| 1. |
- Knudsen, Jette, et al.
(författare)
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Diversity and distribution of floral scent
- 2006
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Ingår i: The Botanical review. - New York : The New York Botanical Garden Press. - 0006-8101 .- 1874-9372. ; 72:1, s. 1-120
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Tidskriftsartikel (refereegranskat)abstract
- A list of 1719 chemical compounds identified from headspace samples of floral scent is presented. The list has been compiled from some 270 published papers, including analyses of 991 species of flowering plants and a few gymnosperms, a sample including seed plants from 90 families and 38 orders. The compounds belong to seven major compound classes, of which the aliphatics, the benzenoids and phenylpropanoids, and, among the terpenes, the mono- and sesquiterpenes, occur in most orders of seeds plants. C5-branched compounds, irregular terpenes, nitrogen-containing compounds, and a class of miscellaneous cyclic compounds have been recorded in about two-thirds of the orders. Sulfur-containing compounds occur in a third of the orders, whereas diterpenes have been reported from three orders only. The most common single compounds in floral scent are the monoterpenes limonene, (E)-β-ocimene, myrcene, linalool, α- and β-pinene, and the benzenoids benzaldehyde, methyl 2-hydroxybenzoate (methyl salicylate), benzyl alcohol, and 2-phenyl ethanol, which occur in 54–71% of the families investigated so far. The sesquiterpene caryophyllene and the irregular terpene 6-methyl-5-hepten-2-one are also common and occur in more than 50% of the families. Orchidaceae are by far the best investigated family, followed by several families known to have many species with strongly scented flowers, such as Araceae, Arecaceae, Magnoliaceae, and Rosaceae. However, the majority of angiosperm families are still poorly investigated. Relationships between floral scent and pollination, chemistry, evolution, and phylogeny are briefly discussed. It is concluded that floral scent chemistry is of little use for phylogenetic estimates above the genus level, whereas the distribution and combinations of floral scent compounds at species and subspecific levels is a promising field of investigation for the understanding of adaptations and evolutionary processes in angiosperms.
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| 2. |
- Abrahamsson, Maria, et al.
(författare)
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Steric influence on the excited-state lifetimes of ruthenium complexes with bipyridyl-alkanylene-pyridyl ligands.
- 2008
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Ingår i: Inorganic Chemistry. - : ACS. - 0020-1669 .- 1520-510X. ; 47:9, s. 3540-3548
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Tidskriftsartikel (refereegranskat)abstract
- The structural effect on the metal-to-ligand charge transfer (MLCT) excited-state lifetime has been investigated in bis-tridentate Ru(II)-polypyridyl complexes based on the terpyridine-like ligands [6-(2,2'-bipyridyl)](2-pyridyl)methane (1) and 2-[6-(2,2'-bipyridyl)]-2-(2-pyridyl)propane (2). A homoleptic ([Ru(2)(2)](2+)) and a heteroleptic complex ([Ru(ttpy)(2)](2+)) based on the new ligand 2 have been prepared and their photophysical and structural properties studied experimentally and theoretically and compared to the results for the previously reported [Ru(1)(2)](2+). The excited-state lifetime of the homoleptic Ru-II complex with the isopropylene-bridged ligand 2 was found to be 50 times shorter than that of the corresponding homoleptic Ru-II complex of ligand 1, containing a methylene bridge. A comparison of the ground-state geometries of the two homoleptic complexes shows that steric interactions involving the isopropylene bridges make the coordination to the central Ru-II ion less octahedral in [Ru(2)(2)](2+) than in [Ru(1)(2))(2+). Calculations indicate that the structural differences in these complexes influence their ligand field splittings as well as the relative stabilities of the triplet metal-to-ligand charge transfer ((MLCT)-M-3) and metal-centered ((MC)-M-3) excited states. The large difference in measured excited-state lifetimes for the two homoleptic Ru-II complexes is attributed to a strong influence of steric interactions on the ligand field strength, which in turn affects the activation barriers for thermal conversion from (MLCT)-M-3 states to short-lived (MC)-M-3 states.
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| 3. |
- Nilsing, Mattias, et al.
(författare)
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Dye-sensitization of the TiO2 rutile (110) surface by perylene dyes : Quantum-chemical periodic B3LYP computations
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:32, s. 12116-12123
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of perylene derivatives on the rutile TiO2(110) surface was studied by quantum-chemical periodic calculations employing the hybrid HF-DFT functional B3LYP. The perylene molecule, which is a possible constituent of dyes in dye-sensitized solar cells, was functionalized by attachment of phosphonic acid or carboxylic acid groups to permit anchoring to the metal oxide surface. The anchor groups were bound to the molecule directly or via different spacer groups, namely --CH2-, -CH2-CH2-, and -CH = CH-. The effects of the anchor and spacer groups on the adsorption geometry and energy, on the electronic structure of the dye-TiO2 interface, and on the electron transfer rates were investigated. The phosphonic acid anchor group was found to bind the perylene derivatives much more strongly to the surface than the carboxylic acid anchor group. The spacer groups were capable of significantly altering electron transfer rates across the dye-metal oxide interface, where the unsaturated groups permitted injection times in the low femtosecond regime.
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| 4. |
- Nilson, Katharina, et al.
(författare)
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STM and XPS characterization of Zinc Phthalocyanine on InSb(001)
- 2008
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 602:2, s. 452-459
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Tidskriftsartikel (refereegranskat)abstract
- Zinc phthalocyanine (ZnPc) adsorbed on the InSb(0 0 1)-c(8 x 2) surface has been studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Coverages from sub-monolayer to monolayer (ML) have been investigated. The molecules form ordered structures on the reconstructed rows of the surface with the molecular plane parallel to the surface. A change in the electronic structure between the sub-ML and higher coverages has been observed. Moreover, in order to study the influence of annealing on the electronic and geometric structures, the samples have been heated to elevated temperatures (about 640 K). In addition, multi-layer ZnPc films have been characterized by XPS measurements.
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| 5. |
- De Vico, Luca, et al.
(författare)
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Chemiluminescence of 1,2-dioxetane. Reaction mechanism uncovered
- 2007
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 111:32, s. 8013-8019
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Tidskriftsartikel (refereegranskat)abstract
- The thermal decomposition of 1,2-dioxetane and the associated production of chemiluminescent products, model for a wide range of chemiluminescent reactions, has been studied at the multistate multiconfigurational second-order perturbation level of theory. This study is in qualitative and quantitative agreement with experimental observations with respect to the activation energy and the observed increase of triplet and singlet excited products as substituents are added to the parent molecule. The, previously incomplete, reaction mechanism of the chemiluminescence of 1,2-dioxetane is now rationalized and described as mainly due to a particular form of entropic trapping.
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| 6. |
- De Vico, Luca, et al.
(författare)
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New general tools for constrained geometry optimizations
- 2005
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 1:5, s. 1029-1037
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Tidskriftsartikel (refereegranskat)abstract
- A modification of the constrained geometry optimization method by Anglada and Bofill (Anglada, J. M.; Bofill, J. M. J. Comput. Chem. 1997, 18, 992-1003) is designed and implemented. The changes include the choice of projection, quasi-line-search, and the use of a Rational Function optimization approach rather than a reduced-restricted-quasi-Newton-Raphson method in the optimization step. Furthermore, we show how geometrical constrains can be implemented in an approach based on nonreclunclant curvilinear coordinates avoiding the inclusion of the constraints in the set of redundant coordinates used to define the internal coordinates. The behavior of the new implementation is demonstrated in geometry optimizations featuring single or multiple geometrical constraints (bond lengths, angles, etc.), optimizations on hyperspherical cross sections (as in the computation of steepest descent paths), and location of energy minima on the intersection subspace of two potential energy surfaces (i.e. minimum energy crossing points). In addition, a novel scheme to determine the crossing point geometrically nearest to a given molecular structure is proposed.
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| 7. |
- Feifel, R., et al.
(författare)
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X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s ->sigma* resonance : Experiment and theory
- 2008
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:6
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Tidskriftsartikel (refereegranskat)abstract
- We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s ->sigma* excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.
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| 8. |
- Helsing, Johan, et al.
(författare)
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Laplace's equation and the Dirichlet-Neumann map: a new mode for Mikhlin's method
- 2005
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Ingår i: Journal of Computational Physics. - : Elsevier BV. - 0021-9991 .- 1090-2716. ; 202:2, s. 391-410
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Tidskriftsartikel (refereegranskat)abstract
- Mikhlin's method for solving Laplace's equation in domains exterior to a number of closed contours is discussed with particular emphasis on the Dirichlet-Neutnann map. In the literature there already exit tyro computational modes for Mikhlin's method. Here a new mode is presented. The new mode is at least as stable as the previous modes. Furthermore, its computational complexity in the number of closed contours is better. As a result. highly. accurate solutions in domains exterior to tens of thousands of closed contours can be obtained on a simple workstation.
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| 9. |
- Krogh, Jesper Wisborg, et al.
(författare)
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The prediction of the nuclear quadrupole splitting of Sn-119 Mossbauer spectroscopy data by scalar relativistic DFT calculations
- 2006
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 12:19, s. 5116-5121
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Tidskriftsartikel (refereegranskat)abstract
- The electric field gradient components for the tin nucleus of 34 tin compounds of experimentally known structures and Sn-119 Mossbauer spectroscopy parameters were computed at the scalar relativistic density functional theory level of approximation. The theoretical values of the electric field gradient components were used to determine a quantity, V, which is proportional to the nuclear quadrupole splitting parameter (Delta E). In a subsequent linear regression analysis the effective nuclear quadrupole moment, Q, was evaluated. The value of (11.9 +/- 0.1) fm(2) is a significant improvement over the non-relativistic result of (15.2 +/- 4.4) fm(2) and is in agreement with the experimental value of (10.9 +/- 0.8) fm(2). The average mean square error Delta E-calcd-Delta E-exptl = +/- 0.3 mm s(-1) is a factor of two smaller than in the non-relativistic case. Thus, the approach has a quality which provides accurate support for the structure interpretation by Sn-119 spectroscopy. It was noted that geometry optimization at the relativistic level does not significantly increase the quality of the results compared with non-relativistic optimized structures. The accuracy in the approach called on us to consider the singlet-triplet state nature of the electronic structure of one of the investigated compounds.
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| 10. |
- Lankinen, Åsa, et al.
(författare)
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Pollen-tube growth rates in Collinsia heterophylla (Plantaginaceae) : one-donor crosses reveal heritability but no effect on sporophytic-offspring fitness
- 2009
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Ingår i: Annals of Botany. - : Oxford University Press (OUP). - 0305-7364 .- 1095-8290. ; 103:6, s. 941-950
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Tidskriftsartikel (refereegranskat)abstract
- Evolutionary change in response to natural selection will occur only if a trait confers a selective advantage and there is heritable variation. Positive connections between pollen traits and fitness have been found, but few studies of heritability have been conducted, and they have yielded conflicting results. To understand better the evolutionary significance of pollen competition and its potential role in sexual selection, the heritability of pollen tube-growth rate and the relationship between this trait and sporophytic offspring fitness were investigated in Collinsia heterophylla. Because the question being asked was if female function benefited from obtaining genetically superior fathers by enhancing pollen competition, one-donor (per flower) crosses were used in order to exclude confounding effects of post-fertilization competition/allocation caused by multiple paternity. Each recipient plant was crossed with an average of five pollen donors. Pollen-tube growth rate and sporophytic traits were measured in both generations. Pollen-tube growth rate in vitro differed among donors, and the differences were correlated with in vivo growth rate averaged over two to four maternal plants. Pollen-tube growth rate showed significant narrow-sense heritability and evolvability in a father-offspring regression. However, this pollen trait did not correlate significantly with sporophytic-offspring fitness. These results suggest that pollen-tube growth rate can respond to selection via male function. The data presented here do not provide any support for the hypothesis that intense pollen competition enhances maternal plant fitness through increased paternity by higher-quality sporophytic fathers, although this advantage cannot be ruled out. These data are, however, consistent with the hypothesis that pollen competition is itself selectively advantageous, through both male and female function, by reducing the genetic load among successful gametophytic fathers (pollen), and reducing inbreeding depression associated with self-pollination in plants with mix-mating systems.
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