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PubMed1992

Antitumor activity of ionic niobocene and molybdenocene complexes in high oxidation states.

Four air-stable niobocene complexes [(C5H5)2NbCl2]+X- with X = BF4, AsF6, SbF6, SO3CF3 and the molybdenocene derivative [(C5H5)2MoCl2]2+[SbF6]2- were investigated for antitumor properties against Ehrlich ascites tumor in female CF1 mice. All compounds are new, salt-like complexes containing a cationic metallocene moiety, where the early transition metals niobium and molybdenum in the high oxidation states +5 and +6 function as central atoms. The niobocene complexes containing tetrafluoroborate (BF4-) or trifluoromethanesulfonate (CF3SO3-) as anions only induced a maximal cure rate of 50% and led to increases in life span of 182% and 178% following application of optimal doses. The other two niobocene compounds with hexafluoroarsenate (AsF6-) and hexafluoroantimonate (SbF6-) as anions and the molybdenocene derivative [(C5H5)2MoCl2]2+[SbF6]2- effected a maximal cure rate of 100% and increases in life span of 346%, 376%, and 332%, respectively, determined on the key date, i.e., on day 90 after transplantation. On applying the niobocene hexafluoroantimonate complex [(C5H5)2NbCl2] +[SbF6]-, the optimal dose range with a cure rate of 100% was rather broad and extended from 20 mg/kg to 40 mg/kg. Correspondingly, the value of the therapeutic index (TI) was high and amounted to 7.2. In the case of the niobocene hexafluoroarsenate and the molybdenocene hexafluoroantimonate complexes, the TI value decreased to 5.3 and 2.6 respectively. Neither impairments of the general condition nor any conspicuous symptoms could be detected after application of therapeutic doses of the five compounds investigated. Compared to the neutral niobocene dichloro complex [(C5H5)2NbCl2], the therapeutic range of the ionic niobocene derivative [(C5H5)2NbCl2]+[SbF6]- was broadened, the TI value markedly elevated from 2.9 to 7.2, and the toxic symptoms were impressively reduced. The niobocene hexafluoroantimonate complex was the most effective compound investigated in the present study.

Animals↗

PubMed2001

Tetrachlorobis(N1-phenylacetamidino-kappaN2)rhenium(IV) at 11 K by X-ray diffraction and at 20 K by neutron diffraction.

The crystal structure of the title compound, [ReCl(4)(C(8)H(10)N(2))(2)], has been determined by X-ray diffraction at 11 K and by neutron diffraction at 20 K. The accurate and extensive data sets lead to more precise determinations than are available from earlier work. The agreement in atomic positional and displacement parameters at these very low temperatures is good. The results will facilitate re-examination of the magnetic structure of the complex. The Re atom lies on a special position and the molecule has twofold crystallographic symmetry.

Journal Article↗

PubMed2003

Galactosylated chitosan (GC)-graft-poly(vinyl pyrrolidone) (PVP) as hepatocyte-targeting DNA carrier. Preparation and physicochemical characterization of GC-graft-PVP/DNA complex (1).

Galactosylated chitosan was conjugated with poly(vinyl pyrrolidone) (PVP) as a hydrophilic group. The complex formation of GC-graft-PVP (GCPVP)/DNA complexes was confirmed by agarose gel electrophoresis. The morphology of the complex observed by atomic force microscopy had a compact and spherical shape, around 40 nm particle sizes at a charge ratio of 3. The binding strength of GCPVP 10K/DNA complex measured by ethidium bromide binding assay was superior to that of the GCPVP 50K/DNA one, probably attributable to its higher flexibility due to the smaller size, whereas the DNase I protection of GCPVP 10K/DNA complex was inferior to that of the GCPVP 50K/DNA one. This indicated that effective complex formation required both higher binding strength and minimal molecular weight of polycation enough to induce the condensation of DNA. The DNA-binding property of GCPVP mainly depended on the molecular weight of chitosan and composition of PVP.

Animals↗

PubMed2001

Oxamato-bridged trinuclear Ni(II)Cu(II)Ni(II) complexes with irregular spin state structures and a binuclear Ni(II)Cu(II) complex with an unusual supramolecular structure: crystal structure and magnetic properties.

Four oxamato-bridged heterotrinuclear Ni(II)Cu(II)Ni(II) complexes of formula ([Ni(bispictn)](2)Cu(pba))(ClO(4))(2).2.5H(2)O (1), ([Ni(bispictn)](2)Cu(pbaOH))(ClO(4))(2).H(2)O (2), ([Ni(cth)](2)Cu(pba))(ClO(4))(2) (3), and ([Ni(cth)](2)Cu(opba))(ClO(4))(2).H(2)O (4) and a binuclear Ni(II)Cu(II) complex of formula [Cu(opba)Ni(cth)].CH(3)OH (5) have been synthesized and characterized by means of elemental analysis, IR, ESR, and electronic spectra, where pba = 1,3-propylenebis(oxamato), pbaOH = 2-hydroxyl-1,3-propylenebis(oxamato), opba = o-phenylenebis(oxamato), bispictn = N,N'-bis(2-pyridylmethyl)-1,3-propanediamine, and cth = rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. The crystal structures of 1, 3, and 5 have been determined. The structures of complexes 1 and 3 consist of trinuclear cations and perchlorate anions, and that of 5 consists of neutral binuclear molecules which are connected by hydrogen bonds and pi-pi interactions to produce a unique supramolecular "double" sheet. In the three complexes, the copper atom in a square-planar or axially elongated octahedral environment and the nickel atom in a distorted octahedral environment are bridged by the oxamato groups, with Cu.Ni separations between 5.29 and 5.33 A. The magnetic properties of all five complexes have been investigated. The chi(M)T versus T plots for 1-4 exhibit the minimum characteristic of antiferromagnetically coupled NiCuNi species with an irregular spin state structure and a spin-quartet ground state. The chi(M)T versus T plot for 5 is typical of an antiferromagnetically coupled NiCu pair with a spin-doublet ground state. The Ni(II)-Cu(II) isotropic interaction parameters for the five complexes were evaluated and are between 102 and 108 cm(-)(1) (H = -JS(Cu).S(Ni)).

Journal Article↗

PubMed2004

Formation and stability of high-spin alkali clusters.

Helium nanodroplet isolation has been applied to agglomerate alkali clusters at temperatures of 380 mK. The very weak binding to the surface of the droplets allows a selection of only weakly bound, high-spin states. Here we show that larger clusters of alkali atoms in high-spin states can be formed. The lack of strong bonds from pairing electrons makes these systems nonmetallic, van der Waals-like complexes of metal atoms. We find that sodium and potassium readily form such clusters containing up to 25 atoms. In contrast, this process is suppressed for rubidium and cesium. Apparently, for these heavy alkalis, larger high-spin aggregates are not stable and depolarize spontaneously upon cluster formation.

Journal Article↗

PubMed1996

Unique Fluxional Behavior. Synthesis, Structure, and Properties of Novel (Diamine)platinum(II) Complexes of 9-Fluorenylidene- and Benzhydrylidenemalonate Ligands.

New (diamine)platinum(II) complexes A(2)PtX(2) (A(2) = trans-(+/-)-1,2-diaminocyclohexane (DACH), tetrahydro-4H-pyran-4,4-diylbis(methylamine)(THPDMA); X(2) = 9-fluorenylidenemalonate(FM), benzhydrylidenemalonate(BHM)) have been synthesized and characterized by means of multinuclear NMR spectroscopy and X-ray analysis. (DACH)Pt(FM) crystallizes in space group P2(1)/c with eight formula units in a cell of dimensions a = 20.071(7) Å, b = 12.717(3) Å, c = 24.512(6) Å, beta = 103.25(2) degrees, and V = 6090(3) Å.(3) (DACH)Pt(BHM) crystallizes in space group P&onemacr; with four molecular units in a cell of dimensions a = 11.048(3) Å, b = 13.639(3) Å, c = 14.043(6) Å, alpha = 90.17(3) degrees, beta = 91.31(4) degrees, gamma = 89.98(3) degrees, and V = 2116(1) Å(3). The platinum atom in both complexes adopts a typical square planar arrangement with two nitrogen atoms in cis position. The 9-fluorenylidene and benzhydrylidene groups of the amine ligands chelated to platinum are strikingly bent up by 88.8(3) and 80.8(2) degrees, respectively, from the platinum square plane in the solid state. Variable temperature (1)H NMR spectra of the title complexes in dimethyl sulfoxide solution reveals that the amine proton resonances are sensitive to the fluxional motion of the remote arylidene groups, and suggests that interconversion occurs between two "bent-up" and "bent-down" forms. The prominent difference between the FM and BHM complexes is observed in solution, due to the presence or absence of the angle constraint of the anionic coligands.

Journal Article↗

PubMed2002

FTIR spectra and normal-mode analysis of a tetranuclear manganese adamantane-like complex in two electrochemically prepared oxidation states: relevance to the oxygen-evolving complex of photosystem II.

The IR spectra and normal-mode analysis of the adamantane-like compound [Mn(4)O(6)(bpea)(4)](n+) (bpea = N,N-bis(2-pyridylmethyl)ethylamine) in two oxidation states, Mn(IV)(4) and Mn(III)Mn(IV)(3), that are relevant to the oxygen-evolving complex of photosystem II are presented. Mn-O vibrational modes are identified with isotopic exchange, (16)O-->(18)O, of the mono-micro-oxo bridging atoms in the complex. IR spectra of the Mn(III)Mn(IV)(3) species are obtained by electrochemical reduction of the Mn(IV)(4) species using a spectroelectrochemical cell, based on attenuated total reflection [Visser, H.; et al. Anal. Chem. 2001, 73, 4374-4378]. A novel method of subtraction is used to reduce background contributions from solvent and ligand modes, and the difference and double-difference spectra are used in identifying Mn-O bridging modes that are sensitive to oxidation state change. Two strong IR bands are observed for the Mn(IV)(4) species at 745 and 707 cm(-1), and a weaker band is observed at 510 cm(-1). Upon reduction, the Mn(III)Mn(IV)(3) species exhibits two strong IR bands at 745 and 680 cm(-1), and several weaker bands are observed in the 510-425 cm(-1) range. A normal-mode analysis is performed to assign all the relevant bridging modes in the oxidized Mn(IV)(4) and reduced Mn(III)Mn(IV)(3) species. The calculated force constants for the Mn(IV)(4) species are f(r)(IV)= 3.15 mdyn/A, f(rOr) = 0.55 mdyn/A, and f(rMnr) = 0.20 mdyn/A. The force constants for the Mn(III)Mn(IV)(3) species are f(r)(IV)= 3.10 mdyn/A, f(r)(III)= 2.45 mdyn/A, f(rOr) = 0.40 mdyn/A, and f(rMnr) = 0.15 mdyn/A. This study provides insights for the identification of Mn-O modes in the IR spectra of the photosynthetic oxygen-evolving complex during its catalytic cycle.

Adamantane↗

PubMed2004

Femtosecond study of Cu(H(2)O) dynamics.

The short-time nuclear dynamics of Cu(H(2)O) is investigated using femtosecond photodetachment-photoionization spectroscopy and time-dependent quantum wave packet calculations. The Cu(H(2)O) dynamics is initiated in the electronic ground state of the complex by electron photodetachment from the Cu(-)(H(2)O) complex, where hydrogen atoms are oriented toward Cu. Several time-resolved resonant multiphoton ionization schemes are used to probe the ensuing reorientation and dissociation. Immediately following photodetachment, the neutral complex is far from its minimum energy geometry and possesses an internal energy comparable to the Cu-H(2)O dissociation energy and undergoes both large-amplitude H(2)O motion and dissociation. Dissociation is observed to occur on three distinct time scales: 0.6, 8, and 100 ps. These results are compared to the results of time-dependent J=0 wave packet calculations, propagating the initial anion vibrational wave functions on the ground-state potential of the neutral complex. An excellent agreement is obtained between the experimental results and the ionization signals derived from the calculated probability amplitudes. Related experiments and calculations are carried out on the Cu(D(2)O) complex, with results very similar to those of Cu(H(2)O).

Computer Simulation↗

PubMed1989

Bis(benzenethiolato)nitrosyl [tris(3,5-dimethyl-1-pyrazolyl)hydroborato]-molybdenum(II) .

[Mo(C15H22BN6)(C6H5S)2(NO)], Mr = 641.5, monoclinic, P2(1)/n, a = 10.898 (1), b = 18.484 (2), c = 15.989 (2) A, beta = 109.81 (1) degree, V = 3030.2 A3, Z = 4, Dx = 1.41, Dm = 1.41 g cm-3, lambda(Mo K alpha) = 0.7173 A, mu = 5.9 cm-1, F(000) = 1320, T = 293 K, wR = 0.047 for 3997 observed reflections. In each complex, the Mo atom is six-coordinate, ligated by a terminal NO group, a tridentate pyrazolylborate ligand and two benzenethiolate ligands. The structure is compared with that of similar complexes and the Mo-S bonding is discussed.

Crystallization↗

PubMed1998

Preparative capillary zone electrophoresis in combination with off-line graphite furnace atomic absorption for the analysis of DNA complexes formed by a new aminocoumarine platinum (II) compound.

Calf thymus DNA was incubated in vitro with a new aminocoumarin platinum (II) complex in order to study its interaction with DNA. The platinated DNA was hydrolyzed enzymatically to the 5'-mononucleotide level using DNAase I and nuclease P1. Analysis of the DNA hydrolysate with capillary zone electrophoresis (CZE), using sample stacking, revealed the presence of unhydrolyzed oligonucleotides in the platinated DNA. A homemade system, using only some plastic pipet tips, was constructed to collect the oligonucleotide fraction during CZE analysis. The platinum content of this fraction was determined using graphite furnace atomic absorption with Zeeman background correction. This system proved to be a useful tool to detect platinated DNA species (with a quantifiable detection limit for the detection of platinum of 0.78 ng). Subsequent gel filtration experiments confirmed the presence of high molecular weight oligonucleotides that were platinated. This was proven by reversal of the platination using thiourea and subsequent enzymatic hydrolysis to 5'-mononucleotides.

Animals↗

PubMed2000

Collisions between metastable hydrogen atoms at thermal energies

The complex interaction potentials arising in the approach of two metastable hydrogen 2s atoms are calculated and the cross sections for ionization, excitation transfer, and elastic scattering are predicted. The measured cross section for associative ionization at E = 4.1 meV equals 2x10(-15) cm (2). We calculate a total ionization cross section of 2x10(-13) cm (2), varying as E(-2/3) at higher energies. Thus it appears that dissociative ionization is the major ionization channel. We find also that double excitation transfer into two excited H(2p) atoms is still more probable with the large cross section of 9x10(-12) cm (2) at E = 4.1 meV varying as E(-1/2) at higher energies. The detection of the resulting Lyman alpha photons would provide a diagnostic test of our predictions.

Journal Article↗

PubMed1992

Crystal structure of papain-succinyl-Gln-Val-Val-Ala-Ala-p-nitroanilide complex at 1.7-A resolution: noncovalent binding mode of a common sequence of endogenous thiol protease inhibitors.

Succinyl-Gln-Val-Val-Ala-Ala-p-nitroanilide corresponding to a common sequence of endogenous thiol protease inhibitors is a noncompetitive reversible inhibitor of papain. In order to elucidate the binding mode of the inhibitor at the atomic level, its complex with papain was crystallized at ca. pH 7.0 using the hanging drop method, and the crystal structure was analyzed at 1.7-A resolution. The crystal has space group P2(1)2(1)2(1), with a = 43.09, b = 102.32, c = 49.69 A, and Z = 4. A total of 47,215 observed reflections were collected on the imaging plates using the same single crystal, and 19,833 unique reflections with Fo > sigma (Fo) were used for structure determination and refinement. The papain structure was determined by use of the atomic coordinates of papain previously reported, and then refined by the X-PLOR program. The inhibitor molecule was located on a difference Fourier map and fitted into the electron density with the aid of computer graphics. The complex structure was finally refined to R = 19.6% including 118 solvent molecules. The X-ray analysis of the complex crystal shows that the inhibitor is located at the R-domain side, not in the center of the binding site created by the R- and L-domains of papain. Such a binding mode of the inhibitor explains well the biological behavior that the inhibitor exhibits against papain. Comparison with the structure of papain-stefin B complex indicates that the structure of the Gln-Val-Val-Ala-Gly sequence itself is not necessarily the essential requisite for inhibitory activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1989

Crystals of wild-type, mutated, derivatized and complexed 50 S ribosomal subunits from Bacillus stearothermophilus suitable for X-ray analysis.

Three-dimensional single crystals of wild-type and mutated 50 S ribosomal subunits from Bacillus stearothermophilus, as well as crystals of reconstituted subunits containing heavy-atom clusters and complexes of these subunits with tRNA and a short nascent polypeptide chain, were grown from polyethylene glycol in the presence of salts at low concentrations. Within experimental error, all these crystals are isomorphous, packed with monoclinic symmetry (C2) in unit cells of a = 300 A, b = 546 A, c = 377 (+/- 1%) A and beta = 112 degrees. Using synchrotron radiation at 85 to 100 K they diffract to 11 A resolution and can be irradiated for hours without disintegrating, so that a complete data set could be collected from a single crystal.

Geobacillus stearothermophilus↗

PubMed2004

Spectroscopic characterization of the oxo-transfer reaction from a bis(mu-oxo)dicopper(III) complex to triphenylphosphine.

The oxygen-atom transfer reaction from the bis(mu-oxo)dicopper(III) complex [Cu(III)(2)(mu-O)(2)(L)(2)](2+), where L =N,N,N',N' -tetraethylethylenediamine, to PPh(3) has been studied by UV-vis, EPR, (1)H NMR and Cu K-edge X-ray absorption spectroscopy in parallel at low temperatures (193 K) and above. Under aerobic conditions (excess dioxygen), 1 reacted with PPh(3), giving O=Ph(3) and a diamagnetic species that has been assigned to an oxo-bridged dicopper(II) complex on the basis of EPR and Cu K-edge X-ray absorption spectroscopic data. Isotope-labeling experiments ((18)O(2)) established that the oxygen atom incorporated into the triphenylphosphine oxide came from both complex 1 and exogenous dioxygen. Detailed kinetic studies revealed that the process is a third-order reaction; the rate law is first order in both complex 1 and triphenylphosphine, as well as in dioxygen. At temperatures above 233 K, reaction of 1 with PPh(3) was accompanied by ligand degradation, leading to oxidative N-dealkylation of one of the ethyl groups. By contrast, when the reaction was performed in the absence of excess dioxygen, negligible substrate (PPh(3)) oxidation was observed. Instead, highly symmetrical copper complexes with a characteristic isotropic EPR signal at g= 2.11 were formed. These results are discussed in terms of parallel reaction channels that are activated under various conditions of temperature and dioxygen.

Journal Article↗

PubMed2003

Sampling and convergence in free energy calculations of protein-ligand interactions: the binding of triphenoxypyridine derivatives to factor Xa and trypsin.

The binding of a set of 10 triphenoxypyridine derivatives to two serine proteases, factor Xa and trypsin, has been used to analyze factors related to sampling and convergence in free energy calculations based on molecular dynamics simulation techniques. The inhibitors investigated were initially proposed as part of the Critical Assessment of Techniques for Free Energy Evaluation (CATFEE) project for which no experimental results nor any assessment of the predictions submitted by various groups have ever been published. The inhibitors studied represent a severe challenge for explicit free energy calculations. The mutations from one compound to another involve up to 19 atoms, the creation and annihilation of net charge and several alternate binding modes. Nevertheless, we demonstrate that it is possible to obtain highly converged results (+/- 5-10 kJ/mol) even for such complex multi-atom mutations by simulating on a nanosecond time scale. This is achieved by using soft-core potentials to facilitate the creation and deletion of atoms and by a careful choice of mutation pathway. The results show that given modest computational resources, explicit free energy calculations can be successfully applied to realistic problems in drug design.

Binding Sites↗

PubMed2006

Water formation on Pt and Pt-based alloys: a theoretical description of a catalytic reaction.

In the past, the modeling of catalytic processes was limited by the size and complexity of the systems involved. However, the enormous progress in both computer power and theoretical methods has made computational modeling a valuable tool in increasing our knowledge of catalytic reactions on the atomic scale. While complex reactions can be studied by dividing the overall reaction into a series of steps calculable by quantum mechanics, the combination with methods appropriate for larger time and length scales enables the gap between these regimes to be bridged. This provides a more realistic modeling of the experimental system and allows important environmental effects such as solvation to be taken into account. In this Minireview we describe some of the main theoretical methodologies that are used to study catalytic properties and reactions on surfaces. Using these methods, we study the seemingly simple reaction of water formation out of hydrogen and oxygen on Pt and Pt/Ni alloy catalysts. To provide a more realistic description we also discuss the interesting effects determined by hydrating the system or using alloy nanoparticles rather than extended surfaces.

Journal Article↗

PubMedDate not supplied

[Effect of platinum and palladium compounds on mitochondrial enzymatic systems].

Effect of platinum and palladium complexes on respiration and ATPase activity in bovine heart tissue as well as on respiration of submitochondrial particles was studied. The highest inhibitory activity was exhibited by the complexes of platinum and palladium with pi-ligands in internal coorhdinational sphere such as ethylene-C H4, norbornadiene-C7H8 and allyl-C3H5. The electron density at the central atom of the complex was not responsible for the inhibitory affect of platinum and palladium on mitochondria.

Adenosine Triphosphatases↗

PubMed1996

Characterization of vectors for gene therapy formed by self-assembly of DNA with synthetic block co-polymers.

Cationic polymers can self-assemble with DNA to form polyelectrolyte complexes capable of gene delivery, although biocompatibility of the complexes is generally limited. Here we have used A-B type cationic-hydrophilic block co-polymers to introduce a protective surface hydrophilic shielding following oriented self-assembly with DNA. Block co-polymers of poly(ethylene glycol)-poly-L-lysine (pEG-pLL) and poly-N-(2-hydroxypropyl)methacrylamide-poly(trimethylammonioethyl methacrylate chloride) (pHPMA-pTMAEM) both show spontaneous formation of complexes with DNA. Surface charge measured by zeta potential is decreased compared with equivalent polycation-DNA complexes in each case. Atomic force microscopy shows that pHPMA-pTMAEM/DNA complexes are discrete spheres similar to those formed between DNA and simple polycations, whereas pEG-pLL/DNA complexes adopt an extended structure. Biological properties depend on the charge ratio of formation. At optimal charge ratio, pEG-pLL/DNA complexes show efficient transfection of 293 cells in vitro, while pHPMA-pTMAEM/DNA complexes are more inert. Both block co-polymer-DNA complexes show only limited cytotoxicity. Careful selection of block co-polymer structure can influence the physicochemical and biological properties of the complexes and should permit design of materials for specific applications, including targeted delivery of genes in vivo.

Cell Survival↗