A Ternary Supramolecular Self-Assembly Model Based on Cyclopentano Cucurbit[5]uril
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TRUCTURE OF ORGANIC COMPOUNDS
A Ternary Supramolecular Self-Assembly Model Based on Cyclopentano Cucurbit[5]uril C. Wanga, S. Y. Chenga, W. W. Zhaoa, X. N. Yanga, K. Z. Zhoua, J. J. Tiana, D. F. Jianga, and P. H. Maa,* a
Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang, 550025 China *e-mail: [email protected] Received January 15, 2020; revised April 12, 2020; accepted April 14, 2020
Abstract—This paper reports on the supramolecular self-assembly of cyclopentano cucurbit[5]uril (CyP5Q[5]), L-phenylalanine (L-Phe), and cadmium ions. The crystal structure is characterized using X-ray diffraction. The results show that the complex belongs to a monoclinic system with P21 space group. Cd2+ and L-Phe are coordinated in two CyP5Q[5] portals via hydrogen bonds and ion-dipole interactions, respectively, so that the outer wall of the cucurbit[n]uril forms a porous channel. Each channel consists of six supramolecular chains, which may accommodate inorganic anions, such as CdCl24 − . DOI: 10.1134/S1063774520070275
INTRODUCTION Cucurbit[n]urils (Q[n]s) belong to the class of macrocyclic compounds following cyclodextrin, calixarene and crown ether, and are new members of the supramolecular family. Research in this area has made significant progress in recent years. Q[n]s were first discovered in 1905 by Behrend in Germany [1]. In 1981, Mock et al. [2], using X-ray diffraction, confirmed that these compounds formed a stereoscopic ring containing a hydrophobic cavity in the middle and a polar carbonyl oxygen atom on both portals. Due to poor solubility, their development was largely restricted; however, several modified Q[n]s were reported [3, 4]. Cyclopentano cucurbit[n]uril was first discovered and reported by Wu in 2008 [5, 6]. Compared to other Q[n]s, it had enhanced solubility, and the introduced cyclopentano group produced superconjugation effects; an increase in the electron cloud density of the portal made Q[n] a good electron donor, which increased its ability to complex metal ions. Recent reports on cyclopentano cucurbit[n]uril mainly included its ability to self-assembly with alkali metals and alkaline earth metals and the separation of rare earth metals [7– 10]. Amino acids are the basic components of proteins. Their special structure is the basis of various biological functions of proteins. Experiments have shown that ion-dipole interactions, hydrogen bonding and hydrophobic interactions are formed between amino acids
and Q[n]s, thereby allowing the two molecules to bind to each other [11]. Since 2000, researchers have reported combinations of Q[n]s with amino acids, peptides, and proteins. For example, Urbach et al. [12–15] explored the interactions between Q[7] and several amino acids, peptides and proteins, and found that Q[n] was more likely to undergo host–guest inclusion with side-group aromatic ring moieties. Scherman used Q[8] to selectively recognize certain amino acids [16]. However, due to the small cavity structure of Q[5], it is difficult to combi
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