Search results for "Acceptor"
showing 10 items of 394 documents
Kinetic solvent effects on the reaction of an aromatic ketone pi,pi* triplet with phenol. rate-retarding and rate-accelerating effects of hydrogen-bo…
2007
Quenching of the 2-benzoylthiophene π,π* triplet, 3BT*, by phenol yields the corresponding ketyl and phenoxyl radicals. Reaction rates were measured in 10 solvents having a range of hydrogen-bond acceptor strengths (β2H values). There appear to be two mechanisms: (i) a bimolecular reaction of 3BT* with “free” (i.e., not H-bonded) phenol in which the 3BT* accepts both a proton and an electron from the phenol, the rate decreasing as β2H increases; (ii) a trimolecular reaction of 3BT* with phenol that is H-bonded to a solvent molecule, PhO−H···S, in which the proton goes to the S and the electron to the 3BT*, the rate increasing as β2H increases.
Charge transfer in the novel donor-acceptor complexes tetra- and hexamethoxypyrene with tetracyanoquinodimethane studied by HAXPES
2012
Abstract The effect of charge transfer (CT) in complexes of the donors tetra - and hexamethoxyprene ( TMP and HMP ) with the classical acceptor tetracyanoquinodimethane ( TCNQ ) was studied using hard X-ray photoemission (HAXPES). Microcrystals of the complex were grown via vapour diffusion from donor–acceptor mixtures. The bulk sensitivity of HAXPES at a photon energy of 6 keV completely eliminates the problem of surface contamination for such delicate organic materials grown from solution. The donor molecules were produced using a novel synthesis route functionalizing polycyclic aromatic hydrocarbons at their periphery. For comparison, spectra were also taken from thin-film samples of the…
Photo- and thermostimulated processes in α-Al2O3
1995
Abstract We reported on the recombination processes determined by the release of electrons from defects connected with the dosimetric 430 K thermostimulated luminescence (TSL) peak as well as with the 260 K TSL peak. These TSL peaks appear in thermochemically reduced α-Al 2 O 3 crystals containing hydrogen and emission of these TSL peaks corresponds to luminescence of the F-center. The X-ray exposure or UV excitation in the absorption band of F-centers at 6.0 eV of reduced α-Al 2 O 3 crystals doped with acceptor impurities results in the appearance of a broad anisotropic complex absorption band in the spectral region 2.5–3.5 eV and in the appearance of a predominant TSL peak at 430 K. Above…
Catalysis in glycine N-methyltransferase: testing the electrostatic stabilization and compression hypothesis.
2006
Glycine N-methyltransferase (GNMT) is an S-adenosyl-l-methionine dependent enzyme that catalyzes glycine transformation to sarcosine. Here, we present a hybrid quantum mechanics/molecular mechanics (QM/MM) computational study of the reaction compared to the counterpart process in water. The process takes place through an SN2 mechanism in both media with a transition state in which the transferring methyl group is placed in between the donor (SAM) and the acceptor (the amine group of glycine). Comparative analysis of structural, electrostatic, and electronic characteristics of the in-solution and enzymatic transition states allows us to get a deeper insight into the origins of the enzyme's c…
Inhibition of FcεRI-mediated Activation of Rat Basophilic Leukemia Cells by Clostridium difficile Toxin B (Monoglucosyltransferase)
1996
Abstract Treatment of rat basophilic leukemia (RBL) 2H3-hm1 cells with Clostridium difficile toxin B (2 ng/ml), which reportedly depolymerizes the actin cytoskeleton, blocked [3H]serotonin release induced by 2,4-dinitrophenyl-bovine serum albumin, carbachol, mastoparan, and reduced ionophore A23187-stimulated degranulation by about 55-60%. In lysates of RBL cells, toxin B 14C-glucosylated two major and one minor protein. By using two-dimensional gel electrophoresis and immunoblotting, RhoA and Cdc42 were identified as protein substrates of toxin B. In contrast to toxin B, Clostridium botulinum transferase C3 that selectively inactivates RhoA by ADP-ribosylation did not inhibit degranulation…
dfh is a Drosophila homolog of the Friedreich's ataxia disease gene
2000
Abstract A putative Drosophila homolog of the Friedreich's ataxia disease gene (FRDA) has been cloned and characterized; it has been named Drosophila frataxin homolog (dfh). It is located at 8C/D position on X chromosome and is spread over 1 kb, a much smaller genomic region than the human gene. Its genomic organization is simple, with a single intron dividing the coding region into two exons. The predicted encoded product has 190 amino acids, being considered a frataxin-like protein on the basis of the sequence and secondary structure conservation when compared with human frataxin and related proteins from other eukaryotes. The closest match between the Drosophila and the human proteins in…
Influence of doped charge transport layers on efficient perovskite solar cells
2018
Planar vacuum deposited p–i–n methyl ammonium lead tri-iodide perovskite solar cells are prepared with different electron and hole transporting layers, either doped or undoped. The effect of these layers on the solar cells performance (efficiency and stability) is studied. The main benefit of using doped layers lies in the formation of barrier free charge extraction contacts to the electrodes. However, this comes at the cost of increased residual absorption (reducing the current density and efficiency of the cells) and a decreased stability. A generic solar cell structure using undoped charge extraction layers is presented, containing a thin layer of a strong electron acceptor in between th…
The origin of slow electron recombination processes in dye-sensitized solar cells with alumina barrier coatings
2004
We investigate the effect of a thin alumina coating of nanocrystalline TiO2 films on recombination dynamics of dye-sensitized solar cells. Both coated and uncoated cells were measured by a combination of techniques: transient absorption spectroscopy, electrochemical impedance spectroscopy, and open-circuit voltage decay. It is found that the alumina barrier reduces the recombination of photoinjected electrons to both dye cations and the oxidized redox couple. It is proposed that this observed retardation can be attributed primarily to two effects: almost complete passivation of surface trap states in TiO2 that are able to inject electrons to acceptor species, and slowing down by a factor of…
Oligo(2,5-thienyleneethynylene)s with Terminal Donor-Acceptor Substitution
2006
Five oligo(2,5-thienyleneethynylene) series (OTE, n = 1–5), namely the push-pull substituted compounds 1b-5b and 1c-5c, the purely donor substituted compounds 1a-5a and two precursor series with protected and deprotected ethynyl end-groups, respectively, were obtained by a convergent synthetic strategy. The extension of the conjugated chromophores in the donor-acceptor OTE (DAOTE) series is superimposed by an intramolecular charge transfer (ICT), which decreases with an increasing number, n, of repeat units. The overall effect is studied by the convergence of the UV/Vis absorption maxima λmax (n) → λ∞ for n → ∞.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Superexchange-mediated electronic energy transfer in a model dyad
2010
On the basis of time-dependent density functional theory (TD-DFT) calculations coupled to the polarizable continuum model (PCM) and single molecule spectroscopic studies, we provide a detailed investigation of excitation energy transfer within a model bi-chromophoric system where a perylene monoimide (PMI) donor is bridged to a terrylene diimide (TDI) acceptor through a ladder-type pentaphenylene (pPh) spacer. We find that the electronic excitation on the PMI donor significantly extends over the bridge giving rise to a partial charge transfer character and inducing a approximately 3-fold increase in the electronic interaction between the chromophores, which explains the failure of the Först…