https://pubs.rsc.org/en/content/articlepdf/2016/cc/c6cc03888c

The death of the Job plot, transparency, open science and online tools, uncertainty estimation methods and other developments in supramolecular chemistry data analysis

Chalcogen bonding is a type of noncovalent interaction in which a covalently bonded chalcogen atom (O, S, Se or Te) acts as an electrophilic species towards a nucleophilic (negative) region(s) in another or in the same molecule. In general, this interaction is strengthened by the presence of an electron-withdrawing group on the electron-acceptor chalcogen atom and upon moving down in the periodic table of elements, from O to Te. Following a short discussion of the phenomenon of chalcogen bonding, this Perspective presents some demonstrative experimental observations in which this bonding is crucial for synthetic transformations, crystal engineering, catalysis and design of materials as synthons/tectons.

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Chalcogen bonding in synthesis, catalysis and design of materials

Continuous variation method, known as Job plot, is the most commonly applied method for the determination of stoichiometry of complex chemical entities for over 100 years. Although, the method was proven successful in the analysis of very stable metal–ligand complexes, we demonstrate that its use in supramolecular chemistry often provides false results. We support this statement with multiple simulations as well as cases studies of several real host–guest systems. We propose an alternative, general method relying on the analysis of residual distribution in titration data fitting. The latter method is more convenient compared to the Job plot and unlike it gives correct results in all real cases studied.

Recognizing the Limited Applicability of Job Plots in Studying Host–Guest Interactions in Supramolecular Chemistry

Cation and anion recognition have both played central roles in the development of supramolecular chemistry. Much of the associated research has focused on the development of receptors for individual cations or anions, as well as their applications in different areas. Rarely is complexation of the counterions considered. In contrast, ion pair recognition chemistry, emerging from cation and anion coordination chemistry, is a specific research field where co-complexation of both anions and cations, so-called ion pairs, is the center of focus. Systems used for the purpose, known as ion pair receptors, are typically di- or polytopic hosts that contain recognition sites for both cations and anions and which permit the concurrent binding of multiple ions. The field of ion pair recognition has blossomed during the past decades. Several smaller reviews on the topic were published roughly 5 years ago. They provided a summary of synthetic progress and detailed the various limiting ion recognition modes displayed by both acyclic and macrocyclic ion pair receptors known at the time. The present review is designed to provide a comprehensive and up-to-date overview of the chemistry of macrocycle-based ion pair receptors. We specifically focus on the relationship between structure and ion pair recognition, as well as applications of ion pair receptors in sensor development, cation and anion extraction, ion transport, and logic gate construction.

Macrocycles as Ion Pair Receptors

Advances in Anion Receptor Chemistry

Anion-tunable control of thermal Z→E isomerisation in basic azobenzene receptors.

The symmetrical molecular receptors 1a and 1b consisting of a photochemically addressable azobenzene tether functionalized with urea hydrogen-bonding groups and d-carbohydrates as chiral selectors were developed to achieve control over the chiral recognition of α-amino acid-derived carboxylates. The photo- and thermally interconvertible planar E-1 and concaved Z-1 were found to exhibit different affinities, selectivities, and binding modes toward these biologically important anions in a highly polar medium (DMSO + 0.5% H2O). Binding affinity for the same enantiomerically pure guest was up to 3 times higher for E-1 than for Z-1 (cf. parameter β). In addition, the rate of thermal Z → E isomerization was found to depend on the chiral binding ability of Z-1, i.e., more strongly bound carboxylate enantiomer as well as higher enantiomer concentration caused faster relaxation to E-1.

Kajetan Dąbrowa

Papers

Recognizing the Limited Applicability of Job Plots in Studying Host–Guest Interactions in Supramolecular Chemistry

Anion-tunable control of thermal Z→E isomerisation in basic azobenzene receptors.

Engineering Light-Mediated Bistable Azobenzene Switches Bearing Urea d-Aminoglucose Units for Chiral Discrimination of Carboxylates

"Unclosed cryptands": a point of departure for developing potent neutral anion receptors.

Chloride-Templated Macrocyclization and Anion-Binding Properties of C2-Symmetric Macrocyclic Ureas from Sucrose