Low-temperature (180 K) crystal structure,electron paramagnetic resonance spectroscopy,and propitious anticonvulsant activities of CuII2(aspirinate)4(DMF)2 and other CuII2(aspirinate)4 chelates

The purpose of this research was to characterize by X-ray crystallography the ternary dimethylformamide (DMF) Cu(II) complex of acetylsalicylic acid (aspirin), in an effort to compare the structure-activity relationships for the anticonvulsant activity of this and other Cu(II)aspirinate chelates. The ternary DMF Cu(II) complex of aspirin was synthesized and crystals grown from a DMF solution were characterized by single crystal X-ray diffraction. This crystalline material was analyzed for anticonvulsant activity in the Maximal Electroshock (MES) Grand Mal and subcutaneous Metrazol (scMET) Petit Mal models of seizure used to detect anticonvulsant activity. The ternary DMF complex was found to be a monomolecular binuclear complex, tetrakis-mu-(acetylsalicylato)bis(dimethylformamido)dicopper(II) [Cu(II)(2)(aspirinate)(4)(DMF)(2)] with the following parameters: monoclinic, space group P2(1)/n, a=12.259 (1), b=10.228 (1), c=16.987 (1) A, beta=92.07 (1) degrees; V=2128.5 (3) A(3); Z=2. The structure was determined at 180 K from 2903 unique reflections (I>1sigma(I)) to the final values of R=0.030 and wR=0.033 using F. This binuclear complex contains four acetylsalicylate bridging ligands which are related to each other in a two by two symmetry center. The four nearest O atoms around each Cu atom form a closely square planar arrangement with the square pyramidal coordination completed by the dimethylformamide oxygen atom occupying an apical position at a distance of 2.154 (1) A. Each Cu atom is displaced towards the DMF ligand by 0.187 A from the plane of the four O atoms. Electron paramagnetic resonance (EPR) spectra of [Cu(II)(2)(aspirinate)(4)(DMF)(2)] crystals show a strong antiferromagnetic coupling of the copper atoms, similar to that observed with other binuclear copper(II)salicylate compounds. Studies used to detect anticonvulsant activity revealed that [Cu(II)(2)(aspirinate)(4)(DMF)(2)] was an effective anticonvulsant in the MES model of seizure but ineffective against scMET-induced seizures. The monomolecular ternary binuclear [Cu(II)(2)(aspirinate)(4)(DMF)(2)] complex is more effective in inhibiting MES-induced seizures than other binuclear or mononuclear Cu(II) chelates of aspirin including: binuclear polymeric [Cu(II)(2)(aspirinate)(4)], [Cu(II)(2)(aspirinate)(4)(H(2)O)], which is anticipated to be less polymeric, and monomolecular ternary [Cu(II)(2)(aspirinate)(4)(DMSO)(2)] and [Cu(II)(aspirinate)(2)(Pyr)(2)]. These and other chelates appear to be more effective in the scMET model of seizure than [Cu(II)(2)(aspirinate)(4)(DMF)(2)]. These structure-activity relationships support the potential efficacy of Cu chelates of aspirin in treating epilepsies.     

Thiolate coordination to Fe(II)-porphyrin NO centers

The interaction of the Fe(II)-porphyrin NO model complex [Fe(TPP)(NO)] (1, TPP=tetraphenylporphyrin) with thiophenolate ligands and tetrahydrothiophene is explored both computationally and experimentally. Complex 1 is reacted with substituted thiophenolates and the obtained six-coordinate adducts of type [Fe(TPP)(SR)(NO)](-) are investigated in solution using electron paramagnetic resonance (EPR) spectroscopy. From the obtained g values and (14)N hyperfine pattern of the NO ligand it is concluded that the interaction of the thiophenolates with the Fe(II) center is weak in comparison to the corresponding 1-methylimidazole adduct. The strength of the Fe-S bond is increased when alkylthiolates are used as evidenced by comparison with the published EPR spectra of ferrous NO adducts in cytochromes P450 and P450nor, which have an axial cysteinate ligand. These results are further evaluated by density functional (DFT) calculations. The six-coordinate model complex [Fe(P)(SMe)(NO)](-) (1-SMe; P=porphine ligand used for the calculations) has an interesting electronic structure where NO acts as a medium strong sigma donor and pi acceptor ligand. Compared to the N-donor adducts with 1-methylimidazole (1-MeIm), etc., donation from the pi(h)( *) orbital of NO to Fe(II) is reduced due to the stronger trans effect of the alkylthiolate ligand. This is reflected by the predicted longer Fe-NO bond length and smaller Fe-NO force constant for 1-SMe compared to the 1-MeIm adduct. Therefore, the Fe(II)-porphyrin NO adducts with trans alkylthiolate coordination have to be described as Fe(II)-NO(radical) systems. The N-O stretching frequency of these complexes is predicted below 1600cm(-1) in agreement with the available experimental data. In addition, 1-SMe has a unique spin density distribution where Fe has a negative spin density of -0.26 from the calculations. The implications of this unusual electronic structure for the reactivity of the Fe(II)-NO alkylthiolate adducts as they occur in cytochrome P450nor are discussed.     

Reaction pathways in the decomposition of hydrogen peroxide catalyzed by copper(II)

The kinetics of the decomposition of H(2)O(2) catalyzed by Cu(II) has been studied by the initial-rate method in aqueous phosphate media at near physiological pH. The activity of the catalyst is increased by [Fe(CN)(6)](3-) and decreased by VO(3)(-), CrO(4)(2-) and Zn(II). Three reaction pathways are involved in the Cu(II)-H(2)O(2) reaction, the kinetic orders of the catalyst being 1 (rate constant k1), 2 (rate constant k2) and 3 (rate constant k3). The three pathways present fractional apparent orders (>1) in H(2)O(2) and base catalysis. The apparent activation energies associated to rate constants k1, k2 and k3 are 102+/-4, 65+/-8 and 61+/-5 kJ mol(-1). Free-radical chain mechanisms are proposed for the three pathways.     

Synergistic anion-directed coordination of ferric and cupric ions to bovine serum transferrin--an inorganic perspective

A series of new iron(III) and copper(II) complexes of bovine serum transferrin (BTf), with carbonate and/or oxalate as the synergistic anion, are presented. The complexes [Fe(2)(CO(3))(2)BTf], [Fe(2)(C(2)O(4))(2)BTf], [Cu(2)(CO(3))(2)BTf] and [Cu(C(2)O(4))BTf] were prepared by standard titrimetric techniques. The oxalate derivatives were also obtained from the corresponding carbonate complexes by anion-displacement. The site-preference of the transition metal-oxalate synergism has facilitated the preparation and isolation of the mononuclear complex [Cu(C(2)O(4))BTf], the mixed-anion complexes [Cu(2)(CO(3))(C(2)O(4))BTf] and [Fe(2)(CO(3))(C(2)O(4))BTf] and the mixed-metal complex [FeCu(C(2)O(4))(2)BTf]. The sensitivity of electron paramagnetic resonance (EPR) spectroscopy to the nature of the synergistic anions at the specific-binding sites of the transferrins has made this physical technique particularly indispensable to this study. None of the other members of the transferrin family of proteins has ever been demonstrated to bind the ferric and cupric ions one after the other, each occupying a separate specific-binding site of the same transferrin molecule, as a response to the coordination restrictions imposed by the oxalate ion. The bathochromic shift of the visible p(pi)-d(pi*) CT band for iron(III)-BTf and the hypsochromic shift of the p(pi)-d(sigma*) CT band for copper(II)-BTf, on replacing carbonate by oxalate as the associated anion, are consistent with the relative positions of these anionic ligands in the spectrochemical series and the nature of the d-type acceptor orbitals involved in the CT transitions. The binding and spectroscopic properties of bovine serum transferrin--a serum transferrin--very nearly mirror those of human serum transferrin, but differ significantly from those of human lactoferrin.     

Low-temperature (180 K) crystal structures of tetrakis-mu-(niflumato)di(aqua)dicopper(II) N,N-dimethylformamide and N,N-dimethylacetamide solvates, their EPR properties, and anticonvulsant activities of these and other ternary binuclear copper(II)niflumate complexes

Two pseudopolymorphs, solvates, of [Cu(2)(II)(niflumate)(4)(H(2)O)(2)] of unknown structure were obtained following solution of [Cu(2)(II)(niflumate)(4)(H(2)O)(2)] in N,N-dimethylacetamide (DMA) or N,N-dimethylformamide (DMF). Low-temperature crystal structures obtained for these solvates revealed that they were ternary aqua DMA and DMF solvates: [Cu(2)(II)(niflumate)(4)(H(2)O)(2)].4DMA and [Cu(2)(II)(niflumate)(4)(H(2)O)(2)].4DMF. Intermolecular hydrogen bonding interactions account for the formation of these stable DMA and DMF solvates. These pseudopolymorphs contain a centrosymmetric binuclear center with Cu-Cu bond distances ranging from 2.6439(7) to 2.6452(9) A; the coordination sphere of Cu(II) is characterized by one long Cu-O (water) bond length of 2.128(3)-2.135(3) A and four short Cu-O (carboxylate) bonds of 1.949(3)-1.977(3) A. Crystal parameters for the DMA pseudopolymorph: a=10.372(1), b=19.625(2), c=17.967(2) A, beta=97.40(1) degrees , V=3626.8(6) A(3); monoclinic system; space group: P2(1)/a and for the DMF pseudopolymorph: a=10.125(2), b=18.647(3), c=19.616(4) A, alpha=74.38(2)(o), beta=88.18(2)(o), gamma=79.28(2)(o), V=3504(1) A(3); triclinic system; space group: P1. EPR spectra of these solids are identical and show strong antiferromagnetic coupling between the copper atoms, similar to the spectrum obtained for [Cu(2)(II)(niflumate)(4)(DMSO)(2)]. The [Cu(2)(II)(niflumate)(4)(H(2)O)(2)], [Cu(2)(II)(niflumate)(4)(H(2)O)(2)].4DMA, [Cu(2)(II)(niflumate)(4)(H(2)O)(2)].4DMF, [Cu(2)(II)(niflumate)(4)(DMF)(2)], and[Cu(2)(II)(niflumate)(4)(DMSO)(2)] evidenced protection against maximal electroshock-induced seizures and Psychomotor seizures at various times after treatment, consistent with the well known antiinflammatory activities of Cu chelates, but failed to protect against Metrazol-induced seizures while evidencing some Rotorod Toxicity consistent with a mechanism of action involving sedative activity.     

Complexation of the antihypertensive drug oxprenolol with copper(II)

The complexation between copper(II) and the antihypertensive drug oxprenolol (HOxp) was studied both in methanol and slightly alkaline aqueous media at Cu:HOxp molar ratio from 1:1 to 1:10. Copper(lI) forms two types of complexes-a mononuclear violet one, CuOxp2, with bidentately bound ligands and a green dimeric one, Cu2Oxp2Cl2, in which the two Cu(II) centres are linked by the ligand through oxygen bridges. The crystal structure of the Cu2Oxp2Cl2 complex consists of two crystallographically non-equivalent centrosymmetric copper dimers. Each copper atom is four-coordinated in a distorted square-planar environment. The Cu2O2 structural core is characterized by a Cu1-O1-Cu1' angle of 104.15(13)degrees (Cu2-O2-Cu2' 104.30(13) degrees) and a relatively short Cu1-Cu1' separation of 3.026(1) A (Cu2-Cu2'-3.023(1) A). Magnetic susceptibility and EPR measurements indicate an antiferromagnetic coupling of the copper(II) centers.     

The 1.6-A crystal structure of the copper(II)-bound bleomycin complexed with the bleomycin-binding protein from bleomycin-producing Streptomyces verticillus.

Bleomycin (Bm) in the culture broth of Streptomyces verticillus is complexed with Cu(2+) (Cu(II)). In the present study, we determined the x-ray crystal structures of the Cu(II)-bound and the metal-free types of Bm at a high resolution of 1.6 and 1.8 A, respectively, which are complexed with a Bm resistance determinant from Bm-producing S. verticillus, designated BLMA. In the current model of Cu(II).Bm complexed with BLMA, two Cu(II).Bm molecules bind to the BLMA dimer. The electron density map shows that the copper ion is clearly defined in the metal-binding domain of the Bm molecule. The metal ion is penta-coordinated by a tetragonal monopyramidal cage of nitrogens and binds to the primary amine of the beta-aminoalanine moiety of Bm. The binding experiment between Bm and BLMA showed that each of the two Bm-binding pockets has a different dissociation constant (K(d)(1) and K(d)(2)). The K(d)(1) value of 630 nm for the first Bm binding is larger than the K(d)(2) value of 120 nm, indicating that the first Bm binding gives rise to a cooperative binding of the second Bm to the other pocket.     

Synthesis, structure and interactions with DNA of novel tetranuclear, [Mn4(II/II/II/IV)] mixed valence complexes

Reaction of Mn(II) with phenoxyalkanoic acids and di-2-pyridyl ketone oxime (Hpko) leads to neutral tetranuclear complexes of the general formula Mn(4)(O)(pko)(4)(phenoxyalkanoato)(4) (phenoxyalkanoic acids: H-mcpa=2-methyl-4-chloro-phenoxy-acetic acid, H-2,4,5-T=2,4,5-trichloro-phenoxy-acetic acid or H3,4-D=3,4-dichloro-phenoxy-acetic acid). The compounds were synthesized by adding di-2-pyridyl ketone oxime to MnCl(2) in the presence of the sodium salts of the alkanoic acids in methanol. The crystal structure of Mn(4)(II/II/II/IV)(O)(pko)(4)(2,4,5-T)(4).2.5CH(3)OH.0.25H(2)O 1 shows that the complex consists of a [Mn(4)(mu(4)-O)](8+) core with a Mn(IV) and 3 Mn(II) ions in octahedral environment and a mu(4)-O atom bridging the four manganese ions. Spectroscopic studies of the interaction of these tetranuclear clusters with DNA showed that these compounds bind to dsDNA. The binding strength of the Mn(4)(II/II/II/IV)(O)(pko)(4)(2,4,5-T)(4) complex for calf thymus DNA is equal to 1.1x10(4)M(-1). Among the deoxyribonucleotides they bind preferentially to deoxyguanylic acid (dGMP). Competitive studies with ethidium bromide (EthBr) showed that the Mn(4)(II/II/II/IV)(O)(pko)(4)(2,4,5-T)(4) complex exhibited the ability to displace the DNA-bound EthBr indicating that the complex binds to DNA via intercalation in strong competition with EthBr for the intercalative binding site. Additionally, DNA electrophoretic mobility experiments showed that all three complexes, at low cluster concentration, are obviously capable of binding to pDNA causing its cleavage (relaxation) at physiological pH and temperature. At higher cluster concentration, catenated dimer forms of pDNA was formed.     

Synthesis,structure and nuclease properties of several ternary copper(II) peptide complexes with 1,10-phenanthroline

Three new ternary peptide-Cu(II)-1,10-phenanthroline (phen) complexes, [Cu(L-ala-gly)(phen)].3.5H(2)O 1, [Cu(L-val-gly)(phen)] 2 and [Cu(gly-L-trp)(phen)].2H(2)O 3, have been prepared and structurally characterised. These compounds exist as distorted square pyramidal complexes with the five co-ordination sites occupied by the tridentate peptide dianion and the two heterocyclic nitrogens of the phenanthroline ligand. The bulk of the lateral chain in the peptide moiety determines the relative disposition of the phen ligand. Thus, in [Cu(L-val-gly)(phen)] 2, the phenanthroline plane is deviated towards the opposite side of the isopropyl group of the L-valine moiety. On the other hand, in [Cu(gly-L-trp)(phen)].2H(2)O 3 the absence of stacking interactions between phen and indole rings and the presence of an intramolecular CH...pi interaction should be pointed out. These complexes exhibit significant differences in their nuclease activity which depends on the nature of the peptidic moiety, the complex [Cu(gly-L-trp) (phen)].2H(2)O 3 being the most active.     

Hydrogen atom abstraction by Cu(II)- and Zn(II)-phenoxyl radical complexes, models for the active form of galactose oxidase

The Cu(II) and Zn(II) complexes of phenoxyl radical species [M(II)(L1*)(NO3)]+ (M=Cu or Zn, L1H: 2-methylthio-4-tert-butyl-6-[[bis[2-(2-pyridyl)ethyl]amino]methyl]phenol ) and [M(II)(L2*)(NO3)]+ (M=Cu or Zn, L2H: 2,4-di-tert-butyl-6-[[bis[2-(2-pyridyl)ethyl]amino]methyl]phenol) are prepared as model complexes of the active form of galactose oxidase (GAO). Hydrogen atom abstraction of 1,4-cyclohexadiene and tert-butyl substituted phenols by the GAO model complexes proceeds very efficiently to give benzene and the corresponding phenoxyl radical or its C-C coupling dimer as the oxidation products, respectively. Kinetic analyses on the oxidation reactions have shown that the hydrogen atom abstraction of the phenol substrates is significantly enhanced by the coordinative interaction of the OH group to the metal ion center of the complex, providing valuable insight into the enzymatic mechanism of the alcohol oxidation. Details of the substrate-activation process have been discussed based on the activation parameters (deltaH* and deltaS*) of the reactions.     

Ternary Cu(II) complexes, Cu(H(-1)L)(ACys-) and Cu(H(-2)L)(ACys-); L = peptides, ACys- = N-acetyl-cysteinate. Analogous complexes to the intermediates in the transport of Cu(II) from Cu(H(-2)L) to cysteine

The Cu(II) in Cu(H(-2)L) has been postulated to be successively transported to cysteine (Cys) as follows; Cu(H(-2)L) <==> Cu(H(-2)L)(Cys*-) <==> Cu(H(-1)L)(Cys*-) --> Cu(H(-1)L)(Cys-), where Cys*- denotes the monodentate Cys-. N-acetyl-cysteinate (ACys-) complexes Cu(H(-2)L)(ACys-) and Cu(H(-1)L)(ACys-), having similar coordination modes to Cu(H(-2)L)(Cys*-) and Cu(H(-1)L)(Cys*-), respectively, exhibited the S --> Cu(II) charge transfer absorption at 325-355 nm and the d-d absorption at 530-610 nm. A linear interrelation existed between the energies of the CD and d-d absorptions. Cu(H(-2)L)(ACys-) were in rapid equilibrium with Cu(H(-1)L)(ACys-). Upon forming the ternary complex, pK(c2) of the parent Cu(H(-1)L) was raised to more than 1.0. The formation constants (K) of the Cu(H(-1)L)(ACys-) species from Cu(H(-1)L) were bigger than those of Cu(H(-2)L)(ACys-) from Cu(H(-2)L). The linear free-energy relationship existed between the free-energy change (deltaG) and the entropy change (deltaS) for the ternary complex formation. The rate constants (k1+) for the Cu(H(-1)L)(Cys-) formation closely correlated with the K values for Cu(H(-2)L)(ACys-). The ternary complexes containing ACys are considered to be analogous complexes to the intermediates in the transport of Cu(II) from peptides to cysteine.     

Iron(III)- and copper(II) complexes of an asymmetric, pentadentate salen-like ligand bearing a pendant carboxylate group

The equilibrium and solution structural properties of the iron(III) and copper(II) complexes of an asymmetric salen-like ligand (N,N'-bis(2-hydroxybenzyl)-2,3-diamino-propionic acid, H(3)bhbdpa) bearing a pendant carboxylate group were characterized in aqueous solution by potentiometric, pH-dependent electron paramagnetic resonance (EPR) and UV-Vis (UV-Visible) measurements. In the equimolar systems the pentadentate ligand forms very stable, differently protonated mononuclear complexes with both metal ions. In the presence of iron(III) {NH, PhO(-), COO(-)}, {2NH, 2PhO(-), COO(-)} and {2NH, 2PhO(-), COO(-), OH(-)} coordinated complexes are dominant. The EPR titrations reflected the presence of microscopic complex formation pathways, leading to the formation of binding isomers in case of Cu(H(2)bhbdpa)(+), Cu(Hbhbdpa) and Cu(bhbdpa)(-). The {2NH, 2PhO(-)+COO(-)/H(2)O} coordinated Cu(bhbdpa) is the only species between pH 6-11. At twofold excess of metal ion dinuclear complexes were detected with both iron(III) and copper(II). In presence of iron(III) a mu-carboxylato-mu-hydroxo-bridged dinuclear complex (Fe(2)(bhbdpa)(OH)(3)) is formed from Fe(H(2)bhbdpa)(2+) through overlapping proton release processes, providing one of the rare examples for the stabilization of an endogenous carboxylate bridged diiron core in aqueous solution. The complex Cu(2)(bhbdpa)(+) detected in the presence of copper(II) is a paramagnetic (S=1) species with relatively weakly coupled metal ions.     

Synthesis, crystal structure, EPR properties, and anti-convulsant activities of binuclear and mononuclear 1,10-phenanthroline and salicylate ternary copper(II) complexes

Two ternary Cu(II) complexes of 1,10-phenanthroline (phen) and singly (Hsal(-)) or dideprotonated (sal(2-)) salicylate ligands were synthesized, their X-ray crystal structure and electron paramagnetic resonance spectral characteristics determined, and evaluated for anti-convulsant activities in the maximal electroshock (MES) and Metrazol models of seizure and Rotorod toxicity. The X-ray crystal structure of [bis(1,10-phenanthroline)-mu-bis(salicylato-O,O')dicopper(II)] dihydrate, 1, ([Cu(II)(2)(phen)(2)(sal)(2)].2[H(2)O]), shows it to be binuclear. This dimer consists of two centrosymmetrically related pseudo-five coordinate Cu(II) atoms 3.242(2) A apart and bridged by two dideprotonated salicylate ligands. The X-ray crystal structure of [bis(1,10-phenanthroline)(salicylato)copper(II)][salicylate] monohydrate, 2, ([Cu(II)(phen)(2)(Hsal)](+)[Hsal](-)[H(2)O]), shows it to be mononuclear. This complex cation exhibits a highly irregular distorted square pyramidal geometry about the Cu(II) atom, (4+1+1*). Each salicylate is singly deprotonated and one of them is ligand bonded in an asymmetric chelating mode. EPR results for 2 indicate that in concentrated DMF solution phen remains bonded to copper but salicylate is likely monodentate in contrast to the situation for 1. However, in dilute DMF solution, both 1 and 2 form the same species, which accounts for the similarity in anti-convulsant activity of the two compounds. Both 1 and 2 were found to be effective in preventing MES-induced seizures and ineffective in preventing Metrazol-induced seizures. Rotorod toxicity, consistent with central nervous system depression, paralleled the observed anti-convulsant activity. It is suggested that the observed anti-convulsant activity is consistent with central nervous system depression as a physiological mechanism in overcoming MES-induced seizures due to MES-induced brain inflammatory disease.     

The crystal structures of copper(II), manganese(II), and nickel(II) complexes of a (Z)-2-hydroxy-N'-(2-oxoindolin-3-ylidene) benzohydrazide--potential antitumor agents

Mononuclear complexes of Cu(II), Ni(II), and Mn(II) with a new Schiff base ligand derived from indoline-2,3-dione and 2-hydroxybenzohydrazide, [Cu(II)(L)(2)], [Ni(II)(L)(2)], and [Mn(II)L.(AcO).2C(2)H(5)OH] [HL=(Z)-2-hydroxy-N'-(2-oxoindolin-3-ylidene)benzohydrazide], have been prepared. The complexes have been structurally characterized by X-ray crystallography. Among the three complexes, the Cu(II) complex had the novel highest antitumor activity.     

Cu(II) complexes with labile apical coordination: Synthesis, crystal structure, H NMR investigation, and oxidation properties of mononuclear [Cu(dien)(2-PhIm)(ClO4)] (1), [Cu(dien)(2-MeBzIm)] (2), complexes

The compounds [Cu(dien)(2-PhIm)(ClO₄)](ClO₄) (1); [Cu(dien)(2-MeBzIm)](ClO₄)₂ (2); where dien = diethylenetriamine, 2-PhIm = 2-phenylimidazole and 2-MeBzIm = 2-methylbenzimidazole, were synthesized and characterized. The complexes possessing [Cu(II)dien] moiety as common, the former containing 2-phenylimidazole, yielded square pyramidal geometry with apical perchlorate coordination [Cu1-O(5) = 2.449 Å], while the latter with 2-methylbenzimidazole formed square planar geometry with weak perchlorate contact [Cu1-O(8) = 2.596 Å] in its apical position. The effect of solvent and the variable temperature ¹H NMR investigation combinedly explore the geometrical rearrangement towards five coordination around Cu(II) metal center by accommodating the solvent molecule in its fifth coordination. Possessing easily labile perchlorate anion, both these complexes were investigated for their oxidation capability using 3,5-di-tert-butyl catechol (DTBC). The rate constant determined for the oxidation of DTBC to corresponding quinone indicates that they are catalytically quite similar and the k_cat of 1 ≈ 2. The crystal structure and the NMR investigations are discussed in detail.     

Plant dispersal, neighbourhood size and isolation by distance

A theoretical relationship between isolation by distance or spatial genetic structure (SGS) and seed and pollen dispersal is tested using extensive spatial-temporal simulations. Although for animals Wright's neighbourhood size N(e) = 4pisigma(2)(t) has been ascertained also, where sigma(2)(t) is the axial variance of distances between parents and offspring, and it was recently confirmed that N(e) = 4pi(sigma(2)(f) + sigma(2)(m))/2 when dispersal of females and males differ, the situation for plants had not been established. This article shows that for a very wide range of conditions, neighbourhood size defined by Crawford's formula N(e) = 4pi(sigma(2)(s) + sigma(2)(p)/2) fully determines SGS, even when dispersal variances of seed (sigma(2)(s)) and pollen sigma(2)(p)) differ strongly. Further, self-fertilization with rate s acts as zero-distance pollen dispersal, and N(e) = 4pi[sigma(2)(s) + sigma(2)(p)(1 - s)/2] fully determines SGS, for most cases where there are both likely parameter values and substantial SGS. Moreover, for most cases, there is a loglinear relationship, I(1) = 0.587 - 0.117 ln(N(e)), between SGS, as measured by I(1), Moran's coefficient for adjacent individuals, and N(e). However, there are several biologically significant exceptions, namely for very low or large N(e), SGS exceeds the loglinear values. There are also important exceptions to Crawford's formula. First, plants with low seed dispersal, high outcross pollen dispersal and high selfing rate show larger SGS than predicted. Second, in plants with very low (near zero) seed dispersal, selfing decreases SGS, opposite expectations. Finally, in some cases seed dispersal is more critical than pollen dispersal, in a manner inconsistent with Crawford's formula.     

New unsymmetric dinuclear Cu(II)Cu(II) complexes and their relevance to copper(II) containing metalloenzymes and DNA cleavage

The new homodinuclear complexes, [Cu(2)(II)(HLdtb)(mu-OCH(3))](ClO(4))(2) (1) and [Cu(2)(II)(Ldtb)(mu-OCH(3))](BPh(4)) (2), with the unsymmetrical N(5)O(2) donor ligand (H(2)Ldtb) - {2-[N,N-Bis(2-pyridylmethyl)aminomethyl]-6-[N',N'-(3,5-di-tert-butylbenzyl-2-hydroxy)(2-pyridylmethyl)]aminomethyl}-4-methylphenol have been synthesized and characterized in the solid state by X-ray crystallography.In both cases the structure reveals that the complexes have a common {Cu(II)(mu-phenoxo)(mu-OCH(3))Cu(II)} structural unit.Magnetic susceptibility studies of 1 and 2 reveal J values of -38.3 cm(-1) and -2.02 cm(-1), respectively, and that the degree of antiferromagnetic coupling is strongly dependent on the coordination geometries of the copper centers within the dinuclear {Cu(II)(mu-OCH(3))(mu-phenolate)Cu(II)} structural unit.Solution studies in dichloromethane, using UV-Visible spectroscopy and electrochemistry, indicate that under these experimental conditions the first coordination spheres of the Cu(II) centers are maintained as observed in the solid state structures, and that both forms can be brought into equilibrium ([Cu(2)(HLdtb)(mu-OCH(3))](2+)=[Cu(2)(Ldtb)(mu-OCH(3))](+)+H(+)) by adjusting the pH with Et(3)N (Ldtb(2-) is the deprotonated form of the ligand).On the other hand, potentiometric titration studies of 1 in an ethanol/water mixture (70:30 V/V; I=0.1M KCl) show three titrable protons, indicating the dissociation of the bridging CH(3)O(-) group.The catecholase activity of 1 and 2 in methanol/water buffer (30:1 V/V) demonstrates that the deprotonated form is the active species in the oxidation of 3,5-di-tert-butylcatechol and that the reaction follows Michaelis-Menten behavior with k(cat)=5.33 x 10(-3)s(-1) and K(M)=3.96 x 10(-3)M. Interestingly, 2 can be electrochemically oxidized with E(1/2)=0.27 V vs.Fc(+)/Fc (Fc(+)/Fc is the redox pair ferrocinium/ferrocene), a redox potential which is believed to be related to the formation of a phenoxyl radical.Since these complexes are redox active species, we analyzed their activity toward the nucleic acid DNA, a macromolecule prone to oxidative damage.Interestingly these complexes promoted DNA cleavage following an oxygen dependent pathway.     

Angular-overlap analysis of the iron(II) site in [2Fe-2S] clusters

The angular-overlap model for Fe(II)S4 centres is used to obtain structural information form the experimental data available for the gav approximately equal to 1.96 and gav approximately equal to 1.91 classes of [2Fe-2S] ferredoxin, showing that it is possible to translate the parameters obtained by Bertrand and Gayda in their non-additive ligand field model (Bertrand, P. and Gayda J.P. (1979 and 1980) Biochim. Biophys. Acta 579, 107-121 and 625, 337-342, respectively) into an additive one. The analysis of the e lambda (lambda = sigma or pi) parameters allowed us to conclude that the Fe(II)S4 chromophores of the two types of [2Fe-2S] metallo-protein are similar to each other, being possible to reproduce nicely the different g tensors introducing only small variations in the angular and bonding parameters.     

Supramolecular structures of metronidazole and its copper(II), cobalt(II) and zinc(II) coordination compounds

In this work we present the synthesis and structural and spectroscopic characterization of Cu(II), Co(II) and Zn(II) coordination compounds with the antibiotic metronidazole ([double bond]emni). Coordination to metal ions is through its imidazolic nitrogen, while the hydroxyethyl and nitro groups act as supramolecular synthons. [Co(emni)(2)Br(2)], and [Zn(emni)(2)X(2)] (X(-)=Cl, Br) stabilize zig-zag chains, and a 2D supramolecular structure is formed by inter-chain contacts through inter-molecular hydrogen-bonding. Pleated sheet or layers are formed by [Co(emni)(2)Cl(2)] and [Cu(emni)(2)Cl(H(2)O)](2)Cl(2), respectively. The dinuclear Cu(II) compound [Cu(emni)mu(O(2)CMe)(2)](2) gives a one-dimensional zig-zag arrangement. The contribution of metal ions in metronidazole coordination compounds is shown in the stabilization of the different aggregate structures.     

Choice of a spin singlet or triplet: electronic properties of Bis-Co(II), Bis-Ni(II), Bis-Cu(II) and Bis-Zn(II) oxygen doubly N-confused hexaphyrin (1.1.1.1.1.1)

Fused hexaphyrins have many physical and chemical properties and can coordinate transition metal ions. In this study, we investigated the geometric structure, charge decomposition analysis (CDA), spin density, frontier molecular orbital (FMO) compositions and absorption spectra of four oxygen doubly N-confused hexaphyrin (1.1.1.1.1.1) (ONCP) complexes with the metal ions Co(II), Ni(II), Cu(II) and Zn(II) (designated ONCP-d-Co, ONCP-d-Ni, ONCP-d-Cu and ONCP-d-Zn). Based on their energies, geometric structures, FMO characteristics and comparison to experiments, ONCP-d-Co and ONCP-d-Cu have the mix-states of the triplet state and broken-symmetry state (antiferromagnetic state) rather than the spin singlet of a closed shell as previously reported. Moreover, based on analyses of the spin density and spin population of the spin triplet ONCP-d-Co and ONCP-d-Cu complexes, the charge transfer in ONCP-d-Cu is greater than that in ONCP-d-Co because the spin density in ONCP-d-Cu is concentrated not only on the Cu ion but also on the ONCP ligand. Thus, the CDA value for ONCP-d-Cu is larger. Finally, through comparative analysis of the FMO compositions and absorption spectra, the complexes and ligand are shown to have very similar absorption spectra with characteristics that arise mainly from π?→?π* transitions both in the B-band and the Q-band, which is due to the FMO compositions being dominated by the highly delocalized conjugated system, rather than by the metal ions. The absorption maxima of the Q-band are ONCP-d-Co (1020 nm)?>?ONCP-d-Zn (1012 nm)?>?ONCP-d-Ni (997 nm)?>?ONCP-d-Cu (988 nm), which is inversely proportional to the energy gap in their FMOs.

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Graphical Abstract The present work investigates the geometric structure, charge decomposition analysis (CDA), spin density, frontier molecular orbital (FMO) compositions and absorption spectra of four oxygen doubly N-confused hexaphyrin (1.1.1.1.1.1) (ONCP) complexes with the metal ions Co(II), Ni(II), Cu(II) and Zn(II) (designated ONCP-d-Co, ONCP-d-Ni, ONCP-d-Cu and ONCP-d-Zn). Based on their energies, geometric structures, FMO characteristics and comparison to experiments, ONCP-d-Co and ONCP-d-Cu have the mix-state of the triplet state and broken-symmetry state (antiferromagnetic state) rather than the spin singlet of a close shell as were previously reported. Meanwhile, ONCP-d-Ni and ONCP-d-Zn show spin singlet structure. The calculated CDA shows the following order: ONCP-d-Cu (1.487)?>?ONCP-d-Ni (1.255)?>?ONCP-d-Co (1.211)?>?ONCP-d-Zn (1.201). Through comparisons of spin density and spin populations of ONCP-d-Co and ONCP-d-Cu, charge transfer between Cu and ligand ONCP is greater than that of Co and ONCP, which makes the CDA value of ONCP-d-Cu obviously larger than that of the other complexes