Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid, Spain.
J Am Chem Soc. 2010 Apr 7;132(13):4710-9. doi: 10.1021/ja908537k.
Several oligo(p-phenylene-vinylene) oligomers capped with a guanosine or a guanine moiety have been prepared via a palladium-catalyzed cross-coupling reaction. Their self-assembly, in both the absence and presence of alkaline salts, has been studied by means of different techniques in solution (NMR, MS, UV-vis, CD, fluorescence), solid state (X-ray diffraction), and on surfaces (STM, AFM). When no salt is added, these pi-conjugated molecules self-associate in a mixture of hydrogen-bonded oligomers, among which the G-quartet structure may be predominant if the steric hindrance around the guanine base becomes important. In contrast, in the presence of sodium or potassium salts, well-defined assemblies of eight functional molecules (8mers) can be formed selectively and quantitatively. In these assemblies, the pi-conjugated oligomers are maintained in a chirally tilted (J-type) stacking arrangement, which is manifested by negative Cotton effects, small bathochromic absorption and emission shifts, and fluorescence enhancements. Furthermore, these self-assembled organic nanostructures, approximately 1.5-2.0 nm high and 8.5 nm wide, exhibit an extraordinary stability to temperature or concentration changes in apolar media, and they can be transferred and imaged over solid substrates as individual nanoparticles, showing no significant dissociation or further aggregation.
几种寡聚（对苯撑乙烯基）寡聚物被带有鸟嘌呤或鸟苷部分的帽封，通过钯催化的交叉偶联反应制备。通过在溶液中使用不同的技术（NMR、MS、UV-vis、CD、荧光）、固态（X 射线衍射）和表面（STM、AFM）研究了它们在没有和存在碱性盐的情况下的自组装。当没有盐添加时，这些π共轭分子在氢键寡聚物的混合物中自组装，其中如果鸟嘌呤碱基周围的空间位阻变得重要，则 G-四聚体结构可能占主导地位。相比之下，在存在钠离子或钾离子盐的情况下，可以选择性地和定量地形成八个功能分子（8mers）的定义良好的组装体。在这些组装体中，π共轭寡聚物保持手性倾斜（J 型）堆叠排列，这表现为负的科顿效应、较小的红移吸收和发射以及荧光增强。此外，这些自组装的有机纳米结构，高度约为 1.5-2.0nm，宽度为 8.5nm，在非极性介质中对温度或浓度变化表现出非凡的稳定性，它们可以作为单个纳米颗粒转移和成像于固体基底上，没有明显的解离或进一步聚集。
