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In recent years, the global perspective of small molecule activation has directed the focus towards biomimetic oxidations. Phenoxazinone synthase and catechol oxidase, two vital metalloenzymes, have drawn the attention of the scientific community towards their catalytic performances. Different transition metal-based complexes have been investigated to mimic their activities, yet many factors related to their mechanistic aspects and structure-activity relationship still lack detailed investigation. To get better insights into these factors, two penta-coordinated cis-dichloro and dibromo Cu(ii) complexes [Cu(L)Cl-2] 1 and [Cu(L)Br-2] 2 (where L = N,N-dimethyl-4,6-di(pyridin-2-yl)-1,3,5-triazin-2-amine) were synthesized and comprehensively characterized through various spectroscopic and analytical tools such as UV-vis, FT-IR, NMR, EPR and ESI-MS. The redox behaviour of ligands as well as both the copper complexes were analysed. The molecular structure of 1 and 2 was elucidated via single-crystal X-ray diffraction analysis and a distorted square pyramidal geometry was determined. The halogen atoms (Cl for 1 and Br for 2) are found to be coordinated in a cis fashion for better substrate attachment. Catalytic performances towards the oxidation of o-aminophenol (OAPH) and 3,5-di-tert-butylcatechol (3,5-DTBC) were investigated using UV-vis spectrophotometry. Significant kinetic parameters towards the catalytic activities for 1 and 2 were determined. In terms of OAPH oxidation ability, both complexes were found to be quite comparable, with 2 having greater catalytic performance (K-cat = 156.7 h(-1)) than 1 (K-cat = 124.5 h(-1)). However, 2 shows remarkably superior activity for 3,5-DTBC oxidation (K-cat = 367.8 h(-1), similar to 4.5 times) than 1 (K-cat = 82.2 h(-1)). The mass spectrometric investigation provides information about the probable mechanistic path towards the oxidation of both the substrates. Iodometric titration experiments were performed to identify H2O2 forma

The activation of molecular oxygen remains a persistent challenge to the scientific community owing to its poor selectivity, especially towards organic substrates. In biological systems, phenoxazinone synthase and catechol oxidase are two copper-based metalloenzymes that have been extensively studied because of their catalytic properties in the formation of a phenoxazinone core and quinones, which subsequently produce value-added compounds. Inspired by the design of a native catechol oxidase metalloenzyme, two copper(ii) complexes (1 and 2) with dipicolylamine (DPA)-derived tridentate ligands L1 (4-methyl-N,N-bis(pyridin-2-ylmethyl)aniline) and L2 (2,4,6-trimethyl-N,N-bis(pyridin-2-ylmethyl)aniline) are synthesized. The tridentate ligands provided similar environmental facilities for attachment with three histidine moieties found in nature and our goal is to understand their biomimicking activity. On the amine nitrogen center, basicity is varied by systematic substitutions via methyl groups, thus affecting the bond strength of the apical chloride atom, which results in increased lability. The ligands were thoroughly characterized using different spectroscopic methods, i.e., FT-IR, H-1 NMR, UV-vis spectroscopy, and ESI mass spectrometry. The molecular structures of 1 and 2 were elucidated using single-crystal X-ray diffraction, which confirms their distorted square pyramidal geometries with two distinct chlorines attached in a cis fashion. The investigation of their catalytic abilities was performed under ambient aerobic conditions in methanol with both o-aminophenol and 3,5-ditertbutyl catechol, which provided kinetic values that correlated with their structural modifications. Toluene-appended 1 (k(cat) 525 h(-1) for o-aminophenol and 612 h(-1) for 3,5-ditertbutyl catechol) showed almost twice the activities of mesitylene-derived 2 (k(cat) 255 h(-1) for o-aminophenol and 343 h(-1) for 3,5-ditertbutyl catechol). Mass spectroscopy supported their probable mechanisms f

DNA being the necessary element in cell regeneration, controlled cellular apoptosis via DNA binding/cleaving is considered an approach to combat cancer cells. The widely prescribed metallodrug cisplatin has shown interactions with the guanine-N7 center, and a plethora of complexes are continually developed to enhance crosslinking properties as well as covalent and non-covalent interactions. Two pentadentate ligands, L1 (1-(6-(1H-benzo[d]imidazol-2-yl)pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine) and L2 (1-(6-(1-methyl-1H-benzo[d]imidazol-2-yl)pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine), were synthesized together with their respective copper(ii) complexes [1](ClO4)(2) and [2](ClO4)(2), which crystallized in a trigonal bipyramidal fashion. Different analytical and spectroscopic methods confirmed their formation, and their redox behaviour was also examined. The interactions of salmon sperm DNA (ss-DNA) with these two complexes were explored using absorbance spectroscopy, and they both exhibited a binding affinity (K-b) of similar to 10(4) M-1. Fluorescence quenching experiments with ethidium bromide (EB)-bound DNA (EB-DNA) were also performed, and Stern-Volmer constant (K-SV) values of 6.93 x 10(3) and 2.34 x 10(4) M-1 for [1](ClO4)(2) and [2](ClO4)(2), respectively, were obtained. Furthermore, DNA conformational changes due to the interactions of both complexes were validated via circular dichroism. We also assessed the DNA cleavage property of these complexes, which resulted in the linearization of circular plasmid DNA. This finding was supported by studying the growth of MDA-MB-231 breast cancer cells upon treatment with both Cu(ii) complexes; IC50 values of 5.34 +/- 1.02 mu M and 0.83 +/- 0.18 mu M were obtained for [1](ClO4)(2) and [2](ClO4)(2), respectively. This validates their affinity towards DNA, and these insights can be further utilized for non-platinum based economical metallodrug development based on first row transition metals.

Phenoxazinone synthase (PHS) is a pentanuclear copper enzyme studied for the last two decades, and though both manganese and copper complexes have been explored extensively, there are only a handful of reports on cobalt mononuclear moieties. In this regard, we have successfully synthesized two cis dichloro cobalt(ii) mononuclear complexes Co(bpy)2Cl2:[1] and Co(L1)2Cl2:[2] with polypyridyl ligands (where bpy = 2,2?-bipyridine, L1 = 2,2?-(1-methyl-1H-1,2,4-triazole-3,5-diyl)dipyridine) and thoroughly characterized them by different spectroscopic and analytical techniques such as FT-IR, 1H NMR, UV-vis spectroscopy and ESI mass spectra. The molecular structures of [1] and [2] are elucidated by single-crystal X-ray diffraction studies. Spectral properties and redox behaviour for both the complexes are examined. The complexes show phenoxazinone synthase activity under ambient conditions and thorough examination of the acquired spectroscopic data imply excellent reactivity for both. Kinetic parameters for both t...

Phenoxazinone synthase (PHS) is a pentanuclear copper enzyme studied for the last two decades, and though both manganese and copper complexes have been explored extensively, there are only a handful of reports on cobalt mononuclear moieties. In this regard, we have successfully synthesized two cis dichloro cobalt(ii) mononuclear complexes Co(bpy)2Cl2:[1] and Co(L1)2Cl2:[2] with polypyridyl ligands (where bpy = 2,2′-bipyridine, L1 = 2,2′-(1-methyl-1H-1,2,4-triazole-3,5-diyl)dipyridine) and thoroughly characterized them by different spectroscopic and analytical techniques such as FT-IR, 1H NMR, UV-vis spectroscopy and ESI mass spectra. The molecular structures of [1] and [2] are elucidated by single-crystal X-ray diffraction studies. Spectral properties and redox behaviour for both the complexes are examined. The complexes show phenoxazinone synthase activity under ambient conditions and thorough examination of the acquired spectroscopic data imply excellent reactivity for both. Kinetic parameters for both the complexes are evaluated and the turnover numbers (kcat value) of these two complexes are 201.24 h-1 and 249.57 h-1 for [1] and [2], respectively, which are quite high compared to those of previously reported similar complexes. The possible mechanistic route is also established with the help of mass spectroscopy and titrimetric analysis is performed to detect hydrogen peroxide that is a key intermediate formed in the catalysis and thus to prove the involvement of molecular oxygen in the oxidation. This report offers an in-depth summary of metal ion involvement and the extent of the phenoxazinone synthase activity. This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.