Antimicrobially Active Zn(II) Complexes of Reduced Schiff Bases Derived from Cyclohexane-1,2-diamine and Fluorinated Benzaldehydes-Synthesis, Crystal Structure and Bioactivity

A series of Schiff base ligands obtained by the condensation of trans-cyclohexane-1,2-diamine and fluorinated benzaldehydes were prepared, followed by their reduction with NaBH₄. The reduced ligands were employed in the synthesis of zinc complexes of the general formula [ZnCl₂(L)]. The structures of both the original and the reduced Schiff bases, as well as of the zinc complexes, were characterized by single-crystal X-ray analysis, along with NMR and IR spectroscopy. The antimicrobial activities of the reduced Schiff bases and their zinc complexes were evaluated in vitro against E. coli, S. aureus, and C. albicans. The compounds containing the 4-(trifluoromethylphenyl) moiety showed marked antibacterial activity. Interestingly, the antimicrobial effect of the zinc complex with this moiety was significantly higher than that of the corresponding free reduced ligand, comparable with ciprofloxacin used as standard. Thus, a synergic effect upon the complexation with zinc can be inferred.

Evaluation of Antiproliferative Palladium(II) Complexes of Synthetic Bisdemethoxycurcumin towards In Vitro Cytotoxicity and Molecular Docking on DNA Sequence

Metallodrugs form a large family of therapeutic agents against cancer, among which is cisplatin, a paradigmatic member. Therapeutic resistance and undesired side effects to Pt(II) related drugs, prompts research on different metal-ligand combinations with potentially enhanced biological activity. We present the synthesis and biological tests of novel palladium(II) complexes containing bisdemethoxycurcumin (BDMC) 1 and 2. Complexes were fully characterized and their structures were determined by X-ray diffraction. Their biological activity was assessed for several selected human tumor cell lines: Jurkat (human leukaemic T-cell lymphoma), HCT-116 (human colorectal carcinoma), HeLa (human cervix epitheloid carcinoma), MCF-7 (human breast adenocarcinoma), MDA-MB-231 (human mammary gland adenocarcinoma), A549 (human alveolar adenocarcinoma), Caco-2 (human colorectal carcinoma), and for non-cancerous 3T3 cells (murine fibroblasts). The cytotoxicity of 1 is comparable to that of cisplatin, and superior to that of 2 in all cell lines. It is a correlation between IC50 values of 1 and 2 in the eight studied cell types, promising a potential use as anti-proliferative drugs. Moreover, for Jurkat cell line, complexes 1 and 2, show an enhanced activity. DFT and docking calculations on the NF-κB protein, Human Serum Albumin (HSA), and DNA were performed for 1 and 2 to correlate with their biological activities.

Electronic structure of Schiff-base peroxo{2,2'-[1,2-phenyl-enebis(nitrilo-methanylyl-idene)]bis-(6-meth-oxy-phenolato)}titanium(IV) monohydrate: a possible model structure of the reaction center for the theoretical study of hemoglobin

An extensive characterization of [Ti(C₂₂H₁₈N₂O₆)]·H₂O was performed by topological analysis according to Bader's quantum theory of atoms in molecules (QTAIM) from the experimentally (multipole model) and theoretically (DFT) determined electron density. To the best of our knowledge, this study is the first example of an experimental electronic structure of a coordination compound in which a peroxo anion is bonded to a 3d central atom. The titanium coordination polyhedron could be described as a deformed tetrahedral pyramid if the midpoint of the peroxide O-O bond (side-on mode) is considered to be in the quasi-apical position. According to the multipole model (MM) results, the titanium atom has a positive QTAIM charge of 2.05 e^- which does not correspond to the formal Ti (IV) oxidation state. On the other hand, the peroxo oxygen atoms O(1) and O(2) have MM QTAIM charges of -0.27 and -0.12, respectively. This asymmetric charge density distribution on the peroxo oxygens is in agreement with the distorted orientation of the O₂ moiety with respect to the titanium atom. Despite the fact that the overall MM charge of the O₂ moiety is more remote from the formal -2 charge than from neutral O₂, the O-O distance remains close to that in the peroxo O₂ ^2- anion. In the case of DFT results, the titanium atom charge is also found to be close to +2, the O₂ ^x- moiety charge is around -1, the optimized O-O distance is shorter by only ca 0.04 Å than the experimental value of 1.5005 (16) Å, and the DFT d-populations on titanium are found to be lower than the experimental MM value. This study is the first experimental electronic structure of a transition metal peroxo complex.

Charge density of 4-methyl-3-[(tetrahydro-2H-pyran-2-yl)oxy]thiazole-2(3H)-thione. A comprehensive multipole refinement, maximum entropy method and density functional theory study

The structure of 4-methyl-3-[(tetrahydro-2H-pyran-2-yl)oxy]thiazole-2(3H)-thione (MTTOTHP) was investigated using X-ray diffraction and computational chemistry methods for determining properties of the nitrogen-oxygen bond, which is the least stable entity upon photochemical excitation. Experimentally measured structure factors have been used to determine and characterize charge density via the multipole model (MM) and the maximum entropy method (MEM). Theoretical investigation of the electron density and the electronic structure has been performed in the finite basis set density functional theory (DFT) framework. Quantum Theory of Atoms In Molecules (QTAIM), deformation densities and Laplacians maps have been used to compare theoretical and experimental results. MM experimental results and predictions from theory differ with respect to the sign and/or magnitude of the Laplacian at the N-O bond critical point (BCP), depending on the treatment of n values of the MM radial functions. Such Laplacian differences in the N-O bond case are discussed with respect to a lack of flexibility in the MM radial functions also reported by Rykounov et al. [Acta Cryst. (2011), B67, 425-436]. BCP Hessian eigenvalues show qualitatively matching results between MM and DFT. In addition, the theoretical analysis used domain-averaged fermi holes (DAFH), natural bond orbital (NBO) analysis and localized (LOC) orbitals to characterize the N-O bond as a single σ bond with marginal π character. Hirshfeld atom refinement (HAR) has been employed to compare to the MM refinement results and/or neutron dataset C-H bond lengths and to crystal or single molecule geometry optimizations, including considerations of anisotropy of H atoms. Our findings help to understand properties of molecules like MTTOTHP as progenitors of free oxygen radicals.

Formation of metal-radical species upon reduction of late transition metal complexes with heteroleptic ligands: an experimental and theoretical study

Three novel transition metal complexes with selenadiazoloquinolones as potential broad spectrum antibiotics in clinical praxis.

Electronic structure of two isostructural `paddle-wheel' complexes: a comparative study

The experimental electron-density distribution in two isostructural complexes, tetra­kis(μ₂-acetato)di­aquadicopper(II) [H₂OCu(ac)₂Cu(ac)₂H₂O] and tetra­kis(μ₂-acetato)di­aquadichromium(II) [H₂OCr(ac)₂Cr(ac)₂H₂O], has been studied and compared.

The experimental electron density distribution in two isostructural and isomorphous complexes, tetra­kis(μ₂-acetato)di­aquadicopper(II) [H₂OCu(ac)₂Cu(ac)₂H₂O] (I) and tetra­kis(μ₂-acetato)diaquadichromium(II), [H₂OCr(ac)₂Cr(ac)₂H₂O] (II), has been obtained from high-resolution X-ray diffraction data in order to shed light on the bonding properties in the compounds studied. It has been shown that from accurate X-ray data it is possible to discuss the bonding capability of the metal atom (Cu/Cr) and the ligands in these complexes. A comparison of results obtained from averaged and non-averaged X-ray data demonstrates that using the non-averaged data and introducing an anisotropic correction for secondary extinction errors provides a more detailed distribution of the electron density in the area of the metal atoms. In both complexes studied, the bonding of the acetate oxygen atom to the central metal atom is significantly affected by the formation of hydrogen bonds. The electron density and its Laplacian at the bond critical point of metal–oxygen coordination bonds for those oxygen atoms not involved in the intermolecular hydrogen bonds are approximately 10% larger compared with the case when oxygen atoms take part in hydrogen bonds with the neighboring water molecules. It is shown that metal–oxygen bonds in a quasi-equatorial plane are typical coordination bonds and differ significantly from the apical metal–oxygen bond. Metal–metal inter­action with a small positive value of the electron density Laplacian at this bond critical point is mainly of electrostatic character. The metal–metal inter­action is definitely not a bond according to the classical definition. Based on a search of the Cambridge Structural Database, it can be argued that there are four typical coordination bonds in the [CuO₆] chromophore, similar to the four Cu—O coordination bonds in the basal plane of the CuO₅ pyramid in one of the complexes under study.

Charge density study of bis(clonixato)bis(ethanol) bis(imidazole)copper(II) complex

An experimental electronic structure of bis(clonixato)bis(ethanol) bis(imidazole)copper(II) complex, [Cu(cln)2(im)2(EtOH)2] (cln=clonixato, im=imidazole) (1) has been obtained from single-crystal X-ray diffraction data collected at 100 K using an Incoatec IμS Ag microfocus source. Metal-ligand (ML) bonds and hydrogen bonds (HBs) have been analysed using topological analysis of the experimental electron density with the atoms in molecules (AIM) approach. The central copper atom is octahedrally coordinated by two oxygen atoms from two clonixato anions and two nitrogen atoms from two imidazole ligands in equatorial plane. In axial positions are two oxygen atoms from two ethanol molecules. AIM analysis establishes that the central copper atom is bonded more strongly to the clonixato anion that to the imidazole or ethanol molecules. AIM analysis of two intramolecular and one intermolecular hydrogen bonds permits to estimate their strength. We show that the hydrogen bonds are strong enough to protect the molecule from decomposition in solvent media and to disable the more reactive imidazole-Cu-clonixato complex from interacting with e.g. a macromolecule. The electrostatic potential of the complex shows a highly positive value on the central atom, so the complex is highly reactive in an interaction with negative ligands.

The convergent synthesis and anticancer activity of broussonetinines related analogues

The convergent synthesis of broussonetinines related congeners 3 and 4 with the simple C₁₃ alkyl side chain and differently configured pyrrolidine skeleton has been achieved. Our approach relied on the [3,3]-sigmatropic rearrangements of chiral allylic substrates derived from d-xylose. Cross metathesis of the common oxazolidinone intermediates 7 and 8 with tridec-1-ene followed by alkylative cyclization completed the construction of both C-alkyl iminosugars. The targeted compounds 3 and 4 were screened for antiproliferative/cytotoxic activities against multiple cancer cell lines by MTT assay. Compound 3 exhibited very good in vitro potency on Caco-2 and Jurkat cell lines with IC₅₀ value of 5.1 μM and 5.8 μM, respectively.

Antimicrobial Activity and Urease Inhibition of Schiff Bases Derived from Isoniazid and Fluorinated Benzaldehydes and of Their Copper(II) Complexes

In order to evaluate the influence of substitution on biological properties of Schiff bases and their metal complexes, a series of differently substituted fluorine-containing Schiff bases starting from the drug isoniazid (isonicotinylhydrazide) were prepared and their structures were established by single-crystal X-ray diffraction. Also, four copper(II) complexes of these Schiff bases were synthesized. The prepared compounds were evaluated for their antimicrobial activity and urease inhibition. Two of the Schiff bases exerted activity against C. albicans. All copper(II) complexes showed excellent inhibitory properties against jack bean urease, considerably better than that of the standard inhibitor acetohydroxamic acid.

New isostructural transition metal complexes with a non-innocent dithiolate ligand

Three new complexes with 3,6-dichlorobenzene-1,2-dithiol (bdtCl2), namely methyltriphenylphosphonium bis(3,6-dichlorobenzene-1,2-dithiolato-κ(2)S,S')cobaltate(1-), (C19H18P)[Co(C6H2Cl2S2)2], (I), bis(methyltriphenylphosphonium) bis(3,6-dichlorobenzene-1,2-dithiolato-κ(2)S,S')cuprate(2-) dimethyl sulfoxide disolvate, (C19H18P)2[Cu(C6H2Cl2S2)2]·2C2H6OS, (II), and methyltriphenylphosphonium bis(3,6-dichlorobenzene-1,2-dithiolato-κ(2)S,S')cuprate(1-), (C19H18P)[Cu(C6H2Cl2S2)2], (III), have been synthesized and characterized by single-crystal X-ray diffraction. The X-ray structure analyses of all three complexes confirm that the four donor S atoms form a slightly distorted square-planar coordination arrangement around the central metal atom. An interesting finding for both the Cu(II) and Cu(III) complexes, i.e. (II) and (III), respectively, is that the coordination polyhedra are principally the same and differ only slightly with respect to the interatomic distances.

Conformational, spectroscopic, and molecular dynamics DFT study of precursors for new potential antibacterial fluoroquinolone drugs

Biological activity, functionality, and synthesis of (fluoro)quinolones is closely related to their precursors (for instance 3-fluoroanilinoethylene derivatives) (i.e., their functional groups, conformational behavior, and/or electronic structure). Herein, the theoretical study of 3-fluoroanilinoethylene derivatives is presented. Impact of substituents (acetyl, methyl ester, and ethyl ester) on the conformational analysis and the spectral behavior is investigated. The B3LYP/6-311++G** computational protocol is utilized. It is found that the intramolecular hydrogen bond N-H···O is responsible for the energetic preference of anti (a) conformer (anti position of 3-fluoroanilino group with respect to the C═C double bond). The Boltzmann ratios of the conformers are related to the differences of the particular dipole moments and/or their dependence on the solvent polarity. The studied acetyl, ethyl ester, and methyl ester substituted fluoroquinolone precursors prefer in the solvent either EZa, ZZa, or both conformers equally, respectively. In order to understand the degree of freedom of rotation of the trans ethyl ester group, B3LYP/6-311G** molecular dynamic simulations were carried out. Vibrational frequencies, electron transitions, as well as NMR spectra are analyzed with respect to conformational analysis, including the effect of the substituent. X-ray structures of the precursors are presented and compared with the results of the conformational analysis.

Charge Density Study of two Ni(III) and Ni(II) complexes

Experimental charge density of two nickel complexes with oxidation state +3 and +2 of composition (CH3(Ph)3P)+[Ni(bdtCl2)2]-, C31H22Cl4S4P1Ni1 [I] and (CH3(Ph)3P)+[Ni(bdtCl2)2]- dimethylsulfoxide solvate, C25H20Cl2S2P1Ni0.5; C2H6SO [II], (bdtCl2 = 3,6-dichloro-1,2-benzenedithiole ), has been studied. The coordination of Ni central atom by bdtCl2 as a non-innocent ligand gives rise to interesting electronic properties. Compounds I and II crystalize in a monoclinic space groups P 21/c and II in P 21/n, respectively. Their coordination is square-planar with the chromophore [NiS4]. Obvious differences for interatomic distances in metallocycles were found. For I in Ni1-S1-C1-C6-S2-Ni1 there are bond lengths of 2.1534(1), 1.7375(5), 1.4144(8), 1.7327(5), 2.1432(1) Å; and in Ni2-S3-C7-C12-S4-Ni2 there are bond lengths of 2.1453(1), 1.7390(5), 1.4133(7), 1.7387(5), 2.1523(1) Å. For II in Ni1-S1-C1-C6-S2-Ni1 there are bond lengths of 2.1776(2), 1.7437(8), 1.4169(11), 1.7431(8), 2.1663(2) Å. Significantly longer distances for II are in good agreement with the lower oxidation state of central atom. Very accurate data for I an II complexes were obtained with Oxford Diffraction CCD GEMINI R diffractometer at 100K. Multipolar refinement and consecutive topological analysis was performed using XD package. Differences in distribution of electron density in both complexes will be disscussed and compared with quantum-chemical calculations at BP86/VTZP level of theory [1]. This work has been supported by Slovak Grant Agency APVV and VEGA (APVV-0202-10 and 1/0679/11).

Synthesis, physicochemical properties and antimicrobial activity of mono-/dinitroxyl amides

Two comparative sets of mono-/dinitroxyl amides were designed and prepared. The novel TEMPO and/or PROXYL derivatives were fully characterised and their spin, redox and antimicrobial properties were determined. Cyclic voltammetry revealed (quasi)reversible redox behavior for most of the studied radicals. Moreover, the electron-withdrawing substituents increased the oxidation potential of nitroxides in comparison to electron-donating groups. While EPR spectra of monoradicals featured the typical three-line signal, the spectra of biradicals showed more complex splitting patterns. The in vitro biological assay revealed that unlike pyrrolidinyl derivatives, the piperidinyl nitroxides significantly inhibited the growth of Staphylococcus sp.

Low-dimensional compounds containing cyanide groups. XXV. Synthesis, spectroscopic properties and crystal structures of two ionic iron(II) complexes with tricyanomethanide: tris(1,10-phenanthroline-κ(2)N,N')iron(II) bis(tricyanomethanide) and tris(2,2'-bipyridine-κ(2)N,N')iron(II) bis(tricyanomethanide) sesquihydrate

Two new diamagnetic coordination compounds, [Fe(phen)3][C(CN)3]2, (I), and [Fe(bpy)3][C(CN)3]2·1.5H2O, (II), have been synthesized and characterized by single-crystal X-ray diffraction analysis, and IR and UV-Vis spectroscopy (phen is 1,10-phenanthroline, C12H8N2, and bpy is 2,2'-bipyridine, C10H8N2). Both compounds are ionic with distorted octahedral [Fe(phen)3](2+) or [Fe(bpy)3](2+) complex cations, with average Fe-N distances of 1.977 (2) and 1.971 (3) Å, respectively, and two uncoordinated planar tricyanomethanide, or [C(CN)3](-), counter-anions balancing the positive charges of the cations. Solvent water molecules and tcm anions in (II) are linked via O-H...N hydrogen bonds into negatively charged layers and the interlayer space is filled by [Fe(bpy)3](2+) cations. The structures of (I) and (II) are stabilized by π-π interactions between the stacked aromatic rings of the phen ligands of two adjacent cations and by O-H...N hydrogen bonds, respectively, and also by π-π stacking interactions between phen and tcm units in (I).

3-Chloro-N-(2-chlorophenyl)benzamide

In the title compound, C₁₃H₉Cl₂NO, the meta-Cl atom in the benzoyl ring is positioned anti to the C=O bond, while the ortho-Cl atom in the aniline ring is positioned syn to the N—H bond. The two aromatic rings are almost coplanar, making a dihedral angle of 4.73 (5)°. The crystal structure is stabilized by N—H⋯O hydrogen bonds, which link the mol­ecules into chains along the b axis.

3-Chloro-N-phenylbenzamide

In the title compound, C₁₃H₁₀ClNO, the meta-chloro group on the benzoyl ring is positioned syn to the C=O bond. The two aromatic rings make a dihedral angle of 88.5 (3)°. In the crystal, N—H⋯O hydrogen bonds link the mol­ecules into C(4) chains propagating in [010].

3-Chloro-N-(2-methylphenyl)benzamide

In the mol­ecular structure of the title compound, C₁₄H₁₂ClNO, the meta-Cl atom in the benzoyl ring is positioned anti to the C=O bond, while the ortho-methyl group in the aniline ring is positioned syn to the N—H bond. The two benzene rings are nearly coplanar [dihedral angle = 3.48 (5)°]. The crystal structure is stabilized by N—H⋯O hydrogen bonds, which link the mol­ecules into chains along the b axis.

N-(3,5-Dimethyl-phen-yl)-4-methyl-benzamide

In the title compound, C₁₆H₁₇NO, the dihedral angle between the two benzene rings is 16.6 (1)°. The crystal structure is stabilized by inter­molecular N—H⋯O hydrogen bonds, which link the mol­ecules into chains running along the c axis.

2-Chloro-N-(4-methylphenyl)benzamide

In the title compound, C₁₄H₁₂ClNO, the ortho-Cl atom in the benzoyl ring is positioned syn to the C=O bond. The benzoyl and aniline benzene rings are tilted relative to each other by 82.8 (1)°. In the crystal, inter­molecular N—H⋯O hydrogen bonds link the mol­ecules into infinite chains running along the c-axis direction.

N-(2-Chlorophenyl)-4-methylbenzamide

The asymmetric unit of the title compound, C₁₄H₁₂ClNO, contains two independent mol­ecules in which the dihedral angles between the two aromatic rings are 51.76 (6) and 51.48 (7)°. The crystal structure is stabilized by inter­molecular N—H⋯O hydrogen bonds, which link the mol­ecules into chains running along the c axis.

N-(2,3-Dimethyl-phen-yl)-4-methylbenzamide

In the mol-ecule of the title compound, C(16)H(17)NO, the two aromatic rings are almost perpendicular to each other [dihedral angle 85.90 (5)°]. The crystal structure is stabilized by inter-molecular N-H⋯O hydrogen bonds which link the mol-ecules, forming C(4) chains running along the c axis.