Smart Polymorphism of Thiacalix[4]arene with Long-Chain Amide Containing Substituents

Abstract

A problem of controlled (smart) formation of polymorphs was solved for a set of tert-butylthiacalix­[4]­arene derivatives with four N-(2-acetoxyethyl)­carbamoylmethoxy substituents at the lower rim with 1,3-alternate, cone, and partial cone conformations. For this, an effective polymorph screening with a reproducible influence of preparation history was achieved using guest vapor inclusion and a standard state of host glass powder. By this procedure with consequent guest release and heating, the ability of the studied calixarenes for polymorphism was investigated and compared as a function of their macrocycle conformation. The data of simultaneous thermogravimetry and differential scanning calorimetry with mass spectrometry of evolved vapors were determined together with the data of powder X-ray diffraction for the initial host samples, intermediate clathrates, and final polymorphs. In addition, single crystal X-ray diffraction data were obtained for four crystalline forms of the studied calixarenes. The results yielded a structure–property relationship, where 1,3-alternate calixarene without an extended H-bonded supramolecular network at least in one crystalline form has a much higher ability for polymorphism than the other two conformations. Thus, 10 polymorphs with essentially different crystal packing were found for this calixarene including a unique tetramorphism with four consecutive melting points of guest-free polymorph and corresponding three crystallization ranges. This ability of 1,3-alternate calixarene is linked with its other smart property: selective crystallization of its compact glass in vapors of binary liquid mixtures, which can be used for visual detection of very small benzene impurities (0.5% (v/v)) in cyclohexane.

Smart Molecular Recognition: From Key-to-Lock Principle to Memory-Based Selectivity

“…The glass of the same calixarene in another conformation allows detecting 1% vol. of benzene in hexane (Gataullina et al, 2017). A similar crystallization behavior was observed for glassy polymers (Gao et al, 2012), which have a less pronounced concentration threshold for the good component in binary solvent due to the incomplete crystallization.…”

“…The activation of this process with guest vapors may be selective. Such selectivity was observed visually for a compact glass of calixarene (Gataullina et al, 2015(Gataullina et al, , 2017 and using an atomic force microscopy for thin amorphous films of dipeptides (Ziganshin et al, 2015). Amorphous dipeptides may have three options in contact with guest vapors depending on the guest molecular structure: (1) crystallization, (2) gel formation, (3) intact host morphology (Ziganshin et al, 2017).…”

“…This is selectivity of guest-induced polymorphism, which is a well-studied phenomenon used for screening of polymorphs (Braga et al, 2010;Petkune et al, 2012;Newman, 2013;Lee, 2014). A corresponding screening technique involves preparing the inclusion compound and removing the included guest (Lee et al, 2013;Gataullina et al, 2017). This is a smart process, where the host may remember molecular structure of a released guest by formation of a specific metastable polymorph (Gataullina et al, 2015).…”

“…In many cases, metastability of a polymorph is in its lower melting point than that of the stable form. Such polymorphs may have more than one melting point with an intermediate exothermic cold crystallization to the more stable forms (Gataullina et al, 2017(Gataullina et al, , 2019. The formation of such polymorphs by guest inclusion and release may be also a kind of molecular recognition when it is selective enough, but in this case the problem is to find sufficient experimental proofs that the host treatment with different guests gives different polymorphs.…”

2D Monomolecular Nanosheets Based on Thiacalixarene Derivatives: Synthesis, Solid State Self-Assembly and Crystal Polymorphism

“…Mention should also be made about polyplexes based on thiacalixarene derivatives, which are used for DNA packaging and have promising applications in biomolecular delivery systems and long-term storage of human genetic material [ 25 ]. Among other things, the controlled (smart) formation of polymorphs based on thiacalixarene derivative are also known [ 30 ]. Thus, according to previous contributions and applications of thiacalix[n]arenes it may be concluded that these macrocycles are promising candidates for constructing 2D nanostructures, especially different polymorphs that can be used in medicine for the development of modern pharmaceuticals, diagnostic agents and new generation materials.…”