Formation Of Dinuclear Complex Research Articles

Complex Formation and Hydrolytic Processes of Protected Peptides Containing the -SXH- Motif in the Presence of Nickel(II) Ion.

Interactions between metal ions and proteins are considered reversible, such as the coordination of a metal ion to a protein or enzyme, but irreversible processes like the oxidative reactions, aggregation or hydrolytic processes may occur. In the presence of Ni(II)-ions selective hydrolysis of the peptides containing the -SXH- or -TXH- motif was observed. Since the side chain of histidine serves as the metal ion binding site for many native proteins, and very often histidine is present in a -SXH- or -TXH- sequence, to study the complex formation and hydrolytic processes in presence of nickel(II) ion four peptides were synthesised: Ac-SKHM-NH2, A3SSH-NH2, A4SSH-NH2, AAAϵKSH-NH2. The Ni(II)-induced hydrolysis of Ac-SKHM-NH2 peptide occurs rapidly in alkaline medium already at room temperature. In two peptides containing -SSH- sequence on the C-termini, the N-terminal part is the major binding site for the nickel(II) ion, but the formation of dinuclear complexes was also observed. In the [Ni2LH-6]2- complex of hexapeptide, the coordination sphere of the metal ions is saturated with deprotonated Ser-O-, which does not result in hydrolysis of the peptide. For A4SSH-NH2, both Ni(II) ions fulfill the conditions for hydrolysis, which was confirmed by HPLC analyses at pH ≈8.2 and 25 °C.

2H1C Mimicry: Bioinspired Iron and Zinc Complexes Supported by N,N,O Phenolate Ligands

AbstractIn pursuit of mimicking the ubiquitous 2H1C motif in mononuclear non‐heme iron enzymes, two new bioinspired N,N,O phenolate ligands, BenzImNNO and ImPh2NNO, are synthesised and their coordination chemistry with zinc(II) and iron(II) is explored. BenzImNNO coordinates by means of an anionic κ3‐N,N,O donor set and readily forms homoleptic bisligated complexes, also in the presence of equimolar amounts of metal salt. In contrast, the increased steric bulk of ImPh2NNO promotes the formation of dinuclear complexes, [M2(ImPh2NNO)2(OTf)2] (M=Fe, Zn), with facially opposing metal sites, as a result of its unique bridging μ2:κ2‐N,N:κ1‐O coordination mode. We investigate the robustness of the ligand's dinucleating coordination mode during oxidative transformations and demonstrate that its coordination mode is retained upon triflate substitution for a biorelevant thiophenolate co‐ligand.

Activation of Substituted Metallocene Catalysts Using Methylaluminoxane

AbstractActivation of the metallocene complexes (n‐C4H9‐(η5‐C5H4))2ZrCl2 (BuCp2ZrCl2) and rac‐1,2‐ethylenebis(1‐η5‐C9H6)ZrCl2 (EBIZrCl2) using methylaluminoxane (MAO) was investigated by electrospray ionization mass spectrometry (ESI‐MS). Formation of dinuclear complexes at low Al : Zr ratios, which is accompanied by catalyst deactivation, occurs in the former case. In contrast, this behavior was not observed at similar Al : Zr ratios in the case of the EBIZrCl2 complex. Both active [BuCp2ZrMe2AlMe2][MAO(Me)] 3 and deactivated [(BuCp2Zr)2(μ‐CH2)μ‐Cl][MAO(Me)] 9 complexes were detected in leaching experiments using a SiO2‐MAO‐supported BuCp2ZrCl2 catalyst and excess MAO. DFT studies of the structure and UV‐Vis spectra calculated for the dinuclear cations 9 detected by ESI‐MS suggest that these species may account for long‐wavelength absorption seen in experimental spectra of complexes like BuCp2ZrCl2 upon activation with MAO.

Synthesis, structure, phase controlled colour tuning of dinuclear Pr(III) and Tb(III) complexes with fluorinated β-diketone and heterocyclic Lewis base as UV light converters

Heteroleptic homo dinuclear complexes, [Pr(fod)3(μ-bpp)Pr(fod)3] and [Tb(fod)3(μ-bpp)Tb(fod)3] (fod is the anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod) and bpp is 2,3-bis(2-pyridyl)pyrazine) have been synthesized and thoroughly characterized. The 1H NMR spectra of the complexes are consistent with the dinuclear complex formation. In the absorption spectra, the 3P2 ← 3H4, 3P1 + 1I6 ← 3H4 and 1D2 ← 3H4 transitions of Pr(III) complex show considerable sensitivity towards the host medium and prominent stark splitting of these transitions is observed in chloroform and dichloromethane. The effect of phase change on photophysical properties of Pr(III) and Tb(III) complexes is investigated by observing the steady state and time resolved fluorescence spectra of the solid complexes, their solutions and PMMA doped thin hybrid films. Intense emission is observed for the PMMA doped hybrid materials of the complexes. In the case of [Pr(fod)3(μ-bpp)Pr(fod)3] complex doped PMMA, additional emission peaks are observed from the high energy excited states (3P2, 1I6, 3P1 and 3P0), indicating that the PMMA facilitates emission from the higher emitting levels. The emitting colour of Pr(III) complex shows phase dependence with the emission of blue and purple light in the solutions, orange in solid state and in the case of PMMA doped hybrid films at a doping concentration of 5 % and 10 %, the Commission Internationale de l'Eclairage (CIE) colour coordinates are in the white region x = 0.351, y = 0.377 and light blue region x = 0.313, y = 0.319, respectively. Intense green light emission is observed for the terbium complex in all media. The semiempirical theoretical tool of Sparkle/PM7 has been used for obtaining the geometry of the complexes.

Photochemical Oxidation of Pt(IV)Me3(1,2-diimine) Thiolates to Luminescent Pt(IV) Sulfinates.

We report the formation of dinuclear complexes from, and photochemical oxidation of, (CH3)3-Pt(IV)(N^N) (N^N = 1,2-diimine derivatives) complexes of thiophenolate ligands to the analogous sulfinates (CH3)3Pt(N^N)(SO2Ph) and structural, spectroscopic, and theoretical studies of the latter revealing tunable photophysics depending upon the 1,2-diimine ligands. Electron-rich thiolate and conjugated 1,2-diimines encourage formation of thiolate-bridged dinuclear complexes; smaller 1,2-diimines or electron-poor thiolates favor mononuclear complexes. Photooxidation of the thiolate ligand yields hitherto unreported Pt(IV)-SO2R complexes, promoted by electron-deficient thiolates such as 4-nitrothiophenol, which exclusively forms the sulfinate complex. Such complexes exhibit expected absorptions due to π-π* ligand transitions of the 1,2-diimines mixed with spin-allowed singlet MLCT (d-π*) at relatively high energy (270-290 nm), as well as unexpected broad, lower energy absorptions between 360 and 490 nm. DFT data indicate that these low energy absorption bands result from excitation of Pt-S and Pt-C σ-bonding electrons to π* orbitals on sulfinate and 1,2-diimine, the latter of which gives rise to emission in the visible range.

Unusual demetalation of iron from [2]ferrocenophane skeleton of di‐nuclear ferracycle carbonyl complex

Photolysis of a hexane solution containing 1,1′‐ bis (trimethylsilylethynyl)ferrocene (1) and Fe (CO)5, under argon at 0 °C led to the formation of dinuclear complexes [Fe (CO)2{η2:η2 – C (SiMe3) = C(C5H4)FeC(C5H4) = C (SiMe3)Fe (CO)3}–μ–CO] (2) and [Fe (CO)2{η2:η2–C (SiMe3) = C(C5H5)–C(C5H5) = C (SiMe3)Fe (CO)3}–μ–CO] (3). DFT calculations support the experimentally observed demetalation of ferrocene unit of 2 to 3 in presence of water. These compounds were comprehensively characterized by IR and 1H and 13C NMR spectroscopy and crystallographically (1 and 3).

Carbonate-bridged dinuclear lanthanide(III) complexes of chiral macrocycle

Mononuclear Eu(III) and Dy(III) complexes of the chiral hexaaza macrocycle L, 2(R),7(R),18(R),23(R)-1,8,15,17,24,31-hexaazatricyclo[25.3.1.1.0.0]-dotriaconta-10,12,14,26,28,30-hexaene have been obtained as chloride derivatives (1 and 2, respectively) and characterized by using spectroscopic methods. The X-ray crystal structure of 2 has been determined. The reaction of two equivalents of mononuclear 1 or 2 complexes with one equivalent of sodium carbonate results in the formation of dinuclear complexes [Eu2L2(µ2-CO3)(H2O)3]Cl43 and [Dy2L2(µ2-CO3)(H2O)3]Cl44, respectively. The X-ray crystal structure of complex 3 reveals two macrocyclic [EuL]3+ units bridged by the carbonate anion. The carbonate anion is bound to the Eu(III) ions using the η1:η2-µ2 bridging mode. The binding of carbonate anions to the [EuL]3+ or [DyL]3+ macrocyclic units has also been studied in solution using spectroscopic methods. The titration of the starting paramagnetic mononuclear chloride derivatives 1 and 2 monitored by 1H NMR spectroscopy revealed initial formation of dinuclear species, followed by the formation of complexes possessing additional carbonate ligands. The dinuclear carbonate complexes 3 and 4 are also formed in the reactions of the respective mononuclear chloride complexes with gaseous CO2. Lanthanide(III) complexes of the chiral hexaaza macrocycle L are effective for catalytic hydrolysis of bis(4-nitrophenyl) phosphate BNPP. Within the series of the studied mononuclear complexes: nitrate derivatives [LnL(NO3)(H2O)](NO3)2 (Ln = Ho, Er), [LnL(H2O)2](NO3)3 (Ln = Tm, Yb, Lu) and chloride derivatives [LnL(H2O)2]Cl3 (Ln = Tm, Yb, Lu, Y) the catalytic activity of the complexes is increased with increasing ionic size. Kinetic studies revealed that most active is the dinuclear europium(III) complex 3 which catalyzes the hydrolysis of BNPP with a rate kobs = 6.5 × 10−5 s−1 (at 0.3 mM concentration of the catalyst) at pH 8.5 and 37 °C.

Structural characterization and cytotoxic evaluation of Cu(II), Co(II) and Ni(II) complexes with herbicide 4-chloro-2-methylphenoxyacetic acid

The purpose of our research was to obtain and characterize Cu(II), Co(II) and Ni(II) complexes with herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA). The structural characterization of compounds in their powder form was based on various laboratory as well as synchrotron X-ray spectroscopic methods, magnetic measurements and atomistic calculations. The anhydrous [Cu(MCPA)2]n complex exhibits a distorted square-planar geometry. [Co(MCPA)2(H2O)4]·H2O and [Ni(MCPA)2(H2O)4]·H2O complexes have octahedral molecular geometry with two MCPA anions acting as monodentate ligands. The X-ray crystal structure analysis performed for Cu(II) complex after its recrystallization from N,N-dimethylformamide solution showed the formation of dinuclear complex with solvent molecules included in the coordination sphere of Cu(II).MCPA herbicide and its Cu(II), Co(II) and Ni(II) complexes showed the low cytotoxicity potential against HaCaT and V79 cells with IC50 in the range from 65 to >100 µM.

A comparative study on the nickel binding ability of peptides containing separate cysteinyl residues.

Nickel(ii) complexes of peptides CSSACS-NH2, ACSSACS-NH2, SSCSSACS-NH2 and GACAAH-NH2 have been studied by potentiometric and various spectroscopic (UV-vis, CD, NMR, and ESI-MS) techniques. All peptides have high nickel(ii) binding ability in the form of square planar complexes and the stability order of the peptides is: CSSACS-NH2 > ACSSACS-NH2 > SSCSSACS-NH2 ∼ GACAAH-NH2. The different metal binding affinities of these peptides are related to the differences in the speciation and in the binding modes of the major species. An almost exclusive formation of bis(ligand) complexes via an (NH2,S-) 5-membered chelate from the amino terminus is characteristic of CSSACS-NH2. The (NH2,N-,S-) tridentate chelate is the major coordination mode of ACSSACS-NH2 but the distant cysteine can also contribute to metal binding. The higher nickel(ii) binding ability of AC[combining low line]SSAC[combining low line]S-NH2 relative to the peptides containing an N-terminal XY-Cys motif may have important biological consequences. For example, the occurrence of the (NH2,N-,S-,S-) donor set is a common feature of both the ACSSACS-NH2 ligand and the nickel(ii) binding loop of the NiSOD enzyme (HC[combining low line]DLPC[combining low line]G…..,). In the case of SSCSSACS-NH2 and GACAAH-NH2 the amino terminus of one peptide can completely saturate the coordination sphere of the nickel(ii) ion via the formation of the (NH2,N-,N-,S-) binding mode. This rules out the formation of bis(ligand) complexes and any contribution of the distant cysteine or histidine to nickel(ii) binding in the 1 : 1 complexes. On the other hand the distant cysteine of SSCSSACS-NH2 and histidine of GACAAH-NH2 can behave as independent metal binding sites for the formation of dinuclear complexes in the presence of excess metal ions.

NOTA Complexes with Copper(II) and Divalent Metal Ions: Kinetic and Thermodynamic Studies.

H3nota derivatives are among the most studied macrocyclic ligands and are widely used for metal ion binding in biology and medicine. Despite more than 40 years of chemical research on H3nota, the comprehensive study of its solution chemistry has been overlooked. Thus, the coordination behavior of H3nota with several divalent metal ions was studied in detail with respect to its application as a chelator for copper radioisotopes in medical imaging and therapy. In the solid-state structure of the free ligand in zwitterionic form, one proton is bound in the macrocyclic cavity through a strong intramolecular hydrogen-bond system supporting the high basicity of the ring amine groups (log Ka = 13.17). The high stability of the [Cu(nota)]- complex (log KML = 23.33) results in quantitative complex formation, even at pH <1.5. The ligand is moderately selective for Cu(II) over other metal ions (e.g., log KML(Zn) = 22.32 and log KML(Ni) = 19.24). This ligand forms a more stable complex with Mg(II) than with Ca(II) and forms surprisingly stable complexes with alkali-metal ions (stability order Li(I) > Na(I) > K(I)). Thus, H3nota shows high selectivity for small metal ions. The [Cu(nota)]- complex is hexacoordinated at neutral pH, and the equatorial N2O2 interaction is strengthened by complex protonation. Detailed kinetic studies showed that the Cu(II) complex is formed quickly (millisecond time scale at cCu ≈ 0.1 mM) through an out-of-cage intermediate. Conversely, conductivity measurements revealed that the Zn(II) complex is formed much more slowly than the Cu(II) complex. The Cu(II) complex has medium kinetic inertness (τ1/2 46 s; pH 0, 25 °C) and is less resistant to acid-assisted decomplexation than Cu(II) complexes with H4dota and H4teta. Surprisingly, [Cu(nota)]- decomplexation is decelerated in the presence of Zn(II) ions due to the formation of a stable dinuclear complex. In conclusion, H3nota is a good carrier of copper radionuclides because the [Cu(nota)]- complex is predominantly formed over complexes with common impurities in radiochemical formulations, Zn(II) and Ni(II), for thermodynamic and, primarily, for kinetic reasons. Furthermore, the in vivo stability of the [Cu(nota)]- complex may be increased due to the formation of dinuclear complexes when it interacts with biometals.

Synthesis, structural studies and biological activity of novel Cu(II) complexes with thiourea derivatives of 4-azatricyclo[5.2.1.02,6]dec-8-ene-3,5-dione

The new Cu(II) complexes of 1/2/3-(bromophenyl)-3-(1,7,8,9-tetramethyl-3,5-dioxo-4-azatricyclo[5.2.1.02,6]dec-8-en-4-yl)thiourea derivatives have been synthesized. The spectroscopic studies together with density functional theory calculations of Cu(II) complexes revealed that two parent ligands coordinate to the copper cation in bidentate fashion via thiocarbonyl S and deprotonated N atoms forming rarely observed four-membered chelate ring, with nearly planar [CuN2S2] moiety. In solid state, the mononuclear complex is formed for thiourea derivative with 3-bromophenyl, whereas for Cu(II) connection with 2- and 4-bromophenyl-thioureas the formation of dinuclear complexes is observed, the latter formed by the stacking of mononuclear complexes.The microbiological activity of novel compounds has been evaluated. The Cu(II) complex with 4-bromophenyl ring connected to the thiourea moiety showed significant inhibition against standard strains of S. aureus and S. epidermidis. The range of minimal inhibitory concentration values is 2–4μg/mL. That compound exhibited antibiofilm potency and effectively inhibited the formation of biofilm of methicillin-susceptive strain of S. epidermidis ATCC 12228. Moreover, the cytotoxicity against the MT-4 cells of all obtained complexes has been evaluated. The complexes turned out to be non-cytotoxic for exponentially growing MT-4.

Coordination environment of new Co(II), Ni(II) and Cu(II) complexes with 4-bromophenoxyacetic acid: Structural, spectroscopic and theoretical studies

We report the synthesis of new Co(II), Ni(II) and Cu(II) complexes with 4-bromophenoxyacetic acid. We characterize these compounds structurally using various laboratory (XRF, IR, UV–vis) and synchrotron (EXAFS, XANES) spectroscopic methods, magnetic measurements and DFT calculations. We found that in the powder form of complexes Co(II) and Ni(II) cations are coordinated by two monodentate carboxylate ligands and the first coordination sphere is completed by water molecules that form an octahedron. The coordination polyhedron of Cu(II) exhibits a distorted tetragonal–pyramidal geometry with two ligands coordinating in bidentate and monodentate fashion via carboxylate O atoms and two water molecules.The X-ray single crystal structure analysis performed for Cu(II) complex after its recrystallization from N,N-dimethylformamide (DMF) solution revealed the formation of dinuclear complex. In crystals, the carboxylate O atoms occupy the bases of two tetragonal pyramids formed around two Cu(II) ions with the DMF molecules in the apical positions.

Potentiometric and spectroscopic studies on the copper(II) complexes of rat amylin fragments. The anchoring ability of specific non-coordinating side chains.

Copper(ii) complexes of peptides modelling the sequence of the 17-22 residues of rat amylin have been studied by potentiometric, UV-Vis, CD and ESR spectroscopic methods. The peptides were synthesized in N-terminally free forms, NH2-VRSSNN-NH2, NH2-VRSSAA-NH2, NH2-VRAANN-NH2, NH2-VRSS-NH2, NH2-SSNN-NH2, NH2-SSNA-NH2 and NH2-AANN-NH2, providing a possibility for the comparison of the metal binding abilities of the amino terminus and the -SSNN- domain. The amino terminus was the primary ligating site in all cases and the formation of only mononuclear complexes was obtained for the tetrapeptides. The thermodynamic stability of the (NH2, N(-), N(-)) coordinated complexes was, however, enhanced by the asparaginyl moiety in the case of NH2-SSNN-NH2, NH2-SSNA-NH2 and NH2-AANN-NH2. Among the hexapeptides the formation of dinuclear complexes was characteristic for NH2-VRSSNN-NH2 demonstrating the anchoring ability of the -SSNN- (SerSerAsnAsn) domain. The complexes of the heptapeptide NH2-GGHSSNN-NH2 were also studied and the data supported the above mentioned anchoring ability of the -SSNN- site.

Molybdenum complex with bulky chelates as a functional model for molybdenum oxidases.

The novel bulky Schiff base chelate ligand [(4,5-diisopropyl-1H-pyrrole-2-yl)methylene]-4-(tert-butyl)aniline ((iPr2)HL) bearing two isopropyl groups close to the pyrrole nitrogen atom reacts with MoCl2(dme)O2 (dme = 1,2-dimethoxyethane) to give the sterically congested complex Mo(VI)((iPr2)L)2O2 ((iPr2)1; OC-6-4-4 configuration). In spite of the increased steric shielding of the [MoO2] unit (iPr2)1 is active in oxygen-atom transfer to PMe3 and PPh3 to give OPMe3 and OPPh3, respectively. Because of the increased steric bulk of the chelate ligand, formation of dinuclear complexes [Mo(V)((iPr2)L)2O]2(μ-O) ((iPr2)3) by comportionation is effectively prevented in contrast to the highly favored formation of [Mo(V)((H2)L)2O]2(μ-O) ((H2)3) with the less bulky ligand (H2)HL. Instead, the smaller PMe3 ligand coordinates to the resulting pentacoordinate intermediate Mo(IV)((iPr2)L)2O ((iPr2)5), giving the hexacoordinate complex Mo(IV)((iPr2)L)2O(PMe3) ((iPr2)2) with OC-6-3-3 configuration. The larger potential ligands PPh3 and OPPh3 are only able to weakly coordinate to (iPr2)5, giving labile and sensitive Mo(IV)((iPr2)L)2O(L) complexes ((iPr2)6, L = PPh3; (iPr2)7, L = OPPh3). Traces of water and dioxygen in solutions of (iPr2)6/(iPr2)7 yield the di(μ-oxido) complex [Mo(V)((iPr2)L)O]2(μ-O)2 ((iPr2)4) with reduced steric congestion due to dissociation of the bulky chelate ligands. According to electron paramagnetic resonance studies, the much more strongly bound small PMe3 ligand in (iPr2)2 can be slowly liberated by one-electron oxidation to Mo(V), with Ag(+) leaving a free coordination site at Mo(V). Hence, essentially pentacoordinate Mo(IV) and Mo(V) complexes are accessible as a result of the increased steric bulk.

Phosphinate Analogues of Ida and Nta with Low Basicity of Nitrogen Atom: Acid-Base and Complexation Properties

Analogues of iminodiacetic acid (H2IDA) and nitrilotriacetic acid (H3NTA) bearing two (hydroxomethyl)methylphosphinate or (2-carboxyethyl)methylphosphinate groups were synthesized. Their acid-base and coordination properties with divalent metal ions (Cu2+, Ni2+ and Zn2+) were studied by potentiometry. The compounds exhibit very low basicity of the amino groups (pKa = 6.2–7.6) due to presence of two electron-withdrawing methylphosphinate groups and, consequently, a low stability of the complexes. In the case of IDA-analogues, the low complex stability results in precipitation of metal hydroxides in neutral region. As expected, NTA-analogues form more stable complexes and, thus, they were also studied in the alkaline region. Presence of additional carboxylate in the 2-carboxyethylphosphinic acid groups results in the formation of dinuclear complexes. Solid-state structures of two compounds were determined by X-ray diffraction analysis. The compounds are protonated on the nitrogen atom and the structures are stabilized by rich hydrogen bond network.

Formation of boron, nickel(II) and iridium(III) complexes with an azophenine derivative: Isomerization, delocalization and extension of the π-conjugated system on coordination

The azophenine N,N′,N″,N‴-tetra-4-ethylphenyl-2,5-diamino-1,4-benzoquinonediimine (4-EtApH2), its diprotonated species [4-EtApH4](ClO4)2 (1) and complexes, the bis(boron difluoride) complex [(BF2)2(μ-4-EtAp)] (2), the mono- and dinuclear nickel(II) complexes [Ni(4-EtApH2)3](ClO4)2 (3) and [{Ni(acac)}2(μ-4-EtAp)] (4), respectively, and the dinuclear iridium(III) complex [{Ir(cp∗)Cl}2(μ-4-EtAp)] (5), have been prepared. The molecular structures of these compounds were determined by X-ray analysis. The coordination environments around the boron center of 2 and the Ni centers of 3 and 4 were tetrahedral, octahedral and square-planar, respectively. Furthermore, each Ir center of 5 was coordinated by two nitrogen atoms from 4-EtAp2−, Cl− and η5-cp∗. Coordination of the ligand to Ni to form 3 caused an isomerization from the para-benzoquinonediimine of 4-EtApH2 to the ortho form, with a bond alternation at each of the two N–C–C–C–N π-systems. Diprotonation and dinuclear complex formation to construct 1, 2, 4 and 5 led to a delocalization of six π-electrons over each of the two N–C–C–C–N moieties connected by single bonds. The π–π∗ transition absorption gradually shifted to longer wavelengths (4-EtApH2≈3→2→1→4≈5), suggesting an extension of the π-conjugation range. Cyclic voltammograms of 3 and 4 showed one and two redox potential(s), respectively.

Copper(II), nickel(II) and zinc(II) complexes of the N-terminal nonapeptide fragment of amyloid-β and its derivatives

Copper(II), nickel(II) and zinc(II) complexes of the nonapeptide fragment of amyloid-β Aβ(1–9) (NH2-DAEFRHDSG-NH2) and its two derivatives: NH2-DAAAAHAAA-NH2 and NH2-DAAAAAHAA-NH2 have been studied by potentiometric, UV–visible and CD spectroscopic methods. The results reveal the primary role of the amino terminus of peptides in copper(II) and nickel(II) binding. The formation of dinuclear complexes was also possible in the copper(II) containing systems but only the first six amino acids from the amino terminus were involved in metal binding in the physiologically relevant pH range. The coordination chemistry of the two alanine mutated peptides is almost the same as that of the native nonapeptide, but the thermodynamic stability of the copper(II) complexes of the mutants is significantly reduced. This difference probably comes from the secondary interactions of the polar side chains of Asp, Glu, Ser and Arg residues present in the native peptide. Moreover, this difference reveals that the amino acid sequence of the N-terminal domains of amyloid peptides is especially well suited for the complexation with copper(II) ions.

Equilibrium of the dinuclear complex formation between organotin(IV) and metal-Schiff base complexes in solution

Equilibrium of the dinuclear complex formation between organotin(IV) and metal-Schiff base complexes in solution

Conformationally Constrained N-Heterocyclic Phosphine–Diimine with Dual Functionality

Condensation of octahydro-2,2'-bipyrimidine with P(NMe2)3 gave a 1,3,2-diazaphospholidine-4,5-diimine 4a in which the "open" (exo/exo) conformation of the diimine unit was enforced by incorporation into a tricyclic molecular backbone. The coordination behavior of this potentially ambident ligand was sampled in reactions with ([(nbd)W(CO)4] and [CpCo(CO)2]) and pnictogen halides ECl3 (E = P, As, Sb). While PCl3 reacted under ring metathesis, all other reactions gave isolable complexes of composition (4a)MLn (MLn = W(CO)5, CpCo(CO), AsCl3, SbCl3); attempted recrystallization of the As-adduct yielded a complex (4a)(AsCl3)2 which was also accessible from reaction of 4a with 2 equiv of AsCl3. Single-crystal X-ray diffraction studies revealed that the ligand in [(4a)W(CO)5] and [(4a)CpCo(CO)] binds through its phosphorus lone-pair; [(4a)SbCl3] and [(4a)(AsCl3)2] contain a T-shaped ECl3 unit which binds to the chelating diimine moiety, and associate further via chloride bridges to give centrosymmetric dimers. Reactions of 4a with excess metal substrates gave no evidence that formation of bimetallic complexes with μ-bridging 1κ(2)(N,N')-2κP-coordination is feasible; the extra AsCl3 moiety in [(4a)(AsCl3)2] avoids this coordination mode by interacting with the peripheral chlorides of the central core. The observed selectivity suggests that ligand 4a specifically addresses transition metal centers with low positive charge and some back-bonding capacity through the phosphorus lone-pair, and electrophiles that behave essentially as "pure" Lewis acids through the diimine unit. This assumption was confirmed by DFT studies which disclosed further that binding of the first metal center deactivates the opposite binding site and thus strongly inhibits the formation of dinuclear complexes.

Copper(I) halide complexes of N-methylbenzothiazole-2-thione: Synthesis, structure, luminescence, antibacterial activity and interaction with DNA

The reactions of copper(I) halides, CuX (X=Cl, Br, I) with N-methylbenzothiazole-2-thione (mbtt), independent of the molar ration chosen (1:2 or 1:3), led to the formation of dinuclear complexes of the formula [CuX(mbtt)2]2, whereas the reactions of CuX and mbtt in the presence of two equivalents of triphenylphosphine (PPh3) afforded mononuclear mixed-ligand complexes of the formula [CuX(PPh3)2(mbtt)]. The molecular structure of a representative compound from each of the two above types of complexes, namely [CuCl(mbtt)2]2 and [CuI(PPh3)2(mbtt)] have been established by single-crystal X-ray diffraction. The new complexes are strongly emissive both in the solid state and in solution. The complexes were also screened for antibacterial activity and their ability to interact with native calf thymus DNA (CT-DNA) in vitro. Both types of complexes showed significant activities against all the bacteria tested as compared to that of standard antibiotic ampicillin, however, the three mixed-ligand complexes including triphenylphosphane as ligand exhibited perceptibly stronger antibacterial activity than the three homoleptic ones possessing only the mbtt ligand. DNA electrophoretic mobility experiments showed that all complexes bind to CT-ds DNA resulting in high molecular weight complexes ending in DNA degradation.