Synthesis, structure, and DNA-binding properties of manganese(II) and zinc(II) complexes with tris(N-methylbenzimidazol-2-ylmethyl)amine ligand

Interactions of Mn complexes with DNA: the relevance of therapeutic applications towards cancer treatment

Manganese (Mn) is one of the most significant bio-metals that helps the body to form connective tissue, bones, blood clotting factors, and sex hormones. It is necessary for fat and carbohydrate metabolism, calcium absorption, blood sugar regulation, and normal brain and nerve functions. It accelerates the synthesis of proteins, vitamin C, and vitamin B. It is also involved in the catalysis of hematopoiesis, regulation of the endocrine level, and improvement of immune function. Again, Mn metalloenzymes like arginase, glutamine synthetase, phosphoenolpyruvate decarboxylase, and Mn superoxide dismutase (MnSOD) contribute to the metabolism processes and reduce oxidative stress against free radicals. Recent investigations have revealed that synthetic Mn-complexes act as antibacterial and antifungal agents. As a result, chemists and biologists have been actively involved in developing Mn-based drugs for the treatment of various diseases including cancer. Therefore, any therapeutic drugs based on manganese complexes would be invaluable for the treatment of cancer/infectious diseases and could be a better substitute for cisplatin and other related platinum based chemotherapeutic drugs. From this perspective, attempts have been made to discuss the interactions and nuclease activities of Mn(II/III/IV) complexes with DNA through which one can evaluate their therapeutic applications.

Role of Gemini Surfactants with Variable Spacers and SiO2 Nanoparticles in ct-DNA Compaction and Applications toward In Vitro/In Vivo Gene Delivery

Compaction of calf thymus DNA (ct-DNA) by two cationic gemini surfactants, 12-4-12 and 12-8-12, in the absence and presence of negatively charged SiO₂ nanoparticles (NPs) (∼100 nm) has been explored using various techniques. 12-8-12 having a longer hydrophobic spacer induces a greater extent of ct-DNA compaction than 12-4-12, which becomes more efficient with SiO₂ NPs. While 50% ct-DNA compaction in the presence of SiO₂ NPs occurs at ∼77 nM of 12-8-12 and ∼130 nM of 12-4-12, but a conventional counterpart surfactant, DTAB, does it at its concentration as high as ∼7 μM. Time-resolved fluorescence anisotropy measurements show changes in the rotational dynamics of a fluorescent probe, DAPI, and helix segments in the condensed DNA. Fluorescence lifetime data and ethidium bromide exclusion assays reveal the binding sites of surfactants to ct-DNA. 12-8-12 with SiO₂ NPs has shown the highest cell viability (≥90%) and least cell death in the human embryonic kidney (HEK) 293 cell lines in contrast to the cell viability of ≤80% for DTAB. These results show that 12-8-12 with SiO₂ NPs has the highest time and dose-dependent cytotoxicity compared to 12-8-12 and 12-4-12 in the murine breast cancer 4T1 cell line. Fluorescence microscopy and flow cytometry are performed for in vitro cellular uptake of YOYO-1-labeled ct-DNA with surfactants and SiO₂ NPs using 4T1 cells after 3 and 6 h incubations. The in vivo tumor accumulation studies are carried out using a real-time in vivo imaging system after intravenous injection of the samples into 4T1 tumor-bearing mice. 12-8-12 with SiO₂ has delivered the highest amount of ct-DNA in cells and tumors in a time-dependent manner. Thus, the application of a gemini surfactant with a hydrophobic spacer and SiO₂ NPs in compacting and delivering ct-DNA to the tumor is proven, warranting its further exploration in nucleic acid therapy for cancer treatment.

Design, synthesis, structural, spectral, and redox properties and phenoxazinone synthase activity of tripodal pentacoordinate Mn(II) complexes with impressive turnover numbers

Catechol oxidase (CO) and phenoxazinone synthase (PHS) are two enzymes of immense significance due to their capability to oxidize catechols and o-aminophenols to o-quinones and phenoxazinones, respectively. In this connection two mononuclear manganese complexes with the molecular framework [Mn^II(Ln)Cl]Cl {L1: tris((1H-benzo[d]imidazol-2-yl)methyl)amine; n = 1 and L2: tris(N-methylbenzimidazol-2-ylmethyl)amine; n = 2} have been designed to be potential catalysts for OAPH (o-aminophenol) oxidation. Both the ligands and their corresponding metal complexes have been successfully synthesized and thoroughly characterized by different spectroscopic and analytical techniques such as FT-IR, ¹H NMR, UV-vis spectroscopy, EPR spectroscopy and ESI mass spectroscopy. The molecular structures of [Mn^II(L1)Cl]Cl (1) and [Mn^II(L2)Cl]Cl (2) have been revealed by a single-crystal X-ray diffraction study. The spectral properties and redox behaviour of both the complexes were examined. Under ambient conditions, 1 and 2 show excellent phenoxazinone synthase activity as both are very susceptible to oxidize o-aminophenol to phenoxazinone. The kinetic parameters for both complexes have been determined by analyzing the experimental spectroscopic data. The turnover numbers (k_cat value) of these two complexes are extremely high, 440 h^-1 and 234 h^-1 for 1 and 2, respectively. The present report offers a thorough overview of information involving the role of the metal ions and their extent of phenoxazinone synthase mimicking activity. The oxidation of o-aminophenol to 2-amino-3H-phenoxazine-3-one (APX) by catalytic oxidation of oxygen (O₂) by the reaction with transition metal complexes has been an important study for the last few decades. The current study evidently showed better performance of our synthesized Mn(II) complexes than all the predecessors. The plausible mechanism has been reiterated based on the experimental data via ESI-MS spectra and considering the concepts from the previously reported mechanisms involved in the formation of hydrogen peroxide (H₂O₂) as an intermediate substrate is fairly indicating the involvement of molecular oxygen in the catalytic cycle.

Selenium nanoparticles synthesized in aqueous extract of Allium sativum perturbs the structural integrity of Calf thymus DNA through intercalation and groove binding

Biomedical application of selenium nanoparticles (SeNPs) demands the eco-friendly composite for synthesis of SeNPs. The present study reports an aqueous extract of Allium sativum (AqEAS) plug-up the current need. Modern spectroscopic, microscopic and gravimetric techniques were employed to characterize the synthesized nanoparticles. Characterization studies revealed the formation of crystalline spherical shaped SeNPs. FTIR spectrum brings out the presence of different functional groups in AqEAS, which influence the SeNPs formation and stabilization. Furthermore the different aspects of the interaction between SeNPs and CT-DNA were scrutinized by various spectroscopic and cyclic voltametric studies. The results reveals the intercalation and groove binding mode of interaction of SeNPs with stacked base pair of CT-DNA. The Stern-Volmer quenching constant (K_SV) were found to be 7.02×10⁶M-¹ (ethidium bromide), 4.22×10⁶ M-¹ (acridine orange) and 7.6×10⁶M-¹ (Hoechst) indicating strong binding of SeNPs with CT-DNA. The SeNPs - CT-DNA interactions were directly visualized by atomic force microscopy. The present study unveils the cost effective, innocuous, highly stable SeNPs intricate mechanism of DNA interaction, which will be a milestone in DNA targeted chemotherapy.

Synthesis and Structure of a Penta- and Hexa-Coordinated Tri-Nuclear Cobalt(II) Complex

The tri-nuclear cobalt(II) complex, [(CoL)2(μ-OAc)2Co]·2CHCl3 (H2L = 5,5'-dimethoxy-2,2'-[(ethylene)dioxybis(nitrilome thylidyne)]diphenol), has been synthesised. Its X-ray structure shows it to contain two acetate ions coordinating to the three cobalt(II) atoms through Co–O–C–O–Co bridges, and four μ-phenoxo-oxygen atoms from two [CoL] chelates also coordinating to the central cobalt(II) atom. The complex possesses two penta- and one hexa-coordinated cobalt atoms. The crystal packing of the CoII complex shows that a 2D-layer supramolecular network parallel to the ab-plane is formed through intermolecular C–H···O and C–H···Cl hydrogen bonding interactions.

Synthesis, Crystal Structure, and Spectra Properties of the Cadmium (II) Complex with Bis(N-allylbenzimidazol-2-ylmethyl)benzylamine

A novel complex of cadmium (II) picrate (pic) with V-shaped ligand bis(N-allylbenzimidazol-2-ylmethyl)benzylamine (babb), with composition [Cd(babb)₂](pic)₂, was synthesized and characterized by elemental analyses and electrical conductivity, IR, and UV/visible spectra. The crystal structure of the complex has been determined by the single-crystal X-ray diffraction. In the complex, the coordination sphere around Cd (II) is distorted octahedral, six nitrogen atoms involved in coordination afforded by two tridentate ligand babb. Moreover, The DNA-binding properties of the ligand babb and Cd (II) complex were investigated by spectrophotometric methods and viscosity measurements, and the results suggest that they bind to DNA via an intercalation binding mode, and the Cd (II) complex shows higher affinity than the ligand.