Institut des Sciences Moléculaires, UMR CNRS no. 5255, Université Bordeaux 1, 351 Cours de la Libération, 33405 Talence Cedex, France.
Chemistry. 2010 May 25;16(20):6056-68. doi: 10.1002/chem.200902995.
Titrations of commercial diaminobutane (DAB) and polyamidoamine (PAMAM) dendrimers by vitamins C (ascorbic acid, AA), B(3) (nicotinic acid), and B(6) (pyridoxine) were monitored by (1)H NMR spectroscopy using the chemical shifts of both dendrimer and vitamin protons and analyzed by comparison with the titration of propylamine. Quaternarizations of the terminal primary amino groups and intradendritic tertiary amino groups, which are nearly quantitative with vitamin C, were characterized by more or less sharp variations (Deltadelta) of the (1)H chemical shift (delta) at the equivalence points. The peripheral primary amino groups of the DAB dendrimers were quaternarized first, but not selectively, whereas a sharp chemical-shift variation was recorded for the inner methylene protons near the tertiary amines, thereby indicating encapsulation, when all the dendritic amines were quaternarized. With DAB-G5-64-NH(2), some excess acid is required to protonate the inner amino groups, presumably because of basicity decrease due to excess charge repulsion. On the other hand, this selectivity was not observed with PAMAM dendrimers. The special case of the titration of the dendrimers by vitamin B(6) indicates only dominant supramolecular hydrogen-bonding interactions and no quaternarization, with core amino groups being privileged, which indicates the strong tendency to encapsulate vitamins. With vitamin B(3), a carboxylic acid, titration of DAB-G3-16-NH(2) shows that only six peripheral amino groups are protonated on average, even with excess vitamin B(3), because protonation is all the more difficult due to increased charge repulsion, as positive charges accumulate around the dendrimer. Inner amino groups interact with this vitamin, however, thus indicating encapsulation presumably with supramolecular hydrogen bonding without much charge transfer.
采用化学位移法，利用核磁氢谱对商品二亚丙基三胺（DAB）和聚酰胺胺（PAMAM）树状大分子与维生素 C（抗坏血酸，AA）、B（3）（烟酸）和 B（6）（吡哆醇）的滴定进行了监测。用丙胺滴定进行了对比分析。与维生素 C 几乎定量发生的末端伯氨基和树枝内叔氨基的季铵化作用，其特征是在等当点处氢化学位移（δ）出现或多或少的急剧变化（Δδ）。DAB 树状大分子的外围伯氨基首先被季铵化，但不是选择性的，而靠近叔胺的内次甲基质子的化学位移变化很尖锐，这表明当所有的树枝状胺都被季铵化时，发生了包合作用。对于 DAB-G5-64-NH2，需要过量的酸来质子化内氨基，这可能是由于由于过多的电荷排斥导致碱性降低。另一方面，这种选择性在 PAMAM 树状大分子中没有观察到。用维生素 B（6）滴定树状大分子的特殊情况表明，只有主要的超分子氢键相互作用，没有季铵化，核心氨基被赋予特权，这表明了强烈的包合维生素的倾向。对于维生素 B（3）（羧酸），DAB-G3-16-NH2 的滴定表明，即使有过量的维生素 B（3），平均也只有六个外围氨基被质子化，这是因为由于正电荷在树状大分子周围积累，增加了电荷排斥，质子化变得更加困难。然而，内氨基与这种维生素相互作用，因此表明包合作用可能是通过超分子氢键进行的，而没有太多的电荷转移。
