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PubMed1989

Bifunctional antitumor compounds: interaction of adriamycin with metallocene dichlorides.

In order to synthesize bifunctional antitumor compounds, the interactions of adriamycin with metallocene dichlorides, Cp2MCl2, where M = Zr, Ti, V, have been studied. Using absorption, fluorescence, and circular dichroism measurements, we have shown that adriamycin is able to coordinate to the three metal ions. The interaction of Cp2ZrCl2 and Cp2VCl2 with adriamycin leads to compounds of 1:2 metal:drug stoichiometry, whereas the interaction of Cp2TiCl2 with adriamycin leads to two types of compounds of 1:2 and 1:1 stoichiometry. The Zr-adriamycin complex, which is unable to dissociate, even at a pH lower than 1, does not display antitumor activity against P-388 leukemia. However Ti-adriamycin complexes, which are more susceptible to dissociation in acidic media, exhibit antitumor activity that compares with that of the free drug. These complexes, unlike adriamycin, do not catalyze the flow of electrons from NADH to molecular oxygen through NADH dehydrogenase. In addition, the presence of metal ions promote the binding of the drug to DNA and erythrocyte ghosts.

Animals↗
PubMed2000

Porphyrazinediols: Synthesis, Characterization, and Complexation to Group IVB Metallocenes.

The first metalated porphyrazinediols 11 have been prepared from (L)-(+)-dimethyl tartrate via conversion into the corresponding dispoke or 2,3-dimethoxy-2,3-butanediyl protected 2,3-dihydroxymaleonitrile, Linstead macrocyclization, transmetalation, and deprotection. Their stability is very dependent on the nature of the metal ion in the cavity of the porphyrazine. Reaction of these porphyrazinediols with metallocene dichlorides led to new solitaire porphyrazines 12 while DDQ oxidation followed by trapping with diaminomaleonitrile afforded new porphyrazine dinitriles 14.

Journal Article↗
PubMed2005

A solid-state 39K and 13C NMR study of polymeric potassium metallocenes.

The quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) and double frequency sweep (DFS)/QCPMG pulse sequences are applied in order to acquire the first solid-state 39K NMR spectra of organometallic complexes, the polymeric main group metallocenes cyclopentadienyl potassium (CpK) and pentamethylcyclopentadienyl potassium (Cp*K). Piecewise QCPMG NMR techniques are used to acquire a high S/N 39K spectrum of the broad central transition of Cp*K, which is ca. 200 kHz in breadth. Analytical and numerical simulations indicate that there is a significant quadrupolar interaction present at both potassium nuclei (C(Q)(39K) = 2.55(6)/2.67(8) MHz and 4.69(8) MHz for CpK (static/MAS) and Cp*K, respectively). Experimental quadrupolar asymmetry parameters suggest that both structures are bent about the potassium atoms (eta(Q)(39K) = 0.28(3)/0.29(3) for CpK (static/MAS) and eta(Q)(39K) = 0.30(3) for Cp*K). Variable-temperature (VT) 39K NMR experiments on CpK elucidate temperature-dependent changes in quadrupolar parameters which can be rationalized in terms of alterations of bond distances and angles with temperature. 13C CP/MAS NMR experiments are conducted upon both samples to quantify the carbon chemical shielding anisotropy (CSA) at the Cp' ring carbon atoms. Ab initio carbon CSA and 39K electric-field gradient (EFG) and CSA calculations are conducted and discussed for the CpK complex, in order to correlate the experimental NMR parameters with molecular structure in CpK and Cp*K. 39K DFS/QCPMG and 13C CP/MAS experiments prove invaluable for probing molecular structure, temperature-dependent structural changes, and the presence of impurities in these systems.

Journal Article↗
PubMed2006

Preparation of nanosheet polyethylene with heterogeneous metallocene catalyst and formation mechanism of nanosheet polyethylene.

Silica with small and regular pore sizes was synthesized by hydrothermal crystallization and investigated with thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption-desorption, and scanning electron microscopy (SEM). The ethylene polymerization was carried out with the silica-supported metallocene catalyst, and the morphology of the resultant polyethylene was investigated with SEM. It was found that the silica could break up into sheet fragments instantaneously during polymerization and the polyethylene could replicate it to obtain nanosheet polyethylene. A possible formation mechanism of the nanosheet polyethylene is proposed.

Catalysis↗
PubMed2006

A DFT study on dinuclear metallocenes RMMR [R= (BCO)5, (BNN)5; M = Be, Mg, Ca, Zn, Cd].

A series of dinuclear metallocenes with formula RMMR [R= (BCO)5, (BNN)5; M = Be, Mg, Ca, Zn, Cd] are investigated via density functional theory. All these compounds contain two M[eta5-(BCO)5] fragments or two M[eta5-(BNN)5] fragments with a direct metal-metal single sigma bond. Detailed NBO analyses show that the metal-ligand interactions are predominantly ionic in nature and each metal atom is in its +1 oxidation state. NBO analyses indicate that the interaction between the B-B bonds and metal-metal antibond has played a role in the stabilities of these compounds.

Journal Article↗
PubMed1998

Ethene-Norbornene Copolymerization with Homogeneous Metallocene and Half-Sandwich Catalysts: Kinetics and Relationships between Catalyst Structure and Polymer Structure. 4. Development of Molecular Weights.

The molecular weights of ethene-norbornene copolymers, produced with various metallocene- and amidocyclopentadienyl-methylaluminoxane (MAO) catalysts, have been determined by high-temperature gel-permeation chromatography: with one exception, increasing molecular weights were found with an increasing norbornene content in the copolymer. This observation is due to the fact that the beta-hydride elimination process is not possible in the case of norbornene, because of special steric conditions of the cis-2,3-exo inserted norbornene; other possible termination reactions are discussed, considering the specialties of the norbornene. The effect of the catalyst structure on the molecular weights is discussed in terms of steric and electronic factors of the different ligands: sterically less hindered ligands produce ethene-norbornene copolymers with relatively low molecular weights; ligands with a larger extension and electron-pushing effect such as the fluorenyl ligand, induced the formation of high molecular weights. Additional alkyl groups at the indenyl or fluorenyl ligand increased the molecular weights additionally.

Journal Article↗
PubMed2005

Diameter-selective encapsulation of metallocenes in single-walled carbon nanotubes.

Encapsulation of organic molecules in carbon nanotubes has opened a new route for the fabrication of hybrid nanostructures. Here we show that diameter-selective encapsulation of two metallocene compounds bis(cyclopentadienyl) cobalt and bis(ethylcyclopentadienyl) cobalt has been observed in single-walled carbon nanotubes. In particular, bis(cyclopentadienyl) cobalt is observed to fill only nanotubes of one specific diameter. Electron transfer from the cobalt ions to the nanotubes has been directly observed through a change in the charge state of the encapsulated molecules. The filling of the tubes is found to induce a red-shift of the photoluminescence emission, which is attributed to the formation of localized impurity states below the conduction band of the nanotubes.

Coated Materials, Biocompatible↗
PubMed2006

The homologous series of 1,1'-ferrocenylenebisdihalophosphanes (C5H4PX2)2Fe (X = F, Cl, Br, I): precursors for the first metallocene bridged bisphosphaalkene.

A facile synthetic access to the homologous series of 1,1'-ferrocenylene bisdihalophosphanes Fc'(PX2)2 (X = F, Cl, Br, I; Fc' = 1,1'-ferrocenediyl = ferrocenylene = -C5H4FeC5H4-) is reported. The 31P NMR spectroscopic data of this series suggest a similar electronic interaction of the -PX(2) unit with the ferrocene system as in monofunctional ferrocenyldihalophosphanes. Crystal structures for Fc'(PCl2)2 and Fc'(PBr2)2 reveal that the nature of the halogen atom within the phosphane unit strongly influences the twist angle of the ferrocene system, while leaving the other structural parameters mostly unaffected. Based on these bisdihalophosphanes, a synthetic access to the first metallocene bridged bisphosphaalkene ((C5H4P=C(t-Bu)OTMS)2Fe) is reported in which the tert-butyl substituents provide sufficient steric pressure to control the E/Z isomeric ratio which leads to the almost exclusive formation of the most stable Z,Z isomer out of the three possible isomers.

Journal Article↗
PubMed2007

Density functional calculations of NMR shielding tensors for paramagnetic systems with arbitrary spin multiplicity: validation on 3d metallocenes.

The calculation of nuclear shieldings for paramagnetic molecules has been implemented in the ReSpect program, which allows the use of modern density functional methods with accurate treatments of spin-orbit effects for all relevant terms up to order Omicron(alpha4) in the fine structure constant. Compared to previous implementations, the methodology has been extended to compounds of arbitrary spin multiplicity. Effects of zero-field splittings in high-spin systems are approximately accounted for. Validation of the new implementation is carried out for the 13C and 1H NMR signal shifts of the 3d metallocenes 4VCp2, 3CrCp2, 2MnCp2, 6MnCp2, 2CoCp2, and 3NiCp2. Zero-field splitting effects on isotropic shifts tend to be small or negligible. Agreement with experimental isotropic shifts is already good with the BP86 gradient-corrected functional and is further improved by admixture of Hartree-Fock exchange in hybrid functionals. Decomposition of the shieldings confirms the dominant importance of the Fermi-contact shifts, but contributions from spin-orbit dependent terms are frequently also non-negligible. Agreement with 13C NMR shift tensors from solid-state experiments is of similar quality as for isotropic shifts.

Journal Article↗
PubMed2006

Tuning the electrical conductivity of nanotube-encapsulated metallocene wires.

We analyze a new family of carbon nanotube-based molecular wires, formed by encapsulating metallocene molecules inside the nanotubes. Our simulations, which are based on a combination of nonequilibrium Green function techniques and density functional theory, indicate that these wires can be engineered to exhibit desirable magnetotransport effects for use in spintronics devices. The proposed structures should also be resilient to room-temperature fluctuations, and are expected to have a high yield.

Journal Article↗
PubMed2000

High-strength welds in metallocene Polypropylene/Polyethylene laminates

Spectacular advances in organometallic chemistry over the past two decades have resulted in single-site catalysts that are revolutionizing production of polyethylene (PE) and isotactic polypropylene (iPP). This report describes an unanticipated benefit of metallocene-catalyzed semicrystalline polyolefins, namely welded joint strengths in PE/iPP laminates that can exceed the cohesive strength of the constituents. We propose that interfacial polymer entanglements, established in the molten state and subsequently anchored in chain-folded lamellae upon crystallization, are responsible for this intrinsic property. The poor adhesion exhibited by traditional Ziegler-Natta-catalyzed polyolefins is shown to derive from the accumulation of amorphous polymer, a by-product of the polymerization reactions, at the interface. These results should facilitate fabrication and improve the properties of composites based on materials that dominate the plastics industry.

Journal Article↗
PubMed1998

Metallocene-catalysed cyclo-olefin copolymers.

Metallocene-catalysed cyclo-olefin copolymers offer medical product designers a substantial range of properties. This article outlines the capabilities of these materials and describes the advances in chemical engineering that allowed their mass production. A range of applications are highlighted.

Alkenes↗
PubMed2007

Muon implantation of metallocenes: ferrocene.

Muon Spin Relaxation and Avoided Level Crossing (ALC) measurements of ferrocene are reported. The main features observed are five high field resonances in the ALC spectrum at about 3.26, 2.44, 2.04, 1.19 and 1.17 T, for the low-temperature phase at 18 K. The high-temperature phase at 295 K shows that only the last feature shifted down to about 0.49 T and a muon spin relaxation peak at about 0.106 T which approaches zero field when reaching the phase transition temperature of 164 K. A model involving three muoniated radicals, two with muonium addition to the cyclopentadienyl ring and the other to the metal atom, is postulated to rationalise these observations. A theoretical treatment involving spin-orbit coupling is found to be required to understand the Fe-Mu adduct, where an interesting interplay between the ferrocene ring dynamics and the spin-orbit coupling of the unpaired electron is shown to be important. The limiting temperature above which the full effect of spin-orbit interaction is observable in the muSR spectra of ferrocene was estimated to be 584 K. Correlation time for the ring rotation dynamics of the Fe-Mu radical at this temperature is 3.2 ps. Estimated electron g values and the changes in zero-field splittings for this temperature range are also reported.

Ferrous Compounds↗
PubMed1986

Iron-containing metallocenes as active site directed inhibitors of the proteinase that cleaves the NH2-terminal propeptides from type I procollagen.

Derivatives of ferrocene (dicyclopentadienyliron) (Fc) were examined as active site directed inhibitors of type I procollagen N-proteinase, the enzyme that cleaves the NH2-terminal propeptides from type I procollagen. The compounds were shown here to be reversible, competitive inhibitors of the enzyme. The effectiveness of the Fc inhibitors varied with modification of the cyclopentadienyl (cp) rings. The monocarboxylic acid (I) and the 1,1'-dicarboxylic acid (II) derivatives of Fc inhibited 50% of the enzymic activity (I50) at concentrations of 1.0 and 0.5 mM, respectively. The Ki values were 0.3 mM for both I and II. Derivatization of the carbonyl alpha to the cp ring of compound I (FcCOCH2CH2COOH, III) increased the inhibitory activity (I50 = 0.100 mM; Ki = 0.065 mM). Removal of the carbonyl alpha to the cp ring of III did not improve inhibitory activity: FcCH2CH2COOH, I50 = 2 mM; FcCH = CHCOOH, I50 = 1.5 mM. The active inhibitory species apparently contained iron in the 3+ valence state since two ferrocenium derivatives were very effective inhibitors: ferrocenium tetrachloroferrate, IV (I50 = 0.030 mM; Ki = 0.004 mM), and carboxyferrocenium hexafluorophosphate, V (I50 less than 0.1 mM; Ki less than 0.05 mM). In addition, reduction of III with ascorbic acid abolished its inhibitory activity. Compounds I and III stabilized the enzyme to heat denaturation in the absence of exogenous calcium; compound IV did not stabilize the enzyme. Further observations indicated that Fc derivatives were specific inhibitors of procollagen N-proteinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Structures, bond energies, heats of formation, and quantitative bonding analysis of main-group metallocenes [E(Cp)2] (E = Be-Ba, Zn, Si-Pb) and [E(Cp)] (E = Li-Cs, B-Tl).

The geometries, metal-ligand bond dissociation energies, and heats of formation of twenty sandwich and half-sandwich complexes of the main-group elements of Groups 1, 2, 13, and 14, and Zn have been calculated with quantum chemical methods. The geometries of the [E(Cp)] and [E(Cp)2] complexes were optimized using density functional theory at the BP86 level with valence basis sets, which have DZP and TZP quality. Improved energy values have been obtained by using coupled-cluster theory at the CCSD(T) level. The nature of the metal-ligand bonding has been analyzed with an energy-partitioning method. The results give quantitative information about the strength of the covalent and electrostatic interactions between En+ and (Cp-)n (n = 1, 2). The contributions of the orbitals with different symmetry to the covalent bonding are also given.

Journal Article↗