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961.
Unmasking the Action of Phosphinous Acid Ligands in Nitrile Hydration Reactions Catalyzed by Arene–Ruthenium(II) Complexes 下载免费PDF全文
Dr. Eder Tomás‐Mendivil Dr. Victorio Cadierno Dr. María I. Menéndez Dr. Ramón López 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(47):16874-16886
The catalytic hydration of benzonitrile and acetonitrile has been studied by employing different arene–ruthenium(II) complexes with phosphinous (PR2OH) and phosphorous acid (P(OR)2OH) ligands as catalysts. Marked differences in activity were found, depending on the nature of both the P‐donor and η6‐coordinated arene ligand. Faster transformations were always observed with the phosphinous acids. DFT computations unveiled the intriguing mechanism of acetonitrile hydration catalyzed by these arene–ruthenium(II) complexes. The process starts with attack on the nitrile carbon atom of the hydroxyl group of the P‐donor ligand instead of on a solvent water molecule, as previously suggested. The experimental results presented herein for acetonitrile and benzonitrile hydration catalyzed by different arene–ruthenium(II) complexes could be rationalized in terms of such a mechanism. 相似文献
962.
Sustainable Synthesis of Chiral Tetrahydrofurans through the Selective Dehydration of Pentoses 下载免费PDF全文
Robert W. Foster Dr. Christopher J. Tame Dr. Dejan‐Krešimir Bučar Prof. Helen C. Hailes Dr. Tom D. Sheppard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):15947-15950
L ‐Arabinose is an abundant resource available as a waste product of the sugar beet industry. Through use of a hydrazone‐based strategy, L ‐arabinose was selectively dehydrated to form a chiral tetrahydrofuran on a multi‐gram scale without the need for protecting groups. This approach was extended to other biomass‐derived reducing sugars and the mechanism of the key cyclization investigated. This methodology was applied to the synthesis of a range of functionalized chiral tetrahydrofurans, as well as a formal synthesis of 3R‐3‐hydroxymuscarine. 相似文献
963.
Azidoethoxyphenylalanine as a Vibrational Reporter and Click Chemistry Partner in Proteins 下载免费PDF全文
Elise M. Tookmanian Prof. Dr. Christine M. Phillips‐Piro Prof. Dr. Edward E. Fenlon Prof. Dr. Scott H. Brewer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(52):19096-19103
An unnatural amino acid, 4‐(2‐azidoethoxy)‐L ‐phenylalanine (AePhe, 1 ), was designed and synthesized in three steps from known compounds in 54 % overall yield. The sensitivity of the IR absorption of the azide of AePhe was established by comparison of the frequency of the azide asymmetric stretch vibration in water and dimethyl sulfoxide. AePhe was successfully incorporated into superfolder green fluorescent protein (sfGFP) at the 133 and 149 sites by using the amber codon suppression method. The IR spectra of these sfGFP constructs indicated that the azide group at the 149 site was not fully solvated despite the location in sfGFP and the three‐atom linker between the azido group and the aromatic ring of AePhe. An X‐ray crystal structure of sfGFP‐149‐AePhe was solved at 1.45 Å resolution and provides an explanation for the IR data as the flexible linker adopts a conformation which partially buries the azide on the protein surface. Both sfGFP‐AePhe constructs efficiently undergo a bioorthogonal strain‐promoted click cycloaddition with a dibenzocyclooctyne derivative. 相似文献
964.
965.
Frontispiece: Gd‐DTPA‐Dopamine‐Bisphytanyl Amphiphile: Synthesis,Characterisation and Relaxation Parameters of the Nanoassemblies and Their Potential as MRI Contrast Agents 下载免费PDF全文
966.
Scott C. Radzinski Jeffrey C. Foster John B. Matson 《Macromolecular rapid communications》2016,37(7):616-621
Bottlebrush polymers are synthesized using a tandem ring‐opening polymerization (ROP) and ring‐opening metathesis polymerization (ROMP) strategy. For the first time, ROP and ROMP are conducted sequentially in the same pot to yield well‐defined bottlebrush polymers with molecular weights in excess of 106 Da. The first step of this process involves the synthesis of a polylactide macromonomer (MM) via ROP of d ,l ‐lactide initiated by an alcohol‐functionalized norbornene. ROMP grafting‐through is then carried out in the same pot to produce the bottlebrush polymer. The applicability of this methodology is evaluated for different MM molecular weights and bottlebrush backbone degrees of polymerization. Size‐exclusion chromatographic and 1H NMR spectroscopic analyses confirm excellent control over both polymerization steps. In addition, bottlebrush polymers are imaged using atomic force microscopy and stain‐free transmission electron microscopy on graphene oxide.
967.
Ravi Madhukar Mawale Mayuri Vilas Ausekar Lubomír Prokeš Virginie Nazabal Emeline Baudet Tomáš Halenkovič Marek Bouška Milan Alberti Petr Němec Josef Havel 《Journal of the American Society for Mass Spectrometry》2017,28(12):2569-2579
Laser desorption ionization using time-of-flight mass spectrometer afforded with quadrupole ion trap was used to study As2Ch3 (Ch = S, Se, and Te) bulk chalcogenide materials. The main goal of the study is the identification of species present in the plasma originating from the interaction of laser pulses with solid state material. The generated clusters in both positive and negative ion mode are identified as 10 unary (S p +/– and As m +/– ) and 34 binary (As m S p +/– ) species for As2S3 glass, 2 unary (Se q +/– ) and 26 binary (As m Se q +/– ) species for As2Se3 glass, 7 unary (Te r +/– ) and 23 binary (As m Te r +/– ) species for As2Te3 material. The fragmentation of chalcogenide materials was diminished using some polymers and in this way 45 new, higher mass clusters have been detected. This novel approach opens a new possibility for laser desorption ionization mass spectrometry analysis of chalcogenides as well as other materials. 相似文献
968.
Jaromíra Chýlková Markéta Tomášková Lenka Janíková Renáta Šelešovská Tomáš Navrátil Petra Chudobová 《Chemical Papers》2017,71(6):1047-1054
A sensitive voltammetric method for the determination of pyrogallol (PY) was developed employing a boron-doped diamond electrode (BDDE). The composition of the supporting electrolyte was investigated during the development of the methodology. Linear sweep voltammetry (LSV) under the optimized experimental conditions was applied for PY determination with a limit of detection and limit of quantification of 0.85 and 2.82 μmol L?1, respectively. These values are satisfactory for application to real samples. The usability of this method for the quantification of pyrogallol was in range from 2.82 to 296.00 μmol L?1. Finally, the developed method was successfully used for the analysis of real samples of biodiesel produced from rapeseed oil and its blend with diesel fuel. Samples of biodiesel and biodiesel blends were analyzed directly in an electrochemical cell, while samples with very low concentrations of PY in biodiesel were extracted with water using the proposed simple and fast process. 相似文献
969.
Rajat Kumar Pal Kamran Haider Divya Kaur William Flynn Junchao Xia Ronald M Levy Tetiana Taran Lauren Wickstrom Tom Kurtzman Emilio Gallicchio 《Journal of computer-aided molecular design》2017,31(1):29-44
As part of the SAMPL5 blinded experiment, we computed the absolute binding free energies of 22 host–guest complexes employing a novel approach based on the BEDAM single-decoupling alchemical free energy protocol with parallel replica exchange conformational sampling and the AGBNP2 implicit solvation model specifically customized to treat the effect of water displacement as modeled by the Hydration Site Analysis method with explicit solvation. Initial predictions were affected by the lack of treatment of ionic charge screening, which is very significant for these highly charged hosts, and resulted in poor relative ranking of negatively versus positively charged guests. Binding free energies obtained with Debye–Hückel treatment of salt effects were in good agreement with experimental measurements. Water displacement effects contributed favorably and very significantly to the observed binding affinities; without it, the modeling predictions would have grossly underestimated binding. The work validates the implicit/explicit solvation approach employed here and it shows that comprehensive physical models can be effective at predicting binding affinities of molecular complexes requiring accurate treatment of conformational dynamics and hydration. 相似文献
970.
Oscar Hernan Madrid-Padilla James Scott 《Journal of computational and graphical statistics》2017,26(3):537-546
We present an approach for penalized tensor decomposition (PTD) that estimates smoothly varying latent factors in multiway data. This generalizes existing work on sparse tensor decomposition and penalized matrix decompositions, in a manner parallel to the generalized lasso for regression and smoothing problems. Our approach presents many nontrivial challenges at the intersection of modeling and computation, which are studied in detail. An efficient coordinate-wise optimization algorithm for PTD is presented, and its convergence properties are characterized. The method is applied both to simulated data and real data on flu hospitalizations in Texas and motion-capture data from video cameras. These results show that our penalized tensor decomposition can offer major improvements on existing methods for analyzing multiway data that exhibit smooth spatial or temporal features. 相似文献