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21.
Abstract— Electrochromism of oriented all- trans -β-apo-8'-carotenoic acid is studied in thin capacitors. The linear electrochromism is very strong, in contrast to that of symmetrical carotenoids. It is proportional to the first derivative of the absorption spectrum. The quadratic electrochromism can be described as a superposition of fractions proportional to the first and second derivatives of the absorption spectrum. The permanent dipole moment difference between the ground state and the excited state of the carotenoic acid molecule is Δμ= 3.6 × 10-29 C·m (±20%) (10.7 Debyes). The polarizability difference parallel to the long axis of the molecule is Δα|| = 1.17 × 10-37 C·m2 ·V-1 (±20%) (1050 Å3 ). Furthermore, the relative permittivity of the solid carotenoic ethyl ester is r = 3.5 ± 0.2.
Δμ is due to the polarizing force of the carboxylic group. This force is equivalent to a mean local electric field of Ft ≅3 × 106 V/cm. Such a "local field" may also be exerted on a symmetrical carotenoid in the membrane of photosynthesis, e.g. by asymmetrical complex formation with a polarizing molecule. To obtain an effective permanent field of F p ≅ 2 × 106 V/cm across the membrane, as postulated in photosynthesis, a local field of F l ≅ 5.5 × 105 V/cm would be sufficient. F p is shown to be directed from inside to outside of the thylakoid. To realize this, e.g. a positive polar (i.e. electron-attracting) complex partner of the carotenoid, located more to the inside of the thylakoid, can be postulated. 相似文献
Δμ is due to the polarizing force of the carboxylic group. This force is equivalent to a mean local electric field of F
22.
23.
Diezemann G 《The Journal of chemical physics》2005,123(20):204510
The aging properties of a simple free-energy landscape model for the primary relaxation in supercooled liquids are investigated. The intermediate scattering function and the rotational correlation functions are calculated for the generic situation of a quench from a high temperature to below the glass transition temperature. It is found that the reequilibration of molecular orientations takes longer than for translational degrees of freedom. The time scale for reequilibration is determined by that of the primary relaxation as an intrinsic property of the model. 相似文献
24.
I. W. Fraser J. L. Garnett I. K. Gregor K. J. Jessop 《Journal of mass spectrometry : JMS》1975,10(1):69-73
Negative ion mass spectra of series of bis-(N, N-dithiocarbamato)nickel(II) complexes of formula [NiS2C·NR1R2]2 (where·NR1R2 ? ·NEt2 ·NPr2, ·NBu2, pyrrolidinyl, piperidyl, morpholinyl, and ·NEtPh) have been obtained by secondary electron capture. Intense molecular anions are given for all compounds, with most fragments originating from these ions. Metastable data indicate that CS2 is eliminated from all molecular anions. 相似文献
25.
Olaf Evers Erich Hdicke Gregor Ley 《Colloids and surfaces. A, Physicochemical and engineering aspects》1994,90(2-3):135-147
The self-consistent mean field model of Scheutjens and Fleer is used to model spherical aggregates of homopolymers and monomer—polymer particles in solution. For homopolymer aggregates we found that the chain ends are preferentially located at the exterior side of the polymer/solvent interface. The distribution of the end segments may be an important parameter in latex film formation. For monomer—polymer particles a “core-shell” structure is found with an extended core containing a monomer—polymer mixture and a thin shell a few nanometres thick strongly enriched with monomer. The monomer-enriched shell seems to function as a solvating envelope for the dangling chain ends. These results are compared with other simulations based on a single chain in a spherical-cavity model. 相似文献
26.
New Oxonium Bromochalcogenates(IV) — Synthesis, Structure, and Properties of [H3O][TeBr5] · 3 C4H8O2 and [H3O]2[SeBr6] Dark red crystals of the composition [H3O][TeBr5] · 3 C4H8O2 ( 1 ) were isolated from a saturated solution of TeBr4 in 1,4-dioxane containing a small amount of water. In this compound (space group P21/m, a = 8.922(4) Å, b = 13.204(7) Å, c = 9.853(5) Å, β = 91.82(4)° at 150 K) a square pyramidal [TeBr5]? anion has been isolated for the first time. The coordination sphere of the anion is completed to a distorted octahedron by weak interaction with a dioxane molecule of the cationic system. The [H3O]+ cations are connected to chains by dioxane molecules. At room temperature the compound is stable only in its mother liquor. Crystalline [H3O]2[SeBr6] ( 2 ) (space group Fm3m, a = 10.421(1) Å at 170 K) is a bromoselenous acid of high symmetry. The [H3O]+ ion is only weakly coordinated by Br atoms of the anion. The anions are isolated octahedral [SeBr6]2? units. The structure is isotypic to the K2[PtCl6] structure. Despite being a halogenochalcogen(IV) acid, 2 exhibits a remarkable thermal stability. Both oxonium compounds were characterized by single-crystal X-ray structure analyses. Vibrational spectra of 2 are reported. 相似文献
27.
Prof. Dr. Axel Reich 《Monatshefte für Mathematik》1982,93(1):33-37
A characterisation of all real Δ≠0 is given, such that $$\overline {f(\sigma + i\Delta \mathbb{N})} = \overline {f(\sigma + i\mathbb{R})} $$ holds for all Dirichlet seriesf(s)=Σa n n ?s and all σ greater than the abscissa of absolute convergence off. For only countably many Δ relation (*) is not valid. By using transcendental results it is shown, that (*) holds in the special case, Δ=1. 相似文献
28.
[reaction: see text] Triptycene-derived compounds have been prepared to serve as conformational equilibrium reporters for direct measurements of arene-arene interactions in the parallel-displaced orientation. A series of such compounds bearing arenes with different substituents were synthesized, and the ratios of the syn and anti conformers were determined by variable-temperature NMR spectroscopy. The syn conformer allows attached arenes to interact with each other while the anti conformer does not. The free energies derived from the syn/anti ratios in chloroform range from slightly positive (0.2 kcal/mol) to considerably negative (-0.98 kcal mol) values. The interactions between the arenes bearing electron-donating groups (EDG) are either negligible or slightly repulsive, while the interactions between arenes bearing electron-withdrawing groups (EWG) are attractive. Intermediate free energy values are obtained for those compounds bearing arenes with one EDG and one EWG. 相似文献
29.
The use of anodic stripping voltammetry (ASV) to determine the labile metal fraction in metal/ fulvic acid equilibrium systems is discussed. A method is described for distinguishing between the contributions of processes in the reduction and oxidation steps to the observed anodic (stripping) current. This method, which facilitates separate examination of the two processes, is based on timed addition of fulvic acids during the deposition step, on pH control, and on measurement of sampled-d.c. ASV peak areas (Faradaic charge) for metal/fulvic acid solutions. Results are presented for copper(Il) and lead(Il) complexes with six colloid-free soil-derived fulvic acids. In contrast to differential-pulse ASV, the stripping current measured by sampled-d.c. ASV showed no measurable contribution from ligand adsorption on the mercury drop. For heterogeneous ligand systems, such as fulvic acid, use of stripping peak heights over-estimates the fraction of non-labile metal complex because peak broadening results from the range of complexes formed in the anodic step. 相似文献
30.
I. K. Gregor 《Journal of mass spectrometry : JMS》1989,24(8):529-534
Reactions in the gas phase of the 13- and 15-electron radical anions [Cr(CO)3]? ˙ and [Cr(CO)4]? ˙ with a series of 27 aldehydes, ketones, esters and ethers have been examined. Sequential alkane eliminations and metal-bonded CO ligand displacements were the principal reactions identified for the RCHO/[Cr(CO)3]? ˙ systems with the latter reaction also common to the RCHO/[Cr(CO)4]? ˙ systems. While [Cr(CO)4]? ˙ was generally unreactive towards ketones R · R'CO, the principal products identified for [Cr(CO)3]? ˙/ketone reactions were the metal-decarbonylated species, respectively [R · R'CO · Cr(CO)x]? ˙ with x = 0–3, and [R · (R' - H2)CO · Cr(CO)2]? ˙. The reaction of [Cr(CO)3]? ˙ with esters RCOOR' proceeds via metal insertion into the alkoxy C? O bond to give end products of the type [R'O · Cr · R(CO)2]? and [R'O? Cr(CO)3]? while the sole ionic products of dialkyl ether/[Cr(CO)3]? ˙ reactions were identified as the alkoxytricarbonylchromium species [RO · Cr(CO)3]?. 相似文献