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Twelve Re(I) tricarbonyl diimine (2,2′-bipyridine and 1,10-phenanthroline) complexes with thiotetrazolato ligands have been synthesised and fully characterised. Structural characterisation revealed the capacity of the tetrazolato ligand to bind to the Re(I) centre through either the S atom or the N atom with crystallography revealing most complexes being bound to the N atom. However, an example where the Re(I) centre is linked via the S atom has been identified. In solution, the complexes exist as an equilibrating mixture of linkage isomers, as suggested by comparison of their NMR spectra at room temperature and 373 K, as well as 2D exchange spectroscopy. The complexes are photoluminescent in fluid solution at room temperature, with emission either at 625 or 640 nm from the metal-to-ligand charge transfer excited states of triplet multiplicity, which seems to be exclusively dependent on the nature of the diimine ligand. The oxygen-sensitive excited state lifetime decay ranges between 12.5 and 27.5 ns for the complexes bound to 2,2′-bipyrdine, or between 130.6 and 155.2 ns for those bound to 1.10-phenanthroline. Quantum yields were measured within 0.4 and 1.5%. The complexes were incubated with human lung (A549), brain (T98g), and breast (MDA-MB-231) cancer cells, as well as with normal human skin fibroblasts (HFF-1), revealing low to moderate cytotoxicity, which for some compounds exceeded that of a standard anti-cancer drug, cisplatin. Low cytotoxicity combined with significant cellular uptake and photoluminescence properties provides potential for their use as cellular imaging agents. Furthermore, the complexes were assessed in disc diffusion and broth microdilution assays against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Escherichia coli (E. coli), and Pseudomonas aeruginosa (P. aeruginosa) bacterial strains, which revealed negligible antibacterial activity in the dark or after irradiation. Show less

Two Zn(ii) complexes based on tetrazol were prepared. Nanoparticles of the complexes can inhibit the proliferation of cancer cells in vitro. This work provided a strategy on designing anticancer materials based on coordination complexes. Show less

Carcinoma, characterized by abnormal growth of cells and tissue, is a ubiquitously leading cause of mortality across the globe due to some carcinogenic factors. Currently, several anticancer agents are commercially available in the global market. However, due to their resistance and cost, researchers are gaining more interest in developing newer novel potential anticancer agents. In the search for new drugs for clinical use, the tetrazole ring system has emerged as an exciting prospect in the optimization studies of promising lead molecules. Among the various heterocyclic agents, tetrazole-containing compounds have shown significant promise in the treatment of a wide range of diseases, particularly cancer. Here, in this review, we focused on several synthetic approaches for the synthesis of tetrazole analogs, their targets for treating cancer along with the biological activity of some of the recently reported tetrazole-containing anticancer agents. Show less

Two Cu(II) compounds based on tetrazole-carboxylate ligands, [Cu(phtza)₂(H₂O)₂]∙3H₂O (1) and [Cu(atzipa)₂]∙2H₂O (2) (phtza = 2,2'-(5,5'-(1,3-phenylene)bis(2H-tetrazole-5,2-diyl))diacetate, atzipa = 3-(5-amino-1H-tetrazol-1-yl)isopropanoic anion), were designed and synthesized by hydrothermal reactions. The X-ray diffraction results show that the two compounds show two-dimensional (2D) layer structures. Nanoprecipitation with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)_-2000] (DSPE-PEG_-2000) contributes to the formation of the nanoparticles (NPs) with excellent water dispersity. In vitro study indicates that the two NPs exert considerable cytotoxicity toward human hepatocellular carcinoma cells (HepG2 and Huh7) with low half-maximal inhibitory concentration (IC₅₀). However, the cytotoxicity of such NPs is negligible in normal cells (HL-7702). The cytotoxicity of these NPs was also investigated by the flow cytometry and Calcein-AM/PI (live/dead) co-stained experiments. The results promise the great potential of these NPs for chemodynamic therapy against cancer cells. Show less

Platinum anticancer drugs inhibit the division of cancer cells through a DNA binding mechanism. The bimetallic platinum compounds have a possibility for blocking DNA replication via the cross-linking of DNA functional groups at different distances. Many compounds with metals of the platinum group have been tested for possible antitumor activity. The main target of their biological action is a DNA molecule. A combined approach to the study of the interaction of DNA with biologically active compounds of this type is proposed. The capabilities of various methods (hydrodynamic, spectral, microscopy) in obtaining information on the type of binding of coordination compounds to DNA are compared. The analysis of DNA binding with platinum binuclear compounds containing pyrazine, tetrazole, 5- methyltetrazole, 3-propanediamine as bridging ligands in a solution was carried out with the methods of circular dichroism (CD), luminescent spectroscopy (LS), low gradient viscometry (LGV), flow birefringence (FB) and atomic force microscopy (AFM). The competitive binding of different platinum compounds to DNA and the analysis of platinum attachment to DNA after protonation of its nitrogen bases simply indicates the involvement of N7 guanine in binding. Fluorescent dye DAPI was also used to recognize the location of platinum compounds in DNA grooves. DNA conformational changes recorded by variations in persistent length, polyelectrolyte swelling, DNA secondary structure, and its stability clarify the molecular mechanism of the biological activity of platinum compounds. Show less

AbstractWell‐defined copolymers containing luminescent iridium and hybrid iridium/rhenium fragments are prepared utilizing parent poly(n‐butyl acrylamide‐co‐N‐(1H‐tetrazol‐5‐yl) acrylamide) as macromolecular chelating species. The parent (co)polymers are prepared via the modification of a precursor poly(pentafluorophenyl acrylate) (polyPFPA) homopolymer, prepared by reversible addition‐fragmentation chain transfer polymerization, with n‐butylamine and 5‐aminotetrazole. Reaction of the parent copolymers with [Ir2(ppy)4(μ−Cl2)] (ppy = 2‐phenylpyridine) yields modified copolymers containing the Ir(ppy)2 fragment as a pendent group. Attachment of the Ir species is confirmed by a combination of photophysical studies, UV–Vis spectroscopy, and visually under irradiation with UV light. Importantly, it is demonstrated that the chelation of the Ir(ppy)2 fragment to a polymeric scaffold does not impact the fundamental photophysical properties of the Ir species. Attachment of a second luminescent metal species, Re(CO)3(phen) (phen = 1,10‐phenanthroline), gives hybrid materials containing Re(I) and Ir(III). The photophysical properties of these hybrid materials are consistent with the presence of both metal species and indicate the occurrence of energy transfer phenomena from the polymer‐bound Ir to Re metal centers. Finally, it is demonstrated that the Ir modified polymers and the Ir/Re hybrid materials offer potential in tissue imaging applications with scope to tune both luminescent properties and biological specificity as evidenced from preliminary brain tissue staining experiments. Show less

Transition metal coordination complexes have provided cancer treatment with new insights to overcome the limitations of current chemotherapeutic agents. Utilization of bifunctional tetrazole–carboxylate ligands with Zn(II) obtained two self-assembled complexes [Zn(HL1)(bipy)3/2(H2O)]·CH3OH·4(H2O) (1) (H3L1 = 1,3,5-tri(2-carboxymethyltetrazol-5-yl) benzene) and [Zn(L2)2(H2O)2]2·2H2O (2) (HL2 = (5-pyridin-3-yl-tetrazol-2-yl)-acetic acid). The X-ray diffraction results showed that the two complexes displayed a two-dimensional (2D) layer structure and a one-dimensional (1D) layer structure. Nanocoprecipitation with DSPE-PEG-2000 resulted in the formation of complex nanoparticles (NPS) with excellent water dispersion. In vitro CCK-8 assay indicated the two NPs exert high cytotoxicity and sensitivity and a low half-maximum inhibitory concentration (IC50) towards HeLa than HepG2 cells. In addition, the cytotoxicity was also confirmed by live/dead co-stained experiments. The presented experimental results showed the 1 and 2 NPs were capable of inhibiting cell proliferation in vitro and may help design coordination complex-based anticancer candidates for cancer cells. Show less

Abstract As a kind of multifunctional materials with high porosity, tunable pore structure and easy functionalization, coordination complexes have been widely used in various fields. Here, three complexes were prepared by self‐assembly with Co(II) ions using tetrazolylacetic acids as ligands, 2,2′,2′′‐(benzene‐1,3,5‐triyltris(2 H ‐tetrazole‐5,2‐diyl)) triacetic acid (H 3 tzpha), 2‐(5‐(pyrazin‐2‐yl)‐2 H ‐tetrazol‐2‐yl) propanoic acid (Hpztzma) and 2‐(5‐(pyridin‐2‐yl)‐2 H ‐tetrazol‐2‐yl) acetic acid (Hpytza), and were characterized by X‐ray crystallography. These complexes can also self‐assemble into nanoparticles (NPs) in aqueous solution by nanocoprecipitation. In vitro CCK‐8 assay on three kind of human cancer cells (HeLa, HepG2 and Huh7) cells showed these Co(II) complexes have the best cytotoxicity against HeLa cells. And complex 1 had a half maximal inhibitory concentration (IC 50 value) of 14.8 μg mL −1 , which was superior to 16.5 μg mL −1 and 15.2 μg mL −1 of complex 2 and 3 . In addition, the effect of different ligands on cancer cell ablation was explored. The results showed the three NPs can effectively inhibit the proliferation of cancer cells in vitro and provided a strategy on designing highly efficient anticancer materials based on coordination complexes. Show less

In this work, three iridium(III) tetrazolato complexes have been designed and successfully synthesized. Beside photophysical properties, their performances in protein staining have been comprehensively investigated in this work for the first time. Notably, these iridium(III) tetrazolato complexes with high quantum efficiency exhibited much better protein staining properties than the commercial agent Coomassie Brilliant Blue (CBB) under the same experimental conditions, which may pave the way to explore new efficient iridium-based protein staining agents both for commercial markets and academic research in the future. Show less

Abstract Novel platinum(II) and palladium(II) chlorido complexes with tetrazole derivatives 1-(2-hydroxyethyl)tetrazole (het) and 1-[tris(hydroxymethyl)methyl]tetrazole (thm), viz. cis-[Pt(het)2Cl2], trans-[Pt(het)2Cl2], trans-[Pt(thm)2Cl2], trans-[Pd(het)2Cl2], and trans-[Pd(thm)2Cl2], were synthesized. The compounds were characterized by elemental and high-resolution electrospray ionization (HRESI) mass spectrometry, high-performance liquid chromatography (HPLC), 1H, 13C and 195Pt nuclear magnetic resonance (NMR) spectroscopy, thermal analyses, and Infrared (IR) spectroscopy. Molecular and crystal structures of trans-[PdL2Cl2] and trans-[PtL2Cl2] (L = het, thm) were established by single-crystal X-ray analysis. The complex cis-[Pt(het)2Cl2] was found to undergo cis–to–trans isomerization upon heating in acetonitrile solution and in the solid state. The synthesized complexes show rather high water solubility lying in the range of 2–10 mg/L. Show less

The review summarizes the advances in medicinal chemistry of tetrazole biologically active compounds and drugs over the past 15 years. Most of the considered compounds are at present actively studied, are in various stages of clinical trials, or have recently been approved for use as pharmaceuticals. Show less

Two new arene ruthenium(II) complexes with chemical formula [Ru2(η6‐p‐cymene)2(μ‐L1)(μ‐Cl)Cl2][Ru]‐1and [Ru(η6‐p‐cymene)(L2)Cl2][Ru]‐2(L1 =5‐phenyl‐2H‐tetrazole andL2= 2‐(2H‐tetrazol‐5‐yl)pyridine) were synthesized by the reaction of [{(η6‐p‐cymene)RuCl2}2] with two bidentate ligands L1 and L2. Both the complexes were structurally characterized using single‐crystal X‐ray diffraction and other analytical techniques. The X‐ray crystal structures of both the complexes revealed the coordination of tetrazolate ligands to two Ru(II) centres in bridging mode in[Ru]‐1, whereas one Ru(II) centre in[Ru]‐2in chelating fashion, with overall pseudo‐octahedral geometry. The resulted complexes were screened for their cytotoxic activity against three different cancer cell lines, HCT116 (colon cancer), HepG2 (liver cancer) and MCF7 (breast cancer) under in vitro conditions. Interestingly,[Ru]‐1showed much higher cytotoxicity with respect to[Ru]‐2against all the screened cancer cell lines and even better than cisplatin. For exploring the mechanism of action of[Ru]‐1, reactive oxygen species (ROS) production, alterations in mitochondrial membrane potential and gene expression profiling of apoptosis related genes (Bcl2, caspase‐3 and caspase‐9) were also evaluated. The cancerous cells treated with[Ru]‐1showed an increase in intracellular ROS levels, disruption of mitochondrial membrane potential, up‐regulation of proapoptotic caspase‐3 and caspase‐9 and down‐regulation of antiapoptotic Bcl2. The results concluded that[Ru]‐1induced apoptosis through oxidative stress mediated activation of intrinsic pathway by generating intracellular ROS, loss of MMP and alteration of expression of apoptosis related genes. In addition, antimetastatic activity of[Ru]‐1was observed by wound healing assay showing anti‐migratory property. The dual properties, antimetastatic activity and high cytotoxicity make[Ru]‐1potent platform for the development of new anticancer agents. Show less

Abstract A series of palladium(II) complexes with 1H- and 2H-tetrazole ligands (2-isopropyl-5-R-2H-tetrazoles and 1H-tetrazol-1-ylcarboxylic acids) was synthesized. Structure of the obtained compounds was confirmed by 1H and 13C NMR spectroscopy, high-resolution mass spectrometry, and single crystal X-ray diffraction analysis. According to the spectrophotometry data, the complexes are weakly bound to DNA. The cytotoxic activity of the obtained palladium complexes was studied in vitro. Show less

Ten manganese(I) tricarbonyl diimine complexes bound to variably functionalised 5‐aryl‐tetrazolato ligands were prepared, and their photochemical properties were investigated. Upon exposure to light at 365 nm, each complex decomposed to its free diimine and tetrazolato ligands, simultaneously dissociating three CO ligands, as evidenced by changes in the IR spectra of the irradiated complexes over time. The anti‐bacterial properties of one of these complexes were tested against Escherichia coli. While the complex displayed no effect on the bacterial growth in the dark, pre‐irradiated solutions inhibited bacterial growth. Comparative studies revealed that the antibacterial properties originate from the presence of free 1,10‐phenanthroline. Show less

Cancer is a leading cause of death worldwide. Even after the availability of numerous drugs and treatments in the market, scientists and researchers are focusing on new therapies because of their resistance and toxicity issues. The newly synthesized drug candidates are able to demonstrate in vitro activity but are unable to reach clinical trials due to their rapid metabolism and low bioavailability. Therefore there is an imperative requisite to expand novel anticancer negotiators with tremendous activity as well as in vivo efficacy. Tetrazole is a promising pharmacophore which is metabolically more stable and acts as a bioisosteric analogue for many functional groups. Tetrazole fragment is often castoff with other pharmacophores in the expansion of novel anticancer drugs. This is the first systematic review that emphasizes on contemporary strategies used for the inclusion of tetrazole moiety, mechanistic targets along with comprehensive structural activity relationship studies to provide perspective into the rational design of high-efficiency tetrazole-based anticancer drug candidates. Show less

Herein, we describe a new family of tris chelate homoleptic Ru (II) complexes, [Ru(N^N)3]2+, where the role of the diimine‐type ligands (N^N) was fulfilled by 2‐pyridyl (PTZ) or 2‐quinolyl tetrazole (QTZ) derivatives decorated with various alkyl substituents at the N‐2 position of the tetrazole ring. The new Ru (II) complexes with general formula [Ru (PTZ‐R)3]2+ and [Ru (QTZ‐R)3]2+, were obtained as mixtures of facial (fac) and meridional (mer) isomers, as suggested by NMR (1H, 13C) experiments, and confirmed in the case of mer‐[Ru (QTZ‐Me)3]2+, by X‐ray crystallography. The photophysical behavior of the tetrazole‐based [Ru(N^N)3]2+ type species was investigated by UV–vis absorption spectroscopy, providing trends typical of polypyridyl Ru (II) complexes. The new homoleptic complexes fac/mer‐[Ru (PTZ‐R)3]2+ and fac/mer‐[Ru (QTZ‐R)3]2+ have been assessed for any eventual antimicrobial activity towards two different bacteria such as Gram‐negative Escherichia coli and Gram‐positive Deinococcus radiodurans. Whereas being inactive toward E. coli, the response of agar disks diffusion tests suggested that some of the new fac/mer Ru (II) complexes could inhibit the growth of D. radiodurans. This effect was further investigated by determining the growth kinetics in liquid medium of D. radiodurans exposed to the fac/mer‐[Ru (PTZ‐R)3]2+ and fac/mer‐[Ru (QTZ‐R)3]2+ complexes at different concentrations. The outcome of these experiments highlighted that the turn‐on of the growth inhibitory effect took place as the linear hexyl chain was appended to the PTZ or QTZ scaffold, suggesting also how the inhibitory activity appeared more pronouncedly exerted by the facial isomers fac‐[Ru (PTZ‐Hex)3]2+ and fac‐[Ru (QTZ‐Hex)3]2+ (MIC = ca. 3.0 μg/ml) with respect to the corresponding meridional isomers (MIC = ca. 6.0 μg/ml). Show less

A rise in atmospheric carbon dioxide levels, following years of burning fossil fuels, has brought about increase in global temperatures and climate change due to the green-house effect. As such, recent efforts aimed at addressing this problem have been directed to the use of carbon dioxide as an inexpensive and non-toxic single carbon source for making chemical products. Herein, we report the use of tetrazolyl complexes as catalysts precursors for hydrogenation of carbon dioxide. Specifically, tetrazolyl compounds bearing phosphorus-sulfur bonds have been synthesized with the view of using these as phosphorus-nitrogen bidentate tetrazolyl ligands that can coordinate to iridium(III) thereby forming heteroatomic five-member complexes. Interestingly, reacting the phosphorus-nitrogen bidentate tetrazolyl ligands with iridium dimer led to serendipitous isolation of chiral-at-metal iridium(III) half-sandwich complexes instead. The complexes were obtained via prior formation non-chiral iridium half-sandwich complexes. The complexes undergo initial phosphorus-sulfur bond heterolysis of the precursor ligands, which then ultimately results in new half-sandwich iridium complexes featuring monodentate phosphine co-ligands with proton responsive functionalities. Conditions necessary to significantly affect the rate of phosphorus-sulfur bond heterolysis in the precursor ligand and the subsequent coordination to iridium have been reported. The complexes served as catalyst precursors and exhibited activity in carbon dioxide and bicarbonate hydrogenation in excellent catalytic activity, at low catalyst loadings, producing concentrated formate solutions exclusively. Catalyst precursors with proton responsive phosphines were found to influence catalytic activity when present as racemates, while ease of dissociation of the ligand from the iridium centre was observed to influence activity in spite of the presence of electron-donating ligands. A test for homogeneity indicated that hydrogenation of carbon dioxide proceeded by homogenous means. Subsequently, the mechanism of the reaction by the iridium catalyst precursors was studied using proton NMR techniques. This revealed that a chiral-at-metal iridium hydride species generated in situ, served as the active catalyst. Show less