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81.
Molecular assays such as immunoassays are often performed using solid carriers and fluorescent labels. In such an assay format
a question can be raised on how much the fluorescence of the label is influenced by the bio-affinity binding events and the
solid carrier surface. Since changes in fluorescence intensity as labels bind to surfaces are notoriously difficult to quantify
other approaches are preferred. A good indicator, independent of the fluorescence intensity of the label, is the fluorescence
lifetime of the marker fluorophore. Changes in fluorescence lifetime reliably indicate the presence of dynamic quenching,
energy transfer or other de-excitation processes. A microsphere based assay system is studied under two-photon excitation.
Changes in fluorescence lifetime are studied as labeled protein conjugates bind on microsphere surfaces – both direct on the
surface and with a few nanometer distance from the surface. Fluorescence signal is measured from individual polystyrene microspheres
and the fluorescence lifetime histogram is simultaneously recorded. The results indicate that self-quenching and quenching
by the polystyrene surface are both present in such a system. However, the effect of the surface can be avoided by increasing
the distance between the surface and the label. Typical distances achieved by a standard sandwich type of assay, are already
sufficient to overcome the surface induced quenching in fluorescence detection. 相似文献
82.
Takuji Magata Yoshimi Hirokawa Yusuke Moriguchi Ryosuke Yokoi Shotaro Nojiri Ryota Miyazaki Sayuri Akasako Rina Takahashi Munetaka Nishida Junya Hakoda Ryota Nakayama Aya Tanaka Naoyoshi Maezaki 《Tetrahedron letters》2019,60(10):718-720
A concise, highly stereoselective synthesis of 2,4- and 2,5-disubstituted thiazole amino acids was developed. These are important building blocks for various biologically active thiazole-containing natural peptides and their regioisomeric analogues. The fundamental reactions are diastereoselective addition of (4- or 5-bromothiazol-2-yl)lithium to N-tert-butanesulfinyl imine with subsequent Pd-catalyzed phenoxycarbonylation. 相似文献
83.
Mikio Fujii Taiki Kuramochi Yuhi Nakakuki Rina Hatazawa Kiju Konno Tatsuo Munakata Yasuaki Hirai 《Tetrahedron letters》2019,60(10):721-725
Gentianine is a metabolite of gentiopicroside and swertiamarin. Several biological activities have been reported for gentianine, such as antiinflammatory and antidiabetic activity, and hypotensive effect. Gentiopicroside is found in 0.9–9.8% content in Gentian root or Gentian scabra root, and Swertiamarin is contained in Swertia herb in 2–10%. These natural products can be potential starting materials for the synthesis of gentianine. This study describes the β-glucosidase-catalyzed hydrolysis of gentiopicroside and swertiamarin in the presence of hydroxylamine to afford gentianine N-oxide, which can be a synthetic precursor of gentianine derivatives. Enzymatic hydrolysis of swertiamarin selectively afforded gentianine N-oxide in 81% yield, whereas gentiopicroside afforded gentianine N-oxide and gentianol N-oxide. Plausible reaction pathways leading to gentianine, gentianol, and their N-oxides were also investigated. 相似文献
84.
Topological winding and unwinding in a quasi-one-dimensional metastable Bose-Einstein condensate are shown to be manipulated by changing the strength of interaction or the frequency of rotation. Exact diagonalization analysis reveals that quasidegenerate states emerge spontaneously near the transition point, allowing a smooth crossover between topologically distinct states. On a mean-field level, the transition is accompanied by formation of gray solitons, or density notches, which serve as an experimental signature of this phenomenon. 相似文献
85.
Dr. Ying Fu Dr. Rina Soni Dr. María J. Romero Dr. Ana M. Pizarro Dr. Luca Salassa Dr. Guy J. Clarkson Jessica M. Hearn Dr. Abraha Habtemariam Prof. Dr. Martin Wills Prof. Dr. Peter J. Sadler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(45):15199-15209
Four chiral OsII arene anticancer complexes have been isolated by fractional crystallization. The two iodido complexes, (SOs,SC)‐[Os(η6‐p‐cym)(ImpyMe)I]PF6 (complex 2 , (S)‐ImpyMe: N‐(2‐pyridylmethylene)‐(S)‐1‐phenylethylamine) and (ROs,RC)‐[Os(η6‐p‐cym)(ImpyMe)I]PF6 (complex 4 , (R)‐ImpyMe: N‐(2‐pyridylmethylene)‐(R)‐1‐phenylethylamine), showed higher anticancer activity (lower IC50 values) towards A2780 human ovarian cancer cells than cisplatin and were more active than the two chlorido derivatives, (SOs,SC)‐[Os(η6‐p‐cym)(ImpyMe)Cl]PF6, 1 , and (ROs,RC)‐[Os(η6‐p‐cym)(ImpyMe)Cl]PF6, 3 . The two iodido complexes were evaluated in the National Cancer Institute 60‐cell‐line screen, by using the COMPARE algorithm. This showed that the two potent iodido complexes, 2 (NSC: D‐758116/1) and 4 (NSC: D‐758118/1), share surprisingly similar cancer cell selectivity patterns with the anti‐microtubule drug, vinblastine sulfate. However, no direct effect on tubulin polymerization was found for 2 and 4 , an observation that appears to indicate a novel mechanism of action. In addition, complexes 2 and 4 demonstrated potential as transfer‐hydrogenation catalysts for imine reduction. 相似文献
86.
Aromatic iodides are prepared from readily available carboxylic acids via oxidative decarboxylation with iodosobenzene diacetate/iodine in carbon tetrachloride. 相似文献
87.
Mithun Kumar Debnath Wako Oyama Yuya Ono Takuya Sugimoto Rina Watanabe Naoki Haraguchi 《Journal of polymer science. Part A, Polymer chemistry》2021,59(11):1072-1083
Polymer microsphere-supported chiral pyrrolidine catalysts were successfully synthesized by a precipitation polymerization incorporating a methacrylate monomer bearing chiral N-Boc-pyrrolidine moiety, followed by removal of the N-Boc groups. The resulting polymeric catalysts were applied to the asymmetric Michael addition reactions of aldehydes with alkyl vinyl ketones. The effects of the comonomer, the molar ratios within the catalyst, the catalyst loading, the temperature, and the solvent on the catalytic performance were investigated in detail. The reactions were found to proceed smoothly in the absence of a solvent. A hydrophobic polystyrene-based chiral pyrrolidine catalyst exhibited high reactivity (up to 97% yield) and enantioselectivity (up to 95% ee) during these reactions. The catalyst could also be recovered and reused up to five times without significant loss of activity. 相似文献
88.
Rotermel Maria V. Samigullina Rina F. Ivanova Irina V. Vladimirova Elena V. Baklanova Inna V. Krasnenko Tatiana I. 《Journal of Sol-Gel Science and Technology》2021,100(3):404-413
Journal of Sol-Gel Science and Technology - The Zn1.9Cu0.1SiO4 pigment was obtained by two variants of “soft” chemistry methods: using sol–gel synthesis in ethanol from TEOS and... 相似文献
89.
Hydrazides and amines were N-formylated by DMF in the presence of tert-butyldimethylsilyl triflate (TBSOTf) at room temperature, in good to excellent yields. 相似文献
90.
Knowledge shifts are essential in the learning process in the mathematics classroom. Our goal in this study is to better understand the mechanisms of such knowledge shifts, and the roles of the individuals (students and teacher) in realizing them. To achieve this goal, we combined two approaches/methodologies that are usually carried out separately: the Abstraction in Context approach with the RBC+C model commonly used for the analysis of processes of constructing knowledge by individuals and small groups of students; and the Documenting Collective Activity approach with its methodology commonly used for establishing normative ways of reasoning in classrooms. This combination revealed that some students functioned as “knowledge agents,” meaning that they were active in shifts of knowledge among individuals in a small group, or from one group to another, or from their group to the whole class or within the whole class. The analysis also showed that the teacher adopted the role of an orchestrator of the learning process and assumed responsibility for providing a learning environment that affords argumentation and interaction. This enables normative ways of reasoning to be established and enables students to be active and become knowledge agents. 相似文献