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51.
Thirty-eight saponins in two chromatographic fractions (QH-B and QH-C) from Quillaja saponaria Molina have been separated by a two-step high-performance liquid chromatography (HPLC) procedure and investigated by electrospray ionisation ion trap multiple-stage mass spectrometry (ESI-ITMS(n)) in positive ion mode. MS(2) and MS(3) spectra of the compounds were investigated by principal component analysis (PCA) and could be classified by partial least squares - discriminant analysis (PLS-DA) according to the structures of the oligosaccharides at C-3 and C-28 of the saponins. Four minor components with novel structures were found in a previously non-investigated fraction of QH-C. The structures of two of these components, J1 and J1a, were predicted by PLS-DA whereas the structures of the two others, J2 and J3, were only partly predicted. The structures of J1 and J1a were composed of structural elements found in the 34 known saponins whereas a new acyl substituent, not included in the training set used for calibration of the PLS-DA models, was found in J2 and J3, making these two components outliers. The complete structures of the four components were confirmed by monosaccharide analysis, MS(n) data and (1)H NMR spectroscopy. 相似文献
52.
Isaksson M Norlin N Westlund PO Johansson LB 《Physical chemistry chemical physics : PCCP》2007,9(16):1941-1951
An extended F?rster theory (EFT) on electronic energy transfer is presented for the quantitative analysis of time-resolved fluorescence lifetime and depolarisation experiments. The EFT, which was derived from the stochastic Liouville equation, yields microscopic information concerning the reorientation correlation times, the order parameters, as well as inter chromophoric distances. Weakly interacting donor and acceptor groups, which reorient and interact in a pair wise fashion, are considered, under isotropic and anisotropic conditions. For the analysis of experiments it is shown that not only do we need to consider the orientational distributions of the transition dipoles, but the internal reorienting molecular dynamics within the pair which is of even greater importance. The latter determines the shape as well as the rate of the observed donor fluorescence and depolarisation decays, which are most often not mono-exponential functions. It is shown that the commonly used F?rster theory is a special case of the EFT. Strategies are presented for applying the EFT, which makes use of Brownian dynamics simulation. 相似文献
53.
Watanabe T Inadomi Y Fukuzawa K Nakano T Tanaka S Nilsson L Nagashima U 《The journal of physical chemistry. B》2007,111(32):9621-9627
Molecular orbital calculations of the complex between DNA-ERE (estrogen response element) and ER (estrogen receptor)-DBD (DNA-binding domain) were performed using the fragment molecular orbital (FMO) method, which enables large-scale MO (molecular orbital) calculations by reducing the computational cost and by significantly increasing efficiency for parallel computation. Such a large system, which contains 3354 atoms, is impractical via conventional MO methods due to the immense computational cost. Details of the interaction between DNA-ERE and ER-DBD were revealed in this study as follows by using the FMO calculations to analyze the interfragment interaction energies (IFIEs) and the electrostatic potentials (ESPs). An area with a high positive ESP is identified on the DNA-binding side of ER-DBD and is the main driving force behind access to the DNA. The position of the ER-DBD monomer can be fixed on a phosphate group of DNA-ERE by the strong electrostatic interactions, whereas the rotation cannot be fixed. In contrast, both the position and rotation of the ER-DBD dimer can be fixed and can therefore form the stable (ER-DBD)2...DNA-ERE complex. Dimerization of the ER-DBD monomers, each of which have a charge of +5 , is mainly due to large attractive interaction energies of the second Zn fragments. The base pairs in the consensus sequence of DNA-ERE interact only with the recognition helix located in the major groove due to the large shielding effect of the phosphate groups of DNA. The recognition helix has weaker interactions with the base pairs than the electrostatic interactions with the phosphate groups. Thus, the DNA-binding machinery of the ER-DBD dimer, which can secure the recognition helix in the major groove of DNA, is crucial for interactions between the recognition helix and base pairs. 相似文献
54.
A new experimental and theoretical approach is presented for the quantitative determination and assignment of the two-photon absorption tensor of fluorophores dissolved in liquid solutions. Two linearly independent time-resolved fluorescence anisotropies and the two-photon polarization ratio were determined from experiments based on using the time-correlated single photon counting technique. The data were analyzed in a global manner under the assumption of prevailing diffusive molecular reorientations and when accounting for the influence of rapid unresolved reorientations. The method has been applied in fluorescence studies of perylene, two-photon excited at 800 nm. The analysis suggests that the two-photon transition is mediated via vibronic coupling including at least two vibrations of different symmetry, and also that the first singlet excited electronic state acts as a dominating intermediate state. 相似文献
55.
Selective pressurized liquid extraction for multi-residue analysis of organochlorine pesticides in soil 总被引:1,自引:0,他引:1
Hussen A Westbom R Megersa N Mathiasson L Björklund E 《Journal of chromatography. A》2007,1152(1-2):247-253
A selective pressurized liquid extraction (SPLE) procedure capable of performing simultaneous extraction and clean-up has been demonstrated for multi-residue analysis of organochlorine pesticides (OCPs) in soil. The final method was performed at 100 degrees C for 3 x 10 min using acetone/n-heptane (1:1, v/v). Florisil was placed inside the extraction cell downstream the sample to remove interfering compounds. Extraction of two soil samples by SPLE gave a recovery which was over 80% for beta-endosulfan, endosulfan sulfate, p,p'-DDT and p,p'-DDE compared to PLE with off-line clean-up. The same trend was observed when applying the SPLE method to a certified reference soil sample (CRM 811-050) containing 13 OCPs, where the SPLE method gave 80-90% recovery vis-à-vis the PLE method with off-line clean-up. Feasibility of the SPLE method was further demonstrated by applying it to five real soil samples collected in Ethiopia. 相似文献
56.
Lüder K Lindfors L Westergren J Nordholm S Kjellander R 《The journal of physical chemistry. B》2007,111(7):1883-1892
The solubility of drugs in water is investigated in a series of papers and in the current work. The free energy of solvation, DeltaG*(vl), of a drug molecule in its pure drug melt at 673.15 K (400 degrees C) has been obtained for 46 drug molecules using the free energy perturbation method. The simulations were performed in two steps where first the Coulomb and then the Lennard-Jones interactions were scaled down from full to no interaction. The results have been interpreted using a theory assuming that DeltaG*(vl) = DeltaG(cav) + E(LJ) + E(C)/2 where the free energy of cavity formation, DeltaG(cav), in these pure drug systems was obtained using hard body theories, and E(LJ) and E(C) are the Lennard-Jones and Coulomb interaction energies, respectively, of one molecule with the other ones. Since the main parameter in hard body theories is the volume fraction, an equation of state approach was used to estimate the molecular volume. Promising results were obtained using a theory for hard oblates, in which the oblate axial ratio was calculated from the molecular surface area and volume obtained from simulations. The Coulomb term, E(C)/2, is half of the Coulomb energy in accord with linear response, which showed good agreement with our simulation results. In comparison with our previous results on free energy of hydration, the Coulomb interactions in pure drug systems are weaker, and the van der Waals interactions play a more important role. 相似文献
57.
Lüder K Lindfors L Westergren J Nordholm S Kjellander R 《The journal of physical chemistry. B》2007,111(25):7303-7311
The solubility of drugs in water is investigated in a series of papers. In this work, we address the process of bringing a drug molecule from the vapor into a pure drug amorphous phase. This step enables us to actually calculate the solubility of amorphous drugs in water. In our general approach, we, on one hand, perform rigorous free energy simulations using a combination of the free energy perturbation and thermodynamic integration methods. On the other hand, we develop an approximate theory containing parameters that are easily accessible from conventional Monte Carlo simulations, thereby reducing the computation time significantly. In the theory for solvation, we assume that DeltaG* = DeltaGcav + ELJ + EC/2, where the free energy of cavity formation, DeltaGcav, in pure drug systems is obtained using a theory for hard-oblate spheroids, and ELJ and EC are the Lennard-Jones and Coulomb interaction energies between the chosen molecule and the others in the fluid. The theoretical predictions for the free energy of solvation in pure amorphous matter are in good agreement with free energy simulation data for 46 different drug molecules. These results together with our previous studies support our theoretical approach. By using our previous data for the free energy of hydration, we compute the total free energy change of bringing a molecule from the amorphous phase into water. We obtain good agreement between the theory and simulations. It should be noted that to obtain accurate results for the total process, high precision data are needed for the individual subprocesses. Finally, for eight different substances, we compare the experimental amorphous and crystalline solubility in water with the results obtained by the proposed theory with reasonable success. 相似文献
58.
Lennart Bergström Sara Stemme Torbjörn Dahlfors Hans Arwin Lars Ödberg 《Cellulose (London, England)》1999,6(1):1-13
Calculations of Hamaker constants using Lifshitz theory require the availability of accurate dielectric data, especially in the visible-ultraviolet region. We present spectroscopic ellipsometry data on well-defined cellulose films of a limited thickness range (100–140 layers) deposited on an oxidised and hydrophobised silicon substrate. The spectral data, representing measurements from a perpendicular orientation to the fibre deposition direction, was used for estimates of the necessary spectral parameters, i.e. the oscillator strengths and characteristic frequencies in the UV-range. Our calculations show that cellulose has a relatively low Hamaker constant in air (58 zJ) and water (8.0 zJ). The implications for the surface energy estimates of cellulose and colloidal interactions between cellulose and various types of fillers and coating colours are indicated. 相似文献
59.
60.
Christoph Bargholtz Jan Becker Lennart Holmberg 《Zeitschrift für Physik A Hadrons and Nuclei》1984,315(3):349-353
The directional correlations betweenL-conversion electrons andL x-rays have been measured. The electrons were emitted in the 86.78keV 2+→0+ transition in160Dy, in the decay of160Tb. The experimental results areA 22(e L -x Li )=0.085 (22),A 22(e L -x Lα )=0.0066 (29),A 22(e L -x Lβ )=0.0000 (27), andA 22(e L -x Lγ )=0.0096 78). These results are in disagreement with published theoretical values. It is suggested that the discrepancy is due to a phase inconsistency in the internal conversion matrix elements and there is good agreement withA 22 values calculated in this work. 相似文献