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Amide proton transfer

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
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
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
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
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
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
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
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
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
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
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
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
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]
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
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
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
Adrienne N Dula, Siddharama Pawate, Lindsey M Dethrage, Benjamin N Conrad, Blake E Dewey, Robert L Barry, Seth A Smith
High-magnetic-field (7 T) chemical exchange saturation transfer (CEST) MRI provides information on the tissue biochemical environment. Multiple sclerosis (MS) affects the entire central nervous system, including the spinal cord. Optimal CEST saturation parameters found via simulation were implemented for CEST MRI in 10 healthy controls and 10 patients with MS, and the results were examined using traditional asymmetry analysis and a Lorentzian fitting method. In addition, T1 - and T2 *-weighted images were acquired for lesion localization and the transmitted B1 (+) field was evaluated to guide imaging parameters...
September 2016: NMR in Biomedicine
Vitaliy Khlebnikov, Nicolas Geades, Dennis W J Klomp, Hans Hoogduin, Penny Gowland, Olivier Mougin
PURPOSE: To compare two pulsed, volumetric chemical exchange saturation transfer (CEST) acquisition schemes: steady state (SS) and pseudosteady state (PS) for the same brain coverage, spatial/spectral resolution and scan time. METHODS: Both schemes were optimized for maximum sensitivity to amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) effects through Bloch-McConnell simulations, and compared in terms of sensitivity to APT and NOE effects, and to transmit field inhomogeneity...
July 25, 2016: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Yingkun Guo, Iris Yuwen Zhou, Suk-Tak Chan, Yu Wang, Emiri T Mandeville, Takahiro Igarashi, Eng H Lo, Xunming Ji, Phillip Zhe Sun
pH-sensitive amide proton transfer (APT) MRI provides a surrogate metabolic biomarker that complements the widely-used perfusion and diffusion imaging. However, the endogenous APT MRI is often calculated using the asymmetry analysis (MTRasym), which is susceptible to an inhomogeneous shift due to concomitant semisolid magnetization transfer (MT) and nuclear overhauser (NOE) effects. Although the intact brain tissue has little pH variation, white and gray matter appears distinct in the MTRasym image. Herein we showed that the heterogeneous MTRasym shift not related to pH highly correlates with MT ratio (MTR) and longitudinal relaxation rate (R1w), which can be reasonably corrected using the multiple regression analysis...
November 1, 2016: NeuroImage
Qi Zhang, Ming-Chen Fu, Hai-Zhu Yu, Yao Fu
Mechanistic study has been carried out on the B(C6F5)3-catalyzed amine alkylation with carboxylic acid. The reaction includes acid-amine condensation and amide reduction steps. In condensation step, the catalyst-free mechanism is found to be more favorable than the B(C6F5)3-catalyzed mechanism, because the automatic formation of the stable B(C6F5)3-amine complex deactivates the catalyst in the latter case. Meanwhile, the catalyst-free condensation is constituted by nucleophilic attack and the indirect H2O-elimination (with acid acting as proton shuttle) steps...
August 5, 2016: Journal of Organic Chemistry
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