Highly Stable Self-Association of 5-(Guanidiniocarbonyl)-1H-pyrrole-2-carboxylate in DMSO – The Importance of Electrostatic Interactions

Abstract

The zwitterionic compound 5‐(guanidiniocarbonyl)‐1H‐pyrrole‐2‐carboxylate (1) self‐assembles to form dimers, which are completely stable in DMSO even at 170 °C or at concentrations of 0.001 mM. This high stability stems from a combination of multiple weak interactions. NMR titrations of 1H‐pyrrole‐2‐carboxylate (5) with (1H‐pyrrole‐2‐carbonyl)guanidinium (6) and [5‐(methoxycarbonyl)‐1H‐pyrrole‐2‐carbonyl]guanidinium (8) led to binding constants of K ≈ 106 mol–1 in DMSO and K ≈ 103 mol–1 in 40% water/DMSO for carboxylate binding by the 2‐(guanidiniocarbonyl)pyrrole moiety. The stability constant for the dimer 12 in DMSO could therefore be estimated as K ≈ 1012 mol–1. In solution, the self‐association process of 1 can be completely disrupted by protonation of the carboxylate group. In the solid state, however, the hydrochloride salt 1+ also exists as a similar but only very weakly hydrogen‐bonded dimer.

Synthetic receptors for neutral nitro derivatives

“…7,8 Recently, guanidinocarbonyl pyrrole receptors were described as well, which displayed high affinities for carboxylates due to the combination of the electrostatic interaction and the binding via a bidentate hydrogen bonding. 3,9,10 The neutral nitro group is one of the isosters of the mono-anionic carboxylate because of structural similarity. 3,11 Therefore, this group should be able to build up hydrogen donor-acceptor networks based on the nitro-urea and nitro-guanidine interactions.…”

C−H···O Interactions as Isofunctional Replacements for N−H···O Interactions − Dimer Formation of Methyl 5-Amidopyrrole-2-carboxylates in the Solid State

“…Interestingly, the structure of the dimer 2·2 is remarkably similar to the X-ray structure of the chloride salt of guanidiniocarbonyl pyrrole acid (3) described previously (Figure 3). [21] In both dimers each molecule forms hydrogen bonds through the carboxyl CO, the pyrrole NH, the amide CO and an additional hydrogen bond donor site XϪH in the amide moiety: the guanidinium NH in 3 and the pyridinium C3ϪH in 2, respectively. In both dimers the four intermolecular contacts have nearly identical distances within Ϯ0.03 Å (see Figure 3).…”

“…[19,20] Herein, we present the crystal structure and a discussion of the binding interactions of self-assembled dimers of the chloride salt of methyl 5-(amidopyridininium)pyrrole-2-carboxylate 2, in which, compared to the previously reported dimers of the chloride salt of 5-(guanidiniocarbonyl)pyrrole-2-carboxylic acid 3, [21] two CϪH···O bonds are isofunctionally replacing two NϪH···O hydrogen bonds.…”

Syntheses, crystal, and molecular structures of Mn(II), Zn(II), and Ce(III) compounds and solution studies of Mn(II), Ni(II), Cu(II), Zn(II), Cd(II), and Ce(III) compounds obtained from a suitable proton transfer compound containing bda and pydcH2 (bda = butane-1,4-diamine; pydcH2 = pyridine-2,6-dicarboxylic acid)

“…Several examples of proton transfer self-assembled systems prepared by employing this strategy including organic heterocyclic amine carboxylates [3], oxalates [4], and squarates [5]. Unfortunately, due to the competitive solvation of donor and acceptor sites by polar solvents, only few systems displaying this ability are known, so far [6,7]. Multidimensional metal-organic compounds (MOCs) constitute a recent class of compounds with high current interest in various areas, e.g., in supramolecular and host-guest chemistry, material science, crystal engineering, catalysis, molecular magnetism, etc.…”