Bis-acyl-/aroyl-hydrazones as multidentate ligands

Reactions of copper(II) bromide with 2,6-diacetylpyridine bis(phenyl-hydrazone) (L)-molecular and crystal structure of L and its mixed-valence complex [CuIIL2][CuI2Br4]

Utilizing X-ray crystallography, the crystal and molecular structures of 2,6-diacetylpyridine bis(phenylhydrazone) (L) were determined. The energetics of the intermolecular interactions in the crystal structure were assessed with computational methods, revealing that dispersion interactions are dominant. The basic structural unit of the crystal packing was revealed to be the herring-bone type arrangement of L molecules. Assignation of the IR spectrum of L with the aid of DFT calculations was performed. Furthermore, new reactions of L with CuBr2 in different solvents are described, which led to the synthesis of the mixed Cu(II)?Cu(I) complex with the formula [CuIIL2][CuI2Br4] (1), and its structural characterization. In the complex cation, two molecules of tridentate N3 ligand are meridionally arranged in a very distorted octahedral environment of a Cu(II) ion. In [Cu2Br4]2-, the bromide ions are arranged in a trigonal-planar geometry around each copper(I) atom. Finally, for ligand, 1, and the previously synthesized complex [CuL2]Br2, the thermal properties were examined. The thermal stability of the complexes were lower than that of the ligand and decrease in the order: L (250?C) > [CuL2]Br2 (221?C) > [CuIIL2][CuI2Br4] (212?C). The differences in thermal stability of the complexes are due to differences in the packing efficacy of the constitutional ions.

Interaction of a Vanadyl Schiff Base Complex with DNA and BSA: A Combination of Experimental and Computational Studies

BACKGROUND AND PURPOSE

Cancer is the primary cause of death in the world. Vanadium (IV) is a metal ion complex which has been proposed as a suitable candidate for cancer treatment. In this study, the interaction of the oxido-vanadium (IV) complex [VOL(bipy)] with salmon sperm DNA and Bovine Serum Albumin (BSA) was investigated through experimental and computational approaches. With the results of this experimental study, the mechanism and parameters related to the interaction of [VOL(bipy)] with DNA and BSA were determined.

MATERIALS AND METHODS

The kinetic interaction of DNA and BSA with [VOL(bipy)] was determined using absorption titration and fluorescence quenching, respectively. Moreover, the possible interactions were calculated by molecular docking prediction using the available software.

RESULTS

The binding constant (Kb) of the complex-DNA interaction was calculated to be 2.34×104 M-1, indicating a relatively strong interaction between the complex and DNA. It was found that the V(IV) complex interacted with DNA through the groove binding mode followed by partial intercalation into the DNA helix. The Kb values obtained for [VOL(bipy)]-BSA interaction were in the range of 1.07×103-5.82×104 M-1. The V(IV) complex was found to prefer the domain I binding pocket of BSA with the ΔGb value of -7.52 kcal/mol.

CONCLUSION

Both experimental and computational analyses confirmed the interaction of the vanadium complex with DNA and BSA. The moderate affinity of [VOL(bipy)] for BSA indicates that this protein is a good candidate for transferring the complex.

The second-order NLO property of a photoswitchable heteroditpioc ion-pair receptor based on 2-pyridyl acylhydrazone linking with 2,6-pyridine bisamide: The impacts of metal cations and anions

A photoswitchable heteroditpioc ion-pair receptor E-1 and its isomeride Z-1 (without the anion binding site), that are based on the 2-pyridyl acylhydrazone linking 2,6-pyridine bisamide, have brought our attention to systematically explore the second-order nonlinear optical (NLO) properties by the density functional theory (DFT). In this work, we mainly studied the influences of metal cations (M = Na⁺, K⁺, Mg²⁺, Ca²⁺, Hg²⁺ and Pb²⁺), anions (X = Cl^-, Br^- and I^-) and ion-pair (NaCl, NaBr and NaI) on NLO responses for the receptor. In addition, the impacts of isomerization and poto-switching processes on NLO response for these systems also have been discussed detailedly. The results show that the isomerization process does not effectively adjust the NLO properties for our studied systems. But the poto-switching process that was triggered by light to capure or release ions plays an important role in improving the NLO properties. The receptors E-1 and Z-1 are excellent candidates to effectively detect metal cation Pb²⁺, because the first hyperpolarizability (β_tot) values of E∗Pb²⁺ and Z∗Pb²⁺ increased by 13 times and 20 times relative to that of receptors E-1 (188.06 a.u.) and Z-1 (270.21 a.u.), respectively. In addition, the receptor E-1 has the possibility to detect anion I^- due to the larger β_tot values compared with other anion-complexes. However, the changes of NLO responses for ion-pair complexes are not obvious compared with corresponding anion-complexes. We are looking forward to the research would be beneficial for further theoretical and experimental studies on recognizing metal cations and anions based on large second-order NLO difference.

Two new zinc(II) and mercury(II) complexes based on N,N'-(cyclohexane-1,2-diylidene)bis(4-fluorobenzohydrazide): synthesis, crystal structures and antibacterial activities

Reaction of N,N'-(cyclohexane-1,2-diylidene)bis(4-fluorobenzohydrazide), C₂₀H₁₈F₂N₄O₂, (L^F), with zinc chloride and mercury(II) chloride produced different types and shapes of neutral coordination complexes, namely, dichlorido[N,N'-(cyclohexane-1,2-diylidene)bis(4-fluorobenzohydrazide)-κ²N,O]zinc(II), [ZnCl₂(C₂₀H₁₈F₂N₄O₂)], (1), and dichlorido[N,N'-(cyclohexane-1,2-diylidene)bis(4-fluorobenzohydrazide)-κ⁴O,N,N',O']mercury(II), [HgCl₂(C₂₀H₁₈F₂N₄O₂)], (2). The organic ligand and its metal complexes are characterized using various techniques: IR, UV-Vis and nuclear magnetic resonance (NMR) spectroscopies, in addition to powder X-ray diffraction (PXRD), single-crystal X-ray crystallography and microelemental analysis. Depending upon the data from these analyses and measurements, a typical tetrahedral geometry was confirmed for zinc complex (1), in which the Zn^II atom is located outside the bis(benzhydrazone) core. The Hg^II atom in (2) is found within the core and has a common octahedral structure. The in vitro antibacterial activities of the prepared compounds were evaluated against two different bacterial strains, i.e. gram positive Bacillus subtilis and gram negative Pseudomonas aeruginosa bacteria. The prepared compounds exhibited differentiated growth-inhibitory activities against these two bacterial strains based on the difference in their lipophilic nature and structural features.

New Hybrid Pyrazole and Imidazopyrazole Antinflammatory Agents Able to Reduce ROS Production in Different Biological Targets

Several anti-inflammatory agents based on pyrazole and imidazopyrazole scaffolds and a large library of substituted catechol PDE4D inhibitors were reported by us in the recent past. To obtain new molecules potentially able to act on different targets involved in inflammation onset we designed and synthesized a series of hybrid compounds by linking pyrazole and imidazo-pyrazole scaffolds to differently decorated catechol moieties through an acylhydrazone chain. Some compounds showed antioxidant activity, inhibiting reactive oxygen species (ROS) elevation in neutrophils, and a good inhibition of phosphodiesterases type 4D and, particularly, type 4B, the isoform most involved in inflammation. In addition, most compounds inhibited ROS production also in platelets, confirming their ability to exert an antiinflammatory response by two independent mechanism. Structure-activity relationship (SAR) analyses evidenced that both heterocyclic scaffolds (pyrazole and imidazopyrazole) and the substituted catechol moiety were determinant for the pharmacodynamic properties, even if hybrid molecules bearing to the pyrazole series were more active than the imidazopyrazole ones. In addition, the pivotal role of the catechol substituents has been analyzed. In conclusion the hybridization approach gave a new serie of multitarget antiinflammatory compounds, characterized by a strong antioxidant activity in different biological targets.

Noncovalent and Dynamic Covalent Chemistry Strategies for Driving Thermoresponsive Phase Transition with Multistimuli and Controlled Encapsulation/Release

We report the development of multiresponsive thermally sensitive polymers through both supramolecular and reversible covalent strategies as well as their use in controlled encapsulation and release. Novel acylhydrazone-based dynamic covalent polymers displaying lower critical solution temperature (LCST) or upper critical solution temperature (UCST) were synthesized. A remarkable control over thermal phase transition can be tuned through multimodes, such as anions, cations, solvent, pH, and competing components. In particular, anion recognition allowed disassembly and thus led to a significant decrease of UCST in dimethyl sulfoxide, and the combination of anion and solvent effects offered additional handle for control. Moreover, the use of anions, cations, as well as pH change was employed for the modulation of LCST-type polymer in water. Furthermore, switching on/off thermoresponsiveness was readily achieved by dynamic covalent exchange. Mechanistic studies also shed light on stimuli-induced changes in aggregation behaviors. Finally, thermally controlled encapsulation and release of hydrophobic and hydrophilic dyes were realized with great repeatability and reversibility, respectively, showing potential in delivery and sensing. The results and strategies described should provide opportunities for many aspects, including dynamic assemblies, complex systems, and adaptive materials.

Discrete and polymeric ensembles based on dinuclear molybdenum(vi) building blocks with adaptive carbohydrazide ligands: from the design to catalytic epoxidation

Discrete and polymeric ensembles based on dimolybdenum(vi) units with adaptive carbohydrazide ligands are described. The polymeric complexes are efficient catalysts for cyclooctene epoxidation under eco-friendly conditions.

Multiple adaptation of constitutional dynamic networks and information storage in constitutional distributions of acylhydrazones

We report a study of the behavior of four dynamic covalent libraries (DCLs) based on acylhydrazones aAbB and of the corresponding square constitutional dynamic networks (CDNs) NA-ND under the effect of three agents, namely, metal cations, base + metal cations and light irradiation; in particular, the successful switching of the CDN NB between two orthogonal distributions results, respectively, from metallo-selection and photo-selection. The four DCLs undergo triple adaptation when subjected to the three agents with the generation of specific CDN distributions characteristic of each of the four DCLs. The ternary outputs displayed by the DCLs present three states (-1, 0 and 1) related to three different constitutional distributions expressed in response to the triple inputs applied. This latter process amounts to the storage of molecular information in dynamic distributions rather than in selective interactions between complementary entities undergoing molecular recognition.

A selective detection approach for copper(ii) ions using a hydrazone-based colorimetric sensor: spectroscopic and DFT study

The development of an efficient and miniaturized analytical approach to determine trace levels of toxic ions in aqueous fluids presents a current research challenge. Hydrazone-based chemosensors are considered potential candidates due to their high sensitivity and selectivity towards heavy metal ions. Computational techniques can be properly implemented to elucidate possible modes of ligand-metal interaction and provide an in-depth understanding of the chemistry involved. The present study reports the use of 3-hydroxy-5-nitrobenzaldehyde-4-hydroxybenzoylhydrazone (3-HNHBH) ligand for highly sensitive, quick and re-usable colorimetric sensing of copper(ii) ions in aqueous media. DFT calculations suggest that the complexation of 3-HNHBH with copper(ii) ions adopts a seesaw coordination geometry and results in the largest HOMO-LUMO gap and most effective coulombic interaction compared to Zn and Ni counterparts. It demonstrated a high selectivity towards copper ions with a detection limit of 0.34 μg L-1. The ligand was readily regenerated using a 0.5 M HCl solution, indicating its feasibility to be used as a re-usable sensor for the convenient detection of copper ions in aqueous media. The influence of metal interference, pH and solvents on the selectivity and regeneration of the ligand was also investigated.

N′-[1-(Pyrazin-2-yl)ethylidene]pyrazine-2-carbohydrazide

The title compoud, C11H10N6O, was synthesized by the condensation reaction of pyrazine-2-carbohydrazide with 2-acetylpyrazine in ethanol. The dihedral angle between the pyrazine rings is 4.7 (3)°. In the crystal, aromatic π–π stacking [centroid–centroid separations = 3.606 (5) and 3.671 (5) Å] connect the molecules into stacks propagating in the [010] direction. A weak C—H...N interaction is also observed. The crystal studied was refined as a two-component twin.

Crystal structure of (μ-trans-1,2-bis-{2-[(2-oxido-phen-yl)methyl-idene]hydrazin-1-yl-idene}ethane-1,2-diolato-κ3O,O',N)bis-[di-tert-butyl-tin(IV)]

The binuclear complex, [Sn2(C4H9)4(C16H10N4O4)], contains two Sn4+ ions, connected by doubly N-deprotonated oxalylbis[(2-oxido-benzyl-idene)hydrazide] ligands, and each Sn4+ ion is linked to two tert-butyl groups. The coordination sphere of each Sn atom is best described as a distorted trigonal bipyramid. Each stannic ion in the complex is in a C2O2N environment. The two homologous parts of the doubly deprotonated ligand are located in trans positions with respect to the C-C bond of the oxalamide group. The oxalamide group exhibits an asymmetric coordination geometry, as seen by the slight difference between the C-O and C-N bond lengths. The three-dimensional network is a multilayer of complex mol-ecules with no strong supramolecular inter-actions.

Conformation-induced light emission switching of N-acylhydrazone systems

Bis-N-acylhydrazones bearing different substituents were found to display different colour emissions, through ESIPT or AIE, as a result of conformation switching, triggered by physical stimuli.

Novel CoIII complexes containing fluorescent coumarin-N-acylhydrazone hybrid ligands: Synthesis, crystal structures, solution studies and DFT calculations

A series of new Co^III complexes of the type [Co(dien)(L1-L3)]ClO₄ (1-3), containing fluorescent coumarin-N-acylhydrazonate hybrid ligands, (E)-N'-(1-(7-oxido-2-oxo-2H-chromen-3-yl)ethylidene)-4-R-benzohydrazonate [where R=H (L1^2-), OCH₃ (L2^2-) or Cl (L3^2-)], were obtained and isolated in the low spin Co^III configuration. Single-crystal X-ray diffraction showed that the coumarin-N-acylhydrazones act as tridentate ligands in their deprotonated form (L^2-). The cation (+1) complexes contain a diethylenetriamine (dien) as auxiliary ligand and their structures were calculated by DFT studies which were also performed for the Co^II (S=1/2 and S=3/2) configurations. The LS Co^II (S=1/2) concentrated the spin density on the O-Co-O axis while the HS Co^II (S=3/2) exhibited a broad spin density distribution around the metallic center. Cyclic voltammetry studies showed that structural modifications made in the L^2- ligands caused a slight influence on the electronic density of the metal center, and the E_1/2 values for the Co^III/Co^II redox couple increased following the electronic effect of the R-substituent, in the order: 2 (R=OCH₃)<1 (R=H)<3 (R=Cl). The theoretical redox potentials (E°) of the process Co^III→Co^II were calculated for both Co^II spin states (S=1/2 and S=3/2) and a better correlation was found for Co^III→Co^II (S=1/2), compared with experimental values vs SHE (E^°_calc=-0.37, -0.36 and -0.32V vs E^°_exp.=-0.371, -0.406 and -0.358V, for 1-3 respectively). Complexes 1-3 exhibited a very intense absorption band around 470nm, assigned by DFT calculations as π-π* transitions from the delocalized coumarin-N-acylhydrazone system. 1-3 were very stable in MeOH for several days. Likewise, 1-3 were stable in phosphate buffer containing sodium ascorbate after 15h, which was attributed to the high chelate effect and σ-donor ability of the L^2- and dien ligands.