Institute for Complex Molecular Systems, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
Chemistry. 2013 Jun 24;19(26):8642-9. doi: 10.1002/chem.201204273. Epub 2013 May 6.
The amide bond is a versatile functional group and its directional hydrogen-bonding capabilities are widely applied in, for example, supramolecular chemistry. The potential of the thioamide bond, in contrast, is virtually unexplored as a structuring moiety in hydrogen-bonding-based self-assembling systems. We report herein the synthesis and characterisation of a new self-assembling motif comprising thioamides to induce directional hydrogen bonding. N,N',N''-Trialkylbenzene-1,3,5-tris(carbothioamide)s (thioBTAs) with either achiral or chiral side-chains have been readily obtained by treating their amide-based precursors with P2S5. The thioBTAs showed thermotropic liquid crystalline behaviour and a columnar mesophase was assigned. IR spectroscopy revealed that strong, three-fold, intermolecular hydrogen-bonding interactions stabilise the columnar structures. In apolar alkane solutions, thioBTAs self-assemble into one-dimensional, helical supramolecular polymers stabilised by three-fold hydrogen bonding. Concentration- and temperature-dependent self-assembly studies performed by using a combination of UV and CD spectroscopy demonstrated a cooperative supramolecular polymerisation mechanism and a strong amplification of supramolecular chirality. The high dipole moment of the thioamide bond in combination with the anisotropic shape of the resulting cylindrical aggregate gives rise to sufficiently strong depolarised light scattering to enable depolarised dynamic light scattering (DDLS) experiments in dilute alkane solution. The rotational and translational diffusion coefficients, D(trans) and D(rot), were obtained from the DDLS measurements, and the average length, L, and diameter, d, of the thioBTA aggregates were derived (L = 490 nm and d = 3.6 nm). These measured values are in good agreement with the value L(w) = 755 nm obtained from fitting the temperature-dependent CD data by using a recently developed equilibrium model. This experimental verification validates our common practice for determining the length of BTA-based supramolecular polymers from model fits to experimental CD data. The ability of thioamides to induce cooperative supramolecular polymerisation makes them effective and broadly applicable in supramolecular chemistry.
酰胺键是一种多功能基团，其定向氢键能力广泛应用于超分子化学等领域。相比之下，硫代酰胺键作为氢键自组装系统中的结构部分的潜力几乎没有得到探索。本文报道了一种新的自组装基序的合成与表征，该基序包含硫代酰胺以诱导定向氢键。通过用 P2S5 处理其酰胺前体，很容易得到具有非手性或手性侧链的 N,N',N''-三烷基苯-1,3,5-三（碳硫酰胺）（硫代 BTAs）。硫代 BTAs 表现出热致液晶行为，并被指定为柱状中间相。IR 光谱表明，强的三倍体分子间氢键相互作用稳定了柱状结构。在非极性烷烃溶液中，硫代 BTAs 自组装成一维螺旋超分子聚合物，由三倍体氢键稳定。通过使用紫外和 CD 光谱的组合进行的浓度和温度依赖性自组装研究表明，存在协同超分子聚合机制和超分子手性的强烈放大。硫代酰胺键的高偶极矩与所得圆柱形聚集体的各向异性形状相结合，导致足够强的去偏振光散射，从而能够在稀烷烃溶液中进行去偏振动态光散射（DDLS）实验。从 DDLS 测量中获得了旋转和平移扩散系数 D(trans)和 D(rot)，并推导出硫代 BTA 聚集体的平均长度 L 和直径 d（L = 490nm 和 d = 3.6nm）。这些测量值与从使用最近开发的平衡模型拟合温度依赖的 CD 数据得到的 L(w) = 755nm 值吻合较好。这种实验验证验证了我们从模型拟合实验 CD 数据确定基于 BTA 的超分子聚合物长度的常用做法。硫代酰胺诱导协同超分子聚合的能力使它们在超分子化学中具有有效性和广泛适用性。
