Experimental and theoretical quantum chemical studies of 2-(2-acetamidophenyl)-2-oxo-N-(pyridin-2-ylmethyl)acetamide and its copper(II) complex: molecular docking simulation of the designed coordinated ligand with insulin-like growth factor-1 receptor (IGF-1R)

Newly synthesized ligand 2-(2- acetamidophenyl)-2-oxo-N-(pyridin-2-ylmethyl)acetamide and its copper(II) complex were characterized by elemental analyses, FT-IR, UV-Vis., ESR, 1H-NMR, and thermal analysis along with the theoretical quantum chemical studies. Combined experimental and theoretical DFT (density functional theory) studies showed the ligand to be a tridentate ligand with three coordinate bonds. The complex was suggested to be in a distorted octahedral structure with dx2-y2 ground state. The activation energy, ΔE*; entropy ΔS*; enthalpy ΔH* and order of reaction has been derived from differential thermogravimetric (DTA) curve, using Horowitz-Metzeger method. The nujol mull electronic spectrum of the ligand and Cu(II) complex have been recorded and the difference of the excited and ground state densities has also been theoretically calculated and plotted to investigate the movement of electrons on excitation. The Cu(II) complex was evaluated for its antibacterial activity against two bacterial species, namely Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Antifungal screening was performed against two species (Condida albicans and Aspergillus flavus). The complex under investigation was found to possess notable biological activity. Molecular docking investigation predicted different types of non-covalent interactions of the synthesized ligand towards Insulin-like growth factor 1 receptor (ID: 5FXR).

Selective copper-catalysed atom transfer radical addition (ATRA) in water under environmentally benign conditions

Simple and green conditions for copper-catalysed ATRA reactions in water have been developed. Firstly, [Cu(ADPA)(H2O)(ClO4)2] (1b, ADPA = 9-[(2,2'-dipicolylamino)methyl]anthracene) was demonstrated to be capable of selectively catalysing the ATRA of CCl4 to styrene using L-ascorbic acid (AsH2) as a reducing agent in organic solvent mixtures under ambient atmosphere. Mechanistic investigation suggested that our ATRA reaction proceeded via a single-electron transfer (SET) mechanism through an inner-sphere complex, which is consistent with the widely accepted mechanism for copper-catalysed ATRA. To perform the reaction in water as a sole solvent, a biocompatible surfactant (2 wt% Tween 20 or Tween 80) was added to improve solubility and increase the local concentration of organic reagents and the copper catalyst. Without the need for a complicated oxygen-free set-up, the ATRA reaction catalysed by this simple aqueous-dispersed system can be performed at a mild temperature (60 °C) and a relatively short reaction time (6 h) using 1 mol% of the catalyst. Furthermore, this facile protocol is also applicable for other alkene substrates demonstrated in this work, resulting in satisfactory to excellent substrate conversion and product yields.

Metal organic frameworks as promising sensing tools for electrochemical detection of persistent heavy metal ions from water matrices: A concise review

Water bodies are being polluted rapidly by disposal of toxic chemicals with their huge entrance into drinking water supply chain. Among these pollutants, heavy metal ions (HMIs) are the most challenging one due to their non-biodegradability, toxicity, and ability to biologically hoard in ecological systems, thus posing a foremost danger to human health. This can be addressed by robust, sensitive, selective, and reliable sensing of metal ions which can be achieved by Metal organic frameworks (MOF) based electrochemical sensors. In the present era, MOFs have caught greater interest in a variety of applications including sensing of hazardous pollutants such as heavy metal ions. So, in this review article, types, synthesis and working mechanism of MOF based sensors is explained to give general overview with updated literature. First time, detailed study is done for sensing of metal ions such as chromium, mercury, zinc, copper, manganese, palladium, lead, iron, cadmium and lanthanide by MOFs based electrochemical sensors. The use of MOFs as electrochemical sensors has attractive success story along with some challenges of the area. Considering these challenges, we attempted to highlight the milestone achieved and shortcomings along with future prospective of the MOFs for employing it in electrochemical sensing devices for HMIs. Finally, challenges and future prospects have been discussed to promote the development of MOFs-based sensors in future.

Structural Characterization of Zinc(II)/Cobalt(II) Complexes of Chiral N-(Anthracen-9-yl)methyl-N,N-bis(2-picolyl)amine and Evaluation of DNA Photocleavage Activity

We designed and synthesized a chiral ligand N-(anthracen-9-ylmethyl)-1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)ethanamine (APPE) DNA photocleavage agent to investigate the effects of chirality of bis(2-picolyl)amine on the DNA photocleavage activity of metal complexes. The structures of Zn^II and Co^II complexes in APPE were analyzed via X-ray crystallography and fluorometric titration. APPE formed metal complexes with a 1 : 1 stoichiometry in both the crystalline and solution states. Fluorometric titration was used to show that the Zn^II and Co^II association constants of these complexes (log K_as) were 4.95 and 5.39, respectively. The synthesized complexes were found to cleave pUC19 plasmid DNA when irradiated at 370 nm. The DNA photocleavage activity of the Zn^II complex was higher than that of the Co^II complex. The absolute configuration of the methyl-attached carbon did not affect DNA cleavage activity and, unfortunately, an achiral APPE derivative without the methyl group (ABPM) was found to perform DNA photocleavage more effectively than APPE. One reason for this may be that the methyl group suppressed the structural flexibility of the photosensitizer. These results will be useful for the design of new photoreactive reagents.

Structures, properties and applications of Cu(II) complexes with tridentate donor ligands

Tridentate ligands offer theree donor atoms to coordinate to metal ions. The remaining vacant coordination sites on the metal ions provided opportunities to implement additional co-ligands to generate complexes with desired properties. Herein we discuss selected examples of Cu(ii) complexes with tridentate ligands utilizing combinations of N, O, S, and Se donors, focusing on effects of ligand flexibility/rigidity on their coordination modes, properties and applications.

Stabilisation of copper(i) polypyridyl complexes toward aerobic oxidation by zinc(ii) in combination with acetate anions: a facile approach and its application in ascorbic acid sensing in aqueous solution

A new approach to stabilise Cu(i) complexes in aqueous solution using Zn(ii) acetate was demonstrated.

Tuning the reactivity of copper complexes supported by tridentate ligands leading to two-electron reduction of dioxygen

Dinuclear copper complex with tridentate ligand and anthracene linkage catalyses 2-electron reduction of O₂.

Synthesis of novel coumarin nucleus-based DPA drug-like molecular entity: In vitro DNA/Cu(II) binding, DNA cleavage and pro-oxidant mechanism for anticancer action

Despite substantial research on cancer therapeutics, systemic toxicity and drug-resistance limits the clinical application of many drugs like cisplatin. Therefore, new chemotherapeutic strategies against different malignancies are needed. Targeted cancer therapy is a new paradigm for cancer therapeutics which targets pathways or chemical entities specific to cancer cells than normal ones. Unlike normal cells, cancer cells contain elevated copper which plays an integral role in angiogenesis. Copper is an important metal ion associated with chromatin DNA, particularly with guanine. Thus, targeting copper via copper-specific chelators in cancer cells can serve as an effective anticancer strategy. New pharmacophore di(2-picolyl)amine (DPA)-3(bromoacetyl) coumarin (ligand-L) was synthesized and characterized by IR, ESI-MS, 1H- and 13C-NMR. Binding ability of ligand-L to DNA/Cu(II) was evaluated using a plethora of biophysical techniques which revealed ligand-L-DNA and ligand-L-Cu(II) interaction. Competitive displacement assay and docking confirmed non-intercalative binding mode of ligand-L with ctDNA. Cyclic voltammetry confirmed ligand-L causes quasi reversible Cu(II)/Cu(I) conversion. Further, acute toxicity studies revealed no toxic effects of ligand-L on mice. To evaluate the chemotherapeutic potential and anticancer mechanism of ligand-L, DNA damage via pBR322 cleavage assay and reactive oxygen species (ROS) generation were studied. Results demonstrate that ligand-L causes DNA cleavage involving ROS generation in the presence of Cu(II). In conclusion, ligand-L causes redox cycling of Cu(II) to generate ROS which leads to oxidative DNA damage and pro-oxidant cancer cell death. These findings will establish ligand-L as a lead molecule to synthesize new molecules with better copper chelating and pro-oxidant properties against different malignancies.

Unique Occurrence of Cationic and Anionic Bis-1,2-diaminocyclohexane Copper(II) Units in a Double Complex Salt

The reaction of (±)-trans-diaminocyclohexane (dach) with copper(ii) sulfate in water resulted in the spontaneous formation of a double complex salt of type [Cu(dach)2(H2O)2][Cu(dach)2(SO4)2]·6H2O, whose X-ray structure confirmed the presence of the same square-planar Cu(dach)22+ coordination motif in both the complex cation and anion. Each copper centre adopts a Jahn–Teller-distorted octahedral geometry. Both axial positions of the metal centre in the complex cation are occupied by water molecules, whereas two monodentate sulfato ions occupy the corresponding sites in the complex anion, leading to a trans N4O2-donor coordination environment in each ion.

Selective Solvent Extraction of Silver(I) by Tris-Pyridyl Tripodal Ligands and X-Ray Structure of a Silver(I) Coordination Polymer Incorporating One Such Ligand

Two tripodal ligands, each derived from 1,1,1-tris(hydroxymethyl)ethane and terminated respectively by 4-pyridyl (L1) and 2-pyridyl groups (L2), have been synthesised. Competitive seven-metal extraction studies (H2O/CHCl3) incorporating equal concentrations of cobalt(ii), nickel(ii), copper(ii), zinc(ii), silver(i), cadmium(ii), and lead(ii) in the aqueous phase and L1 or L2 in the organic phase showed selective extraction of silver(i) in each case. A parallel solvent extraction experiment involving a related tripodal tris-pyridyl ligand (L3) based on a 1,3,5-substituted aryl ring scaffold and incorporating thioether sulfurs in each tripod arm also showed extraction selectivity for silver(i); extraction efficiencies towards this metal ion fall in the order L3 > L1 > L2. Physical data are in accord with L1 forming a capsule-like complex of type [Ag3L12]3+ in which silver ions link pairs of pyridyl groups from different ligands. In contrast, L2 yields a complex of type [Ag2L2(NO)3]n whose X-ray structure showed it to be a two-dimensional coordination polymer in which the three pyridyl donors of each L2 coordinate to three silver(i) centres, two of which are crystallographically distinct, with the centres also bonded to bidentate and/or bridging bidentate nitrato groups.

Synthesis and Structural Characterisation of Palladium(II) Complexes with N,N′,N-Tridentate N′-Substituted N,N-Di(2-picolyl)amines and their Application to Methyl Methacrylate Polymerisation

The reaction of [Pd(CH3CN)2Cl2] with N′-substituted N,N-di(2-picolyl)amine-based ancillary ligands, for example N,N-di(2-picolyl)cyclohexylmethylamine (L1), N,N-di(2-picolyl)benzylamine (L2), N,N-di(2-picolyl)aniline (L3), and 1,4-bis[bis(2-pyridylmethyl)aminomethyl]benzene (L4), in the presence of NaClO4 in ethanol yields a new series of [(NN′N)PdCl]X (X = ClO4, Cl) complexes, i.e. mononuclear [LnPdCl]ClO4 (Ln = L1, L2, L3) and binuclear [L4Pd2Cl2]Cl2. X-Ray crystallographic analysis determined that the Pd atom in complexes [(NN′N)PdCl]X showed a slightly distorted square-planar geometry involving three nitrogen atoms and a chlorido ligand. Moreover, the unit cell included a ClO4– or Cl– anion as the counterion. The complex [L1PdCl]ClO4 showed the highest catalytic activity for the polymerisation of methyl methacrylate in the presence of modified methylaluminoxane at 60°C among the mononuclear PdII complexes. Specifically, the activity of binuclear [L4Pd2Cl2]Cl2 was 2-fold higher than the corresponding mononuclear [L2PdCl]ClO4 per active palladium metal centre.

Infinite copper(II) coordination architectures from a resonative aminotriazine-derived tripodal ligand: synthesis, structures, and magnetic properties

The ligand 2,4,6-tris(2-picolylamino)-1,3,5-triazine (o-H3tpat) with essentially resonative structure and two copper(II)-based one-dimensional coordination chain structures, [Cu3Cl5(o-H2tpat)(H2O)]·MeOH·CH2Cl2 (1) and [Cu2(o-H2tpat)(H2O)(MeOH)(NO3)2](NO3)·3MeOH (2), with different structural patterns have been synthesized and characterized using single crystal X-ray diffraction analysis. For o-H3tpat, two crystalline forms showing different solid-state structural features are obtained from MeOH/Et2O (form I) and CH2Cl2/Et2O (form II), respectively. The o-H3tpat form I adopts an asymmetric-configured all-amino resonative tautomer with three cis-trans-trans-arranged pyridyl groups, whereas the o-H3tpat form II adopts also an identical resonative structure but where two of the three pyridyl groups are in a cis-manner and the third one is nearly coplanar with the central aminotriazine core. On the other hand, the designed tripodal ligand in both Cu(II)-complexes serves as a monoanion, o-H2tpat(-), which suits a propeller-configured all-imino resonative structure in 1 and a syn-anti-configured amino-imino-imino resonative structure in 2. These observations significantly indicate that the o-H3tpat ligand can self-adjust and interconvert its conformation via a possible structure transformation associated with proton-shift to adapt a change in the crystallization and self-assembly reaction systems. In the magnetic point of view, 1 is treated as repeated chains composed of infinite {Cu6Cl10} units wherein the hexanuclear unit is further decomposed to one {Cu(II)4Cl6} and two magnetically isolated {Cu(II)Cl2} subunits. Antiferromagnetic interactions are found for the Cu4 subunits (g = 2.33, 2J1 = -5.6 cm(-1), 2J2 = -8.6 cm(-1), 2J3 = -4.1 cm(-1), and J4 held to zero). For 2, it is considered as an infinite chain that composes of Cu2 units antiferromagnetically coupled (g = 2.03, 2J1 = -0.2 cm(-1)). The small antiferromagnetic exchange constants in both 1 and 2 suggest that the unpaired spins do not effectively interact through the tripodal o-H2tpat(-) ligands.

Mechanism of "turn-on" fluorescent sensors for mercury(II) in solution and its implications for ligand design

The tendency of a Hg(II) ion to strongly quench fluorescence of potential fluorescent sensors is explored. Fluorescence measurements show the expected order of the chelation-enhanced fluorescence (CHEF) effect of Zn(II) > Cd(II) >> Hg(II) ~ Cu(II), which is interpreted as (1) unpaired electrons causing the weak CHEF effect for Cu(II) and (2) the order Zn(II) > Cd(II) >> Hg(II) reflecting the "heavy atom" effect, which may be due to increasing spin-orbit coupling constants (ζ) for Zn(II) < Cd(II) << Hg(II). The structures of mercury(II) complexes of N-(9-anthracenylmethyl)-N-(2-pyridinylmethyl)-2-pyridinemethanamine (ADPA) are reported. [Hg(ADPA)Cl(2)HgCl(2)] (1) has one Hg(II) held by two bridging chlorides, while the other Hg(II) is coordinated to the ADPA ligand. The latter Hg(II) has a nearest π contact of 3.215 Å with a C atom from the anthracenyl group, which falls in the range of reported Hg-C π contacts with aromatic groups. This contact may be important in quenching the fluorescence of the Hg(II)/ADPA complex. A density functional theory study shows that the Hg-C interaction is strong enough to prevent a simple HOMO → LUMO transition of the fluorophore. In fact, the S(0) → S(1) and S(2) transitions in the Hg(II)/ADPA complex have significant charge-transfer character to mercury. An important aspect of the coordination geometry of Hg(II) is illustrated by 1, where Hg(II) tends to form a few (often only two) short bonds to the more covalently binding donor atoms present, with much longer bonds to other donor atoms. The Hg-N bonds to the two pyridyl N-donor atoms of ADPA in 1 are relatively short at 2.212(8) and 2.224(8) Å, while that to the central saturated N-donor atom of ADPA is long at 2.603(8) Å. The latter long Hg-N bond may allow a photoinduced electron-transfer (PET) effect, quenching the fluorescence of the anthracenyl fluorophore. The structure of [Hg(ADPA)Br(2)] (2) reflects the more covalent binding of the two bromine ligands compared to the clorine ligands of 1, with much longer Hg-C contacts with the anthracenyl fluorophore and a Hg-N contact with the saturated N atom of ADPA of 2.917 Å. The latter long Hg-N contact is related to the nearly negligible fluorescence of the ADPA complex in the presence of added Br(-). The addition of extra ligands to the Hg(II)/ADPA complex produces a weak increase in the fluorescence intensity for OH(-) ~ Cl(-) >> Br(-) > I(-), which is discussed in terms of an increasing PET effect, and to collisional quenching. The ligand design principles for generating turn-on sensors for mercury suggested by this work are discussed.

Phosphorescent sensor for robust quantification of copper(II) ion

A phosphorescent sensor based on a multichromophoric iridium(III) complex was synthesized and characterized. The construct exhibits concomitant changes in its phosphorescence intensity ratio and phosphorescence lifetime in response to copper(II) ion. The sensor, which is reversible and selective, is able to quantify copper(II) ions in aqueous media, and it detects intracellular copper ratiometrically.