Lilianna Chęcińska

Reproducibility and transferability of topological data: experimental charge density study of two modifications of L-alanyl-L-tyrosyl-L-alanine

Two crystalline modifications of the tripeptide L-Ala-L-Tyr-L-Ala, which have different solvent molecules in the crystal structure (water and ethanol for modifications 1 and 2), were the subject of experimental charge density studies based on high resolution X-ray data collected at ultra-low temperatures of 9 K (1) and 20 K (2), respectively. The molecular structures and the intermolecular interactions were found to be rather similar in the two crystal lattices, so that this study allowed the reproducibility of the charge density of a given molecule in different (but widely comparable) crystalline environments to be examined. With respect to bond topological and atomic properties, the agreement between the two modifications of the title tripeptide was in the same range as found from the comparison with the previously reported results of tri-L-alanine. It follows that the reproducibility and transferability of quantitative topological data are comparable and that within the accuracy of experimental charge density work the replacement of the central amino acid residue L-Ala by L-Tyr has no significant influence, neither on bond nor on the atomic properties of the oligopeptide main chain. Intermolecular interactions in the form of hydrogen bonds were characterized quantitatively and qualitatively by topological criteria and by mapping the charge density distribution on the Hirshfeld surface.

Experimental and theoretical electron-density study of three isoindole derivatives: topological and Hirshfeld surface analysis of weak intermolecular interactions

A combined experimental and theoretical study of three isoindole derivatives was made on the basis of a topological analysis of their electron-density distributions. Experimental electron densities were determined from high-resolution X-ray diffraction data sets measured with synchrotron radiation at 100 K, whereas theoretical calculations were performed using DFT methods at the B3LYP\6-311++G(3df,3pd) level of approximation. Both experimental and theoretical models are in good agreement with each other. Since the analysed structures possess a variety of hydrogen-bonding interactions, weak intermolecular contacts of C-H···C(π), C,N(π)···C,N(π) and H···H types were subject to our special interest and are discussed in detail. They were characterized quantitatively and qualitatively by topological properties using Baders Atoms in Molecules theory and by mapping the electron-density distribution, electrostatic potential and a geometric function on the Hirshfeld surface. This way the forces and directions of intermolecular interactions as present on the molecular surfaces were depicted and described. These interactions not only guide crystal packing, but are likewise important for recognition processes involving (aza)isoindole fragments in a biological environment.

Electron density studies on hydrogen bonding in two chromone derivatives

The experimental electron densities of two chromone derivatives have been determined from X-ray synchrotron diffraction data at low temperature (100 K). Topological analysis of the electron density has been used to analyze the formation of resonance-assisted hydrogen bonds (RAHBs). Geometrical and topological parameters confirm π-electron delocalization within the hydrogen-bonded ring. In addition, weak C-H···O interactions were identified in both structures. Hydrogen-bond energies allowed medium and weak hydrogen bonds to be distinguished.

Substituent effect in 2-benzoylmethylenequinoline difluoroborates exhibiting through-space couplings. Multinuclear magnetic resonance, X-ray diffraction, and computational study.

The series of nine 2-benzoylmethylenequinoline difluoroborates have been synthesized and characterized by multinuclear magnetic resonance, X-ray diffraction (XRD), and computational methods. The through-space spin-spin couplings between (19)F and (1)H/(13)C nuclei have been observed in solution. The NMR chemical shifts have been correlated to the Hammett substituent constants. The crystal structures of six compounds have been solved by XRD. For two derivatives the X-ray wave function refinement was performed to evaluate the character of bonds in the NBF(2)O moiety by topological and integrated bond descriptors.

A comparison of electron density from Hirshfeld-atom refinement, X-ray wavefunction refinement and multipole refinement on three urea derivatives

Electron density distributions of three urea derivatives N-methylurea, N-phenylurea and N,N′-diphenylurea were determined by single-crystal X-ray diffraction. High-resolution data were measured with synchrotron radiation. Data were subjected to a multipole refinement using the Hansen–Coppens multipole model, to Hirshfeld-atom refinement with and without a surrounding cluster of point charges/dipoles and to X-ray wavefunction refinement. Electron density distributions were evaluated in terms of deformation and residual electron density plots as well as bond critical points, atomic volumes and charges as defined in Baders Theory of Atoms In Molecules. Given a sufficiently extended basis-set Hirshfeld-atom refinement yields results superior to multipole model refinements; best figures of merit were achieved by X-ray wavefunction refinement. Results indicate how conventional crystallographic studies can be systematically improved.

Synthesis, Characterization, and Antimicrobial Activity of Silver(I) and Copper(II) Complexes of Phosphate Derivatives of Pyridine And Benzimidazole

Two silver(I) complexes—{[Ag(4‐pmOpe)]NO3}n and [Ag(2‐bimOpe)2]NO3—and three copper(II) complexes—[Cu4Cl6O(2‐bimOpe)4], [CuCl2(4‐pmOpe)2], and [CuCl2(2‐bis(pm)Ope]—were synthesized by reaction of silver(I) nitrate or copper(II) chloride with phosphate derivatives of pyridine and benzimidazole, namely diethyl (pyridin‐4‐ylmethyl)phosphate (4‐pmOpe), 1H‐benzimidazol‐2‐ylmethyl diethyl phosphate (2‐bimOpe), and ethyl bis(pyridin‐2‐ylmethyl)phosphate (2‐bis(pm)Ope). These compounds were characterized by 1H, 13C, and 31P NMR as well as IR spectroscopy, elemental analysis, and ESIMS spectrometry. Additionally, molecular and crystal structures of {[Ag(4‐pmOpe)]NO3}n and [Cu4Cl6O(2‐bimOpe)4] were determined by single‐crystal X‐ray diffraction analysis. The antimicrobial profiles of synthesized complexes and free ligands against test organisms from the ATCC and clinical sources were determined. Silver(I) complexes showed good antimicrobial activities against Candida albicans strains (MIC values of ∼19 μM). [Ag(2‐bimOpe)2]NO3 was particularly active against Pseudomonas aeruginosa and methicillin‐resistant Staphylococcus epidermidis, with MIC values of ∼5 and ∼10 μM, respectively. Neither copper(II) complexes nor the free ligands inhibited the growth of test organisms at concentrations below 500 μg mL−1.

Synthesis, single-crystal and solution structure analysis and in vitro cytotoxic activity of two novel complexes of ruthenium(II) with in situ formed flavanone-based ligands.

Synthesis, structure and properties of two new flavanone complexes of Ru(ii) are described. The new complexes form during the reaction of ruthenium(iii) chloride with 3-aminoflavone (3-af) dissolved in an aliphatic alcohol. The formed products depend on the alcohol used and were found to be: cis-dichloridobis(3-imino-2-methoxyflavanone)ruthenium(ii)·3H(2)O (1) from a methanolic solution and cis-dichloridobis(3-imino-2-ethoxyflavanone)ruthenium(ii)·2H(2)O (2) from an ethanolic solution, in which the original ligand 3-af had been converted by dehydrogenative alcoholysis to an entirely new ligand. This paper presents the X-ray structure and detailed (1)H-NMR analysis of both new compounds, as well as the study of their antiproliferative activity. The coordination of Ru(ii) is octahedral with [RuCl(2)N(2)O(2)] chromophores, having trans chlorides and common Ru-L distances. Both 1 and 2 are highly cytotoxic towards the cisplatin resistant EJ and L1210 cell lines, and both complexes are as active as cisplatin in the sensitive cell lines. They display the ability to overcome cisplatin resistance in the drug resistant sub-lines EJcisR and L1210R. The present evidence suggests that the mechanism of biological activity may be different for these ruthenium compounds compared to cisplatin.

Antibacterial Activity and Cytotoxicity of Silver(I) Complexes of Pyridine and (Benz)Imidazole Derivatives. X-ray Crystal Structure of [Ag(2,6-di(CH2OH)py)2]NO3

Selected aspects of the biological activity of a series of six nitrate silver(I) complexes with pyridine and (benz)imidazole derivatives were investigated. The present study evaluated the antibacterial activities of the complexes against three Gram-negative strains: Pseudomonas aeruginosa ATCC 15442, Escherichia coli ATCC 25922 and Proteus hauseri ATCC 13315. The results were compared with those of silver nitrate, a silver sulfadiazine drug and appropriate ligands. The most significant antibacterial properties were exerted by silver(I) complexes containing benzimidazole derivatives. The cytotoxic activity of the complexes was examined against B16 (murine melanoma) and 10T1/2 (murine fibroblasts) cells. All of the tested silver(I) compounds were not toxic to fibroblast cells in concentration inhibited cancer cell (B16) viability by 50%, which ranged between 2.44–28.65 µM. The molecular and crystal structure of silver(I) complex of 2,6-di(hydroxymethyl)pyridine was determined by single-crystal X-ray diffraction analysis. The most important features of the crystal packing and intermolecular non-covalent interactions in the Ag(I) complex were quantified via Hirshfeld surface analysis.

Influence of selected inorganic counter-ions on the structure and antimicrobial properties of silver(I) complexes with imidazole-containing ligands

Water-soluble silver(I) complexes containing the 4(5)-(hydroxymethyl)imidazole ligand with the formula [Ag(4-CH2OHimH)2]X (where X = NO3−, ClO4−, CF3COO−, BF4− and SO3CH3−) were synthesized. The complexes were characterized by NMR (1H and 13C) and IR spectroscopy, ESI-MS spectrometry and EA. The molecular structures of three complexes were confirmed by X-ray crystallography. The antimicrobial activity of the silver(I) complexes were evaluated against six strains of microorganisms: Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa, Proteus hauseri and Candida albicans. All tested silver complexes displayed excellent antibacterial properties against Gram-positive bacteria. Among them, the complex containing the trifluoroacetate counter-ion exhibited the highest antibacterial activity, with MIC values 2 to 3-fold lower than that required by silver sulfadiazine.

Structural studies of (N-phenylthioureidoalkyl- and -aryl)phosphonates

The crystal structures of three (N-phenylthioureidoalkyl- and -aryl)phosphonates, i.e. diphenyl [(3-phenylthioureido)phenylpropyl]phosphonate, diphenyl [1-(3-phenylthioureido)benzyl]phosphonate and diphenyl [2,2-dimethyl-1-(3-phenylthioureido)propyl]phosphonate, have been determined by X-ray diffraction. The conformations of the title molecules, the geometry of the thioureide fragments and molecular packing arrangements are analyzed and compared with literature data.