A Proton Transfer Compound of Piperazine with Pyridine-2,6-dicarboxylic Acid and Its Palladium(II) and Thallium(III) Complexes – Synthesis, Characterization and Crystal Structure

Novel Tl(III) complexes containing pyridine-2,6-dicarboxylate derivatives with selective anticancer activity through inducing mitochondria-mediated apoptosis in A375 cells

Three novel Tl(III) complexes (C1), (C2) and (C3) were synthesized using the one-pot reactions of pyridine dicarboxylic acid derivatives, 2-aminobenzimidazole and/or 4-aminopyridine, and also thallium(III) nitrate trihydrate metal salt. The structure of all three complexes was determined by the single-crystal X-ray diffraction. C1 and C2 were realized to be isostructural with disordered square anti-prismatic geometry and for C3 arrangement of the distorted tricapped triangular prism was proposed. Cyclic voltammetry measurements on the complexes exhibited that formal potential values are more positive for C1 (E⁰' 0.109 V) and C3 (E⁰' 0.244 V) compared to C2 (E⁰' -0.051 V), versus Ag/AgCl under argon. Moreover, cytotoxicity of the compounds was evaluated in vitro against two cancer cell lines including a human melanoma (A375), a human colon adenocarcinoma (HT29), and also one normal cell human foreskin fibroblast (HFF). The selective and potent cytotoxicity effect was exhibited by C1 and C3 on cancer cell lines. The apoptosis through a caspase-dependent mitochondrion pathway was confirmed by ROS production, MMP reduction, p53 activation, Bax up-regulation, and Bcl-2 down-regulation, cytochrome c release, procaspase-9, and 3 expression, for A375 cells treated to C1 and C3. According to similar cellular uptake of the complexes in A375 cell line, the generation of ROS was considered as an effective agent to justify the inhibition effect C1 and C3 on mentioned cells. Furthermore, arresting the cell cycle in the G2-M phase and inducing apoptosis were indicated by these two complexes.

Statistically disordered short hydrogen bonds in (pipzH2)(cdoH)2 and a comparison with (pipzH2)(cdo)·H2O (pipz is piperazine and cdoH2 is chelidonic acid)

Two related proton-transfer compounds, namely piperazine-1,4-diium 4-oxo-4H-pyran-2,6-dicarboxylate monohydrate, C(4)H(12)N(2)(2+)·C(7)H(2)O(6)(2-)·H(2)O or (pipzH(2))(cdo)·H(2)O, (I), and piperazine-1,4-diium bis(6-carboxy-4-oxo-4H-pyran-2-carboxylate), C(4)H(12)N(2)(2+)·2C(7)H(3)O(6)(-) or (pipzH(2))(cdoH)(2), (II), were obtained by the reaction of 4-oxo-4H-pyran-2,6-dicarboxylic acid (chelidonic acid, cdoH(2)) and piperazine (pipz). In (I), both carboxyl H atoms of chelidonic acid have been transferred to piperazine to form the piperazine-1,4-diium ion. The structure is a monohydrate. All potential N-H donors are involved in N-H···O hydrogen bonds. The water molecule spans two anions via the 4-oxo group of the pyranose ring and a carboxylate O atom. The hydrogen-bonding motif is essentially two-dimensional. The structure is a pseudomerohedral twin. In the asymmetric unit of (II), the anion consists of monodeprotonated chelidonic acid, while the piperazine-1,4-diium cation is located on an inversion centre. The single carboxyl H atom is disordered in two respects. Firstly, the disordered H atom is shared equally by both carboxylic acid groups. Secondly, the H atom is statistically disordered between two positions on either side of a centre of symmetry and is engaged in a very short hydrogen-bonding interaction; the relevant O···O distances are 2.4549 (11) and 2.4395 (11) Å, and the O-H···O angles are 177 (6) and 177 (5)°, respectively. Further hydrogen bonding of the type N-H···O places the (pipzH(2))(2+) cations in pockets formed by the chains of (cdoH)(-) anions. In contrast with (I), the (pipzH(2))(2+) cations form hydrogen-bonding arrays that are perpendicular to the anions, yielding a three-dimensional hydrogen-bonding motif. The structures of both (I) and (II) also feature π-π stacking interactions between aromatic rings.

Hexa-kis-(dimethyl sulfoxide-κO)thallium(III) trinitrate

The title compound, [Tl(C₂H₆OS)₆](NO₃)₃, consists of six dimethyl sulfoxide (DMSO) mol­ecules coordinated to a Tl^III atom, which lies on a axis, and three nitrate anions (3. symmetry) to neutralize the charge. The coordination polyhedron around the Tl^III atom is octa­hedral, defined by six O atoms of the DMSO mol­ecules. In the crystal structure, C—H⋯O hydrogen bonds are observed. One of the nitrate groups exhibits half-occupation.

Hemipiperazinediium bis-(pyridine-2,6-dicarboxyl-ato-κO,N,O')gallate(III) pyridine-2,6-dicarboxylic acid dihydrate

The asymmetric unit of the title compound, (C₄H₁₂N₂)_0.5[Ga(pydc)₂]·pydcH₂·2H₂O, where pydcH₂ is pyridine-2,6-dicarboxylic acid, C₇H₅NO₄, contains one half of a centrosymmetric piperazinediium dication, one anion, one uncoord­inated pydcH₂ mol­ecule and two uncoordinated water mol­ecules, one of which is disordered over two sites in a 1:1 ratio. In the anion, the Ga^III ion is coordinated by four O atoms [Ga—O = 1.9706 (16)–2.0494 (15) Å] and two N atoms [Ga—N = 1.9660 (18) and 1.9709 (17) Å] from two pydc ligands in a distorted octa­hedral geometry. The crystal structure exhibits inter­molecular O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds and π–π inter­actions [centroid–centroid distances of 3.5359 (13) and 3.6550 (14) Å].

Butane-1,4-diammonium bis-(pyridine-2,6-dicarboxyl-ato)cuprate(II) trihydrate

In the title compound, (C₄H₁₄N₂)[Cu(C₇H₃NO₄)₂]·3H₂O or (bdaH₂)[Cu(pydc)₂]·3H₂O (where bda is butane-1,4-diamine and pydcH₂ is pyridine-2,6-dicarboxylic acid), the Cu^II atom is coordinated by four O atoms [Cu—O = 2.0557 (16)–2.3194 (16) Å] and two N atoms [Cu—N = 1.9185 (18) and 1.9638 (18) Å] from two chelating rings of the pydc²⁻ anions, which act as tridentate ligands. The geometry of the resulting CuN₂O₄ coordination can be described as distorted octa­hedral. The the two pydc²⁻ fragments are almost perpendicular to one another [77.51 (11)°]. To balance the charges, two centrosymmetric protonated butane-1,4-diammonium, (bdaH₂)²⁺ cations are present. In the crystal structure, extensive O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds [D⋯A = 2.720 (2)–3.446 (3) Å], ion pairing, C—O⋯π [O⋯π = 3.099 (2) Å] and π–π stacking inter­actions between the pydc²⁻ rings [centroid–centroid distance = 3.5334 (15) Å] contribute to the formation of a three-dimensional supra­molecular structure.

Tris(piperazinediium) bis-[tris-(pyridine-2,6-dicarboxyl-ato)neodymate(III)] 15.33-hydrate

The title compound, (C(4)H(12)N(2))(3)[Nd(C(7)H(3)NO(4))(3)](2)·15.33H(2)O or (pipzH(2))(3)[Nd(pydc)(3)](2)·15.33H(2)O (in which pipz is piperazine and pydcH(2) is pyridine-2,6-dicarboxylic acid), was synthesized by the reaction of NdCl(3)·6H(2)O with the proton-transfer compound (pipzH(2))(pydc) in aqueous solution. The nine donor atoms of the three pydc(2-) ligands form a distorted tricapped trigonal-prismatic arrangement around the Nd(III) center. Considerable C-O⋯π stacking inter-actions between CO groups of carboxyl-ate fragments and aromatic rings of pydc(2-) with distances of 3.135 (5)-3.255 (5) Å are observed. In the crystal structure, a wide range of hydrogen-bonding [of the types O-H⋯O, N-H⋯O and C-H⋯O, with D⋯A distances ranging from 2.608 (10) to 3.278 (7) Å], ion-pairing and C-O⋯π stacking interactions connect the various components into a supra-molecular structure. There is a high degree of solvent disorder in the structure; the occupancies of five water molecules refined to 0.6, 0.5, 0.4, 0.25 and 0.25.

Piperazinediium bis-(2-carboxy-pyridine-3-carboxyl-ate)

The asymmetric unit of the title salt, C(4)H(12)N(2) (2+)·2C(7)H(4)NO(4) (-) or pipzH(2) (2+)·2(py-2,3-dcH(-)), prepared by a reaction between pyridine-2,3-dicarboxylic acid (py-2,3-dcH(2)) and piperazine (pipz), contains a monoanion and half of a centrosymmetric dication. The anionic fragment individually has two intra-molecular hydrogen bonds, an almost linear O-H⋯O bond between two carboxyl-ate groups and a C-H⋯O bond between the aromatic ring and carboxyl-ate group. Other O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds are responsible for three-dimensional expansion of the structure.