophobic chain
作者:Norihiro Yamada、Kenji Okuyama、Takeshi Serizawa、Masashi Kawasaki、Shinichiro Oshima
DOI:10.1039/p29960002707
日期:——
N-4-[4-(10-Trimethylammoniodecyloxy)phenylazo]benzoyl}-L-alanine alkyl ester bromides with n-C6 to -C13 alkyl chains have been newly synthesized. The bilayer aggregates absorbed at 355 nm when the number of carbons was even and at 320 nm when odd. Regardless of whether the number was even or odd, X-ray diffraction patterns suggested a chain penetration structure, where the tail chains in one molecular layer penetrated into the opposite molecular layer, and hence every other azobenzene group was distributed into the opposite layers. However, a remarkable splitting of the CH2 scissoring band into 1473 and 1463 cm–1 indicated perpendicular alignments of the trans-zigzag planes of the chains containing an even number of carbons, whereas the singlet CH2 scissoring band at 1465 cm–1 indicated parallel alignments of the planes of the chains containing an odd number of carbons. In accord with the chain packing, when the amphiphiles possess an even number of carbons, the adjacent neighbouring azobenzenes in each layer were arranged perpendicular to each other. The perpendicular location causes a loss of interchromophore interaction, giving λmax at 355 nm. In contrast, the azobenzenes in the bilayers of the amphiphiles containing an odd number of carbons were all parallel to each other. Because the molecules were tilted above about 60°, a H aggregate should be predominantly formed, which absorbed at 320 nm. In addition, the amphiphiles containing an even number of carbons formed stronger H bonding than those containing an odd number of carbons.
新合成了具有 n-C6 至 -C13 烷基链的 N-4-[4-(10-三甲氨基碘癸氧基)苯基偶氮]苯甲酰基}-L-丙氨酸烷基酯溴化物。碳原子数为偶数时,双层聚合体在 355 纳米波长处吸收;碳原子数为奇数时,在 320 纳米波长处吸收。无论碳数是偶数还是奇数,X 射线衍射图样都显示出一种链渗透结构,即一个分子层中的尾链会渗透到另一个分子层中,因此每个其他偶氮苯基团都会分布到相反的分子层中。然而,CH2 剪切带明显分裂为 1473 和 1463 cm-1,这表明含有偶数碳原子的链的反之字形平面垂直排列,而 1465 cm-1 处的单色 CH2 剪切带则表明含有奇数碳原子的链的平面平行排列。根据链的堆积情况,当两亲化合物具有偶数个碳时,每层中相邻的偶氮苯相互垂直排列。相互垂直的位置会导致色团间的相互作用消失,从而使 λmax 波长达到 355 nm。相比之下,含有奇数个碳的两亲化合物双分子层中的偶氮苯则彼此平行。由于分子倾斜度超过约 60°,因此应主要形成 H 聚合物,在 320 纳米波长处吸收。此外,碳数为偶数的两亲化合物形成的 H 键比碳数为奇数的两亲化合物更强。