Exploiting the Hydrogen Bond Donor/Acceptor Properties of PN‐Heterocycles: Selective Anion Receptors for Hydrogen Sulfate

Abstract

We describe two novel hybrid receptors combining ap hosphorus-/nitrogen-containing (PN) phosphonamidate heterocycle with urea recognition units in an arylethynyl backbone.Structural, spectroscopic and computational studies reveal that the origin of superior binding for hydrogen sulfate (HSO 4 À )a nion is correlated with the formation of strong hetero-complementary hydrogen bonds with the phosphonamidate motif.W ef urther demonstrate that the hybrid host system is capable of capturing/transporting the HSO 4 À anion from an aqueous,b iphasic system. Selective detection and recognition of various anions haveattracted substantial attention. [1] Hydrogen sulfate (bisulfate, HSO 4 À )i so fc onsiderable interest owing to its concern as ac ontaminant in agricultural and industrial fields. [2] This hydroxyanion is am oderate acid (pK a % 2.0) [3] and is abundant in aqueous sulfuric acid and salt solutions.M eanwhile, the important sulfate (SO 4 2À )a nion will equilibrate with bisulfate ions in low pH environment. Hydrogen sulfate is the most prevalent inorganic component in lower and upper atmospheric aerosols and plays ar ole in aerosol homogeneous nucleation. [4] Additionally,t he HSO 4 À anion can also act as an important and effective catalyst for various chemical transformations. [5] As aresult, the design and development of various artificial host molecules for HSO 4 À anion binding has become ahighly desirable target in supramolecular chemistry.Unfortunately,d evelopment of synthetic receptors that are capable of selective recognition and binding toward HSO 4 À has proven challenging because of its H-bonding donor/acceptor nature as well as its unique tetrahedral geometry. [6] Over the past few decades,o nly ah andful of selective receptors for HSO 4 À have been documented. [7,8] These molecular systems are mainly composed of the wellknown acidic (N À H, O À H) and/or neutral (C À H) hydrogen bond (HB) donors and basic nitrogen atoms (such as amine, imine,imidazole,orpyridine motifs) [7] or carbonyl [8] motifs as the perceived HB accepting sites.T he resulting multidentate and/or macrocyclic architectures with convergent and complementary HB contacts typically give rise to strong anion binding affinities in solution phase,a lthough selectivity is often far from optimum. Furthermore,stabilization of HSO 4 À by complexation with receptors bearing basic moieties in the solid state has always been challenging since the protic oxyanion is susceptible to proton transfer to the host molecules. [7b,d] Hydroxyanions including HSO 4 À are wellknown to dimerize by forming anti-electrostatic, self-complementary (O À H) anion ···O anion hydrogen bonds in crystal structures, [9,10] or are prone to undergo proton transfer to generate SO 4 2À ion, [11] both of which would facilitate the electrostatic contacts with the HB donors due to the pronounced and unitary negative charge density.A saconsequence,t hese competitive processes make co-crystallization of host-guest complexes involving HSO 4 À asignificant challenge.Asearc...

Naphtho[2,1-e]-1,2-azaphosphorine 2-Oxide Derivatives: Synthesis, Optoelectronic Properties, and Self-Dimerization Phenomena

“…More recently, we described the preparation of a series of linearly fused naphtho­[2,3- e ]-1,2-azaphosphorine-2-oxides 7 exhibiting considerably large Stokes shifts; however, their low quantum efficiencies could limit optoelectronic applications to some extent. Also, it is of fundamental importance to unravel the factors that influence H-bonding within these systems, not only to predict their self-association behavior but also to provide insights into elaborating these compounds as molecular recognition motifs . Herein, we report the synthesis, electronic characterization, and self-dimerization behavior of a series of angular naphtho-fused PN-heterocyclic systems that exhibit enhanced quantum yields over their linearly fused congeners.…”

“…Also, it is of fundamental importance to unravel the factors which determine the capabilities of the H-bonding within these systems, not only to predict their self-association behaviour but also to provide insights into designing molecular recognition motifs. 12 Following ongoing interests in the development of PN heterocycles, herein we report the synthesis, electronic characterization and selfdimerization behaviour of angular naphtho-fused PN-heterocyclic systems.…”

“…Also, it is of fundamental importance to unravel the factors that influence H-bonding within these systems, not only to predict their selfassociation behavior but also to provide insights into elaborating these compounds as molecular recognition motifs. 13 Herein, we report the synthesis, electronic characterization, and self-dimerization behavior of a series of angular naphtho-fused PN-heterocyclic systems that exhibit enhanced quantum yields over their linearly fused congeners.…”

Urea Derivatives as Functional Molecules: Supramolecular Capsules, Supramolecular Polymers, Supramolecular Gels, Artificial Hosts, and Catalysts

“…Johnson and Haley et al developed variousu rea based anion receptors 26-29 having arylethynyl frameworks (Figure 19). [128][129][130][131][132] 2,6-Bis(2-anilinoethynyl)pyridine-based bisurea 26 recognizes anionss uch as halide ions, and their binding affinitiesa re activated by protonation of the central pyridine ring. [130] From this finding, Johnson and Haley et al developed 2,6-bis(2-anilinoethynyl)benzene-basedb is-urea 27.…”

Tripodal Squaramide Derivative as a Neutral Chloride Ionophore for Whole Blood and Sweat Chloride Measurement

“…These receptors for anionic species are mainly neutral compounds and most of them contain ureas, thioureas, squaramides, pyrroles, amides, and sulfonamides as the binding groups. The receptors mainly interact with anions by polarized NÀ H fragments that form hydrogen bonding [27][28][29]. These compounds have been studied as anion transmembrane transporters [30][31], fluorescent anion sensors [32][33] and ionophores [25][26] in polymeric membranes.…”