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PubMedDate not supplied

[Phosphorescence of octaethylchlorine, isobacteriooctaethylchlorine and their metal complexes].

The phosphorescence of dihydrooctaethylporphin (octaethylchlorin or OEC), of its complexes with magnesium, zinc, copper and palladium, and of zinc and palladium complexes of isobacteriooctaethylchlorin (5,6,7,8-tetrahydrooctaethylporphin with adjacent hydrogenated pyrrole rings or THOEP-ADJ) has been investigated. The phosphorescence spectra and phosphorescence excitation spectra as well as the ratio of fluorescence and phosphorescence yields and the triplet state lifetume have been measured. It has been shown that the singlet-triplet interval is about 4100 cm-1 for OEC complexes and about 4300 cm-1 for THOEP-ADJ complexes, and depends wealky on the nature of the metal atom forming the complex. The triplet level position of chlorophyll alpha is discussed. It is concluded that the maximum of chlorophyll alpha phosphorescence spectrum must be located at 895 nm.

Copper↗
PubMedDate not supplied

[Computer analysis of the spatial structure of the amphotericin channel].

Energy of Amphotericin B cholesterol complex in a membrane was calculated by the method of atom--atomic potentials. The complex is shown to have two stable states. One of them is stabilized by electrostatic interactions between charged groups of neighbouring antibiotic molecules due to a decline of the molecules to the pore radius. Another state with radial orientation of antibiotic molecules and smaller pore diameter is stabilized mainly by van-der-Waals forces. A conclusion is made that transitions between open and closed states may result from small shifts and turn of all the antibiotic molecules in the complex.

Amphotericin B↗
PubMed2004

Structure of the dimeric PufX-containing core complex of Rhodobacter blasticus by in situ atomic force microscopy.

We have studied photosynthetic membranes of wild type Rhodobacter blasticus, a closely related strain to the well studied Rhodobacter sphaeroides, using atomic force microscopy. High-resolution atomic force microscopy topographs of both cytoplasmic and periplasmic surfaces of LH2 and RC-LH1-PufX (RC, reaction center) complexes were acquired in situ. The LH2 is a nonameric ring inserted into the membrane with the 9-fold axis perpendicular to the plane. The core complex is an S-shaped dimer composed of two RCs, each encircled by 13 LH1 alpha/beta-heterodimers, and two PufXs. The LH1 assembly is an open ellipse with a topography-free gap of approximately 25 A. The two PufXs, one of each core, are located at the dimer center. Based on our data, we propose a model of the core complex, which provides explanation for the PufX-induced dimerization of the Rhodobacter core complex. The QB site is located facing a approximately 25-A wide gap within LH1, explaining the PufX-favored quinone passage in and out of the core complex.

Benzoquinones↗
PubMed2002

Hydrogen atom abstraction by a chromium IV oxo complex derived from O2.

The Cr(III) hydroxide [TptBu,MeCr(OH)(pz'H)] BARF (1) is produced by reaction of [TptBu,MeCr(pz'H)]BARF with [TptBu,MeCr(O2)(pz'H)]BARF or oxygen atom donors ONMe3 or PhIO in Et2O. However, reaction of [TptBu,MeCr(pz'H)]BARF with PhIO in pure CH2Cl2 yields the Cr(IV) oxo complex [TptBu,MeCr(O)(pz'H)]BARF (2). 2 abstracts hydrogen atoms from organic molecules with weak C-H bonds to form 1. Both 1 and 2 have been structurally characterized.

Journal Article↗
PubMed2001

Kinetics and mechanisms of catalytic oxygen atom transfer with oxorhenium(V) oxazoline complexes.

The rhenium(V) monooxo complexes (hoz)2Re(O)Cl (1) and [(hoz)2Re(O)(OH2)][OTf] (2) have been synthesized and fully characterized (hoz = 2-(2'-hydroxyphenyl)-2-oxazoline). A single-crystal X-ray structure of 2 has been solved: space group = P1, a = 13.61(2) A, b = 14.76(2) A, c = 11.871(14) A, alpha = 93.69(4) degrees, beta = 99.43(4) degrees, gamma = 108.44(4) degrees, Z = 4; the structure was refined to final residuals R = 0.0455 and Rw = 0.1055. 1 and 2 catalyze oxygen atom transfer from aryl sulfoxides to alkyl sulfides and oxygen-scrambling between sulfoxides to yield sulfone and sulfide. Superior catalytic activity has been observed for 2 due to the availability of a coordination site on the rhenium. The active form of the catalyst is a dioxo rhenium(VII) intermediate, [Re(O)2(hoz)2]+ (3). In the presence of sulfide, 3 is rapidly reduced to [Re(O)(hoz)2]+ with sulfoxide as the sole organic product. The transition state is very sensitive to electronic influences. A Hammett correlation plot with para-substituted thioanisole derivatives gave a reaction constant rho of -4.6 +/- 0.4, in agreement with an electrophilic oxygen transfer from rhenium. The catalytic reaction features inhibition by sulfides at high concentrations. The equilibrium constants for sulfide binding to complex 2 (cause of inhibition), K2 (L x mol(-1)), were determined for a few sulfides: Me2S (22 +/- 3), Et2S (14 +/- 2), and tBu2S (8 +/- 2). Thermodynamic data, obtained from equilibrium measurements in solution, show that the S=O bond in alkyl sulfoxides is stronger than in aryl sulfoxides. The Re=O bond strength in 3 was estimated to be about 20 kcal x mol(-1). The high activity and oxygen electrophilicity of complex 3 are discussed and related to analogous molybdenum systems.

Catalysis↗
PubMed2000

Atomic force microscopy with carbon nanotube probe resolves the subunit organization of protein complexes.

Among many scanning probe microscopies, atomic force microscopy (AFM) is a useful technique to analyse the structure of biological materials because of its applicability to non-conductors in physiological conditions with high resolution. However, the resolution has been limited to an inherent property of the technique; tip effect associated with a large radius of the scanning probe. To overcome this problem, we developed a carbon nanotube probe by attaching a carbon nanotube to a conventional scanning probe under a well-controlled process. Because of the constant and small radius of the tip (2.5-10 nm) and the high aspect ratio (1:100) of the carbon nanotube, the lateral resolution has been much improved judging from the apparent widths of DNA and nucleosomes. The carbon nanotube probes also possessed a higher durability than the conventional probes. We further evaluated the quality of carbon nanotube probes by three parameters to find out the best condition for AFM imaging: the angle to the tip axis; the length; and the tight fixation to the conventional tip. These carbon nanotube probes, with high vertical resolution, enabled us to clearly visualize the subunit organization of multi-subunit proteins and to propose structural models for proliferating cell nuclear antigen and replication factor C. This success in the application of carbon nanotube probes provides the current AFM technology with an additional power for the analyses of the detailed structure of biological materials and the relationship between the structure and function of proteins.

Carbon↗
PubMed2002

Syntheses and structures of P-anilino-P-chalcogeno- and P-anilino-P-iminodiazasilaphosphetidines and their group 12 and 13 metal compounds.

The P-anilino-P-chalcogeno(imino)diazasilaphosphetidines [Me(2)Si(mu-N(t)Bu)(2)P=E(NHPh)] (E = O (3), S (4), Se (5), N-p-tolyl (6)) were synthesized by oxidizing the P-anilinodiazasilaphosphetidine [Me(2)Si(N(t)Bu)(2)P(NHPh)] (2) with cumene hydroperoxide, sulfur, selenium, and p-tolyl azide, respectively. The lithium salt of 4 reacted with thallium monochloride to produce ([Me(2)Si(mu-N(t)Bu)(2)P=S(NPh)-kappaN-kappaS]Tl)(7), which features a two-coordinate thallium atom. Treatment of 4-6 with AlMe(3) gave the monoligand dimethylaluminum complexes ([Me(2)Si(mu-N(t)Bu)(2)P=E(NPh)-kappaN-kappaE]AlMe(2)) (E = S (8), Se (9), N-p-tolyl (10)), respectively. In these complexes the aluminum atom is tetrahedrally coordinated by one chelating ligand and two methyl groups, as a single-crystal X-ray analysis of 8 showed. A 2 equiv amount of 4-6 reacted with diethylzinc to produce the homoleptic diligand complexes ([Me(2)Si(mu-N(t)Bu)(2)P=E(NPh)-kappaN-kappaE](2)Zn)(E = S (11), Se (12), N-p-tolyl (13)). A crystal-structure analysis of 11 revealed a linear tetraspirocycle with a tetrahedrally coordinated, central zinc atom.

Journal Article↗
PubMed2002

Evolution of gas-filled nanocracks in crystalline solids.

In this work, the evolution of gas-filled cracks under gas implantation and subsequent annealing is studied on the basis of an elastic continuum approach. The observed growth limitation of He-filled nanocracks in SiC is attributed to their stabilization by the formation of circular dislocation dipoles. The formation and Ostwald ripening of bubble-loop complexes at elevated temperatures is modeled in terms of gas atom exchange between such complexes coupled with local matrix atom exchange between bubbles and loops of the same complex. The scaling laws derived for the time dependence of bubble and loop sizes are found to be in good agreement with experimental data.

Journal Article↗
PubMed1996

Atomic force microscopic analysis of the influence of the molecular weight of poly(L)lysine on the size of polyelectrolyte complexes formed with DNA.

We are developing self-assembling micellar vehicles based on multifunctional block copolymers as well-defined synthetic vehicles suitable for safe in vivo delivery of DNA. As a first stage, DNA expression vectors (6 kb) were condensed with poly(L)lysine of different molecular weights (3970-224 500) to form polyelectrolyte complexes and analysed by atomic force microscopy (AFM). Discrete complexes were formed in every case, although the highest molecular weight poly(L)lysine preparation (224 500) produced large complexes with significant polydispersity (diameters ranging from 120-300 nm), while the smallest poly(L)lysine (3970) produced more homogeneous complexes with diameters ranging from 20-30 nm. Poly (L)lysine preparations of molecular weight 53 700 and 23 800 produced complexes of intermediate size and poly-dispersity. The mean volumes of the complexes formed using poly(L)lysine 224 500 and 3970 were 606 000 nm3 and 3700 nm3, respectively. Polyelectrolyte complexes formed using low molecular weight poly(L)lysine also showed significantly decreased cytotoxicity. Given restrictions of access to many cellular targets and the need for good biocompatibility, synthetic vectors based on DNA condensed with low molecular weight polycations may be more appropriately developed for general use.

Cell Survival↗
PubMed1996

Two New Antiferromagnetic Nickel(II) Complexes Bridged by Azido Ligands in the Cis Position. Effect of the Counteranion on the Crystal Structure and Magnetic Properties.

Two new nickel(II) end-to-end azido-bridged compounds, cis-catena-[NiL(2)(&mgr;-N(3))](n)()(ClO(4))(n)().nH(2)O (1) and [Ni(2)L(4)(&mgr;-N(3))(2)](PF(6))(2) (2), were synthesized and characterized; L is 2-(aminoethyl)pyridine. The crystal structures of 1 and 2 were solved. Complex 1: monoclinic system, space group P2(1)/a, a = 8.637(2) Å, b = 18.9995(7) Å, c = 12.3093(7) Å, beta = 105.92(2) degrees, Z = 4. Complex 2: triclinic system, space group P&onemacr;, a = 9.139(7) Å, b = 10.124(3) Å, c = 12.024(2) Å, alpha = 70.407(14) degrees, beta = 84.19(2) degrees, gamma = 67.67(4) degrees, Z = 1. In the two complexes the nickel atom is situated in a similarly distorted octahedral environment. The two complexes are different; 1 is a one-dimensional helicoidal complex with the two L ligands and the two end-to-end azido bridges in a cis arrangement while complex 2 is a dinuclear system with two end-to-end azido bridges, indicating the extreme importance of the counteranion present (ClO(4)(-) for 1 and PF(6)(-) for 2). The magnetic properties of the two compounds were studied by susceptibility measurements vs temperature. The chi(M) vs T plot for 1 shows the shape for a weakly antiferromagnetically coupled nickel(II) one-dimensional complex without a maximum until 4 K. In contrast, for complex 2 the shape of the chi(M) vs T curve shows a maximum near 40 K, indicating medium antiferromagnetic coupling. From the spin Hamiltonian -J(ij)()S(i)()S(j)(), J values for 1 and 2 were less than -1 and -29.1 cm(-)(1), respectively. The magnetic behavior for 1 and 2 may be explained in terms of the overlap between magnetic orbitals, taking into account the torsion of the Ni(II) atoms and azido-bridging ligands in the two structures.

Journal Article↗
PubMed2005

Atomic model of the E. coli membrane-bound protein translocation complex SecYEG.

The Sec complex forms the core of a conserved machinery transporting proteins across or into membranes. In Escherichia coli SecYEG is active as an oligomer, but the structure predicts that the protein-conducting channel is formed by the monomer. A homology model of the E.coli complex was built using the atomic structure of Methanococcus jannaschii SecYEbeta. Another structure of the membrane-bound dimer was then determined by fitting the homology model to an 8A map of SecYEG determined by electron microscopy. We found that the substrate-binding site of the dimer has opened slightly and the plug domain moved toward the outside. This new position retains the channel in a closed state. These differences partially reflect the movements that have been proposed to occur during channel gating. Further opening of the substrate-binding pocket to bind and release bound substrate and displacement of the plug during secretion, presumably rely on the action of the partner proteins. The contacts arising at the dimer interface in the environment of the lipid bilayer may have activated the assembly.

Cryoelectron Microscopy↗
PubMed2003

[Kinetics and mechanism of oxygen atom transfer reactions between iron (II) isocyanide complexes and (CH3)3NO].

Kinetics and mechanism of reactions between iron (II) isocyanide complexes [FeL5 (CN)] Br (1, L = -CNCH2Ph); trans- [FeL4 (CN)2] 2, L = -CNCH2Ph) and oxygen atom transfer agent (CH3)3NO have been investigated in dichloromethane by UV-visible and Infrared spectrophotometers at different temperatures. The results revealed that the reactions proceed with second order and the rate law is rate = k2 [isocyanide complex] x [(CH3)3NO]. delta S not equal to and delta H not equal to for the reaction between complex 1 and (CH3)3NO are -25.34 +/- 1.67 cal.(mol.K)-1 and 12.71 +/- 0.49 kcal.mol-1 respectively. However, there is no reaction between 2 and (CH3)3NO. The reaction mechanism was proposed and the factors affecting the reaction rate were also discussed.

Bromides↗
PubMed2006

Investigation of silver binding to polyamidoamine (PAMAM) dendrimers by ESI tandem mass spectrometry.

Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was used to probe the binding of silver ions and reduced silver species with polyamidoamine generation 1 amine-terminated (PAMAMG1NH2) and generation 2 hydroxyl-terminated (PAMAMG2OH) dendrimers. At Ag(+)/PAMAMG2OH molar ratios of </=1, 1:1 complexes are observed, while at ratios >1, 2:1 and low abundance 3:1 complexes emerge. Similar results were observed for PAMAMG1NH2. The collisional activated dissociation (CAD) patterns of the dendrimer ions are characterized by losses of amidoamine branches resulting largely from hydrogen migration and cleavage reactions. Ag+/dendrimer complexes are characterized by the loss of a dendrimer branch from the complex, with the silver ion remaining bound to a dendrimer fragment. When the Ag+-bound dendrimer complexes are reduced by hydrazine, low abundance complexes, whose m/z values are consistent with ones containing zerovalent silver species, are observed in the mass spectra. Complexes with three silver atoms are observed in the spectrum containing PAMAMG1NH2, and complexes with four and five silver atoms are observed with PAMAMG2OH. The CAD fragmentation patterns of the complexes formed after the silver reduction are different than those observed for complexes containing one silver ion and are characterized by the ejection of all silver species, possibly as a cluster, leaving the intact dendrimer ion. Experiments with Cu+, Cu2+, and Pt2+ binding to PAMAMG2OH were also done, but reduced metal clusters were not observed in the mass spectra after the addition of hydrazine.

Journal Article↗
PubMed1997

Ferrocene-Based Tris(1-pyrazolyl)borates: A New Approach to Heterooligometallic Complexes and Organometallic Polymers Containing Transition Metal Atoms in the Backbone.

Starting from mono- and bifunctional ferrocene-based tris(1-pyrazolyl)borates, a novel route to oligonuclear complexes is presented, which incorporates transition metal centers differing substantially in their chemical nature. Both binuclear organometallics FcB(pz)(3)ML(n)() (Fc: ferrocenyl. pz: 1-pyrazolyl. ML(n)(): Tl, 1-Tl; Mo(CO)(3)Li, 1-MoLi; Mo(CO)(2)(eta(3)-methylallyl), 1-Mo; ZrCl(3), 1-Zr) and trinuclear complexes 1,1'-fc[B(pz)(3)ML(n)()](2) (fc: ferrocenylene. ML(n)(): Tl, 2-Tl; Mo(CO)(3)Li, 2-MoLi; Mo(CO)(2)(eta(3)-methylallyl), 2-Mo) have been prepared. The trinuclear compound [FcB(4-SiMe(3)pz)(3)](2)Fe, 1-FeSi, has been investigated as a model system for organometallic coordination polymers, consisting of the bifunctional linker 1,1'-fc[B(pz)(3)](2)(2)(-) and transition metal ions M(n)()(+). X-ray crystallography shows 1-Tl to establish a polymeric structure in the solid state, while 1-Mo features the usual tridentate coordination mode of the scorpionate ligand (C(25)H(25)BFeMoN(6)O(2); a = 8.756(1) Å, b = 12.154(1) Å, c = 12.927(1) Å, alpha = 105.26(1) degrees, beta = 102.29(1) degrees, gamma = 105.09(1) degrees; triclinic space group P&onemacr;; Z = 2). With the exception of 1,2-Tl, the anodic oxidation of the ferrocene moiety is generally reversible; cyclic voltammetry measurements indicate the two Mo centers in 2-Mo and the two Fc moieties in 1-FeSi to be noncommunicating.

Journal Article↗
PubMed2006

Crystal chemical information to be obtained from the bond-number equality concept.

Based on the bond-number equality concept an equation is derived for anion complexes of normal valence compounds with triangularly and/or tetrahedrally coordinated central atoms and anions having one, two, three and four bonds to central atoms: %delta = 4 - (n/m') x [2 - %A[1] + %A[3] + 2 x %A[4]]. %Delta is the ratio of the number of central atoms with triangular anion coordination to the sum of all central atoms in the anion complex. n/m' is the ratio of the number of all A anions to the number of all central atoms C' in the anion complex. %A[1] is the ratio of the number of anions with one bond to a central atom to the sum of all anions in the anion complex. %A[3] and %A[4] are defined accordingly. The equation can be used to formulate the possible crystal chemical formulae, which are characterized by partitions of central atoms and anions according to their bond numbers. Nitridosilicates and selected oxoborates are treated as examples of applications of the equation.

Journal Article↗
PubMed2006

Hydrogen atom abstraction by a mononuclear ferric hydroxide complex: insights into the reactivity of lipoxygenase.

The lipoxygenase mimic [Fe(III)(PY5)(OH)](CF3SO3)2 is synthesized from the reaction of [Fe(II)(PY5)(MeCN)](CF3SO3)2 with iodosobenzene, with low-temperature studies suggesting the possible intermediacy of an Fe(IV) oxo species. The Fe(III)-OH complex is isolated and identified by a combination of solution and solid-state methods, including EPR and IR spectroscopy. [Fe(III)(PY5)(OH)](2+) reacts with weak X-H bonds in a manner consistent with hydrogen-atom abstraction. The composition of this complex allows meaningful comparisons to be made with previously reported Mn(III)-OH and Fe(III)-OMe lipoxygenase mimics. The bond dissociation energy (BDE) of the O-H bond formed upon reduction to [Fe(II)(PY5)(H2O)]2+ is estimated to be 80 kcal mol(-1), 2 kcal mol(-1) lower than that in the structurally analogous [Mn(II)(PY5)(H2O)]2+ complex, supporting the generally accepted idea that Mn(III) is the thermodynamically superior oxidant at parity of coordination sphere. The identity of the metal has a large influence on the entropy of activation for the reaction with 9,10-dihydroanthracene; [Mn(III)(PY5)(OH)]2+ has a 10 eu more negative DeltaS++ value than either [Fe(III)(PY5)(OH)]2+ or [Fe(III)(PY5)(OMe)]2+, presumably because of the increased structural reorganization that occurs upon reduction to [Mn(II)(PY5)(H2O)]2+. The greater enthalpic driving force for the reduction of Mn(III) correlates with [Mn(III)(PY5)(OH)]2+ reacting more quickly than [Fe(III)(PY5)(OH)]2+. Curiously, [Fe(III)(PY5)(OMe)]2+ reacts with substrates only about twice as fast as [Fe(III)(PY5)(OH)]2+, despite a 4 kcal mol(-1) greater enthalpic driving force for the methoxide complex.

Anthracenes↗
PubMed2004

Ba2AuTl7: an intermetallic compound with a novel condensed structure.

In this novel motif, thallium and gold atoms define a complex three-dimensional [AuTl(7)] polyanion in which the barium atoms fill pentagonal cages that are part of highly condensed infinite channels. Relativistic effects appear to be significant in the short Au-Tl and Tl-Tl distances and the bonding by the more electronegative gold.

Journal Article↗