Selectivity of a thiosemicarbazonatocopper(II) complex towards duplex RNA. Relevant noncovalent interactions both in solid state and solution

Thiosemicarbazones and their metal derivatives have long been screened as antitumor agents, and their interactions with DNA have been analysed. Herein, we describe the synthesis and characterization of compounds containing [CuL]+ entities (HL = pyridine-2-carbaldehyde thiosemicarbazone) and adenine, cytosine or 9-methylguanine, and some of their corresponding nucleotides. For the first time, crystal structures of adenine- and 9-methylguanine-containing thiosemicarbazone complexes are reported. To the best of our knowledge, the first study on the affinity thiosemicarbazone–RNA is also provided here. Experimental and computational studies have shown that [CuL(OH2)]+ entities at low concentration intercalate into dsRNA poly(rA)·poly(rU) through strong hydrogen bonds involving uracil residues and π–π stacking interactions. In fact, noncovalent interactions are present both in the solid state and in solution. This behaviour diverges from that observed with DNA duplexes and creates an optimistic outlook in achieving selective binding to RNA for subsequent possible medical applications.Obra Social “la Caixa” (OSLC-2012-007), Ministerio de Economía y Competitividad and FEDER funds (CTQ2013-48937-C2-1-P, CTQ2015-70371- REDT, MAT2012-34740 and CTQ2014-58812-C2-2-R), Junta de Castilla y León (BU237U13), the Basque Government (IT-779- 13), Gerencia Regional de Salud, Consejería de Sanidad, Junta de Castilla y León (GRS 1023/A/14 and GR172)

Distortion Isomerism of Cu(II) Chloride Adducts with Bis(2-benzimidazolyl)ethane. Synthesis, Characterization, X-ray Structures and Spectroscopy of Four Different Isomers

Metals in Catalysis, Biomimetics & Inorganic Material

Cobalt(II), nickel(II) and copper(II) complexes of some O-hydroxycrotonophenones

Metal(II) complexes of the type ML2,nB [M = CuII, NiII, CoII; L = 2- hydroxy-5-X-crotonophenone where X = H, CH3, Cl; B = H2O, pyridine; n = 0, 1, 2] have been obtained and investigated. With the help of element analyses, magnetic measurements, ligand field and infrared spectra and thermal studies, the structure and the nature of bonding have been established. The anhydrous copper(II) chelates are monomeric and possess trans-square-planar configuration while the corresponding cobalt(II) and nickel(II) compounds are polymeric and possess high-spin trans-octahedral configuration. All the base adducts possess high-spin trans-octahedral structure with lesser tendency toward dissociation in solution. Infrared studies indicate that v(C=O) and v(M-O) are affected by metal ion and phenyl substitutions and adduct formation. The order of stabilities, namely Cu > Ni > Co, derived from v(M-O) parallels the crystal field stabilization energies. Substitution in the phenyl ring of the complexes produces shifts in v(M-O) which are related to the resonance capacities of the substituents. The relatively high ligand field strength of o-hydroxycrotonophenone compared to salicylaldehyde is attributed to the conjugation of C=O with C=C which lowers the energy of the π 3∗ orbital leading to extensive back-bonding with dπ orbitals of the metal

Copper(II)-disulphide interaction in copper complexes containing salicylaldimine and pyridylaldimine ligands: synthesis, spectra and redox behaviour

Copper(II) complexes of Schiff base ligands formed by the condensation of cystamine (cys) or 2,2'-diaminodiphenyl-disulphide (ddds) with salicylaldehyde (sal) or pyridine-2-carboxaldehyde (pal), and also their C=N reduced analogues, have been isolated and characterised. The e.p.r. spectra of the complexes reveal a d x 2-y2 ground state and exhibit low A|| and g|| values. The spectral results suggest equatorial coordination of disulphide in a square-based geometry. The π -delocalisation, unsaturation and flexibility in the ligands affect the ligand field, charge transfer and e.p.r. spectral parameters as well as the redox behaviour

Effect of Extensive Conjugation of Coordinated Imine on Nature of Bonding & Structure of Cu(II), Ni(II) & Co(II) Complexes of 2'-Hydroxychalccneimine

670-67

Stereochemistry of copper (II), nickel (II) and cobalt (II) 2'-hydroxy-5'-X-chalconeoxime complexes

Cu (II), Ni (II) and Co (II) complexes of the type ML2,2B where L = 2'-hydroxy-5'-X-chalconeoxime (X = H, CH3, Cl) and B = water or pyridine have been obtained from chalconeoximes and by reacting the preformed metal (II) chalcone complexes with hydroxylamine. They have been characterised on the basis of elemental and thermal analyses, conductivity and magnetic measurements and ligand field and m spectra. All the complexes are high-spin octahedral species in contrast to the low-spin square planar Ni (II) and Co (II) salicylaldoxime complexes. IR spectral studies indicate that conjugation is relatively damped in chalconeoxime. The lower ligand field strangth of the oxime is attributed to the weak M-N bonding and less extensive dπ -π∗ 3 back-bonding. Replacement of water by pyridine weakens metal-oximino bond in the complexes

DNA binding and cleavage properties of certain tetrammine ruthenium(II) complexes of modified 1,10-phenanthrolines - effect of hydrogen-bonding on DNA-binding affinity

A series of ruthenium(II) mixed ligand complexes of the type [Ru(NH3)4(L)]2+, where L=imidazo[4,5-f][1,10]phenanthroline (ip), 2-phenylimidazo[4,5-f][1,10]phenanthroline (pip), 2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline (hpip), 4,7-diphenyl-1,10-phenanthroline (dip), naphtha[2,3-a]dipyrido[3,2-h:2',3'-f]phenazine-5,18-dione (qdppz), 5,18-dihydroxynaphtho[2,3-a]dipyrido[3,2-h:2',3'-f]phenazine (hqdppz), have been isolated and characterized. The interaction of these complexes with calf thymus DNA (CT DNA) has been explored by using absorption, emission, and circular dichroic spectral methods, thermal denaturation studies and viscometry. All these studies suggest the involvement of the modified phenanthroline 'face' rather than the ammonia 'face' of the complexes in DNA binding. An intercalative mode of DNA binding, which involves the insertion of the modified phenanthroline ligands in between the base pairs, is suggested. The results from absorption spectral titration and circular dichroism (CD), thermal denaturation and viscosity experiments indicate that the qdppz and hqdppz complexes (Kb~106 and ΔTm=11-13 ° C) bind more avidly than the ip, pip and hpip complexes (Kb~105, ΔTm=6-8 ° C). Intramolecular hydrogen bonding in the hpip and hqdppz complexes increases the surface area of the intercalating diimines and enhances the DNA binding affinity substantially. The ammonia co-ligands of the complexes are possibly involved in hydrogen bonding with the intrastrand nucleobases to favour intercalation of the extended aromatic ligands. Circular dichroism spectral studies reveal that all the complexes effect certain structural changes on DNA duplex; [Ru(NH3)4(ip)]2+ induces a B to A transition while [Ru(NH3)4(qdppz)]2+ a B to ψ conformational change on CT DNA. Cleavage efficiency of the complexes were determined using pBR322 supercoiled plasmid DNA. All the complexes, except hqdppz complex, promote the cleavage of supercoiled plasmid (form I) to relaxed circular form (form II)

Spectral and electrochemical behaviour of some copper(II) complexes with CuO₄ chromophore

803-808A few mixed ligand complexes of the type Cu(TCA)(L) [where TCA = trichloroacetic acid; L=2, 2, 6, 6-tetramethyl-3, 5-heptanedione (DPM), 2, 6-dimethyl-3, 5-heptanedione (DMHD) and o- hydroxybenzophenone (OHBP)] have been prepared and characterised by IR, electronic and EPR spectral data and compared with those of the corresponding CuL2 and other Cu(TCA)(L) chelates [where L=acetylacetone (ACAC), ethylacetoacetate (EAA), salicylaldehyde (SAL) and o-hydroxyacetophenone (OHAP)] to illustrate the nature of bonding of TCA with Cu(II). The Cull/CuI redox potentials of the bis-chelates vary in the order, DPM OHAP DMHD > ACAC > EAA: SAL 2 by TCA leads to a decrease in the delocalisation of electron density, more in o-hydroxyarylcarbonyl rather than in β-diketonate complexes