Addition reaction of azido-exTTFs to C60: synthesis of fullerotriazoline and azafulleroid electroactive dyads

[structure: see text] The addition reaction of azido-exTTFs to C(60) affords electroactive fullerotriazoline and azafulleroid dyads, which behave as amphoteric redox systems. Fluorescence experiments and transient absorption spectroscopy reveal that excitation of the fullerene moiety leads to radical pair lifetimes that are 2 orders of magnitude higher than those previously reported for related fullerotriazolines.     

Factors affecting gas-phase deuterium scrambling in peptide ions and their implications for protein structure determination

In this report, we evaluate the validity of using hydrogen/deuterium exchange in combination with collision-induced dissociation mass spectrometry (CID MS) for the detailed structural and conformational investigation of peptides and proteins. This methodology, in which partly deuterated peptide ions are subjected to collision-induced dissociation in the vacuum of a mass spectrometer, has emerged as a useful tool in structural biology. It may potentially provide quantitatively the extent of deuterium incorporation per individual amino acid in peptides and proteins, thus providing detailed structural information related to protein structure and folding. We report that this general methodology has limitations caused by the fact that the incorporated deuterium atoms migrate prior or during the CID MS analysis. Our data are focused on a variety of transmembrane peptides, incorporated in a lipid bilayer, in which the near-terminal amino acids that anchor at the lipid-water interface are systematically varied. Our findings suggest that, under the experimental conditions we use, the extent of intramolecular hydrogen scrambling is strongly influenced by experimental factors, such as the exact amino acid sequence of the peptide, the nature of the charge carrier, and therefore most likely by the gas-phase structure of the peptide ion. Moreover, the observed scrambling seems to be independent of the nature of the peptide fragment ions (i.e., protonated B and Y' ' ions, and sodiated A and Y' ions). Our results strongly suggest that scrambling may be reduced by using alkali metal cationization instead of protonation in the ionization process.     

Influence of initial oxygen coverage and magnetic moment on the NO decomposition on rhodium (111)

In this study, density functional theory calculations were performed to investigate the influence of oxygen preoccupation on the nitrogen oxide decomposition on rhodium. Besides gauging the coverage dependence of the adsorption energy of NO on the (111) rhodium facet, the influence of the initial oxygen coverage on the kinetics and thermodynamics of the nitrogen oxide decomposition reaction was also studied. The results are discussed with respect to a novel NOx decomposition catalyst. Furthermore, the influence of spin effects on the adsorption geometry as well as the adsorption energy is examined. It will be addressed why spin effects only have a minor influence on the behavior of NO on a rhodium surface.     

Serum estradiol measurement by solid-phase chemiluminescence immunoassay and direct radioimmunoassay

Estradiol017β is determined in serum extracts by solid-phase chemiluminescence immunoassay. The results are compared with those obtained from unextracted serum in routine conditions with a commercial radioimmunoassay (r.i.a.) kit. For the chemiluminescence procedure, a purified monoclonal antibody to estradiol-6-carboxymethyloxime/bovine serum albumin and the homologous chemiluminescent marker conjugate estradiol-6-carboxymethyloxime aminobutylethylisoluminol are used. Bound and free ligand are separated by washing and simple centrifugation. Results obtained by the chemiluminescence assay (y) and by r.i.a. (x) on 170 serum specimens from women during ovulation induction showed good correlation (y = 1.01x ? 16 with r = 0.95). The methods are similar in selectivity, detection limit (ca. 10 ng l^?1) and precision (interassay relative standard deviation, 8–13%).     

Functional Polyoxometalate Thin Films via Electrostatic Layer-by-Layer Self-Assembly

Polyoxometalates (POMs) comprise a structurally diverse class of inorganic transition metal oxygen clusters which—owing to their unique electronic properties—hold promise for a host of technological applications such as electrochromic windows, sensors, or heterogeneous catalysts, prototypic examples of which will be briefly exemplified. The integration of POMs into functional architectures and devices, however, necessitates the development of general methods that allow positioning these clusters in well-defined supramolecular architectures, thin films, or mesophases. This short review highlights recent advances in the preparation of composite multilayers fabricated by electrostatic layer-by-layer self-assembly (ELSA) of POMs and a variety of water-soluble cationic species, including transition metal complexes, cationic surfactants, polycations and bipolar pyridine.     

Sulfur Compounds. 183. A Derivative of Perthiocarbonic Acid H2CS4: X-ray structural analysis of bis(triphenylmethyl) perthiocarbonate (Ph3C)2CS4

The molecular structure of Ph₃CSSC(S)SCPh₃ · CS₂ has been determined by X-ray structural analysis. The substance crystallizes in the triclinic crystal system [a = 884.9(2) pm, b = 1 039.5(2) pm, c = 2 064.6(3) pm, α = 75.86(1)°, β = 79.83(2)°, γ = 77.31(5)°, Z = 2, space group P1 ]. The CS₃ group is planar; the S? S-bond (201.4 pm) forms an angle of 5.7° with the CS₃ plane. The torsional angle CSSC equals 96.3°. (Ph₃C)₂CS₄ was obtained by reaction of TosNSCl₂ (Tos = p-MeC₆H₄SO₂) with Ph₃CSH in CS₂ in the presence of triethylamine. The reaction mechanism is discussed.     

Modulating charge-transfer interactions in topologically different porphyrin-C60 dyads

Control over the interchromophore separation, their angular relationship, and the spatial overlap of their electronic clouds in several ZnP-C(60) dyads (ZnP=zinc porphyrin) is used to modulate the rates of intramolecular electron transfer. For the first time, a detailed analysis of the charge transfer absorption and emission spectra, time-dependent spectroscopic measurements, and molecular dynamics simulations prove quantitatively that the same two moieties can produce widely different electron-transfer regimes. This investigation also shows that the combination of ZnP and C(60) consistently produces charge recombination in the inverted Marcus region, with reorganization energies that are remarkably low, regardless of the solvent polarity. The time constants of electron transfer range from the mus to the ps regime, the electronic couplings from a few tens to several hundreds of cm(-1), and the reorganization energies remain below 0.54 eV and can be as low as 0.16 eV.     

Organofluorine compounds and fluorinating agents

Starting with 1,2,4,6-tetra-O-acetyl-3-O-dodecyl-β-d-glucose (1), mixed alkyl-perfluoroalkyl substituted sugar derivatives with an anomeric perfluoroalkylthio group and an O-alkyl group in the 3 position were synthesized via 2,4,6-tri-O-acetyl-3-O-dodecyl-1-thio-β-d-glucose (4). The latter was S-perfluorohexylated with 1-iodoperfluorohexane in a dithionite initiated reaction yielding perfluorohexyl 2,4,6-tri-O-acetyl-3-O-dodecyl-1-thio-β-d-glucopyranoside (5). Experiments with the aim compound 5 completely to deacetylate ended in surprising results. Thus, methanolic methanolate solution produced the orthoester 7 as the result of α-fluoride replacement by methoxy groups as well as the methyl glucoside 8 as the result of a transglycosylation reaction. Alumina supported cesium fluoride cleaved regioselectively the two acetyl groups in the 4- and 6-position yielding perfluorohexyl 2-O-acetyl-3-O-dodecyl-1-thio-β-d-glucopyranoside (10). A complete deacetylation of 5 to amphiphile 11 succeeded only with methanolic tert-butanolate. However, the products 8 and 10 were likewise formed.     

Binucleare Nickel(0)-Komplexe mit „Schlangenliganden”︁ vom 1-Azadientyp: Modellsysteme der oxidativen Kopplung von 1-Azadienen und 1,3-Dienen am Nickel(0)

Binuclear Nickel(0) Complexes with “Snake Ligands” of 1-Azadiene Type: Model Systems of the Oxidative Coupling of 1-Azadienes and 1.3-Dienes at Nickel(0) Synthesis, properties, and reactions of dimeric nickel(0) complexes with special 1-azadiene typ ligands (“snake ligands”) are described. The X-ray analysis of a typical compound (Bis-(bis-cinnamaldehyde-N,N'-propylendiimine)-dinickel(0)) shows that both central atoms have the coordination number 3. The four 1-azadiene groups are coordinated in a different way: unidendate coordination by N-Ni(1) bond and bidendate coordination by N-Ni(1) and olefine-Ni(2) bond. The compound is a good model system for the oxidative coupling reaction of 1-azadienes with 1.3-dienes at 2 nickel(0) centres. IR and electronic spectra show other complexes with this type of ligands to have an analogous coordination sphere.     

Comparative study of electrochemically directed assembly versus conventional self-assembly of thioacetyl-terminated oligo(phenylene ethynylene)s on gold and platinum surfaces

The assembly of thioacetyl-terminated oligo(phenylene ethynylene)s (OPEs) on Au and Pt surfaces under an electric potential (electrochemical assembly, EA) was compared to assembly at an open circuit (conventional self-assembly, CSA). Cyclic voltammetry and ellipsometry were used to characterize the adsorption kinetics of self-assembled monolayers formed by these two techniques. The adsorption rate of the EA was remarkably faster at positive potentials but slower at negative potentials than that of the CSA, The EA at 400 mV proceeded about 800 times faster than the CSA when exposed to the same solution concentrations. The adsorption rates of both EA and CSA were found to be dependent on the molecular structures of OPEs. OPEs containing electron-donating groups assemble faster than those with electron-withdrawing groups. The amount of time that the thioacetyl-terminated OPE is in the presence of the base, for removal of the acetyl group to generate the thiolate, is called the deprotection time. Deprotection times play a critical role in achieving the maximum difference in adsorption rates between the EA and the CSA. The assembly must be initiated no later than 5 min after the basic deprotection is commenced so that the thiolate concentration remains low. The difference in the adsorption rates between EA and CSA might enable selective deposition of certain OPEs onto specific electrodes.