2,2''''—双〔2—(邻甲酰肟苯氧基)乙基〕醚与过渡金属配合物的合成及性质研究

含氮配位原子的希夫碱型化合物在分析化学、合成化学、药学等方面有广泛的应用。近十多年来,随着新药物的研制和生物无机化学的发展,其研究正在不断深入。肟类化合物在结构上与希夫碱型化合物主要不同之处是在于它与氮原子相连的基团是羟基,它在适当的条件下可参与金属配位或形成氢键,研究其配位模式有较重要的理论意义。我们合成了一个新的含醚氧链的双肟化合物,2,2＇—双[2—(邻甲酰肟苯氧基)乙基]醚(H_2BFO)。本     

Spectrophotometry Determination of Copper and Palladium Using Some 1,3,5-Triphenylformazans

A new rapid and accurate method for the spectrophotometric microdetermination of Cu(II) and Pd(II) using some 1,3,5-triphenylformazans (I) is given. The optimum conditions for the formation of the complexes are extensively investigated. The ligands form 1:1 and 1:2 (M:L) complexes with Cu and Pd ions, Beer's law is obeyed up to 3.8 and 6.5 ppm Cu and Pd respectively. The influence of foreign ions is investigated. The ligands were used successfully as indicators in spectrophotometric titration of Cu and Pd ions with EDTA and CDTA.     

First bivalent palladium and platinum cyanoximates: synthesis, characterization, and biological activity

A series of five cyanoximes (compounds having the general formula NC-C(=NOH)-R, where R is an amide or carboxylic ester group) have been synthesized and spectroscopically and structurally characterized. These are 2-cyano-2-isonitrosoacetamide (later HACO), 2-cyano-2-isonitrosothioacetamide (HTCO), 2-cyano-2-isonitrosoethylacetate (HECO), 2-cyano-2-isonitroso-N-piperidinylacetamide (HPiPCO), and 2-cyano-2-isonitroso-N-morpholinylacetamide (HMCO). A high yield method of synthesis was developed for the last two previously unknown amidocyanoximes. Variable temperature (13)C NMR studies in DMSO-d(6) solutions allowed the determination of rotational energy barriers for these two new cyanoximes. The HPiPCO and HMCO oxime molecules adopt a trans-anti configuration in the solid state according to X-ray analysis. Reactions between aqueous solutions of K(+)L(-) (L = cyanoximate anions: TCO(-), PiPCO(-), and MCO(-)) and K(2)[MCl(4)] (M = Pd, Pt) resulted in the formation of ML(2) complexes. The crystal structure of Pd(MCO)(2).DMSO was determined and showed the formation of coplanar dimeric [Pd(MCO)](2) units with 3.13 A Pd...Pd separation. The complex adopts cis geometry with anions being in the nitroso form. In the presence of bivalent Pd and Pt, ACO(-) and ECO(-) anions completely or partially hydrolyze in aqueous solutions to the dianion of 2-cyano-2-isonitrosoacetic acid (AACO(2-)). The crystal structure of the product of the hydrolysis reaction, K(2)[Pd(AACO)(2)].4H(2)O, was determined. Data revealed planar and cis geometry of the [Pd(AACO)(2)](2)(-) anion where cyanoximes are in the nitroso form and adopt a cis-anti configuration. All synthesized cyanoxime ligands and nine of their Pd(II) and Pt(II) complexes were tested in vitro on antiproliferating activity using human cervical cancer HeLa cell lines, and cisplatin as a positive control substance. Two out of the nine studied complexes, Pd(MCO)(2) and Pt(MCO), were found to be active compounds inflicting death on 28% and 16% of the cells, respectively, with 55% value for the cisplatin under the same conditions.     

Coordination chemistry of silanedithiolato ligands derived from cyclotrisilathiane: synthesis and structures of complexes of iron(II), cobalt(II), palladium(II), copper(I), and silver(I)

The coordination chemistry of chelating silanedithiolato ligands has been investigated on Fe(II), Co(II), Pd(II), Cu(I), and Ag(I). Treatment of M(OAc)(2) (M = Fe, Co, Pd) with cyclotrisilathiane (SSiMe(2))(3) in the presence of Lewis bases resulted in formation of Fe(S(2)SiMe(2))(PMDETA) (1), Fe(S(2)SiMe(2))(Me(3)TACN) (2), Co(S(2)SiMe(2))(PMDETA) (3), and Pd(S(2)SiMe(2))(PEt(3))(2) (4) (PMDETA = N,N,N',N',N' '-pentamethyldiethylenetriamine; Me(3)TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane). The analogous reactions of M(OAc) (M = Cu, Ag) in the presence of PEt(3) gave rise to the dinuclear complexes M(2)[(SSiMe(2))(2)S](PEt(3))(3) [M = Cu (5), Ag (6)]. Complexes were characterized in solution by (1)H, (31)P[(1)H], and (29)Si[(1)H] NMR and in the solid state by single-crystal X-ray diffraction. Mononuclear complexes 1-3 have a four-membered MS(2)Si ring, and these five-coordinate complexes adopt trigonal-bipyramidal (for the PMDETA adducts) or square-pyramidal (for the Me(3)TACN adduct) geometries. In dimer 6, the (SSiMe(2))(2)S(2)(-) silanedithiolato ligand bridges two metal centers, one of which is three-coordinate and the other four-coordinate. The chelating effect of silanedithiolato ligands leads to an increase in the stability of silylated thiolato complexes.     

Structures of Ni(II), Pd(II) and Cu(II) complexes with 1,2-<Emphasis Type="Italic">bis</Emphasis>(5,5,5-trifluoro-4-oxopent-2-en-2-amino)benzene

A new fluorine-containing tetradentate ligand 1,2-bis(5,5,5-trifluoro-4-oxopent-2-en-2-amino)benzene and its complexes with Ni(II), Pd(II) and Cu(II) are characterized by single crystal X-ray diffraction. It is found that the enaminoketone fragments of the ligand are identical in bond lengths and angles; they are almost planar, and make the angles of 51.3° to the plane of the benzene ring. The structures of Ni(II), Pd(II), and Cu(II) complexes are similar and have a saddle-shape configuration. The metal ions have square planar coordination and are located almost in the center of the N₂O₂ square. The average M-N bond lengths are longer than M-O ones by 0.014 Å and 0.034 Å for the Ni(II) and Cu(II) complexes respectively, while in the Pd(II) complex, M-O is longer than M-N by 0.029 Å. The average chelate angles N-M-O in the complexes are: N-Ni-O 95.12°; N-Pd-O 95.68°; N-Cu-O 93.88°.     

Synthesis and coordination chemistry of an alkyne functionalised bis(pyrazolyl)methane ligand

The alkyne functionalised bidentate N-donor ligand (2-propargyloxyphenyl)bis(pyrazolyl)methane was prepared in high yield from the reaction of (2-hydroxyphenyl)bis(pyrazolyl)methane with propargyl bromide in the presence of base. A series of transition-metal complexes including [MCl2] (M=Cu, Co, Ni, Zn, Pt), [M2](NO3)2 (M=Cu, Co, Ni, Zn), [Ag]NO3 and [Pd(dppe)](OTf)2 were prepared and characterised by spectroscopic techniques. In addition, ligand as well as the Co(II) and Zn(II) complexes [CoCl2]2, [ZnCl2] were structurally characterized by single-crystal X-ray diffraction. The organometallic gold(I) and platinum(II) acetylide complexes [Pz2CH(C6H(4)-2-OCH2C[triple bond, length as m-dash]CAuPPh3)] and trans-[{Pz2CHC6H(4)-2-OCH2C[triple bond, length as m-dash]C}2Pt(PPh3)2] were prepared from and [AuCl(PPh3)] and trans-[PtCl2(PPh3)2], respectively. Treatment of these complexes with [Pd(OTf)2(dppe)] or [Cu(MeCN)4]PF6 results in formation of the cationic, mixed-metal complexes, which were isolated (Pt/Pd, Au/Pt) or detected by electrospray mass spectrometry (Au/Cu, Pt/Cu).     

Tetradentate bis(o-iminobenzosemiquinonate(1-)) pi radical ligands and their o-aminophenolate(1-) derivatives in complexes of nickel(II), palladium(II), and copper(II)

The coordination chemistries of the potential tetradentate ligands N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)ethylenediamine, H4[L1], the unsaturated analogue glyoxal-bis(2-hydroxy-3,5-di-tert-butylanil), H2[L2], and N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2-dimethylpropylenediamine, H4[L3], have been investigated with nickel(II), palladium(II), and copper(II). The complexes prepared and characterized are [Ni(II)(H3L1)2] (1), [Ni(II)(HL2)2].5/8CH2Cl2 (2), [Ni(II)(L3**)] (3), [Pd(II)(L3**)][Pd(II)(H2L3) (4), and [Cu(II)(H2O)(L4)] (5), where (L4)2- is the oxidized diimine form of (L3)4- and (L3**)2- is the bis(o-iminosemiquinonate) diradical form of (L3)4-. The structures of compounds 1-5 have been determined by single crystal X-ray crystallography. In complexes 1 and 2, the ligands (H3L1)- and (HL2)- are tridentate and the nickel ions are in an octahedral ligand environment. The oxidation level of the ligands is that of an aromatic o-aminophenol. 1 and 2 are paramagnetic (mu(eff) approximately 3.2 mu(B) at 300 K), indicating an S = 1 ground state. The diamagnetic, square planar, four-coordinate complexes 3 and [Pd(II)(L3**)] in 4 each contain two antiferromagnetically coupled o-iminobenzosemiquinonate(1-) pi radicals. Diamagnetic [Pd(II)(H2L3)] in 4 forms an eclipsed dimer via four N-H.O hydrogen bonding contacts which yields a nonbonding Pd.Pd contact of 3.0846(4) A. Complex 5 contains a five-coordinate Cu(II) ion and two o-aminophenolate(1-) halves in (L4)2-. The electrochemistries of complexes 3 and 4a ([Pd(II)(L3**)] of 4) have been investigated, and the EPR spectra of the monocations and -anions are reported.     

An allosteric synthetic catalyst: metal ions tune the activity of an artificial phosphodiesterase

A trinuclear metal complex of general formula (L-H)M3(Mf)2 represents the first allosteric low molecular weight catalyst. L is a polyaza ligand having a tetradentate and two bidentate metal binding sites, Ms is a "structural" (allosteric) metal, and Mf are functional (catalytic) metals which interact with a substrate. In mononuclear [(L-H)Ms]+ complexes [(L-H)Cu(MeOH)]ClO4 (1a). [(L-H)Cu]NO3 x 2H2O (1b), [(L-H)Ni]ClO4 x 4H2O (2), and [(L-H)Pd]ClO4 x 2H2O (3), prepared from L and M2+ salts, the metal is strongly bound by an in-plane N4-coordination (confirmed by X-ray crystal structure determination of la). Formation of trinuclear complexes [(L-H)MsCu2]5+, with two functional Cu2+ ions coordinated to the bidentate sites of L, was evidenced in solution by photometric titration and by isolation of [(L-H)Cu3][PO4][ClO4]2 x 9H2O (4). The trinuclear complexes catalyze the cleavage of RNA-analogue 2-(hydroxypropyl)-p-nitrophenyl phosphate (HPNP), an activated phosphodiester. From a kinetic analysis of the cleavage rate at various HPNP concentrations, parameters KHPNP (the equilibrium constant for binding of HPNP to [(L-H)MsCu2]5+ and kcat (first-order rate constant for cleavage of HPNP when bound to the catalyst) were derived: KM= 170 (Ms= Cu2+), 340 (Ms = Ni2+), 2,600 (Ms = Pd2+) M(-1), kcat = 17 x 10(-3) (Ms= Cu2+) 3.1 x 10(-3) (Ms=Ni2+), 0.22 x 10(-3) (Ms = Pd2+) s(-1). Obviously, the nature of the allosteric metal ion Ms strongly influences both substrate affinity and reactivity of the catalyst [(L-H)MsCu2]5+. Our interpretation of this observation is that subtle differences in the ionic radius of Ms and in its tendency to distort the N4-Ms coordination plane have a significant influence on the conformation of the catalyst (i.e., preorganization of functional Cu2+ ions) and thus on catalytic activity.     

Structural characterization,thermal investigation and biological activity of metal complexes containing Schiff Base ligand (Z)‐3‐(1‐((4,6‐dimethyl‐1H‐pyrazolo[3,4‐b] pyridin‐3‐yl)imino)ethyl)‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one

A new series of metal complexes containing Co(II), Pd(II), Fe(III) chloride and Cu(II) salts (chloride, bromide, sulphate and perchlorate) have been prepared with Schiff base ligand ( HL ). The synthesized compounds were elucidated using elemental analyses, spectral techniques, molar conductance, magnetic measurements and thermogravimetric studies. The analytical data established (1 M:1 L) stoichiometry for complexes ( 1 ), ( 2 ), ( 4 ), ( 6 ) and ( 7 ) as well as (1 M:2 L) and (2 M:3 L) stoichiometry for complexes ( 5 ) and ( 3 ), respectively. As a result, the ligand HL coordinates in complexes ( 1 ), ( 2 ), ( 4 ), ( 6 ) as a monobasic tridentate ONN moiety via the oxygen atom of the deprotonated phenolic OH, the nitrogen atoms of the azomethine and the imine group in pyrazolopyridine ring. While, it behaves as a neutral bidentate in complexes ( 3 , 7 ), chelates via oxygen and nitrogen atoms of enolic OH and azomethine groups. Also, in complex ( 5 ) Cu²⁺ ion binds via NO sits of two ligand molecules in its monobasic and neutral forms. The magnetic moment and electronic spectral data proposed octahedral structure for complexes ( 2 , 3 and 7 ) as well as triagonal bipyramidal and square pyramidal geometry for complexes ( 1 and 4 ), while, chelates ( 5 ) and ( 6 ) possess square planar geometry. TG/DTG studies confirmed the chemical formula for these complexes and established the thermal decomposition processes ended with the formation of metal or metal oxides contaminated with carbon residue. An axial electron spin resonance spectra were suggested for Cu(II) complexes pointing to ²B_1g as a ground state with hyperfine structure for complex ( 4 ). In vitro antibacterial and antioxidant activities were performed for HL ligand and its metal complexes. The biological studies indicate that complex ( 3 ) has better antibacterial activity compared to the ligand and the other complexes.     

Spectroscopic studies of transition metal complexes with a N-donor tetradentate(N4) 12-membered macrocylic ligand

Chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), copper(II), ruthenium(III), iridium(III), palladium(II) and platinum(II) complexes were synthesized with a 12-membered 1,4,7,10-tetraazadodeca-5,6,11,12-tetraene macrocylic ligand (L) and characterized by elemental analysis, molar conductance, magnetic susceptibility, IR, electronic, EPR and M?ssbauer [Fe(III)] spectral studies. The molar conductance measurements of all the complexes in DMF solution correspond to non-electrolytic nature for M(L)Cl2 complexes [where M=Mn(II), Co(II), Ni(II), Cu(II)], 1:1 electrolytes for M'(L)Cl3 complexes [where M'=Cr(III), Fe(III), Ru(III) and Ir(III)] and 1:2 electrolytes for M'(L)Cl2 complexes [where M'=Pd(II) and Pt(II)]. Thus, the complexes may be formulated as [M(L)C1(2)], [M'(L)C1(2)]C1 and [M'(L)]C1(2), respectively [where L=ligand]. All complexes were of the high-spin type and found to have six-coordinate octahedral geometry except the Pd(II) and Pt(II) complexes which were four coordinate, square planar and diamagnetic.     

Potentiometric, spectroscopic and thermal studies on the metal chelates of 1-(2-thiazolylazo)-2-naphthalenol

The synthesis and characterization of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pd(II) and UO2(II) chelates of 1-(2-thiazolylazo)-2-naphthalenol (TAN) were reported. The dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically at 25 degrees C and 0.1 M ionic strength. The solid complexes were characterized by elemental and thermal analyses, molar conductance, IR, magnetic and diffuse reflectance spectra. The complexes were found to have the formulae [M(L)2] for M = Mn(II), Co(II), Ni(II), Zn(II) and Cd(II); [M(L)X].nH2O for M = Cu(II) (X = AcO, n = 3), Pd(II) (X = Cl, n = 0) and UO2(II) (X = NO3, n = 0), and [Fe(L)Cl2(H2O)].2H2O. The molar conductance data reveal that the chelates are non-electrolytes. IR spectra show that the ligand is coordinated to the metal ions in a terdentate manner with ONN donor sites of the naphthyl OH, azo N and thiazole N. An octahedral structure is proposed for Mn(II), Fe(III), Co(II), Ni(II), Zn(II), Cd(II) and UO2(II) complexes and a square planar structure for Cu(II) and Pd(II) complexes. The thermal behaviour of these chelates shows that water molecules (coordinated and hydrated) and anions are removed in two successive steps followed immediately by decomposition of the ligand molecule in the subsequent steps. The relative thermal stability of the chelates is evaluated. The final decomposition products are found to be the corresponding metal oxides. The thermodynamic activation parameters, such as E*, delta H*, delta S* and delta G* are calculated from the TG curves.     

Description of the ground-state covalencies of the bis(dithiolato) transition-metal complexes from X-ray absorption spectroscopy and time-dependent density-functional calculations

The electronic structures of [M(L(Bu))(2)](-) (L(Bu)=3,5-di-tert-butyl-1,2-benzenedithiol; M=Ni, Pd, Pt, Cu, Co, Au) complexes and their electrochemically generated oxidized and reduced forms have been investigated by using sulfur K-edge as well as metal K- and L-edge X-ray absorption spectroscopy. The electronic structure content of the sulfur K-edge spectra was determined through detailed comparison of experimental and theoretically calculated spectra. The calculations were based on a new simplified scheme based on quasi-relativistic time-dependent density functional theory (TD-DFT) and proved to be successful in the interpretation of the experimental data. It is shown that dithiolene ligands act as noninnocent ligands that are readily oxidized to the dithiosemiquinonate(-) forms. The extent of electron transfer strongly depends on the effective nuclear charge of the central metal, which in turn is influenced by its formal oxidation state, its position in the periodic table, and scalar relativistic effects for the heavier metals. Thus, the complexes [M(L(Bu))(2)](-) (M=Ni, Pd, Pt) and [Au(L(Bu))(2)] are best described as delocalized class III mixed-valence ligand radicals bound to low-spin d(8) central metal ions while [M(L(Bu))(2)](-) (M=Cu, Au) and [M(L(Bu))(2)](2-) (M=Ni, Pd, Pt) contain completely reduced dithiolato(2-) ligands. The case of [Co(L(Bu))(2)](-) remains ambiguous. On the methodological side, the calculation led to the new result that the transition dipole moment integral is noticeably different for S(1s)-->valence-pi versus S(1s)-->valence-sigma transitions, which is explained on the basis of the differences in radial distortion that accompany chemical bond formation. This is of importance in determining experimental covalencies for complexes with highly covalent metal-sulfur bonds from ligand K-edge absorption spectroscopy.     

Polynuclear palladium complexes with 3,5-dimethylpyrazolate exhibiting three different coordination modes

The characterisation of dinuclear pyrazolato-bridged Pd(II) complexes, [(Pd(mu-dmpz)Cl(Hdmpz))2] (1) and [(Pd(mu-dmpz)(dmpz)(Hdmpz))2] (2) (Hdmpz=dimethylpyrazole), has been carried out. An X-ray study of compound 2 reveals the existence of intramolecular N-H...N hydrogen bonds between neighbouring dmpz groups. Compound 2 has been deprotonated and both acidic hydrogen atoms substituted by two metal atoms of Cu(I), Ag(I) or Au(I) to give the tetranuclear compounds [Pd2M2(mu(2)-dmpz-kappaN,N')6] (M=Cu, Ag, Au). The structure of these compounds resembles a box with a small cavity inside. There are also three pi-electron-rich clefts between each of the three pairs of azolato rings, capable of further complexation. The reactions of [Pd2M2(mu(2)-dmpz-kappaN,N')6] (M=Cu, Ag, Au) with AgClO4 render compounds of the type [(Pd2M2(mu(2)-dmpz-kappaN,N')2(-)(mu(3)-dmpz-kappaN,N',C4)4Ag2(mu(2)-O2ClO2))2] (M=Cu, Ag, Au). The X-ray structures of crystals obtained from a solution of compounds [(Pd2M2(mu(2)-dmpz-kappaN,N')2(mu(3)-dmpz-kappaN,N',C4)4Ag2(mu(2)-O(2)ClO2))2] (M=Ag, Au) in acetone reveals a [(Pd2M2(mu(2)-dmpz-kappaN,N')2(mu(3)-dmpz-kappaN,N',C4)4Ag(OCMe2)(OClO3)Ag(mu(2)-O2ClO2))2] stoichiometry, indicating that only two of the three pi-electron-rich clefts have been used to accommodate Ag+ ions. Each of the silver atoms are located in between two 3,5-dmpz rings and are eta(1)-bonded to the C4 atom of each group.     

On the prospects of polynuclear complexes with acetylenedithiolate bridging units

The generation of polynuclear complexes with one, two, or four acetylenedithiolate bridging units via the isolation of eta2-alkyne complexes of acetylenedithiolate K[Tp'M(CO)(L)(C2S2)] (Tp'=hydrotris(3,5-dimethylpyrazolyl)borate, M=W, L=CO (K-3a), M=Mo, L=CNC6H3Me2 (K-3b)) is reported. The strong electronic cooperation of Ru and W in the heterobimetallic complexes [(eta5-C5H5)(PPh3)Ru(3a)] (4a) and [(eta5-C5H5)(Me2C6H3NC)Ru(3a)] (4b) has been elucidated by correlation of the NMR, IR, UV-vis, and EPR-spectroscopic properties of the redox couples 4a/4a+ and 4b/4b+ with results from density functional calculations. Treatment of M(II) (M=Ni, Pd, Pt) with K-3a and K-3b afforded the homoleptic bis complexes [M(3a)2] (M=Ni (5a), Pd (5b), Pt (5c)), and [M(3b)2] (M=Pd (6a) and Pt (6b)), in which the metalla-acetylendithiolates exclusively serve as S,S'-chelate ligands. The vibrational and electronic spectra as well as the cyclic voltammetry behavior of all the complexes are compared. The structural analogy of 5a/5b/5c and 6a/6b with dithiolene complexes is only partly reflected in the electronic structures. The very intense visible absorptions involve essential d orbital contributions of the central metal, while the redox activity is primarily attributed to the alkyne complex moiety. Accordingly, stoichiometric reduction of 5a/5b/5c yields paramagnetic complex anions with electron-rich alkyne complex moieties being indistinguishable in the IR time scale. K-3a forms with Cu(I) the octanuclear cluster [Cu(3a)]4 (7) exhibiting a Cu4(S2C2)4W4 core. The nonchelating bridging mode of the metalla-acetylenedithiolate 3a- in 7 is recognized by a high-field shift of the alkyne carbon atoms in the 13C NMR spectrum. X-ray diffraction studies of K[Tp'(CO)(Me3CNC)Mo(eta2-C2S2)] (K-3c), 4b, 6a, 6b, and 7 are included. Comparison of the molecular structures of K-3c and 7 on the one hand with 4b and 6a/6b on the other reveals that the small bend-back angles in the latter are a direct consequence of the chelate ring formation.     

Self-assembly luminescent heteroheptanuclear complexes with metal diphosphine and metal thiolate as components

Self-assembly between the building blocks [M2(mu-dppm)2(MeCN)2]2+ (M = Cu or Ag; dppm = bis(diphenylphosphino)methane) and M'(aet)2 (aet = 2-aminoethanethiolate) afforded luminescent heterohepta-nuclear complexes [Cu4M'3(mu-dppm)3(mu 3-aet)4(mu-aet)2]4+ (M' = Ni 1; Pd 2) or heterotrinuclear complexes [Ag2M'(mu-dppm)2(mu-aet)2]2+ (M' = Ni 3, Pd 4).     

噻吩甲酰基吡唑啉酮缩乙二胺配合物的合成、表征及生物活性

A new ligand N,N′-bis［(1-phenyl-3-methyl-5-oxo-4-pyrazolinyl)-2-thenoylmethylidyne］ethyl-enediimine (HPMTHP)₂en and its five complexes have been sythesized. These complexes have the general formula ［M(PMTHP)₂en］, where M=Cu(Ⅱ), Ni(Ⅱ)     

A survey of diamagnetic probes for copper2+ binding to the prion protein. 1H NMR solution structure of the palladium2+ bound single octarepeat

The prion protein (PrP(C)) is a copper binding cell surface glycoprotein which when misfolded causes transmissible spongiform encephalopathies. The cooperative binding of Cu2+ to an unstructured octarepeat sequence within PrP(C) causes profound folding of this region. The use of NMR to determine the solution structure of the octarepeat region of PrP with Cu2+ bound has been hampered by the paramagnetic nature of the Cu2+ ions. Using NMR we have investigated the binding of candidate diamagnetic replacement ions, to the octarepeat region of PrP. We show that Pd2+ forms diamagnetic complexes with the peptides HGGG, HGGGW and QPHGGGWGQ with 1:1 stoichiometry. The 1H NMR spectra indicate that these peptides are in slow-exchange between free and bound Pd2+ on the chemical-shift time-scale. We demonstrate that the Pd-peptide complex forms slowly with a time taken to reach half-maximal signal of 3 hours. Other candidate metal ions, Ni2+, Pt2+ and Au3+, were investigated but only the Pd2+ complexes gave resolvable 1H NMR spectra. We have determined the solution structure of the QPHGGGWGQ-Pd 1:1 complex using 71 NOE distance restraints. A backbone RMSD of 0.30 A was observed over residues 3 to 7 in the final ensemble. The co-ordinating ligands consist of the histidine imidazole side chain N epsilon, the amide N of the second and third glycines with possibly H2O as the fourth ligand. The co-ordination geometry differs markedly from that of the HGGGW-Cu crystal structure. This survey of potential replacement metal ions to Cu2+ provides insight into the metal specificity and co-ordination chemistry of the metal bound octarepeats.     

Synthesis, spectroscopic characterization and redox reactivity of some transition metal complexes with salicylaldimines bearing 2,6-di-phenylphenol

New bidentate N-(2,6-di-phenyl-1-hydroxyphenyl) salicylaldimines bearing X=H and 3,5-di-t-butyl substituents on the salicylaldehyde ring, L(x)H, and their copper(II) complexes, M(Lx)2, (M=Cu(II), Co(II), Pd(II), Ni(II) and Zn(II)) have been synthesized and characterized by IR, UV/vis, 1H NMR, 13C NMR, ESR spectroscopy, magnetic susceptibility measurements, as well as their oxidation with PbO(2) and reduction (for Cu(Lx)2) with PPh(3) were investigated. ESR studies indicate that oxidation of M(Lx)2 produces ligand-centered M(II)-phenoxyl radical species. The Cu(Lx)2 complexes, unlike others M(Lx)2, are readily reduced by PPh3 via intramolecular electron transfer from ligand to copper(II) to give unstable radical intermediates which are converted to another stable secondary radical species. The analysis of ESR spectra of Cu(Lx)(2), Co(L1)(2) and generated phenoxyl radicals are presented.     

Synthesis and studies on metal coordination with a novel carboxyamide ligand

Novel complexes of Co(II), Ni(II), Cu(II) and Pd(II) with the new ligand [N,N'-bis(2-carboxy-1-oxo-phenelenyl)ethylenediamine] (H2L) have been synthesized and characterized on the basis of elemental analyses, magnetic susceptibility, thermal, infrared, electronic, 1H NMR and EPR spectral studies. Infrared and 1H NMR spectra show that H2L acts as a binegative tetradentate ligand. Coordination occurs through deprotonated carboxylate oxygens and nondeprotonated amido nitrogens in all the complexes. Electronic spectral studies and magnetic moment values suggest N2O2 coordination around each metal centre with strong field square planar chromophores. The probable structures of the complexes have been assigned on the basis of spectral studies. The complex formation between M(II) [M(II) = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)] and (L2-) has also been studied potentiometrically in 75% aqueous DMF at 25 degrees C in 0.1 M NaClO4. The stability constants were found to follow the order: Mn(II) < Co(II) < Ni(II) < Cu(II) > Zn(II).     

Rearrangement and complexation of 5-substituted-1,3,4-thiadiazolidine-2-thiones with divalent transition metals

The reactions of a variety of divalent transition metal ions with 3-methyl-5-(2-hydroxypheny)-, 3-methyl-5-(2-thienyl)-and 3-methyl-5-(2-furyl)-1,3,4-thiadiazolidine-2-thiones (htt, ttt and ftt, respectively) are accompanied by opening of the thiadiazolidine ring and rearrangement to the corresponding Schiff base (Hhts, Htts and Hfts, respectively) with the concomitant formation of complexes of the general formulae, [M(hts)] (M=Ni, Cu, Zn or Pd), [M(hts) (py)] (M=Ni, Cu), [Co(Hhts)hts)], and [ML₂] (M=Ni, Cu, Zn or Cd); L=tts or fts). The complexes have been characterised by physico-chemical and spectroscopic methods. The fungitoxicities of the corresponding Schiff base metal complexes have been investigated. TMC 2568