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Poonam Patyar, Gurpreet Kaur, Tarnveer Kaur
Apparent molar volumes <mml:math xmlns:mml=""> <mml:mrow> <mml:mo>(</mml:mo> <mml:msub> <mml:mi>ϕ</mml:mi> <mml:mi>V</mml:mi> </mml:msub> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> of glycine/l-alanine in water and in aqueous citric acid (CA) solutions of varying concentrations, i.e. (0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) mol·kg-1 were determined from density measurements at temperatures T  = (288...
2018: Journal of Solution Chemistry
Sergey Milikisiyants, Maxim A Voinov, Antonin Marek, Morteza Jafarabadi, Jing Liu, Rong Han, Shenlin Wang, Alex I Smirnov
Over the past decades pulsed electron-electron double resonance (PELDOR), often called double electron-electron resonance (DEER), became one of the major spectroscopic tools for measurements of nanometer-scale distances and distance distributions in non-crystalline biological and chemical systems. The method is based on detecting the amplitude of the primary (3-pulse DEER) or refocused (4-pulse DEER) spin echo for the so-called "observer" spins when the other spins coupled to the former by a dipolar interaction are flipped by a "pump" pulse at another EPR frequency...
December 5, 2018: Journal of Magnetic Resonance
Yang Xiong, Zhuanzhuan Du, Haohua Chen, Zhao Yang, Qiuyuan Tan, Changhui Zhang, Lei Zhu, Yu Lan, Min Zhang
A novel chiral phosphine-urea bifunctional ligand has been developed for Cu-catalyzed asymmetric 1,3-dipolar cycloaddition of iminoesters with methacrylonitrile, a long-standing challenging substrate in asymmetric catalysis. Distortion-interaction energy analysis based on density functional theory (DFT) calculations reveals that the distortion energy plays an important role in the observed enantioselectivity, which can be attributed to the steric effect between the phosphine ligand and the dipole reactant. DFT calculations also indicate that nucleophilic addition is the enantioselectivity-determining step and hydrogen bonding between the urea moiety and methacrylonitrile assists in control of the diastereo- and enantioselectivity...
December 13, 2018: Journal of the American Chemical Society
Wen-Jing Xiao, Yi Wei, Song Liu, Miao-Miao Li, Yi Li, Yu Lan, Liang-Qiu Lu
An enantioselective [5+2] cycloaddition of vinylethylene car-bonates and α-diazoketones was achieved for the first time by merging photoactivation and asymmetric Pd catalysis. The key to the success of this method is the enantioselective trapping of Pd-containing, 1,5-dipolar intermediates by ketenes, a class of reactive C2 synthons, which were generated in an in situ and traceless manner under visible light irradiation. Through this trapping, a variety of 7-membered lactones bearing challenging chiral quaternary stereocenters can be accessed in a facile man-ner with good efficiency and high enantioselectivity (up to 99% yield and 96:4 er)...
December 12, 2018: Journal of the American Chemical Society
Ziad T I Alkayar, Iain Coldham
A cascade or domino sequence of condensation of hydroxylamine and an aldehyde to give an oxime, cyclization to a nitrone, and intramolecular 1,3-dipolar cycloaddition has been successfully employed where there is branching at C-4 as a route to the iboga alkaloids. Cyclization occurs with displacement of chloride as a leaving group and intramolecular cycloaddition occurs with an alkene as a dipolarophile. The reaction gives an azabicyclo[2.2.2]octane product containing a fused isoxazolidine as a single stereoisomer and this was converted to an isoquinuclidine that completed a formal synthesis of the alkaloid (±)-19-hydroxyibogamine...
December 12, 2018: Organic & Biomolecular Chemistry
Kai-Kai Wang, Yan-Li Li, Zhan-Yong Wang, Meng-Wei Hu, Ting-Ting Qiu, Bao-Ku Zhu
A cross 1,3-dipolar cycloaddition of two different ylides between C,N-cyclic azomethine imines with an in situ-generated nonstabilized azomethine ylide from an N-benzyl precursor was realized. The reactions afforded a clean and facile access to diverse fused tricyclic 1,2,4-hexahydrotriazines in high yields (up to 96%). The chemical structures of the typical compounds were confirmed by X-ray single-crystal structure analysis.
December 12, 2018: Organic & Biomolecular Chemistry
Surya Pratap, Fatima Naaz, Srinivas Reddy, Kunal K Jha, Kalicharan Sharma, Dinakar Sahal, Mymoona Akhter, Devanna Nayakanti, Halmuthur M S Kumar, Vandana Kumari, Kailash Pandey, Syed Shafi
A series of spiroisoxazoline analogues of artemisinin was synthesized by employing 1,3-dipolar cycloaddition between various in situ generated nitrile oxides and artemisitene. All the synthesized compounds were tested for their anti-proliferative and anti-malarial activities. Among the compounds tested, compound 11a was found to be potent against the HCT-15 cancer cell line with IC50  = 4.04 μM when compared to 5-fluorouracil (IC50  = 35.53 μM). DNA cell cycle analysis shows that 11a was inhibiting cell proliferation at the G2/M phase...
December 10, 2018: Archiv der Pharmazie
Sundaravel Vivek Kumar, Gandhi Uma Rani, Manohar Divyalakshmi, Nattamai Bhuvanesh, Shanmugam Muthusubramanian, Subbu Perumal
Expedient synthesis of benzosuberone-tethered spirooxindoles was accomplished by a three-component 1,3-dipolar cycloaddition reaction between azomethine ylide (generated in situ) and arylidene benzosuberone. This protocol offers good yield and wide functional group tolerance under mild reaction condition with high regio- and stereoselectivities.
December 10, 2018: Molecular Diversity
Krishnendu Kundu, Marie Ramirez Cohen, Akiva Feintuch, Daniella Goldfarb, Shimon Vega
Dynamic Nuclear Polarization (DNP) is an efficient technique for enhancing NMR signals by utilizing the large polarization of electron spins to polarize nuclei. The mechanistic details of the polarization transfer process involve the depolarization of the electrons resulting from microwave (MW) irradiation (saturation), as well as electron-electron cross-relaxation occurring during the DNP experiment. Recently, electron-electron double resonance (ELDOR) experiments have been performed under DNP conditions to map the depolarization profile along the EPR spectrum as a consequence of spectral diffusion...
December 11, 2018: Physical Chemistry Chemical Physics: PCCP
Madhur Srivastava, Jack H Freed
This paper is a continuation of the method introduced by Srivastava and Freed (2017) that is a new method based on truncated singular value decomposition (TSVD) for obtaining physical results from experimental signals, without any need for Tikhonov regularization or other similar methods that require a regularization parameter. We show here how to estimate the uncertainty in the SVD-generated solutions. The uncertainty in the solution may be obtained by finding the minimum and maximum values over which the solution remains converged...
December 10, 2018: Journal of Physical Chemistry. A
Erik C Cook, Debashish Sahu, Monique Bastidas, Scott Anthony Showalter
The pancreatic and duodenal homeobox 1 (Pdx1) is an essential pancreatic transcription factor. The C-terminal intrinsically disordered domain of Pdx1 (Pdx1-C) has a heavily biased amino acid composition; most notably, 18 of 83 residues are proline, including a hexa-proline cluster near the middle of the chain. For these reasons, Pdx1-C is an attractive target for structure characterization, given the availability of suitable methods. To determine the solution ensembles of disordered proteins, we have developed a suite of 13C direct-detect NMR experiments that provide high spectral quality, even in the presence of strong proline enrichment...
December 10, 2018: Journal of Physical Chemistry. B
Scott L Carnahan, Bryan J Lampkin, Pranjali Naik, Michael P Hanrahan, Igor I Slowing, Brett VanVeller, Gang Wu, Aaron J Rossini
The ubiquity of oxygen in organic, inorganic, and biological systems has stimulated the application and development of 17O solid-state NMR spectroscopy as a probe of molecular structure and dynamics. Unfortunately, 17O solid-state NMR experiments are often hindered by the combination of broad NMR signals and low sensitivity. Here, it is demonstrated that fast MAS and proton detection with the D-RINEPT pulse sequence can be generally applied to enhance the sensitivity and resolution of 17O solid-state NMR experiments...
December 7, 2018: Journal of the American Chemical Society
Raquel Mejías, Patricia Hernández Flores, Marina Talelli, José L Tajada-Herráiz, Maria Brollo, Yadileiny Portilla, María Del Puerto Morales, Domingo F Barber
Magnetic hyperthermia has a significant potential to be a new breakthrough for cancer treatment. The simple concept of nanoparticle-induced heating by the application of an alternating magnetic field has attracted much attention, as it allows the local heating of cancer cells, which are considered more susceptible to hyperthermia than healthy cells, while avoiding the side effects of traditional hyperthermia. Despite the potential of this therapeutic approach, the idea that local heating effects due to the application of alternating magnetic fields on magnetic nanoparticle-loaded cancer cells can be used as a treatment is controversial...
December 7, 2018: ACS Applied Materials & Interfaces
Jonas Christoffersson, Christopher Aronsson, Michael Jury, Robert Selegård, Daniel Aili, Carl-Fredrik Mandenius
Liver cell culture models are attractive in both tissue engineering and for development of assays for drug toxicology research. To retain liver specific cell functions, the use of adequate cell types and culture conditions, such as a 3D orientation of the cells and a proper supply of nutrients and oxygen, are critical. In this article, we show how extracellular matrix mimetic hydrogels can support hepatocyte viability and functionality in a perfused liver-on-a-chip device. A modular hydrogel system based on hyaluronan and poly(ethylene glycol) (HA-PEG), modified with cyclooctyne moieties for bioorthogonal strain-promoted alkyne-azide 1,3-dipolar cycloaddition (SPAAC), was developed, characterized, and compared for cell compatibility to hydrogels based on agarose and alginate...
December 5, 2018: Biofabrication
Ashima Singh, Harjinder Singh, J M Khurana
We have reported synthesis of a novel 1,2,3-triazole conjugate of lithocholic acid by 1,3-dipolar cycloaddition reaction. The molecular properties such as geometry, conformations, bond lengths and dihedral angles were investigated theoretically. The bond order analysis was performed using Wiberg bond order (WBO), Fuzzy bond order (FBO) and Laplacian bond order (MBO) method. Electronic properties of molecule such as electrostatic surface potential analysis, frontier molecular orbital analysis, reduced density gradient, total density of states, and global chemical reactivity indices have been investigated...
November 22, 2018: Computational Biology and Chemistry
A Trautmann, P Ilzhöfer, G Durastante, C Politi, M Sohmen, M J Mark, F Ferlaino
We report on the first realization of heteronuclear dipolar quantum mixtures of highly magnetic erbium and dysprosium atoms. With a versatile experimental setup, we demonstrate binary Bose-Einstein condensation in five different Er-Dy isotope combinations, as well as one Er-Dy Bose-Fermi mixture. Finally, we present first studies of the interspecies interaction between the two species for one mixture.
November 23, 2018: Physical Review Letters
M A Sentef, M Ruggenthaler, A Rubio
So far, laser control of solids has been mainly discussed in the context of strong classical nonlinear light-matter coupling in a pump-probe framework. Here, we propose a quantum-electrodynamical setting to address the coupling of a low-dimensional quantum material to quantized electromagnetic fields in quantum cavities. Using a protoypical model system describing FeSe/SrTiO3 with electron-phonon long-range forward scattering, we study how the formation of phonon polaritons at the two-dimensional interface of the material modifies effective couplings and superconducting properties in a Migdal-Eliashberg simulation...
November 2018: Science Advances
Máryury Flores-Sumoza, Jackson J Alcázar, Edgar Márquez, José R Mora, Jesús Lezama, Esneyder Puello
In this work, the minimum energy structures of 22 4-pyridone derivatives have been optimized at Density Functional Theory level, and several quantum molecular, including electronic and thermodynamic descriptors, were computed for these substrates in order to obtain a statistical and meaningful QSAR equation. In this sense, by using multiple linear regressions, five mathematical models have been obtained. The best model with only four descriptors (r² = 0.86, Q² = 0.92, S.E.P = 0.38) was validated by the leave-one-out cross-validation method...
December 1, 2018: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Frédéric A Perras, Marek Pruski
The so-called t1 noise, which arises due to random instabilities in the spectrometer hardware, remains the primary source of noise that limits the sensitivity of most 2D NMR experiments, particularly in the expanding group of solid-state NMR methods that utilize dipolar-recoupling. In this communication we revisit the relationship between the signal intensity and the t1 noise produced. It is shown that since the latter scales linearly with the signal strength, the use of a conventional relaxation delay of 1...
November 26, 2018: Journal of Magnetic Resonance
Qing Xu, Haicheng Liu, Jianping Liu, Xiaokai Cheng, Xiaojuan Jia, Lei Yu
Addition of DMSO is capable of accelerating the aqueous hydrolysis of organohalides to alcohols greatly, providing a neutral, more efficient, milder and more economic new process. Mechanistic studies using 18O-DMSO and 18O-H2O showed that, contrary to the opinion that DMSO works as a dipolar solvent to enhance water's nucleophilicity, DMSO's accelerating effect comes from a complete oxygen transfer from DMSO to organohalides through generation of ROS+Me2·X- salts via C-O bonding, followed by O-S bond disassociated hydrolysis of ROS+Me2·X- with water...
December 3, 2018: ChemSusChem
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