Characterization of a single molecule DNA switch in free solution

We have studied a donor-acceptor fluorophore-labeled DNA switch where the acceptor is Alexa-647, a carbocyanine dye, in solution at the single molecule level to elucidate the fluorescence switching mechanism. The acceptor, which is in an initial high fluorescence trans state, undergoes a photoisomerization reaction resulting in two additional states during its sub-millisecond transit across the probe volume. These two states are assigned to a nonfluorescent triplet trans state that strongly quenches the donor emission and a singlet cis state that blocks the fluorescence resonance energy transfer (FRET) pathway and gives rise to donor-only fluorescence. The formation of these states is faster than the transit time, so that all three states are approximately equally populated under our experimental conditions. The acceptor dye can stick to the DNA in all these states, with the rate of unsticking determining the rate of isomerization into the other states. Measurement of the rate of change of the FRET signal therefore provides information about the fluorophore-DNA intramolecular dynamics. These results explain the large zero peak in the proximity ratio, often seen in single molecule FRET experiments, and suggest that photoinduced effects may be important in single molecule FRET experiments using carbocyanine dyes. They also suggest that for fast photoinduced switching the interactions of the acceptor dye with the DNA and other surfaces should be prevented.     

A Minor New Flavone from Scutellaria baicalensis Georgi

A new flavone,6,2′-dihydroxy-5,7,8,6′-tetramethoxyflavone,was isolated from the roots of Scutellaria baicalensis. Its structure was established on the basis of spectral evidences.     

Synthesis of Nicotinic Acid by Potassium Dichromate Oxidation

IntroductionNicotinic acid,whose IUPAC name is 3-pyridine formic acid,also known as Vitamine B5,ismainly used as an additive in food,drink andforage industry[1— 3 ] .In medical practice,it is usedto cure pellagra and other relative vitaminedeficiency illness. It is also an intermediate for thesynthesis of important medicines and chemicalmaterials[1,4] . In China,the demand of nicotinicacid is very big. However,there are manyproblems in the current preparation methods ofnicotinic acid,such…     

弱相互作用构筑的二维、三维冠醚配合物{[K(18-C-6)2(C2H4Cl2)}[Ni(dmit)2]2和[K(18-C-6)][Ni(dmit)2]的合成与结构

研究了18－冠－6与NiCl·6H2O,K2dmit(dmit=4,5-dimercapto-1,3-dithiole- 2-thione,C3S5^2－）在不同溶剂中反应生成的两个标题配合物{[K(18-C-6)]2 (C2H4Cl2)}[Ni(dmit)2]2（1）和[K(18-C-6)][Ni(dmit)2](2)。通过元素分析、红 外光谱、单晶X射线衍射进行了表征。1和2均属三斜晶系,空间群P1^-.1的晶体学 数据：a=1.0272(2)nm,b=1.2282(3)nm,c=1.4205(3)nm,α=113.473(3)°,β=90. 609(3)°,γ=91.439(3)°,V=1.6430(6)nm^3,Z=2,F（000)=876,R1=0.0503。2的 晶体学数据：a=0.8502(2)nm,b=1.2178(4)nm,c=1.5118(4)nm,α=86.454(5)°,β =77.734(5)°,γ=85.364(5)°,V=1.5228(8)nm^3,Z=2,F(000)=774,R1=0.0565。配 合物1,2分别通过K…S,K…Cl,S…S和K…S,S…S弱相互作用形成二维、三维网状 结构。     

基体辅助激光解吸电离飞行时间质谱和热裂解色谱/质谱研究聚酯型聚氨酯链结构

聚酯型聚氨酯样品用基体辅助激光裂解离子化质谱(MALDI-TOF/MS)和热裂解色谱质谱(PYGC/MS)方法进行了鉴定,PYGV/MS方法可检出PU的一些组成单元的化学结构,但PYGC/MS中大多数的峰,无法从常规的标准化合物的质谱数据库中检索到,而MALDI-MS方法,可明确测出PU试样各种单元的组合、聚合度及PU长链的序列分布,质量数范围可达2300.     

球形钴离子模板缩聚物的制备及其吸附性能研究

以钴离子为模板,四乙烯五胺为功能基配体,反相悬浮聚合制备出球形钴离子模板缩聚物。该模板缩聚物对钴离子的吸附性能显著优于相应的非模板缩聚物。说明应用离子模板技术可提高普通吸附树脂的吸附性能。可望在环境、医学等领域获得实际应用。     

原位红外光谱法研究沸石催化剂上苯与乙烯烷基化反应

采用原位红外光谱技术,于１２０￣２００℃下,对沸石催化剂上苯与乙烯烷基化的反应机理进行了探讨,结果表明,乙烯,苯和乙苯吸附在催化剂的同一类活性中心上,它们之间存在着竞争吸附,乙烯的吸附能力较苯和乙苯强;吸附的乙烯可与吸附的苯或乙苯发生烷基化反应。催化剂上已吸附乙烯时,由于乙烯在强吸附位上吸附较牢,苯和乙苯不易吸附,烷基化反应难以进行,且吸附的乙烯间可发生反应。乙烯与乙苯的反应内烯与异丙苯的反应难于     

High-throughput lipidomics analysis to discover lipid biomarkers and profiles as potential targets for evaluating efficacy of Kai-Xin-San against APP/PS1 transgenic mice based on UPLC–Q/TOF–MS

Lipid metabolism has a significant function in the central nervous system and Alzheimer's disease (AD) is an age-related senile disease characterized by central nerve degeneration. The pathological development of AD is closely related to lipid metabolism disorders. To reveal the influence of Kai-Xin-San (KXS) on lipid metabolism in APP/PSI transgenic mice and potential therapeutic targets for treating AD, brain tissue samples were collected and analyzed by high-throughput lipidomics based on UPLC–Q/TOF-MS. The collected raw data were processed by multivariate data analysis to discover the potential biomarkers and lipid metabolic profiles. Compared with the control wild-type mouse group, nine potential lipid biomarkers were found in the AD model group, of which seven were up-regulated and two were down-regulated. Orally administrated KXS can reverse the changes in these potential biomarkers. Compared with the model group, a total of six differential metabolites showed a recovery trend and may be potential targets for KXS to treat AD. This study showed that high-throughput lipidomics can be used to discover the perturbed pathways and lipid biomarkers as potential targets to reveal the therapeutic effects of KXS.     

A simple sol–gel hydrothermal method for the synthesis of defective TiO2 nanocrystals with excellent visible-light photocatalytic activity

Research on Chemical Intermediates - Defective TiO2 nanocrystals (D-TiO2) were synthesized by a simple, mild and green sol–gel hydrothermal method. The as-prepared sample possesses a high...