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首页> 外文期刊>Chemistry: A European journal >Encapsulation of Small Polar Guests in Molecular Apple Peels
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Encapsulation of Small Polar Guests in Molecular Apple Peels

机译：分子苹果皮中小极性客体的封装

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Three aromatic oligoamides have been prepared that have alternating 1,6-diaminopyridine and 1,6-pyridi-nedicarboxylic acid units at the center of the sequence and two 8-amino-2-quinolinecarboxylic acid units at each extremity. The three oligomers differ in the number-3, 5, or 7-of pyridine units in the sequence. They were designed to adopt helically folded conformations in solution and in the solid state. The sequence of monomers was chosen so that the diameter of the helix is larger in the center than at each extremity, and hence they resemble helically wrapped apple peels. According to modeling studies, the pyridine units were expected to define a polar hollow within the helix that is large enough to accommodate small polar guests, whereas the quinolineunits at each end of the oligomeric sequences were expected to completely cap the hollow and transform the helix cavities into a closed shell that may act as a capsule. Crystallographic studies demonstrate that the oligomers do fold into helices that define a cavity isolated from the surrounding medium in the solid state. Depending on the number of pyridine rings, one or two water molecules are bound within the capsules. The crystal structure of a capsule fragment shows that MeOH can also be hosted by the largest oligomer. Solution NMR studies confirm that binding of water also occurs in solution with the same stoichiometry as observed in the solid state. The capsules have distinct signals depending on whether they are empty, half-full, or full, and these species are in slow exchange on the NMR timescale at low temperature. Indeed, the binding and release of water molecules requires a significant conformational distortion of the helix that slows down these processes. The addition of small polar molecules such as methanol, hydrazine, hydrogen peroxide, or formic acid to the largest capsule leads to the observation of new sets of NMR signals of the capsules that were assigned to complexes with these guests. However, water appears to be the preferred guest.
机译：已经制备了三种芳族低酰胺，其在序列中心具有交替的1，6-二氨基吡啶和1，6-吡啶-二羧酸单元，并且在每个末端具有两个8-氨基-2-喹啉羧酸单元。三种低聚物在序列中的吡啶单元的数目分别为3、5或7。它们被设计为在溶液和固态下采用螺旋折叠的构象。选择单体的顺序，以使螺旋的直径在中心大于每个末端，因此它们类似于螺旋包裹的苹果皮。根据建模研究，预计吡啶单元会在螺旋中定义一个极性大的空心，足以容纳小的极性宾客，而寡聚序列每一端的喹啉单元则有望完全覆盖空心并转变螺旋腔放入可以充当胶囊的封闭外壳中。晶体学研究表明，低聚物确实折叠成螺旋状，从而形成了与周围固态介质隔离的空腔。根据吡啶环的数目，一个或两个水分子结合在胶囊内。胶囊片段的晶体结构表明，最大的低聚物也可以容纳MeOH。溶液NMR研究证实，与固体状态下观察到的化学计量相同，溶液中也会发生水的结合。根据胶囊是空的，半满的还是满的，胶囊具有不同的信号，并且这些物质在低温下在NMR时标上的交换缓慢。实际上，水分子的结合和释放需要螺旋的显着构象变形，从而减慢了这些过程。在最大的胶囊中添加小极性分子（例如甲醇，肼，过氧化氢或甲酸）会导致观察到新的胶囊NMR信号集，这些信号被分配给这些客体的复合物。但是，水似乎是首选的客人。

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