Search Results (17)

Heterogeneous catalysts comprising immobilized nickel(II) complexes bearing a fluorine- or trifluoromethyl-substituted iminopyridine ligand (X_n-C₆H_5–n-N=C (CH₃)-C₅H₅N, X = F or CF₃) in fluorotetrasilicic mica interlayers were prepared by reacting Ni²⁺-exchange fluorotetrasilicic mica with the appropriate ligand. Upon activating the precatalyst with triethylaluminum or triisobutylaluminum, the generated active species showed catalytic activity for ethylene oligomerization, yielding low-molecular-weight polyethylene (PE), ethylene oligomers, and wax-like PE. The oligomer distribution almost agreed with what we expected according to the Schultz–Flory distribution. However, the amount of solid products was much higher than the theoretical value, indicating that at least two active species were formed, i.e., the oligomer and low-molecular-weight PE. The precatalyst with a 2,4-F₂C₆H₃ group on the imino nitrogen atom activated by triethylaluminum showed the highest catalytic activity for ethylene oligomerization (408 g-C₂ g-cat⁻¹ h⁻¹), with selectivities to the liquid and solid products of 51.0% and 11.5%, respectively, with the rest of the product corresponding to wax-like PE. Meanwhile, the highest selectivity to the liquid product (66.7% at 233 g-C₂ g-cat⁻¹ h⁻¹) was obtained using the precatalyst with a 2-FPh group on the imino nitrogen atom activated by triisobutylaluminum. Full article

Recent advances in designing multinuclear late transition metal catalysts for the oligo-/polymerization of olefins emphasize the great interest and promising approaches in the preparation and application of these catalytic systems. Accordingly, in this study, two dinuclear macrocyclic bis(iminopyridine) Fe- and Co-based complexes (FC and CC) were prepared at moderate yields through a one-pot template reaction. Upon activation by MMAO, not only did the catalysts show reasonable activities for the oligomerization of ethylene but also showed high selectivity for the production of tetramers (α-C₈). With respect to the catalyst structure, FC demonstrated higher catalyst activity (9.45 g mol⁻¹ Fe h⁻¹ × 10⁵ vs. 8.75 × 10⁵ g mol⁻¹ Co h⁻¹) along with higher selectivity for α-C₈ production compared to CC (96.6 vs. 96.1%). Both catalysts had thermal stability up to 70 °C, with FC being much more active and stable than CC under identical conditions. On the other hand, polymerization parameters had an influence on the catalyst performance and oligomer distribution. Moreover, molecular calculations were employed for geometry optimization and structural determination, which was consistent with the experimental results. Full article

One of the most urgent threats to public health worldwide is the ongoing rise of multidrug-resistant (MDR) bacterial strains. Among the most critical pathogens are MDR-Klebsiella pneumoniae strains. The lack of new antibiotics has led to an increased need for non-antibiotic antimicrobial therapies. Photodynamic therapy (PDT) has become increasingly significant in treating MDR bacteria. PDT uses photosensitizer compounds (PS) that generate reactive oxygen species (ROS) when activated by light. These ROS produce localized oxidative stress, damaging the bacterial envelope. A downside of PDT is the limited bioavailability of PSs in vivo, which can be enhanced by conjugating them with carriers like nanoparticles (NPs). Zinc nanoparticles possess antibacterial properties, decreasing the adherence and viability of microorganisms on surfaces. The additive or synergistic effect of the combined NP-PS could improve phototherapeutic action. Therefore, this study evaluated the effectiveness of the copper(I)-based PS CuC1 compound in combination with Zinc Oxide NP, ZnONP, to inhibit the growth of both MDR and sensitive K. pneumoniae strains. The reduction in bacterial viability after exposure to a PS/NP mixture activated by 61.2 J/cm² of blue light photodynamic treatment was assessed. The optimal PS/NP ratio was determined at 2 µg/mL of CuC1 combined with 64 µg/mL of ZnONP as the minimum effective concentration (MEC). The bacterial gene response aligned with a mechanism of photooxidative stress induced by the treatment, which damages the bacterial cell envelope. Additionally, we found that the PS/NP mixture is not harmful to mammalian cells, such as Hep-G2 and HEK-293. In conclusion, the CuC1/ZnONP combination could effectively aid in enhancing the antimicrobial treatment of infections caused by MDR bacteria. Full article

Antibiotic resistance is currently a global health emergency. Metallodrugs, especially metal coordination complexes, comprise a broad variety of candidates to combat antibacterial infections. In this work, we designed a new family of Schiff base zinc(II) complexes with iminopyridine as an organic ligand and different inorganic ligands: chloride, nitrate, and acetate. The antibacterial effect of the Zn(II) complexes was studied against planktonic bacterial cells of Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) strains. The results showed a moderate biocide activity in both types of planktonic bacteria, which arises from the metal complexation to the Schiff base ligand. Importantly, we confirmed the crucial effect of the metal, with Zn(II) improving the activity of Cu(II) counterparts previously reported. On the other hand, the impact of the inorganic ligands was not significant for the antibacterial effect but was relevant for the complex solubility. Finally, as proof of concept of topical antibacterial formulation, we formulated an emulsion containing the most lipophilic Zn(II) complex and confirmed a sustained release for 24 h in a vertical cell diffusion assay. The promising activity of iminopyridine Zn(II) complexes is potentially worth exploring in more detailed studies. Full article

Two complexes, related to the active site of [FeFe]-hydrogenases, [Fe₂(CO)₄(κ²-pma)(µ-bdt)] (1) and [Fe₂(CO)₄(κ²-pma)(µ-pdt)] (2) (bdt = benzene-1,2-dithiolate, pdt = propane-1,2-dithiolate) featuring the diaza chelate ligand trans-N-(2-pyridylmethylene)aniline (pma) were prepared, in order to study the influence of such a redox ligand, potentially non-innocent, on their redox behaviours. Both complexes were synthesized by photolysis in moderate yields, and they were characterized by IR, ¹H and ¹³C{¹H} NMR spectroscopies, elemental analyses and X-ray diffraction. Their electrochemical study by cyclic voltammetry, in the presence and in the absence of protons, revealed different behaviours depending on the aliphatic or aromatic nature of the dithiolate bridge. Density functional theory (DFT) calculations showed the role of the pma ligand as an electron reservoir, allowing the rationalization of the proton reduction process of complex 1. Full article

Fenebrutinib is an orally available Bruton tyrosine kinase inhibitor. It is currently in multiple phase III clinical trials for the management of B-cell tumors and autoimmune disorders. Elementary in-silico studies were first performed to predict susceptible sites of metabolism and structural alerts for toxicities by StarDrop WhichP450™ module and DEREK software; respectively. Fenebrutinib metabolites and adducts were characterized in-vitro in rat liver microsomes (RLM) using MS3 method in Ion Trap LC-MS/MS. Formation of reactive and unstable intermediates was explored using potassium cyanide (KCN), glutathione (GSH) and methoxylamine as trapping nucleophiles to capture the transient and unstable iminium, 6-iminopyridin-3(6H)-one and aldehyde intermediates, respectively, to generate a stable adducts that can be investigated and analyzed using mass spectrometry. Ten phase I metabolites, four cyanide adducts, five GSH adducts and six methoxylamine adducts of fenebrutinib were identified. The proposed metabolic reactions involved in formation of these metabolites are hydroxylation, oxidation of primary alcohol to aldehyde, n-oxidation, and n-dealkylation. The mechanism of reactive intermediate formation of fenebrutinib can provide a justification of the cause of its adverse effects. Formation of iminium, iminoquinone and aldehyde intermediates of fenebrutinib was characterized. N-dealkylation followed by hydroxylation of the piperazine ring is proposed to cause the bioactivation to iminium intermediates captured by cyanide. Oxidation of the hydroxymethyl group on the pyridine moiety is proposed to cause the generation of reactive aldehyde intermediates captures by methoxylamine. N-dealkylation and hydroxylation of the pyridine ring is proposed to cause formation of iminoquinone reactive intermediates captured by glutathione. FBB and several phase I metabolites are bioactivated to fifteen reactive intermediates which might be the cause of adverse effects. In the future, drug discovery experiments utilizing this information could be performed, permitting the synthesis of new drugs with better safety profile. Overall, in silico software and in vitro metabolic incubation experiments were able to characterize the FBB metabolites and reactive intermediates using the multistep fragmentation capability of ion trap mass spectrometry. Full article

3,4-Enhanced polymerization of isoprene catalyzed by late transition metal with high activity remains one of the great challenges in synthetic rubber chemistry. Herein, a library of [N, N, X] tridentate iminopyridine iron chloride pre-catalysts (Fe 1–4) with the side arm were synthesized and confirmed by the element analysis and HRMS. All the iron compounds served as highly efficient pre-catalysts for 3,4-enhanced (up to 62%) isoprene polymerization when 500 equivalent MAOs were utilized as co-catalysts, delivering the corresponding high-performance polyisoprenes. Furthermore, optimization via single factor and response surface method, it was observed that the highest activity was obtained by complex Fe 2 with 4.0889 × 10⁷ g·mol(Fe)⁻¹·h⁻¹ under the following conditions: Al/Fe = 683; IP/Fe = 7095; t = 0.52 min. Full article

A family of dinuclear iron (II) compounds with iminopyridine-based ligands displays selective cytotoxic activity against cancer cell lines. All compounds have IC₅₀ values 2–6 fold lower than that of cisplatin, and 30–90 fold lower than that of carboplatin for the tumor cell lines assayed. Comparing the IC₅₀ values between tumor and non-tumor cell lines, the selectivity indexes range from 3.2 to 34, compound 10, [Fe₂(4)₂(CH₃CN)₄](BF₄)₄, showing the highest selectivity. Those compounds carrying substituents on the iminopyridine ring show the same cytotoxicity as those without substituents. However, the electronic effects of the substituents on position 6 may be important for the cytotoxicity of the complexes, and consequently for their selectivity. All compounds act over DNA, promoting cuts on both strands in the presence of reactive oxygen species. Since compound 10 presented the highest selectivity, its cytotoxic effect was further characterized. It induces apoptosis, affects cell cycle phase distribution in a cell-dependent manner, and its cytotoxic effect is linked to reactive oxygen species generation. In addition, it decreases tumor cell migration, showing potential antimetastatic effects. These properties make compound 10 a good lead antitumor agent among all compounds studied here. Full article

Chain-end functionalized polymers play an important role in the field of building complex macromolecular structures. In this study, we have synthesized and characterized four dibenzhydryl iminopyridine Ni(II) complexes bearing remote flexible substituents (Et and n-Bu) to provide hyperbranched ethylene oligomers in ethylene oligomerization with moderate to good activities. Most notably, toluene-end-functionalized hyperbranched ethylene oligomers were obtained under elevated temperature conditions and validated by NMR. The tandem catalysis of ethylene oligomerization and the subsequent Friedel–Crafts addition of the resulting unsaturated products to toluene molecules was proposed as the cause of the observed phenomenon. Full article

Biofilm formation is a critical health concern, involved in most human bacterial infections. Combatting this mechanism, which increases resistance to traditional antibiotics and host immune defences, requires novel therapeutic approaches. The remarkable biocide activity and the monodispersity of carbosilane metallodendrimers make them excellent platforms to evaluate the impact of different structural parameters on the biological activity. In this work, we explore the influence of iminopyridine ring substituents on the antibacterial activity against planktonic and biofilm Staphylococcus aureus. New families of first-generation Ru(II) and Cu(II) metallodendrimers were synthesised and analysed, in comparison to the non-substituted counterparts. The results showed that the presence of methyl or methoxy groups in meta position to the imine bond decreased the overall positive charge on the metal ion and, subsequently, the activity against planktonic bacteria. However, it seemed a relevant parameter to consider for the prevention of biofilm formation, if they contribute to increasing the overall lipophilicity. An optimum balance of the charge and lipophilicity of the metallodrug, accomplished through structural design, will provide effective biocide agents against bacteria biofilms. Full article

Nickel-based ethylene polymerization catalysts have unique features, being able to produce macromolecules with a variable content of branches, resulting in polymers ranging from semicrystalline plastics to elastomers to hyperbranched amorphous waxes and oils. In addition to Brookhart’s α-diimine catalysts, iminopyridine Ni(II) complexes are among the most investigated systems. We report that Ni(II) complexes bearing aryliminopyridine ligands with bulky substituents both at the imino moiety and in the 6-position of pyridine afford either hyperbranched low molecular weight polyethylene oils or prevailingly linear crystalline polyethylenes or both, depending on the ligand structure and the reaction conditions. The formation of multiple active species in situ is suggested by analysis of the post-polymerization catalyst residues, showing the partial reduction of the imino function. Some related arylaminopyridine Ni(II) complexes were also synthesized and tested, showing a peculiar behavior, i.e., the number of branches of the produced polyethylenes increases while ethylene pressure increases. Full article

A series of 6-arylimino-2-(2-(1-phenylethyl)naphthalen-1-yl)iminopyridines and their iron(II) and cobalt(II) complexes (Fe1–Fe5, Co1–Co5) were synthesized and routinely characterized as were Co3 and Co5 complexes, studied by single crystal X-ray crystallography, which individually displayed a distorted square pyramidal or trigonal bipyramid around a cobalt center. Upon treatment with either methyluminoxane (MAO) or modified methyluminoxane (MMAO), all complexes displayed high activities regarding ethylene polymerization even at an elevated temperature, enhancing the thermostability of the active species. In general, iron precatalysts showed higher activities than their cobalt analogs; for example, 10.9 × 10⁶ g(PE) mol⁻¹ (Co) h⁻¹ by Co4 and 17.0 × 10⁶ g(PE) mol⁻¹ (Fe) h⁻¹ by Fe4. Bulkier substituents are favored for increasing the molecular weights of the resultant polyethylenes, such as 25.6 kg mol⁻¹ obtained by Co3 and 297 kg mol⁻¹ obtained by Fe3. A narrow polydispersity of polyethylenes was observed by iron precatalysts activated by MMAO, indicating a single-site active species formed. Full article

A series of vanadium complexes bearing iminopyridine bidentate ligands with various electronic and steric properties: V1 [CH₂Ph], V2 [CMe₂CH₂CMe₃], V3 [Ph] and V4 [2,6-ⁱPr₂Ph] were prepared and characterized by IR spectroscopy and microanalytical analysis. The catalytic capacity of all the complexes has been investigated for isoprene polymerization and was controlled by tuning the ligand structure with different N-alkyl and N-aryl groups. Activated by methylaluminoxane (MAO), the aryl-substituted complex V3 [Ph] exhibited high cis-1,4 selectivity (75%), and the resultant polymers had high molecular weights (M_n = 6.6 × 10⁴) and narrow molecular weight distributions (PDI = 2.3). This catalyst showed high activity up to 734.4 kg polymer (mol V)⁻¹ h⁻¹ with excellent thermostability even stable at 70 °C. Compared to the traditional VCl₃/MAO catalytic system, iminopyridine-supported V(III) catalysts displayed higher catalytic activities and changed the selectivity of monomer enchainment from trans-1,4 to cis-1,4. Full article

A series of iminopyridine complexes of Fe(II) and Co(II) complexes bearing fluorinated aryl substituents were synthesized for the polymerization of isoprene. The structures of complexes 3a, 2b and 3b were determined by X-ray diffraction analysis. Complex 3a contained two iminopyridine ligands coordinated to the iron metal center forming an octahedral geometry, whereas 2b adopted a chloro-bridged dimer, and 3b featured with two patterns of cobalt centers bridged via chlorine atoms. Complexes 2b and 3b represented rare examples of chlorine bridged bimetallic Co(II) complexes. The fluorine substituents effects, particularly on catalytic activity and polymer properties such as molecular weight and regio-/stereo-selectivity were investigated when these complexes were employed for isoprene polymerization. Among the Fe(II)/methylaluminoxane (MAO) systems, the 4-CF₃ substituted iminopyridine Fe(II) complex 1a was found as a highly active isoprene polymerization catalyst exhibiting the highest activity of 10⁶ g·(mol of Fe)⁻¹·h⁻¹. The resultant polymer displayed lower molecular weight (M_n = 3.5 × 10⁴ g/mol) and moderate polydispersity index (PDI = 2.1). Furthermore, the ratio of cis-1,4-/3,4 was not affected by the F substituents. In the series of Co(II)/AlEt₂Cl binary systems, complexes containing electron-withdrawing N-aryl substituents (R = 4-CF₃, 2,6-2F) afforded higher molecular weights polyisoprene than that was obtained by the complex containing electron-donating N-alkyl substituents (R = octyl). However, ternary components system, complex/MAO/[Ph₃C][B(C₆F₅)₄] resulted in low molecular weight polyisoprene (M_n < 2000) with high trans-1,4-unit (>95%). Full article

A series of alkyl- and aryl-substituted iminopyridine Fe(II) complexes 1a–7a and Co(II) complexes 2b, 3b, 5b, and 6b were synthesized. The activator effect, influence of temperature, and, particularly, the alkyl and aryl substituents’ effect on catalytic activity, polymer molecular weight, and regio-/stereoselectivity were investigated when these complexes were applied in isoprene polymerization. All of the Fe(II) complexes afforded polyisoprene with high molecular weight and moderate cis-1,4 selectivity. In contrast, the Co(II) complexes produced polymers with low molecular weight and relatively high cis-1,4 selectivity. In the iminopyridine Fe(II) system, the alkyl and aryl substituents’ effect exhibits significant variation on the isoprene polymerization. In the iminopyridine Co(II) system, there is little influence observed on isoprene polymerization by alkyl and aryl substituents. Full article