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Photo induced excited state dynamical processes of cinchonine alkaloid dication (C++) have been studied over a wide range of temperature using steady state and nanosecond time-resolved fluorescence spectroscopic
techniques. The temperature-dependent fluorescence studies of C++ clearly indicate the existence of two distinct emitting species having their own characteristic decay rates. The shorter-lived
species shows a usual temperature dependence with increasing non-radiative deactivation at higher temperatures, while the
longer-lived species show features resembling to the excited state solvent relaxation process with a large solvent relaxation
time (τ
r ∼ 6 ns). The species emitting in the lower energy side, having longer decay time is found to be more sensitive towards chloride
ion quenching and has a charge transfer character. Further, concentration quenching with decrease in τ
r of long lived species shows the possibility of energy migration along with solvent relaxation in C++. 相似文献
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K. Stastny K. Frgalova A. Hera M. Vass M. Franek 《Journal of chromatography. A》2009,1216(46):8187-8191
An improved LC-MS/MS method for the determination of semicarbazide in whole egg is described. Waters OASIS-MCX cation exchange purification cartridges increased the sensitivity for analysis by LC-MS/MS. The validation study was carried out according to criteria and requirements of Commission Decision 2002/657/EC for confirmatory analysis and provided the data as follows: The correlation coefficient for the matrix calibration curve, in the range of 0–5 μg kg−1, was r = 0.9968. The detection capability and decision limit, measured according to ISO11843-2, were CCα = 0.20 μg kg−1 and CCβ = 0.25 μg kg−1. Repeatability (CVSr) and within-laboratory reproducibility (CVSwr) determined for the concentration levels of 0.2, 0.5 and 1.0 μg kg−1 SEM ranged from 11.9 to 5.7% and 11.8 to 6.3%, respectively. The validated method was applied to investigate SEM stability in incurred materials (egg homogenates) during long-term storage at −20 °C and 4 °C. The study proved by a two-sampling test that SEM at levels of 17. 7, 1.2, 10.6 and 0.47 μg kg−1 was stable for up to 12 months. 相似文献
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In the framework of the dynamical mean field theory, we investigate the densities of states of the fermionic and bosonic branches
of the spectrum of the asymmetric Hubbard model, which is used to describe a strongly correlated two-sort (A, B) system of
fermions (electrons). To solve the effective one-site problem, we develop an approximate analytic approach based on the Kadanoff-Baym
generating functional method. This technique allows constructing the irreducible part (the mass operator) of the particle
Green’s function in the form of a formal expansion in powers of the coherent potential. In the first order, the scheme reproduces
the so-called generalized approximation Hubbard-III. To improve it, we develop a self-consistent method for calculating both
the fermionic and bosonic Green’s functions. As U → ∞ in the Falicov-Kimball limit for the asymmetric Hubbard model, when
the particles of sort B become localized, we find the spectral densities ρB and ρAB of states of both branches and consider the changes of their forms depending on temperature and particle concentrations.
Comparing with the exact thermodynamic dependences μB(nB), we establish the applicability limits of the self-consistent generalized approximation Hubbard-III.
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Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 154, No. 1, pp. 164–182, January, 2008. 相似文献
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MR Seyedsayamdost S Cleto G Carr H Vlamakis M João Vieira R Kolter J Clardy 《Journal of the American Chemical Society》2012,134(33):13550-13553
Interrogation of the evolutionary history underlying the remarkable structures and biological activities of natural products has been complicated by not knowing the functions they have evolved to fulfill. Siderophores-soluble, low molecular weight compounds-have an easily understood and measured function: acquiring iron from the environment. Bacteria engage in a fierce competition to acquire iron, which rewards the production of siderophores that bind iron tightly and cannot be used or pirated by competitors. The structures and biosyntheses of "odd" siderophores can reveal the evolutionary strategy that led to their creation. We report a new Serratia strain that produces serratiochelin and an analog of serratiochelin. A genetic approach located the serratiochelin gene cluster, and targeted mutations in several genes implicated in serratiochelin biosynthesis were generated. Bioinformatic analyses and mutagenesis results demonstrate that genes from two well-known siderophore clusters, the Escherichia coli enterobactin cluster and the Vibrio cholera vibriobactin cluster, were shuffled to produce a new siderophore biosynthetic pathway. These results highlight how modular siderophore gene clusters can be mixed and matched during evolution to generate structural diversity in siderophores. 相似文献
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