排序方式: 共有42条查询结果,搜索用时 453 毫秒
31.
Kaletaş BK Mandl C van der Zwan G Fanti M Zerbetto F De Cola L König B Williams RM 《The journal of physical chemistry. A》2005,109(29):6440-6449
Arcyriarubin A and arcyriaflavin A, two strongly emissive and intensely colored natural products containing both two indoles and a maleimide unit, are investigated (in the flavin the two indole moieties are coupled by a cyclization). The photophysical properties of these compounds were studied in several solvents using UV-vis absorption, steady-state and time-resolved emission, nano- and femtosecond transient absorption spectroscopy. Furthermore, the effect of complexation with zinc(II) 1,4,7,11-tetraazacyclododecane on the photophysical properties of these natural products has been investigated. The chemical structures of the compounds would suggest a charge transfer (CT) character in the ground and/or excited states, since indole is a well-known electron donor and maleimide is a good electron acceptor. Their solvatochromic behavior was investigated by using the Kamlet-Taft approach and indicates only a small CT character in the excited state. This is substantiated by the time-resolved spectroscopy and the complexation study. Molecular orbital calculations indicate that there are no electronic transitions in which a large electron density is transferred from one indole unit to the maleimide part. All calculated orbitals show a strong delocalization of the electron density over the whole molecule. These findings corroborate the experimental results. Whereas the two compounds do have a substantial (calculated) ground-state dipole moment (6 D) and show some solvatochromic behavior, they behave more like conjugated aromatic systems than like electron donor-acceptor systems. 相似文献
32.
Concentrations of 38 elements in brown coal, bottom ash and size fractionated ESP coal ash from the Belchatów I Power Plant
were determined by INAA. Based on enrichment factors calculated relatively to iron and average crustal rock composition as
a function of particle size the elements are grouped into three classes: Group I, elements that show little or no enrichment
in the small particles /Na, Mg, Al, K, Sc, Ti, Mn, Co, Rb, Cs, Ba, La, Ce, Sm, Eu, Lu, and Th/; Group II, elements whose enrichment
increases greatly with decreasing particle size /Cl, Zn, As, Se, Br, Cd, Sb, and I/; and Group III, elements whose behaviour
is intermediate to that of elements in Group I and II /Ca, V, Cr, Ni, Cu, Ga, Sr, Mo, In, W, and Au/. 相似文献
33.
Elzbieta W. Kaleta Lee A. Applegate Ronald D. Ley † 《Photochemistry and photobiology》1991,54(5):747-752
Exposure of an established marsupial cell line, PtK2 (Potorous tridactylus), to ultraviolet radiation (UVR) from an FS-40 sunlamp (280-400 nm) resulted in a fluence-dependent release of radiolabeled arachidonic acid (AA) from cell membranes. Post-UVR, but not pre-UVR, exposure to photoreactivating light reversed UVR-induced pyrimidine dimers in DNA and suppressed the UVR-induced release of AA. These data indicate that DNA damage contributes to the release of AA from membrane phospholipids. 相似文献
34.
Dr. Jacopo Perego Dr. Charl X. Bezuidenhout Prof. Silvia Bracco Dr. Sergio Piva Dr. Giacomo Prando Cristian Aloisi Prof. Pietro Carretta Dr. Jiří Kaleta Thi Phuong Le Prof. Piero Sozzani Dr. Andrea Daolio Prof. Angiolina Comotti 《Angewandte Chemie (International ed. in English)》2023,62(5):e202215893
Fluorinated Metal-Organic Frameworks (MOFs), comprising a wheel-shaped ligand with geminal rotating fluorine atoms, produced benchmark mobility of correlated dipolar rotors at 2 K, with practically null activation energy (Ea=17 cal mol−1). 1H T1 NMR revealed multiple relaxation phenomena due to the exchange among correlated dipole-rotor configurations. Synchrotron radiation X-ray diffraction at 4 K, Density Functional Theory, Molecular Dynamics and phonon calculations showed the fluid landscape and pointed out a cascade mechanism converting dipole configurations into each other. Gas accessibility, shown by hyperpolarized-Xe NMR, allowed for chemical stimuli intervention: CO2 triggered dipole reorientation, reducing their collective dynamics and stimulating a dipole configuration change in the crystal. Dynamic materials under limited thermal noise and high responsiveness enable the fabrication of molecular machines with low energy dissipation and controllable dynamics. 相似文献
35.
Marzenna Klimaszewska Sabina Grska Grzegorz apienis Beata Kaleta Sandra Grska Marta Kaszowska Maciej Dawidowski Andrzej Gamian Radoslaw Zagodon Andrzej Grski Jadwiga Turo 《Molecules (Basel, Switzerland)》2021,26(17)
We previously described the biosynthesis, isolation, and immunosuppressive activity of the selenium-containing polysaccharide fraction isolated from the mycelial culture of Lentinula edodes. Structural studies have shown that the fraction was a protein-containing mixture of high molar mass polysaccharides α- and β-glucans. However, which of the components of the complex fraction is responsible for the immunosuppressive activity non-typical for polysaccharides of fungal origin has not been explained. In the current study, we defined four-polysaccharide components of the Se-containing polysaccharide fraction determined their primary structure and examined the effect on T- and B-cell proliferation. The isolated Se-polysaccharides, α-1,4-glucan (Mw 2.25 × 106 g/mol), unbranched β-1,6-d-glucan, unbranched β-1,3-d-glucan and β-1,3-branched β-1,6-d-glucan (Mw 1.10 × 105 g/mol), are not typical as components of the cell wall of L. edodes. All are biologically active, but the inhibitory effect of the isolated polysaccharides on lymphocyte proliferation was weaker, though more selective than that of the crude fraction. 相似文献
36.
37.
We study the Feynman-Kac semigroup generated by the Schrödinger operator based on the fractional Laplacian ??(???Δ)α/2???q in R d , for q?≥?0, α?∈?(0,2). We obtain sharp estimates of the first eigenfunction φ 1 of the Schrödinger operator and conditions equivalent to intrinsic ultracontractivity of the Feynman-Kac semigroup. For potentials q such that lim|x| →?∞? q(x)?=?∞ and comparable on unit balls we obtain that φ 1(x) is comparable to (|x|?+?1)???d???α (q(x)?+?1)???1 and intrinsic ultracontractivity holds iff lim|x| →?∞? q(x)/log|x|?=?∞. Proofs are based on uniform estimates of q-harmonic functions. 相似文献
38.
An HPLC method using C18-modified silica as stationary phase has been developed for environmental trace analysis of nine (fluoro)quinolones. Detection is done by fluorescence measurement or MS using the modes of SIM and selected reaction monitoring (SRM). Best separation is achieved with a gradient consisting of 50 mM formic acid and methanol, which is fully compatible with MS coupling. LOQs (S/N of 10) for fluorescence detection are between 10 and 60 microg/L, depending on the analyte. MS detection (SIM and SRM) yields LOQs that are better by a factor of at least an order of magnitude. Sample preconcentration and sample clean-up is accomplished by SPE (preconcentration factor of 1000), leading to LOQs in the low ng/L range. Recoveries of the preconcentration procedure are better than 80% for all analytes. The suitability for real samples has been demonstrated by analyzing surface waters, municipal waste waters, sewage treatment plant effluents, sewage sludge, and sediment taken from rivers and fish ponds. The method should also be useful for determination of residues of (fluoro)quinolones in food or other matrices. The degradation of the (fluoro)quinolones has been examined over 5 days in order to get information about the decomposition rate and the degradation products eventually occurring in the environment. 相似文献
39.
Concentration of 38 elements in size-fractionated brwon and hard coal ash from two Polish power plants have been measured by instrumental neutron activation analysis (INAA). Based on the enrichment factors calculated relative to iron and average crustal rock composition, the elements are grouped into three classes: Group I elements show little or no enrichment in the small fraction; Group II elements increase their enrichment with decreasing particle size; the behaviour of Group III elements is intermediate between those of elements in Groups I and II. 相似文献
40.
Kaleta K Ruhmann M Theilmann O Beweries T Roy S Arndt P Villinger A Jemmis ED Schulz A Rosenthal U 《Journal of the American Chemical Society》2011,133(14):5463-5473
The reaction of the low-valent metallocene(II) sources Cp(2)Ti(η(2)-Me(3)SiC(2)SiMe(3)) (7) and Cp(2)Zr(py)(η(2)-Me(3)SiC(2)SiMe(3)) (11, Cp = η(5)-cyclopentadienyl, py = pyridine) with carbodiimides RN═C═NR (R = Cy, i-Pr, p-Tol) leads to the formation of five membered hetero-metallacycloallenes Cp(2)M{Me(3)SiC═C═C[N(SiMe(3))(R)]-N(R)} (9M-R) (M = Ti, R = i-Pr; M = Zr, R = Cy, i-Pr, p-Tol). Elimination of the alkyne (as the hitherto known reactivity of titanocene and zirconocene alkyne complexes would suggest) was not observed. The molecular structures of the obtained complexes were confirmed by X-ray studies. Moreover, the structure and bonding of the complexes 9Zr-Cy and 9Zr-p-Tol was investigated by DFT calculations. 相似文献