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51.
Several different models have been proposed to explain the origin of the complex anti-hole features observed in hole-burned (HB) spectra of excitonically coupled systems such as photosynthetic complexes. This lack of consensus presents a serious constraint on the interpretation of HB spectra and the underlying electronic structures of these systems. To resolve this problem we present results of modeling studies of non-resonant HB spectra taking uncorrelated excitation energy transfer and excitonic interactions into account. Simplified analytical results are compared with Monte Carlo simulations in which excitonic interactions are explicitly taken into account in order to disentangle a number of distinct effects. It is shown that these effects can accurately account for both hole shapes and the broad anti-hole structure observed in excitonically coupled systems. We argue that these models will provide a necessary framework for probing the electronic structure of these systems via HB spectroscopy. 相似文献
52.
Véronique Vacchina Sébastien Oguey Catherine Ionescu David Bravo Ryszard Lobinski 《Analytical and bioanalytical chemistry》2010,398(1):435-449
A method was developed for the determination of metal complexes with glycine (glycinates, [M(Gly)x(H2O)y(SO4)z]n, where M denotes Zn, Cu, Mn and Fe) in premix samples used for the preparation of animal feeds enriched in essential trace
elements. The method was based on the extraction of the glycinates with 10 mM ammonium acetate (pH 7.4) followed by their
determination using capillary electrophoresis with ICP MS detection. The stability of the glycinates in solution was verified
by electrospray TOF-MS. Each supplement was shown to be a mixture of complexes, with polymerization degrees ranging from n = 1 to n = 4 (depending on the metal), that were fully or partially dehydrated. The metal glycine complex moiety was found to be preserved
during capillary electrophoresis. The detection limits, calculated as three times the standard deviation of the blank plus
the blank, were between 0.05 and 0.2 μg mL−1 (as the metal), and the calibration curves were linear, allowing the analysis of premix samples. Repeatability for glycinate
standards was below 12%, and analytical precision was typically within 15%. 相似文献
53.
Density functional theory (DFT) calculations show that in vacuum such α-diketone as 1-(pyridin-2-yl)-4-(quinolin-2-yl)butane-2,3-dione
is much less stable than its enolimine–enaminone ((1Z,3Z)-3-hydroxy-4-(pyridin-2-yl)-1-(quinolin-2(1H)-ylidene)but-3-en-2-one) and dienaminone tautomers ((1Z,3Z)-1-(pyridin-2-yl)-4-(quinolin-2-yl)buta-1,3-diene-2,3-diol). Other its tautomers (multiple basic and acidic centers in their
molecules enable multiple proton transfer to take place) are even more labile. Strength of the intramolecular hydrogen bonds
and aromatic character of the (quasi)rings [proved by the Harmonic Oscillator Model of Aromaticity (HOMA) index] in their
molecules were found to be responsible for the observed tautomeric preferences. Polar and basic solvent disfavors and favors
the enolimine and enaminone tautomers, respectively. 相似文献
54.
DFT studies on tautomeric preferences. Part 3: Proton transfer in 2-(8-acylquinolin-2-yl)-1,3-diones
8-Acetyl- and 8-benzoyl-2-(quinolin-2-yl) derivatives of 1,3-diketones were studied from point of view of their tautomeric
preferences. Effective electron delocalization and strong hydrogen bonds were found to be responsible for high stability of
the enaminone form (the most stable tautomer). Density functional theory (DFT) calculations prove that enolimine and ketimine
species are less favored. Contribution of the zwitterionic resonance structures to the enaminone form is most significant
in 2-(quinolin-2(1H)-ylidene)-2H-indene-1,3-dione derivatives. Formation of the bifurcated hydrogen bonds was found to take place only in 8-acetyl derivatives.
One of these bonds is of the RAHB (Resonance Assisted Hydrogen Bond) type. There is a steric interaction of the pyridine β-hydrogen
and carbonyl oxygen atoms in the enaminone tautomers. 相似文献
55.
Beata Zielińska Ewa Borowiak-Palen Ryszard J. Kalenczuk 《Journal of Physics and Chemistry of Solids》2011,72(2):117-123
Fe-, Ni-, Co- and Ag- loaded NaNbO3 catalysts were prepared and their activities have been investigated in the reaction of photocatalytic hydrogen generation. Me/NaNbO3 were synthesized by impregnation of NaNbO3 in an aqueous solution of metal nitrates and then by calcination at the temperature of 400 °C. The crystallographic phases and optical and vibronic properties were examined by X-ray diffraction (XRD) and diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic methods, respectively. Morphology and chemical composition of the produced samples were studied using a high-resolution transmission electron microscope (HR-TEM) and an energy dispersive X-Ray spectrometer (EDX) as its mode. The detailed analysis has revealed that all the investigated catalysts exhibit high crystallinity and the presence of Fe2O3, NiO, Co3O4 and Ag2O oxides on Me/NaNbO3 was confirmed. Finally, the influence of different metal loadings (Fe, Ni, Co and Ag) on the photocatalytic activity of NaNbO3 for photocatalytic hydrogen generation has been investigated. Here we report that among all the Me/NaNbO3 photocatalysts Ag-loaded NaNbO3 exhibited higher photocatalytic efficiency for photocatalytic hydrogen generation than NaNbO3. 相似文献
56.
Adam Liwo Jarosław Pillardy Rajmund Kaźmierkiewicz Ryszard J. Wawak Małgorzata Groth Cezary Czaplewski Stanisaw Ołdziej Harold A. Scheraga 《Theoretical chemistry accounts》1999,101(1-3):16-20
A united-residue model of polypeptide chains developed in our laboratories with united side-chains and united peptide groups
as interaction sites is presented. The model is designed to work in continuous space; hence efficient global-optimization
methods can be applied. In this work, we adopted the distance-scaling method that is based on continuous deformation of the original
rugged energy hypersurface to obtain a smoothed surface. The method has been applied successfully to predict the structures
of simple motifs, such as the three-helix bundle structure of the 10-58 fragment of staphylococcal protein A in de novo folding
simulations and more complicated motifs in inverse-folding simulations.
Received: 24 April 1998 / Accepted: 4 August 1998 / Published online: 2 November 1998 相似文献
57.
We study the variational equations for solitons in noncommutative scalar field theories in an even number of spatial dimensions. We prove the existence of spherically symmetric solutions for a sufficiently large noncommutativity parameter θ and we prove the absence of spherically symmetric solutions for small θ. 相似文献
58.
59.
Sylwia Studzińska Sandra Mounicou Joanna Szpunar Ryszard Łobiński Bogusław Buszewski 《Analytica chimica acta》2015
This text presents a novel method for the separation and detection of phosphorothioate oligonucleotides with the use of ion pair ultra high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry The research showed that hexafluoroisopropanol/triethylamine based mobile phases may be successfully used when liquid chromatography is coupled with such elemental detection. However, the concentration of both HFIP and TEA influences the final result. The lower concentration of HFIP, the lower the background in ICP-MS and the greater the sensitivity. The method applied for the analysis of serum samples was based on high resolution inductively coupled plasma mass spectrometry. Utilization of this method allows determination of fifty times lower quantity of phosphorothioate oligonucleotides than in the case of quadrupole mass analyzer. Monitoring of 31P may be used to quantify these compounds at the level of 80 μg L−1, while simultaneous determination of sulfur is very useful for qualitative analysis. Moreover, the results presented in this paper demonstrate the practical applicability of coupling LC with ICP-MS in determining phosphorothioate oligonucleotides and their metabolites in serum within 7 min with a very good sensitivity. The method was linear in the concentration range between 0.2 and 3 mg L−1. The limit of detection was in the range of 0.07 and 0.13 mg L−1. Accuracy varied with concentration, but was in the range of 3%. 相似文献
60.