An ion-selective electrode for acetate based on (α,α,α,α)-5,10,15,20-tetrakis[2-(4-fluorophenylureylene)phenyl]porphyrin as an ionophore that has no metal center and forms hydrogen bonds to the analyte is described. At pH 7.0 (0.1 M HEPES-NaOH buffer), the electrode based on this ionophore and cationic sites (50 mol % relative to the ionophore) responds to acetate in a linear range from 1.58 × 10(-)(4) to 1.58 × 10(-)(2) M with a slope of -54.8 ± 0.8 mV/decade and a detection limit of (3.06 ± 1.15) × 10(-)(5) M. Selectivity coefficients determined with the separate solution method (SSM) indicate that interferences of hydrophobic inorganic anions are relatively small (log[Formula: see text] (SSM):  NO(3)(-), +0.68; SCN(-), +0.60; NO(2)(-), +0.22; I(-), +0.20; ClO(4)(-), +0.12; Br(-), -0.13). Responses to anions that are good hydrogen bond acceptors, i.e., Cl(-), HSO(3)(-), and HCO(3)(-), were Nernstian and were weaker than the response to acetate (log[Formula: see text] (SSM): -0.54, -0.56, and -1.34, respectively). Negligibly small responses were observed for very hydrophilic anions, i.e., F(-), SO(4)(2)(-), and H(2)PO(4)(-)/HPO(4)(2)(-). While aliphatic carboxylates such as formate, propanoate, pyruvate, and lactate gave Nernstian responses similar to acetate, interferences of salicylate and benzoate were considerably decreased in comparison with electrodes based on cationic sites only. Concentrations of acetic acid in vinegar samples were determined by direct potentiometry and agreed with values determined by a standard enzymatic method.

A series of neutral, urea-appended, free-base porphyrins and their Zn(II) complexes have been synthesized and characterized. The (α,α,α,α)-5,10,15,20-tetrakis(2-(arylurea)phenyl)porphyrins bind strongly (K (M-1) > 103−105) to chloride anion in DMSO-d 6 and also in the more competitive solvent system DMSO-d 6/D2O (88:12, v/v) and bromide anion in DMSO-d 6, as revealed by 1H NMR titration studies. The porphyrin derivatives exhibited significant binding selectivity since they complexed with the spherical Cl- and Br- to a much greater extent than with the tetrahedral H2PO4 - and HSO4 - and the trigonal NO3 - anions in DMSO-d 6. Indeed, the selectivity trend Cl- > Br- ≫ H2PO4 - > HSO4 - > NO3 - is novel for any neutral urea-anion binding system. On the other hand, the corresponding metalloporphyrins exhibited a decrease in binding strength and selectivity in DMSO-d 6. The stoichiometry of binding for the anions and porphyrins was determined to be 1:1. The enthalpy of complexation was determined to be highly favorable and the entropy of complexation determined to be unfavorable from a variable-temperature 1H NMR experiment with a 1:1 tetrabutylammonium bromide/porphyrin complex. X-ray crystallography revealed (α,α,α,α)-5,10,15,20-tetrakis(2-(4-chlorophenylurea)phenyl)porphyrin to be the first coordination complex of an anion (chloride and bromide) bound by a neutral free-base porphyrin. The binding motif consisted of the halide, buried deep within the porphyrin pocket, bound by two adjacent urea functional groups via four hydrogen bonds, with the two remaining urea functional groups involved in hydrogen bonding to solvent molecules. The crystal structure of the tetrabutylammonium halide−porphyrin complex showed additional Coulombic interaction between the electron-poor sulfur of a pocket-bound, hydrogen-bonded DMSO and halide anion.

A mixture of equal amounts of CuBr−SMe2, LiBr, and LiSPh in THF at 0 °C furnished a new soluble copper catalyst that was highly efficient at coupling primary, secondary, tertiary, aryl, vinyl, and allylic Grignard reagents to primary tosylates and primary Grignard reagents to secondary tosylates and mesylates, all with the use of only 1 equiv of Grignard reagent. The new catalyst was shown to be much more reactive than copper catalysts CuBr and Li2CuCl4 and more efficient in the transference of secondary and tertiary alkyl groups than lower order cuprates (Gilman reagents) and demonstrated more reactivity than the lower order cuprates with its ability to couple primary Grignard reagents to secondary sulfonates. The Grignard reagent/catalyst system was compatible with an ester functionalized tosylate, thus proving to be more chemoselective than a Grignard reagent without the catalyst. The catalyst exhibited good reactivity below room temperature, and with the addition of 6% v/v of HMPA to the catalyst solution, excellent yields of coupled product were obtained within a 25−67 °C temperature range. 1H NMR demonstrated that the catalyst solution consisted of several species that most likely were composed of copper ligated with thiophenol, THF, and LiBr in aggregated forms.

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The synthesis of alpha,alpha-5,10-diurea and alpha,alpha,alpha-5,10,15-triurea picket porphyrins are detailed in this report. In previous reports, these porphyrins, along with alpha,alpha,alpha,alpha-5,10,15,20-tetraurea picket porphyrin, were used to demonstrate the important role one buried solvent molecule plays in the selectivity and stoichiometry of binding inorganic anions. Building on prior work, this report discusses the results of acetate anion binding studies between tetra- and diurea picket porphyrins (the latter does not contain a buried solvent molecule in the anion-receptor complex), compares differences in thermodynamic data obtained from van't Hoff plots of a porphyrin anion receptor able to utilize buried solvent in its binding motif with one that does not, and compares the crystal structure of a tetraurea porphyrin 1-chloride anion complex that contains buried solvent with new X-ray crystal structures of tetraurea porphyrin 1-dichloride or bisdihydrogenphosphate anion complexes that contain no buried solvent. Data from our previous work, and the work described herein, demonstrates that one buried solvent molecule provides stability to the receptor-anion complex that is similar in energy to a moderately strong hydrogen bond.

[reaction: see text] The crystal structure of a tetraurea picket porphyrin-chloride anion complex has previously shown the anion to be situated between two adjacent ureas and hydrogen bonded via four NH protons (J. Am. Chem. Soc. 1998, 120, 11684-11692). The porphyrin receptor also binds a DMSO molecule and utilizes it as a participant in its anion recognition unit, in a manner similar to enzymes that bind water for use as part of their substrate recognition unit. The bound solvent molecule determines the anion-binding affinity, selectivity, and stoichiometry of binding. With a bound DMSO molecule, the tetraurea picket porphyrin is a highly selective receptor for chloride anion and binds all anions with a 1:1 binding stoichiometry. Absent the buried DMSO molecule, the receptor is selective for phosphate anion and binds chloride and phosphate anions with both 1:1 and 1:2 receptor-anion stoichiometries. Additionally, a remarkable reversal in the selectivity of anion complexation between various picket porphyrin receptors is observed, wherein the binding constant ratios change over 3 orders of magnitude as the receptor's number of urea pickets change from four to two. The latter receptor has no urea pickets available to bind to solvent after complexation with an anion. The results demonstrate that anion complexation with hydrogen-bonding receptors in a competitive solvent is enhanced when a ubiquitous solvent molecule is incorporated into the binding motif. In this way, competitive solvent adds to the overall complexation energy and thereby strengthens binding rather than weakens it, as commonly believed. The results are pertinent to drug design, for they suggest that pharmaceuticals need not be completely desolvated to selectively bind to their biological target when water can be included in the binding motif.

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