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51.
Marsman AW Havenith RW Bethke S Jenneskens LW Gleiter R van Lenthe JH Lutz M Spek AL 《The Journal of organic chemistry》2000,65(15):4584-4592
Long-range sigma-pi interactions in tetrahydro4H-thiopyran end-capped oligo(cyclohexylidenes) were identified by He(I) photoelectron spectroscopy (PES) and ab initio RHF/6-31G* calculations. The vertical ionization energies Ivj of the highest occupied molecular orbitals (MO's) were assigned using Koopmans' theorem (Iv,j = -epsilonj) and by correlation with the ionizations of related reference compounds. The experimental (PES) and theoretical (RHF/6-31G*) results are in good agreement. For tercyclohexylidene derivatives which contain two nonconjugated pi-bonds splittings deltaIv,j of the pi-bands in the range from approximately 0.5 to 0.7 eV (delta-epsilonj approximately 0.6 to 0.9 eV). For the bi- and tercyclohexylidene compounds containing two sulfur atoms at their alpha- and omega-end positions the pi-type sulfur lone pair bands [Lppi(S)] split significantly by deltaIvj approximately 0.3 to 0.4 eV (delta-epsilonj approximately 0.3 to 0.4 eV), i.e. sigma-pi interactions over distances of ca. 8 and 12 A, respectively, occur. The magnitude of the interactions and the observed splittings are independent of the anti and syn conformations of the oligo(cyclohexylidene) hydrocarbon skeletons. RHF/6-31G* Natural Bond Orbital analyses reveal that the Hax-C-C-Hax precanonical MO's (PCMO's) centered on the cyclohexyl-type rings are paramount for the relay of the through-bond sigma-pi interactions; no through-space sigma-pi interactions were identified. 相似文献
52.
Schadewaldt P Kamalanathan L Hammen HW Wendel U 《Rapid communications in mass spectrometry : RCM》2003,17(24):2833-2838
An established gas chromatography/mass spectrometry (GC/MS) method, devised for stable-isotope dilution analysis of plasma galactose, was developed to allow determination of erythrocyte (red blood cell, RBC) concentrations of galactose-1-phosphate and other primary metabolites relevant in galactosaemia. Galactose-1-phosphate was enzymatically converted to galactose, and the aldononitrile pentaacetate derivative was separated by gas chromatography and determined by mass spectrometry using chemical ionisation and selected ion monitoring of the [MH-60](+) ion. U-(13)C-Labelled standard was used for quantification. Comparative measurements were conducted using established fluorimetric and radiometric enzymatic methods. The GC/MS analysis for galactose-1-phosphate was linear (range examined 0-600 micromol/L(RBC), packed cells), of acceptable repeatability at low and high concentrations (within and between run CVs <15%), with a limit of quantification of 0.01 micromol/L(RBC). With samples from patients with classical galactosaemia there was a linear correlation with conventional enzymatic assays (r(2) > 0.927). In erythrocytes from post-absorptive patients under treatment, Q188R-heterozygous parents, and healthy subjects, galactose-1-phosphate concentrations (mean +/- SD) were found to be 142 +/- 38 (n = 41), 1.4 +/- 0.2 (n = 8), and 1.9 +/- 0.5 (n = 33) micromol/L(RBC), respectively. In comparison, free galactose concentrations were 3.8 +/- 1.7, 0.49 +/- 0.19, and 0.43 +/- 0.20 mol/L(RBC), respectively. The procedure allowed simultaneous galactitol analysis and proved to be useful to trace incorporation of (13)C-label into erythrocyte galactose metabolites in a D-[1-(13)C]galactose in vivo turnover study. 相似文献
53.
It is demonstrated how, in a plane film at small film thickness, the orientational order of the hydrocarbon segments of the molecules present in lipid films translates into an increase of the macroscopic normal stress from the film meniscus (film-forming bulk phase) to the proper film phase. 相似文献
54.
S. Ananda Weerawarna Michael Guha-Biswas Wendel L. Nelson 《Journal of heterocyclic chemistry》1991,28(5):1395-1403
An improved laboratory scale synthesis of bufuralol ( 1 ) and 1″-oxobufuralol ( 4 ) was accomplished. The intermediate benzofurans were prepared via aromatization of 2,3-dihydrobenzofurans or by a one-step acidcatalyzed cyclization from 2,2-diethoxyethyl 4-bromo-6-ethyl-2-formylphenyl ether ( 23 ). Base-catalyzed cyclization of 3-(5-bromo-3-ethyl-2-hydroxyphenyl)-1.2-epoxypropane ( 16 ) provided the key intermediate, 5-bromo-7-ethyl-2-hydroxymethyl-2,3-dihydrobenzofuran ( 17 ). Selective functionalization of the C-2 and C-7 positions of the benzofuran ring system was accomplished to afford both 1 and 4 . 相似文献
55.
Performance of a fast fiber based UV/Vis multiwavelength detector for the analytical ultracentrifuge
Holger M. Strauss Engin Karabudak Saroj Bhattacharyya Andreas Kretzschmar Wendel Wohlleben Helmut Cölfen 《Colloid and polymer science》2008,286(2):121-128
The optical setup and the performance of a prototype UV/Vis multiwavelength analytical ultracentrifuge (MWL-AUC) is described
and compared to the commercially available Optima XL-A from Beckman Coulter. Slight modifications have been made to the optical
path of the MWL-AUC. With respect to wavelength accuracy and radial resolution, the new MWL-AUC is found to be comparable
to the existing XL-A. Absorbance accuracy is dependent on the light intensity available at the detection wavelength as well
as the intrinsic noise of the data. Measurements from single flashes of light are more noisy for the MWL-AUC, potentially
due to the absence of flash-to-flash normalization in the current design. However, the possibility of both wavelength and
scan averaging can compensate for this and still give much faster scan rates than the XL-A. Some further improvements of the
existing design are suggested based on these findings. 相似文献
56.
Wohlleben W Bartels FW Boyle M Leyrer RJ 《Langmuir : the ACS journal of surfaces and colloids》2008,24(10):5627-5635
We report opal photonic crystals that are self-assembled from functional polymer particles. We randomly copolymerized functional side-chain monomers containing motifs that form homodimers or heterobridges. These include ether or methylene bridges, hydrazone bridges, acids for anhydride formation, low- T g copolymers or physical cross-links by hydrogen bonds and/or polarity. To generate particles that are monodisperse, spherical, and functionalized, we combined emulsifier-free synthesis with swelling synthesis steps. Laser diffraction from centimeter-sized beams, white-light interferometry, and atomic force microscopy demonstrates symmetry and homogeneity across the entire crystal without the loss of interstitial volume. Compared to the stability of nonfunctional particles, the stability of the crystal against immersion in water and isopropanol was enhanced from 10 to a perfect 100%. One of the successful approaches (methylene bridges from N-methylolmethacrylamid) is triggered by thermal activation, but as shown, this is operative far from the trivial regime of sintering. We demonstrate successful infiltration with and solvation of a laser-polymerizable resin, thus enabling the processing of 3D photonic waveguide structures. 相似文献
57.
58.
Bodner A Renn W Wendel U Schadewaldt P 《Isotopes in environmental and health studies》1996,32(2-3):237-246
Abstract A seven compartment model was applied for evaluation of oral L-[1-(13)C]leucine loading tests (38 μmol/kg body wt.) in healthy volunteers. The model comprises transport and absorption in stomach and gut into a central L-leucine-compartment which is connected to a protein compartment and to the compartment of the corresponding 2-oxo acid. CO(2) release from the latter occurs in a fast and a slow compartment into the central CO(2) compartment for exhalation. Using the fmins routine of MATLAB for parameter estimation, a good agreement was obtained between calculated and actually measured kinetics of (13)C-labelled metabolites and a mean in vivo L-leucine oxidation of 0.365 ± 0.071 μmol/kg per min (n = 5) was computed. Plausibility of the model was checked by predicting in vivo leucine oxidation rates from primed continuous infusion tests (priming: L-[1-(13)C]leucine, 5 μmol/kg; NaH(13)CO(2), 1.2 μmol/kg; infusion: L-[1-(13)C]leucine, 5 μmol/kg per h). In 5 tested volunteers, the experimental L-leucine oxidation rate amounted to 0.358 ± 0.105 μmol/kg per min versus predicted 0.324±0.099 μmol/kg per min. Possible causes for some observed intraindividual variations are discussed. 相似文献
59.
Abbott T Akiba Y Beavis D Bloomer MA Bond PD Chasman C Chen Z Chu YY Cole BA Costales JB Crawford HJ Cumming JB Debbe R Engelage J Fung SY Gushue S Hamagaki H Hansen O Hayano RS Hayashi S Homma S Huang HZ Ikeda Y Juricic I Kang J Katcoff S Kaufman S Kimura K Kitamura K Kurita K Ledoux RJ Levine MJ Miake Y Morse RJ Moskowitz B Nagamiya S Olness J Parsons CG Remsberg LP Sakurai H Sarabura M Stankus P Steadman SG Stephans GS Sugitate T Tannenbaum MJ van Dijk JH Videbaek F Vient M Vincent P 《Physical review D: Particles and fields》1992,45(11):3906-3920
60.
Backes C Karabudak E Schmidt CD Hauke F Hirsch A Wohlleben W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(44):13176-13184
We report on the extensive characterization of single-walled carbon nanotubes (SWCNTs) dispersed in a variety of surfactants, such as sodium dodecyl benzene sulfonate (SDBS), sodium cholate (SC), and three synthesized perylene-based surfactants, by using differential sedimentation in H(2)O and D(2)O. Multidimensional evaluation of the absorption profiles over radius, wavelength, and time allows the determination of the anhydrous specific volumes of the SWCNT-surfactant complexes as well as the concentration of the surfactant reservoir in free micelles with very slow sedimentation coefficients (<1 Svedberg). Among the perylene bisimide surfactants, the smallest derivative is densely adsorbed on the nanotube backbone with an anhydrous specific volume significantly above that of SC or SDBS. Bulky Newkome dendritic groups on one or both ends of the perylene moiety gradually reduce the adsorption density, in accord with the absolute adsorption between 0.66 and 1.7 mmol surfactant per gram SWCNTs. Furthermore, hydrodynamic analysis reveals that SDBS favors the "tails-on" configuration. The distribution of sedimentation coefficients of SWCNTs prepared by high-pressure carbon monoxide decomposition (HiPco) is broader and shifted to faster sedimentation than those prepared by using cobalt-molybdenum catalysis (CoMoCAT), which reflects the polydispersity in diameter and length. 相似文献