Enantioselectivity and stereoselectivity in the reactions of the enantiomers of the platinum complex [PtCl2(ahaz)] (ahaz = 3(R)- or 3(S)-aminohexahydroazepine) with DNA

The platinum-DNA adduct profile formed by the R- and S-enantiomers of [PtCl₂(ahaz)] (ahaz = 3(R)-aminohexahydroazepine or 3(S)-aminohexahydroazepine) on reaction with salmon sperm DNA were characterised using HPLC and GFAAS (graphite furnace atomic absorption spectrometry) analyses. At a platinum to nucleotide ratio (R_t) equalling 0.05, the R-enantiomer forms a substantially larger amount (approximately 60%) of monofunctional adducts than the S-enantiomer (less than 35%). Fewer intrastrand GpG adducts are formed by the R-enantiomer (approximately 21%) than the S-enantiomer (approximately 37%). For both enantiomers, two isomeric GpG adducts, corresponding to the different orientations of the primary amine of ahaz ligand with respect to the O6 atom of the 5′ guanine, were observed in the ratios of 1:1.3 and 1:4.3 for the R- and S-enantiomers, respectively. The reasons for this enantioselectivity and stereoselectivity are discussed.     

A structural study of the hydrated and the dimethylsulfoxide, N,N′-dimethylpropyleneurea, and N,N-dimethylthioformamide solvated iron(II) and iron(III) ions in solution and solid state

The structures of the solvated iron(II) and iron(III) ions have been studied in solution and solid state by extended X-ray absorption fine structure (EXAFS) in three oxygen donor solvents, water, dimethylsulfoxide (Me₂SO), N,N′-dimethylpropyleneurea (DMPU), and one sulfur donor solvent, N,N-dimethylthioformamide (DMTF); these solvents have different coordination and solvation properties. In addition, the structure of hexakis(dimethylsulfoxide)iron(III) perchlorate has been determined crystallographically to support the determination of the corresponding solvate in solution. The hydrated, the dimethylsulfoxide and N,N-dimethylthioformamide solvated iron(II) ions show regular octahedral coordination in both solution and solid state with mean Fe-O, Fe-O, and Fe-S bond distances of 2.10, 2.10, and 2.52 Å, respectively, whereas the N,N′-dimethylpropyleneurea iron(II) solvate is five-coordinated, d(Fe-O) = 2.06 Å. The compounds vary in color from light green (hydrate) to dark orange or red (DMPU). The hydrated iron(III) ion in aqueous solution and the dimethylsulfoxide solvated iron(III) ions in solution and solid state show the expected octahedral coordination, the Fe-O bond distances are 2.00 Å for both, whereas the N,N′-dimethylpropyleneurea iron(III) solvate is found to be five-coordinated with a mean Fe-O bond distance of 1.99 Å. The N,N-dimethylthioformamide solvated iron(III) ion in the solid perchlorate salt is tetrahedrally four-coordinated, the mean Fe-S bond distance is 2.20 Å. Iron(III) is reduced with time to iron(II) in N,N-dimethylthioformamide solution. The compounds vary in color from pale yellow (hydrate) to blackish red (DMPU).     

A joint computational and experimental study of a novel dioxomolybdenum(VI) complex bearing chiral N,N-dimethyllactamide ligand

A new cis-dioxomolybdenum complex MoO₂(DMLA)₂ (DMLA = N,N-dimethyllactamide) has been synthesized and characterized by X-ray crystallography, H NMR and IR spectroscopies and electronic structure calculations at DFT/B3LYP level. This compound (chemical formula C₁₀H₂₀MoO₆N₂) crystallizes in the orthorhombic space group P2₁2₁2₁ with Z = 4, a = 6.9357(2) ?, b = 11.8761(4) ?, c = 17.7251(5), V = 1460.00(8) ?³ and renders a slightly distorted octahedral structure with two long Mo-O bonds (2.253(3) ? and 2.257(3) ?) trans to each of the MoO groups and with two short Mo-O bonds of 1.942(3)4 ? cis to them. The MoO bond length are 1.715(3) and 1.704(3) ?). Each lactamide ligand is bidentate; they are coordinated in their deprotonated form with the carbonyl oxygen occupying a position trans to the MoO moiety while the deprotonated hydroxyl oxygen is located cis to them. Structural characterization is complemented by DFT/B3LYP calculations.     

Very-long-chain iso and anteiso branched fatty acids in N-acylphosphatidylethanolamines from a natural cyanobacterial mat of Calothrix sp.

A combination of TLC, ESI-MS/MS and GC-MS was used to identify unusual molecular species of N-acylphosphatidylethanolamines containing very-long-chain anteiso branched fatty acids (VLCFAs) from Calothrix sp. collected in Antarctica and determine their component VLCFA up to 33-methyltetratriacontanoic acid as picolinyl ester derivatives using GC-MS.     

Synthesis, characterization and structure of a new zinc(II) complex containing the hexadentate N,N′,N,N′-bis[(2-hydroxy-3,5-di-tert-butylbenzyl)(2-pyridylmethyl)]-ethylenediamine ligand: Generation of phenoxyl radical species

This work summarizes the results of our studies on the structural, spectral and redox properties of a mononuclear zinc(II) complex with the new H₂L ligand (H₂L = N,N′,N,N′-bis[(2-hydroxy-3,5-di-tert-butylbenzyl)(2-pyridylmethyl)]-ethylene diamine). The crystal structure of the complex [Zn^II(HL)] · ClO₄ (1) was determined by X-ray crystallographic analysis. The structure of this complex consists of a discrete mononuclear cation [Zn^II(HL)]⁺, in a strongly distorted geometry with a slight tendency toward a distorted square pyramidal geometry, as reflected by the structural index parameter τ of 0.44. The zinc(II) cation is coordinated to one oxygen and four nitrogen atoms: the pyridine nitrogen atoms (N22 and N32), tertiary amine nitrogen atoms (N1 and N4) and phenolate oxygen atom (O10). ¹H and ¹³C NMR spectral data show a rigid solution structure for 1 in agreement with X-ray structure. Potentiometric studies of complex 1 were also performed and revealed three titratable protons which are attributed to the protonation/deprotonation of two phenol groups (p[K]_a1 = 4.04 and p[K]_a3 = 11.34) and dissociation of a metal-bound water molecule (p[K]_a2 = 7.8). The phenolate groups in complex 1 are suitably protected by bulky substituents (tert-butyl) in the ortho- and para-positions, which through electrochemical oxidation generate a one-electron oxidized phenoxyl species in solution. This radical species was characterized by UV-Vis, EPR and electrochemical studies. The Zn(II)-phenoxyl radical species is of bioinorganic relevance, since its spectroscopic, redox and reactivity properties can be used to establish the role of phenoxyl radicals in biological and catalytical systems.     

Coordination compounds of Cd(II) with several bidentate-NN′ and tridentate-NN′N nitrogen donor ligands. Cd NMR studies of monomeric compounds containing nitrogen donor atoms

Reaction of CdCl₂ with N-alkylaminopyrazole ligands 1-[(2-ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[(2-(tert-butylamino)ethyl)]-3,5-dimethylpyrazole (deat), bis-[(3,5-dimethylpyrazolyl)methyl]ethylamine (bdmae), and bis-[(3,5-dimethylpyrazolyl)ethyl]ethylamine (ddae) in absolute ethanol yields [CdCl₂(NN′)] (NN′ = deae (1), deat (2)), [CdCl₂(bdmae)] (3), and [CdCl(ddae)]₂[CdCl₄] (4). The Cd(II) complexes have been characterised by elemental analyses, conductivity measurements, IR, ¹H, ¹³C{¹H} and ¹¹³Cd NMR spectroscopies, and X-ray diffraction methods. ¹H and ¹¹³Cd NMR experiments at variable temperature for 3 and 4 show that dynamic processes are taking place in solution. We report the measurements of ¹¹³Cd NMR chemical shift data for complexes 1-4 in solution. X-ray crystal structures for complexes 2 and 3 have been determined. The Cd(II) is coordinated to the deat ligand, in 2, by one nitrogen atom of the pyrazolyl group and one nitrogen atom of the amine. It finishes a tetrahedral geometry with two chlorine atoms. The bdmae ligand is linked to Cd(II), in 3, by two nitrogens atoms of the pyrazolyl groups and one amine nitrogen, along with two chlorine atoms, in a distorted trigonal bipyramidal geometry.     

Unilateral eyestalk ablation reduces neurolipofuscin accumulation rate in the contralateral eyestalk of a crustacean, Pacifastacus leniusculus

Use of the lipofuscin ageing method as a crustacean fisheries research tool requires a calibration of tissue lipofuscin concentration to chronological age that is applicable to the natural population under investigation. Current approaches, involving known-age individuals or analysis of cohorts in neurolipofuscin concentration frequency distributions of the wild population, have advantages and disadvantages. A possible alternative that could be applied to individuals of unknown age involves initial biopsy of lipofuscin-loaded tissue from an eyestalk followed, after a known time period, by sampling of the second eyestalk, providing two successive lipofuscin measurements from the same individual and, thus, the neurolipofuscin accumulation rate in the intervening period. We tested the feasibility of this approach by examining the effect of eyestalk removal itself on subsequent lipofuscin accumulation in the remaining eyestalk using known-age individuals of a convenient decapod model, the signal crayfish, Pacifastacus leniusculus. By comparison with untreated controls, a 61% reduction in average neurolipofuscin accumulation rate in the remaining eyestalk occurred. It is hypothesized that this represents either slowed lipofuscinogenesis due to reduced oxidative metabolism or glycosylation, or increased lipofuscin loss due to enhanced proteolytic or phagocytic activity. It is recommended that the proposed ablation technique not be used for calibration of lipofuscin-based age determinations due to its unpredictable effect on lipofuscin accumulation.     

Crystal structure and ligational aspects of the mesogenic Schiff base, N,N′-di-(4-hexadecyloxysalicylidene)diaminoethane, with some rare earth metal ions

A mesogenic Schiff base, N,N′-di-(4-hexadecyloxysalicylidene)diaminoethane, H₂dhdsde (abbreviated as H₂L¹) that exhibit smectic-C (SmC) mesophase, was synthesized and its structure studied by elemental analyses, mass, NMR & IR spectra and single crystal XRD (triclinic space group with Z = 1) techniques. Bi-dentate bonding of the Schiff base in the mesogenic La^III complex was implied on the basis of IR & NMR spectral data. As per the spectral studies of the complexes, the Zwitterionic species of the ligand (H₂L¹) coordinates to Ln^III ion through two phenolate oxygens rendering the overall geometry around the metal ion to distorted square antiprism (Ln = La, Pr, Nd, Sm, Eu) and monocapped octahedron (Ln = Gd, Tb, Dy, Ho).     

The auration of 2-hydroxy-pyridine (2-pyridone): preparative and structural studies and a comparison with reactions of related aliphatic O,N-donors

In a study of the isolobal analogy between the proton H⁺ and the ligand-backed gold(I) cations [(R₃P)Au]⁺, the reaction of the mixture of 2-pyridone/2-hydroxy-pyridine tautomers with [(Ph₃P)Au]BF₄ has been investigated. It affords the 1:1 complex with the gold atom N-bonded to the 2-hydroxy-pyridine tautomer: {(Ph₃P)Au[NC₅H₄-(OH-2)]}⁺BF₄ ⁻, which is related to known salts with the 2-hydroxy-pyridinium cation such as [HNC₅H₄(OH-2)]⁺Cl⁻. The structure was derived from analytical and spectroscopic data and from a comparison with the salt [(Ph₃P)Au(pyr)]BF₄, prepared and investigated structurally as a reference compound. An analogue was also prepared with 2-dimethylamino-ethanol as a substrate, which also affords the N-bonded complex [(Ph₃P)Au([Me₂NCH₂CH₂OH)]⁺BF₄ ⁻, the structure of which has been determined. The OH group is not attached to the gold atom but engaged in hydrogen bonding with the counterion. By contrast, in the complex [(Ph₃P)Au(Me₂NCH₂CH₂NMe₂)]⁺BF₄ ⁻ synthesized similarly with tmeda and crystallized as the dichloromethane solvate, one nitrogen atom is bonded firmly to the metal atom, but the second nitrogen atom is also weakly engaged in coordinative bonding. The compound is fluxional in solution, where a site exchange is observed which is rapid on the NMR time scale. The reaction of two equivalents of [(Ph₃P)Au]BF₄ with an alkali 2-pyridinolate, prepared from the above tautomeric mixture and sodium metal or a potassium alkoxide, yields the diaurated product {N,O-[(Ph₃P)Au]₂(NC₅H₄-O-2)}BF₄. In the crystal structure determination of a sesqui-solvate with dichloromethane it has been shown that one gold atom is attached solely to the nitrogen atom and the other solely to the oxygen atom. The dinuclear cations are associated into cyclic dimers through head-to-tail aurophilic bonding. From the geometrical characteristics of the core unit of the cations the ligand can be assigned a 2-pyridinolate form featuring pyridine and phenolate donor sites.     

The diterpene acids in the bled resins of three pacific kauri, Agathis vitiensis, A. Lanceolata and A. Macrophylla

The composition of the diterpene acids in the bled resins of three kauri pines, Agathis vitiensis from Fiji, A. lanceolata from New Caledonia, and A. macrophylla from the Solomon Islands has been determined by extraction, methylation and chromatography. The results are compared with Agathis species from Australia and New Zealand.     

Histopathology of Aerococcus viridans var. homari infection (Gaffkemia) in the lobster, Homarus americanus, and a comparison with histological reactions to a gram-negative species, Pseudomonas perolens

Histological response of lobsters to injection of Aerococcus viridans var. homari, cause of gaffkemia, was followed over a 14-day period. Salient features in infected lobsters, Homarus americanus, were: aggregations of hemocytes occurring in hemal spaces throughout the tissues and increasing in number and size with time; the early phagocytosis of bacteria by the system of fixed phagocytes (FPs) present in hemal spaces of the hepatopancreas; and premature release of differentiating hemocytes from the hemopoietic tissue, so that by 14 days that tissue consisted mainly of large stem cells. Mass release of differentiating hemocytes presumably occurred to replace hemocytes lost from the circulation by their incorporation into aggregations or by lysis of individual cells ruptured through the pressure of phagocytized bacteria that were multiplying in them. Bacteria and their remains were present in FPs at 2 days but not visible in single or aggregated hemocytes until 6 days, when free bacteria were also present in the hemolymph. By 6 days, all bacteria, whether phagocytized or free, appeared normal and were surrounded by nonstaining halos that extended well beyond the stainable capsular material. As predicted earlier in physiological studies, gaffkemia is a nontoxic, noninvasive bacteremia. There was hemal stasis and consequent injury in the antennal gland due to free and aggregated hemocytes that occluded hemal spaces of that organ, but other tissues and organs appeared normal except for depletion of glycogen. Aggregations of hemocytes were present in lobsters 2 and 12 days after injection of a nonpathogenic, Gram-negative bacterium, Pseudomonas perolens. Unlike the case with gaffkemia, necrotic hemocytes were common in the aggregations, presumably in response to damage by endotoxin. A further difference was that aggregations were common in the heart of P. perolens-injected lobsters but rare in the heart of gaffkemic lobsters. Bacteria were not seen in hemolymph, hemocytes, or other cells of P. perolens-injected lobsters.     

Crystal structure and fluorescence of a europium (III) complex: EuCl3(2,2′-bipyridine N,N dioxide) · 2CH3OH

We report the synthesis and characterization of a seven coordinate europium complex, [EuCl₃(C₁₀H₈N₂O₂) ·  2CH₃OH]. The growing interest in developing efficient light conversion molecular devices (LCMDs) necessitates the need for new fluorescent materials. Ideal physicochemical properties of the materials include ligand absorption, efficient metal to ligand transfer, and strong luminescence with a relatively long decay time. The design of such material requires distinct absorbing (ligand) and emitting (metal ion) components. While Eu³⁺ cation has a non-degenerate emitting level, 2,2′-bipyridine N,N dioxide is a heterocyclic ligand known to exhibit strong luminescence. Additional characterization is also described, including single crystal X-ray diffraction, IR and UV-Vis spectroscopies and elemental analysis.     

Synthetic, structural and spectroscopic studies of complexes derived from the copper(II) perchlorate/succinamic acid/N,N′-donor tertiary reaction systems

The use of succinamic acid (H₂sucm) in Cu(ClO₄)₂·6H₂O/N,N′-donor [2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 4,4′-bipyridine (4,4′-bpy)] reaction mixtures yielded compounds [Cu₂(Hsucm)₃(bpy)₂](ClO₄)·0.5MeOH (1·0.5MeOH), [Cu₂(Hsucm)(OH)(H₂O)(bpy)](ClO₄)₂ (2), [Cu₄(Hsucm)₅(dmbpy)₄]_n(ClO₄)_3n·nH₂O ·0.53nMeOH (3·nH₂O·0.53nMeOH), [Cu₂(Hsucm)₂(dmbpy)₂(H₂O)₂](ClO₄)₂·2H₂O (4·2H₂O), [Cu₂(Hsucm)₂(phen)₂(H₂O)₂](ClO₄)₂·1.8MeOH (5·1.8MeOH), [Cu₂(Hsucm)₂(phen)₂(MeOH)₂](ClO₄)₂·MeOH (6·MeOH) and [Cu(Hsucm)₂(H₂O)(4,4′-bpy)]_n (7). The succinamate(−1) ligand exists in five different coordination modes in the structures of 1-7, i.e. the common syn, syn μ₂-κO:κO′ in 1-6, the μ₂-κ²O in 1, the μ₂-κ²O:κO′ in 1, the μ₃-κ²O:κ²O′ in 3, and the monodentate κO in 7. The primary amide group of Hsucm⁻ remains uncoordinated and participates in intra- and intermolecular hydrogen bonding interactions leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm⁻ ligands. The thermal decomposition of representative complexes was monitored by TG/DTG and DTA measurements.     

Synthesis, structure, cytotoxic activities and DNA-binding properties of tetracopper(II) complexes with dissymmetrical N,N′-bis(substituted)oxamides as ligands

To compare the cytotoxicities and the DNA-binding properties in tetranuclear complexes with different bridging ligands, two tetracopper(II) complexes with formulae of [Cu₄(oxbe)₂Cl₂(bpy)₂]·4H₂O (1) and [Cu₄(oxbm)₂Cl₂(bpy)₂]·2H₂O (2) were synthesized, where H₃oxbe and H₃oxbm stand for N-benzoato-N′-(2-aminoethyl)oxamide and N-benzoato-N′-(1,2-propanediamine)oxamide, respectively, and bpy is 2,2′-bipyridine. Complex 1 was characterized by elemental analyses, IR and electronic spectra and single-crystal X-ray diffraction. The crystal structure reveals the presence of the circular tetranuclear copper(II) cations which are assembled by a pair of cis-oxamido-bridged dinuclear copper(II) units through carboxyl bridges. The crystal structure of complex 2 has been reported in our previous paper. However, the bioactivities were not studied. Cytotoxicities experiments reveal that both the two complexes exhibit cytotoxic effects against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549, and complex 1 has the better activities than those of complex 2. The results of the interactions between the two complexes and herring sperm DNA (HS-DNA) suggest that the two complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants of 3.93 × 10⁴ M⁻¹ (1) and 2.48 × 10⁴ M⁻¹ (2). These results indicated that the bridging ligands may play an important role in the cytotoxicities and the DNA-binding properties of tetranuclear complexes.     

Synthesis, characterization, and magnetic properties of new homotrinuclear bis(oxamato) copper(II) complexes with an asymmetric central N,N′-bridge

The new mononuclear bis(oxamato) complex [n-Bu₄N]₂[Cu(obbo)] (1) (obbo=o-benzyl-bis(oxamato)) has been synthesized as a precursor for trinuclear oxamato-bridged transition metal complexes. Starting from 1 the homotrinuclear complexes [Cu₃(obbo)(pmdta)₂(NO₃)](NO₃)·CH₂Cl₂·H₂O (2) and [Cu₃(obbo)(tmeda)₂(NO₃)₂(dmf)] (3) have been prepared, where pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, tmeda = N,N,N′,N′-tetramethylethylenediamine and dmf = dimethylformamide. The crystal structures of 1-3 were solved. The magnetic properties of 2 and 3 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter values of −111 cm⁻¹ (2) and −363 cm⁻¹ (3) were obtained.     

Effects of electronic structure on chiral induction in outer-sphere electron transfer reactions of complexes with the C3 symmetric ligand, 1,4,7-triazacyclononane-1,4,7-tris[2′(R)-2′-propionate](-3)

The ligand 1,4,7-triazacyclononane-1,4,7-tris[2′(R)-2′-propionate](-3)((R)-tacntp³⁻), binds stereospecifically to transition metal ions. The structures of the complexes [Cr((R)-tacntp)]·NaBr and [Fe((R)-tacntp)]·H₂O have been determined by X-ray crystallography. Both complexes have the Λ-configuration but the conformation of the chelate rings in Λ-[Cr((R)-tacntp)] is (λ,λ,λ) with a geometry close to octahedral while in Λ-[Fe((R)-tacntp)] it is (δ,δ,δ) and the geometry is closer to that of a trigonal prism. Chiral induction in the electron transfer reactions of Λ-[Co((R)-tacntp)], Λ-[Fe((R)-tacntp)] and Λ-[Mn((R)-tacntp)] with [Co((RR,SS)-chxn)₃]²⁺ has been investigated. All three reactions are outer-sphere and four isomeric [Co((RR,SS)-chxn)₃]³⁺ products are identified in each case. The oxidants Λ-[Fe((R)-tacntp)] and Λ-[Mn((R)-tacntp)] show very similar selectivities, quite different from those of Λ-[Co((R)-tacntp)]. Reasons for this behavior are discussed.     

The use of solvatochromic mixed copper(II) chelates with N,N,N′,N′-tetramethylethylenediamine and tropolonato or hinokitiolato ligands, [Cu(trop/hino)(tmen)]B(C6H5)4, as indicator for Lewis basicity of solvents and low-coordinating anions

Mixed copper(II) chelates, [Cu(trop/hino)(tmen)]B(C₆H₅)₄, were prepared with a tropolonato or hinokitiolato ligands (trop/hino) and N,N,N′,N′-tetramethylethylenediamine (tmen). These chelates were, as expected, quite similar to the corresponding acetylacetonato analog [Cu(acac)(tmen)]B(C₆H₅)₄, being fairly soluble in a large number of solvents and remarkably solvatochromic in them. They were also useful as excellent Lewis basicity indicators in solution because their d-d bands continuously shift to red in wider ranges with increasing DN (donor number) of solvent. The examination on addition of various anions to these solvatochromic systems led to a quantitative view of the competition between solvent molecule and anion for coordination to metal center.     

Functional and structural roles of the N-terminal extension in Methanosarcina acetivorans protoglobin

Functional and structural properties of protoglobin from Methanosarcina acetivorans, whose Cys(101)E20 residue was mutated to Ser (MaPgb*), and of mutants missing either the first 20 N-terminal amino acids (MaPgb*-ΔN20 mutant), or the first 33 N-terminal amino acids [N-terminal loop of 20 amino acids and a 13-residue Z-helix, preceding the globin fold A-helix; (MaPgb*-ΔN20Z mutant)] have been investigated. In keeping with the MaPgb*-ΔN20 mutant crystal structure, here reported at 2.0 Å resolution, which shows an increased exposure of the haem propionates to the solvent, the analysis of ligand binding kinetics highlights high accessibility of ligands to the haem pocket in ferric MaPgb*-ΔN20. CO binding to ferrous MaPgb*-ΔN20 displays a marked biphasic behavior, with a fast binding process close to that observed in MaPgb* and a slow carbonylation process, characterized by a rate-limiting step. Conversely, removal of the first 33 residues induces a substantial perturbation of the overall MaPgb* structure, with loss of α-helical content and potential partial collapse of the protein chain. As such, ligand binding kinetics are characterized by very slow rates that are independent of ligand concentration, this being indicative of a high energy barrier for ligand access to the haem, possibly due to localized misfolding. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.