Efficient Oxidation and Destabilization of Zn(Cys)4 Zinc Fingers by Singlet Oxygen

Singlet oxygen (¹O₂) plays an important role in oxidative stress in all types of organisms, most of them being able to mount a defense against this oxidant. Recently, zinc finger proteins have been proposed to be involved in its cellular detection but the molecular basis of this process still remains unknown. We have studied the reactivity of a Zn(Cys)₄ zinc finger with ¹O₂ by combinations of spectroscopic and analytical techniques, focusing on the products formed and the kinetics of the reaction. We report that the cysteines of this zinc finger are oxidized to sulfinates by ¹O₂. The reaction of the ZnS₄ core with ¹O₂ is very fast and efficient with almost no physical quenching of ¹O₂. A drastic (ca. five orders of magnitude) decrease of the Zn²⁺ binding constant was observed upon oxidation. This suggests that the Zn(Cys)₄ zinc finger proteins would release their Zn²⁺ ion and unfold upon reaction with ¹O₂ under cellular conditions and that zinc finger sites are likely targets for ¹O₂.     

Tripodal Ligands: Design of Distorted Coordination Polyhedra in Biomimetic Metal Complexes. Crystal structures of [Zn(SCN)(ntb)](SCN) · iPrpOH and [Fe(acac)(ntb)](ClO4)2 · 2CH2Cl2 · iPrpOH,ntb = N-tris(2-benzimidazolylmethyl)amine

The tripodal ligand N-tris(2-benzimidazolylmethyl)-amine (ntb) was used for the preparation of zinc(II) and iron(III) complexes, [Zn(SCN)(ntb)](SCN) · ⁱPrpOH ( 1 ) and [Fe(acac)(ntb)](ClO₄)₂ · 2CH₂Cl₂ · ⁱPrpOH ( 2 ). 1 has a highly distorted trigonal-bipyramidal ZnN₅ coordination geometry. The donor atoms are nitrogens of one amine, three benzimidazoles and one SCN^?. A striking feature of the complex is the length of the Zn? N_amine bond of 2.539(6)Å. The octahedral N₄O₂ coordination sphere of the iron in 2 is less distorted than that of the zinc in 1 . The metal is surrounded by an amine and three benzimidazole nitrogens of the ligand and two oxygens of the bidentate acetylacetonate co-ligand. The Fe? O bond lengths differ by about 0.1 Å. As for the unusual long Zn? N bond in 1 this is a result of a trans effect. 1 crystallizes in the space group P1 with: a = 9.530(1)Å, b = 13.402(1)Å, c = 13.578(2)Å, α = 98.83(1), β = 95.19(1), γ = 101.21(1)°, Z = 2; 2 is also triclinic, space group P1 , with: a = 9.875(6)Å, b = 12.929(10)Å, c = 18.635(15)Å, α = 94.95(8)°, β = 101.01(6)°, γ = 111.09(4)°, Z = 2.     

Thermodynamic Stability Versus Kinetic Lability of ZnS4 Core

Density Functional Theory and post‐Hartree Fock calculations reveal an unusual energy profile for Zn? S and Zn? N bond dissociation reactions in several [Zn(SR)₄]^2? and [Zn(Im)(SR)₃]^? complexes. The Zn? S bond dissociation in tetrathiolate dianions, which is highly exothermic in the gas phase, proceeds through a late transition state which can be rationalized on the basis of an avoided crossing resulting from Coulomb repulsion between the anionic fragments and ligand‐to‐metal charge‐transfer in the [Zn(SR)₄]^2? complexes. When solvation models for water, DMSO, or acetonitrile are included, some complexes become stable while others are metastable, so this constitutes the first theoretical model which is in full agreement with the experimental data for various [Zn(SR)₄]^2?, [Zn(SR)₃]^?, and [Zn(Im)(SR)₃]^? complexes. The analysis given here indicates that the Zn(Cys)₄ and Zn(His)(Cys)₃ cores of numerous proteins are metastable with respect to Zn? S and Zn? N bond dissociation, respectively. This is consistent with the kinetic lability at the zinc‐centers and illustrates that in nature, thermodynamic stability is imparted upon the zinc cores by the protein environment.     

Aqua(benzene‐1,3‐dicarboxylato)zinc(II)

The title compound, poly­[[aqua­zinc(II)]‐μ‐benzene‐1,3‐di­carboxyl­ato‐O¹:O^1′:O²], [Zn(C₈H₄O₄)(H₂O)]_n, forms a metal–organic coordination network that consists of tetrahedral Zn atoms bonded to one water mol­ecule and three carboxyl­ate groups. Isophthalate groups bridge the four‐coordinate Zn centers to generate two‐dimensional architectures in the ac plane. These planar zinc isophthalate motifs are linked by infinite C=O?H—O—H interactions along the a axis to form a chiral framework. The observed polar structural pattern originates due to the distorted tetrahedral Zn centers [O—Zn—O 100.7 (2)–136.0 (1)°] and the alignment of the water mol­ecules. Bridging isophthalate groups align to form approximate centrosymmetric motifs.     

Two New Polyoxovanadate‐supported Transition Metal Complexes: [Zn(en)2][Zn(en)2(H2O)2][{Zn(en)(enMe)}As6V15O42(H2O)]·4H2O and [Zn2(enMe)2(en)3][{Zn(enMe)2}As6V15O42(H2O)]·4H2O

Two novel As‐V‐O cluster supported transition metal complexes, [Zn(en)₂][Zn(en)₂(H₂O)₂][{Zn(en)(enMe)}As₆V₁₅O₄₂(H₂O)]·4H₂O ( 1 ) and [Zn₂(enMe)₂(en)₃][{Zn(enMe)₂}As₆V₁₅O₄₂(H₂O)]·4H₂O ( 2 ), have been hydrothermally synthesized. The single X‐ray diffraction studies reveal that both compounds consist of discrete noncentral polyoxoanions [{Zn(en)(enMe)}As₆V₁₅O₄₂(H₂O)]^4? or [{Zn(enMe)₂}As₆V₁₅O₄₂(H₂O)]^4? cocrystallized with respective zinc coordination complexes. Interestingly, compounds 1 and 2 exhibit the first two polyoxovanadates containing As₈V₁₅O₄₂‐(H₂O)]^6? cluster decorated by only one transition metal complex. Crystal data: 1 , monoclinic, P2₁/n, a = 14.9037(4) Å, b = 18.1243(5) Å, c = 27.6103(7) Å, β = 105.376(6)°, Z = 4; 2 monoclinic, P2₁/n, a = 14.9786(7) Å, b = 33.0534(16) Å, c = 14.9811(5) Å, Z = 4.     

Crystal structure of diacetato-bis(2-methyl-2-propylamine)zinc(II)

The diacetato-bis(2-methyl-2-propylamine)zinc(II) compound crystallizes in the triclinic system, space group P-1 with unit cell parameters a = 10.0144(10)Å, b = 10.2687(10)Å, c = 10.5149(10)Å. α = 115.184(2)°, β = 97.489(2)°, γ = 114.066(2)°, ν = 830.85(14)ų. The obtained solid state structure of (^tBuNH₂)₂Zn(OOCCH₃)₂ shows both inter- and intramolecular NH—O hydrogen bond interactions which are analyzed.     

Wie steuert man die Koordination in Zinkkomplexen?? Untersuchungen mit Hydridotris(3-phenylpyrazolyl)borat als Ligand

How to Steer the Coordination of Zinc Complexes? Investigations with Hydridotris(3-phenylpyrazolyl)borate as a Ligand The crystal structure analyses of the zinc complexes L_PhZnCl ( A ) and Zn(L_Ph)₂ ( B ) of the potentially tridentate nitrogen ligand L_Ph^? = HB(3-Phpz)₃^? Phpz = 3-Phenylpyrazolyl) unexpectedly show tetrahedral coordination of the metal ion in both cases. The bisligand zinc complex B is formed by decomposition of unstable hydroxy and alkoxy complexes of the formula L_PhZnOR. As a further product of that reaction a complex of the formula [η³B(3-Phpz)₃Zn(3-PhpzH)]⁺ClO₄^? could be identified which is a first example for the cationic species L_PhZn(neutral ligand)⁺. A crystallizes in the trigonal system with lattice constants of a = 11.449(2) and c=11.365(2) Å, space group P3 , Z = 2, d_calc. = 1.365mg/mm³. B crystallizes in the orthorhombic system with a = 22.675(3), b = 10.797(2), and c = 19.699(3) Å, space group Pbcn; Z = 4, d_calc. = 1.306 mg/mm³. The crystal structures were determined from 1 687 ( A ) and 2 341 ( B ) observed X-ray data and refined to R = 0.03 and 0.04, respectively. A was characterized as a chlorotripod complex with symmetry 3-C₃ and a distorted tetrahedral coordination of the Zn atom (angle Cl? Zn? N 122.9(1)° and N? Zn? N′ 93.3(1)°), while B was identified as a bisligand complex with symmetry 2-C₂ and again a distorted tetrahedral coordination of the Zn atom (angles N? Zn? N 101.5(1) up to 118.9(1)°).     

A hexanuclear discrete assembly and a two dimensional coordination polymer constructed from heterotrinuclear [(CuL)2Zn]2+ nodes and dicyanamide spacer (H2L = salen type Schiff base ligands)

Two new Cu(II)–Zn(II) complexes as a discrete hexanuclear cluster [{(CuL¹)₂Zn}₂(μ_1,5-N(CN)₂)₂](ClO₄)₂ (1) and a two dimensional (2D) coordination polymer [(CuL²)₂Zn(μ_1,5-N(CN)₂)₂]_n (2) have been isolated by mixing two similar tetradentate Schiff bases H₂L¹ (N,N′-bis(ɑ-ethylsalicylidene)-1,3-propanediamine) and H₂L² (N,N′-bis(salicylidene)-1,3-pentanediamine) separately with Cu(ClO₄)₂·6H₂O, Zn(ClO₄)₂·6H₂O and NaN(CN)₂ ?at same reaction condition. The heterometallic complexes have been structurally characterized by single crystal X-ray analyses showing that both are formed by angular trinuclear nodes and μ_1,5-dicyanamide spacers. The trinuclear nodes ([(CuL¹)₂Zn]²⁺ in 1 and [(CuL²)₂Zn]²⁺ in 2 are produced in situ from their corresponding reactants. The two Schiff base ligands coordinating the Cu(II) ions through the N₂O₂ donor set are additionally bonded to a Zn(II) ion with the four phenoxido oxygen atoms that act as bridging atoms. The zinc ion completes its coordination geometry with two terminal nitrogen atoms of two different dicyanamide spacers. The orientation of spacers from zinc ion are convergent in 1 whereas divergent in 2. Thus, two [(CuL¹)₂Zn]²⁺ nodes are interconnected by double μ_1,5-dicyanamide bridges via Zn(II) centres to form discrete hexanuclear assembly of complex 1. On the other hand, [(CuL²)₂Zn]²⁺ nodes in 2 are joined by μ_l,5-dicyanamide that bridge Zn(II) to Cu(II) centres of symmetry related units in order to construct a 2D coordination polymer. Consequently, the final coordination environment around Zn(II) is octahedral in both complexes whereas that around Cu(II) are square planar and square pyramidal in 1 and 2 respectively.     

Die Kristallstruktur von Bis(N,N-Diethyl-N′-benzoylselenoureato)zink(II)

The Crystal Structure of Bis(N,N-Diethyl-N′-benzoylselenoureato)zinc(II) . Zn(C₁₂H₁₅N₂OSe)₂ crystallizes in the acentric orthorhombic space group Pca2₁. The cell parameters are a = 16.914(5), b = 13.492(4), c = 11.705(5) Å and Z = 4. The structure was solved with Patterson and direct methods and was refined to a final R-value of 7,05%. Zn^II is coordinated to two N,N-Diethyl-N′-benzoylselenoureato molecules, which are bidentately coordinated through their oxygen and selenium atoms to form a distorted tetrahedron. The Zn? Se bond lenghts are 2.394(3) and 2.369(4) Å, the Zn? O bond lengths are 1.971(11) and 1.974(12) Å.     

The multiple conformational charge states of zinc(II) coordination by 2His‐2Cys oligopeptide investigated by ion mobility‐mass spectrometry,density functional theory and theoretical collision cross sections

Whether traveling wave ion mobility‐mass spectrometry (IM‐MS), B3LYP/LanL2DZ density functional theory, and ion size scaled Lennard‐Jones (LJ) collision cross sections (CCS) from the B3LYP optimized structures could be used to determine the type of Zn(II) coordination by the oligopeptide acetyl‐His₁‐Cys₂‐Gly₃‐Pro₄‐Tyr₅‐His₆‐Cys₇ (amb₅) was investigated. The IM‐MS analyses of a pH titration of molar equivalents of Zn(II):amb₅ showed that both negatively and positively charged complexes formed and coordination of Zn(II) increased as the His and Cys deprotonated near their pKa values. The B3LYP method was used to generate a series of alternative coordination structures to compare with the experimental results. The method predicted that the single negatively charged complex coordinated Zn(II) in a distorted tetrahedral geometry via the 2His‐2Cys substituent groups, whereas, the double negatively charged and positively charged complexes coordinated Zn(II) via His, carbonyl oxygens and the C‐terminus. The CCS of the B3LYP complexes were calculated using the LJ method and compared with those measured by IM‐MS for the various charge state complexes. The LJ method provided CCS that agreed with five of the alternative distorted tetrahedral and trigonal bipyramidal coordinations for the doubly charged complexes, but provided CCS that were 15 to 31 Ų larger than those measured by IM‐MS for the singly charged complexes. Collision‐induced dissociation of the Zn(II) complexes and a further pH titration study of amb_5B, which included amidation of the C‐terminus, suggested that the 2His‐2Cys coordination was more significant than coordinations that included the C‐terminus. Copyright © 2016 John Wiley & Sons, Ltd.     

Role of Ligand in the Selective Production of Hydrogen from Formic Acid Catalysed by the Mononuclear Cationic Zinc Complexes [(L)Zn(H)]+ (L=tpy,phen, and bpy)

A series of zinc-based catalysts was evaluated for their efficiency in decomposing formic acid into molecular hydrogen and carbon dioxide in the gas phase using quadrupole ion trap mass spectrometry experiments. The effectiveness of the catalysts in the series [(L)Zn(H)]⁺, where L=2,2′:6′,2′′-terpyridine (tpy), 1,10-phenanthroline (phen) or 2,2′-bipyrydine (bpy), was found to depend on the ligand used, which turned out to be fundamental in tuning the catalytic properties of the zinc complex. Specifically, [(tpy)Zn(H)]⁺ displayed the fastest reaction with formic acid proceeding by dehydrogenation to produce the zinc formate complex [(tpy)Zn(O₂CH)]⁺ and H₂. The catalysts [(L)Zn(H)]⁺ are reformed by decarboxylating the zinc formate complexes [(L)Zn(O₂CH)]⁺ by collision-induced dissociation, which is the only reaction channel for each of the ligands used. The decarboxylation reaction was found to be reversible, since the zinc hydride complexes [(L)Zn(H)]⁺ react with carbon dioxide yielding the zinc formate complex. This reaction was again substantially faster for L=tpy than L=phen or bpy. The energetics and mechanisms of these processes were modelled using several levels of density functional theory (DFT) calculations. Experimental results are fully supported by the computational predictions.     

Die Kristallstruktur von (PPh4)2[Mo2(O2C?Ph)4Br2] · 2 CH2Br2

Crystal Structure of (PPh₄)₂[Mo₂(O₂C? Ph)₄Br₂] · 2 CH₂Br₂ The title compound, prepared by the reaction of Mo₂(O₂C? Ph)₄ with PPh₄Br and PPh₄N₃, respectively, under the assistance of CH₂Br₂, was characterized by an X-ray structure determination. Space group P2₁/n, Z = 2, R = 0.074 (5261 independent observed reflexions). The lattice dimensions are at ?70°C: a = 1562.9, b = 1406.2, c = 1662.1 pm, β = 94.11°. the compound consists of PPh₄^⊕ ions, CH₂Br₂ molecules, and centrosymmetric anions [Mo₂(O₂C? Ph)₄Br₂]^2?. The axis Br? Mo?Mo–Br is nearly linear (bond angle 175.6°) with bond lengths MoMo = 212.3 pm and Mo? Br = 303 pm, corresponding with a weak electrostatic Mo? Br bond. In the FIR spectrum the Mobr stretching vibration is found at 85 cm^?1, which corresponds with the low value of the force constant of 0.24 N · cm^?1.     

CrIII-Phthalocyaninate: Darstellung,Eigenschaften und Kristallstruktur von l-Bis(triphenylphosphin)iminium-trans-di(nitrito(O))phthalocyaninato(2–)-chromat(III)

Cr^III Phthalocyaninates: Synthesis, Properties, and Crystal Structure of l-Bis(triphenylphosphine)iminium trans-Di(nitrito(O))phthalocyaninato(2–)chromate(III) [Cr(H₂O)₂Pc^2?]I_x reacts with excess (PNP)NO₂ in dimethylformamide to yield less soluble greenblack l-bis(triphenylphosphine)iminium trans-di(nitrito(O))phthalocyaninato(2–)chromate(III), ^l(PNP)^trans[Cr(ONO)₂Pc^2?], which crystallizes in the triclinic space group P1 (No. 2) with Z = 2. The Cr atom is in the center of the Pc^2? ligand and the two nitrite ions are monodentate O-coordinated in a mutually trans arrangement to the Cr atom. The Cr? O and Cr? N_iso bond distances are 1.9898(14) und 1.981(2) Å, respectively. The geometric data of the coordinated nitrite ion are: d(N? O) = 1.307(2) Å; d(N? O) = 1.205(2) Å; ?(O? N? O) = 113.7(2)°; ?(Cr? O? N) = 116.85(12)°. The non-bonding O atoms are trans to the Cr atom. The Pc^2? ligand is slightly saddled. Three weak spin-allowed trip-quartet(TQ) transitions (in 10³ cm^?1): TQ1 (8.20) < TQ2 (11.3) < TQ3 (20.33) and the characteristic π-π* transitions of the Pc^2? ligand: B (14.68) < Q₁ (27.1) < Q₂ (29.0) < N (35.4) are observed in the UV-VIS-NIR spectrum. Prominent luminescence spectra are obtained by excitation within the TQ1 region, in which the spin-forbidden trip-sextet transition at 7376 cm^?1 dominates at low temperatures (T < 50 K). The vibrational spectra are discussed. In coincidence of the excitation lines with TQ3, v_s(Cr? O) at 378 cm^?1 is selectively resonance Raman (RR) enhanced. v_as(Cr? O) is observed in the FIR spectrum at 391 cm^?1. The following internal vibrations (in cm^?1) of the nitrito ligand are in the MIR spectrum: v_as(N? O)/1447 > v_as(N? O)/1018/1029 > δ(O? N? O)/828 and in the RR-spectrum: v_s(N? O)/1410 > v_s(N? O)/952, the last followed by three overtones.     

[(bmpyr)2{Zn(OC6H3(NO2)2)4}]: Influence of an Ionic Liquid on Liquid/Liquid Extraction of Metal Ions in a Biphasic System

The compound [(bmpyr)₂{Zn(OR)₄}] (OR = 2,4‐dinitriphenolate) has been prepared from Zn(NO₃)₂·6H₂O and sodium 2,4‐dinitrophenolate in a biphasic aqueous ionic liquid (Butyl‐methyl‐pyrrolidinium trifluoromethylsulfonate [bmpyr][OTf]) system. The presence of the anionic zinc complex in [bmpyr][OTf] is made possible by the exchange of the ionic liquid anions into the aqueous phase for the zinc complex. [(bmpyr)₂{Zn(OR)₄}] was characterized in solution by ¹³C‐ and ¹H‐NMR spectroscopy and in the solid state by crystal structure determination. The zinc complex represents the first type of a zinc complex with more than two phenolate ligands.     

Reactions of O2(1Δg) with atomic nitrogen and hydrogen

The reactions of electrically dicharged nitrogen and hydrogen with O₂(¹Δ_g) is probabnly slower than with ground state O₂. ON the other hand, the reaction of H-atoms with O₂(¹Δ_g) was found to occur with a rate constant k=(2,5±0.5)× 10^?14 cm³ molecule^?1 sec^?1, although it was not posible to establish whether the reaction produced OH radicals or simply represented physical quenching.     

Mechanism of the quenching of O2(1Δ g ) by erbium tetra(4-tert-butyl)phthalocyanine

The quenching of singlet molecular oxygen (¹O₂, ¹Δ _g ) by Er³⁺ tetra(4-tert-butyl)phthalocyanine in benzene was studied by the luminescence method. The quenching was demonstrated to be controlled by a physical-chemical mixed mechanism, with donor-acceptor interactions being the main contributor to the physical quenching of ¹O₂.     

Activation of SO2 with [(η5‐C5Me5)2Ln(THF)2] (Ln=Eu,Yb) Leading to Dithionite and Sulfinate Complexes

The reaction of decamethylytterbocene [(η⁵‐C₅Me₅)₂Yb(THF)₂] with SO₂ at low temperature gave two new compounds, namely, the Yb^III dithionite/sulfinate complex [{(η⁵‐C₅Me₅)₂Yb(μ₃,1κ²O^1,3,2κ³O^2,2′,4‐S₂O₄)}₂{(η⁵‐C₅Me₅)Yb(μ,1κO,2κO′‐C₅Me₅SO₂)}₂] ( 1 ) and the Yb^III dithionite complex [{(η⁵‐C₅Me₅)₂Yb}₂(μ,1κ²O^1,3,2κ²O^2,4‐S₂O₄)] ( 2 ). After extraction of 1 , the mixture was heated to give the dinuclear tetrasulfinate complex [{(η⁵‐C₅Me₅)Yb}₂(μ,κO,κO’‐C₅Me₅SO₂)₄] ( 3 a ). In contrast, from the reaction of [(η⁵‐C₅Me₅)₂Eu(THF)₂] with SO₂ only the tetrasulfinate complex [{(η⁵‐C₅Me₅)Eu}₂(μ,κO,κO’‐C₅Me₅SO₂)₄] ( 3 b ) was isolated. Two major reaction pathways were observed: 1) reductive coupling of two SO₂ molecules to form the dithionite anion S₂O₄^2?; and 2) nucleophilic attack of one metallocene C₅Me₅ ligand on the sulfur atom of SO₂. The compounds presented are the first dithionite and sulfinate complexes of the f‐elements.     

五-和六配位的三核锌配合物{[ZnL(OAc)]2Zn}∙CH3COCH3的合成，晶体结构及荧光性质

合成并结构表征了一种新型的线性三核锌(II)配合物,{[ZnL(OAc)]2Zn}∙CH3COCH3（H2L：乙二氧双(5-溴-2-羟基苯亚甲基胺)）。X-射线结构表明配合物中三个锌(II)离子配位到了两个四齿的L2-单元和两个桥联的的乙酸根基团。围绕两端的Zn(1) 或 Zn(1)#1原子形成了扭曲的四方锥配位几何体,围绕中心Zn(2) 原子构成了一个稍微扭曲的八面体配位结构。同时,观察到锌(II)配合物能发出蓝绿色荧光,其最大发射波长为464 nm。     

Zinc(II) and Cadmium(II) Complexes of the 3‐(2‐Pyridyl)‐5,6‐diphenyl‐1,2,4‐triazine (PDPT) Ligand,Structural Studies of [Zn(PDPT)2Cl(ClO4)] and [Cd(PDPT)2(NO3)(ClO4)]

Two new mixed‐anion zinc(II) and cadmium(II) complexes of 3‐(2‐pyridyl)‐5,6‐diphenyl‐1,2,4‐triazine (PDPT) ligand, [Zn(PDPT)₂Cl(ClO₄)] and [Cd(PDPT)₂(NO₃)(ClO₄)], have been synthesized and characterized by elemental analysis, IR‐ and ¹H NMR spectroscopy. The single crystal X‐ray analyses show that the coordination number in these complexes is six with four N‐donor atoms from two “PDPT” ligand and two of the anionic ligands, ZnN₄ClO_perchlorate, CdN₄O_nitrateO_perchlorate. Self‐assembly of these compounds in the solid state via π–π‐stacking interactions is discussed.