PubMed Health⌕ Search

Biomedical subjects

Agnieszka Plutecka

Publications and source records attributed to Agnieszka Plutecka.

8 recordsLinked to original sources
PubMed2006

Hydrogen-bonding and pi-pi interactions in 2-amino-4,6-dimethylpyrimidinium salicylate.

In the crystal structure of the title compound, C6H10N3+.C7H5O3-, the asymmetric unit contains four crystallographically independent 2-amino-4,6-dimethylpyrimidinium and salicylate ions (Z = 8). In each of these, one of the pyrimidine N atoms is protonated, and the carboxylate group of the salicylate ion interacts with the pyrimidine group through a pair of N-H...O hydrogen bonds, forming an R2(2)(8) motif. The pyrimidine cations also form base pairs via a pair of N-H...N hydrogen bonds (involving the amino group and the unprotonated ring N atom), forming another R2(2)(8) motif. Three such R2(2)(8) motifs, fused together, constitute a closed cyclic aggregate, and the linking of these aggregates, arranged in consecutive layers, can be analysed in terms of off-face stacking interactions.

Crystallography, X-Ray↗
PubMed2006

Trianglamines--readily prepared, conformationally flexible inclusion-forming chiral hexamines.

Trianglamines, macrocyclic heteraphanes, were readily synthesised through a [3+3] cyclocondensation of (R,R)-1,2-diaminocyclohexane with terephthalaldehyde, followed by NaBH4 reduction and N-alkylation. The macrocyclic ring shows a remarkable ability to change its conformation, as a consequence of rotation about the C-N bonds or nitrogen inversion due to protonation or N-alkylation, as revealed by circular dichroism spectra, computational modelling and X-ray diffraction analysis. The flexible natures of the trianglamine macrocycles allow ready accommodation of a variety of guest molecules to form crystalline inclusion complexes of highly diversified interpenetrating structures.

Amines↗
PubMed2006

Relationship between structure and photoinitiating abilities of selected bromide salts of 2-oxo-2,3-dihydro-1H-imidazo[1,2-a]pyridine (IMP): influence of the solvent and the substitution in benzaldehyde on the course of its reaction with IMP.

2-Oxo-2,3-dihydro-1H-imidazo[1,2-a]pyridinium bromide and its C3-substituted derivatives have been synthesized and structurally characterized by X-ray crystallography and quantum chemical calculations. Their potential as photoinitiators for free-radical polymerization has been investigated experimentally and compared with theoretical results. It has been established that the course of the reaction that introduces the substituted benzylidene group to the imidazole ring is different in the protic and dipolar aprotic solvents, and also depends on the character of the substituent, as the energy change in the reaction favours either R1R2C=CHR3 or R1R2CH-CH(OCH3)R3 formation.

Journal Article↗
PubMed2005

Hydrogen-bonding patterns in pyrimethaminium dinitrate.

The title compound, 2,4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidine-1,3-diium dinitrate, C12H15ClN42+.2NO3-, contains two crystallographically independent pyrimethamine (PMN) molecules, which differ in the relative orientations of the pyrimidine and benzene rings and of the ethyl substitutents. In both pyrimethamine molecules, all the pyrimidine N atoms are protonated, unlike most related compounds, in which only one pyrimidine N atom is protonated. The two pyrimethamine moieties are bridged by a variety of N-HO(nitrate) interactions, including some three-centre hydrogen bonds.

Crystallography, X-Ray↗
PubMed2005

New type of bonding formed from an overlap between pi aromatic and pi C=O molecular orbitals stabilizes the coexistence in one molecule of the ionic and neutral meso-ionic forms of imidazopyridine.

New bis(imidazo)pyridine dye has been synthesized and tested as a potential photoinitaitor for free-radical polymerization induced with the visible emission of an argon ion laser. The X-ray analysis based on data collected at 170 and 130 K, as well as density functional theory (DFT) calculations, revealed the presence of two different forms of imidazopyridine rings within the same molecule. These two forms of the same moiety had not only different geometries but different electronic structures as well. One of the imidazopyridine rings was in the ionic form, while the other was in the meso-ionic form. DFT calculations provided an explanation for such an observed phenomena. The averaging of ionic and meso-ionic forms of imidazopyridine rings within the same molecule is hindered because of an attractive interaction between them. Analysis of electronic density revealed that, indeed, a new type of bonding is formed as the result of an overlap between pi aromatic and pi C=O molecular orbitals. This bonding, like the hydrogen bond, is primarily of electrostatic character, and its energy was estimated at 3.5 kcal/mol.

Bromides↗
PubMed2005

Hydrogen-bonding patterns in 2-amino-4,6-dimethylpyrimidinium hydrogen sulfate.

In the title compound, C6H10N3+.HSO4-, the asymmetric unit consists of a hydrogen sulfate anion and a 2-amino-4,6-dimethylpyrimidinium cation. The hydrogen sulfate anions self-assemble through O-H...O hydrogen bonds, forming supramolecular chains along the b axis, while the organic cations form base pairs via N-H...N hydrogen bonds. The aminopyrimidinium cations join to the sulfate anions via a pair of hydrogen bonds donated from the pyrimidinium protonation site and from the exo amine group cis to the protonated site.

Crystallography, X-Ray↗
PubMed2005

Conformational response of tartaric acid to derivatization: role of 1,3-dipole-dipole interactions.

The four-carbon chain in (R,R)-tartaric acid derivatives is predominantly antiperiplanar (trans) in the acid, its salts, esters, and NH-amides, while (-)-synclinal (gauche) conformer is the most abundant in N,N'-tetraalkyltartramides. Trialkylsilylation or tert-butylation of the hydroxy groups at C2 and C3 does not appear to affect the conformational preference of NH-tartramides, but it does change the conformational equilibrium in the case of tartrates (toward (-)-gauche) and N,N'-tetraalkyltartramides (toward trans), as judged from the NMR data. X-ray diffraction data point to the stabilizing role of antiparallel dipole-dipole interactions due to the 1,3-CO/CH bonds. These interactions can be found in the trans and (-)-gauche conformers but are not possible for the (+)-gauche conformers of (R,R)-tartaric acid derivatives. This rationalizes small proportion of (+)-gauche conformers in tartaric acid derivatives and points to a significance of 1,3-dipole-dipole interactions. The conformation around the C1-C2 (and C3-C4) bond is different in tartrates (O-C-C=O, syn) and tartramides (O-C-C=O, anti); the CD data (n-pi* band) show that O-silylation or O-tert-butylation brings about conformational changes around the C1-C2 bond in the case of N,N'-tetraalkyldiamides only.

Journal Article↗