Dipartimento di Scienze della Vita e dell'Ambiente, Biophysics Research Group, Università Politecnica delle Marche, via Brecce Bianche, I-60131 Ancona, Italy.
J Phys Chem B. 2013 Jan 31;117(4):1095-103. doi: 10.1021/jp3121929. Epub 2013 Jan 22.
Lipophilic guanilic derivatives (lipoGs) dissolved in organic solvents can undergo different self-assembly pathways based on different H-bonded motifs, e.g., the cyclic discrete G-quartet, which forms in the presence of alkali-metal ions, and the "infinite" tape-like G-ribbon observed in the absence of ions. Using in-solution small-angle X-ray scattering, we analyzed a series of lipoGs dissolved in cyclohexane in the presence of different salts. The formation of G-quartet based supramolecular aggregates has been confirmed, evidencing the coexistence equilibrium of octamers and noncovalent molecular nanowires (the so-called G-quadruplexes). By global fitting the scattering data, the concentration of the two kinds of particles as well as the nanowire length have been derived as a function of temperature for the different compounds and salts. The thermodynamic parameters show that the self-assembly aggregation process is enthalpy driven, while the observed enthalpy-entropy compensation suggests that similar stacking interactions control the self-assembly of the different compounds. However, the strength of the stacking interactions, and then the nanowire stability, depends on the nature of templating cations and on their capacity to fill the central cavity of quadruplexes, with the order Sr(+) < Na(+) ≲ K(+).
疏水性胍基衍生物（lipoGs）溶解在有机溶剂中可以根据不同的氢键模式经历不同的自组装途径，例如，在存在碱金属离子的情况下形成的环状离散 G-四聚体，以及在没有离子的情况下观察到的“无限”带状 G-带。使用溶液中的小角度 X 射线散射，我们分析了一系列溶解在环己烷中的 lipoGs 存在不同盐的情况。已经证实了基于 G-四聚体的超分子聚集体的形成，证明了八聚体和非共价分子纳米线（所谓的 G-四链体）共存平衡的存在。通过对散射数据进行全局拟合，我们推导出了不同化合物和盐在不同温度下两种粒子的浓度以及纳米线长度的函数。热力学参数表明，自组装聚集过程是由焓驱动的，而观察到的焓熵补偿表明，相似的堆积相互作用控制着不同化合物的自组装。然而，堆积相互作用的强度，然后是纳米线的稳定性，取决于模板阳离子的性质及其填充四链体中心腔的能力，顺序为 Sr(+) < Na(+) ≲ K(+)。
