Search results for "solu"

On what terms and why the thermodynamic properties of polymer solutions depend on chain length up to the melt

2003

Theoretical considerations based on chain connectivity and conformational variability of polymers have lead to an uncomplicated relation for the dependence of the Flory-Huggins interaction parameter, chi, on the volume fraction of the polymer, phi, and on its number of segments, N. The validity of this expression is being tested extensively by means of vapor pressure measurements and inverse gas chromatography (complemented by osmotic and light scattering data from literature) for solutions of poly(dimethylsiloxane) in the thermodynamically vastly different solvents n-octane (n-C8), toluene (TL), and methylethylketone (MEK) over the entire range of composition for at least six different mol…

Characterization of poly(N-alkylanilines) by Raman spectroscopy

2007

Abstract Thin films of poly( N -alkylaniline) were synthesized in acidic aqueous solution and in mixtures of aqueous and organic solvents. The polymer films (alkyl = methyl, ethyl, propyl and butyl) were characterized by Raman spectroscopy with the excitation wavelengths of 514.5, 632.8 and 780 nm. The main Raman bands have been characterized for the leucoemeraldine, emeraldine and pernigraniline oxidation states between −0.2 and 0.8 V (vs. Ag|AgCl). This fundamental study shows that the structure of the half-oxidized emeraldine form contains quinoid units, which supports the commonly accepted oxidation and reduction scheme of poly( N -alkylanilines).

Impedance spectroscopy characterization of functionalized alumina membranes

2005

Abstract Anodic alumina membranes have been impregnated with a protonic conductor either by immersion or by vacuum permeation of a saturated aqueous solution of CsHSO4 for different times. Synthetized salt, obtained through the reaction of cesium carbonate with sulphuric acid (in excess), contained a small quantity of Cs2SO4. Unmodified membranes consist of amorphous Al2O3 with a regular distribution of pores (average diameter: 200 nm) and are stable up to 850 °C. Long impregnation times caused partial dissolution of alumina, with formation of Al(HSO4)3 on the front surfaces as well as into pore walls. From the frequency dispersion of the impedance, the “macroscopic conductivity” of membran…

Not just size and shape: spherically symmetrical d5 and d10 metal ions give different coordination nets with 4,2′:6′,4″-terpyridines

2010

Functionalized 4,2′:6′,4″-terpyridine ligands have been used to provide a divergent N,N′-donor set for the formation of coordination polymers containing {Zn2(µ-OAc)4} or {Mn3(µ-OAc)4(OAc)2} scaffolds. Single-stranded coordination polymers are produced from the reactions of 4′-(4-bromophenyl)-4,2′:6′,4″-terpyridine (1) and 4′-(4-methylthiophenyl)-4,2′:6′,4″-terpyridine (2) with Zn(OAc)2·2H2O. In [Zn2(1)(OAc)4]n and [Zn2(2)(OAc)4]n, the two outer nitrogen donors of the 4,2′:6′,4″-terpyridine ligands, bind to the axial sites of {Zn2(µ-OAc)4} units to generate coordination polymer chains which are π-stacked so that the V-shaped ligand domains are interleaved. When Mn(OAc)2·4H2O is treated with …

Human neuroglobin: crystals and preliminary X-ray diffraction analysis

2002

Neuroglobin, a recently discovered member of the haemoglobin superfamily, is primarily expressed in the brain of humans and other vertebrates, where it has been proposed to enhance O(2) supply in response to hypoxia or ischaemia, protecting the neuron from hypoxic injury. Neuroglobin is the first example of a vertebrate haemoglobin in which a hexacoordinate haem geometry has been detected. A triple mutant (replacing three Cys residues) of human neuroglobin (151 amino acids) has been expressed in Escherichia coli, purified and crystallized in two crystal forms, the best of which diffracts to 1.95 A resolution using synchrotron radiation. The crystals belong to space group P2(1), with unit-ce…

1991

The sanidic polyamide [NM-Ph(CO 2 R) 3 (CO 2 Me)-NMCO-Ph(OR) 2 CO] n (R=C 12 H 25 ) is studied. It is shown that this polymer has a biaxial structure with quasi 2-D long range translational correlations. The correlations in one direction are limited by the length of the molecule. The oriented regions are separated by regions in which the molecules are less oriented

Small-Angle Scattering Techniques for Analyzing Conformational Transitions in Hemocyanins

2004

Publisher Summary The precise delivery of oxygen from respiratory surfaces to the tissues is mediated by cooperative and allosterically regulated carrier proteins, such as hemoglobin or hemocyanin. To establish cooperativity, these proteins must be able to adopt different conformations. These conformations are characterized by different ligand affinities, which have their basis in different structures as is the case for the deoxy and oxy states of human hemoglobin. To understand the cooperative interaction of these molecules at the molecular level, the structures of these conformations must be resolved and the transitions between them must be monitored. Because of the nature of sample prepa…

Homochiral self-assembly of biocoordination polymers: anion-triggered helicity and absolute configuration inversion

2015

The different natures of the weakly coordinating anions – triflate or perchlorate – in the Cu2+-mediated self-assembly of cytidine monophosphate nucleotide play a fundamental role in the homochiral resolution process, yielding one-dimensional copper(II) coordination polymers of opposite helicity that can be easily inverted, in a reversible way, by changing the nature of the anion as revealed by circular dichroism experiments both in solution and in the solid state.

Interactions of metal ions with two quinolone antimicrobial agents (cinoxacin and ciprofloxacin)

2002

Several novel metal-quinolone compounds have been synthesized and characterized by analytical, spectroscopic and X-ray diffraction methods. The crystal structure of the four compounds, Na(2)[(Cd(Cx)3)(Cd(Cx)3(H2O))].12H2O, [Co(Cp)2(H2O)2].9H2O, [Zn(Cp)2(H2O)2].8H2O and [Cd(HCp)2(Cl)2].4H2O, is presented and discussed: HCx=1-ethyl-1,4-dihydro-4-oxo(1,3)-dioxolo(4,5-g)cinnoline-3-carboxylic acid and HCp=1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylic acid. In all these compounds the quinolone acts as a bidentate chelate ligand that binds through one carboxylate oxygen atom and the exocyclic carbonyl oxygen atom. Complexes of ciprofloxacin were screened for th…

SEVERAL COORDINATION MODES OF 5-AMINO-1,3,4-THIADIAZOLE-2-SULFONAMIDE (HATS) WITH Cu(II), Ni(II) AND Zn(II): MIMETIC TERNARY COMPLEXES OF CARBONIC AN…

2001

Abstract The coordination properties of 5-amino-1,3,4-thiadiazole-2-sulfonamide (Hats) with Cu(II), Ni(II) and Zn(II) ions, are analyzed. Although the ligand presents several donor atoms, we have only observed three coordination behaviors: (i) as a monodentate ligand through the Nsulfonamido atom, (ii) as a bridging ligand linking the metal ions through the Nsulfonamido and Nthiadizole atoms and (iii) as a bridging ligand linking metal ions through the N and O atoms of the sulfonamidate group. It is noteworthy that coordination mode (iii) is observed for the first time in heterocyclic sulfonamides complexes. In addition, the conformation of the Hats as counter-ion is analyzed and compared w…