Seventeen-Membered Water Cluster Resulting from Recognition of Solvated Anions on Brucinium Corrugated Layers

2019

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Studying the mechanisms of racemic resolution of the model compound N-(3-nitrobenzoyl)aspartic acid by formation and fractional crystallization of brucinium diastereomeric salts, we found that depending on the environment (solvents) the recognition leads to effective or ineffective racemic resolution. During successful racemic resolution, bis(brucinium)-N-(3-nitrobenzoyl)-L-aspartate hydrate methanol solvate precipitates as the first fraction. In turn, double salts and solid solution are formed in the fruitless racemic resolution. Formation of the double salt results from recognition of centrosymmetric anionic dimers on the common brucinium corrugated layer. The common brucinium corrugated layer together with its solvation sphere participates in recognition of the anions, leading to formation of the solid solution. Changing the solvent system according to its dielectric constant, more dispersive or more directional interactions gain importance. The racemic resolution and formation of bis(brucinium)-N-(3-nitrobenzoyl)-L-aspartate hydrate methanol solvate are related to three-point recognition of the anions by brucinium self-assembly.

Section: ■ Discussionmentioning

confidence: 99%

How To Control Recognition: From Brucinium Double Salts to Racemic Resolution

Ganczar

2019

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“…By studying mechanisms of molecular recognition during fractional crystallization of diastereomeric salts, the useful method for racemic resolution of organic acids or bases, 5 we noticed that the nature of recognition depends upon the resolving agent. 6,7 In most crystals of diastereomeric salts of commonly used resolving agent for separation of racemic carboxylic acids, characteristic N−H + ···O − hydrogen bonds systems between ions of resolving agent and resolved compound, defined by a single graph set, are present. 8−14 In this respect, brucine and strychnine are unique because common self-assemblies of ions of the alkaloids, governed by weak-like C−H···O/π and vdW interactions only, usually are not significantly affected by incorporation of ions of a resolved compound.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Anions of resolved acid or anions together with their solvation sphere have been recognized on the surface of the brucinium or strychninium self-assembly. 7 However, anions of an acid can also undergo self-recognition and resulting homo-or heterochiral anionic self-assembly can conduce or preclude racemic resolution. 15−17 Formation of homo-or heterochiral hydrogen-bonded dimeric units by anions of N-(3,5-dinitrobenzoyl)amino acid (alaninate or serinate) precluded their racemic resolution by fractional crystallization of brucinium diastereomeric salts.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Intermolecular cohesions can be determined by the quantitative evaluation of crystal potentials and forces. , Presence of characteristic structural motifs in a given group of compounds may indicate a priority of their formation during molecular recognition. By studying mechanisms of molecular recognition during fractional crystallization of diastereomeric salts, the useful method for racemic resolution of organic acids or bases, we noticed that the nature of recognition depends upon the resolving agent. , In most crystals of diastereomeric salts of commonly used resolving agent for separation of racemic carboxylic acids, characteristic N–H + ···O – hydrogen bonds systems between ions of resolving agent and resolved compound, defined by a single graph set, are present. − In this respect, brucine and strychnine are unique because common self-assemblies of ions of the alkaloids, governed by weak-like C–H···O/π and vdW interactions only, usually are not significantly affected by incorporation of ions of a resolved compound. Therefore, contrary to many diastereomeric salts of the other resolving agents, weak interactions play a crucial role in molecular recognition in brucinium or strychninium diastereomeric salts.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, contrary to many diastereomeric salts of the other resolving agents, weak interactions play a crucial role in molecular recognition in brucinium or strychninium diastereomeric salts. Anions of resolved acid or anions together with their solvation sphere have been recognized on the surface of the brucinium or strychninium self-assembly . However, anions of an acid can also undergo self-recognition and resulting homo- or heterochiral anionic self-assembly can conduce or preclude racemic resolution. − …”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dielectrically Controlled Priority of Interactions in Molecular Recognition

2014

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It was shown previously that formation of brucinium double salts during attempts of racemic resolution of N-(3,5-dinitrobenzoyl)amino acid (alanine or serine) by fractional crystallization of brucinium diastereomeric salts is related to the self-recognition of anions of the amino acid derivatives into dimeric units stabilized by a set of hydrogen bonds (Białonśka, A. and Ciunik, A. Why Is the Resolution of Certain Racemic Modifications Inefficient? Formation of Diastereomeric Double Salts of Brucinium. Cryst. Growth Des. 2013, 13, 111−120). Similar dimeric units were observed in brucinium diastereomeric salts precipitated from methanol solutions containing brucine and one enantiomer of the amino acid derivative. To test if the ability of the anions to form dimeric units can be weakened, an increase of dielectric constant of solutions from which the brucinium salts precipitated was applied. In this approach, three new crystalline forms of brucinium salts with enantiomeric N-(3,5-dinitrobenzoyl)serine were obtained. Two of them belong to Z' > 1 structure, and occurrence of the Z' > 1 structures is discussed. In the new crystalline forms, a set of hydrogen bonds that stabilizes the dimeric units is replaced by interactions of the anions with solvent molecules, and the anions are linked to each other at most by lone hydrogen bonds. Recognition between cationic and anionic species by ionic N−H + ···O − hydrogen bonds, observed in the previously reported crystal structures of brucinium N-(3,5-dinitrobenzoyl)-L-serinate 3.88-hydrate and in the new form, brucinium N-(3,5-dinitrobenzoyl)-L-serinate brucine 11.5-hydrate, is precluded by formation of π···π stacking interactions between the anions and brucine molecules as well as by separation of the anions and cations by the extended net of hydrogen-bonded water molecules.

Discrete Cuboidal 15- and 16-Membered Water Clusters in Brucine 3.86-Hydrate, Water Release and Its Consequences

Ilczyszyn

et al. 2014

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Up to now, three brucine hydrates are known, brucine di-, tetra-, and 5.25-hydrate. All of them were obtained from solutions containing the additive diethanolamine, adenosine, and urea, respectively. Studying the role of the additives on crystallization of the brucine hydrates, we obtained a new, kinetically favored brucine 3.86-hydrate. In crystals of brucine 3.86-hydrate, large 15- and 16-membered water clusters of cuboidal topology are encapsulated in cages formed between honeycomb-like brucine layers. Dehydration of the brucine hydrate leads to formation of the known anhydrous brucine, giving insight into a mechanism of the dehydration process, in which a shift of brucine ribbons in the honeycomb-like layers leads to an openining of channels and water release. A collapse of brucine layers after the water release results in formation of the common anhydrous brucine. The anhydrous brucine undergoes a phase transition at 249 K in the cooling mode and at 277 K in the heating mode. The phase transition is attributable to a huge shift of brucine corrugated layers in relation to each other. The phase transition for anhydrous brucine obtained by dehydration is accompanied by thermal effects one order larger than anhydrous brucine, obtained by crystallization from acetone solution.