Redox-induced ligand reorganization and helicity inversion in copper complexes of N,N-dialkylmethionine derivatives

N,N'-Dipicolyl, bis(stilbylvinylpyridylmethyl), and diquinaldyl methionine derivatives form stable Cu(II) complexes with metal ligation by three nitrogen atoms and the carboxylate. One-electron reduction results in the exchange of carboxylate for sulfide in the complexes. This ligand reorganization is accompanied by inversion of the helical orientation of the two arms containing nitrogen heterocycles, resulting in nearly mirror image circular dichroism spectra. This paper provides details for the synthesis of these complexes and the evidence for the remarkable stereochemical interconversion that accompanies the reduction reaction. Detailed analysis of the electronic spectra of the ligands and metal complexes is provided along with X-ray crystallographic structures of Cu(II) and Zn(II) complexes of the N,N'-dipicolylmethionine complexes.     

Octahedral Complexes with Predetermined Helical Chirality: Xylene-Bridged Bis([4,5]-pineno-2,2'-bipyridine) Ligands (Chiragen[o-, m-, p-xyl]) with Ruthenium(II)

Tetradentate ligands are obtained by joining two optically active [4,5]-pineno-2,2'-bipyridine molecules in a stereoselective reaction, where two new stereogenic centers are created. These ligands are new members of the chiragen family that form OC-6 complexes with predetermined helical chirality. Ru(II) complexes with 4,4'-dimethyl-2,2'-bipyridine occupying the remaining coordination sites have been synthesized with all three new ligands. Characterization of the ruthenium complexes by NMR spectroscopy confirm C(2)-symmetric structures in solution. CD spectra show that the complexes are composed of only one helical diastereomer with the expected absolute configurations. In addition, a strong chiral amplification is observed, if precursors of low enantiomeric purity are used. This is due to the inability of ligands that are heterochiral in the two bpy moieties to coordinate to one center. X-ray structural data were obtained for the complex Delta-[RuCG[o-xyl](4,4'-DMbpy)](PF(6))(2). Crystal data (Mo Kalpha, 298 K): trigonal, space group R3, a = 52.986(4) ?, c = 10.545(1) ?, V = 25639(4) ?(3), Z = 18, R1 = 0.087, and wR2 = 0.0986 for 2609 observed reflections.     

M and P double helical complexes of copper(I) with bis-imino bis-quinoline enantiomerically pure chiral ligands

The enantiomerically pure bis-imino bis-quinoline ligands R,R-ImQ and S,S-ImQ have been prepared by Schiff condensation of 2-quinoline carboxyaldehyde with the pure R,R and S,S enantiomers of trans-1,2-diaminocyclohexane. Both ligands form 2:2 helical complexes with CuI perchlorate, and the crystal and molecular structure of [Cu2(R,R-ImQ)2]ClO4.H2O have been determined by X-ray diffraction methods: the [Cu2(R,R-ImQ)2]2+ molecular cation is a chiral double helix of M handedness, in which the two ligands are entertwined in such an arrangement that half of each ligand is not equivalent to the other half of the same ligand. Coupled circular dichroism and 1H NMR studies reveal that in CH3CN solution a rearrangement takes place toward a more symmetric helical structure (in which the two halves of the same ligand become equivalent), which maintains the same handedness found in the solid state and is a pure M isomer. Solid state and CH3CN solution CD experiments confirm that [Cu2(S,S-ImQ)2]ClO4.H2O, both in solution and in the solid state, is a pure double helix of P handedness, i.e., the enantiomer of the species containing the R,R ligand.     

The PcoC copper resistance protein coordinates Cu(I) via novel S-methionine interactions

The E. coli copper resistance protein PcoC enhances survival of a bacterium under conditions of extreme copper stress. This small protein has no cysteines, but does have an unusual methionine-rich sequence motif, suggesting that methionine ligation may be important in Cu binding. It is shown that PcoC binds both Cu(I) and Cu(II), in addition to binding Hg(II) and Ag(I). Previously crystallographic studies of PcoC had shown that the apo protein adopts a beta-barrel fold typical of that seen for blue-copper electron-transfer proteins. However, in contrast with electron-transfer proteins, where the Cu(I) and Cu(II) structures are nearly identical, X-ray absorption spectra show that the structures of the Cu site in reduced and oxidized PcoC are dramatically different. Cu(II) PcoC has a tetragonal Cu structure in which the Cu is coordinated to O or N ligands, including at least two histidine ligands. Cu(I) PcoC has a trigonal site with two methionine ligands. This is the first well-characterized example of a methionine-rich protein Cu binding site, demonstrating a new type of biological Cu coordination chemistry.     

DINUCLEAR COPPER(II) COMPLEXES WITH 3-FURANCARBOXYLIC ACID AND 2-THIOPHENCARBOXYLIC ACID

Abstract

The structures of Cu(II) 3-furancarboxylate and Cu(II) 2-thiophenate denoted hereafter as Cu-3F and Cu-2T, respectively, were determined. The structures are dinuclear, bridged by bidentate ligands. The coordination about copper is square pyramidal. The pKa of the respective acids is a factor influencing changes in Cu-Cu distances. The differences in hydrogen bond patterns and packing are described.     

Dinuclear bis-beta-diketonato ligand derivatives of iron(III) and copper(II) and use of the latter as components for the assembly of extended metallo-supramolecular structures

A range of 1,3-aryl linked, bis-beta-diketone derivatives (LH2) has been employed to synthesise neutral bis(ligand), dinuclear complexes incorporating square-planar copper(II) and tris(ligand) dinuclear helical derivatives containing octahedral iron(III). The 1H NMR spectra of the free ligands contain singlet peaks at ca. 16.2 ppm, indicative of enolic protons, confirming that the (bis) enol tautomer is present in solution. An X-ray structure of a ligand from the series incorporating tert-butyl terminal substituents confirms that the same tautomer persists in the solid and that the relative orientation of the bis-beta-diketone fragments is such that the coordination vectors lie at approximately 120 degrees to each other. The planar, dinuclear copper complexes form 1 : 2 adducts with pyridine and 4-(dimethylamino)pyridine, confirmed by X-ray structures, that incorporate five-coordinate metal centres. Based on this behaviour, the prospect of linking copper centres in the dinuclear complexes using the difunctional heterocyclic bases, 4,4'-bipyridine, 4,4'-trans-azopyridine and pyrazine as co-ligands has been probed. However, 4,4'-bipyridine was observed to coordinate through only one of its heterocyclic nitrogen atoms in the solid state to form a 1 : 2 ([Cu2(L)2]: 4,4'-bipyridine) adduct, analogous to the structures obtained with the above mono-functional nitrogen bases. Nevertheless, an X-ray structure determination shows that the related difunctional base, 4,4'-trans-azopyridine, coordinates in a bridging fashion via both its heterocyclic nitrogen atoms on alternate sides of each planar [Cu2(L)2] unit to produce an infinite one dimensional metallo chain. In contrast, with pyrazine, a new neutral, discrete assembly of type [Cu4(L)4(pyrazine)2] is formed. The X-ray structure shows that two planar dinuclear complexes are linked by two pyrazine molecules in a sandwich arrangement such that the coordination environment of each copper ion is approximately square pyramidal with the overall tetranuclear structure thus taking the form of a 'dimer of dimers'.     

Model complexes of cobalt-substituted matrix metalloproteinases: tools for inhibitor design

The tetrahedral cobalt(II) complex [(Tp(Ph,Me))CoCl] (Tp(Ph,Me) = hydrotris(3,5-phenylmethylpyrazolyl)borate) was combined with several hydroxypyridinone, hydroxypyridinethione, pyrone, and thiopyrone ligands to form the corresponding [(Tp(Ph,Me))Co(L)] complexes. X-ray crystal structures of these complexes were obtained to determine the mode of binding for each ligand L. The structures show that the [(Tp(Ph,Me))Co(L)] complexes are pentacoordinate complexes, with a general tendency toward square pyramidal geometry. The electronic, EPR, and paramagnetic NMR spectroscopy of the [(Tp(Ph,Me))Co(L)] complexes have been examined. The frozen-solution EPR spectra are indicative of pentacoordination in frozen solution, while the NMR indicates some dynamics in ligand binding. The findings presented here suggest that [(Tp(Ph,Me))Co(L)] complexes can be used as spectroscopic references for investigating the mode of inhibitor binding in metalloproteinases of medicinal interest. Potential limitations when using cobalt(II) model complexes are also discussed.     

Development of a Synthetic Route to Unsymmetrical Triphosphine Ligands and an Investigation of Their Coordination Chemistry with Nickel and Palladium

Chiral tridentate phosphines, R(2)P(CH(2))(3)PPh(CH(2))(2)PPh(2) where R = C(6)H(5), p-ClC(6)H(4), and p-FC(6)H(4), can be prepared from simple starting materials, (R(3)P, I(CH(2))(3)I, and Ph(2)P(CH(2))(2)PPh(2)), in a few stages involving phosphonium salts and phosphine oxides as intermediates. Crystalline diamagnetic complexes of nickel(II) and palladium(II) have been isolated. In solution these show first-order 12 line (31)P NMR spectra consistent with three nonequivalent phosphorus nuclei coupled to one another in a square planar geometry. A single X-ray crystallographic study of NiI(2){P(CH(2))(3)PPh(CH(2))(2)PPh(2)} showed that this was square pyramidal in the solid state with a weakly held apical iodo ligand.     

New chiral Schiff base–Cu(II) complexes as cyclopropanation catalysts

A series of chiral Schiff base ligands 1–4, derived from (1R,2S)-(+)-cis-1-amino-2-indanol and other chiral amines with substituted salycilaldehydes were synthesized and transformed to the corresponding Cu(II) complexes. Molecular structures of six Cu(II) complexes were determined by X-ray crystallographic studies. The structures show the metal ion in a distorted square planar geometry with dimeric or monomeric structures, depending on the ligand denticity. The potential use of these complexes in asymmetric Cyclopropanation was explored.     

A foldamer-based chiroptical molecular switch that displays complete inversion of the helical sense upon anion binding

Chiral indolocarbazole dimers fold into a helical conformation by virtue of intramolecular hydrogen bonds, as demonstrated by (1)H NMR and CD spectra and optical rotations. In particular, the optical properties of the dimers were found to be extremely sensitive to the nature of the solvent, depending on whether they are folded or not. The helical sense of the dimers can be reversibly switched by binding sulfate ion, which gives rise to complete inversion of the CD spectra. The binding mode and absolute stereochemistry of the sulfate complexes was unequivocally determined by single-crystal X-ray structures, which are all consistent with the CD and (1)H NMR spectra in solution.     

Trinuclear Cu(II) complexes of a chiral N6O3 amine

Enantiopure trinuclear Cu(II) complexes 3 and 4 of macrocyclic amine 1 derived from the 3 + 3 condensation of 2,6-diformyl-4-methylphenol and (1S,2S)-1,2-diaminocyclohexane have been synthesized and characterized by ESI MS and NMR spectroscopy. The X-ray crystal structures of both complexes have been determined. The structure of the chloride derivative 3 indicates unusual combination of distorted tetragonal bipyramidal, square pyramidal and square geometries of the three Cu(II) ions bound by macrocycle 1. The acetate complex 4 also exhibits unsymmetrical trinuclear core with the bridging and terminal acetate anions. The complexation of Cu(II) ions by macrocycle 1 has been studied using potentiometric methods and both protonation and binding constants of 1 have been determined. The distribution of the complex forms indicates cooperative binding of three metal ions by 1. The overall magnetic behaviour for 3 corresponds to an antiferromagnetically coupled triangular system. Compound 4 shows the presence of antiferromagnetic coupling (J = -74.9(1) cm(-1)) between the metal centers in equilateral triangular array.     

Characterization and biological activities of two copper(II) complexes with diethylenetriamine and 2,2'-bipyridine or 1,10-phenanthroline as ligands

Two new mixed ligand copper(II) complexes with diethylenetriamine, 2,2'-bipyridine and 1,10-phenanthroline have been synthesized. The crystal and molecular structures of [Cu(dien)(phen)](ClO(4))(2) and [Cu(dien)(bipy)](BF(4))(2) (dien=diethylenetriamine, phen=1,10-phenanthroline, bipy=2,2'-bipyridine) were determined by X-ray crystallography from single crystal data. These two complexes have similar structures. The EPR spectral data also suggest that these complexes have distorted square pyramidal geometry about copper(II). Anti-microbial and superoxide dismutase activities of these complexes have also been measured. They show the higher SOD activity than the corresponding simple Cu(II)-dien/Cu(II)-PMDT (PMDT=N,N,N',N',N'-pentamethyldiethylenetriamine) complexes because of a strong axial bond of one of the nitrogen atoms of the alpha-diimine. Both the complexes have been found to cleave plasmid DNA in the presence of co-reductants such as ascorbic acid and glutathione.     

Plasticity of the nickel(II) coordination environment in complexes with hemilabile phosphino thioether ligands

A series of homoligated Ni(II) complexes formed from two phosphino thioether (P,S) chelating ligands has been synthesized and characterized. Interestingly, this included octahedral Ni(II) complexes which, unlike previously characterized d(8) Rh(I), Pt(II), and Pd(II) analogues, exhibit in situ exchange processes centered around chloride ligand dissociation. This was verified and studied through the controlled abstraction from and introduction of chloride ions to this system, which showed that these processes proceed through complexes with square pyramidal, tetrahedral, and square planar geometries. These complexes were studied with a variety of characterization methods, including single-crystal X-ray diffraction studies, solution (31)P{(1)H} NMR spectroscopy, UV-vis spectroscopy, and DFT calculations. A general set of synthetic procedures that involve the use of coordinating and noncoordinating counteranions, as well as different hemilabile ligands, to mediate geometry transformations are presented.     

Antimicrobial,antioxidant and SOD activities of copper(II) complexes derived from 2-aminobenzothiazole derivatives

A series of Cu(II) complexes have been synthesized from bidentate Schiff base ligands (by condensation of Knoevenagel condensate of acetoacetanilide (obtained from substituted benzaldehydes and acetoacetanilide) and 2-aminobenzothiazole). They were characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR, UV–vis., molar conductance, magnetic moment, ESR spectra and electrochemical studies. Based on the magnetic moment, ESR, and electronic spectral data, a distorted square planar geometry has been suggested for the complexes. Antibacterial and antifungal screening of the ligands and their complexes reveal that all the complexes show higher activities than the ligands. The antioxidant activities of the ligands and complexes were determined by superoxide and hydroxyl radical scavenging methods in vitro, indicating that the complexes exhibit more effective antioxidant activity than the ligands alone. The results show that the Cu(II) complexes also have similar superoxide dismutase activity to that of native Cu, Zn-SOD. All complexes exhibit suitable Cu(II)/Cu(I) redox potential (E_1/2) to act as synthetic antioxidant enzyme mimics.     

Structural and luminescence studies of nickel(II) and copper(II) complexes with (1R,2R)-cyclohexanediamine derived unsymmetric Schiff base

Unsymmetrical Schiff base obtained by the condensation reaction of (1R,2R)(-)cyclohexanediamine with 2-hydroxybenzaldehyde and 2-hydroxynaphthaldehyde was used as a ligand for copper(II) and nickel(II). The ligand and complexes were characterized by circular dichroism (CD), UV-VIS, fluorescence, IR and (1)H (NOE diff), NOESY and (13)C NMR (ligand) spectra. The X-ray crystal structures solved for (1R,2R)(-)chxn(salH)(naftalH) and Cu(II)(1R,2R)(-)chxn(sal)(naftal) revealed tetrahedral distortion of coordination sphere in the solid phase. The [Cu(1R,2R)(-)chxn(sal)(naftal)]·0.5EtOH·1.25H(2)O complex crystallized in the monoclinic chiral C2 space group with two molecules in the asymmetric unit as well as disordered ethanol and water molecules. For both molecules Cu(II) ions were found in square-planar environments and adopts conformation described as "semi-open armed", because of distinctly oriented arms according to cyclohexane ring defined by three torsion angles. The thin layers of the ligands, copper(II) and nickel(II) complexes were deposited on Si(111) by a spin coating method and characterized with scanning electron microscopy SEM/EDS and fluorescence spectra. The ligand layers exhibit the most intensive fluorescence band at 498 nm, which can be assigned to emission transition π* → n of Schiff base ligand. For copper(II) layers the most intensive band from intraligand transition at 550 nm was observed. The highest intensity band was registered for the layer obtained when rotation speed was 1000 rpm and time 20 s. The nickel(II) complex layers fluorescence spectra exhibit an intensive band at 564 nm. The emission maxima of the copper(II) and nickel(II) complexes are shifted towards longer wavelength in comparison to the free ligand layers. CD spectra of the complexes in solution are characteristic for tetrahedral planar distortion of the chelate ring. The (1)H NMR NOE diff were measured and the position of the nearest hydrogen atoms in the cyclohexane and aromatic rings were discussed, suggesting the tetrahedral distortion of the central ion of the coordination sphere in solution.     

Synthesis,characterization, NLO study,and antimicrobial activities of metal complexes derived from 3-(3-(2-hydroxyphenyl)-3-oxoprop-1-enyl)-4H-chromen-4-one and sulfanilamide

A series of metal(II) complexes ML (where M?=?Cu(II), Co(II), Ni(II), Zn(II), Mn(II), Cd(II), and VO(II)) have been prepared from 3-(3-(2-hydroxyphenyl)-3-oxoprop-1-enyl)-4H-chromen-4-one and sulfanilamide. The structures of the complexes have been investigated by elemental analysis, magnetic susceptibility, molar conductance, IR, UV-Vis, NMR, mass, and ESR spectral studies. Conductivity measurements reveal that the complexes are non-electrolytes, except the oxovanadium complex. Spectral and other data show square pyramidal geometry for oxovanadium and octahedral for the other complexes. The redox behaviors of the copper and vanadyl complexes have been studied through cyclic voltammetry. Antimicrobial activities of the compounds against several microorganisms indicate that some complexes have higher activity than free ligand. The compounds may serve as photoactive materials as indicated from their characteristic fluorescence properties. The second harmonic generation efficiency of the ligand was found to be higher than that of urea and KDP.     

A complete series of copper(II) halide complexes (X = F, Cl, Br, I) with a novel Cu(II)-C(sp3) bond

A complete series of copper(ii) halide complexes [CuX(tptm)](X = F (), Cl (), Br (), I (); tptm = tris(2-pyridylthio)methyl) with a novel Cu(II)-C(sp(3)) bond has been prepared by the reactions of [Cu(tptm)(CH(3)CN)]PF(6)(.PF(6)) with corresponding halide sources of KF or n-Bu(4)NX (X = Cl, Br, I), and the trigonal bipyramidal structures have been confirmed by X-ray crystallography and/or EPR spectroscopy. The iodide complex easily liberates the iodide anion in acetonitrile forming the acetonitrile complex as a result. The EPR spectra of the complexes showed several superhyperfine structures that strongly indicated the presence of spin density on the halide ligands through the Cu-X bond. The results of DFT calculations essentially matched with the X-ray crystallographic and the EPR spectroscopic results. Cyclic voltammetry revealed a quasi-reversible reduction wave for Cu(II)/Cu(I) indicating a trigonal pyramidal coordination for Cu(I) states. A coincidence of the redox potential for all [CuX(tptm)](0/+) processes indicates that the main oxidation site in each complex is the tptm ligand.     

Bistable copper complexes of bis-thia-bis-quinoline ligands

The new ligands R,R-trans-S,S'-bis[methyl(2'-quinolyl)]-1,2-dithiacyclohexane, cis-S,S'-bis[methyl(2'-quinolyl)]-1,2-dithiacyclohexane, and 1,6-bis(2'-quinolyl)-2,5-dithiahexane have been synthesized and their complexes with Cu(I) and Cu(II) prepared. The ligand/metal systems are bistable, as the complexes with copper in both its oxidation states are stable under the same conditions as solids and in solution. The crystal and molecular structure of [Cu(I)(1,6-bis(2'-quinolyl)-2,5-dithiahexane)]ClO(4) has been determined by X-ray diffraction and reveals that the complex is monomeric, with the ligand folding around the Cu(+) cation, imparting to it a tetrahedral coordination. UV-vis, MS-ESI, and NMR data indicate that the same is found for the Cu(I) complexes of all three ligands. Also, the Cu(II) complexes are monomeric, but with a square arrangement of the ligands around Cu(2+). On changing the oxidation state, the change in the geometrical arrangement is fast and complete in less than 80 ms, as demonstrated by cyclic voltammetry experiments. In the CV profiles, the oxidation and reduction events take place at separated E(ox) and E(red) values, with no return wave even at the fastest scan rates. In the E(ox)-E(red) interval (which ranges from 450 to 650 mV, depending on the ligand), the ligand/copper system can thus exist in one of its two states, depending on its history, and thus display electrochemical hysteretical behavior. The electrochemical cycle leading from the tetrahedral [Cu(I)(ligand)](+) to the square [Cu(II)(ligand)](2+) complex (and vice versa) is reversible and repeatable without degradation, as checked by coupled UV-vis-controlled potential coulometry experiments.     

Synthesis,characterization, EPR,electrochemical, and in situ spectroelectrochemical studies of salen-type oxovanadium(IV) and copper(II) complexes derived from 3,4-diaminobenzophenone

A new half unit and some new symmetrical or asymmetrical VO(IV) and Cu(II) complexes of tetradentate ONNO Schiff base ligands were synthesized. The probable structures of the complexes have been proposed on the basis of elemental analyses and spectral (IR, UV–Vis, electron paramagnetic resonance, ESI-MS) data. VO(IV) and Cu(II) complexes exhibit square pyramidal and square-planar geometries, respectively. The complexes are non-electrolytes in dimethylformamide (DMF) and dimethylsulfoxide. Electrochemical behaviors of the complexes were studied using cyclic voltammetry and square wave voltammetry. Half-wave potentials (E _1/2) are significantly influenced by the central metal and slightly influenced by the nature of substituents on salen. While VO(IV) complexes give VO^IV/VO^V redox couples and a ligand-based reduction process, Cu(II) complexes give only a ligand-based reduction. In situ spectroelectrochemical studies were employed to determine the spectra of electrogenerated species of the complexes and to assign the redox processes. The g-values were calculated for all these complexes in polycrystalline state at 298?K and in frozen DMF (113?K). The evaluated metal–ligand bonding parameters showed strong in-plane σ-bonding for some Cu(II) complexes.     

Self assembled tetranuclear Cu4(II), Ni4(II) [2 × 2] square grids and a dicopper(II) complex of heterocycle based polytopic ligands - Magnetic studies

The ditopic ligand PyPzOAP (N-[(Z)-amino(pyridin-2-yl)methylidene]-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazonic acid) and the polytopic ligand 2-PzCAP (N'(3),N'(5)-bis[(1E)-1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3,5-dicarbohydrazide) were synthesized in situ by condensation of methyl imino picolinate with 5-methyl-1-(2-pyridyl) pyrazole-3-carbohydrazide and 2-acetyl pyridine with pyrazole-3,5-dicarbohydrazide respectively. The ligands PyPzOAP and PzOAP (reported earlier, Dalton Trans., 2007, 1229) self-assemble to form homoleptic [2 × 2] tetranuclear M(4) (M = Cu(II) and Ni(II)) square grids structures [Cu(4)(PyPzOAP)(4)](NO(3))(4) (1), [Cu(4)(PzOAP)(4)](ClO(4))(4) (2) and [Ni(4)(PyPzOAP)(4)](NO(3))(4)·8H(2)O·2CH(3)CN (3). While the ligand 2-PzCAP forms a dicopper(II) complex [Cu(2)(2-PzCAP)(OH)(NO(3))(H(2)O)](NO(3))·2H(2)O (4). The complex 1 is a perfect square grid (a = 4.201 ?), whereas, 2 and 3 are almost square grids. All these compounds have been characterized by X-ray structural analyses and variable temperature magnetic susceptibility measurements. EPR studies have also been carried out for complexes 1, 2 and 4. In the Cu(4) grid (1), all the Cu(II) centers are in a distorted octahedral environment with N(4)O(2) chromophore, while, in complex 2, all four Cu(II) centers have a square pyramidal environment with N(3)O(2) chromophore. In complex 3, all four Ni(II) centers have distorted octahedral geometry with N(4)O(2) chromophore. In compound 4, the Cu(II) centers are in square pyramidal environment with N(3)O(2) chromophore. The magnetic properties of compounds 1 and 2 show the presence of intramolecular ferromagnetic exchange interaction (J = 5.88 cm(-1) for 1 and 4.78 cm(-1) for 2). The complex 3 shows weak intramolecular antiferromagnetic interaction (J = -4.02 cm(-1)). While, complex 4, shows strong antiferromagnetic behavior (J = -443 cm(-1)).