Divalent Transition Metal Ions Research Articles

Complexes of Iron(II), Cobalt(II), and Nickel(II) with DOTA-Tetraglycinate for pH and Temperature Imaging Using Hyperfine Shifts of an Amide Moiety.

Paramagnetic complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA4-) derivatives have shown potential for molecular imaging with magnetic resonance. DOTA-tetraglycinate (DOTA-4AmC4-) coordinated with lanthanide metal ions (Ln3+) demonstrates pH/temperature sensing with Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) and Chemical Exchange Saturation Transfer (CEST), respectively, detecting nonexchangeable (e.g., -CHy, where 3 ≥ y ≥ 1) and exchangeable (e.g., -OH or -NHx, where 2 ≥ x ≥ 1) protons. Herein, we report paramagnetic complexes of divalent transition-metal ions (M2+ = Fe2+, Co2+, Ni2+) with DOTA-4AmC4- that endow a unique amide proton (-NH) moiety for pH/temperature sensing. Crystallographic data reveal that DOTA-4AmC4- coordinates with M2+ through oxygen and nitrogen donor atoms, ranging in coordination numbers from 8-coordinate in Fe(II)DOTA-4AmC2-, 7-coordinate in Co(II)DOTA-4AmC2-, and 6-coordinate in Ni(II)DOTA-4AmC2-. The -CHy protons in M(II)DOTA-4AmC2- displayed modest pH/temperature sensitivities, but -NH protons exhibited higher intensity, suggesting prominent BIRDS properties. The pH sensitivity was the highest for Ni(II)DOTA-4AmC2- (1.42 ppm/pH), followed by Co(II)DOTA-4AmC2- (0.21 ppm/pH) and Fe(II)DOTA-4AmC2- (0.16 ppm/pH), whereas temperature sensitivities were comparable (i.e., 0.22, 0.13, and 0.17 ppm/°C, respectively). The CEST image contrast for -NH in M(II)DOTA-4AmC2- was much weaker compared to that of Ln(III)DOTA-4AmC-. Given its high pH sensitivity and low cytotoxicity, Ni(II)DOTA-4AmC2- shows promise for use in preclinical BIRDS-based pH imaging.

Ultrabroadband mid-infrared emission and gas sensing of cobalt-doped chalcogenide glass ceramics.

Mid-infrared (MIR) gain materials are of great significance for the development of MIR tunable fiber lasers. Herein, for the first time, to the best of our knowledge, it is found that Ga2Se3 nanocrystals distributed in chalcogenide glass ceramics can provide new tetrahedral-coordinated sites that can be used to activate ultrabroadband MIR emissions of divalent transition metal ions, such as Co2+. Under the excitation of a 1550 nm diode laser, the transparent Ge-Ga-Se glass ceramic embedded with Co2+: Ga2Se3 nanocrystals shows an intense 2.5-5.5 µm ultrabroadband emission. The peak wavelength is located at ∼4.2 µm and the full width at half maximum exceeds 2 µm. Such emission properties, originating from the dual lattice sites of Ga3+ ions, are superior to those of transparent chalcogenide glass ceramics embedded with Co2+: ZnSe nanocrystals. Moreover, the gas detection system built based on the glass ceramic shows a sensitivity of 45.9 ppm for butane gas. Therefore, the chalcogenide glass ceramics embedded with active Co2+: Ga2Se3 nanocrystals have great potential in MIR tunable fiber lasers and gas sensing.

Theoretical Analysis of Coordination Geometries in Transition Metal-Histidine Complexes Using Quantum Chemical Calculations.

A theoretical investigation utilizing density functional theory (DFT) calculations was conducted to explore the coordination complexes formed between histidine (His) ligands and various divalent transition metal ions (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+). Conformational exploration of the His ligand was initially performed to assess its stability upon coordination. Both 1:1 and 1:2 of metal-to-ligand complexes were scrutinized to elucidate their structural features and the relative stability of the complexes. This study examined the ability of His to act as a bidentate or tridentate coordinating ligand, along with the differences in coordination geometry when solvent effects were incorporated. The reduced density gradient (RDG) analysis and local electron attachment energy (LEAE) analysis were employed to elucidate the interaction planes and the nucleophilic and electrophilic properties. The electronic properties were analyzed through electrostatic potential (ESP) maps and natural population analysis (NPA) of atomic charge distributions. This computational study provides valuable insights into the diverse coordination modes of His and its interactions with divalent transition metal ions, contributing to a better understanding of the role of this amino acid ligand in the formation of transition metal complexes. The findings can aid in the design and construction of self-assembled structures involving His-metal coordination.

Inhibitor binding to metal-substituted metalloenzyme: Sulfonamide affinity for carbonic anhydrase IX

Transition metal ions are structural and catalytic cofactors of many proteins including human carbonic anhydrase (CA), a Zn-dependent hydrolase. Sulfonamide inhibitors of CA recognize and form a coordination bond with the Zn ion located in the active site of the enzyme. The Zn ion may be removed or substituted with other metal ions. Such CA protein retains the structure and could serve as a tool to study metal ion role in the recognition and binding affinity of inhibitor molecules. We measured the affinities of selected divalent transition metal ions, including Mn, Fe, Co, Ni, Cu, Cd, Hg, and Zn to metal-free CA isozymes CA I, CA II, and CAIX by fluorescence-based thermal shift assay, prepared metal-substituted CAs, and determined binding of diverse sulfonamide compounds.Sulfonamide inhibitor binding to metal substituted CA followed a U-shape pH dependence. The binding was dissected to contributing binding-linked reactions and the intrinsic binding reaction affinity was calculated. This value is independent of pH and protonation reactions that occur simultaneously upon binding native CA and as demonstrated here, to metal substituted CA. Sulfonamide inhibitor binding to cancer-associated isozyme CAIX diminished in the order: Zn > Co > Hg > Cu > Cd > Mn > Ni. Energetic contribution of the inhibitor-metal coordination bond was determined for all above metals. The understanding of the principles of metal influence on ligand affinity and selectivity should help design new drugs targeting metalloenzymes.

Transition metal complexes of the (2,2,2-trifluoroethyl)phosphinate NOTA analogue as potential contrast agents for 19F magnetic resonance imaging.

A new hexadentate 1,4,7-triazacyclononane-based ligand bearing three coordinating methylene-(2,2,2-trifluoroethyl)phosphinate pendant arms was synthesized and its coordination behaviour towards selected divalent (Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) and trivalent (Cr3+, Fe3+, Co3+) transition metal ions was studied. The ligand forms stable complexes with late divalent transition metal ions (from Co2+ to Zn2+) and the complexes of these metal ions are formed above pH ∼3. A number of complexes with divalent metal ions were structurally characterized by means of single-crystal X-ray diffraction. The complex of the larger Mn2+ ion adopts a twisted trigonally antiprismatic geometry with a larger coordination cavity and smaller torsion of the pendant arms, whereas the smaller ions Ni2+, Cu2+ and Zn2+ form octahedral species with a smaller cavity and larger pendant arm torsion. In the case of the Co2+ complexes, both coordination arrangements were observed. The complexes with paramagnetic metal ions were studied from the point of view of potential utilization in 19F magnetic resonance imaging. A significant shortening of the 19F NMR longitudinal relaxation times was observed: a sub-millisecond range for complexes of Cr3+, Mn2+ and Fe3+ with symmetric electronic states (t2g3 and HS-d5), the millisecond range for the Ni2+ and Cu2+ complexes and tens of milliseconds for the Co2+ complex. Such short relaxation times are consistent with a short distance between the paramagnetic metal ion and the fluorine atoms (∼5.5-6.5 Å). Among the redox-active complexes (Mn3+/Mn2+, Fe3+/Fe2+, Co3+/Co2+, Cu2+/Cu+), the cobalt complexes show sufficient stability and a paramagnetic-diamagnetic changeover with the redox potential lying in a physiologically relevant range. Thus, the Co3+/Co2+ complex pair can be potentially used as a smart redox-responsive contrast agent for 19F MRI.

Mercury selective hydrogelation of a pyridinyl substituted terpyridine ligand

We report the addition of aqueous solution of different divalent transition metal ions M2+ (M = Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg) to a dilute acidic solution of 4′-(pyridin-2-yl)-2,2′:6′,2″-terpyridine (L). An irreversible, translucent, and thixotropic hydrogel was selectively produced in the case of Hg(II). FESEM and HR-TEM images of Hg(II)-hydrogel showed non-uniform, fibrous, and cross-linked gel morphology. Further, the hydrogel was treated with sodium salts of different anions (F−, I−, Br−, Cl−, SO42−, NO3−, HCO3−, SO32−) in water. The iodide ion showed unusual behavior by forming a yellow precipitate of the hydrogel with a plate-like structure, as observed from FESEM images. DFT study has also been conducted to understand the aggregation behavior in Hg(II) based hydrogel. We also synthesized the mercury complex HgCl2L and characterized it by 1H NMR, elemental analysis, and mass spectrometry.

Synthesis, Spectral Characterization and Biological Evaluation of Glutaric acid based Macrocyclic Complexes

In the presence of divalent transition metal ions in their chloride forms, glutaric acid and o-phenylenediamine were used to design and synthesize a unique series of macrocyclic complexes. The UV-Visible, IR, ESR, and ESI-MS spectroscopy methods were used to analyze these newly designed complexes. In order to evaluate their thermal behavior, TGA analysis was employed. The intended general formula for the produced complexes was [M(L)X2] (L = ligand, X = Cl- and M = Co2+, Ni2+ and Cu2+). The central metal ions are surrounded by octahedral environment. These macrocyclic complexes were tested for their antimicrobial effectiveness against the selected bacterial strains (Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, and Escherichia coli), as well as fungi strains (Aspergillus niger and Candida albicans) and their efficacy was compared to that of standard drugs Streptomycin and Itraconazole respectively. Moreover, the antioxidant activity of the macrocyclic complexes were also assessed using the DPPH assay.

(Invited) Melanin-Inspired Functionalization of Single-Walled Carbon Nanotubes for Optical Detection of Metals

The accumulation of metal ions in organisms and the presence of heavy metals in water cause adverse effects on ecosystems and result in numerous human health issues such as cancer and neurogenerative diseases. Therefore, the development of novel platforms for metal-scavenging and rapid metal detection for in situ applications are of high importance. Here, this challenge is tackled by taking advantage of the metal chelation ability of a melanin-inspired material in combination with the near-infrared (NIR) fluorescence response of single-walled carbon nanotubes (SWCNTs) to surface binding. SWCNTs are functionalized by a melanin-like substance, obtained by enzymatic oxidative polymerization of a fluorenylmethyloxycarbonyl-tyrosine (FmocY) precursor. The resulting multicomponent system (SWCNT-FmocYOx) serves as a metal-ion scavenging platform that concurrently reports on metal binding with optical signal transduction. Upon binding of a library of mostly divalent transition metal-ions, the fluorescence emission of the functionalized SWCNTs is modulated, showing a concentration-dependent response with a limit of detection in the nanomolar range. Metal-binding and removal from water of up to 98% are further shown via inductively coupled plasma mass spectrometry. The SWCNT-FmocYOx hybrid system presents a novel platform with NIR optical signal for real-time feedback on metal-ion scavenging.

Quantifying metal-binding specificity of CcNikZ-II from Clostridium carboxidivorans in the presence of competing metal ions

Many proteins bind transition metal ions as cofactors to carry out their biological functions. Despite binding affinities for divalent transition metal ions being predominantly dictated by the Irving-Williams series for wild-type proteins, in vivo metal ion binding specificity is ensured by intracellular mechanisms that regulate free metal ion concentrations. However, a growing area of biotechnology research considers the use of metal-binding proteins in vitro to purify specific metal ions from wastewater, where specificity is dictated by the protein's metal binding affinities. A goal of metalloprotein engineering is to modulate these affinities to improve a protein's specificity towards a particular metal; however, the quantitative relationship between the affinities and the equilibrium metal-bound protein fractions depends on the underlying binding mechanisms. Here we demonstrate a high-throughput intrinsic tryptophan fluorescence quenching method to validate binding models in multi-metal solutions for CcNikZ-II, a nickel-binding protein from Clostridium carboxidivorans. Using our validated models, we quantify the relationship between binding affinity and specificity in different classes of metal-binding models for CcNikZ-II. We further illustrate the potential relevance of data-informed models to predicting engineering targets for improved specificity.

Crystal Field Splitting Energy (Δo) and Racah Parameters (B) of Some Metal-Saccharine and Metal-Saccharine-Ethylenediamine Complexes

[M(sac)2(H2O)4].2H2O [sac = saccharinato anion, M = Fe(II), Co(II), Ni(II), and Cu(II)], and [M(sac)2(en)2].2H2O [sac = saccharinato anion, en = ethylenediamine, M = Fe(II), Co(II), Ni(II) and Cu(II)] were prepared in an aqueous medium. The compounds are crystalline of different colors and are ambiently stable. By examining their physico-chemical properties and relevant literature, the metal(II) ions in both [M(sac)2(H2O)4].2H2O and [M(sac)2(en)2].2H2O complexes are octahedrally coordinated. In the former by four neutral H2O molecules and two monoanionic sac ligands while in later, the octahedral sites fulfilled by two neutral bidentate ethylenediamine molecules and two monoanionic sac ligands. Splitting of the crystal field (Δo) and Racah parameter (B) of two sets of complexes [M(sac)2(H2O)4].2H2O and [M(sac)2(en)2].2H2O are estimated from their electronic spectra using Tanabe-Sugano diagram of Co(II) and Ni(II) complexes while Δo values of Fe(II) and Cu(II) derivatives are calculated directly from their absorption maxima. Our experimental results show that for the studied ligands and the divalent transition metal ions, the Δo values vary according to the following order: Cu(II) > Fe(II) > Co(II) > Ni(II). Dhaka Univ. J. Sci. 71(1): 6-12, 2023 (Jan)

High-resolution structures with bound Mn2+ and Cd2+ map the metal import pathway in an Nramp transporter.

Transporters of the Nramp (Natural resistance-associated macrophage protein) family import divalent transition metal ions into cells of most organisms. By supporting metal homeostasis, Nramps prevent diseases and disorders related to metal insufficiency or overload. Previous studies revealed that Nramps take on a LeuT fold and identified the metal-binding site. We present high-resolution structures of Deinococcus radiodurans (Dra)Nramp in three stable conformations of the transport cycle revealing that global conformational changes are supported by distinct coordination geometries of its physiological substrate, Mn2+, across conformations, and by conserved networks of polar residues lining the inner and outer gates. In addition, a high-resolution Cd2+-bound structure highlights differences in how Cd2+ and Mn2+ are coordinated by DraNramp. Complementary metal binding studies using isothermal titration calorimetry with a series of mutated DraNramp proteins indicate that the thermodynamic landscape for binding and transporting physiological metals like Mn2+ is different and more robust to perturbation than for transporting the toxic Cd2+ metal. Overall, the affinity measurements and high-resolution structural information on metal substrate binding provide a foundation for understanding the substrate selectivity of essential metal ion transporters like Nramps.

Hydroxybenzoate salts of cobalt(II), manganese(II), and nickel(II): synthesis, crystal structure, Hirshfeld surface analyses, and thermal behavior

The reaction of hydroxybenzoates with divalent first row transition metal ions afforded four mononuclear complexes, [M(OH2)6](dhbzc)2·2H2O (M = Co2+, 1 or Mn2+, 2), [Ni(OH2)6](hbzc)2·2H2O (3) and [Ni(OH2)5(hbzc)](hbzc)·3H2O (4) (where dhbzc− = 2,6-dihydroxybenzoate and hbzc− = 4-hydroxybenzoate). The complexes were characterized by single crystal and powder X-ray diffraction analyses, infrared spectroscopy, and thermogravimetric analysis. Results showed that the hydrogen bonds present in dhbzc− impaired its coordination to Co2+ and Mn2+. Thereafter, Hirshfeld surface analyses (HS) and 2D fingerprint plots were used to investigate the intermolecular contacts in 1–4. The offset π···π stacking of the dhbzc− counterions in 1 and 2 lead to C···C close contacts over C···H/H···C ones. Complexes 3 and 4 presented the usual herringbone aromatic-based packing for the hbzc− rings with a predominance of C···H/H···C close contacts. The existence of water molecules in the crystal lattices of 1–4 was determined by TG analyses, which proved the presence of coordinated and uncoordinated water molecules. The thermal decomposition patterns were analyzed in light of the percentage of the strongest intermolecular close contacts.

Application of DFT/TD-DFT Frameworks in the Drug Delivery Mechanism: Investigation of Chelated Bisphosphonate with Transition Metal Cations in Bone Treatment

Carbon nanotubes (CNTs) are applied in a drug delivery system, which can be reacted with different structures such biomolecules. Bones have vital functions and are the locations of biochemical reactions in cells that might be exposed various diseases. As different metal ions are integral components of bone tissue with different functions in the physiological cellular medium as well as in bone treatment, they can be used differently as a basis or as a supplement for various materials in the field of bone repair. Therefore, this research aims to represent the recent progress in conjugated bisphosphonate (BP)-divalent transition metal ions of Mn2+, Fe2+, and Co2+ with an emphasis on the properties of interaction with a (6, 6) armchair carbon nanotube as a nanocarrier to exhibit the potential biomedical application of drug delivery. In this article, “CNT” linked to “BP“ of alendronic acid, ibandronic acid, neridronic acid, and pamidronic acid, which are chelated to transition metal cations of Mn2+, Fe2+, and Co2+, was investigated based on DFT insights for obtaining the electron charge density. Transition metals chelating with phosphonate groups, which are large with six O atoms with negative charges, are active in generating chelated complexes with the bisphosphonates [BPs- Mn2+/Fe2+/Co2+] through the status of drug design. In this work, B3LYP/6-311+G(d,p)/lanl2dz we have estimated the susceptibility of CNT for conjugating alendronic acid, ibandronic acid, neridronic acid, and pamidronic acid, which are chelated to transition metal cations of Mn2+, Fe2+, and Co2+ through NMR, NQR, IR, UV-VIS spectroscopy, and HOMO-LUMO analysis. Finally, the obtained results have confirmed that the possibility of applying CNT and BPs of alendronic acid, ibandronic acid, neridronic acid, and pamidronic acid becomes suitable in transition metal chelating for delivery application. The calculated HOMO–LUMO energy gaps for BPs of alendronic acid, ibandronic acid, neridronic acid, and pamidronic acid at the B3LYP/6-311+G (d,p) level have revealed that the energy gap reflects the chemical activity of the molecule.

Derivatives of cyclam-1,8-diacetic acid: Synthesis and complexes with divalent transition metal ions

1,4,8,11-tetraazacyclotetradecane-1,8-diacetatic acid, H2te2a, and series of its derivative bearing two substituted N-benzyl groups were synthesized and their complexes were studied. Series of CoII and ZnII complexes was prepared in the solid-state and X-ray diffraction analysis showed that the metal ions are hexacoordinated by four nitrogen atoms of the macrocycle and two oxygen atoms of the carboxylate pendants. The two oxygen atoms were in cis and trans mutual position in the CoII and ZnII complexes, respectively. Potentiometric study of CoII, ZnII, CuII and NiII-H2te2a systems showed that the complexes are highly thermodynamically stable and the ligand is selective for CuII ions (logK = 27.5) over the other ions (logK = 21–22). UV-VIS and electrochemical data for the CoII-H2te2a system showed that complexation was rather slow (several hours at pH 4.5, 25 °C) and the complex undergoes slow oxidation with air oxygen.

A Theoretical Study of Tris-(<i>o</i>-benzoquinonediimine)-First-Row Divalent Transition Metal Complexes

The ligand o-phenylenediamine (opda) and its oxidized form, o-benzoquinonediimine (bqdi), act as a fascinating candidate coordinating toward transition metal ions leading to the photochemical hydrogen production in absence of photosensitizers. Herein, we report the systematic study of the interaction between the oxidized form bqdi ligand, tris-(o-benzoquinonediimine) with divalent first-row transition metal series using DFT calculations. The lowest energy structures, bond length, binding energies, frontier molecular orbital analysis, natural bond orbitals, and global reactivity descriptor were calculated using B3LYP/6-311G(d,P) level of theory. The time dependent-DFT at the CAM-B3LYP/6-311+G(d,p) level of theory was applied to determine the electronic structures and the optical spectra. The theoretical binding trend of the divalent first-row transition metal series is decreasing as follows: Cu >Ti > V > Co > Ni > Fe > Cr > Zn >Mn. Among them, the binding potency of iron (II) by the bqdi ligand was not predominantly sturdy as compared to other first-row divalent transition metal ions. The origin of strong coordination with Fe(II) is attributed to its extra capability to induce covalent coordination of bqdi ligands. The complex exhibited two strong peaks at 370 nm and 452 nm, due to the HOMO-3 to LUMO+1 and HOMO-1 to LUMO transitions, respectively. Natural bond orbital analysis showed that the major interaction happens between the N lone pair electrons of the ligand with an anti-bonding orbital of metal ions, in which Ti showed the highest interaction energy than other metal ions. The present systemic DFT study of bqdi ligands with the first-row transition metals strongly encourages the future establishment of photochemical hydrogen production in absence of photosensitizers.

Synthesis, Characterization, Biological Activity and Molecular Docking Studies of Phthalic Acid based Macrocyclic Transition Metal Complexes

A novel series of macrocyclic complexes of [M(L)Cl2] (M = Co(II), Ni(II) and Cu(II), L = macrocyclic ligand) were synthesized by template condensation method using 3,4-diaminotoluene and phthalic acid in the presence of divalent transition metal ions e.g., Co(II), Ni(II) and Cu(II) in their chloride form. These synthesized metal complexes were fully characterized by spectroscopic techniques, namely UV-Visible, IR, ESR and ESI-MS. Their thermal behaviour was determined by TGA and DTA. Further these macrocyclic complexes were screened for antimicrobial activity against bacterial species (Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli) and fungi (Aspergillus niger and Candida albicans) and then compared against standard drug streptomycin and itraconazole, respectively. In addition to these the antioxidant activity of the macrocyclic complexes were also investigated through scavenging effect on the DPPH radicals. Finally, the biological potency of synthesized compounds was evaluated using Auto Dock Vina. All the synthesized macrocyclic complexes were found to be potent against bacterial and fungal species, which suggest their potential application as antibacterial and antifungal agents.

Transition metal complexes of cyclam with two 2,2,2-trifluoroethylphosphinate pendant arms as probes for 19F magnetic resonance imaging.

A new cyclam-based ligand bearing two methylene(2,2,2-trifluoroethyl)phosphinate pendant arms was synthesized and its coordination behaviour towards selected divalent transition metal ions [Co(II), Ni(II), Cu(II), Zn(II)] was studied. The ligand was found to be very selective for the Cu(II) ion according to the common Williams-Irving trend. Complexes with all the studied metal ions were structurally characterized. The Cu(II) ion forms two isomeric complexes; the pentacoordinated isomer pc-[Cu(L)] is the kinetic product and the octahedral trans-O,O'-[Cu(L)] isomer is the final (thermodynamic) product of the complexation reaction. Other studied metal ions form octahedral cis-O,O'-[M(L)] complexes. The complexes with paramagnetic metal ions showed a significant shortening of 19F NMR longitudinal relaxation times (T1) to the millisecond range [Ni(II) and Cu(II) complexes] or tens of milliseconds [Co(II) complex] at the temperature and magnetic field relevant for 19F magnetic resonance imaging (MRI). Such a short T1 results from a short distance between the paramagnetic metal ion and the fluorine atoms (∼6.1-6.4 Å). The complexes show high kinetic inertness towards acid-assisted dissociation; in particular, the trans-O,O'-[Cu(L)] complex was found to be extremely inert with a dissociation half-time of 2.8 h in 1 M HCl at 90 °C. Together with the short relaxation time, it potentially enables in vitro/in vivo utilization of the complexes as efficient contrast agents for 19F MRI.

Supramolecular chemistry of two new bis(1,2,3-triazolyl)pyridine macrocycles: metal complexation, self-assembly and anion binding.

Two new macrocycles containing the bis(1,2,3-triazolyl)pyridine (btp) motif were prepared in high yields from a btp diazide precursor (1). Solution 1H NMR studies show that this diazide undergoes self-assembly with divalent transition metal ions to form ML2 complexes with pendant azide groups, apparently suitable for conversion into metal-templated catenanes; however attempts to form these catenanes were unsuccessful. Instead a new macrocycle containing two btp motifs was prepared, which forms a nanotube structure in the solid state. Reduction of the azide groups to amines followed by amide bond formation was used to convert 1 into macrocycle 8 containing btp and isophthalamide functionalities. This macrocycle binds halide and oxalate anions in acetonitrile solely through the isophthalamide motif, and binds aromatic dicarboxylates very strongly through both the isophthalamide amide donors and the btp triazole donors. The macrocycle was complexed with Pd(II) and the resulting complexes were shown to bind strongly to halide anions. The solid state structures of [Pd·8·X]BF4 (X = Cl-, Br-, I-) were investigated by X-ray crystallography, which showed that [Pd·8·Br] forms an unusual "chain of dimers" structure assembled by metal complexation, N-H⋯Br- hydrogen bonding and short Pd⋯Pd contacts.

Research on three complex compounds of divalent first-row transition metal ions having the Schiff base derived from sulfanilamide and N-acetylisatin as bidentate ligand

The present paper aims to describe the research performed on three complex compounds formed by divalent first-row transition metal ions – namely M = Co(II), Ni(II) and Zn(II) (representing the complex kernels) with the Schiff base derived from the condensation of sulfanilamide with N-acetylisatin (which proved itself to be able to act as a bidentate ligand in all these cases). This Schiff base is N-(1-acetyl-2-oxoindolin-3-ylidene)-4-aminobenzenesulfonamide, which appears twice in each complex, but is not the only ligand in the structure, as two water molecules are also part of the coordination sphere; there also is an ionization sphere, represented by two chloride ions whose role is to equilibrate the electrical charge of the complex kernel (all the ligands being charge-free) – the general molecular formula of the complexes being thus: [ML2(H2O)2]Cl2. From the electrical point of view, we dealt with three complex compounds that all showed themselves to be electrolytes. As far as magnetic properties are concerned, two of them proved themselves to be paramagnetic, whereas the last one was found to be diamagnetic. After adding different spectral data, corroborating them with the prior information and with the elemental analysis – we have drawn the conclusion that the complexes are six-coordinated, so they all will tend to adopt an octahedral geometry.

Syzgium cumini extract- a natural naked eye colorimetric sensor for selective and sensitive detection of Fe2+ in aqueous medium

Detection of metal ions using colorimetric technique offers a key to the development of a selective methodology to the qualitative analysis of the metal ions. In the current investigation, the utilization of abundantly available natural resource has been done wherein a simple fruit extract from Syzgium cumini in water offered a natural sensor to detect as well as eliminate Fe2+ ions, a pollutant from potable water. In the Indian subcontinent, the tropical fruit Syzgium cumini, also known as jamun in the local language, is widely grown. Anthocyanin is the main component of Syzgium cumini extract (SCE). Anthocyanin has been shown to form stable coordination complexes with heavy metal ions such as Al3+, Sn3+, and others. As a result, divalent transition metal ions such as Cu, Mn, Co, Fe, and Ni, which are possible metal contaminants in the environment, were chosen for this investigation. Only Fe2+ ions generated a Prussian blue coloured complex with SCE and the complex could be removed with a simple centrifugation process. The sensitivity of SCE towards Fe2+ ions was found to be in the region of 1 ppm, indicating that this green approach is extremely sensitive and selective.