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Amide proton transfer

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https://www.readbyqxmd.com/read/27918442/some-brief-notes-on-theoretical-and-experimental-investigations-of-intramolecular-hydrogen-bonding
#1
REVIEW
Lucjan Sobczyk, Dorota Chudoba, Peter M Tolstoy, Aleksander Filarowski
A review of selected literature data related to intramolecular hydrogen bonding in ortho-hydroxyaryl Schiff bases, ortho-hydroxyaryl ketones, ortho-hydroxyaryl amides, proton sponges and ortho-hydroxyaryl Mannich bases is presented. The paper reports on the application of experimental spectroscopic measurements (IR and NMR) and quantum-mechanical calculations for investigations of the proton transfer processes, the potential energy curves, tautomeric equilibrium, aromaticity etc. Finally, the equilibrium between the intra- and inter-molecular hydrogen bonds in amides is discussed...
December 2, 2016: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/27885356/magnetization-transfer-and-amide-proton-transfer-mri-of-neonatal-brain-development
#2
Yang Zheng, Xiaoming Wang, Xuna Zhao
Purpose. This study aims to evaluate the process of brain development in neonates using combined amide proton transfer (APT) imaging and conventional magnetization transfer (MT) imaging. Materials and Methods. Case data were reviewed for all patients hospitalized in our institution's neonatal ward. Patients underwent APT and MT imaging (a single protocol) immediately following the routine MR examination. Single-slice APT/MT axial imaging was performed at the level of the basal ganglia. APT and MT ratio (MTR) measurements were performed in multiple brain regions of interest (ROIs)...
2016: BioMed Research International
https://www.readbyqxmd.com/read/27883128/modeling-the-archetype-cysteine-protease-reaction-using-dispersion-corrected-density-functional-methods-in-oniom-type-hybrid-qm-mm-calculations-the-proteolytic-reaction-of-papain
#3
Attila Fekete, István Komáromi
A proteolytic reaction of papain with a simple peptide model substrate N-methylacetamide has been studied. Our aim was twofold: (i) we proposed a plausible reaction mechanism with the aid of potential energy surface scans and second geometrical derivatives calculated at the stationary points, and (ii) we investigated the applicability of the dispersion corrected density functional methods in comparison with the popular hybrid generalized gradient approximations (GGA) method (B3LYP) without such a correction in the QM/MM calculations for this particular problem...
November 24, 2016: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/27787988/coordination-chemistry-and-f-element-complexation-by-diethylenetriamine-n-n%C3%A2-bis-acetylglycine-n-n-n%C3%A2-triacetic-acid
#4
Colt R Heathman, Travis S Grimes, Peter R Zalupski
Potentiometric and spectroscopic techniques were used to evaluate the coordination behavior and thermodynamic features of trivalent f-element complexation by diethylenetriamine-N,N″-bis(acetylglycine)-N,N',N″-triacetic acid (DTTA-DAG) and its di(acetylglycine ethyl ester) analogue [diethylenetriamine-N,N″-bis(acetylglycine ethyl ester)-N,N',N″-triacetic acid (DTTA-DAGEE)]. Protonation constants and stability constants of trivalent lanthanide complexes (except Pm(3+)) were determined by potentiometry...
October 27, 2016: Inorganic Chemistry
https://www.readbyqxmd.com/read/27747930/quantitative-analysis-of-the-z-spectrum-using-a-numerically-simulated-look-up-table-application-to-the-healthy-human-brain-at-7t
#5
Nicolas Geades, Benjamin A E Hunt, Simon M Shah, Andrew Peters, Olivier E Mougin, Penny A Gowland
PURPOSE: To develop a method that fits a multipool model to z-spectra acquired from non-steady state sequences, taking into account the effects of variations in T1 or B1 amplitude and the results estimating the parameters for a four-pool model to describe the z-spectrum from the healthy brain. METHODS: We compared measured spectra with a look-up table (LUT) of possible spectra and investigated the potential advantages of simultaneously considering spectra acquired at different saturation powers (coupled spectra) to provide sensitivity to a range of different physicochemical phenomena...
October 17, 2016: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/27732585/catalytic-alkylation-of-remote-c-h-bonds-enabled-by-proton-coupled-electron-transfer
#6
Gilbert J Choi, Qilei Zhu, David C Miller, Carol J Gu, Robert R Knowles
Despite advances in hydrogen atom transfer (HAT) catalysis, there are currently no molecular HAT catalysts that are capable of homolysing the strong nitrogen-hydrogen (N-H) bonds of N-alkyl amides. The motivation to develop amide homolysis protocols stems from the utility of the resultant amidyl radicals, which are involved in various synthetically useful transformations, including olefin amination and directed carbon-hydrogen (C-H) bond functionalization. In the latter process-a subset of the classical Hofmann-Löffler-Freytag reaction-amidyl radicals remove hydrogen atoms from unactivated aliphatic C-H bonds...
October 12, 2016: Nature
https://www.readbyqxmd.com/read/27722530/a-comparison-of-the-experimental-and-theoretical-charge-density-distributions-in-two-polymorphic-modifications-of-piroxicam
#7
Felcia Lai, Jonathan J Du, Peter A Williams, Linda Váradi, Daniel Baker, Paul W Groundwater, Jacob Overgaard, James A Platts, David E Hibbs
Experimental charge density distribution studies of two polymorphic forms of piroxicam, β-piroxicam (1) and piroxicam monohydrate (2), were carried out via high-resolution single crystal X-ray diffraction experiments and multipole refinement. The asymmetric unit of (2) consists of two discrete piroxicam molecules, (2a) and (2b), and two water molecules. Geometry differs between (1) and (2) due to the zwitterionic nature of (2) which results in the rotation of the pyridine ring around the C(10)-N(2) bond by approximately 180°...
October 10, 2016: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/27714249/proton-coupled-electron-transfer-in-the-reduction-of-carbonyls-using-smi2-h2o-implications-for-the-reductive-coupling-of-acyl-type-ketyl-radicals-with-smi2-h2o
#8
Shicheng Shi, Roman Szostak, Michal Szostak
Samarium diiodide-water (SmI2-H2O) reagents have emerged as some of the most practical systems enabling reduction and reductive cyclizations of ketyl radicals. Recently, this reaction manifold has been extended to acyl-type radicals generated from cyclic polar carboxylic acid derivatives. However, the relationship between the fundamental electron- and proton-transfer steps in the generation of ketyl-type radicals with SmI2-H2O remains unclear. An intriguing scenario involves an initial proton-coupled electron transfer (PCET) mechanism from SmI2-H2O to the carbonyl group...
September 26, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27690156/chemical-exchange-saturation-transfer-for-predicting-response-to-stereotactic-radiosurgery-in-human-brain-metastasis
#9
Kimberly L Desmond, Hatef Mehrabian, Sofia Chavez, Arjun Sahgal, Hany Soliman, Radoslaw Rola, Greg J Stanisz
PURPOSE: The purpose of this work was to determine the predictive value of chemical exchange saturation transfer (CEST) metrics in brain metastases treated with stereotactic radiosurgery (SRS). METHODS: CEST spectra at a radiofrequency power of 0.52 µT were collected on a 3 Tesla (T) magnetic resonance imaging from 25 patients at three time points: pretreatment, 1 week, and 1 month post-treatment. Amide proton transfer-weighted images and maps of the amplitude and width of Lorentzian-shaped CEST peaks and the relaxation-compensated AREX metric were constructed at the offset frequencies of amide, amine, and relayed nuclear Overhauser effect (NOE) from aliphatic groups as well as the broad magnetization transfer effect...
September 30, 2016: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/27689907/irida-%C3%AE-ketoimines-derived-from-hydrazines-to-afford-metallapyrazoles-or-n-n-bond-cleavage-a-missing-metallacycle-disclosed-by-a-theoretical-and-experimental-study
#10
Itziar Zumeta, Claudio Mendicute-Fierro, Itxaso Bustos, Miguel A Huertos, Antonio Rodríguez-Diéguez, José M Seco, Eider San Sebastian, María A Garralda
Unprecedented metallapyrazoles [IrH2{Ph2P(o-C6H4)CNNHC(o-C6H4)PPh2}] (3) and [IrHCl{Ph2P(o-C6H4)CNNHC(o-C6H4)PPh2}] (4) were obtained by the reaction of the irida-β-ketoimine [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNNH2))H}] (2) in MeOH heated at reflux in the presence and absence of KOH, respectively. In solution, iridapyrazole 3 undergoes a dynamic process due to prototropic tautomerism with an experimental barrier for the exchange of ΔGcoal(⧧) = 53.7 kJ mol(-1). DFT calculations agreed with an intrapyrazole proton transfer process assisted by two water molecules (ΔG = 63...
October 17, 2016: Inorganic Chemistry
https://www.readbyqxmd.com/read/27618473/fine-control-over-site-and-substrate-selectivity-in-hydrogen-atom-transfer-based-functionalization-of-aliphatic-c-h-bonds
#11
Michela Salamone, Giulia Carboni, Massimo Bietti
The selective functionalization of unactivated aliphatic C-H bonds over intrinsically more reactive ones represents an ongoing challenge of synthetic chemistry. Here we show that in hydrogen atom transfer (HAT) from the aliphatic C-H bonds of alkane, ether, alcohol, amide, and amine substrates to the cumyloxyl radical (CumO(•)) fine control over site and substrate selectivity is achieved by means of acid-base interactions. Protonation of the amines and metal ion binding to amines and amides strongly deactivates the C-H bonds of these substrates toward HAT to CumO(•), providing a powerful method for selective functionalization of unactivated or intrinsically less reactive C-H bonds...
October 7, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27610465/catalytic-proton-coupled-electron-transfer-from-metal-hydrides-to-titanocene-amides-hydrazides-and-imides-determination-of-thermodynamic-parameters-relevant-to-nitrogen-fixation
#12
Iraklis Pappas, Paul J Chirik
The hydrogenolysis of titanium-nitrogen bonds in a series of bis(cyclopentadienyl) titanium amides, hydrazides and imides by proton coupled electron transfer (PCET) is described. Twelve different N-H bond dissociation free energies (BDFEs) among the various nitrogen-containing ligands were measured or calculated, and effects of metal oxidation state and N-ligand substituent were determined. Two metal hydride complexes, (η(5)-C5Me5)(py-Ph)Rh-H (py-Ph = 2-pyridylphenyl, [Rh]-H) and (η(5)-C5R5)(CO)3Cr-H ([Cr](R)-H, R= H, Me) were evaluated for formal H atom transfer reactivity and were selected due to their relatively weak M-H bond strengths yet ability to activate and cleave molecular hydrogen...
October 3, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/27587949/emerging-techniques-in-brain-tumor-imaging-what-radiologists-need-to-know
#13
REVIEW
Minjae Kim, Ho Sung Kim
Among the currently available brain tumor imaging, advanced MR imaging techniques, such as diffusion-weighted MR imaging and perfusion MR imaging, have been used for solving diagnostic challenges associated with conventional imaging and for monitoring the brain tumor treatment response. Further development of advanced MR imaging techniques and postprocessing methods may contribute to predicting the treatment response to a specific therapeutic regimen, particularly using multi-modality and multiparametric imaging...
September 2016: Korean Journal of Radiology: Official Journal of the Korean Radiological Society
https://www.readbyqxmd.com/read/27554437/a-simple-primary-amide-for-the-selective-recovery-of-gold-from-secondary-resources
#14
Euan D Doidge, Innis Carson, Peter A Tasker, Ross J Ellis, Carole A Morrison, Jason B Love
Waste electrical and electronic equipment (WEEE) such as mobile phones contains a plethora of metals of which gold is by far the most valuable. Herein a simple primary amide is described that achieves the selective separation of gold from a mixture of metals typically found in mobile phones by extraction into toluene from an aqueous HCl solution; unlike current processes, reverse phase transfer is achieved simply using water. Phase transfer occurs by dynamic assembly of protonated and neutral amides with [AuCl4 ](-) ions through hydrogen bonding in the organic phase, as shown by EXAFS, mass spectrometry measurements, and computational calculations, and supported by distribution coefficient analysis...
September 26, 2016: Angewandte Chemie
https://www.readbyqxmd.com/read/27548755/-15-n-heteronuclear-chemical-exchange-saturation-transfer-mri
#15
Haifeng Zeng, Jiadi Xu, Nirbhay N Yadav, Michael T McMahon, Bradley Harden, Dominique Frueh, Peter C M van Zijl
A two-step heteronuclear enhancement approach was combined with chemical exchange saturation transfer (CEST) to magnify (15)N MRI signal of molecules through indirect detection via water protons. Previous CEST studies have been limited to radiofrequency (rf) saturation transfer or excitation transfer employing protons. Here, the signal of (15)N is detected indirectly through the water signal by first inverting selectively protons that are scalar-coupled to (15)N in the urea molecule, followed by chemical exchange of the amide proton to bulk water...
September 7, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/27532323/chromophoric-dyads-for-the-light-driven-generation-of-hydrogen-investigation-of-factors-in-the-design-of-multicomponent-photosensitizers-for-proton-reduction
#16
Po-Yu Ho, Bo Zheng, Daniel Mark, Wai-Yeung Wong, David W McCamant, Richard Eisenberg
Two new dyads have been synthesized and studied as photosensitizers for the light-driven generation of H2 from aqueous protons. One of the dyads, Dy-1, consists of a strongly absorbing Bodipy (dipyrromethene-BF2) dye and a platinum diimine benzenedithiolate (bdt) charge transfer (CT) chromophore, denoted as PtN2S2. The two components are connected through an amide linkage on the bdt side of the PtN2S2 complex. The second dyad, Dy-2, contains a diketopyrrolopyrrole dye that is linked directly to the acetylide ligands of a Pt diimine bis(arylacetylide) CT chromophore...
September 6, 2016: Inorganic Chemistry
https://www.readbyqxmd.com/read/27524192/-preliminary-application-of-amide-proton-transfer-imaging-signal-in-acute-ischemic-stroke
#17
X J Luo, M Chen, C Zhang, G D Song, C M Li, T Gong, J Y Zhou
OBJECTIVE: To apply amide proton transfer magnetic resonance imaging (APT-MRI) technique to acute ischemic stroke, and to discuss clinical values of the APT-MRI main parameter - MTRasym(3.5 ppm). METHODS: A total of 18 emergency admitted patients, with acute ischemic stroke from Beijing Hospital, were recruited from March to November 2015. Eventually, 18 patients (male 14, female 4, average age 72 years old, age ranged from 52 to 92 years, symptom onset ≤24 hours, 2 patients≤ 6 hours) were included in this study...
August 2, 2016: Zhonghua Yi Xue za Zhi [Chinese medical journal]
https://www.readbyqxmd.com/read/27490691/steric-and-electronic-influence-on-proton-coupled-electron-transfer-reactivity-of-a-mononuclear-mn-iii-hydroxo-complex
#18
Derek B Rice, Gayan B Wijeratne, Andrew D Burr, Joshua D Parham, Victor W Day, Timothy A Jackson
A mononuclear hydroxomanganese(III) complex was synthesized utilizing the N5 amide-containing ligand 2-[bis(pyridin-2-ylmethyl)]amino-N-2-methyl-quinolin-8-yl-acetamidate (dpaq(2Me) ). This complex is similar to previously reported [Mn(III)(OH)(dpaq(H))](+) [Inorg. Chem. 2014, 53, 7622-7634] but contains a methyl group adjacent to the hydroxo moiety. This α-methylquinoline group in [Mn(III)(OH)(dpaq(2Me))](+) gives rise to a 0.1 Å elongation in the Mn-N(quinoline) distance relative to [Mn(III)(OH)(dpaq(H))](+)...
August 15, 2016: Inorganic Chemistry
https://www.readbyqxmd.com/read/27489348/structure-of-fully-protonated-proteins-by-proton-detected-magic-angle-spinning-nmr
#19
Loren B Andreas, Kristaps Jaudzems, Jan Stanek, Daniela Lalli, Andrea Bertarello, Tanguy Le Marchand, Diane Cala-De Paepe, Svetlana Kotelovica, Inara Akopjana, Benno Knott, Sebastian Wegner, Frank Engelke, Anne Lesage, Lyndon Emsley, Kaspars Tars, Torsten Herrmann, Guido Pintacuda
Protein structure determination by proton-detected magic-angle spinning (MAS) NMR has focused on highly deuterated samples, in which only a small number of protons are introduced and observation of signals from side chains is extremely limited. Here, we show in two fully protonated proteins that, at 100-kHz MAS and above, spectral resolution is high enough to detect resolved correlations from amide and side-chain protons of all residue types, and to reliably measure a dense network of (1)H-(1)H proximities that define a protein structure...
August 16, 2016: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/27472068/synthetic-applications-of-proton-coupled-electron-transfer
#20
Emily C Gentry, Robert R Knowles
Redox events in which an electron and proton are exchanged in a concerted elementary step are commonly referred to as proton-coupled electron transfers (PCETs). PCETs are known to operate in numerous important biological redox processes, as well as recent inorganic technologies for small molecule activation. These studies suggest that PCET catalysis might also function as a general mode of substrate activation in organic synthesis. Over the past three years, our group has worked to advance this hypothesis and to demonstrate the synthetic utility of PCET through the development of novel catalytic radical chemistries...
August 16, 2016: Accounts of Chemical Research
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