Synthetic routes to mixed-ligand cobalt(III) dithiocarbamato complexes containing imidazole, amine and pyridine donors and the X-ray crystal structure of a cobalt(III) bis(dithiocarbamato) histamine complex

The binuclear cobalt complex [Co(2)(Me(2)dtc)(5)](+) reacts with a range of nitrogen donor ligands L' or L' to form an equimolar mixture of Co(Me(2)dtc)(3) and the mixed-ligand complexes [Co(Me(2)dtc)(2)(L')(2)](+) or [Co(Me(2)dtc)(2)(L')](+), where (L')(2) is two monodentate ligands and (L') is one bidentate ligand. The complexes prepared by this route contain the monodentate ligands L'=1-methyl-imidazole, 1-methyl-5-nitro-imidazole and benzimidazole, all of which coordinate to cobalt through an imidazole nitrogen atom. Symmetrical bidentate ligand complexes contain the bisimidazole L'=2,2'-bis(4,5-dimethylimidazole), the diamine L'=1,2-diaminobenzene and the pyridine donors L'=2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine and 1,10-phenanthroline. Two examples of complexes with unsymmetrical bidentate imidazole-amine donors were prepared in which L'=4-(2-aminoethyl)imidazole (histamine) and 2-aminomethylbenzimidazole. All new complexes were fully characterised, and the X-ray crystal structure of the histamine complex [Co(Me(2)dtc)(2)(hist)]ClO(4) is also reported.     

Kinetic study of catalytic CO(2) hydration by water-soluble model compound of carbonic anhydrase and anion inhibition effect on CO(2) hydration

A kinetic study of CO(2) hydration was carried out using the water-soluble zinc model complex with water-soluble nitrilotris(2-benzimidazolylmethyl-6-sulfonate) L1S, [L1SZn(OH(2))](-), mimicking the active site of carbonic anhydrase, in the presence and absence of anion inhibitors NCS(-) and Cl(-). The obtained rate constants k(cat) for CO(2) hydration were 5.9x10(2), 1. 7x10(3), and 3.1x10(3) M(-1) s(-1) at 5, 10, and 15 degrees C, respectively: the k(cat)=ca. 10(4) M(-1) s(-1) extrapolated towards 25 degrees C has been the largest among the reported k(cat) using zinc model complexes for carbonic anhydrase. It was also revealed that NCS(-), Cl(-) and acetazolamide play a role of inhibitors by the decrease of k(cat): 7x10(2) and 2x10(3) M(-1) s(-1) for NCS(-) and Cl(-) at 15 degrees C, respectively. The sequence of their magnitudes in k(cat) is Cl(-) approximately acetazolamide>NCS(-), where the sequence Cl(-)>NCS(-) is confirmed for native carbonic anhydrase. The difference of k(cat) or k(obs) between NCS(-) and Cl(-) resulted from that between the stability constants K(st)=2x10(3) for [L1SZn(NCS)](2-) and 1x10(2) M(-1) for [L1SZnCl](2-) in D(2)O: for water-insoluble tris(2-benzimidazolylmethyl)amine L1, K(st)=1.8x10(4) for [L1Zn(NCS)](2-) and 1.5x10(3) M(-1) for [L1ZnCl](2-)in CD(3)CN/D(2)O (50% v/v). The crystal structure of anion-binding zinc model complexes [L1Zn(OH(2))](0.5)[L1ZnCl](0.5) (ClO(4))(1.5) 1(0.5)2(0.5)(ClO(4))(1.5) was revealed by X-ray crystallography. The geometry around Zn(2+) in 1 and 2 was tetrahedrally coordinated by three benzimidazolyl nitrogen atoms and one oxygen atom of H(2)O, or Cl(-).     

Cobalt complexes of terpyridine ligand: crystal structure and photocleavage of DNA

Two new cobalt complexes, [Co(pytpy)(2)](ClO(4))(2), 1, and [Co(pytpy)(2)](ClO(4))(3), 2 where pytpy=pyridine terpyridine, have been synthesized and characterized. Single-crystal X-ray structure of both the complexes has been resolved. The structure shows the complexes to be a monomeric cobalt(II) and cobalt(III) species with two pytpy ligands coordinated to the metal ion to give a six coordinate complex. Both cobalt(II) and cobalt(III) complexes crystallize in meridional configuration. The interaction of these complexes with calf thymus DNA has been explored by using absorption, emission spectral, electrochemical studies and viscosity measurements. From the experimental results the DNA binding constants of 1 and 2 are found to be (1.97+/-0.15)x10(4)M(-1) and (2.7+/-0.20)x10(4)M(-1) respectively. The ratio of DNA binding constants of 1 and 2 have been estimated to be 0.82 from electrochemical studies, which is in close agreement with the value of 0.73 obtained from spectral studies. The observed changes in viscosity of DNA in the presence of increasing amount of complexes 1 and 2 suggest intercalating binding of these complexes to DNA. Results of DNA cleaving experiments reveal that complex 2 efficiently cleaves DNA under photolytic conditions while complex 1 does not cleave DNA under similar conditions.     

Synthesis, crystal structure, cytotoxic activity and DNA-binding properties of the copper (II) and zinc (II) complexes with 1-[3-(2-pyridyl)pyrazol-1-ylmethyl]naphthalene

A new ligand L, 1-[3-(2-pyridyl)pyrazol-1-ylmethyl]naphthalene, and its two metal complexes, [Cu(L)3](ClO4)2 (1) and [Zn(L)3](ClO4)2(H2O)2 (2), have been synthesized and characterized. The crystal structure of complex 1 was determined by single crystal X-ray diffraction, which crystallized in monoclinic, space group P2(1)/n with unit cell parameters, a = 12.710(4) angstroms, b = 12.135(3) angstroms, c = 33.450(9) angstroms, beta = 93.281(5) degrees and Z = 4. The Cu atom was six-coordinated to N(1), N(2), N(4), N(5), N(7) and N(8) from three L ligands and formed a slightly distorted octahedral geometry. Complexes 1 and 2, and ligand L were subjected to biological tests in vitro using three different cancer cell lines (HL-60, BGC-823 and MDA-MB-435). Complex 1 showed significant cytotoxic activity against three cancer cell lines. The interactions of complexes 1 and 2, and ligand L with calf thymus DNA were then investigated by thermal denaturation, viscosity measurements and spectrophotometric methods. The experimental results indicated that complexes 1 and 2 bound to DNA by intercalative mode via the ligand L. The intrinsic binding constants of complexes 1 and 2, and ligand L with DNA were 1.8 x 10(4), 5.4 x 10(3) and 2.76 x 10(3) M(-1), respectively.     

Apoptosis induction and inhibition of H-ras overexpression by novel trans-[PtCl2(isopropylamine)(amine')] complexes

Hitherto, it has been generally accepted as a paradigm of the biochemical pharmacology of platinum antitumor drugs that a cis configuration of the leaving groups is necessary for antitumor activity of platinum compounds. However, it has been recently observed that certain trans-platinum complexes have both in vitro and in vivo antitumor activity. We previously reported the synthesis, characterization and cytotoxic activity against ras-transformed cells of several trans-[PtCl2LL'] complexes where L and L' are asymmetric aliphatic amines (L = dimethylamine and butylamine, L' = isopropylamine). The results reported in this paper show that the compounds trans-[PtCl2(isopropylamine)(dimethylamine)] and trans-[PtCl2(isopropylamine)(butylamine)] kill Pam 212-ras cisplatin resistant cells through apoptosis induction. Moreover, Western blot data show that both compounds inhibit overexpression of H-ras oncogene in Pam 212-ras cells. Altogether, these data indicate that, in contrast with cis-DDP, the apoptotic activity of these novel trans-Pt(II) compounds in ras-transformed cells is associated with their ability to abolish ras-overexpression.     

Stability and nickel binding properties of peptides designed as scaffolds for the stabilization of NiII-Fe4S4 bridged assemblies

Helix-loop-helix peptides containing 63 residues (HC(4)H(2), HC(4)HC, HC(5)H), designated by their sequence and content of histidyl (H) and cysteinyl (C) residues, have been previously synthesized for the purpose of stabilizing certain bridged metal sites in proteins. These peptides bind one Fe(4)S(4) cluster by means of a ferredoxin tricysteinyl consensus sequence and an additional Cys residue, and one Ni(II) atom (HC(4)H(2), HC(5)H) in predesigned binding sites. In this investigation, the apopeptides and their Fe(4)S(4) derivatives are shown to be relatively stable to unfolding by guanidine hydrochloride, indicating stability of secondary structure. With this property demonstrated, Ni(II) binding equilibria have been evaluated in the terms of site-specific (Scatchard model) and stepwise (stoichiometric) binding constants. Two peptides were designed to have preformed CysHis(3) (HC(4)H(2)) and Cys(2)His(2) (HC(5)H) binding sites. The data indicate one strong binding site in each peptide with preferred binding constants k(1)=4.4x10(5) M(-1)(HC(4)H(2)) and 2.7x10(5) M(-1)(HC(5)H). Based on X-ray absorption spectroscopic data, these binding steps are associated with the formation of the desired coordination units Ni(II)CysHis(3) and Ni(II)Cys(2)His(2). For peptide HC(4)HC, k(1)=2.5x10(5) M(-1), but the binding site could not be fully identified. Collective evidence from this and prior investigations supports the presence of the bridged assemblies Ni(II)-(mu(2)-S x Cys)-[Fe(4)S(4)], stabilized by a scaffolding effect in peptides HC(4)H(2) and HC(5)H. The assembly Ni(II)-X-[Fe(4)S(4)] is the minimal structure of the A-Cluster of carbon monoxide dehydrogenase adduced from spectroscopic evidence; bridge X is currently unidentified. These results suggest that de novo designed peptides may serve as scaffolds for the construction of native bridged sites in proteins. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00775-001-0320-4.     

Chromophore-protein-water interactions in the L intermediate of bacteriorhodopsin: FTIR study of the photoreaction of L at 80 K.

Using FTIR spectroscopy, perturbations of several residues and internal water molecules have been detected when light transforms all-trans bacteriorhodopsin (BR) to its L intermediate having a 13-cis chromophore. Illumination of L at 80 K results in an intermediate L' absorbing around 550 nm. L' thermally converts to the original BR only at >130 K. In this study, we used the light-induced transformation of L to L' at 80 K to identify some amino acid residues and water molecules that closely interact with the chromophore and distinguish them from those residues not affected by the photoreaction. The L minus L' FTIR difference spectrum shows that the chromophore in L' is in the all-trans configuration. The perturbed states of Asp96 and Val49 and of the environment along the aliphatic part of the retinal and Lys216 seen in L are not affected by the L --> L' photoreaction. On the other hand, the environments of the Schiff base of the chromophore, of Asp115, and of water molecules close to Asp85 returned in L' to their state in which they originally had existed in BR. The water molecules that are affected by the mutations of Thr46 and Asp96 also change to a different state in the L --> L' transition, as indicated by transformation of a water O-H vibrational band at 3497 cm-1 in L into an intense peak at 3549 cm-1 in L'. Notably, this change of water bands in the L --> L' transition at 80 K is entirely different from the changes observed in the BR --> K photoreaction at the same temperature, which does not show such intense bands. These results suggest that these water molecules move closer to the Schiff base as a hydrogen bonding cluster in L and L', presumably to stabilize its protonated state during the BR to L transition. They may contribute to the structural constraints that prevent L from returning to the initial BR upon illumination at 80 K.     

Modeling of Ni-Fe-center of Ni-CO-dehydrogenases by nickel complexes with thiaazaligands

Three new nickel(II) complexes with ligands 1,8-bis(2'-pyridyl)-3,6-dithiaoctane (Pdto) and dithiosemicarbazone of 4,7-dithiadecane-2,9-dione (DtdtzH2) of composition Ni(Pdto)(H2O)2(ClO4)2, Ni(DtdtzH2)(ClO4)2 and Ni(Dtdtz) were prepared, their molecular structures, spectral and redox-properties were studied. The possibilities of chemical reduction of Ni(Pdto)(H2O)2(ClO4)2 to nickel(I) and nickel(0) species and the reaction of nickel(I) complex with CO were shown, which may be described as the modeling of one of the stages of reactions with CO on active Ni-Fe-site of Ni-CO-dehydrogenases. It was found that Ni(DtdtzH2)(ClO4)2 reacted with (Et4N)2[Fe4S4(SBz)4] (BzSH = C6H5 CH2SH) forming adduct. In the row of studied complexes Ni(Pdto) (H2O)2(ClO4)2 may be described as the best structural model of Ni-Fe-site of Ni-CO-dehydrogenases on the redox properties.     

Design and synthesis of new models for diiron biosites

In order to mimic dinuclear active sites of some non-heme diiron proteins, ten new polydentate and potentially dinucleating ligands have been synthesized. Each ligand contains a carboxylate moiety designed to bridge two metal atoms. These central carboxylate moieties are derived from substituted benzoic acids that in turn are linked to terminal nitrogen or oxygen donors by spacers so that framework-type polydentate ligands similar to the polypeptide frames in diiron metallobiosites are formed. Reaction of these ligands with Fe(ClO4)3 x 9H2O leads to ferric mu-oxo-mu-carboxylato iron complexes of the general formulas [Fe2O(L)2(H2O)2](ClO4)2 and [Fe2O(L)(BzO)](ClO4)2 (L = ligand), containing one or two immobilized bridging carboxylates, respectively. While X-ray crystallography shows that some of these complexes are dimers or network polymers in the solid state, electrospray ionization mass spectrometry (ESMS) and spectroscopic data (UV-Vis, NMR, Móssbauer) indicate that they dissociate to monomeric Fe2O units in dilute CH3CN solutions.     

Synthesis and spectroscopic and fungicidal characterization of hydroxamic acids and their metal chelates

Hydroxamic acid chelates of the type ML2, ML2', and ML2" where M = Cu(II), Ni(II) or Co(II) and L = N,2'-diphenylacetohydroxamic acid (N,2'-DPAHA), L' = 2,2'-diphenylacetohydroxamic acid (2,2'-DPAHA), and L" = 2-phenylacetohydroxamic acid (2-PAHA) have been isolated and characterized on the basis of elemental analysis and infrared and magnetic data. These metal chelates were screened for their fungicidal activity. The testing against fungi has been carried out by slide germination technique against Alternaria alternata and by inhibition zone technique against Fusarium oxysporum and Aspergillus flavus. The fungicidal activity of chelates and their parent ligand has been compared with the commercial fungicide, Dithane M-45, screened under similar conditions.     

X-ray absorption spectroscopy of xanthine oxidase. The molybdenum centres of the functional and the desulpho forms.

X-ray absorption spectra have been recorded for the molybdenum K-edge region of xanthine oxidase. Both the absorption edge and the extended fine structure (e.x.a.f.s.) regions were investigated. Spectra were obtained for samples of the desulpho enzyme as well as for mixtures of this with the active enzyme. The spectrum of the pure active form was then obtained by difference. The desulpho enzyme shows a pronounced step in the absorption edge, of a type previously associated terminal oxygen ligands. In the active enzyme this step has decreased markedly. Satisfactory simulations of the e.x.a.f.s. spectrum of the desulpho enzyme could be obtained by assuming the molybdenum to be bonded to two terminal oxygen atoms (Mo = O about .175 nm), two sulphur atoms (presumably from cysteine residues, Mo-S about .0250 nm) and one sulphur atom (presumably from a methionine residue, Mo-S about 0.290 nm). E.x.a.f.s. of the active enzyme differed appreciably from this. In keeping with earlier proposals [Gutteridge, Tanner & Bray (1978) Biochem. J. 175, 887-897], the spectrum of the active enzyme could be simulated if a sulphur atom at about 0.225 nm (i.e. presumably a terminal sulphur atom) replaced one of the terminal oxygen atoms of the desulpho from, with small changes in the other bond distances. Validity of the interpretative procedures, which involved phase shift and amplitude calculations ab initio, was demonstrated by using low molecular weight compounds of known structure.     

The tetra-manganese complex of photosystem II during its redox cycle - X-ray absorption results and mechanistic implications

Using X-ray absorption spectroscopy (XAS), relevant information on structure and oxidation state of the water-oxidizing Mn complex of photosystem II has been obtained for all four semi-stable intermediate states of its catalytic cycle. We summarize our recent XAS results and discuss their mechanistic implications. The following aspects are covered: (a) information content of X-ray spectra (pre-edge feature, edge position, extended X-ray absorption fine-structure (EXAFS), dichroism in the EXAFS of partially oriented samples); (b) S(1)-state structure; (c) X-ray edge results on oxidation state changes; (d) EXAFS results on structural changes during the S-state cycle; (e) a structural model for the Mn complex in its S(3)-state; (f) XAS-based working model for the S(2)-S(3) transition; (g) XAS-based working model for the S(0)-S(1) transition; (h) potential role of hydrogen atom abstraction by the Mn complex. Finally, we present a specific hypothesis on the mechanism of dioxygen formation during the S(3)-(S(4))-S(0) transition. According to this hypothesis, water oxidation is facilitated by manganese reduction that is coupled to proton transfer from a substrate water to bridging oxides.     

Application of stripping voltammetry and microelectrodes in vitro biocompatibility and in vivo toxicity tests of AISI 316L corrosion products.

Adsorptive stripping voltammetric procedures, using mercury film microelectrodes, were optimised and applied to quantify total iron, chromium and nickel in samples of osteoblast-like cells culture medium and mice organs (liver, kidney and spleen) obtained from, respectively, in vitro and in vivo 316L stainless steel corrosion products biocompatibility and toxicity studies. The methods were based on the pre-concentration of the iron-catechol complex by adsorption at the potential of -1.80 V (vs. Ag/AgCl), of the chromium-diethylenetriaminepentaacetic acid complex at -1.00 V or -1.15 V (vs. Ag/AgCl) and of the nickel-dimethylglyoxime complex at -0.70 V (vs. Ag/AgCl). The detection limits achieved for each metal ion (i) in the culture medium were 1.93x10(-8) mol/L Fe, 2.80x10(-10) mol/L Cr and 7.70x10(-9) mol/L Ni for a collection time of 30 s, 40 s and 10 s, respectively, and (ii) in the mice organ solutions were 1.37x10(-8) mol/L Fe, 1.54x10(-8) mol/L Cr and 1.58x10(-9) mol/L Ni for an adsorption time of 25 s, 25 s and 15 s, respectively. The accuracy of the proposed procedures was verified by comparison of the results obtained by adsorptive stripping voltammetry with those attained by atomic absorption spectrometry for the same set of samples and good agreement was found. The in vitro study showed that stainless steel corrosion products affect the expression of the osteogenic phenotype. The in vivo mice model, used to investigate the systemic effects provoked by the corrosion products per se, indicated that Fe, Cr and Ni are partially accumulated in the organs studied and that Ni induced the more significant morphological alterations.     

The nickel site of Bacillus pasteurii UreE, a urease metallo-chaperone, as revealed by metal-binding studies and X-ray absorption spectroscopy

UreE is a homodimeric metallo-chaperone that assists the insertion of Ni(2+) ions in the active site of urease. The crystal structures of UreE from Bacillus pasteurii and Klebsiella aerogenes have been determined, but the details of the nickel-binding site were not elucidated due to solid-state effects that caused disorder in a key portion of the protein. A complementary approach to this problem is described here. Titrations of wild-type Bacillus pasteurii UreE (BpUreE) with Ni(2+), followed by metal ion quantitative analysis using inductively coupled plasma optical emission spectrometry (ICP-OES), established the binding of 2 Ni(2+) ions to the functional dimer, with an overall dissociation constant K(D) = 35 microM. To establish the nature, the number, and the geometry of the ligands around the Ni(2+) ions in BpUreE-Ni(2), X-ray absorption spectroscopy data were collected and analyzed using an approach that combines ab initio extended X-ray absorption fine structure (EXAFS) calculations with a systematic search of several possible coordination geometries, using the Simplex algorithm. This analysis indicated the presence of Ni(2+) ions in octahedral coordination geometry and an average of two histidine residues and four O/N ligands bound to each metal ion. The fit improved significantly with the incorporation, in the model, of a Ni-O-Ni moiety, suggesting the presence of a hydroxide-bridged dinuclear cluster in the Ni-loaded BpUreE. These results were interpreted using two possible models. One model involves the presence of two identical metal sites binding Ni(2+) with negative cooperativity, with each metal ion bound to the conserved His(100) as well as to either His(145) or His(147) from each monomer, residues found largely conserved at the C-terminal. The alternative model comprises the presence of two different binding sites featuring different affinity for Ni(2+). This latter model would involve the presence of a dinuclear metallic core, with one Ni(2+) ion bound to one His(100) from each monomer, and the second Ni(2+) ion bound to a pair of either His(145) or His(147). The arguments in favor of one model as compared to the other are discussed on the basis of the available biochemical data.     

S1-state model of the O2-evolving complex of photosystem II

We introduce a quantum mechanics/molecular mechanics model of the oxygen-evolving complex of photosystem II in the S(1) Mn(4)(IV,III,IV,III) state, where Ca(2+) is bridged to manganese centers by the carboxylate moieties of D170 and A344 on the basis of the new X-ray diffraction (XRD) model recently reported at 1.9 ? resolution. The model is also consistent with high-resolution spectroscopic data, including polarized extended X-ray absorption fine structure data of oriented single crystals. Our results provide refined intermetallic distances within the Mn cluster and suggest that the XRD model most likely corresponds to a mixture of oxidation states, including species more reduced than those observed in the catalytic cycle of water splitting.     

Metal-ion environment in solid Mn(II), Co(II) and Ni(II) hyaluronates

Amorphous powders and films of some metal hyaluronate complexes of general composition (C14H20O11N)2 x xH2O (M = Mn2+, Ni2+ and Co2+) have been prepared at pH 5.5-6.0. The coordination geometry around the metal ions has been analyzed by EXAFS (extended X-ray absorption fine structure) and FTIR spectroscopy. Mn2+, Ni2+, and Co2+ ions are coordinated to carboxylate oxygen atoms and water molecules. The process of local geometry formation round the metal ions is sensitive to sample preparation.     

The metal site of stellacyanin: EXAFS studies of the Cu(II), Cu(I), Ni(II) and Co(II) derivatives

Extended X-ray absorption fine structure (EXAFS) studies of Cu(II) (oxidized), Cu(I) (reduced), Ni(II) and Co(II) stellacyanin from Rhus vernicifera are reported. For Cu(II) stellacyanin, the coordination by three close ligands, viz. 2 N and 1 S, with the presence of smaller shells pointing to imidazole coordination, indicates similarities with the coordination in other so-called type 1 or 'blue'-copper proteins. Upon reduction, slightly longer ligand distances and an additional sulphur ligand are found. Ni(II) and Co(II) stellacyanin resemble Cu(I) and Cu(II) stellacyanin, respectively, in ligand distances, but have a tendency for three rather than two N (or O) ligands in the first shell. The results are compared with the three-dimensional model derived from 1H-NMR relaxation measurements for Co(II) stellacyanin, and are consistent with the proposal that apart from the three close ligands found in all blue-copper proteins, a sulphur from a disulphide bridge and the amide oxygen from an asparagine residue come to within coordinating distance of the metal in stellacyanin.     

An extended-X-ray-absorption-fine-structure study of freeze-dried and solution ovotransferrin. Evidence for water co-ordination at the metal-binding sites.

Our previous extended-X-ray-absorption-fine-structure (e.x.a.f.s.) study has shown that the probable iron environment in chicken ovotransferrin involves two low-Z ligands (consistent with phenolate linkages) at 0.185(1) nm and four low-Z ligands at 0.204(1) nm [Garratt, Evans, Hasnain & Lindley (1986) Biochem. J. 233, 479-484]. Herein we provide additional information from the e.x.a.f.s. and near-edge structure suggestive of a decrease in the co-ordination number of ovotransferrin-bound iron upon freeze-drying. These effects are reversible, and exposure of the freeze-dried material to a humid atmosphere results in reversion to the solution spectra. Progressive rehydration was monitored by using e.p.r. spectroscopy and was confirmed by recording the high-resolution X-ray-absorption near-edge structure (x.a.n.e.s.). The results suggest the presence of a labile water molecule at the iron-binding sites of ovotransferrin in solution.     

X-ray absorption fine structure study of the atomic and electronic structure of molybdenum disulfide intercalation compounds with transition metals

The local structures of ‘host’ and ‘guest’ layers of MoS₂ intercalated with M(OH)₂ (M=Mn, Co and Ni) prepared via interaction of single-layer MoS₂ dispersions and solutions of M²⁺ salts were studied by X-ray absorption spectroscopy. According to M K-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) results, the electronic structure and atomic environment of the M atoms in the intercalates are similar to that of the crystalline hydroxides M(OH)₂. In the Ni intercalate, Mo K-edge EXAFS revealed a structural change of the ‘host’ MoS₂ layers similar to that reported for water dispersions of MoS₂ single layers. S K-edge XANES data indicate that the change is associated with increased electron density on the S atoms in the matrix. SO₄²⁻ and Mo″⁻ (4 < n < 6) were detected in the intercalated materials exposed to air, suggesting that transition metal intercalation may increase the susceptibility of the MoS₂ layers to oxidation.     

Interpreting the visible absorption bands of 1,4-(dihydroxy)-9,10-anthraquinone and its metal chelates

The visible absorption spectra of 1,4-(dihydroxy)-9,10-anthraquinone and of Co(II), Ni(II), Cu(II) and Zn(II) chelates have been studied in different organic solvents. This system provides a model for the anthracycline antibiotics and their metal chelates. The band structure of the spectrum has been determined using the second and fourth derivatives of the spectrum. The visible absorption band of the parent molecule can be assigned to a single electronic state with a reduced dipole moment in the excited state; structure in this band is ascribed to two overlapping vibrational progressions. In contrast, the dianion (hydroxy protons removed) shows a single electronic state with an increased dipole moment in the excited state; structure in this band can be assigned to a single vibrational progression. All of the metal chelates show spectra which are similar in appearance to that of the dianion although the identity of the metal determines the bathochromic shift of the absorption band. Titration of 1,4-dihydroxyanthraquinone with Cu(ClO4)2.6H2O demonstrates that three chelates with metal-to-ligand ratios of 1:2, 1:1 and 2:1 can form depending on the identity of the metal, ratio of metal to ligand, and donor character of the solvent.