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Switchable solvent

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https://www.readbyqxmd.com/read/30106581/tuning-regioselectivity-of-wacker-oxidation-in-one-catalytic-system-small-change-makes-big-step
#1
Kang-Fei Hu, Xiao-Shan Ning, Jian-Ping Qu, Yan-Biao Kang
A regioselectivity switchable aerobic Wacker-Tsuji oxidation has been developed using catalytic tert-butyl nitrite as a simple organic redox cocatalyst. By solely switching the solvent, either substituted aldehydes or ketones could be prepared under mild aerobic conditions in good yields, respectively. A mechanistic explanation for the selectivity control is proposed.
August 14, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/30093667/dual-stimuli-responsive-rotaxane-branched-dendrimers-with-reversible-dimension-modulation
#2
Xu-Qing Wang, Wei Wang, Wei-Jian Li, Li-Jun Chen, Rui Yao, Guang-Qiang Yin, Yu-Xuan Wang, Ying Zhang, Junlin Huang, Hongwei Tan, Yihua Yu, Xiaopeng Li, Lin Xu, Hai-Bo Yang
With the aim of mimicking biological machines, in which the delicate arrangement of nanomechanical units lead to the output of specific functions upon the external stimulus, the construction of dual stimuli-responsive rotaxane-branched dendrimers was realized in this study. Starting from a switchable organometallic [2]rotaxane precursor, the employment of a controllable divergent approach allowed for the successful synthesis of a family of rotaxane-branched dendrimers up to the third generation with 21 switchable rotaxane moieties located on each branch...
August 9, 2018: Nature Communications
https://www.readbyqxmd.com/read/30035355/sodium-dodecyl-sulfate-sensitized-switchable-solvent-liquid-phase-microextraction-for-the-preconcentration-of-protoberberine-alkaloids-in-rhizoma-coptidis
#3
Shuang Hu, Jiao Xue, Xiao Yang, Xuan Chen, Run-Qin Wang, Xiao-Hong Bai
A sodium dodecyl sulfate sensitized switchable solvent liquid-phase microextraction method was developed and applied to the preconcentration of active alkaloids in Rhizoma coptidis followed by high-performance liquid chromatography determination. Before extraction, non-ionic triethylamine was converted to its cationic form in the presence of carbon dioxide. Then, the ionic solvent carrying target analytes was once more reverted to its non-ionic form by adding sodium hydroxide, as well as phase separation and analytes enrichment were realized simultaneously...
July 23, 2018: Journal of Separation Science
https://www.readbyqxmd.com/read/29983073/morphology-evolution-of-stimuli-responsive-triblock-copolymer-modulated-by-polyoxometalates
#4
Junyan Tan, Dandan Chong, Yue Zhou, Rong Wang, Xinhua Wan, Jie Zhang
Polyoxometalate (POM) H3 PMo12 O40 was coassembled with stimuli-responsive triblock copolymer poly(ethylene oxide)- block-polystyrene- block-poly(2-(dimethylamino)ethyl methacrylate) (PEO- b-PS- b-PDMAEMA) by electrostatic interactions. Depending on the POM contents, the hybrid complexes can self-assemble into a series of morphologies: micelles, rods, toroids, and vesicles. Unlike traditional morphology transition of amphiphilic block copolymer derived from a broad range of hydrophobic volume fractions, POM-induced morphology transitions just occurred in a narrow range of volume fractions...
July 31, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/29966417/gold-catalyzed-post-ugi-ipso-cyclization-with-switchable-diastereoselectivity
#5
Anton A Nechaev, Kristof Van Hecke, Manzoor Zaman, Stepan Kashtanov, Liviu Ungur, Olga P Pereshivko, Vsevolod A Peshkov, Erik V Van der Eycken
A gold-catalyzed post-Ugi ipso-cyclization for the diastereoselective synthesis of spirocyclic pyrrol-2-one-dienone system is described. Tuning the catalytic system, solvent, and temperature allowed selectively attaining two sets of diastereoisomers. The scope of the process has been evaluated, and a putative mechanistic model was proposed.
July 11, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29951526/determination-of-microalgal-lipid-content-and-fatty-acid-for-biofuel-production
#6
REVIEW
Zhipeng Chen, Lingfeng Wang, Shuang Qiu, Shijian Ge
Biofuels produced from microalgal biomass have received growing worldwide recognition as promising alternatives to conventional petroleum-derived fuels. Among the processes involved, the downstream refinement process for the extraction of lipids from biomass greatly influences the sustainability and efficiency of the entire biofuel system. This review summarizes and compares the current techniques for the extraction and measurement of microalgal lipids, including the gravimetric methods using organic solvents, CO2 -based solvents, ionic liquids and switchable solvents, Nile red lipid visualization method, sulfo-phospho-vanillin method, and the thin-layer chromatography method...
2018: BioMed Research International
https://www.readbyqxmd.com/read/29921871/tailoring-exciton-and-excimer-emission-in-an-exfoliated-ultrathin-2d-metal-organic-framework
#7
Wei-Ming Liao, Jian-Hua Zhang, Shao-Yun Yin, He Lin, Xingmin Zhang, Jihong Wang, Hai-Ping Wang, Kai Wu, Zheng Wang, Ya-Nan Fan, Mei Pan, Cheng-Yong Su
Two-dimensional (2D) metal-organic frameworks have exhibited a range of fascinating attributes, of interest to numerous fields. Here, a calcium-based metal-organic framework with a 2D layered structure has been designed. Dual emissions relating to intralayer excimers and interlayer trapped excitons are produced, showing excitation-dependent shifting tendency, characteristic of a low dimensional semiconductor nature. Furthermore, the layer stacking by weak van der Waals forces among dynamically coordinated DMF molecules enables exfoliation and morphology transformation, which can be achieved by ultrasound in different ratios of DMF/H2 O solvents, or grinding under appropriate humidity conditions, leading to nano samples including ultrathin nanosheets with single or few coordination layers...
June 19, 2018: Nature Communications
https://www.readbyqxmd.com/read/29892908/vortex-assisted-switchable-liquid-liquid-microextraction-for-the-preconcentration-of-cadmium-in-environmental-samples-prior-to-its-determination-with-flame-atomic-absorption-spectrometry
#8
Merve Fırat, Süleyman Bodur, Büşra Tışlı, Cansu Özlü, Dotse Selali Chormey, Fatma Turak, Sezgin Bakırdere
In this study, a switchable solvent was used to preconcentrate trace amounts of Cd from aqueous solution for its determination by flame atomic absorption spectrometry (FAAS). Protonation of N,N-dimethylbenzylamine by dry ice (solid CO2 ) made it water soluble, and addition of sodium hydroxide converted it back to its original nonionic state for phase separation and subsequent extraction of Cd. A slotted quartz tube (SQT) was attached to the flame burner head to increase the residence time of Cd atoms in the light path...
June 12, 2018: Environmental Monitoring and Assessment
https://www.readbyqxmd.com/read/29879351/solvent-mixing-to-induce-molecular-motor-aggregation-into-bowl-shaped-particles-underlying-mechanism-particle-nature-and-application-to-control-motor-behavior
#9
Linda E Franken, Yuchen Wei, Jiawen Chen, Egbert J Boekema, Depeng Zhao, Marc C A Stuart, Ben L Feringa
Control over dynamic functions in larger assemblies is key to many molecular systems, ranging from responsive materials to molecular machines. Here we report a molecular motor that forms bowl-shaped particles in water and how confinement of the molecular motor affects rotary motion. Studying the aggregation process in a broader context, we provide evidence that, in the case of bowl-shaped particles, the structures are not the product of self-assembly, but a direct result of the mixing a good solvent and a (partial) non-solvent and highly independent of the molecular design...
June 27, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29850689/homoallylglycine-residues-are-superior-precursors-to-orthogonally-modified-thioether-containing-polypeptides
#10
Pesach Perlin, Eric G Gharakhanian, Timothy J Deming
Homoallylglycine N-carboxyanhydride, Hag NCA, monomers were synthesized and used to prepare polypeptides containing Hag segments with controllable lengths of up to 245 repeats. Poly(l-homoallylglycine), GHA, was found to adopt an α-helical conformation, which provided good solubility in organic solvents and allowed high yield functionalization of its alkene side-chains via radical promoted addition of thiols. The conformations of these derivatives were shown to be switchable between α-helical and disordered states in aqueous media using thioether alkylation or oxidation reactions...
June 12, 2018: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/29774656/accurate-and-sensitive-determination-of-selected-hormones-endocrine-disruptors-and-pesticides-by-gas-chromatography-mass-spectrometry-after-the-multivariate-optimization-of-switchable-solvent-liquid-phase-microextraction
#11
Dotse Selali Chormey, Süleyman Bodur, Dilgeş Baskın, Merve Fırat, Sezgin Bakırdere
Switchable solvent liquid-phase microextraction was combined with gas chromatography and mass spectrometry to improve the sensitivity and accuracy for the determination of selected endocrine disruptors, pesticides, and hormones. The extraction method was used to complement gas chromatography with mass spectrometry by preconcentrating analytes for trace determinations. A Box-Behnken experimental design was used to evaluate the main variables and their interaction effects, and optimum parameters were selected based on the model of experimented results...
May 17, 2018: Journal of Separation Science
https://www.readbyqxmd.com/read/29732087/spironaphthoxazine-switchable-dyes-for-biological-imaging
#12
Yaoyao Xiong, Andreas Vargas Jentzsch, Johannes W M Osterrieth, Erdinc Sezgin, Igor V Sazanovich, Katharina Reglinski, Silvia Galiani, Anthony W Parker, Christian Eggeling, Harry L Anderson
Recent developments in super-resolution microscopy have significantly expanded the requirements for switchable dyes, leading to demand for specially designed molecular switches. We report the synthesis and characterization of a spironaphthoxazine photochromic switch (a derivative of palatinate purple) displaying high photoconversion (85-95%) under readily accessible 405 nm light, broad absorption in the visible, and excellent fatigue resistance. The indole substituent on this spironaphthoxazine is twisted out of conjugation with the naphthalene unit, yet it is crucial for activation with visible light...
March 21, 2018: Chemical Science
https://www.readbyqxmd.com/read/29674019/development-of-a-new-ph-assisted-homogeneous-liquid-liquid-microextraction-by-a-solvent-with-switchable-hydrophilicity-application-for-gc-ms-determination-of-methamphetamine
#13
Siamak Kiani Shahvandi, Mohammad Hossein Banitaba, Hamid Ahmar
In this study, a new method based on homogeneous liquid-phase microextraction was developed for the determination of methamphetamine (MA) in urine samples. Dipropylamine (DPA), as a solvent with switchable hydrophilicity, was used as the extraction solvent and can be miscible/immiscible based on variable pH values of the aqueous sample solution. The effects of operational extraction parameters such as DPA volume, temperature, the amount of added acid and base solutions, and NaCl content of the sample were investigated...
July 1, 2018: Talanta
https://www.readbyqxmd.com/read/29665113/switchable-synthesis-of-z-homoallylic-boronates-and-e-allylic-boronates-by-enantioselective-copper-catalyzed-1-6-boration
#14
Yunfei Luo, Steven M Wales, Stamatis E Korkis, Iain D Roy, William Lewis, Hon Wai Lam
The enantioselective Cu-catalyzed 1,6-boration of (E,E)-α,β,γ,δ-unsaturated ketones is described, which gives homoallylic boronates with high enantiomeric purity and unexpectedly high Z-selectivity. By changing the solvent, the outcome can be altered to give E-allylic boronates.
June 12, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29659114/cobalt-catalyzed-intramolecular-reactions-between-a-vinylcyclopropane-and-an-alkyne-switchable-5-2-cycloaddition-and-homo-ene-pathways
#15
Chunlin Wu, Naohiko Yoshikai
Cobalt-diphosphine catalysts have been found to promote intramolecular reactions between a vinylcyclopropane and an alkyne to selectively afford either the [5+2] cycloaddition product or the homo-ene reaction product under solvent control. The former product is exclusively formed in noncoordinating 1,2-dichloroethane, whereas the latter is dominant in coordinating solvents, such as acetonitrile and dimethylacetamide. Furthermore, a highly enantioselective variant of the homo-ene reaction afforded chiral tetrahydrofuran, pyrrolidine, and cyclopentane derivatives bearing 1,3-diene and alkylidene substituents...
May 28, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29623706/ph-induced-rotation-of-lidless-lipase-lipa-from-bacillus-subtilis-at-lipase-detergent-interface
#16
Sudip Das, Sundaram Balasubramanian
Lipases exhibit a unique process during the catalysis of the hydrolysis of triglyceride substrates called interfacial activation. Surfactants are used as cosolvents with water not only to offer a less polar environment to the lipases needed for their interfacial activation but also to solvate the substrate which are poorly soluble in water. However, the presence of detergent in the medium can affect both the lipase and the substrate, making the construction of a microkinetic model for lipase activity in the presence of the detergent difficult...
May 10, 2018: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/29616818/magnetic-sponge-behavior-via-electronic-state-modulations
#17
Jun Zhang, Wataru Kosaka, Kunihisa Sugimoto, Hitoshi Miyasaka
A reversible magnetic change in response to external stimuli is a desired function of molecular magnetic materials. The magnetic change induced by a change in the intrinsic spin is significant because the magnetic change is inevitable and could become drastic. In this study, we demonstrate a reversible magnetic change closely associated with electronic state modulations, as well as structural modifications realized by solvation/desolvation cycles of a magnetic sponge. The compound was a D2 A-type layered magnet, [{Ru2 (O2 CPh-2,3,5-Cl3 )4 }2 (TCNQMe2 )]·4DCM (1; 2,3,5-Cl3 PhCO2 - = 2,3,5-trichlorobenzoate; TCNQMe2 = 2,5-dimethyl-7,7,8,8-tetracyanoquinodimethane; DCM = dichloromethane), where [Ru2 (O2 CPh-2,3,5-Cl3 )4 ] ([Ru2 II,II ]) is an electron donor (D) and TCNQMe2 is an electron acceptor (A)...
April 25, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29581285/water-mediated-conformational-preselection-mechanism-in-substrate-binding-cooperativity-to-protein-kinase-a
#18
Piotr Setny, Marta D Wiśniewska
Substrate binding cooperativity in protein kinase A (PKA) seems to involve allosteric coupling between the two binding sites. It received significant attention, but its molecular basis still remains not entirely clear. Based on long molecular dynamics of PKA and its complexes, we characterized an allosteric pathway that links ATP binding to the redistribution of states adopted by a protein substrate positioning segment in favor of those that warrant correct binding. We demonstrate that the cooperativity mechanism critically depends on the presence of water in two distinct, buried hydration sites...
April 10, 2018: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/29512250/an-easily-accessible-ionic-aggregation-induced-emission-luminogen-with-hydrogen-bonding-switchable-emission-and-wash-free-imaging-ability
#19
Yuncong Chen, Weijie Zhang, Zheng Zhao, Yuanjing Cai, Junyi Gong, Ryan T K Kwok, Jacky W Y Lam, Herman H Y Sung, Ian D Williams, Ben Zhong Tang
Ionic fluorophores are powerful tools for the study of environmental science and bio-imaging. However, traditional ionic dyes usually require long synthetic steps and suffer from a quenching effect caused by aggregation. A water-soluble ionic aggregation-induced emission luminogen called DBTA is presented, which is readily accessed by a one-step reaction. The switchable emission manipulated by hydrogen bonding provided solid evidence for the restriction of intramolecular motions as the mechanism of aggregation-induced emission...
April 23, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29511836/an-effervescence-assisted-switchable-fatty-acid-based-microextraction-with-solidification-of-floating-organic-droplet-for-determination-of-fluoroquinolones-and-tetracyclines-in-seawater-sediment-and-seafood
#20
Ming Gao, Jun Wang, Xiukai Song, Xin He, Randy A Dahlgren, Zhenzhong Zhang, Shaoguo Ru, Xuedong Wang
This study developed a new effervescence-assisted switchable fatty acid-based microextraction combined with solidification of a floating organic-droplet (EA-SFAM-SFO) for simple and rapid determination of fluoroquinolones and tetracyclines in seawater, sediment, and seafood. Five medium-chain fatty acids (pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, and nonanoic acid) were tested as an extraction solvent, given their ability to change between hydrophobic and hydrophilic forms by pH adjustment...
April 2018: Analytical and Bioanalytical Chemistry
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