Köhler Karen, Meister Annette, Förster Günter, Dobner Bodo, Drescher Simon, Ziethe Friederike, Richter Walter, Steiniger Frank, Drechsler Markus, Hause Gerd, Blume Alfred
MLU Halle-Wittenberg, Institut für Physikalische Chemie, Mühlpforte 1, 06108 Halle, Germany.
MLU Halle-Wittenberg, Institut für Pharmazeutische Chemie, Wolfgang-Langenbeck-Str. 4, 06120 Halle, Germany.
Soft Matter. 2006 Dec 12;2(1):77-86. doi: 10.1039/b514163j.
The phase behavior of the symmetric long-chain bolaamphiphile dotriacontan-1,1'-diyl-bis[2-(dimethylammonio)ethyl phosphate] (MePE-C32-MePE) was investigated in aqueous suspensions of different pH by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FT-IR). At pH 5 the compound exhibits excellent properties as a hydrogelator by forming a dense network of helically structured nanofibrils with a diameter of 3-4 nm. The phase behavior of MePE-C32-MePE is compared with the previously examined trimethylammonio analogue PC-C32-PC, whose self-assembly process seems to be exclusively driven by hydrophobic interactions. At pH 5, MePE-C32-MePE can form intermolecular hydrogen bonds between the headgroups, which causes a significantly higher stability of the nanofibrils up to at least 75 °C. In contrast, no pronounced gelling properties are observed at pH 10. Obviously, the negatively charged headgroups seem to prevent the suspension from gelling. Nevertheless, nanofibrils are formed, but at 75 °C a fragmentation into smaller aggregates occurs due to the lack of stabilizing effect of intermolecular hydrogen bonds and the destabilizing effect of the negatively charged headgroups.
通过透射电子显微镜（TEM）、差示扫描量热法（DSC）和傅里叶变换红外光谱（FT-IR），研究了对称长链双性离子型两亲分子三十二烷-1,1'-二基-双[2-(二甲基铵基)乙基磷酸酯]（MePE-C32-MePE）在不同pH值的水悬浮液中的相行为。在pH值为5时，该化合物通过形成直径为3-4nm的螺旋结构纳米纤维致密网络，表现出作为水凝胶剂的优异性能。将MePE-C32-MePE的相行为与之前研究的三甲基铵类似物PC-C32-PC进行了比较，后者的自组装过程似乎完全由疏水相互作用驱动。在pH值为5时，MePE-C32-MePE可以在头基之间形成分子间氢键，这使得纳米纤维在至少75°C时具有显著更高的稳定性。相比之下，在pH值为10时未观察到明显的胶凝性能。显然，带负电荷的头基似乎阻止了悬浮液胶凝。然而，纳米纤维仍会形成，但在75°C时，由于分子间氢键缺乏稳定作用以及带负电荷头基的去稳定作用，会发生碎片化形成较小聚集体。
