HgII Ions Research Articles

Rhodol Derivatives as Selective Fluorescent Probes for the Detection of HgII Ions and the Bioimaging of Hypochlorous Acid.

Two sensors, 1 with a spirolactone group and 2 with a spirolactam group containing a phenyl isothiocyanate moiety, based on rhodol, were designed and synthesized in order to obtain materials with excellent optical properties for the detection of environmentally and biologically important Hg2+ and hypochlorous acid (HClO) ions. The crystal structure of 1 revealed two moieties, a rhodamine‐like portion with a spirolactone and a fluorescein‐like portion without a spirolactone. In the absence of analyte, 1 produced an optical output with a maximum absorption and emission at 475 and 570 nm, respectively, which was attributed to the fluorescein‐like moiety without a spirolactone. In contrast, the rhodamine‐like moiety containing a spirolactone was activated by the addition of H+ or Hg2+ ions, and 1 yielded new absorption and emission peaks at 530 and 612 nm, respectively. Further functionalization with a phenyl isothiocyanate group afforded 2, a fluorescent probe for HClO. High selectivity and sensitivity towards the hypochlorite ion were anticipated, owing to the stoichiometric and irreversible formation of a thiosemicarbazide group, which led to dramatic fluorescence responses. With good functionality at physiological pH, probe 2 was successfully used to image HClO in HeLa cells.

A one-dimensional HgII coordination polymer based on bis-(pyridin-3-ylmeth-yl)sulfane.

The reaction of mercury(II) chloride with bis-(pyridin-3-ylmeth-yl)sulfane (L, C12H12N2S) in methanol afforded the title crystalline coordination polymer catena-poly[[di-chlorido-mercury(II)]-μ-bis-(pyridin-3-ylmeth-yl)sulfane-κ2N:N'], [HgCl2L] n . The asymmetric unit consists of one HgII cation, one L ligand and two chloride anions. Each HgII ion is coordinated by two pyridine N atoms from separate L ligands and two chloride anions. The metal adopts a highly distorted tetra-hedral geometry, with bond angles about the central atom in the range 97.69 (12)-153.86 (7)°. Each L ligand bridges two HgII ions, forming an infinite -(Hg-L) n - zigzag chain along the b axis, with an Hg⋯Hg separation of 10.3997 (8) Å. In the crystal, adjacent chains are connected by inter-molecular C-H⋯Cl hydrogen bonds, together with Hg-Cl⋯π inter-actions [chloride-to-centroid distance = 3.902 (3) Å], that form between a chloride anion and the one of the pyridine rings of L, generating a two-dimensional layer extending parallel to (101). These layers are further linked by inter-molecular C-H⋯π hydrogen bonds, forming a three-dimensional supra-molecular network.

Flexibility and stabilization of HgII-mediated C:T and T:T base pairs in DNA duplex.

Owing to their great potentials in genetic code extension and the development of nucleic acid-based functional nanodevices, DNA duplexes containing HgII-mediated base pairs have been extensively studied during the past 60 years. However, structural basis underlying these base pairs remains poorly understood. Herein, we present five high-resolution crystal structures including one first-time reported C–HgII–T containing duplex, three T–HgII–T containing duplexes and one native duplex containing T–T pair without HgII. Our structures suggest that both C–T and T–T pairs are flexible in interacting with the HgII ion with various binding modes including N3–HgII–N3, N4–HgII–N3, O2–HgII–N3 and N3–HgII–O4. Our studies also reveal that the overall conformations of the C–HgII–T and T–HgII–T pairs are affected by their neighboring residues via the interactions with the solvent molecules or other metal ions, such as SrII. These results provide detailed insights into the interactions between HgII and nucleobases and the structural basis for the rational design of C–HgII–T or T–HgII–T containing DNA nanodevices in the future.

Formation of NH,NR N‐Heterocyclic Carbene Complexes through Mercuration of Mono‐N‐substituted Benzimidazoles

A simple two‐step method to prepare NH,NR N‐heterocyclic carbene (NHC) complexes is described herein. In the first step, the reactions of N‐substituted benzimidazoles (R‐BimH) with Hg(OAc)2 in the presence of NaBr rendered 12‐membered mercuramacrocycles [Hg4(R‐Bim)4Br4] [R = Me, pyridyl (Py), Bn]. These complexes consist of four HgII ions bridged by four benzimidazolyl anions through N and C atoms. This reaction presumably proceeds through an initial N‐complexation of the benzimidazole to the HgII ion. Consequently, C2‐H becomes more acidic, and even an acetate anion can promote the deprotonation at C2 to form the C‐metalated products. The second step involves the protonation of these mercuramacrocycles with HBF4·OEt2 to give the protic complexes featuring the NH,NR–NHC ligands of general formula [(R‐BimH)2Hg][BF4]2 (R = Me, Py, Bn).

Mercury Complexes with Tripodal Pseudopeptides Derived from D ‐Penicillamine Favour a HgS 3 Coordination

The pseudopeptides L4 and L5 are built on a nitrilotriacetic scaffold and functionalized with three D-penicillamine (D-Pen) units. D-Pen is an interesting building block and a bulkier analogue of cysteine with the β-methylene hydrogen atoms replaced by larger methyl groups. The two sulfur ligands L4 and L5 are studied here with the toxic HgII ion. The formation of the two mononuclear complexes HgL4 and HgL5 is demonstrated by 1H NMR spectroscopy and mass spectrometry and the tristhiolato coordination is unambiguously evidenced by the UV absorption signatures. An important feature is the stabilization of the HgS3 coordination mode at the expense of the generally preferred HgS2 linear coordination. It appears that the hindered D-Pen pseudopeptide L5 is capable of stabilizing the unusual HgS3 coordination over a large pH range in water, pH > 5.5. This water-soluble compound can therefore be considered as a promising chelating agent for mercury detoxification.

Doubly Thiocyanato(S,N)-Bridged Dinuclear Complexes of Mercury(II) from the Use of 2-pyridyl Oximes as Capping Ligands

The reactions between Hg(SCN)2 and the 2-pyridyl oximes, 2-pyridine aldoxime (paoH), methyl 2-pyridyl ketone oxime (mepaoH), pyridine-2-amidoxime (NH2paoH) and di-2-pyridyl ketone oxime (dpkoxH), have been investigated. The products in Me2CO or Me2CO/MeOH are the dinuclear complexes [Hg2(SCN)4(paoH)2] (1), [Hg2(SCN)4(mepaoH)2] (2), [Hg2(SCN)4(NH2paoH)2] (3) and [Hg2(SCN)4(dpkoxH)2] (4), whose structures have been determined by single-crystal X-ray crystallography. The molecular structures consist of centrosymmetric dinuclear molecules in which the two HgII ions are bridged by two bidentate bridging 1: 1: (1,3) SCN- groups forming a planar (1, 2) or non-planar (3, 4), 8-membered metallacyclic ring. The HgII centers are each chelated by a N(2-pyridyl), N(oxime)-bidentate ligand and are bound to one terminal S-bonded thiocyanato group. Due to the very long HgII-N (bridging SCN-) distances in 3, this complex can also be described as pseudodimer. The second 2-pyridyl ring of each dpkoxH ligand in 4 remains uncoordinated. The 2D lattice of 1 and 2 is built through H-bonding and - stacking interactions. Hydrogen bonds and S...S interactions generate 3D networks in 3 and 4. The IR spectra of the complexes are discussed in terms of the coordination modes of the ligands involved (SCN-, 2-pyridyl oximes). 1H NMR spectra in d6-DMSO indicate that the complexes decompose in solution. Keywords: Coordination chemistry, crystal structures, dinuclear mercury(II) complexes, 1H NMR spectra, infrared spectroscopy, oxime group, 2-pyridyl oxime ligands, thiocyanato ligands.

G-quadruplex-based logic gates for HgII and AgI ions employing a luminescent iridium(iii) complex and extension of metal-mediated base pairs by polymerase.

We report herein the synthesis of a series of cyclometallated iridium(iii) complexes as luminescent G-quadruplex-selective probes, which were used to construct AND, OR and INHIBIT logic gates for the detection of HgII and AgI ions. To our knowledge, this is the first time that the C-AgI-T mismatched base pair has been used for the construction of luminescent assays or logic gates.

A simple but highly selective and sensitive fluorescence reporter for toxic CdII ion via excimer formation

High selectivity and fluorescence sensitivity of a well-recognized antiexcitotoxic and anticonvulsant drug, kynurenic acid (KA), toward CdII ion has been demonstrated by UV–vis, fluorescence, 1H NMR spectroscopy in combination with computational calculations. Upon complexation with CdII, KA exhibits a distinct excimer emission at 528nm along with monomer emission at 402nm. The sensing ability of drug KA toward CdII ion is distinctly different from sensing for HgII or CuII ion. KA can form dimer by intermolecular O–H⋯O hydrogen bonding between the –COOH groups. Presence of CdII metal ions promotes dimer formation in the excited state which exhibits excimer fluorescence.

Synthesis, Structures, and Properties of Four Novel HgII Complexes Based on Pyridine Acylamide Ligands

In this work we synthesised four new pyridine acylamide complexes [HgI2(L1)] (1) and (2), [HgI2(L2)2] (3), and [HgI2(L3)]n (4) (L1 = N,N′-bis(3-pyridylmethyl)benzene-1,4-dicarboxamide, L2 = N4,N4′-bis(pyridin-3-yl)-[1,1′-biphenyl]-4,4′-dicarboxamide, L3 = N1,N3-bis(pyridin-3-ylmethyl)isophthalamide) by solvo(hydro)thermal reaction. Compounds 1 and 2 are supramolecular isomers prepared via variation of the reaction solvent, in which the HgII centres are bridged by L1 ligands to form one-dimensional (1D) helical chain or 1D meso-helical chain, respectively. Careful inspection of the structures reveal that formation of the isomers are mainly induced by the distinct configuration of L1 ligand and slight differences in coordination geometry of the HgII ions. Complex 3 shows a novel Z-shaped zero-dimensional structure with a L2–HgI2–L2–HgI2–L2 arrangement. In complex 4, flexible L3 ligands link HgI2 units to construct a 1D helical chain with an overall chiral structure, derived from spontaneous resolution. Luminescence properties of these four novel complexes were also explored.

Tuning of Silver Cluster Emission from Blue to Red Using a Bio-Active Peptide in Water

Blue, green, and red emitting silver quantum clusters have been prepared through green chemical approach by using a bio-active peptide glutathione (reduced) in a 50 mM phosphate buffer at pH 7.46. This study describes fluorescence emission tuning of the silver clusters by making different sized Ag clusters using slightly different reaction conditions keeping the same stabilizing ligand, reducing agent, solvent system, and silver salt precursor. The preparation procedure of these silver quantum clusters is new and highly reproducible. Each of these clusters shows very interesting fluorescence properties with large stokes shifts, and the quantum yields of blue, green, and red clusters are 2.08%, 0.125%, and 1.39%, respectively. These silver quantum clusters have been characterized by using different techniques including fluorescence spectroscopy, UV-vis spectroscopy, field-emission gun transmission electron microscopic (FEG-TEM) imaging and MALDI-TOF MS analyses. MALDI-TOF MS analyses show that the size of these blue, green and red emitting silver clusters are Ag5 (NC1, nanoclusters 1), Ag8 (NC2, nanoclusters 2) and Ag13 (NC3, nanoclusters 3), respectively, by using 2,5-dihydroxybenzoic acid as a matrix. These clusters are stable in broad ranges of pH. The NC3 (red emitting) has been successfully utilized for selective and sensitive detection of toxic Hg(II) ions in water by using even naked eyes, fluorometric, and calorimetric studies. The lower limit of detection of Hg(II) ions in water has been estimated to be 126 and 245 nM from fluorometric and UV-vis analyses, respectively. Enthalpy change (ΔH) during this Hg(II) sensing process is 2508 KJ mol(-1).

Crystal Structure of Metallo DNA Duplex Containing Consecutive Watson–Crick‐like T–HgII–T Base Pairs

AbstractThe metallo DNA duplex containing mercury‐mediated T–T base pairs is an attractive biomacromolecular nanomaterial which can be applied to nanodevices such as ion sensors. Reported herein is the first crystal structure of a B‐form DNA duplex containing two consecutive T–HgII–T base pairs. The HgII ion occupies the center between two T residues. The N3‐HgII bond distance is 2.0 Å. The relatively short HgII‐HgII distance (3.3 Å) observed in consecutive T–HgII–T base pairs suggests that the metallophilic attraction could exist between them and may stabilize the B‐form double helix. To support this, the DNA duplex is largely distorted and adopts an unusual nonhelical conformation in the absence of HgII. The structure of the metallo DNA duplex itself and the HgII‐induced structural switching from the nonhelical form to the B‐form provide the basis for structure‐based design of metal‐conjugated nucleic acid nanomaterials.

Crystal Structure of Apo‐ and Metalated Thiolate containing RNase S as Structural Basis for the Design of Artificial Metalloenzymes by Peptide‐Protein Complementation

AbstractRibonuclease S (RNase S) is a versatile model system to introduce non‐canonical amino acids into a protein scaffold by self‐assembly of the protein complex from S‐protein and S‐peptide. We have introduced two cysteines into the S‐peptide replacing lysine‐7 and glutamine‐11 of the α‐helical region of this peptide. The crystal structure of this variant was determined in the apo state and in complex with HgII ions. These structures serve as a template for the construction of artificial hybrid catalysts based on RNase S, e.g. for phosphanyl amino acids complexing transition metal ions for organometallic catalysis.

Synthesis, Crystal Structure, and Properties of the First Organomercury Dimer Derived from PMP

AbstractThe organomercury dimer [Hg2(PMP)Cl2]2·DMF (1) (PMP = 1‐phenyl‐3‐methyl‐2‐pyrazolin‐5‐one) was prepared by the reaction of mercury chloride with PMP and characterized by elemental analysis, IR spectroscopy, TG, and single‐crystal X‐ray diffraction analysis. The title compound crystallizes in the triclinic space group P$\bar{1}$, with a = 7.4298(6), b = 9.0313(8), c = 12.4145(13) Å, V = 760.50(12) Å3, Z = 1. Each mercury(II) atom is tricoordinated to one chlorine atom, one carbon atom of the pyrazole ring from one PMP, and one oxygen atom from another PMP. The coordination arrangement around the mercury atom is T‐shaped. This is the first structural report on an organomercury derivative of PMP. The distance between the two HgII ions is 3.2735(8) Å, which indicates the presence of weak Hg···Hg interactions. Meanwhile, 1 can be connected by intermolecular C–H···Cl hydrogen bonding and weak Hg···O/Cl/N interactions to form a three dimensional network. The thermal stability and antibacterial activity of 1 were studied. The binding of 1 with calf thymus DNA was investigated by absorption spectroscopy and viscometry.

Formation of a Thymine‐HgII‐Thymine Metal‐Mediated DNA Base Pair: Proposal and Theoretical Calculation of the Reaction Pathway

A reaction mechanism that describes the substitution of two imino protons in a thymine:thymine (T:T) mismatched DNA base pair with a Hg(II) ion, which results in the formation of a (T)N3-Hg(II)-N3(T) metal-mediated base pair was proposed and calculated. The mechanism assumes two key steps: The formation of the first Hg(II)-N3(T) bond is triggered by deprotonation of the imino N3 atom in thymine with a hydroxo ligand on the Hg(II) ion. The formation of the second Hg(II)-N3(T) bond proceeds through water-assisted tautomerization of the remaining, metal-nonbonded thymine base or through thymine deprotonation with a hydroxo ligand of the Hg(II) ion already coordinated to the thymine base. The thermodynamic parameters ΔGR =-9.5 kcal mol(-1), ΔHR =-4.7 kcal mol(-1), and ΔSR =16.0 cal mol(-1) K(-1) calculated with the ONIOM (B3LYP:BP86) method for the reaction agreed well with the isothermal titration calorimetric (ITC) measurements by Torigoe et al. [H. Torigoe, A. Ono, T. Kozasa, Chem. Eur. J. 2010, 16, 13218-13225]. The peculiar positive reaction entropy measured previously was due to both dehydration of the metal and the change in chemical bonding. The mercury reactant in the theoretical model contained one hydroxo ligand in accord with the experimental pKa value of 3.6 known for an aqua ligand of a Hg(II) center. The chemical modification of T:T mismatched to the T-Hg(II)-T metal-mediated base pair was modeled for the middle base pair within a trinucleotide B-DNA duplex, which ensured complete dehydration of the Hg(II) ion during the reaction.

Design of Polymer-Brush-Grafted Magnetic Nanoparticles for Highly Efficient Water Remediation

Highly efficient removal of mercury(II) ions (Hg(II)) from water has been reported by employing polymer-brush-functionalized magnetic nanoparticles (MNPs). Surface-initiated conventional radical polymerization (SI-cRP) was used to grow poly(2-aminoethyl methacrylate hydrochloride) (poly-AEMA·HCl) polymer chains on magnetite nanoparticles (Fe3O4), followed by the transformation of pendant amino groups into dithiocarbamate (DTC) groups, which showed high chelating affinity toward Hg(II) ions. This polymer-brush-based DTC-functionalized MNP (MNPs-polyAEMA·DTC) platform showed the complete removal of Hg(II) from aqueous solutions. The Hg(II) ion removal capacity and efficiency of MNPs-polyAEMA·DTC were compared with its monolayer analogue, which was derived from the direct transformation of amino groups of (3-aminopropyl) triethoxysilane (APTES)-functionalized MNPs (MNPs-APTES) to DTC functional groups (MNPs-DTC). The surface chemical modifications and higher chelating functional group density, in the case of MNPs-polyAEMA·DTC, were ascertained by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), physical property measurement system (PPMS), attenuated total reflectance infrared (ATR-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The Hg(II) ion removal capacity and efficiency of monolayer and polymer-brush-based DTC-functionalized MNPs (MNPs-DTC and MNPs-polyAEMA·DTC, respectively) were evaluated and compared by studying the effect of various factors on the percentage removal of Hg(II) such as adsorbent amount, temperature, and contact time. Furthermore, the adsorption behavior of MNPs-DTC and MNPs-polyAEMA·DTC was analyzed by applying Langmuir and Freundlich adsorption isotherm models. In addition, the adsorption thermodynamics, as well as the adsorption kinetics, were also evaluated in detail. The higher surface functional group density of MNPs-polyAEMA·DTC led to superior remediation characteristics toward Hg(II) ions than its monolayer analogue.

Surface Plasmon Tunability and Emission Sensitivity of Ultrasmall Fluorescent Copper Nanoclusters

Ultrasmall copper nanoparticles have been synthesized using copper(II) salt as precursor by hydrazine reduction in the presence of citric acid and cetyltrimethylammonium bromide facilitating the growth of stable copper nanoparticles with an average diameter of <2 nm. The corresponding surface plasmon resonances were monitored under variable microenvironments, and it is seen that these tiny copper nanoparticles form aggregates under stipulated reaction conditions. It is noted that ultrasmall copper nanoparticles do not exhibit any characteristic surface plasmon band in the visible region; rather, a continuous absorption is seen over the entire UV–vis region. However, a well-defined plasmon absorption band makes its appearance while the particles are aggregated in close-packed assembly. These results demonstrate that the maximum of surface plasmon resonance is red-shifted from that of isolated particles because of electromagnetic interaction between the particles. The aggregation process is manifested upon changes of pH, anionic surfactant, etc. and is not reversible, i.e., the aggregates could not be re-dispersed into ultrasmall particles. The effect of addition of electrolyte has been monitored to study the surface plasmon damping of the copper nanoparticles. The plasmonic sensitivity of the copper nanoparticle aggregates has been elicited by the determination of amino acid chain length with exquisite sensitivity because of enormous electromagnetic field at the junction of the particles in the aggregates. Interestingly, the as-synthesized ultrasmall copper nanoclusters exhibit excellent fluorescence properties with a narrow emission profile. The emission properties of these copper nanoclusters have been utilized as an indicator for selective and ultrasensitive detection of highly toxic HgII ions in water in the nanomolar detection limit.

Diversity in supramolecular self-assembly through hydrogen-bonding interactions of non-coordinated aliphatic –OH group in a series of heterodinuclear CuIIM (M = NaI, ZnII, HgII, SmIII, BiIII, PbII and CdII)

The syntheses, and structural characterization of seven heterodinuclear complexes: [CuII (HL)NaI(NO3)(MeOH)] (1), [CuII(HL)ZnII(H2O)(NO3)](NO3) (2), [CuII(HL)HgII(Cl)2] (3), [CuII(H2O)(HL)SmIII(NO3)3] (4), [CuII(H2O)(HL)BiIII(NO3)3] (5), [CuII(HL)PbII(NO3)2] (6) and [CuII(HL)CdII(NO3)2] (7) are reported, where H3L=N,N′-bis(3-methoxysalicylaldiimine)-1,3-propylene-2-ol. Compounds 1 and 3 crystallize in the monoclinic P21/n space group, 4, 5 and 7 in the monoclinic P21/c space group, while the space group of complexes 2 and 6 is triclinic P1¯. The X-ray crystallography reveals that the structures of all the complexes consist of diphenoxo-bridged heterometallic cores in which CuII metal ion is trapped in N2O2 compartment of the Schiff-base ligand, while the second metal ion is present in the larger and open O4 [O(phenoxo)2O(methoxy)2] compartment. NaI and ZnII ions in 1 and 2, respectively, are six coordinated, while PbII ion in 6 and CdII ion in 7 are eight coordinated. HgII ion in 3 is six coordinated, while both SmIII and BiIII ions in 4 and 5, respectively, are surrounded by 10 oxygen atoms involving four O atoms from the outer compartment of the ligand and six from three chelating nitrates. In all the cases, non-coordinated –OH group plays significant role in the construction of diverse supramolecular aggregates through hydrogen bonding: two dimensional (2D) in 1 and 3, one dimensional (1D) in 2, 4, 5 and 6, while dimeric in 7. In addition to the structural diversity, the structural resemblance of bismuth(III) with member of a lanthanum family, samarium(III), is noted. In fact, they are found to be isostructural and isomorphous in the present study. Most importantly, compound 3 exhibits a rare feature of helical twisting for the coordinated Schiff-base ligand that arises due to the fact that the metal ion is too large to fit into the wider O4 compartment.

Catena-Poly[[chlorido[1-(3-nitrophenyl)-2-(triphenylphosphoranylidene)ethanone-κC2]mercury(II)]-μ-chlorido

In the title organometallic polymer, [HgCl2(C26H20NO3P)]n, the monodentate 1-(3-nitro­phen­yl)-2-(triphenyl­phospho­ran­yl­­idene)ethanone ligand is coordinated to the HgII atom through the methine C atom. The HgII atom is four-coordinated in a distorted tetra­hedral geometry by one terminal Cl atom, two bridging Cl atoms, and one C atom from the ylidic ligand, resulting in a polymeric chain parallel to [010]. The terminal Cl atom is more strongly bound to the HgII ion [2.3916 (9) Å] than the bridging Cl atoms. The bridge is asymmetric, as indicated by the two different Hg—Cl(bridging) bond lengths [2.5840 (8) and 2.7876 (8) Å]. Intra­molecular C—H⋯O and weak C—H⋯Cl contacts stabilize the polymeric chain. In the crystal, adjacent chains inter­act via C—H⋯O hydrogen bonds.

Di-μ-chlorido-bis-[(2-amino-4-methyl-pyridine-κN)-chloridomercury(II)

In the centrosymmetric dinuclear title compound, [Hg2Cl4(C6H8N2)2], the HgII ion is four-coordinated by one pyridine N atom from a 2-amino-4-methyl­pyridine ligand, one terminal Cl atom and two bridging Cl atoms. A distorted tetra­hedral geometry is formed around each HgII ion. The crystal packing is stabilized by intra- and inter­molecular N—H⋯Cl hydrogen bonding. There are also π–π stacking inter­actions in the structure, with centroid-to-centroid distances of 3.594 (6) Å.

Catena-Poly[[dichloridomercury(II)]-μ-{N-[(E)-pyridin-2-ylmethylidene-κN]pyridin-3-amine-κ2N1:N3}

In the title coordination polymer, [HgCl2(C11H9N3)]n, the HgII ion is coordinated by three N atoms from two N-[(E)-pyridin-2-yl­methyl­idene]pyridin-3-amine (L) ligands and two chloride anions in a distorted trigonal–bipyramidal geometry. The two pyridine rings in L form a dihedral angle of 50.0 (2)°. L ligands bridge adjacent HgCl2 units into polymeric chains propagating in [010]. The crystal packing is further stabilized by weak inter­molecular C—H⋯Cl hydrogen bonds and π–π inter­actions between the pyridine rings, with a centroid–centroid separation of 3.529 (9) Å.