Molecular Recognition of Trigonal Oxyanions Using a Ditopic Salt Receptor:  Evidence for Anisotropic Shielding Surface around Nitrate Anion

Abstract

A ditopic, macrobicyclic receptor with adjacent anion and cation binding sites is able to extract a range of monovalent salts into chloroform solution. The structures of the receptor complexed with KAcO, LiNO(3), NaNO(3), KNO(3), and NaNO(2) are characterized in solution by NMR spectroscopy and in the solid state by X-ray crystallography. The sodium and potassium salts are bound to the receptor as contact ion-pairs, with the metal cation located in the receptor's crown ether ring and the trigonal oxyanion hydrogen bonded to the receptor NH residues. The solid-state structure of the LiNO(3) complex has a bridging water molecule between the cation and anion. In all solid-state structures, the trigonal oxyanion is not located symmetrically inside the receptor cavity. It appears that anion orientation is controlled by a complex interplay of steric factors, coordination bonding to the metal cation, and hydrogen bonding with the receptor NH residues. An important feature with this latter effect is the fact that hydrogen bonds directed toward the oxygen lone pairs on a trigonal oxyanion are stronger than hydrogen bonds to the pi-electrons. In solution, the (1)H NMR spectra of the nitrate and nitrite salt complexes are noteworthy because several receptor signals, including the NH protons, undergo unusual upfield movements in chemical shift upon complexation. This is a reflection of the diamagnetic anisotropy of these trigonal oxyanions. The magnetic shielding surface for the NO(3)(-) anion is calculated using density functional theory and shown to have a shielding region directly above the central nitrogen.

Study of quantitative interactions of potato and corn starch granules with ions in diluted solutions of heavy metal salts

“…Furthermore, the phosphate groups of potato starch effectively hindered penetration of the granules by nitrate anions so they should be situated on the granule surface. This process might be facilitated by formation of hydrogen bonds between nitrate lone pair electrons and hydrogen atoms of -OH groups at the granule surface like those described for nitrate ions and -NH groups (Mahoney et al, 2005). The granule zeta potentials did not change after treatment the starch with CuCl 2 .…”

Calix[4]pyrrole-Based Ion Pair Receptors

“…43 forms strong complexes with trigonal oxyanions, such as NO 3 -and OAc -, as well as with the halide anions. 59 Proton NMR spectral studies provided confirmation that compound which has an additional pyrrole-derived hydrogen bond donor site. Proton NMR spectroscopic titrations revealed that the affinity of ditopic receptor 1.46 for Cl -is three times higher than 1.43.…”

Solubilizing Sodium Fluoride in Acetonitrile: Synthesis, Molecular Structure, and Complexation Behavior of Bis(organostannyl)methyl‐Substituted Crown Ethers

“…[1][2][3][4][5][6][7][8][9] Recent developments have focused on the recognition of heavy-metal salts such as nickel or copper sulfate for hydrometallurgical applications. [10][11][12] Welldesigned binding sites that combine electrostatic or hydrogen-bonding interactions enable ditopic host molecules to do this.…”