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Jhen-Kuei Yu, Han-Wei Chien, Yi-Jung Lin, Praneeth Karanam, Yu-Heng Chen, Wenwei Lin
An organobase-directed, regiodivergent 1,3-dipolar cycloaddition of azomethine ylides and 2-hydoxybenzylidene indandiones is reported. The scarcely explored reversal of the nucleophilic site in azomethine ylides has been exploited for their regiodivergent (3+2) cycloaddition, which subsequently resulted in two different cascade processes to generate functionally distinct chromenopyrrolidines in a diversity oriented manner.
August 17, 2018: Chemical Communications: Chem Comm
Lukas Jackalin, Boris B Kharkov, Andrei V Komolkin, Sergey V Dvinskikh
Direct dipolar spin couplings are informative and sensitive probes for a wide range of dynamic processes and structural properties at atomic, molecular and supramolecular levels in liquid crystals and other anisotropic materials. Usually, heteronuclear 13C-1H dipolar couplings in liquid crystals with natural 13C abundance are measured. Recording 13C-15N NMR dipolar spectra in unlabeled materials is challenging because of the unfavorable combination of two rare isotopes. Here we design and compare various experimental strategies to measure short- and long-range heteronuclear 13C-15N dipolar couplings in liquid crystalline samples with high molecular orientational order...
August 17, 2018: Physical Chemistry Chemical Physics: PCCP
Tiago Venâncio, Lyege Magalhaes Oliveira, Tomasz Pawlak, Javier Ellena, Nubia Boechat, Steven P Brown
Experimental 13 C solid-state magic-angle spinning (MAS) NMR as well as DFT (gauge-including projector augmented wave) GIPAW calculations were used to probe disorder and local mobility in diethylcarbamazine citrate, (DEC)+ (citrate)- . This compound has been used as the first option drug for the treatment of filariasis, a disease endemic in tropical countries and caused by adult worms of Wuchereria bancrofti, which is transmitted by mosquitoes. We firstly present 2D 13 C-1 H dipolar-coupling mediated heteronuclear correlation spectra recorded at moderate spinning frequency, to explore the intermolecular interaction between DEC and citrate molecules...
August 16, 2018: Magnetic Resonance in Chemistry: MRC
Michael F Faulkner, Liang Qin, A C Maggs, Werner Krauth
We apply the irreversible event-chain Monte Carlo (ECMC) algorithm to the simulation of dense all-atom systems with long-range Coulomb interactions. ECMC is event-driven and exactly samples the Boltzmann distribution. It neither uses time-step approximations nor spatial cutoffs on the range of the interaction potentials. Most importantly, it need not evaluate the total Coulomb potential and thus circumvents the major computational bottleneck of traditional approaches. It only requires the derivatives of the two-particle Coulomb potential, for which we discuss mutually consistent choices...
August 14, 2018: Journal of Chemical Physics
Beat Rolf Vögeli, Liliya Vugmeyster
Cross-correlated relaxation (CCR) in multiple-quantum coherences differs from other relaxation phenomena in its theoretical ability to be mediated across an infinite distance. The two interfering relaxation mechanisms may be dipolar interactions, chemical shift anisotropies, chemical shift modulations or quadrupolar interactions. These properties make multiple-quantum CCR an attractive probe for structure and dynamics of biomacromolecules not accessible from other measurements. Here, we review the use of multiple-quantum CCR measurements in dynamics studies of proteins...
August 15, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Zhao-Bo Hu, Zhao-Yang Jing, Miao-Miao Li, Lei Yin, Yan-Dong Gao, Fei Yu, Tuo-Ping Hu, Zhenxing Wang, You Song
Two cobalt complexes with similar structures were synthesized using quinoline-2-carboxylic acid (HL) as the ligand. Both complexes are six-coordinated in antitriangular prism coordination geometries. There are one and four molecule units per cell for 1 and 2, respectively, with nearest Co-Co distances of 7.129 and 5.855 Å, respectively, which lead to their intermolecular interactions zj'. Both complexes are field-induced single-ion magnets. Complex 1 shows single slow relaxation under Hdc = 1.5 kOe attributed to the moment reversal, while complex 2 shows double slow relaxation resulting from intermolecular dipolar interaction and moment reversal, respectively...
August 15, 2018: Inorganic Chemistry
Harry Macpherson, Stuart Cornes, Shen Zhou, Kyriakos Porfyrakis
An N@C60 -containing C60 tetramer was synthesized by quadruple 1,3-dipolar cycloaddition (Prato) reaction. This molecule demonstrates the N@C60 qubit's ability to form covalently linked arrays. Furthermore, it provides a promising scaffold with which to measure multiple qubit-qubit interactions; which must be well characterized for a functioning quantum information processing architecture.
July 2018: Royal Society Open Science
Silvia Roscales, Nicole Bechmann, Daniel Holger Weiss, Martin Köckerling, Jens Pietzsch, Torsten Kniess
Novel valdecoxib-based cyclooxygenase-2 inhibitors were synthesized in one step via 1,3-dipolar cycloaddition of nitrile oxides with a series of eleven aryl alkynes, six of them described for the first time. Application of Ru(ii)-catalysis leads preferably to the formation of the 3,4-diaryl-substituted isoxazoles, while under thermal heating with base the 3,5-diaryl substitution pattern is favoured. The new the 3,4-diaryl-substituted isoxazoles possessing a small substituent (H and Me) displayed high COX-2 inhibition affinity (IC50 = 0...
March 1, 2018: MedChemComm
Gaochan Wu, Yun Gao, Dongwei Kang, Boshi Huang, Zhipeng Huo, Huiqing Liu, Vasanthanathan Poongavanam, Peng Zhan, Xinyong Liu
We report herein the design and synthesis of a series of 11 novel tacrine-1,2,3-triazole derivatives via a Cu(i)-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC) reaction. The newly synthesized compounds were evaluated for their inhibition activity against Electrophorus electricus acetylcholinesterase (AChE) and horse serum butyrylcholinesterase (BChE) as potential drug targets for Alzheimer's disease (AD). Among the designed compounds, compound 8a2 exhibited potent inhibition against AChE and BChE with IC50 values of 4...
January 1, 2018: MedChemComm
Martin D Gelenter, Mei Hong
We introduce a pulsed third-spin assisted recoupling experiment that produces high-intensity long-range 15N-13C cross peaks using low radiofrequency (rf) energy. This Proton-Enhanced Rotor-echo Short Pulse IRradiATION Cross Polarization (PERSPIRATIONCP) pulse sequence operates with the same principle as the Proton-Assisted Insensitive-Nuclei Cross Polarization (PAINCP) experiment, but uses only a fraction of the rf energy by replacing continuous-wave 13C and 15N irradiation with rotor-echo 90º pulses. Using formyl-MLF and β1 immunoglobulin binding domain of protein G (GB1) as model proteins, we demonstrate experimentally how PERSPIRATIONCP polarization transfer depends on the CP contact time, rf power, pulse flip angle, and 13C carrier frequency, and compare the PERSPIRATIONCP performance with the performances of PAINCP, RESPIRATIONCP, and SPECIFICCP for measuring 15N-13C cross peaks...
August 14, 2018: Journal of Physical Chemistry. B
Carla Rigling, Jessica K Kisunzu, Jörg Duschmalé, Daniel Häussinger, Markus Wiesner, Marc-Olivier Ebert, Helma Wennemers
Peptides have become valuable as catalysts for a variety of different reactions, but little is known about the conformational properties of peptidic catalysts. We investigated the conformation of the peptide H-dPro-Pro-Glu-NH2 , a highly reactive and stereoselective catalyst for conjugate addition reactions, and the corresponding enamine intermediate in solution by NMR spectroscopy and computational methods. The combination of nuclear Overhauser effects (NOEs), residual dipolar couplings (RDCs), J-couplings, and temperature coefficients revealed that the tripeptide adopts a single predominant conformation in its ground state...
August 14, 2018: Journal of the American Chemical Society
Hiroki Nagashima, Aany Sofia Lilly Thankamony, Julien Trébosc, Lionel Montagne, Gwendal Kerven, Jean-Paul Amoureux, Olivier Lafon
We introduce a novel heteronuclear dipolar recoupling based on the R21 -1 symmetry, which uses the tanh/tan (tt) shaped pulse as a basic inversion element and is denoted R21 -1 (tt). Using first-order average Hamiltonian theory, we show that this sequence is non-γ-encoded and that it reintroduces the |m| = 1 spatial component of the Chemical Shift Anisotropy (CSA) of the irradiated isotope and its heteronuclear dipolar interactions. Using numerical simulations and one-dimensional (1D) 27 Al-{31 P} through-space D-HMQC (Dipolar Heteronuclear Multiple-Quantum Correlation) experiments on VPI-5, we compare the performances of this recoupling to those of other non-γ-encoded |m| = 1 heteronuclear recoupling schemes: REDOR (Rotational-Echo DOuble Resonance), SFAM (Simultaneous Frequency and Amplitude Modulation) and R42 -1 (tt)...
July 20, 2018: Solid State Nuclear Magnetic Resonance
Xinghua Chen, Mei Peng, Hao Huang, Yangfan Zheng, Xiaojun Tao, Chunlian He, Yi Xiao
An operationally simple method with 100% atom economy has been developed for the synthesis of various N-(quinolin-2-yl)amides via the TsOH·H2O-mediated N-amidation of quinoline N-oxides using inexpensive and commercially available nitriles as the amidation reagents. Mechanistic exploration suggested that the reaction probably proceeds through an acid-assisted 1,3-dipolar cycloaddition and an N-O bond cleavage followed by a dehydro-aromatization process.
August 13, 2018: Organic & Biomolecular Chemistry
Mami Akisada, Ryo Kimura, Yoshimitsu Tachi, Shuichi Suzuki, Keiji Okada, Masatoshi Kozaki
A dendrimer with rigid branched terminal components was prepared by a copper-catalyzed Hüisgen 1,3-dipolar cycloaddition reaction. A zinc 5,15-diethynyl-10,20-bis(3,5-di- tert-butylphenyl)porphyrin unit was incorporated at the core of the dendrimer as a receptor site for an added pyridyl ligand. The appearance of an absorption band characteristic of the planar conformer of conjugated chains in the terminal components suggested that the dendrimer adopts a folded higher-order structure in dichloromethane at 25 °C...
August 13, 2018: Journal of Organic Chemistry
Sure Siva Prasad, Narra Rajashekar Reddy, Sundarababu Baskaran
A one-pot iminium ion based strategy has been developed for the synthesis of structurally novel iminosugar based hybrid molecules. Iminium ion derived from L-rhamnoselactol-mesylatereactedwith electron rich aromatic systems in an inter/intra molecular fashion to furnish pyrrolidine-based iminosugar C-aryl glycosides with high degree of stereoselectivity.Iminium ion also reacted readily with active methylene compounds such as 4-hydroxycoumarin, 4-hydroxyquinolinone and lawsone to provideiminosugarC-coumarin/quinolinone/naphthoquinonyl glycosides in very good yields...
August 13, 2018: Journal of Organic Chemistry
Jan Jadżyn, Jolanta Swiergiel
This paper presents the molecular basis for the quite different behavior of the viscosity of 1,2- and 1,n-diols in dependence of the length of the alkyl part of the molecules of these compounds. The experimental data on the dipolar orientational effects revealed a decidedly different role of that part of the molecules in creating a microstructure of both the hydrogen-bonded liquids. In the case of 1,n-diols, an increase in the alkyl radical length, i.e. an increasing of the distance between the OH groups within the molecule, highly stimulates molecular self-assembly in form of gradually longer and wider ribbon-like clusters...
August 13, 2018: Physical Chemistry Chemical Physics: PCCP
Violeta Fuentes-Landete, Karsten W Köster, Roland Böhmer, Thomas Loerting
Isotope effects accompanying the order-disorder transition of ice XIV to ice XII are studied using calorimetry, X-ray diffraction, and dielectric spectroscopy. Particular emphasis is placed on the impact of the cooling rate applied during high-pressure production and during ambient-pressure recooling on the degree of hydrogen order in the low-temperature ice XIV phase. For specimens from D2O, ordering is harder to achieve in the sense that despite smaller cooling rates, the degree of order is less than in crystals produced from H2O...
August 13, 2018: Physical Chemistry Chemical Physics: PCCP
Mauricio Acelas, Vladimir V Kouznetsov, Arnold R Romero Bohórquez
A novel and highly efficient synthetic approach for the expedite construction of new octahydroacridine-isoxazole- and octahydroacridine-1,2,3-triazole-based molecular hybrids is first reported. Rapid access to the octahydroacridine core was achieved in a highly diastereoselective fashion via cationic Povarov reaction of N-propargyl anilines and citronella essential oil (Cymbopogon nardus). The subsequent 1,3-dipolar and Cu (I) catalyzed alkyne-azide cycloaddition reaction of the terminal alkyne fragment with the corresponding oxime or azide affords the desired 3,5-isoxazoles and 1,2,3-triazoles, respectively, as interesting molecular hybrid models for pharmacological studies...
August 11, 2018: Molecular Diversity
Andrew Cho, Roozbeh Eskandari, Vesselin Z Miloushev, Kayvan R Keshari
Although dissolution dynamic nuclear polarization is a robust technique to significantly increase magnetic resonance signal, the short T1 relaxation time of most 13 C-nuclei limits the timescale of hyperpolarized experiments. To address this issue, we have characterized a non-synthetic approach to extend the hyperpolarized lifetime of 13 C-nuclei in close proximity to solvent-exchangeable protons. Protons exhibit stronger dipolar relaxation than deuterium, so dissolving these compounds in D2 O to exchange labile protons with solvating deuterons results in longer-lived hyperpolarization of the 13 C-nucleus 2-bonds away...
August 2, 2018: Journal of Magnetic Resonance
Prashanth S Venkataram, Jan Hermann, Alexandre Tkatchenko, Alejandro W Rodriguez
Thermal radiative phenomena can be strongly influenced by the coupling of phonons and long-range electromagnetic fields at infrared frequencies. Typically employed macroscopic descriptions of thermal fluctuations often ignore atomistic effects that become relevant at nanometric scales, whereas purely microscopic treatments ignore long-range, geometry-dependent electromagnetic effects. We describe a mesoscopic framework for modeling thermal fluctuation phenomena among molecules near macroscopic bodies, conjoining atomistic treatments of electronic and vibrational fluctuations obtained from density functional theory in the former with continuum descriptions of electromagnetic scattering in the latter...
July 27, 2018: Physical Review Letters
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