New N4-Donor Ligands as Supramolecular Guests for DNA and RNA: Synthesis, Structural Characterization, In Silico, Spectrophotometric and Antimicrobial Studies.

The present work reports the synthesis of new N4-donor compounds carrying p-xylyl spacers in their structure. Different Schiff base aliphatic N-donors were obtained synthetically and subsequently evaluated for their ability to interact with two models of nucleic acids: calf-thymus DNA (CT-DNA) and the RNA from yeast Saccharomyces cerevisiae (herein simply indicated as RNA). In more detail, by condensing p-xylylenediamine and a series of aldehydes, we obtained the following Schiff base ligands: 2-thiazolecarboxaldehyde (L1), pyridine-2-carboxaldehyde (L2), 5-methylisoxazole-3-carboxaldehyde (L3), 1-methyl-2-imidazolecarboxaldehyde (L4), and quinoline-2-carboxaldehyde (L5). The structural characterisation of the ligands L1-L5 (X-ray, 1H NMR, 13C NMR, elemental analysis) and of the coordination polymers {[CuL1]PF6}n (herein referred to as Polymer1) and {[AgL1]BF4}n, (herein referred to as Polymer2, X-ray, 1H NMR, ESI-MS) is herein described in detail. The single crystal X-ray structures of complexes Polymer1 and Polymer2 were also investigated, leading to the description of one-dimensional coordination polymers. The spectroscopic and in silico evaluation of the most promising compounds as DNA and RNA binders, as well as the study of the influence of the 1D supramolecular polymers Polymer1 and Polymer2 on the proliferation of Escherichia coli bacteria, were performed in view of their nucleic acid-modulating and antimicrobial applications. Spectroscopic measurements (UV-Vis) combined with molecular docking calculations suggest that the thiazolecarboxaldehyde derivative L1 is able to bind CT-DNA with a mechanism different from intercalation involving the thiazole ring in the molecular recognition and shows a binding affinity with DNA higher than RNA. Finally, Polymer2 was shown to slow down the proliferation of bacteria much more effectively than the free Ag(I) salt.

Synthesis and Characterization of Lanthanide Metal Ion Complexes of New Polydentate Hydrazone Schiff Base Ligand.

The new homodinuclear complexes of the general formula [Ln2L3(NO3)3] (where HL is newly synthesized 2-((2-(benzoxazol-2-yl)-2-methylhydrazono)methyl)phenol and Ln = Sm3+ (1), Eu3+ (2), Tb3+ (3a, 3b), Dy3+ (4), Ho3+ (5), Er3+ (6), Tm3+ (7), Yb3+ (8)), have been synthesized from the lanthanide(III) nitrates with the polydentate hydrazone Schiff base ligand. The flexibility of this unsymmetrical Schiff base ligand containing N2O binding moiety, attractive for lanthanide metal ions, allowed for a self-assembly of these complexes. The compounds were characterized by spectroscopic data (ESI-MS, IR, UV/Vis, luminescence) and by the X-ray structure determination of the single crystals, all of which appeared to be different solvents. The analytical data suggested 2:3 metal:ligand stoichiometry in these complexes, and this was further confirmed by the structural results. The metal cations are nine-coordinated, by nitrogen and oxygen donor atoms. The complexes are two-centered, with three oxygen atoms in bridging positions. There are two types of structures, differing by the sources of terminal (non-bridging) coordination centers (group A: two ligands, one nitro anion/one ligand, two nitro anions, group B: three ligands, three anions).

Synthesis and Spectroscopic Investigations of Schiff Base Ligand and Its Bimetallic Ag(I) Complex as DNA and BSA Binders.

Generation of well-defined potential metallotherapeutics for cancer treatment, one of the most population-threatening diseases, is challenging and an active area of modern research in view of their unique properties and thus multiple possible pathways of action in cells. Specifically, Schiff base ligands were recognized as very promising building blocks for the construction of stable and active complexes of numerous geometries and topologies. Incorporation of Ag(I) ions allows for the formation of flat complexes with potential unoccupied coordination sites, thus giving rise to specific interactions between the metallotherapeutic and biomolecule of interest. Herein, we present the design, synthesis and characterization of new Schiff base ligand L and its Ag(I) bimetallic complex [Ag2L2]2+ with two planar moieties formed around the metal ions and connected through cyclohexane rings, confirmed by X-ray measurements. The compounds were described in context of their potential use as anticancer drugs through DNA and BSA binding pathways by several spectroscopic methods (CD, UV-Vis, fluorescence). We revealed that both, L and [Ag2L2]2+, interact with similar affinity with CT-DNA (Kb~106 M-1), while they differ in the type and strength of interactions with the model albumin-BSA. [Ag2L2]2+ binds BSA in both a dynamic and static manner with the Ksv = 8.8 × 104 M-1 in the Trp-134 and Trp-213 sites, whereas L interacts with BSA only dynamically (KSV = 2.4 × 104 M-1). This found further confirmation in the CD studies which revealed a reduction in α-helix content in the albumin of 16% in presence of [Ag2L2]2+.

Synthesis and Spectroscopic Investigation of a Hexaaza Lanthanum(III) Macrocycle with a Hybrid-Type G4 DNA Stabilizing Effect.

Herein we present a mononuclear lanthanum(III) complex obtained in a template cyclocondensation reaction of lanthanum(III) nitrate salt, 1,2-propanediamine, and 2,6-diacetylpyridine (LaPA complex). A preliminary investigation of the biological potential of this compound was conducted using a biomedically relevant target Tel26. We found that, different from parallel G4, antiparallel G4, and duplex DNA, only a hybrid-type G4 structure of Tel26 in a K+ solution was significantly stabilized by ≥7 °C, which emerged in our UV melting studies. Moreover, LaPA induced structural changes in the Tel26 structure in a K+-deprived solution, suggesting that it may also lead to conformational changes in "non-G4" telomeric DNA.

Disordered structure of propane-1,2-diaminium dichloride.

In the title compound, C(3)H(12)N(2) (2+)·2Cl(-), the cations are disordered over two well resolved positions in a 0.525 (13):0.475 (13) ratio. The disorder involves two C atoms which assume positions that make an almost mirror-sym-metrical system. Similar disorder is observed both at room temperature and at 120 (1) K. The conformation of the NCCN chain in both components is close to trans (the torsion angles ca ±170°), while that of CCCN chain is close to gauche (±50°). In the crystal, a network of relatively strong N-H⋯Cl hydrogen bonds connects the cations and anions into one-cation-deep layers parallel to (001); there are R(2) (4)(8) and R(2) (4)(11) ring motifs within the plane. The planes are only loosely connected by van der Waals contacts and electrostatic inter-actions between cations and anions.

N,N'-bis(2-hydroxybenzylidene)pentane-1,5-diamine.

In the title potential O,N,N',O'-tetradentate Schiff base ligand {systematic name: 2,2'-[pentane-1,5-diylbis(nitrilomethylidyne)]diphenol}, C(19)H(22)N(2)O(2), the mutual orientation of the three planar fragments determines the conformation of the molecule. The dihedral angles between the planes of the two salicylidene groups and the plane of the central extended pentane chain are 78.4 (2) and 62.0 (3) degrees, and the angle between the terminal ring planes is 55.4 (1) degrees. Strong intramolecular O-H...N hydrogen bonds close almost-planar six-membered rings, and the O-H bonds are elongated as a result of hydrogen-bond formation.

Cadaverinium dichloride: a case of centro-non-centrosymmetric ambiguity.

In the title salt, also known as pentane-1,5-diammonium dichloride, C(5)H(16)N(2)(2+)x2Cl(-), the cation exists in an ideal fully extended conformation and lies on a mirror plane in the space group Pbam. In the crystal structure, layers of cations are hydrogen bonded with Cl(-) anions, which occupy the space between the layers. This kind of packing leads to a short unit-cell parameter of 4.463 (1) Angstrom. This structure is another case of centro-non-centrosymmetric ambiguity; the best results were obtained in a centrosymmetric space group, with the disordered NH(3) groups accounting for the non-centrosymmetric 'component'.

Redetermination of sperminium tetrachloride.

In the title compound, 1,5,10,14-tetraazoniatetradecane tetrachloride, C(10)H(30)N(4)(4+).4Cl(-), the sperminium tetracation lies on a centre of symmetry. The two central C-N-C-C torsion angles are gauche and of opposite signs, and all the other torsion angles are trans. All NH groups participate in the three-dimensional hydrogen-bond network, which is additionally strengthened by C-H.Cl interactions.