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Acceptor Molecules (acceptor + molecule)
Selected AbstractsImproving the ON/OFF Ratio and Reversibility of Recording by Rational Structural Arrangement of Donor,Acceptor MoleculesADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Ying Ma Abstract Organic molecules with donor,acceptor (D,A) structure are an important type of material for nanoelectronics and molecular electronics. The influence of the electron donor and acceptor units on the electrical function of materials is a worthy topic for the development of high-performance data storage. In this work, the effect of different D,A structures (namely D,,,A,,,D and A,,,D,,,A) on the electronic switching properties of triphenylamine-based molecules is investigated. Devices based on D,,,A,,,D molecules exhibit excellent write,read,erase characteristics with a high ON/OFF ratio of up to 106, while that based on A,,,D,,,A molecules exhibit irreversible switching behavior with an ON/OFF ratio of about (3.2,×,101),(1,×,103). Moreover, long retention time of the high conductance state and low threshold voltage are observed for the D,A switching materials. Accordingly, stable and reliable nanoscale data storage is achieved on the thin films of the D,A molecules by scanning tunneling microscopy. The influence of the arrangement of the D and A within the molecular backbone disclosed in this study will be of significance for improving the electronic switching properties (ON/OFF current ratio and reversibility) of new molecular systems, so as to achieve more efficient data storage through appropriate design strategies. [source] Comparing Spin-Selective Charge Transport through Donor,Bridge,Acceptor Molecules with Different Oligomeric Aromatic Bridges,ANGEWANDTE CHEMIE, Issue 16 2010Der, -Wert, der die exponentielle Abstandsabhängigkeit der Singulett- und Triplett-Ladungsrekombinationswege charakterisiert, wurde für drei Donor-Brücke-Akzeptor(DBA)-Moleküle bestimmt. p -Phenylethinylen- und Fluorenon-Brücken ergaben ähnliche , -Werte, p -Phenylen-Brücken dagegen deutlich andere (siehe Bild). Somit hängt , für Singulett- wie Triplett-Ladungsrekombinationen nicht von der Brücke, sondern vom System ab. [source] Synthesis and Self-Assembly of Functionalized Donor,,,Acceptor Molecules.CHEMINFORM, Issue 24 2005Hengfeng Li Abstract For Abstract see ChemInform Abstract in Full Text. [source] A New Donor,Acceptor,Donor Polyfluorene Copolymer with Balanced Electron and Hole Mobility,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2007A. Gadisa Abstract A new alternating polyfluorene copolymer poly[2,7-(9,9-dioctylfluoren)- alt -5,5-(5,,8,-di-2-thienyl-(2,,3,-bis-(3,,-octyloxyphenyl)-quinoxaline))] (APFO-15), which has electron donor,acceptor,donor units in between the fluorene units, is synthesized and characterized. This polymer has a strong absorption and emission in the visible range of the solar spectrum. Its electroluminescence and photoluminescence emissions extend from about 560 to 900 nm. Moreover, solar cells with efficiencies in excess of 3.5,% have been realized from blends of APFO-15 and an electron acceptor molecule, a methanofullerene [6,6]-phenyl-C61 -butyric acid methyl ester (PCBM). It has also been observed that electron and hole transport is balanced both in the pure polymer phase and in polymer/PCBM bulk heterojunction films, which makes this material quite attractive for applications in opto-electronic devices. [source] Can improvement in photosynthesis increase crop yields?PLANT CELL & ENVIRONMENT, Issue 3 2006STEPHEN P. LONG ABSTRACT The yield potential (Yp) of a grain crop is the seed mass per unit ground area obtained under optimum growing conditions without weeds, pests and diseases. It is determined by the product of the available light energy and by the genetically determined properties: efficiency of light capture (,i), the efficiency of conversion of the intercepted light into biomass (,c) and the proportion of biomass partitioned into grain (,). Plant breeding brings , and ,i close to their theoretical maxima, leaving ,c, primarily determined by photosynthesis, as the only remaining major prospect for improving Yp. Leaf photosynthetic rate, however, is poorly correlated with yield when different genotypes of a crop species are compared. This led to the viewpoint that improvement of leaf photosynthesis has little value for improving Yp. By contrast, the many recent experiments that compare the growth of a genotype in current and future projected elevated [CO2] environments show that increase in leaf photosynthesis is closely associated with similar increases in yield. Are there opportunities to achieve similar increases by genetic manipulation? Six potential routes of increasing ,c by improving photosynthetic efficiency were explored, ranging from altered canopy architecture to improved regeneration of the acceptor molecule for CO2. Collectively, these changes could improve ,c and, therefore, Yp by c. 50%. Because some changes could be achieved by transgenic technology, the time of the development of commercial cultivars could be considerably less than by conventional breeding and potentially, within 10,15 years. [source] Noncovalent Functionalization, Exfoliation, and Solubilization of Graphene in Water by Employing a Fluorescent Coronene CarboxylateCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2010Anupama Ghosh Single-layer graphene stabilization: An efficient methodology to make stable aqueous solutions of single-layer graphene has been demonstrated by exploiting charge-transfer interactions with a coronene tetracarboxylate acceptor molecule (see figure). Microscopic studies reveal exfoliation of few-layer graphene and selective stabilization of single-layer graphene in large quantities. [source] Donor/Conductor/Acceptor Triads Spatially Organized on the Micrometer-Length Scale: An Alternative Approach to Photovoltaic CellsCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Francesc Abstract We have used porous anodised Al2O3 membranes as inert matrix for constructing and organizing spatially ternary donor/conductor/acceptor (DCA) systems exhibiting photovoltaic cell activity on the micrometric-length scale. These DCA triads were built stepwise by first growing a conducting polymer inside the membrane pores, thus forming nanorods that completely fill the internal pore space of the membrane. Then, an electron donor and an electron acceptor were adsorbed one on each side of the membrane, so that they were separated by a distance equal to the membrane thickness (ca. 60,,m), but electronically connected through the conductive polymer. When this device was placed between two electrodes and irradiated with visible light, electrons jumped from the donor molecule, crossed the membrane from side to side through the conductive polymer (a journey of about 60,,m!) until they finally reach the acceptor molecule. In so doing, an electric voltage was generated between the two electrodes, capable of maintaining an electric current flow from the membrane to an external circuit. Our DCA device constitutes the proof of a novel concept of photovoltaic cells, since it is based on the spatial organization at the micrometric scale of complementary, but not covalently linked, electron-donor and electron-acceptor organic species. Thus, our cell is based in translating photoinduced electron transfer between donors and acceptors, which is known to occur at the molecular nanometric scale, to the micrometric range in a spatially organised system. In addition our cell does not need the use of liquid electrolytes in order to operate, which is one of the main drawbacks in dye-sensitised solar cells. [source] Quantum Dots Arrangement and Energy Transfer Control via Charge-Transfer Complex Achieved on Poly(Phenylene Ethynylene)/Schizophyllan NanowiresCHEMISTRY - AN ASIAN JOURNAL, Issue 9 2009Tomohiro Shiraki Abstract Assemblies of organic and inorganic compounds in the nanoscale region have contributed to the development of novel functional materials toward future applications, including sensors and opto-electronics. We succeed in fabricating hybrid nanowires composed of a conjugated polymer and semiconductor quantum dots (QDs) by a supramolecular assembly technique. The 1-D fashion of the nanowire structure is obtained by the polymer wrapping of cationic poly(phenylene ethynylene) (PPE) with helix-forming polysaccharide schizophyllan (SPG). The electrostatic interaction between cationic PPE and anionic QDs affords the nanowires decorated with QDs. Upon addition of an acceptor molecule, tetranitrofluorenone (TNF), the charge-transfer (CT) complex between PPE and TNF is formed, resulting in energy transfer from the QDs to PPE arising from the induced spectral overlap. Furthermore, the employment of the conjugated polymer allows highly sensitive quenching of the QD's emission by raising the transmission efficiency to the CT complexed electron deficient sites along the polymer backbone. [source] Phylogenetic analysis of condensation domains in the nonribosomal peptide synthetasesFEMS MICROBIOLOGY LETTERS, Issue 1 2005Niran Roongsawang Abstract Condensation (C) domains in the nonribosomal peptide synthetases are capable of catalyzing peptide bond formation between two consecutively bound various amino acids. C-domains coincide in frequency with the number of peptide bonds in the product peptide. In this study, a phylogenetic approach was used to investigate structural diversity of bacterial C-domains. Phylogenetic trees show that the C-domains are clustered into three functional groups according to the types of substrate donor molecules. They are l -peptidyl donors, d -peptidyl donors, and N -acyl donors. The fact that C-domain structure is not subject to optical configuration of amino acid acceptor molecules supports an idea that the conversion from l to d -form of incorporating amino acid acceptor occurs during or after peptide bond formation. l -peptidyl donors and d -peptidyl donors are suggested to separate before separating the lineage of Gram-positive and Gram-negative bacteria in the evolution process. [source] Quantum-Chemical Characterization of the Origin of Dipole Formation at Molecular Organic/Organic InterfacesADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Igor Avilov Abstract Recent experiments have reported a vacuum level shift at the interface between organic materials due to the formation of an interface dipole layer. On the basis of quantum-chemical calculations, this paper sheds light on the factors contributing to the formation of an interface dipole between an electron donor and an electron acceptor, considering as model system a complex made of tetrathiafulvalene (TTF) as a donor and tetracyanoquinodimethane (TCNQ) as an acceptor. The results indicate that the interface dipole is governed both by charge-transfer and polarization effects and allow for disentangling of their respective contributions. Two regimes of charge transfer can be distinguished depending on the strength of the electronic coupling: a fractional charge transfer occurs in the strong coupling regime while only integer charges are transferred when the coupling is weak. The polarization contribution can be significant, even in the presence of a pronounced charge transfer between the donor and acceptor molecules. The values of ionization potential and electron affinity of the donor and acceptor molecules may experience shifts as large as several tenths of an eV at the interface with respect to the isolated compounds. [source] Composites of Graphene with Large Aromatic MoleculesADVANCED MATERIALS, Issue 31 2009Qi Su A novel approach to functionalize graphene with large aromatic donor and acceptor molecules consisting of nanographene units is presented, producing an unprecedented class of graphene and nanographene composites with tunable electronic properties. The stability of aqueous dispersion of graphene sheets is greatly enhanced, and a large number of monolayer and double-layer graphene sheets could be facilely fabricated on the substrates [source] Characterization of an acyl-CoA: carboxylate CoA-transferase from Aspergillus nidulans involved in propionyl-CoA detoxificationMOLECULAR MICROBIOLOGY, Issue 3 2008Christian B. Fleck Summary Filamentous fungi metabolize toxic propionyl-CoA via the methylcitrate cycle. Disruption of the methylcitrate synthase gene leads to an accumulation of propionyl-CoA and attenuates virulence of Aspergillus fumigatus. However, addition of acetate, but not ethanol, to propionate-containing medium strongly reduces the accumulation of propionyl-CoA and restores growth of the methylcitrate synthase mutant. Therefore, the existence of a CoA-transferase was postulated, which transfers the CoASH moiety from propionyl-CoA to acetate and, thereby, detoxifying the cell. In this study, we purified the responsible protein from Aspergillus nidulans and characterized its biochemical properties. The enzyme used succinyl-, propionyl- and acetyl-CoA as CoASH donors and the corresponding acids as acceptor molecules. Although the protein displayed high sequence similarity to acetyl-CoA hydrolases this activity was hardly detectable. We additionally identified and deleted the coding DNA sequence of the CoA-transferase. The mutant displayed weak phenotypes in the presence of propionate and behaved like the wild type when no propionate was present. However, when a double-deletion mutant defective in both methylcitrate synthase and CoA-transferase was constructed, the resulting strain was unable to grow on media containing acetate and propionate as sole carbon sources, which confirmed the in vivo activity of the CoA-transferase. [source] Charge carrier dissociation and recombination in polymer solar cellsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2009Carsten Deibel Abstract In polymer:fullerene solar cells, the origin of the losses in the field-dependent photocurrent is still controversially debated. We contribute to the ongoing discussion by performing photo-induced charge extraction measurements on poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61 butyric acid methyl ester solar cells in order to investigate the processes ruling charge carrier decay. Calculating the drift length of photogenerated charges, we find that polaron recombination is not limiting the photocurrent for annealed devices. Additionally, we applied Monte Carlo simulations on blends of conjugated polymer chain donors with acceptor molecules in order to gain insight into the polaron pair dissociation. The dissociation yield turns out to be rather high, with only a weak field dependence. With this complementary view on dissociation and recombination, we stress the importance of accounting for polaron pair dissociation, polaron recombination as well as charge extraction when considering the loss mechanisms in organic solar cells. [source] Unusual hydrate stabilization in the two-dimensional layered structure of quinacrinium bis(2-carboxy-4,5-dichlorobenzoate) tetrahydrate, a proton-transfer compound of the drug quinacrineACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Graham Smith The crystal structure of the hydrated proton-transfer compound of the drug quinacrine [rac- N,-(6-chloro-2-methoxyacridin-9-yl)- N,N -diethylpentane-1,4-diamine] with 4,5-dichlorophthalic acid, C23H32ClN3O2+·2C8H3Cl2O4,·4H2O, has been determined at 200,K. The four labile water molecules of solvation in the structure form discrete ...O,H...O,H... hydrogen-bonded chains parallel to the quinacrine side chain, the two N,H groups of which act as hydrogen-bond donors for two of the water acceptor molecules. The other water molecules, as well as the acridinium H atom, also form hydrogen bonds with the two anion species and extend the structure into two-dimensional sheets. Between these sheets there are also weak cation,anion and anion,anion ,,, aromatic ring interactions. This structure represents the third example of a simple quinacrine derivative for which structural data are available but differs from the other two in that it is unstable in the X-ray beam due to efflorescence, probably associated with the destruction of the unusual four-membered water chain structures. [source] Glycosyltransferases and their AssaysCHEMBIOCHEM, Issue 14 2010Dr. Gerd K. Wagner Abstract Glycosyltransferases (GTs) are a large family of enzymes that are essential in all domains of life for the biosynthesis of complex carbohydrates and glycoconjugates. GTs catalyse the transfer of a sugar from a glycosyl donor to a variety of acceptor molecules, for example, oligosaccharides, peptides, lipids or small molecules. Such glycosylation reactions are central to many fundamental biological processes, including cellular adhesion, cell signalling and bacterial- and plant-cell-wall biosynthesis. GTs are therefore of significant interest as molecular targets in chemical biology and drug discovery. In addition, GTs have found wide application as synthetic tools for the preparation of complex carbohydrates and glycoconjugates. In order to exploit the potential of GTs both as molecular targets and synthetic tools, robust and operationally simple bioassays are essential, especially as more and more protein sequences with putative GT activity but unknown biochemical function are being identified. In this minireview, we give a brief introduction to GT biochemistry and biology. We outline the relevance of GTs for medicinal chemistry and chemical biology, and describe selected examples for recently developed GT bioassays, with a particular emphasis on fluorescence-based formats. [source] Photoinduced Electron Transfer in ,-Cyclodextrin-Based Supramolecular Dyads: A Free-Energy-Dependence StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2006Bijitha Balan Abstract Photoinduced electron transfer (PET) between ,-cyclodextrin-appended pyrene (PYCD) and a few acceptor molecules was studied in aqueous solutions. The pyrene moiety in PYCD is located above the narrower rim of the ,-CD and is fully exposed to water. The acceptors are monocyclic organic molecules and, upon dissolution in water in the presence of PYCD, a fraction of the donor,acceptor systems is present as supramolecular dyads and the remaining fraction as free molecules. Free-energy-dependence studies showed that electron transfer in the supramolecular dyads follows the Marcus equation. The donor,acceptor coupling and the reorganization energy were determined from fits of the data to the Marcus equation. The electronic coupling was found to be similar to those reported for hydrogen-bonded systems. It appears that the actual ,out values are somewhat lower than values calculated with the continuum model. The experimental design has also allowed, for the first time, a visual demonstration of the inverted region on the basis of the raw fluorescence lifetime data. [source] Very Long-Range Effects: Cooperativity between Anion,, and Hydrogen-Bonding InteractionsCHEMPHYSCHEM, Issue 13 2009Xavier Lucas Abstract The interplay between two important non-covalent interactions involving aromatic rings (namely anion,, and hydrogen bonding) is investigated. Very interesting cooperativity effects are present in complexes where anion,, and hydrogen bonding interactions coexist. These effects are found in systems where the distance between the anion and the hydrogen-bond donor/acceptor molecule is as long as ,11 Å. These effects are studied theoretically using the energetic and geometric features of the complexes, which were computed using ab initio calculations. We use and discuss several criteria to analyze the mutual influence of the non-covalent interactions studied herein. In addition we use Bader's theory of atoms-in-molecules to characterize the interactions and to analyze the strengthening or weakening of the interactions depending upon the variation of the charge density at the critical points. [source] | ||||||||||||||||