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https://www.readbyqxmd.com/read/29741214/efficiency-of-water-soluble-nitroxide-biradicals-for-dynamic-nuclear-polarization-in-rotating-solids-at-9-4-t-bctol-m-and-cyolyl-totapol-as-new-polarizing-agents
#1
Michel Geiger, Anil Jagtap, Monu Kaushik, Han Sun, Daniel Stöppler, Snorri Sigurdsson, Björn Corzilius, Hartmut Oschkinat
Nitroxide biradicals are very efficient polarizing agents in magic angle spinning (MAS) cross effect (CE) dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR). Many recently synthesized, new radicals show superior DNP-efficiency in organic solvents but suffer from insufficient solubility in water or glycerol/water for biological applications. We report DNP efficiencies for two new radicals, the particularly well-water soluble bcTol-M and cyolyl-TOTAPOL, and include a comparison with three known biradicals, TOTAPOL, bcTol, and AMUPol...
May 9, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29738244/toward-full-zigzag-edged-nanographenes-peri-tetracene-and-its-corresponding-circumanthracene
#2
Murugan Rathamony Ajayakumar, Yubin Fu, Ji Ma, Felix Hennersdorf, Hartmut Komber, Jan J Weigand, Alexey Alfonsov, Alexey A Popov, Reinhard Berger, Junzhi Liu, Klaus Müllen, Xinliang Feng
Zigzag-edged nanographene with two rows of fused linear acenes, called as n-peri-acene (n-PA), is considered as potential building unit in the arena of organic electronics. n-PAs with four (peri-tetracene, 4-PA), five (peri-pentacene, 5-PA) or more benzene rings in a row have been predicted to show open-shell character, which would be attractive for the development of unprecedented molecular spintronics. However, solution-based synthesis of open-shell n-PA has thus far not been successful because of the poor chemical stability...
May 8, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29732067/tuning-the-redox-non-innocence-of-a-phenalenyl-ligand-toward-efficient-nickel-assisted-catalytic-hydrosilylation
#3
Gonela Vijaykumar, Anand Pariyar, Jasimuddin Ahmed, Bikash Kumar Shaw, Debashis Adhikari, Swadhin K Mandal
In this report, a ligand-redox assisted catalytic hydrosilylation has been investigated. A phenalenyl ligand coordinated nickel complex has been utilized as an electron reservoir to develop a base metal-assisted catalyst, which very efficiently hydrosilylates a wide variety of olefin substrates under ambient conditions. A mechanistic investigation revealed that a two-electron reduced phenalenyl based biradical nickel complex plays the key role in such catalysis. The electronic structure of the catalytically active biradical species has been interrogated using EPR spectroscopy, magnetic susceptibility measurements, and electronic structure calculations using a DFT method...
March 14, 2018: Chemical Science
https://www.readbyqxmd.com/read/29716199/reference-dependence-of-the-two-determinant-coupled-cluster-method-for-triplet-and-open-shell-singlet-states-of-biradical-molecules
#4
Jesse J Lutz, Marcel Nooijen, Ajith Perera, Rodney J Bartlett
We study the performance of the two-determinant (TD) coupled-cluster (CC) method which, unlike conventional ground-state single-reference (SR) CC methods, can, in principle, provide a naturally spin-adapted treatment of the lowest-lying open-shell singlet (OSS) and triplet electronic states. Various choices for the TD-CC reference orbitals are considered, including those generated by the multi-configurational self-consistent field method. Comparisons are made with the results of high-level SR-CC, equation-of-motion (EOM) CC, and multi-reference EOM calculations performed on a large test set of over 100 molecules with low-lying OSS states...
April 28, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29714815/b-heterocyclic-carbene-arising-from-charge-shift-a-computational-verification
#5
Congjie Zhang, Fan Fan, Zhimin Wang, Jinshuai Song, Chunsen Li, Yirong Mo
1-Borabicyclo(1.1.0)but-2(3)-ene (1BB) is a singlet biradical with two single electrons which can form an ionic resonance structure via charge-shift. The ionic resonance structure is a B-heterocyclic carbene (BHC) which can act as carbene, Lewis base, L- and Z-type ligands to give adducts and complexes. Using a range of quantum methods, we designed four types of stable compounds (A-D) derived from 1BB. These compounds retain the unique features of 1BB. As a consequence, we investigated the structures, stability and Wiberg bond orders (WBIs) of the Lewis adducts of A-D with Lewis acids (BePh₂, BH₃, AlH₃, AlCl₃, C₅BH₅ and C₁₃BH₉), as well as the Cu(I), Ag(I) and Au(I) complexes...
May 1, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29714383/push-pull-quinoidal-porphyrins
#6
Martin J Smith, Iain M Blake, William Clegg, Harry L Anderson
A family of push-pull quinoidal porphyrin monomers has been prepared from a meso-formyl porphyrin by bromination, thioacetal formation, palladium-catalyzed coupling with malononitrile and oxidation with DDQ. Attempts at extending this synthesis to a push-pull quinoidal/cumulenic porphyrin dimer were not successful. The crystal structures of the quinoidal porphyrins indicate that there is no significant contribution from singlet biradical or zwitterionic resonance forms. The crystal structure of an ethyne-linked porphyrin dimer shows that the torsion angle between the porphyrin units is only about 3°, in keeping with crystallographic results on related compounds, but contrasting with the torsion angle of about 35° predicted by computational studies...
May 1, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/29692539/comparing-the-diagnostic-efficacy-of-full-field-digital-mammography-with-digital-breast-tomosynthesis-using-birads-score-in-a-tertiary-cancer-care-hospital
#7
Divya Singla, Arvind K Chaturvedi, Abhinav Aggarwal, S A Rao, Dibyamohan Hazarika, Vivek Mahawar
Introduction: Breast cancer is one of the leading cancers in females worldwide, and its incidence has been rising at an exponential pace in the last 10 years even in India. Mammography has been the mainstay for detection of breast cancer over decades and has gradually advanced from screen film to full-field digital mammography. Recently, tomosynthesis has evolved as an advanced imaging investigation for early diagnosis of breast lesions in both diagnostic and screening settings. Aim of Study: To compare and evaluate the impact of digital breast tomosynthesis (DBT) compared to full-field digital mammography (FFDM) in the interpretation of BIRADS score in both diagnostic and screening settings...
January 2018: Indian Journal of Radiology & Imaging
https://www.readbyqxmd.com/read/29682875/photochemical-generation-of-chiral-n-b-x-heterocycles-via-heteroaromatic-c-x-bond-scission-x-s-o-and-boron-insertion
#8
Soren K Mellerup, Cally Li, Julian Radtke, Xiang Wang, Quan-Song Li, Suning Wang
Chiral organoboron compounds with a chelate backbone and mesityl/heterocycle substituents on boron (thienyl, furyl and derivatives) undergo a quantitative phototransformation yielding rare, chiral N,B,X-embedded heterocycles (b) (e.g. base-stabilized 1,2-thiaborinines and 1,2-oxaborinines). Boriranes (a) were observed as intermediates in some of these transformations. Oxaborinines display further photoreactivity, generating 4a,12b-dihydro-benzo[h][1,2]-oxaborinino-[4,3-f]quinolones through a sequential conrotatory electrocyclization and [1,5]-H shift...
April 23, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29657941/investigation-of-frequency-distribution-of-breast-imaging-reporting-and-data-system-birads-classification-and-epidemiological-factors-related-to-breast-cancer-in-iran-a-7-year-study-2010-2016
#9
Mehri Sirous, Parisa Sotoodeh Shahnani, Amirmasoud Sirous
Background: The first cause of women mortality due to cancer is breast cancer. Mammography plays a central part in early detection of breast cancers. The screening methods can play a major role to reduce the morbidity and mortality rate due to this malignancy. We sought the basic data in this study on our population because knowing about the baseline data is apt and vital. Materials and Methods: In this study, data were collected from a questionnaire, contained baseline bio data information, and mammographic imaging of the patients came during 7 years...
2018: Advanced Biomedical Research
https://www.readbyqxmd.com/read/29619170/efficient-cross-effect-dynamic-nuclear-polarization-without-depolarization-in-high-resolution-mas-nmr
#10
Frédéric Mentink-Vigier, Guinevere Mathies, Yangping Liu, Anne-Laure Barra, Marc A Caporini, Daniel Lee, Sabine Hediger, Robert G Griffin, Gaël De Paëpe
Dynamic nuclear polarization (DNP) has the potential to enhance the sensitivity of magic-angle spinning (MAS) NMR by many orders of magnitude and therefore to revolutionize atomic resolution structural analysis. Currently, the most widely used approach to DNP for studies of chemical, material, and biological systems involves the cross-effect (CE) mechanism, which relies on biradicals as polarizing agents. However, at high magnetic fields (≥5 T), the best biradicals used for CE MAS-DNP are still far from optimal, primarily because of the nuclear depolarization effects they induce...
December 1, 2017: Chemical Science
https://www.readbyqxmd.com/read/29593258/oxygen-radical-character-in-group-11-oxygen-fluorides
#11
Lin Li, Tony Stüker, Stefanie Kieninger, Dirk Andrae, Tobias Schlöder, Yu Gong, Lester Andrews, Helmut Beckers, Sebastian Riedel
Transition metal complexes bearing terminal oxido ligands are quite common, yet group 11 terminal oxo complexes remain elusive. Here we show that excited coinage metal atoms M (M = Au, Ag, Cu) react with OF2 to form hypofluorites FOMF and group 11 oxygen metal fluorides OMF2 , OAuF and OAgF. These compounds have been characterized by IR matrix-isolation spectroscopy in conjunction with state-of-the-art quantum-chemical calculations. The oxygen fluorides are formed by photolysis of the initially prepared hypofluorites...
March 28, 2018: Nature Communications
https://www.readbyqxmd.com/read/29584951/reversible-valence-photoisomerization-between-closed-shell-quinoidal-and-open-shell-biradical-form
#12
Ayako Tokunaga, Katsuya Mutoh, Takeshi Hasegawa, Jiro Abe
We report here a kinetic study on the thermal equilibrium process between the biradical form and the quinoidal form starting from the singlet biradical form alone. Photochromic phenoxyl-imidazolyl radical complex repeatedly generates biradical species upon UV light irradiation, and the following thermal equilibrium process responsible for the valence isomerization from the open-shell singlet biradical to the closed-shell quinoidal form is observed in the microsecond time region. The thermodynamic parameters for the equilibrium process were determined for the first time by nanosecond laser flash photolysis...
March 27, 2018: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/29573493/magnetic-interaction-through-non-conjugated-framework-observed-in-back-to-back-connected-triazinyl-nitroxyl-biradical-derivatives
#13
Yusuke Takahashi, Ryo Matsuhashi, Youhei Miura, Naoki Yoshioka
Three hetero-biradical derivatives having a structure of a back-to-back connected benzotriazinyl and tetramethyl or tetraethylisoindoline N-oxyl sharing a common benzo ring, 1-tBu, 1-Ph, and 2-tBu were synthesized and characterized by single crystal X-ray analyses, variable-temperature magnetic susceptibility studies, and DFT calculations. Temperature dependences of the magnetic susceptibility of 1-tBu, 1-Ph, and 2-tBu exhibit broad maxima at 70, 71, and 43 K, respectively. Though these radical derivatives form a columnar or chained assembly in the solid state, magnetic measurement of the polymer diluted sample and computational results imply that the magnetic property of the polycrystalline sample can be explained by two-spin system with an intramolecular antiferromagnetic interaction...
March 24, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29492506/trapping-of-transient-heavy-pnictogen-centred-biradicals
#14
J Bresien, A Hinz, A Schulz, A Villinger
Since the heavy biradicals [E(μ-NTer)]2 (E = Sb, Bi) are only of fleeting existence in solution, they were generated in situ and trapped by [2 + 2] addition reactions utilizing alkynes such as tolan (Ph-C[triple bond, length as m-dash]C-Ph). The structure, biradical character and bonding of [E(μ-NTer)]2 biradicals as well as their addition products are discussed on the basis of computations and experimental data.
March 26, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/29460881/-vacuum-assisted-excision-of-focal-dysplasia-of-mammary-glands-single-center-experience
#15
S S Skurikhin, I N Milkevich, I A Bolotin, V A Odintsov, A I Buynyakova, E B Zhogoleva, Yu V Suvorova
AIM: To assess the diagnostic significance and safety of vacuum-assisted resection in patients with focal breast cancer BIRADS category 3 and 4. MATERIAL AND METHODS: The procedure was performed in 50 women aged 22 to 51 years (35.1±2.6 years). RESULTS: There were no any complications immediately after vacuum resection. Tissue of the neoplasm was removed in full in all patients. Benign and malignant tumors were observed in 94 and 6% cases respectively...
2018: Khirurgiia
https://www.readbyqxmd.com/read/29459343/a-quasi-optical-and-corrugated-waveguide-microwave-transmission-system-for-simultaneous-dynamic-nuclear-polarization-nmr-on-two-separate-14-1-t-spectrometers
#16
Thierry Dubroca, Adam N Smith, Kevin J Pike, Stuart Froud, Richard Wylde, Bianca Trociewitz, Johannes McKay, Frederic Mentink-Vigier, Johan van Tol, Sungsool Wi, William Brey, Joanna R Long, Lucio Frydman, Stephen Hill
Nuclear magnetic resonance (NMR) is an intrinsically insensitive technique, with Boltzmann distributions of nuclear spin states on the order of parts per million in conventional magnetic fields. To overcome this limitation, dynamic nuclear polarization (DNP) can be used to gain up to three orders of magnitude in signal enhancement, which can decrease experimental time by up to six orders of magnitude. In DNP experiments, nuclear spin polarization is enhanced by transferring the relatively larger electron polarization to NMR active nuclei via microwave irradiation...
April 2018: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/29455042/trapping-of-1-2-cyclohexadiene-a-dft-mechanistic-study-on-the-reaction-of-1-2-cyclohexadiene-with-olefins-and-nitrones
#17
Emmanuel Amoah Boafo, Kwabena Darko, Bright Aryeh Afriyie, Richard Tia, Evans Adei
The mechanistic aspects of cycloaddition reactions of 1,2-cyclohexadiene with olefins and nitrones have been investigated with DFT calculations. The results show that the cycloaddition reactions of 1,2-cyclohexadiene with olefins do not go through a concerted pathway (one-step mechanism) but rather a stepwise one involving the formation of a biradical intermediate which then closes to form final cycloadduct. Electron-withdrawing substituents on the 1,2-cyclohexadiene decrease the activation barrier of the biradical-forming step but increase the barrier of the product-forming step and product stability, while electron-donating substituents on the 1,2-cyclohexadiene increase the barriers for both the biradical-forming step and the product-forming step but decrease the product stability...
May 2018: Journal of Molecular Graphics & Modelling
https://www.readbyqxmd.com/read/29431772/the-reactivity-of-cyclopropyl-cyanide-in-titan-s-atmosphere-a-possible-pre-biotic-mechanism
#18
E López, D Ascenzi, P Tosi, J M Bofill, J de Andrés, M Albertí, J M Lucas, A Aguilar
Cyclopropyl cyanide and other simple nitriles detected in Titan's atmosphere could be precursors leading to the formation of organic macromolecules in the atmosphere of Saturn's largest satellite. Proposing a thermodynamically possible mechanism that explains their formation and supports experimental results represents a difficult challenge. Experiments done in the Atomic and Molecular Physics Laboratory at the University of Trento (AMPL) have studied the ion-molecule reaction between cyclopropyl cyanide and its protonated form, with reaction products being characterized by mass spectrometry...
February 28, 2018: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/29427198/can-the-synthetic-c-view-images-be-used-in-isolation-for-diagnosing-breast-malignancy-without-reviewing-the-entire-digital-breast-tomosynthesis-data-set
#19
Mark C Murphy, Louise Coffey, Ailbhe C O'Neill, Cecily Quinn, Ruth Prichard, Sorcha McNally
AIMS AND OBJECTIVES: The aim of this study was to determine if the synthetic C view acquired at digital breast tomosynthesis (DBT) would give adequate information to confirm a malignancy and could obviate the need to review all the tomosynthesis image data set. METHODS: All patients with biopsy-proven breast cancer recalled from screening mammograms between May and September 2016 were included for review. For each patient, the screening 2D mammogram, the synthetic C view, and the DBT images were reviewed by three breast radiologists and each assigned a BIRADS code...
February 9, 2018: Irish Journal of Medical Science
https://www.readbyqxmd.com/read/29420892/probing-ionic-liquid-electrolyte-structure-via-the-glassy-state-by-dynamic-nuclear-polarization-nmr-spectroscopy
#20
Marc-Antoine Sani, Pierre-Alexandre Martin, Ruhamah Yunis, Fangfang Chen, Maria Forsyth, Michaël Deschamps, Luke A O'Dell
Dynamic nuclear polarization (DNP)-enhanced solid-state NMR spectroscopy has been used to study an ionic liquid salt solution (N-methyl-N-propyl-pyrrolidinium bis(fluorosulfonyl)imide, C3 mpyrFSI, containing 1.0 m lithium bis(fluorosulfonyl)imide, 6 LiFSI) in its glassy state at a temperature of 92 K. The incorporation of a biradical to enable DNP signal enhancement allowed the proximities of the lithium to the individual carbon sites on the pyrrolidinium cation to be probed using a 13 C-6 Li REDOR pulse sequence...
March 1, 2018: Journal of Physical Chemistry Letters
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