Group IIB Metal Ions Research Articles

Use of group IIB metal ions as charge carriers for collision-induced dissociation of glycopeptide and glycan.

Dissociation of biomolecules by tandem mass spectrometry (MS/MS) generates a variety of fragment ions which provide useful information for the structural characterization of biomolecules. Different fragmentation strategies result in different mass spectra for the same molecule and thus provide distinct features. Charge carriers play important roles in determining the dissociation pathways of the target precursor ions. The use of various transition metals ions as charge carriers of glycopeptide and glycan might provide additional structural information and needs to be investigated. A 9.4T SolariX FTICR mass spectrometer was used for collision-induced dissociation (CID) of glycopeptide and glycan. Group IIB metal ions, including Zn2+ , Cd2+ and Hg2+ , were used as charge carriers. Glycopeptide NLTK-M5 G2 and glycan G1F were used as the model systems. For Zn2+ - and Cd2+ -adducted species, cross-ring cleavages, glycosidic cleavages and cleavages along the peptide backbone could be obtained. There is a high degree of similarity in their CID spectra with that of Mg2+ ion-adducted glycopeptide species. For Hg2+ -adducted species, only glycosidic cleavages were observed in high abundance. The formation of doubly-charged ions (M2+ ) and a series of [f-H]+ fragments indicated unique dissociation pathways for Hg2+ -adducted glycopeptide. Zn2+ and Cd2+ -adducted glycopeptide species produced similar dissociation CID spectra, whereas Hg2+ -adducted species produced significantly different CID spectra. Similar CID dissociation features were also observed for Group IIB metal ions adducted glycan species. These results demonstrated that different metal ions might be used to tune the dissociation behaviors of glycopeptides and glycans.

Detection of Zn2+, Cd2+, Hg2+, and Pb2+ ions through label-free poly-L-glutamic acid

Detection of heavy metal ions in water is important for environmental sustainability and food safety. Current fluorescent sensors interact with metal ions directly through chelation or chemical reactions. Those sensors are expensive to produce and often can detect only one ion at a time. Here we report a fluorescent turn-on sensor that can detect three group IIB metal ions and Pb2+ ions through label-free polypeptides in water. In our sensor-polypeptide mixture, Zn2+, Cd2+, Hg2+, and Pb2+ ions induce helix formation and inter-chain aggregation in poly-L-α-glutamic acid (PGA). The acridinium-based sensor molecules incorporate into the polypeptides and emit strongly with characteristic color for each group IIB ion under UV lamp. By adjusting the size of polypeptides or the length of the side chain carboxyl groups, we can selectively turn off or turn on the sensor emission for Hg2+ ions.

Doping Group IIB Metal Ions into Quantum Dot Shells via the One‐Pot Decomposition of Metal‐Dithiocarbamates

Almost half of solar energy reaching the Earth is in the infrared, and for solar cells, IR absorbing/emitting quantum dots are highly effective photovoltaic materials. As a possible approach to generating such materials, an investigation into the incorporation of group IIB metal ions during the shelling of II–VI and III–V semiconductor core/shell quantum dots is presented. Quantum dot shells consist of ZnS and an additional metal sulphide, obtained from the decomposition of metal dithiocarbamate single‐source precursors. Resultant quantum dots are characterized and interrogated using transmission electron microscopy, high‐resolution transmission electron microscopy, electron diffraction, time‐of‐flight‐secondary ion mass spectroscopy, X‐ray photoelectron spectroscopy, energy dispersive X‐ray spectroscopy, photoluminescence emission and lifetime spectroscopy, and UV–vis spectroscopy. It is demonstrated that on incorporation of an additional metal sulphide during shelling, photoluminescence properties change dramatically according to the element and indeed, its concentration. Tunable infrared emission is achieved for Hg addition, thus a one‐pot method for the synthesis of infrared emitting quantum dots from visible luminescent cores is hereby developed.

Diethyldithiocarbamate-mediated zinc ion chelation reveals role of Cav2.3 channels in glucagon secretion

Peptide-hormone secretion is partially triggered by Ca2+ influx through voltage-gated Ca2+ channels (VGCCs) and gene inactivation of Zn2+-sensitive Cav2.3-type VGCCs is associated with disturbed glucose homeostasis in mice. Zn2+ has been implicated in pancreatic islet cell crosstalk and recent findings indicate that sudden cessation of Zn2+ supply during hypoglycemia triggers glucagon secretion in rodents. Here we show that diethyldithiocarbamate (DEDTC), a chelating agent for Zn2+ and other group IIB metal ions, differentially affects blood glucose and serum peptide hormone level in wild-type mice and mice lacking the Cav2.3-subunit. Fasting glucose and glucagon level were significantly higher in Cav2.3-deficient compared to wild-type mice, while DEDTC Zn2+-chelation produced a significant and correlated increase of blood glucose and serum glucagon concentration in wild-type but not Cav2.3-deficient mice. Glucose tolerance tests revealed severe glucose intolerance in Zn2+-depleted Cav2.3-deficient but not vehicle-treated Cav2.3-deficient or Zn2+-depleted wildtype mice. Collectively, these findings indicate that Cav2.3 channels are critically involved in the Zn2+-mediated suppression of glucagon secretion during hyperglycemia. Especially under conditions of Zn2+ deficiency, ablation or dysfunction of Cav2.3 channels may lead to severe disturbances in glucose homeostasis.

A series of novel ferrocene‐based dipeptide receptors for electrochemistry and biological activity

Synthesis of ferrocene‐based dipeptide receptors FcL1, FcL2, FcL3, FcL4, FcL5 was carried out by the acylation reaction of ferrocenecarboxylic acid with dipeptide esters. Compounds were characterized by IR, 1H NMR, 13C NMR and elemental analysis. Single‐crystal X‐ray analysis of FcL3 showed it has two independent chiral molecules and the two chiral atoms (C12 and C35) are in R configuration. Their cyclic voltammetric behaviors showed a pair of well‐defined and stable redox waves in the potential range 0.00–1.00 V. The configuration of the metals influenced the receptor's characteristics greatly, and at the same time the FcL compounds could selectively sense group IIB metal ions Zn2+, Cd2+ and Hg2+. The biological activities of FcL1, FcL2, FcL3, FcL4, FcL5 were studied against the tested bacteria; among them, FcL4 showed significant activity against all five bacterial strains tested. Copyright © 2013 John Wiley & Sons, Ltd.

Formation of Peptide Radical Cations (M+·) in Electron Capture Dissociation of Peptides Adducted with Group IIB Metal Ions

Peptides adducted with different divalent Group IIB metal ions (Zn(2+), Cd(2+), and Hg(2+)) were found to give very different ECD mass spectra. ECD of Zn(2+) adducted peptides gave series of c-/z-type fragment ions with and without metal ions. ECD of Cd(2+) and Hg(2+) adducted model peptides gave mostly a-type fragment ions with M(+•) and fragment ions corresponding to losses of neutral side chain from M(+•). No detectable a-ions could be observed in ECD spectra of Zn(2+) adducted peptides. We rationalized the present findings by invoking both proton-electron recombination and metal-ion reduction processes. As previously postulated, divalent metal-ions adducted peptides could adopt several forms, including (a) [M + Cat](2+), (b) [(M + Cat - H) + H](2+), and (c) [(M + Cat - 2H) + 2H](2+). The relative population of these precursor ions depends largely on the acidity of the metal-ion peptide complexes. Peptides adducted with divalent metal-ions of small ionic radii (i.e., Zn(2+)) would form predominantly species (b) and (c); whereas peptides adducted with metal ions of larger ionic radii (i.e., Hg(2+)) would adopt predominantly species (a). Species (b) and (c) are believed to be essential for proton-electron recombination process to give c-/z-type fragments via the labile ketylamino radical intermediates. Species (c) is particularly important for the formation of non-metalated c-/z-type fragments. Without any mobile protons, species (a) are believed to undergo metal ion reduction and subsequently induce spontaneous electron transfer from the peptide moiety to the charge-reduced metal ions. Depending on the exothermicity of the electron transfer reaction, the peptide radical cations might be formed with substantial internal energy and might undergo further dissociation to give structural related fragment ions.

Force fields including charge transfer and local polarization effects: Application to proteins containing multi/heavy metal ions

The question whether molecular dynamics (MD) simulations can yield reliable structural and dynamical properties of metalloproteins depend on the accuracy of the force field, i.e., the potential energy function (PEF) and associated parameters modeling the interactions of the metal ion of interest with water and protein ligands. Previously, we had developed a CTPOL PEF for protein simulations of Zn(2+) bound to Cys(-) and/or His(0) that includes charge transfer and local polarization effects as well as metal van der Waals parameters that reproduce the structural and thermodynamical properties of 22 dications. Here, we evaluate if the CTPOL PEF and the new metal parameters (referred to as the CTPOLa force field) can be applied to proteins containing polynuclear metal-binding sites and heavy toxic metal ions, using the CdZn(2)-Cys(9) beta-domain of rat liver metallothionein-2 and the Hg(2+)-bound 18-residue peptide from MerP as test systems. Using the CTPOLa force field, simulations of the beta-domain of rat liver metallothionein-2 totaling 19 ns could preserve the experimentally observed CdZn(2)-Cys(9) complex geometry and overall protein structure, whereas simulations neglecting charge transfer and local polarization effects could not. However, the CTPOLa force field cannot reproduce the experimentally observed linear bicoordination of Hg(2+) in the MerP peptide without adding an angular restraint to the CTPOL PEF to correct the angle distribution about Hg(2+). Thus, the force fields presented herein for the group IIB metal ions can be applied to simulation studies of proteins containing polynuclear metal-binding sites and heavy metal ions in aqueous solution. PEF neglecting charge transfer and local polarization effects in conjunction with vdW parameters adjusted to reproduce the structural and thermodynamical properties of only the metal ion in question could not yield an accurate representation of the metal-binding site and overall protein structure.

Coordination architectures of 2-(1H-tetrazol-5-yl)pyrazine with group IIB metal ions: luminescence and structural dependence on the metal ions and preparing conditions

The influence of the nature of metal ions and reaction conditions on the formation of group IIB metal coordination architectures of a tetrazole ligand, 2-(1H-tetrazol-5-yl)pyrazine (HL), and the luminescent properties of some complexes have been investigated. At room temperature, the reactions of Zn(NO3)2∙6H2O (or ZnCl2) and Cd(NO3)2∙6H2O with HL gave rise to two reported complexes, [M(L)2(H2O)2] (1 and 2, Acta Crystallogr., Sect. C, 2006, 62, m614; Acta Crystallogr., Sect. E, 2006, 62, m2841), respectively. However, under hydrothermal conditions, the same reactions yield 1 and another complex, {[Cd2(L)4](H2O)0.25}n (3), respectively. In both preparation conditions mentioned above, the HL ligand reacts with Hg(OAc)2 (or HgBr2) to give complexes, [Hg(L)2]n (4), [Hg(L)2]n (5) and [Hg(L)Br]n (6) with different structures. 1 and 2 have a similar mononuclear structure and in the crystal structure such molecules are further assembled together to form a 3-D α-Pt topological framework with O–H⋯N hydrogen bonds. 4 possesses a 1-D chain structure, in which the Cd(II) center is six-coordinated, with all coordination sites being occupied by N atoms of the ligands. Furthermore, such chains are interlinked via π⋯π interactions to form a 3-D framework. 4 has a 2-D (6,3) topological structure, in which the Hg(II) center is six-coordinated to six N atoms of L, and the L ligand takes a chelating-bridging mode similar to that in 3. 5 has a 2-D (4,4) topological layer structure with the metal center being six-coordinated, and the six coordination sites are held by N atoms from four L ligands, taking different coordination modes. Moreover, such planes are generated to form a 3-D structure via two kinds of π⋯π interactions. 6 is a 2-D layer with the Hg(II) coordinating to a Br atom and three N atoms of three tetrazole rings from different L ligands. This result shows that the metal ions and reaction conditions have significant influence on the group IIB metal complexes of this multifunctional ligand, and the intramolecular/intermolecular weak interactions are likely to play important roles in the formation of such complexes, especially linking the discrete subunits or low-dimensional entities into high-dimensional frameworks. In addition, the luminescent studies of HL and 1, 2, 3 and 6 indicate that they display blue emissions with different densities in the solid state at room temperature.

Role of the conserved histidines in the Zn module of the copper-activated transcription factors in yeast

The Amt1 and Ace1 transcription factors from Candida glabrata and Saccharomyces cerevisiae are activated by the formation of a tetracopper thiolate cluster resulting in Cu4Zn1Amt1 complexes. An independent Zn module exists within the N-terminal 40 residues of Amt1 and Ace1. There are two conserved histidyl residues within this module. His25 serves as a Zn(II) ligand for the S3N1 site. Thus, Zn(II) ligands are provided by cysteinyl thiolates of Cys11, Cys14, Cys23 and His25. The Zn module is a stably folded domain that binds group IIb metal ions with high affinity. Mutations in Amt1 and Ace1 genes within codons encoding Zn(II) cysteinyl ligands markedly attenuate the ability of Amt1 and Ace1 to mediate Cu-induced expression of metallothionein genes. Thus, the Zn modules in Amt1 and Ace1 are functionally important. A second histidine, His18, is conserved in the Zn module of these metal-activated factors. His18 does not serve a major structural role, but appears important functionally in Ace1 and Amt1.

Effects of the group IIB metals (Cd, Zn and Hg) on the permeability of the crystalline lens of the toad ( Bufo marinus)

1. 1. Cd, Zn, Hg and methyl mercury chloride (on anterior, not posterior) decrease the potential difference and short-circuit current across the lens of the toad. 2. 2. When translenticular Na transport was abolished, these metals were still effective. When Na was removed from the anterior, the effects of Cd and Zn were abolished, whereas Hg and CH 3 Hg continued to act. Lenses in vitro accumulated Na and lost K in the presence of Cd and Hg but Zn or CH 3Hg had no effect. 3. 3. O 2 consumption in vitro was reduced by Zn, Hg and CH 3Hg, but not Cd. In the absence of Na, Hg and CH 3Hg still decreased O 2 consumption indicating a general toxic effect. 4. 4. The group IIB metal ions alter the electrical parameters and permeability of the crystalline lens but they act in different ways which reflects their varied chemical properties.

Leucine aminopeptidase: A zinc metalloenzyme

The leucine aminopeptidase of the supernatant fraction of porcine kidney is instantaneously inhibited by orthophenanthroline, bipyridyl, cupferron, sodium diethyldithiocarbamide, sodium sulfide, and sodium cyanide. All of these inhibitions are reversed by addition of group IIb metal ions in appropriate quantity to the reaction mixture. During purification of the enzyme under conditions which minimize the addition of extraneous metal, the zinc-to-protein ratio in the fractions rises to a final value between 4 and 6 g-atoms per 300,000 g of protein, as estimated by three independent analytical methods, while the content of all other metals falls to negligible levels. Removal of the zinc from the purified enzyme or its replacement by cadmium results in loss of enzyme activity in proportion to the loss of zinc. Replacement of the cadmium in cadmium leucine aminopeptidase by zinc restores native levels of activity. Manganese can also partially replace the zinc of the purified enzyme yielding a derivative more active toward both leucine amide and leucine p-nitroanilide than the native enzyme. These data suggest that leucine aminopeptidase is a zinc metalloenzyme.