The self-assembled monolayers (SAMs) of the three isomers of aminothiophenol, ATP, have been studied by means of electrochem., in-situ STM and XPS. We find that the isomers are organized differently. The organization is presumably governed by their intermol. and surface interactions. Moreover, the chem. and phys. characteristics of the interface are significantly and differently affected by the isomers comprising the SAMs. The electrochem. of the modified surface as well as the bare gold surface in contact with the thiol-contg. electrolyte, copper deposition and palladium(II) extn. have been studied for the 2-, 3- and 4-ATP monolayers. The organization of the layers has been investigated by STM. In essence, we find that the different isomers are likely to adopt an orientation that is perpendicular to the surface. While 4-ATP forms the densest monolayer, 2-ATP probably interacts with the gold surface with both the amino and the mercapto groups. Moreover, STM images indicate the partial formation of more than a monolayer. This is supported by XPS measurements and electrochem. and can be attributed to the SAM modification soln., i.e. sulfuric acid, which allows the formation of sulfate-bridged ATP bilayers. The chem. and phys. characteristics of the interfaces are governed by the different organization as well as by the individual chem. properties of each isomer. [on SciFinder(R)]
The electrochem. of functionalized self-assembled monolayers on Hg is studied by cyclic voltammetry and AC voltammetry. The results suggest that thiols can be adsorbed either chem. or phys. depending on the Hg potential. The transformation between these two states occurs via an oxidn.-redn. process. While a multi-layer of short chemisorbed thiols is formed under pos. potentials than the oxidn.-redn. process, a dense monolayer is self-assembled under more neg. potentials. [on SciFinder(R)]
The antiaromatic corannulene dianion, Cor2-, undergoes photoejection of an electron to yield an intimate cage complex of Cor.- and the electron. Part of the complex species undergoes cage recombination, k(rec)(1) = 1.1 x 10(6) s(-1), while the other part of complex separates, k(s) = 2.3 x 10(6) s(-1), and yields Cor(.-) and a Li+/e(-) ion pair. Diffusional recombination of the later products proceeds with a bimolecular rate constant corresponding to k(rec)(2) = 1.3 x 10(9) M-1 s(-1). Time-resolved laser flash-photolysis and FT-EPR experiments are used to characterize the transient species.
Quantum dots present the chemist with the opportunity to synthesize atomic-like building blocks with made-to-measure electronic properties. For the theorists this allows a study of the same Hamiltonian for a range of parameters. Hen we consider a lattice of quantum dots, where the dots can be prepared with a narrow distribution of properties but are never quite identical. This is unlike an ordered lattice of atoms or molecules. We report computations of the frequency-dependent dielectric response of a two-dimensional array of quantum dots, as a function of the distance between the dots. When the dots are not closely packed, the response is dominated by the Coulomb repulsion of electrons (of opposite spin) on a given dot. This gives rise to an insulator-metal transition as the expanded array is compressed. The interplay between the three effects, the ``disorder'' due to the size, shape, and environmental fluctuations of the dots, the coupling of adjacent dots, and the Coulomb repulsion are studied as functions of the lattice spacing. The computations are performed in the approximation where each dot carries one valence electron, but these electrons are fully correlated so as to fully account for the Coulomb blocking. This is possible by a diagonalization of the Hamiltonian in a many-electron basis. Comparison is made with experimental results for the dielectric response, as described in a companion to this paper.
We demonstrate the fabrication and characterization of an organic light-emitting diode (OLED) device based on self-assembled poly(4-vinyl-pyridine) (P4VPy) with poly(N-vinyl-carbazole) (PVK) and 2-(4-biphenylyl)-5-(4-tert-butyphenyl)-1,3,4-oxidiazole (PBD) as transport layers. The self-assembly is based on the electrostatic attraction of oppositely-charged polymers. We have shown here that we can use this self-assembled methodology to fabricate alternating multilayers, not only by the poly(phenyl-vinylene) (PPV) and derivatives, but also by partial protonation of P4VPy, by which the charge on P4VPy is generated by the protonation process. The multilayered structures are characterized by specular X-ray reflectivity (XRR), UV absorption, photoluminescence (PL) and electroluminescence (EL).
Caenorhabditis elegans has a single lamin gene, designated lmn-1 (previously termed CeLam-1). Antibodies raised against the lmn-1 product (Ce-lamin) detected a 64-kDa nuclear envelope protein. Ce-lamin was detected in the nuclear periphery of all cells except sperm and was found in the nuclear interior in embryonic cells and in a fraction of adult cells. Reductions in the amount of Ce-lamin protein produce embryonic lethality. Although the majority of affected embryos survive to produce several hundred nuclei, defects can be detected as early as the first nuclear divisions. Abnormalities include rapid changes in nuclear morphology during interphase, loss of chromosomes, unequal separation of chromosomes into daughter nuclei, abnormal condensation of chromatin, an increase in DNA content, and abnormal distribution of nuclear pore complexes (NPCs). Under conditions of incomplete RNA interference, a fraction of embryos escaped embryonic arrest and continue to develop through larval life. These animals exhibit additional phenotypes including sterility and defective segregation of chromosomes in germ cells. Our observations show that lmn-1 is an essential gene in C. elegans, and that the nuclear lamins are involved in chromatin organization, cell cycle progression, chromosome segregation, and correct spacing of NPCs.
A combination of experimental, molecular dynamics, and kinetics modeling studies is applied to a system of concentrated aqueous sodium chloride particles suspended in air at room temperature with ozone. irradiated at 254 nanometers to generate hydroxyl radicals. Measurements of the observed gaseous molecular chlorine product are explainable only if reactions at the air-water interface are dominant. Molecular dynamics simulations show the availability of substantial amounts of chloride ions for reaction at the interface, and quantum chemical calculations predict that in the gas phase chloride ions will strongly attract hydroxl radicals. Model extrapolation to the marine boundary Layer yields daytime chlorine atom concentrations that are in good agreement with estimates based on field measurements of the decay of selected organics over the Southern Ocean and the North Atlantic. Thus, ion-enhanced interactions with gases at aqueous interfaces may play a more generalized and important role in the chemistry of concentrated inorganic salt solutions than was previously recognized.
Lay summary:
Why does information technology (IT) in the public sector of countries with advanced IT achievements lag so far behind the private sector? Using Israel as a case study, the article demonstrates that political interests in the public sector compromise the efficient use of IT. The article finds that IT projects and advances are used by politicians and bureaucrats to consolidate power and advance agency-centric interests. This leads to government gridlock instead of improved services to citizens.
Publication significance:
The article addresses a pressing issue for democratic systems: do advanced IT tools improve the quality of democratic accountability and service delivery or is the political context an overriding factor? The article finds that if the political context is one of protecting and advancing personal and agency-centric interests then IT advances become utilized in political power-struggles. Whilst costing taxpayers dearly, IT advances do not improve accountability or service delivery to citizens.
A novel fluorescence immunoassay based on specific interaction of an antibody with an antigen preadsorbed onto fluorescer (perylene) microparticles (mean diam. 0.8-1.0 μm) is described. The microparticles of perylene are formed by pptn. in IgG soln., and the obtained dispersion is stable in the protein at concns. higher than 1 mg ml-1. Dissolving the particles in a suitable solvent leads to fluorescence when exciting by light of a proper wavelength. The dependencies of the fluorescence intensity on the concns. of antigen, antibody and fluorescer were studied. [on SciFinder(R)]
An FTIR study reveals the complex zwitterion (R2C−–Py+–H) in a polymeric chain of poly(4-vinylpyridine), which results from self-protonation of the latter in a pyridine solution. Presumably this complex ion, together with the observed strongly hydrogen-bonded network, is responsible for the formation of a gel with unique tunable emission properties.
The complete characterization of polycyclic aromatic hydrocarbons (PAHs) and tetrasubstituted ethylenes is critical to an understanding of their reactivity, for which NMR is an important tool. Chemical shifts can provide a direct measure of charge distribution and aromaticity. Unfortunately, COSY, NOESY and heteronuclear correlation cannot provide a complete assignment of the NMR spectra for some carbon-rich PAHs with symmetrical bay regions. The protons in the bay regions would yield NOE signals if they were not symmetrical. Natural substitution of C-12 with C-13 can be used to break the symmetry and yield these useful NOE signals. Using gradient-assisted editing, unequivocal assignments have been achieved for some previously problematic molecules. Copyright (C) 2000 John Wiley & Sons, Ltd.
Marguerite de Valois, queen of France in the late 15th century, is the main character in the melodramatic novel 'La Reine Margot' by Alexandre Dumas. Professional historians have been unable to separate this fictional portrayal from the actual woman, partly because of their inability to admit the influence of sexual desire.
