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11.
Detection of autofluorescence at the skin surface is highly influenced by melanin and hemoglobin. Epidermal absorption and scattering may also be an influencing factor and is represented in this article as a quantitative parameter, epidermal thickness. To examine this parameter we measured the 370 nm fluorescence in vivo after excitation with 330 nm and the 455 nm fluorescence after excitation with 330 and 370 nm. Measurements were performed on sun-exposed skin at the dorsal aspect of the forearm and shoulder and on nonexposed buttock skin. Skin pigmentation and redness of the same body sites were measured by reflectance spectroscopy. The thickness of the stratum corneum and the cellular part of epidermis was quantified by light microscopy of skin biopsies. Multiple regression analysis was used to find correlations between autofluorescence and the potential influencing factors. We found a highly significant correlation of skin autofluorescence with pigmentation and redness for both emission wavelengths (Em). A small but significant correlation to epidermal thickness was found only for excitation wavelength (Ex) 370 nm and Em455 nm if body site was included in the analysis. No correlation between Ex330:Em370 and Ex330:Em455 and thickness of epidermis was found. For practical use, correction of skin autofluorescence for pigmentation is essential, correction for redness is of less importance and correction for epidermal thickness is unnecessary. 相似文献
12.
Lindorff-Larsen K Kristjansdottir S Teilum K Fieber W Dobson CM Poulsen FM Vendruscolo M 《Journal of the American Chemical Society》2004,126(10):3291-3299
The denatured state of a protein contains important information about the determinants of the folding process. By combining site-directed spin-labeling NMR experiments and restrained computer simulations, we have determined ensembles of conformations that represent the denatured state of the bovine acyl-coenzyme A binding protein (ACBP) at three different concentrations of guanidine hydrochloride. As the experimentally determined distance information corresponds to weighted averages over a broad ensemble of structures, we applied the experimental restraints to a system of noninteracting replicas of the protein by using a Monte Carlo sampling scheme. This procedure permits us to sample ensembles of conformations that are compatible with the experimental data and thus to obtain information regarding the distribution of structures in the denatured state. Our results show that the denatured state of ACBP is highly heterogeneous. The high sensitivity of the computational method that we present, however, enabled us to identify long-range interactions between two regions, located near the N- and C-termini, that include both native and non-native elements. The preferential formation of these contacts suggests that the sequence-dependent patterns of helical propensity and hydrophobicity are important determinants of the structure in the denatured state of ACBP. 相似文献
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14.
Maj-Britt Schmidt Andersen Mette Kristensen Claudine Manach Estelle Pujos-Guillot Sanne Kellebjerg Poulsen Thomas Meinert Larsen Arne Astrup Lars Dragsted 《Analytical and bioanalytical chemistry》2014,406(7):1829-1844
While metabolomics is increasingly used to investigate the food metabolome and identify new markers of food exposure, limited attention has been given to the validation of such markers. The main objectives of the present study were to (1) discover potential food exposure markers (PEMs) for a range of plant foods in a study setting with a mixed dietary background and (2) validate PEMs found in a previous meal study. Three-day weighed dietary records and 24-h urine samples were collected three times during a 6-month parallel intervention study from 107 subjects randomized to two distinct dietary patterns. An untargeted UPLC-qTOF-MS metabolomics analysis was performed on the urine samples, and all features detected underwent strict data analyses, including an iterative paired t test and sensitivity and specificity analyses for foods. A total of 22 unique PEMs were identified that covered 7 out of 40 investigated food groups (strawberry, cabbages, beetroot, walnut, citrus, green beans and chocolate). The PEMs reflected foods with a distinct composition rather than foods eaten more frequently or in larger amounts. We found that 23 % of the PEMs found in a previous meal study were also valid in the present intervention study. The study demonstrates that it is possible to discover and validate PEMs for several foods and food classes in an intervention study with a mixed dietary background, despite the large variability in such a dataset. Final validation of PEMs for intake of foods should be performed by quantitative analysis. Figure
Examples of two urinary exposure markers for cabbage (left) and beetroot (right) found in the study from an untargeted LC‐MS metabolomics analysis of urine samples and self‐reported food intake data 相似文献
15.
用强子–弦级联模型JPCIAE及相应的Monte Carlo事例产生器研究相对论性核–核碰撞中带电粒子多重数的赝快度密度对能量和中心度的依赖关系.无需另调任何模型参数的条件下,此模型可以同时较好地描述相对论性pp实验数据及PHOBOS和PHENIX实验组的Au+Au实验数据.本文指出:因〈Npart〉并非严格定义的物理量,致使实验上和理论上确定〈Npart〉有一定任意性,从而使得每参加者核子对的带电粒子赝快度密度随着〈Npart〉的增加可能逐渐增大,也可能逐渐减小,因此用它来区分粒子产生机制是欠妥的. 相似文献
16.
T. Andersen O. Poulsen P.S. Ramanujam 《Journal of Quantitative Spectroscopy & Radiative Transfer》1976,16(6):521-527
The zero-field level-crossing technique has been used to determine radiative lifetimes of excited states in singly ionized zinc, cadmium, and mercury. The excited levels in Zn(II), Cd(II) and Hg(II) were populated by collisions between fast ions and helium gas. Particular attention has been paid to the systematic errors occurring in radiative lifetimes by this technique. The results are compared with the lifetimes obtained by beam-foil, phase-shift, delayed-coincidence techniques and theoretical calculations. 相似文献
17.
Bis-sulfonamides are demonstrated to be promising candidates for the efficient activation of carbonyl compounds through hydrogen bonding. Exemplified by three carbonyl addition reactions: Mukaiyama-aldol, hetero Diels-Alder and Friedel-Crafts reactions we show that bis-triflamides or bis-nonaflamides of commercially available chiral diamines act as chiral Br?nsted-acid catalysts, leading to the optically active products in moderate to excellent yields and with enantioselectivities up to 73% ee. 相似文献
18.
Sancho-García JC Brédas JL Beljonne D Cornil J Martínez-Alvarez R Hanack M Poulsen L Gierschner J Mack HG Egelhaaf HJ Oelkrug D 《The journal of physical chemistry. B》2005,109(11):4872-4880
Various end-substituted distyrylbenzenes have been synthesized to serve as guest molecules in inclusion compounds to promote efficient energy transport along one-dimensional channels. Their optical and photophysical properties have been characterized at both experimental and theoretical levels. All molecules display a large transition dipole moment between the ground state and lowest excited state and hence a short radiative lifetime (on the order of 1-2 ns). They also exhibit a large spectral overlap between the emission and absorption spectra, which enables efficient energy transport between molecules arranged in a head-to-tail configuration in nanochannels. Hopping rates on the order of 10(12) s(-1) are calculated at a full quantum-chemical level; this is much larger than the radiative lifetimes and opens the way for energy migration over large distances. Changes in the nature of the terminal substituents are found to modulate the optical properties weakly but to impact significantly the energy transfer rates. 相似文献
19.
利用溶液聚合和成酰胺反应合成了多功能梳状两亲性共聚物,聚(甲基丙烯酸-co-甲基丙烯酸十八酯)-(乙醇胺-乙二胺叶酸)(PSM-EE-FA).用红外光谱(FTIR),核磁共振(1H-NMR)及凝胶渗透色谱(GPC)表征了该聚合物的结构及分子量分布.实验结果证明合成了该聚合物,其数均分子量(Mn)为28600,多分散性为1.375.用该两亲梳状聚合物包覆油溶性CdSe/ZnS量子点,通过相转移作用,得到水溶性靶向量子点(PSM-EE-FA-QDs).该水溶性量子点溶液具有较好的稳定性.通过紫外-可见(UV-Vis)及荧光发射光谱分析对该量子点的光学性质进行研究.结果表明,PSM-EE-FA-QDs的紫外-可见光谱及荧光发射光谱峰形与原量子点基本一致.由于量子点表面聚合物层的形成,峰位发生少量红移.该量子点水溶液的荧光强度是原量子点氯仿溶液的98%,荧光产率是原量子点氯仿溶液的95%.动态光散射(DLS)及透射电镜(TEM)测试结果表明水溶性量子点分布均匀.合成的水溶性量子点不但光学性能稳定,而且聚合物及水溶性量子点的合成方法较为简便. 相似文献
20.