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Amide proton transfer

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https://www.readbyqxmd.com/read/29034505/in-vivo-characterization-of-the-downfield-part-of-1-h-mr-spectra-of-human-brain-at-9-4-t-magnetization-exchange-with-water-and-relation-to-conventionally-determined-metabolite-content
#1
Nicole D Fichtner, Ioannis-Angelos Giapitzakis, Nikolai Avdievich, Ralf Mekle, Daniel Zaldivar, Anke Henning, Roland Kreis
PURPOSE: To perform exchange-rate measurements on the in vivo human brain downfield spectrum (5-10 ppm) at 9.4 T and to compare the variation in concentrations of the downfield resonances and of known upfield metabolites to determine potential peak labels. METHODS: Non-water-suppressed metabolite cycling was used in combination with an inversion transfer technique in two brain locations in healthy volunteers to measure the exchange rates and T1 values of exchanging peaks...
October 16, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/29030880/direct-saturation-corrected-chemical-exchange-saturation-transfer-mri-of-glioma-simplified-decoupling-of-amide-proton-transfer-and-nuclear-overhauser-effect-contrasts
#2
Iris Yuwen Zhou, Enfeng Wang, Jerry S Cheung, Dongshuang Lu, Yang Ji, Xiaoan Zhang, Giulia Fulci, Phillip Zhe Sun
PURPOSE: Chemical exchange saturation transfer (CEST) MRI has shown promise in tissue characterization in diseases like stroke and tumor. However, in vivo CEST imaging such as amide proton transfer (APT) MRI is challenging because of concomitant factors such as direct water saturation, macromolecular magnetization transfer, and nuclear overhauser effect (NOE), which lead to a complex contrast in the commonly used asymmetry analysis (MTRasym). Here, we propose a direct saturation-corrected CEST (DISC-CEST) analysis for simplified decoupling and quantification of in vivo CEST effects...
October 13, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/29028326/ratiometric-ph-imaging-with-a-co-ii-2-mri-probe-via-cest-effects-of-opposing-ph-dependences
#3
Agnes E Thorarinsdottir, Kang Du, James H P Collins, T David Harris
We report a Co2-based magnetic resonance (MR) probe that enables the ratiometric quantitation and imaging of pH through chemical exchange saturation transfer (CEST). This approach is illustrated in a series of air- and water-stable Co(II)2 complexes featuring CEST-active tetra(carboxamide) and/or hydroxyl-substituted bisphosphonate ligands. For the complex bearing both ligand types, variable-pH CEST and NMR analyses reveal highly-shifted carboxamide and hydroxyl peaks with intensities that increase and decrease with increasing pH, respectively...
October 13, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29024066/a-comparison-of-exogenous-and-endogenous-cest-mri-methods-for-evaluating-in-vivo-ph
#4
Leila R Lindeman, Edward A Randtke, Rachel A High, Kyle M Jones, Christine M Howison, Mark D Pagel
PURPOSE: Extracellular pH (pHe) is an important biomarker for cancer cell metabolism. Acido-chemical exchange saturation transfer (CEST) MRI uses the contrast agent iopamidol to create spatial maps of pHe. Measurements of amide proton transfer exchange rates (kex ) from endogenous CEST MRI were compared to pHe measurements by exogenous acido-CEST MRI to determine whether endogenous kex could be used as a proxy for pHe measurements. METHODS: Spatial maps of pHe and kex were obtained using exogenous acidoCEST MRI and an endogenous CEST MRI analyzed with the omega plot method, respectively, to evaluate mouse kidney, a flank tumor model, and a spontaneous lung tumor model...
October 11, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/28989630/efficient-stabilisation-of-a-dihydrogenphosphate-tetramer-and-a-dihydrogenpyrophosphate-dimer-by%C3%A2-a-cyclic-pseudopeptide-containing-1-4-disubstituted-1-2-3-triazole-moieties
#5
Disha Mungalpara, Arto Valkonen, Kari Rissanen, Stefan Kubik
A cyclic pseudooctapeptide 2 is described containing 1,4-disubstituted 1,2,3-triazole moieties. This compound features eight converging hydrogen bond donors along the ring, namely four amide NH and four triazole CH groups, which enable 2 to engage in interactions with anions. While fully deprotonated sulfate anions exhibit only moderate affinity for 2, protonated anions such as dihydrogenpyrophosphate and dihydrogenphosphate anions are strongly bound. Complexation of the phosphate-derived anions involves sandwiching of a dihydrogenpyrophosphate dimer or a dihydrogenphosphate tetramer between two pseudopeptide rings...
September 1, 2017: Chemical Science
https://www.readbyqxmd.com/read/28942555/the-applicability-of-amide-proton-transfer-imaging-in-the-nervous-system-focus-on-hypoxic-ischemic-encephalopathy-in-the-neonate
#6
REVIEW
Yang Zheng, Xiaoming Wang
In recent years, magnetic resonance imaging (MRI) has become more widely used in neonatal hypoxic-ischemic encephalopathy (HIE), involving, for example, evaluation of cerebral edema, white matter fiber bundle tracking, cerebral perfusion status, and assessment of brain metabolites. MRI has many imaging modalities. However, its application for assessing changes in the internal environment at the tissue and cellular level after hypoxia-ischemia remains a challenge and is currently the focus of intense research...
September 23, 2017: Cellular and Molecular Neurobiology
https://www.readbyqxmd.com/read/28932452/crystal-structure-of-a-1-1-2-2-tetra-chloro-ethane-solvated-hydrazinecarbo-thio-amide-compound
#7
Sayed Riyadh, David L Hughes, Musa A Said
The title compound, [(1-{4-[2-(2,4-di-hydroxy-phen-yl)diazen-1-yl]phen-yl}ethyl-idene)amino]-thio-urea, 1,1,2,2-tetra-chloro-ethane monosolvate, C15H15N5O2S·C2H2Cl4, was prepared from 4-(4-acetyl-phenyl-diazendi-yl)resorcinol and thio-semicarbazide and recrystallized from mixed solvents of tetra-chloro-ethane and n-hexane. (1)H NMR and X-ray diffraction data are in support of the thione tautomeric form. The X-ray analysis shows the mol-ecule crystallizes as a zwitterion, with proton transfer from the nominal phenol to the azide group; the N-N bond length is 1...
September 1, 2017: Acta Crystallographica. Section E, Crystallographic Communications
https://www.readbyqxmd.com/read/28921821/iridium-catalyzed-direct-c-h-amidation-polymerization-step-growth-polymerization-by-c-n-bond-formation-via-c-h-activation-to-give-fluorescent-polysulfonamides
#8
Yoon-Jung Jang, Soon-Hyeok Hwang, Tae-Lim Choi
We report a powerful strategy for activation of C-H bonds to produce polysulfonamides by an atom-economical and green method using iridium-catalyzed direct C-H amidation polymerization (DCAP). After screening various directing groups, additives, silver salts, concentrations, and temperatures to optimize DCAP, high-molecular-weight (up to 149 kDa) and defect-free polysulfonamides were synthesized from various bis-sulfonyl azides. Although these polymers do not have conventional fluorescent conjugated cores, they emit blue light with large Stokes shifts and high quantum yields upon photoexcitation owing to an excited-state intramolecular proton-transfer process...
September 15, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28912676/chemical-exchange-saturation-transfer-mri-signal-loss-of-the-substantia-nigra-as-an-imaging-biomarker-to-evaluate-the-diagnosis-and-severity-of-parkinson-s-disease
#9
Chunmei Li, Min Chen, Xuna Zhao, Rui Wang, Haibo Chen, Wen Su, Shuhua Li, Baohui Lou, Guodong Song, Shuai Zhang, Jintao Zhang, Jinyuan Zhou
The early diagnosis of Parkinson's disease (PD) and the accurate evaluation of disease severity are crucial for intervention and treatment in PD patients. In this study, we applied chemical exchange saturation transfer (CEST) imaging to patients at different stages of PD and explored the clinical value of the CEST signal loss of the substantia nigra as an imaging biomarker of PD. The measured CEST signal intensities (including amide proton transfer-weighted or APTw, and total CEST or CESTtotal) of the substantia nigra in PD patients showed a significantly decreased tendency with PD progression...
2017: Frontiers in Neuroscience
https://www.readbyqxmd.com/read/28833781/catalytic-carbon-carbon-bond-forming-reactions-of-weakly-acidic-carbon-pronucleophiles-using-strong-br%C3%A3-nsted-bases-as-catalysts
#10
Yasuhiro Yamashita, Shu Kobayashi
Catalytic carbon-carbon bond-forming reactions of weakly acidic carbon pronucleophiles with N-aryl imines, α,β-unsaturated amides, and others under proton-transfer conditions were developed by designing strongly basic reaction intermediates known as product bases. The reactions proceed smoothly in the presence of a catalytic amount of strong base such as KH or alkaline metal amides. Modification of the metal cations by using chiral macrocyclic crown ethers allowed catalytic asymmetric 1,4-addition reactions to proceed with high enantioselectivities...
August 23, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28808429/fast-reliable-3d-amide-proton-transfer-imaging-of-brain-tumors-at-3t-with-variably-accelerated-sensitivity-encoding-vsense
#11
Yi Zhang, Hye-Young Heo, Shanshan Jiang, Paul A Bottomley, Jinyuan Zhou
The clinical use of amide proton transfer (APT) imaging is hindered by long scan times. Accuracy generally limits the use of conventional sensitivity encoding (SENSE) methods in APT, to an acceleration factor of 2. A novel variably-accelerated sensitivity encoding (vSENSE) method can provide more accurate results and therefore substantially higher overall acceleration factors than conventional SENSE. Here, vSENSE is further developed to eliminate the requirement that one fully-sampled APT frame be acquired, and extended to three dimensions (3D)...
April 2017: Proceedings of the International Society for Magnetic Resonance in Medicine ... Scientific Meeting and Exhibition
https://www.readbyqxmd.com/read/28799280/amide-proton-transfer-weighted-imaging-to-differentiate-malignant-from-benign-pulmonary-lesions-comparison-with-diffusion-weighted-imaging-and-fdg-pet-ct
#12
Yoshiharu Ohno, Yuji Kishida, Shinichiro Seki, Masao Yui, Mitsue Miyazaki, Hisanobu Koyama, Takeshi Yoshikawa
PURPOSE: To compare the capability of amide proton transfer-weighted (APTw) imaging, diffusion-weighted imaging (DWI), and FDG-PET/CT for the differentiation of malignant from benign pulmonary nodules. MATERIALS AND METHODS: In all, 82 consecutive patients with pulmonary nodules underwent APTw imaging and DWI with a 3T system, and FDG-PET/CT. All nodules were divided as either malignant (n = 49) or benign (n = 39) groups based on pathological and follow-up examinations...
August 11, 2017: Journal of Magnetic Resonance Imaging: JMRI
https://www.readbyqxmd.com/read/28792111/solid-state-nmr-h-n-c-h-and-h-n-c-c-3d-4d-correlation-experiments-for-resonance-assignment-of-large-proteins
#13
Hugo Fraga, Charles-Adrien Arnaud, Diego F Gauto, Maxime Audin, Vilius Kurauskas, Pavel Macek, Carsten Krichel, Jia-Ying Guan, Jerome Boisbouvier, Remco Sprangers, Cécile Breyton, Paul Schanda
Solid-state NMR spectroscopy can provide insight into protein structure and dynamics at the atomic level without inherent protein size limitations. However, a major hurdle to studying large proteins by solid-state NMR spectroscopy is related to spectral complexity and resonance overlap, which increase with molecular weight and severely hamper the assignment process. Here the use of two sets of experiments is shown to expand the tool kit of (1) H-detected assignment approaches, which correlate a given amide pair either to the two adjacent CO-CA pairs (4D hCOCANH/hCOCAcoNH), or to the amide (1) H of the neighboring residue (3D HcocaNH/HcacoNH, which can be extended to 5D)...
October 6, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
https://www.readbyqxmd.com/read/28763201/tracking-reactive-water-and-hydrogen-bonding-networks-in-photosynthetic-oxygen-evolution
#14
Bridgette A Barry, Udita Brahmachari, Zhanjun Guo
In oxygenic photosynthesis, photosystem II (PSII) converts water to molecular oxygen through four photodriven oxidation events at a Mn4CaO5 cluster. A tyrosine, YZ (Y161 in the D1 polypeptide), transfers oxidizing equivalents from an oxidized, primary chlorophyll donor to the metal center. Calcium or its analogue, strontium, is required for activity. The Mn4CaO5 cluster and YZ are predicted to be hydrogen bonded in a water-containing network, which involves amide carbonyl groups, amino acid side chains, and water...
August 1, 2017: Accounts of Chemical Research
https://www.readbyqxmd.com/read/28750319/theoretically-obtained-insight-into-the-mechanism-and-dioxetanone-species-responsible-for-the-singlet-chemiexcitation-of-coelenterazine
#15
Chun-Gang Min, Paulo J O Ferreira, Luís Pinto da Silva
Coelenterazine is a widespread bioluminescent substrate for a diverse set of marine species. Moreover, its imidazopyrazinone core is present in eight phyla of bioluminescent organisms. Given their very attractive intrinsic properties, these bioluminescent systems have been used in bioimaging, photodynamic therapy of cancer, as gene reporter and in sensing applications, among others. While it is known that bioluminescence results from the thermolysis of high-energy dioxetanones, the mechanism and dioxetanone species responsible for the singlet chemiexcitation of Coelenterazine are not fully understood...
September 2017: Journal of Photochemistry and Photobiology. B, Biology
https://www.readbyqxmd.com/read/28745750/asymmetric-alkylation-of-remote-c-sp-3-h-bonds-by-combining-proton-coupled-electron-transfer-with-chiral-lewis-acid-catalysis
#16
Wei Yuan, Zijun Zhou, Lei Gong, Eric Meggers
The catalytic asymmetric alkylation of the remote, unactivated δ-position of N-alkyl amides was enabled by the combination of visible-light-induced proton-coupled electron transfer, 1,5-hydrogen atom transfer, and chiral Lewis acid catalysis in up to 82% yield and up to 97% ee.
August 8, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28739967/reactions-of-biologically-inspired-hydride-sources-with-b-c6f5-3
#17
Lewis C Wilkins, Nicolò Santi, Louis Y P Luk, Rebecca L Melen
The combination of 1-benzyl-1,4-dihydropyridines with the strong Lewis acid, B(C6F5)3, generates a stable pyridinium borohydride species in high yields (94%) in as little as 10 min. This use of biologically inspired hydride sources further builds on the recent work of new hydride donors in the formation of borohydrides. When functionalizing the dihydropyridine with an amide or carboxylic acid moiety, a disproportionation reaction composed of a series of protonation/reduction steps is observed upon the addition of B(C6F5)3 As a result, one equivalent of dihydropyridine undergoes net hydrogenation, whereas the other is dehydrogenated yielding the pyridinium counterpart in a transfer hydrogenation-type mechanism...
August 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28733991/ph-sensitive-amide-proton-transfer-effect-dominates-the-magnetization-transfer-asymmetry-contrast-during-acute-ischemia-quantification-of-multipool-contribution-to-in-vivo-cest-mri
#18
Yin Wu, Iris Yuwen Zhou, Dongshuang Lu, Emiri Manderville, Eng H Lo, Hairong Zheng, Phillip Zhe Sun
PURPOSE: To determine the origins of in vivo magnetization transfer asymmetry contrast during acute ischemic stroke, particularly in the diffusion lesion, perfusion lesion, and their mismatch using a middle cerebral artery occlusion rat model of acute stroke. METHODS: Adult male Wistar rats underwent multiparametric MRI of diffusion, perfusion, T1 , and amide proton transfer (APT) imaging at 4.7 T following a middle cerebral artery occlusion procedure. A multipool Lorentzian model, including the nuclear Overhauser effect, magnetization transfer, direct water saturation, amine and amide chemical exchange saturation transfer effects, was applied for Z-spectrum fitting to determine the sources of in vivo magnetization transfer asymmetry following acute stroke...
July 21, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/28729292/amide-proton-transfer-imaging-allows-detection-of-glioma-grades-and-tumor-proliferation-comparison-with-ki-67-expression-and-proton-mr-spectroscopy-imaging
#19
C Su, C Liu, L Zhao, J Jiang, J Zhang, S Li, W Zhu, J Wang
BACKGROUND AND PURPOSE: Prognosis in glioma depends strongly on tumor grade and proliferation. In this prospective study of patients with untreated primary cerebral gliomas, we investigated whether amide proton transfer-weighted imaging could reveal tumor proliferation and reliably distinguish low-grade from high-grade gliomas compared with Ki-67 expression and proton MR spectroscopy imaging. MATERIALS AND METHODS: This study included 42 patients with low-grade (n = 28) or high-grade (n = 14) glioma, all of whom underwent conventional MR imaging, proton MR spectroscopy imaging, and amide proton transfer-weighted imaging on the same 3T scanner within 2 weeks before surgery...
July 20, 2017: AJNR. American Journal of Neuroradiology
https://www.readbyqxmd.com/read/28717802/a-computational-study-on-the-mechanism-of-ynamide-mediated-amide-bond-formation-from-carboxylic-acids-and-amines
#20
Song-Lin Zhang, Hai-Xing Wan, Zhu-Qin Deng
This paper reports a computational study elucidating the reaction mechanism for ynamide-mediated amide bond formation from carboxylic acids and amines. The mechanisms have been studied in detail for ynamide hydrocarboxylation and the subsequent aminolysis of the resulting adduct by an amine. Ynamide hydrocarboxylation is kinetically favorable and thermodynamically irreversible, resulting in the formation of a key low-lying intermediate CP1 featuring geminal vinylic acyloxy and sulfonamide groups. The aminolysis of CP1 by the amine is proposed to be catalyzed by the carboxylic acid itself that imparts favourable bifunctional effects...
August 2, 2017: Organic & Biomolecular Chemistry
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