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At least 1,225 records · Page 68Linked to original sources
PubMed2005

"Heavy fluorous" cyclopentadienes and cyclopentadienyl complexes with three to five ponytails: facile syntheses from polybromocyclopentadienyl complexes, phase properties, and electronic effects.

The reactions between [(eta5-C5H(5-x)Br(x))M(CO)3] (M = Re, Mn; x = 1, 3, 4, 5) and [IZn[(CH2)(n)R(f8)]] (n = 2, 3; R(f8) = (CF2)7CF3) in the presence of [Cl2PdL2] catalysts give the title complexes [[eta5-C5H(5-x)[(CH2)(n)R(f8)]x]M(CO)3]. In the case of x = 5, the major product is actually [[eta5-C5H[(CH2)(n)R(f8)]4]M(CO)3], in which one of the bromides has been substituted by hydride. Minor amounts of multiple hydride substitution products are formed, all of them readily separable on fluorous silica gel. Irradiation of the manganese complexes in CF3C6H5/MeOH/ether gives uncoordinated cyclopentadienes, which can be deprotonated and reattached to other metals. Partition coefficients have been measured (CF3C6F11/toluene): complexes with three or more ponytails are highly fluorophilic, with values of > 99.8: < 0.2. The IR [symbol: see text]CO bands have been used to probe the inductive effects of the ponytails at the metal centers.

Journal Article↗
PubMed1995

Theory of the mobility-shift assay of nonspecific protein-DNA complexes governed by conditional probabilities: the HU:DNA complex.

Complexes of an 88 bp DNA and the HU protein were studied by both experimental and theoretical electrophoretic mobility-shift analyses. Experimental analysis defined the stoichiometry of binding and estimated an apparent intrinsic dissociation constant (Kd = 1 to 3 x 10(-7) M) for the HU:DNA complexes. The theory of conditional probabilities was applied to the binding of HU to DNA in order to fix the initial equilibrium composition of mixtures to be assayed theoretically by the mobility-shift procedure. Electrophoretic mobility-shift patterns were obtained by numerical solution of a set of simultaneous transport-reaction equations, in which the chemical kinetic term is formulated in terms of dissociation of the different DNA:HU complexes in gel cages. The computed patterns simulated the experimental patterns describing the titration of a fixed concentration of an 88 bp DNA fragment with dimeric HU. These insightful results provide guidelines for interpretation of the electrophoretic behavior of systems in which a ligand binds nonspecifically to DNA. In particular, the narrow unresolved zone observed both experimentally and theoretically beyond 50-60% saturation is a reaction zone characteristic of noncooperative ligand-binding governed by conditional probabilities. The discrepancy between the theoretically assigned and experimental values of the intrinsic binding constant is attributed to an HU-induced change in the conformation of DNA.

Bacterial Proteins↗
PubMed1993

Complexation of moricizine with nicotinamide and evaluation of the complexation constants by various methods.

The solubility of the antiarrhythmic drug moricizine at physiologic pH is very low. Precipitation after rapid intravenous injection of the hydrochloride salt of moricizine could be a concern. The enhancement of solubility of moricizine near physiologic pH via complexation with nicotinamide was examined as a potential solubilization technique. The studies were performed in pH 6 and pH 7 phosphate buffers at 25 degrees C by the phase solubility method. Moricizine formed 1:1 and 1:2 complexes with nicotinamide at pHs of 6 and 7. The complexation constants K1:1 and K1:2 were estimated by a previously described scheme and equation and compared with those obtained by fitting a line and a parabola to the equations derived from the scheme for both the approximate and exact solutions. The data were best represented by a parabolic regression analysis of the exact solution of the derived equation with values for K1:1 and K1:2 at pH 6 of 16.60 and 0.93 M-1, respectively, and at pH 7 of 7.70 and 5.41 M-1, respectively.

Chromatography, High Pressure Liquid↗
PubMed2002

Copper-psychoactive drug complexes: a voltammetric approach to complexation by 1,4-benzodiazepines.

Copper complexation by the 1,4-benzodiazepines medazepam, diazepam, flurazepam, nitrazepam, and clonazepam was investigated using differential pulse polarography and cyclic voltammetry at a mercury electrode in 0.10 M KNO3 and pH 7.0 +/- 0.1. Because the 1,4-benzodiazepines are easily reduced at a mercury electrode through the two-electron reduction of the 4,5-azomethine functional group, copper reduction, as well as that of the ligands, was analyzed under varying experimental conditions. In most situations adsorption phenomena occurred and their influence on voltammetric signals had to be carefully analyzed. The voltammetric behavior was then interpreted in terms of complex formation. The results showed that all benzodiazepines can act as ligands toward copper(II) ions, forming 1:1 and 1:2 complexes with similar stabilities. The stoichiometric acidity constants of the benzodiazepines under study were also determined by potentiometric titration in water-ethanol medium and 0.10 M KNO3 and then extrapolated to 0% concentration of ethanol.

Benzodiazepines↗
PubMed2001

Does learning a complex task have to be complex? A study in learning decomposition.

Many theories of skill acquisition have had considerable success in addressing the fine details of learning in relatively simple tasks, but can they scale up to complex tasks that are more typical of human learning in the real world? Some theories argue for scalability by making the implicit assumption that complex tasks consist of many smaller parts, which are learned according to basic learning principles. Surprisingly, there has been rather sparse empirical testing of this crucial assumption. In this article, we examine this assumption directly by decomposing the learning in the Kanfer-Ackerman Air-Traffic Controller Task (Ackerman, 1988) from the learning at the global level all the way down to the learning at the keystroke level. First, we reanalyze the data from Ackerman (1988) and show that the learning in this complex task does indeed reflect the learning of smaller parts at the keystroke level. Second, in a follow-up eye-tracking experiment, we show that a large portion of the learning at the keystroke level reflects the learning even at a lower, i.e., attentional level.

Attention↗
PubMed1997

The first glimpse of a complex of nitrogenase component proteins by solution X-ray scattering: conformation of the electron transfer transition state complex of Klebsiella pneumoniae nitrogenase.

An essential feature of the mechanism of nitrogenase, the enzyme responsible for biological nitrogen fixation, is the formation of a transient electron transfer complex between the MoFe protein containing the active site at which N2 is reduced, and the Fe protein, which functions as a specific electron donor to the MoFe protein. We have obtained high quality solution X-ray scattering data using synchrotron X-rays of a stable putative electron transfer complex, (MoFe-protein)(Fe-protein.ADP.AIF4)2, of Klebsiella pneumoniae and used the model-independent approach based on the multipole expansion method to provide a stable and unique shape restoration at approximately 15 A resolution. The biological significance of this first molecular structure of a nitrogenase complex is discussed.

Azotobacter vinelandii↗
PubMed1975

Phosphopyridoxal complexes with histamine and histidine. (2) The influence of presumed complex on histidine decarboxylase activity in rat gastric mucosa.

It was found that in vitro, histidine and histamine form a complex compound with pyridoxal-5'-phosphate (PLP). The purpose of the present experiments was to find whether formation of this complex can influence histidine decarboxylase activity. It was found that excess PLP inhibits rat's gastric mucosa histidine decarboxylase activity in vitro. The inhibitory action of PLP depends on the histidine concentration and is independent on the amount of crude enzyme preparation. The histidine-PLP complex did not influence enzyme activity. The possible mechanisms of the inhibitory action of PLP on histidine decarboxylase activity are discussed.

Animals↗
PubMed1999

The effect of locally implanted complexes of adriamycin-hydroxyapatite complexes on tumor--study of a new alternative treatment for hepatic cancer.

A new targeting anticancer system was prepared by using hydroxyapatite particles (2 mm in diameter) as carrier material and adriamycin as anticancer agent. The adsorption and release properties of the complexes were assayed by fluorometry in vivo and in vitro and the curative effect on W-256 sarcoma of rat was observed. The results showed that one particle of hydroxyapatite could adsorb approximately 0.08 mg adriamycin and they can maintain a steady and slow release of adriamycin from hydroxyapatite for one month. When hydroxyapatite-adriamycin complexes were implanted into the liver of rat, liver adriamycin concentration at the implanted region was obviously higher than that achieved by injection of adriamycin solution. The locally implanted complexes obviously inhibited the growth of subcutaneous implanted tumor of rat, and increased the survival rate of rat with implanted liver tumor.

Animals↗
PubMed2006

Importance of the DsrMKJOP complex for sulfur oxidation in Allochromatium vinosum and phylogenetic analysis of related complexes in other prokaryotes.

In the phototrophic sulfur bacterium Allochromatium vinosum, sulfur of oxidation state zero stored in intracellular sulfur globules is an obligate intermediate during the oxidation of sulfide and thiosulfate. The proteins encoded in the dissimilatory sulfite reductase (dsr) locus are essential for the oxidation of the stored sulfur. DsrMKJOP form a membrane-spanning complex proposed to accept electrons from or to deliver electrons to cytoplasmic sulfur-oxidizing proteins. In frame deletion mutagenesis showed that each individual of the complex-encoding genes is an absolute requirement for the oxidation of the stored sulfur in Alc. vinosum. Complementation of the DeltadsrJ mutant using the conjugative broad host range plasmid pBBR1-MCS2 and the dsr promoter was successful. The importance of the DsrMKJOP complex is underlined by the fact that the respective genes occur in all currently sequenced genomes of sulfur-forming bacteria such as Thiobacillus denitrificans and Chlorobaculum tepidum. Furthermore, closely related genes are present in the genomes of sulfate- and sulfite-reducing prokaryotes. A phylogenetic analysis showed that most dsr genes from sulfide oxidizers are clearly separated of those from sulfate reducers. Surprisingly, the dsrMKJOP genes of the Chlorobiaceae all cluster together with those of the sulfate/sulfite-reducing prokaryotes, indicating a lateral gene transfer at the base of the Chlorobiaceae.

Bacterial Proteins↗
PubMed2004

Flutolanil and carboxin resistance in Coprinus cinereus conferred by a mutation in the cytochrome b560 subunit of succinate dehydrogenase complex (Complex II).

A gene that confers resistance to the systemic fungicide flutolanil was isolated from a mutant strain of the basidiomycete Coprinus cinereus. The flutolanil resistance gene was mapped to a chromosome of approximately 3.2 Mb, and a chromosome-specific cosmid library was constructed. Two cosmid clones that were able to transform a wild-type, flutolanil-sensitive, strain of C. cinereus to resistance were isolated from the library. Analysis of a subclone containing the resistance gene revealed the presence of the sdhC gene, which encodes the cytochrome b560 subunit of the succinate dehydrogenase (SDH) complex (Complex II) in the mitochondrial membrane. Comparison between the sdhC gene of a wild-type strain and that of a mutant strain revealed a single point mutation, which results in the replacement of Asn by Lys at position 80. Measurements of succinate-cytochrome c reductase activity in the transformants with mutant sdhC gene(s) suggest that flutolanil resistance of the fungus is caused by a decrease in the affinity of the SDH complex for flutolanil. This sdhC mutation also conferred cross-resistance against another systemic fungicide, carboxin, an anilide that is structurally related to flutolanil. In other organisms carboxin resistance mutations have been found in the genes sdhB and sdhD, but this is the first demonstration that a mutation in sdhC can also confer resistance. The mutant gene cloned in this work can be utilized as a dominant selectable marker in gene manipulation experiments in C. cinereus.

Amino Acid Sequence↗
PubMed2004

Delineation of complex chromosomal rearrangements: evidence for increased complexity.

There is an assumption of parsimony with regard to the number of chromosomes involved in rearrangements and to the number of breaks within those chromosomes. Highly complex chromosome rearrangements are thought to be relatively rare, with the risk for phenotypic abnormalities increasing as the number of chromosomes and chromosomal breaks involved in the rearrangement increases. We report here five cases of de novo complex chromosome rearrangements, each with a minimum of four breaks. Deletions were found in four cases, and in at least one case, a number of genes or potential genes might have been disrupted. This study highlights the importance of the detailed delineation of complex rearrangements, beginning with high-resolution chromosome analysis, and emphasizes the utility of fluorescence in situ hybridization in combination with the data available from the Human Genome Project as a means to delineate such rearrangements.

Abnormalities, Multiple↗
PubMed1997

Recombination in a balanced complex translocation of a mother leading to a balanced reciprocal translocation in the child. Review of 60 cases of balanced complex translocations.

We report an unusual case of a balanced reciprocal translocation with a recombinant chromosome which has arisen from a familial balanced complex translocation. Fluorescence in situ hybridization studies were essential for the identification of the breakpoints. A review of 60 cases of balanced complex translocations (BCT) has revealed three cases similar to ours. Carriers of BCT have a high risk of having spontaneous abortions or a child with an unbalanced karyotype. Certain types of balanced rearrangements involving an insertion can give rise to a simpler balanced translocation as a result of crossover. Our observations support the assumption that the chance that a de novo balanced complex translocation is associated with an abnormal phenotype increases with the number of breakpoints.

Abortion, Habitual↗
PubMed1985

Formation of alpha-tocopherol complexes with fatty acids. Nature of complexes.

Using ultraviolet spectrophotometry and 1H-NMR high-resolution spectroscopy, it has been demonstrated that the formation of alpha-tocopherol complexes with free fatty acids occurs via two types of interaction, namely formation of a hydrogen bond between the alpha-tocopherol chromanol nucleus hydroxyl and the carboxyl group of a fatty acid, and interaction of the fatty acid acyl chains with the chromanol nucleus methyl groups. The second interaction is significantly enhanced by an increase in the number of double bonds in the fatty acid molecule, which results in restriction of the molecular mobility of alpha-tocopherol. The proposed structural model of alpha-tocopherol-fatty acid complexes has been confirmed by the use of molecular models. It has been assumed that the efficiency of complex formation of natural tocopherols with fatty acids is correlated with their biological activity.

Fatty Acids↗
PubMed1984

Copper complexes at N- and C-site of ovotransferrin: quantitative determination and visible absorption spectrum of each complex.

Copper complexes at the two sites of ovotransferrin (TF) differed markedly in the rate of Cu release by EDTA. During the reaction, lambda max of the remaining Cu-Tf complex shifted to red side, while the difference spectrum of FenCu2-nTf vs. FenTf in which the N-site had been preferentially occupied with Fe had lambda max at blue side from that of Cu2Tf, 440 nm. From these results, the intrinsic spectrum for Cu-complex at each site was assigned: lambda max 450 nm for N- and 430 nm for C-site. The differences in the release rate and the spectrum can be used for the identification of the two domains of Tf and for the analysis of metal-binding behavior of each site.

Animals↗
PubMed1985

Hydrodynamic studies of a DNA-protein complex. Elongation of single stranded nucleic acids upon complexation with the gene 32 protein of phage T4 deduced from electric field-induced birefringence experiments.

Short DNA and RNA fragments complexed with the helix destabilizing protein of bacteriophage T4, GP32, have been studied in solution by electric birefringence and circular dichroism. The birefringence of the complexes is positive and the magnitude indicates that the DNA and RNA fragments become linear and rigid upon protein binding. The field free decay is biphasic. On the basis of a rigid rod approximation the slow relaxation time leads to a base-base distance along the helix axis in the complex from 4.3 to 5.6 A, an elongation of at least 50% compared to single-stranded DNA.

Birefringence↗
PubMed1977

Crossed immunoelectrophoresis as applied to studies on complex formation. The binding of heparin to antithrombin III and the antithrombin III--thrombin complex.

A two-dimensional immunoelectrophoretic method has been used to obtain information on the binding of heparin to purified antithrombin III and the antithrombin III--thrombin complex. The difference in mobility of the components in a gel containing heparin enables distinction between free and complexed forms of antithrombin III. The results obtained with purified preparations show that heparin is bound more strongly to antithrombin III than to the antithrombin III--thrombin complex. In plasma heparin is bound to several components, only a fraction being bound to antithrombin III. Several components containing antithrombin III are detectable in serum.

Animals↗
PubMed1988

Shape of the myosin head in the rigor complex. Three-dimensional image reconstruction of the actin-tropomyosin-heavy meromyosin complex.

The structure of the actin-tropomyosin-heavy meromyosin rigor complex was studied by image analysis of electron micrographs. The arrowhead of the rigor complex has a whisker-like structure with a dense turning point at the "barb" of the arrowhead. The neck region of the myosin head in the reconstructed three-dimensional image is present in the area corresponding to the dense point. It is concluded that at least one extra-thin area contributes to the neck region, and that the two heads in the heavy meromyosin molecule join a double helical rope beyond the end of the large head (G in this study). (This is different from previous interpretations). It is also concluded that the heavy meromyosin has a short bent part near the head/rod junction in the rigor complex.

Actins↗
PubMed1996

Experimental haemorrhage and blood component transfusion in humans: no change in plasma concentration of thrombin-antithrombin complex and plasmin-antiplasmin complex.

The influence of haemorrhage and blood transfusion on primary haemostasis, coagulation and fibrinolysis was investigated in ten healthy male volunteers. Acute loss of 10% of the blood volume did not give any significant alteration in thrombin- antithrombin III (TAT) complex and plasmin-alpha 2-antiplasmin (PAP) complex levels compared with a control series. The skin bleeding time with the Simplate II device was not altered after the 10% blood loss. Acute loss of 10% of blood volume followed by transfusion of packed red cells or stored plasma did not resulted in any significant change in bleeding time, TAT and PAP complex levels. It could be concluded that a controlled haemorrhage does not give any detectable changes of the platelet dependent primary haemostasis, blood coagulation and fibrinolysis. Transfusion of one unit of packed red cells or stored plasma does not seem to adversely affect the haemostasis.

Adult↗