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101.
A Monte Carlo simulation of the concentration dependence of the fluorescence quantum yield M and emission anisotropyr
M of a system containing dye molecules in the form of monomers M and clusters T (statistical pairs and trimers) playing the role of the imperfect traps for nonradiative excitation energy transfer (NET) has been carried out. The simulation has been made for determined values of Förster critical distancesR
0
MM
andR
0
MT
and for several values ofR
0
TM
andR
0
TT
, assuming that the energy may be transferred from M* to T as well as from T* to M (reverse nonradiative energy transfer, RNET). It was shown that the RNET process in the range of high concentrations may strongly change the values ofr
M as well as those of M. For emission anisotropyr
M an effect of repolarization was observed which decreases rapidly with increasingR
0
TM
andR
0
TT
. A very good agreement between the simulation results of M and the theoretical model with no adjustable parameters was found. In the model, the RNET process and influence of correlation between active molecules on energy migration among monomers were taken into account. 相似文献
102.
Piotr Bojarski Leszek Kulak Czeslaw Bojarski Alfons Kawski 《Journal of fluorescence》1995,5(4):307-319
High-accuracy Monte Carlo simulations of the time-dependent excitation probabilityG
s
(t) and steady-state emission anisotropyr
M
/r
0M
for one-component three-dimensional systems were performed. It was found that the values ofr
M
/r
0M
obtained for the averaged orientation factor
only slightly overrate those obtained for the real values of the orientation factor
ik
2
. This result is essentially different from that previously reported. Simulation results were compared with the probability coursesG
s
(t) andR(t) obtained within the frameworks of diagrammatic and two-particle Huber models, respectively. The results turned out to be in good agreement withR(t) but deviated visibly fromG
s
(t) at long times and/or high concentrations. Emission anisotropy measurements on glycerolic solutions of Na-fluorescein and rhodamine 6G were carried out at different excitation wavelengths. Very good agreement between the experimental data and the theory was found, with ex0-0 for concentrations not exceeding 3.5·10–2 and 7.5·10–3
M in the case of Na-fluorescein and rhodamine 6G, respectively. Up to these concentrations, the solutions investigated can be treated as one-component systems. The discrepancies observed at higher concentrations are caused by the presence of dimers. It was found that for
ex
<0-0 (Stokes excitation) the experimental emission anisotropies are lower than predicted by the theory. However, upon anti-Stokes excitation (ex>0-0), they lie higher than the respective theoretical values. Such a dispersive character of the energy migration can be explained qualitatively by the presence of fluorescent centers with 0-0 transitions differing from the mean at 0-0. 相似文献
103.
Invariance properties of the multipole expansion with respect to the choice of the coordinate system
The physical interpretation of intermolecular interactions is usually based on the well-known multipole expansion of the inverse of the interparticle distance. The interaction energy is then interpreted as a sum of terms arising from the interaction of various multipole moments of both systems. It is supposed that the interaction energy calculated via the truncated multipole expansion generally depends on the choice of local coordinate systems through the coordinate dependence of the multipole moments. In this paper we prove that each term of the multipole expansion given in the form ∑k = 1 Ck/Rk is invariant with respect to identical translations and arbitrary rotations of the local coordinate systems. The invariant form of the convergence criterion of the multipole expansion is given and discussed. 相似文献
104.
Handong Li Leszek Czuchajowski William R. Trumble 《Journal of heterocyclic chemistry》1997,34(3):999-1003
A new type of porphyrinyl-nucleoside was synthesized by the Heck reaction of meso-tri(4-pyndyl)-p-acrylamidophenylporphyrin with (+)5-iodo-2′-deoxyuridine. The porphyrin used in this reaction was also applied in obtaining a water soluble porphyrin polymer and a copolymer with acrylamide. The porphyrinyl-nucleoside and the polymer and copolymer were investigated for their interaction with ds DNA, oligonucleotides and oligonucleotide duplexes. The extend of the red-shift of the Soret band of porphyrins and the slowing of the mobolity of DNA during electrophoresis of the interacting systems suggested that intercalation of cationic porphyrin units into ds DNA cannot be solely responsible for the observed phenomena. 相似文献
105.
Valensin D Mancini FM Łuczkowski M Janicka A Wisniewska K Gaggelli E Valensin G Łankiewicz L Kozlowski H 《Dalton transactions (Cambridge, England : 2003)》2004,(1):16-22
The copper(II) binding features of the APP(145-155) and APP(145-157) fragments of the amyloid precursor protein, Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-NH2 and Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 were studied by NMR spectroscopy and NMR findings were supported by UV-vis, CD and EPR spectra. Potentiometric measurements were performed only for the more soluble Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 peptide fragment. The following was shown: (i) the imidazole rings of all the three His residues are involved in metal coordination; (ii) metal binding induces ionisation of Leu-148 and His-149 amide nitrogens that complete the donor set to copper(II) in the species dominant at neutral pH; (iii) the unusual coordination scheme of the His-Xxx-His-Xxx-His consensus sequence justifies the high specificity for Cu(II) when compared to SOD-like or albumin-like peptides or even in amyloid Abeta fragments. The present findings may represent the key for interpreting the observed requirement of His residues conservation for the redox cycling between Cu(II) and Cu(I) by soluble APP. 相似文献
106.
Cheng-yi LiiChia-ding Liao Leszek StobinskiPiotr Tomasik 《European Polymer Journal》2002,38(8):1601-1606
Polymerization of ethylene was initiated by low-pressure glow plasma generated in this gas. Depending on starch present in this plasma polymerization could be considered either as graft-polymerization of ethylene onto starch or homopolymerization. Result of the treatment of cassava, corn, potato, rice Indica, sweet potato, and waxy corn starches with ethylene plasma was analyzed by means of high-performance size exclusion chromatography, X-ray powder diffraction, thermogravimetry, digestion with β-amylase, and scanning electron microscopy. Analyses suggested that graft-polymerization occurred on sweet potato and rice starch. With other starches homopolymerization of ethylene on granules took place. 相似文献
107.
Teobald Kupka Michał Stachów Leszek Stobiński Jakub Kaminský 《Magnetic resonance in chemistry : MRC》2013,51(8):463-468
The 3He nuclear magnetic shieldings were calculated for single helium atom, its dimer, simple models of fullerene cages (He@Cn), and single wall carbon nanotubes. The performances of several levels of theory (HF, MP2, DFT‐VSXC, CCSD, CCSD(T), and CCSDT) were tested. Two sets of polarization‐consistent basis sets were used (pcS‐n and aug‐pcS‐n), and an estimate of 3He nuclear magnetic shieldings in the complete basis set limit using a two‐parameter fit was established. Theoretical 3He results reproduced accurately previously reported theoretical values for helium gas, dimer, and helium probe inside several fullerene cages. Excellent agreement with experimental values was achieved. 3He nuclear magnetic shieldings of single helium atom approaching various points of benzene ring were tested, and an impact of 3He confinement within fullerene cages of different size on the 3He chemical shift was determined. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
108.
Leszek Zaraska Grzegorz D. Sulka Marian Jasku?a 《Journal of Solid State Electrochemistry》2011,15(11-12):2427-2436
The through-hole porous anodic aluminum oxide (AAO) membranes were fabricated by a simple two-step anodization of aluminum in 0.3?M oxalic acid, 0.3?M sulfuric acid, and 2?wt.% phosphoric acid solutions under different operating conditions followed by the removal of the remaining Al substrate and the pore opening/widening process. The effect of duration of the second anodizing step on the thickness of the porous oxide layer and the influence of other anodizing conditions such as applied voltage, type of electrolyte, and purity of the substrate on the rate of porous oxide growth were discussed in detail. The pore opening procedure for all synthesized membranes was optimized, and the influence of the duration of chemical etching on structural features of AAO membranes, especially pore diameter, was studied. The rate of pore widening was established for AAO membranes formed in various anodizing electrolytes and for different temperatures of 5?wt.% H3PO4 used for alumina dissolution. 相似文献
109.
Zdzisław Denkowski Leszek Gasiński Nikolaos S. Papageorgiou 《Nonlinear Analysis: Theory, Methods & Applications》2007
In this paper we study semilinear hemivariational inequalities at resonance. Assuming a partially anticoercive nonsmooth potential we prove an existence and a multiplicity theorem. The method of the proof is variational and in the multiplicity result, we employ the nonsmooth local linking theorem. 相似文献
110.
Barbara Pieczyrak Leszek Jurczyszyn Barbara Stankiewicz 《Czechoslovak Journal of Physics》2006,56(1):85-92
We present theoretical study of structural and electronic properties of SiC(001)-p(2 × 1)-Si-terminated surface and the formation
of its STM images. Ab initio calculations independently performed with the use of plane-wave and local-orbital basis have shown that the structure of
this surface is built up by long symmetric silicon dimers, which agrees with the results of previous ab initio studies done by other authors. STM simulations show that the variation of the tunneling current along substrate surface very
well reproduces the localization properties of occupied and unoccupied surface states (π, π*). We have found that the tensile
stress applied along dimers axis causes the buckling of surface dimers and transfer of the charge between dimers atoms. This
result suggests that the buckling of silicon surface dimers observed in LEED measurements might be caused by external stress.
Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005. 相似文献