Cascade Complex Research Articles

A Perfect Linear Cu−NNN−Cu Unit Inside the Cryptand Cavity and Perchlorate Entrapment within the Channel Formed by the Cascade Complex

Dicopper complexes of bis-tren cryptand L1 having 1,4-xylyl spacers, becoming a potential receptor for perfect linear recognition of N3-, generate a Cu-NNN-Cu unit inside the cryptand cavity. Solid-state packing of this cascade complex shows the formation of a thorough channel which encapsulate perchlorate anion within the channel.

Caspase-dependent and -independent pathways for cadmium-induced apoptosis in cultured kidney proximal tubule cells

The nephrotoxic metal cadmium at micromolar concentrations induces apoptosis of rat kidney proximal tubule (PT) cells within 3-6 h of exposure. The underlying cell death pathways remain poorly defined. Using Hoechst 33342/ethidium bromide nuclear staining and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell death assays, 10-50 microM cadmium induced apoptosis of immortalized rat kidney cells derived from the S1-segment of PT at 6 and 24 h, but necrosis at 24 h only. Cadmium (10-50 microM) also caused mitochondrial cytochrome c (cyt. c)- and apoptosis-inducing factor release at 24 h, but not at 6 h, as measured by immunofluorescence imaging and immunoblotting. Caspases-9 and -3 were activated only by 10 microM cadmium for 24 h, and accordingly apoptosis was significantly reduced by the respective inhibitors (z-LEHD-fmk, z-DEVD-fmk; 10 microg/ml) at 24 h, but not at 6 h, without affecting necrosis. At 6 h, 10 microM cadmium increased the activity of the calcium-activated protease calpain, but not at 24 h, and calpain inhibitors (ALLN, PD 150606; 10-30 microM) blocked apoptosis by 10 microM cadmium at 3-6 h. However, PD-150606 also attenuated caspase-3 activity and apoptosis at 24 h, suggesting calpain-dependent caspase activation. Thus cadmium-induced apoptosis of PT cells involves a complex and sensitive interplay of signaling cascades involving mitochondrial proapoptotic factors, calpains and caspases, whose activation is also determined by cadmium concentration and the duration of cadmium exposure.

Hexaazamacrocycle Containing Pyridine and Its Dicopper Complex as Receptors for Dicarboxylate Anions

AbstractThe host–guest binding interactions of the hexaazamacrocycle [26]py2N4, in its tetraprotonated form H4[26]py2N44+ as well as in its dicopper(II) complex [Cu2([26]py2N4)(H2O)4]4+, with dicarboxylate anions of different stereoelectronicrequirements, such as oxalate (ox2–), malonate (mal2–), succinate (suc2–), fumarate (fu2–) and maleate (ma2–), were evaluated. The association constants were determined using potentiometric methods in aqueous solution, at 298.0 K and 0.10 mol·dm–3 KCl. These values for the tetraprotonated ditopic receptor with the dicarboxylate anions revealed that the main species in solution corresponds to the formation of {H4[26]py2N4(A)}2+ (pH ≈ 4–9), A being the substrate anion. The values determined are not especially high, but the receptor exhibits selectivity for the malonate anion. The study of the cascade complexes revealed several species in solution, involving mononuclear and dinuclear complexes, mainly protonated and hydrolysed species, as well as the expected complexes [Cu2([26]py2N4)(A)(H2O)x]2+ or [Cu2([26]py2N4)(A)2(H2O)y]. Ox2– and mal2– form cascade complexes with only one anion, which will necessarily bridge the two copper atoms because of the symmetrical arrangement of the dinuclear complex. The two other studied anions, suc2– and ma2–, form species involving two substrate anions, although species with only one suc2– anion were also found. UV/Vis and EPR spectroscopy have shown that the dicopper complex can operate as a sensor to detect and quantitatively determine oxalate spectrophotometrically because of the red shift of the maximum of the visible band observed by addition of ox2– to an aqueous solution of the dinuclear copper complex. However the selectivity of [Cu2([26]py2N4)(H2O)4]4+ as a receptor for ox2– in the studied series is not sufficiently high to detect ox2– spectrophotometrically in the presence of the other anions. Molecular dynamics simulations indicated that the H4[26]py2N44+ receptor provides a large and flexible cavity to accommodate the studied anions. Molecular recognition is based in electrostatic interactions rather than in multiple hydrogen‐bonding interactions acting cooperatively. By contrast, the [Cu2([26]py2N4)]4+ receptor has a well‐shaped cavity with adequate size to uptake these anions as bridging ligands with formation of four Cu–O bonds. The ox2– anion is encapsulated within the cascade complex while the remaining anions are located above the N6 macrocyclic plane, suggesting a selective coordination behaviour of this receptor. In spite of our molecular simulation being carried out in gas phase, the modelling results are consistent with the solution studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Discontinuity in fish assemblages across an elevation gradient in a southern Appalachian watershed, USA

Abstract – We examine patterns in fish species assemblages in the Toxaway and Horsepasture rivers, two high elevation streams in North Carolina, USA. This region is noted for extreme topographical relief, high cumulative annual rainfall and many rare and endemic plants and animals. The study area encompasses a portion of the Blue Ridge Escarpment and the associated Brevard Fault Zone. We hypothesise that major waterfalls and cascade complexes have acted to limit invasion and colonisation by fishes from downstream. This hypothesis is supported by longitudinal fish assemblage patterns in our study streams. Fish species richness in Toxaway River increased from 4 to 23 between Lake Toxaway and Lake Jocassee, a distance of 10 river km. We found similar discontinuities in neighbouring Horsepasture River and Bearwallow Creek. We found no instances of species replacement along this elevation gradient, and the trend in increased diversity downstream showed discontinuities coincident with sharp elevation breaks. With regard to theories posited to explain community formation in headwater stream fish communities (especially in those characterised by high topographical relief), we suggest coloniser ‘access’ may be more important than other factors including competitive interactions.

Localized Feedback Phosphorylation of Ste5p Scaffold by Associated MAPK Cascade

Scaffold proteins play pivotal roles during signal transduction. In Saccharomyces cerevisiae, the Ste5p scaffold protein is required for activation of the mating MAPK cascade in response to mating pheromone and assembles a G protein-MAPK cascade complex at the plasma membrane. To serve this function, Ste5p undergoes a regulated localization event involving nuclear shuttling and recruitment to the cell cortex. Here, we show that Ste5p is also subject to two types of phosphorylation and increases in abundance as a result of MAPK activation. During vegetative growth, Ste5p is basally phosphorylated through a process regulated by the CDK Cdc28p. During mating pheromone signaling, Ste5p undergoes increased phosphorylation by the mating MAPK cascade. Multiple kinases of the mating MAPK cascade contribute to pheromone-induced phosphorylation of Ste5p, with the mating MAPKs contributing the most. Pheromone induction or overexpression of the Ste4p Gbeta subunit increases the abundance of Ste5p at a post-translational step, as long as the mating MAPKs are present. Increasing the level of MAPK activation increases the amount of Ste5p at the cell cortex. Analysis of Ste5p localization mutants reveals a strict requirement for Ste5p recruitment to the plasma membrane for the pheromone-induced phosphorylation. These results suggest that the pool of Ste5p that is recruited to the plasma membrane selectively undergoes feedback phosphorylation by the associated MAPKs, leading to an increased pool of Ste5p at the site of polarized growth. These findings provide evidence of a spatially regulated mechanism for post-activation control of a signaling scaffold that potentiates pathway activation.

Parallels in Cation and Anion Coordination: A New Class of Cascade Complexes

Parallels in Cation and Anion Coordination: A New Class of Cascade Complexes

Parallels in cation and anion coordination: a new class of cascade complexes.

Parallels in cation and anion coordination: a new class of cascade complexes.

Activation of the Wnt Pathway Interferes with Serum Response Element-driven Transcription of Immediate Early Genes

Mutational activation of the Wnt signaling pathway is a common early event in colorectal tumorigenesis, and the identification of target genes regulated by this pathway will provide a better understanding of tumor progression. Gene expression profiling on oligonucleotide microarrays revealed reduced expression of the immediate early genes fos and fosB following stimulation of cells by Wnt-1. Further analysis demonstrated that serum or 12-O-tetradecanoylphorbol-13-acetate activation of several immediate early genes including fos, fosB, junB, and egr1 was inhibited by Wnt signaling. Wnt signaling inhibited transcriptional activation driven by the serum response element without altering the activation of the extracellular signal-regulated kinase cascade or ternary complex formation at the fos serum response element promoter. The Wnt-mediated repression of c-Fos, FosB, and JunB expression was consistent with a decrease in their binding to an AP-1 promoter element and decreased target gene transcription. The expression of fos, fosB, junB, and egr1 was also repressed in human colon tumors relative to patient matched normal tissue. By contrast, the fos family member fra-1 was up-regulated in the human colon tumors, suggesting a compensatory mechanism for the reduction in fos and fosB expression. The results indicate that Wnt signaling can repress the expression of certain immediate early genes, and that this effect is consistent with changes in gene expression observed in human colorectal tumors.

Complexation properties of a heteroditopic cryptand towards CuII and NiII, crystal structures of the cryptand and its nickel(II) cascade complex

The crystal structure of the heteroditopic cryptand (L) formed by Schiff-base condensation of tris(2-aminoethyl)amine and 2,2′,2″-nitrilotris(ethyleneoxy)tris(benzaldehyde) followed by reduction with NaBH 4 has been determined. The molecule has an endo-endo conformation with a pseudo-three-fold symmetry axis passing through the two bridgehead nitrogens. This symmetry is maintained in chloroform solution as indicated by its 1 H NMR spectrum. The cryptand accepts a metal ion (Cu II , Zn II or Ni II ) inside the cavity forming mononuclear cryptates of general formula [ML][ClO 4 ] 2 . The metal ion occupies the N 4 end of the cavity. The light blue CuN 4 chromophore thus formed exhibits an axial EPR spectrum with very small A ∥ value (63 × 10 -4 cm -1 ) and a low-energy ligand-field band. Nickel(II) initially forms a blue [NiL][ClO 4 ] 2 complex which on dissolving in moist MeCN solution crystallizes as purple rectangular parallelopipeds with the formulation [NiL(H 2 O)(MeCN)][ClO 4 ] 2 ·H 2 O·2MeCN. The crystal structure of this complex has also been determined. The Ni II ion is octahedrally co-ordinated with the equatorial sites occupied by the three secondary amino N atoms of the cryptand and the N atom of the bound MeCN. The axial sites are occupied by the bridgehead N and the O atom of the water molecule which enters the cavity forming a cascade complex.

Odd-membered higher heterocalixarene architecture featuring cage conformation. Synthesis and X-ray structure analysis of a 1:2:2 inclusion cascade complex with acetone and dichloromethane

J. Trepte, M. Czugler, K. Gloe and E. Weber, Chem. Commun., 1997, 1461 DOI: 10.1039/A702861J

The SH3-Domain Protein Bem1 Coordinates Mitogen-Activated Protein Kinase Cascade Activation with Cell Cycle Control in Saccharomyces cerevisiae

The mating mitogen-activated protein kinase (MAPK) cascade has three major outputs prior to fusion: transcriptional activation of many genes, cell cycle arrest in the G1 phase, and polarized growth. Bem1 localizes near the cortical actin cytoskeleton and is essential for polarized growth during mating. Here we show that Bem1 is required for efficient signal transduction and coordinates MAPK cascade activation with G1 arrest and mating. bem1delta null mutants are defective in G1 arrest and transcriptional activation in response to mating pheromone. Bem1 protein stimulates Fus3 (MAPK) activity and associates with Ste5, the tethering protein essential for activation of the MAPK kinase kinase Ste11. Bem1-Ste5 complexes also contain Ste11, Ste7 (MAPK kinase), and Fus3, suggesting that Ste5 localizes the MAPK cascade to Bem1. Strikingly, Bem1 also copurifies with Far1, a Fus3 substrate required for G1 arrest and proper polarized growth during mating. These and other results suggest that Bem1 may cross-link the Ste5-MAPK cascade complex to upstream activators and specific downstream substrates at the shmoo tip, thus enabling efficient circuitry for G1 arrest and mating.

Cascade complex formation by phosphate in the cobalt(II)/[30]aneN 10 anaerobic system

The interaction of phosphate with the mono- and binuclear cobalt(II) complexes of [30]aneN 10 (1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane) has been studied by potentiometry in 0.15 mol dm −3 NaClO 4 solution at 298.15 K under anaerobic conditions. The stable species [CoH 2([30]aneN 10)PO 4] +, [CoH 4([30]aneN 10)PO 4] 3+, [Co 2H([30]aneN 10)PO 4] 2+, [Co 2H 2([30]aneN 10)PO 4] 3+ and [Co 2H 3([30]aneN 10)PO 4] 4+, where the phosphate anion is directly bound to the metal ions or acts as a second sphere ligand, are formed and their stability constants have been determined. The results obtained allowed for the selection of suitable conditions for the study of dioxygen uptake.

Encapsulated copper ions: Cryptates and cascade complexes.

Encapsulated copper ions: Cryptates and cascade complexes.

Cascade complexes of an octaaza cryptand: co-ordinated azide with linear M–NNN–M geometry

The octaamino cryptand, L2, obtained by tetrahydroborate reduction of the [2 + 3] condensation product of tris(2-ethylamino)amine with terephthalaldehyde, acts as a host for pairs of protons or first-series transition-metal cations. An X-ray crystallographic structure determination of [H4L2]4+ reveals a pair of protons held at opposite ends of the molecule by strong intramolecular hydrogen bonding of each proton to two of the amino nitrogen atoms. Pairs of transition-metal cations co-ordinated to the amino N-donors accommodate mono- and tri-atomic bridging ligands, such as OH– or imidazolate, generating weak to moderate antiferromagnetic interaction. Dicopper(II)µ-azido complexes have been prepared where the combination of a large zero-field splitting in the ESR spectrum and a near Curie-law dependence of magnetic susceptibility on temperature seems to suggest a triplet ground state. Together with other unusual spectroscopic properties of the bridging azide group, this is believed to derive from a near-linear alignment of the M–NNN–M assembly.

ChemInform Abstract: Conformational Properties of the THYME Polyethers. The Bis‐THYME Cylinder: A Three‐Dimensional Analogue of 18‐Crown‐6.

AbstractThe title compound (II) is characterized by molecular mechanics calculations and as the free ligand, as the toluene solvate, and as a novel cascade complex (K2(OH2)·(III))2+(PtCl3·DMSO)22‐ by means of crystal structures (space group of (II)·toluene: P1, Z=1 and P21/c, Z=2 for the other two cases).

Synthesis and complexing properties of a chiral macrocyclic molecular receptor with convergent binding sites

Two novel hosts: 15-crown-5 and N-benzyl-aza-15-crown-5 incorporating a boron-containing D-mannopyranosidic unit form more stable cascade complexes with (S)-amino acid sodium or potassium salts than with the respective (R)-enantiomers. Complexes with sodium salts are more stable than the corresponding complexes with potassium salts as revealed by variable-temperature NMR measurements. Strong non-bonded interaction between the sugar unit and the α-substituents of the amino acids results in enantiomeric differentiation and destabilization of the complex. Complex formation is interpreted in terms of ion-pair inclusion by macrocyclic ring and nitrogen-boron interaction.

Overall Aerodynamic Performance of an Annular Flat-Plate Airfoil Cascade

THE aerodynamic design of turbomachiner y blading is specified by means of design systems wherein the flow is assumed to be two-dimensional with losses determined from empirical correlations. However, with the continuing requirements for improved efficiency and increased thrust-to-weight ratio, it is evident that new analyses that consider the fundamental three-dimensional flow phenomena existing in blade-row flow passages must be developed, verified by concise data, and subsequently implemented in the design process. Numerical solutions are currently being developed to predict the three-dimensional flow through turbomachine blade rows. To overcome the complexities associated with the flow conditions and the internal geometries, these numerical solutions of necessity involve many computational and physical assumptions. This paper describes experiments performed in a large-scale, subsonic annular cascade facility specifically designed to provide three-dimensional aerodynamic data suitable for code verification. In particular, to minimize the complexities associated with cascade geometry and complex airfoil profiles, the detailed overall threedimensional aerodynamic performance of an extensively instrumented flat-plate airfoil cascade has been experimentally determined over a range of incidence angle values. All of the resulting data are analyzed and correlated with appropriate predictions. Contents

Photoresponsive Crown Ethers. Part 11. Azobenzene‐Pillared Cylindrical Macrocycle As a Photoresponsive Receptor

AbstractA cylindrical ionophore (1) in which two diaza‐crown ethers are linked by two azobenzene pillars serves as a photoresponsive host molecule. In alkaline solution containing K+, (1) forms a cascade complex with dianionic guest molecules, but photoirradiated (1) which has a shortened cylinder cannot bind the guest molecules so effectively as (1). (1) solubilised in acidic aqueous solution by protonation of four tertiary nitrogens provides a hydrophobic cavity to bind several anionic azo dyes. The association is also suppressed by photoirradiation. The results indicate that parallel array of the azobenzene segments in (1) provides a host cavity and the photoinduced structural change is readily reflected by the association tendency. This is the first example for the photoresponsive inclusion complex.

Complexes of γ‐Cyclodextrin with Crown Ethers, Cryptands, Coronates, and Cryptates

Cascade complexes are comparable with a set of three interfitting dolls: γ-cyclodextrin (γ-CD)—a ring of eight glucose molecules—accommodates a small crown ether (see model) or cryptand, which in turm can take up a cation. The [12] crown-4-LiSCN complex and the [2.2.1] ⊂ Ca(SCN)2 cryptate from crystalline cascade complexes of stoichiometry 1:1 and 2:1, respectively, with γ-CD from aqueous solution.

ChemInform Abstract: CRYPTATES: INCLUSION COMPLEXES OF MACROPOLYCYCLIC RECEPTOR MOLECULES

AbstractReview: Bericht über einen Vortrag, der auf dem "26th International Congress of Pure and Applied Chemistry" in Tokyo v. 4.9.