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Amide proton transfer

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https://www.readbyqxmd.com/read/28526431/measurement-of-apt-using-a-combined-cert-arex-approach-with-varying-duty-cycles
#1
Zhongliang Zu, Hua Li, Junzhong Xu, Xiao-Yong Zhang, Moritz Zaiss, Ke Li, Mark D Does, John C Gore, Daniel F Gochberg
The goal is to develop an imaging method where contrast reflects amide-water magnetization exchange, with minimal signal contributions from other sources. Conventional chemical exchange saturation transfer (CEST) imaging of amides (often called amide proton transfer, or APT, and quantified by the metric MTRasym) is confounded by several factors unrelated to amides, such as aliphatic protons, water relaxation, and macromolecular magnetization transfer. In this work, we examined the effects of combining our previous chemical exchange rotation (CERT) approach with the non-linear AREX method while using different duty cycles (DC) for the label and reference scans...
May 16, 2017: Magnetic Resonance Imaging
https://www.readbyqxmd.com/read/28474409/amide-proton-transfer-cest-of-the-cervical-spinal-cord-in-multiple-sclerosis-patients-at-3t
#2
Samantha By, Robert L Barry, Alex K Smith, Bailey D Lyttle, Bailey A Box, Francesca R Bagnato, Siddharama Pawate, Seth A Smith
PURPOSE: The ability to evaluate pathological changes in the spinal cord in multiple sclerosis (MS) is limited because T1 - and T2 -w MRI imaging are not sensitive to biochemical changes in vivo. Amide proton transfer (APT) chemical exchange saturation transfer (CEST) can indirectly detect amide protons associated with proteins and peptides, potentially providing more pathological specificity. Here, we implement APT CEST in the cervical spinal cord of healthy and MS cohorts at 3T. METHODS: APT CEST of the cervical spinal cord was obtained in a cohort of 10 controls and 10 MS patients using a novel respiratory correction methodology...
May 5, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/28455264/using-functional-and-molecular-mri-techniques-to-detect-neuroinflammation-and-neuroprotection-after-traumatic-brain-injury
#3
Wenzhu Wang, Hong Zhang, Doon-Hoon Lee, Jintao Yu, Tian Cheng, Michael Hong, Shanshan Jiang, Heng Fan, Xi Huang, Jinyuan Zhou, Jian Wang
This study was designed to investigate whether functional and molecular MRI techniques are sensitive biomarkers for assessment of neuroinflammation and drug efficacy after traumatic brain injury (TBI) in rats. We subjected rats to a controlled cortical impact model and used behavioral tests, histology, and immunofluorescence to assess whether flavonoid pinocembrin provides cerebral protection and improves functional recovery. Most importantly, we used multiple noninvasive structural, functional, and molecular MRI techniques to examine whether the pinocembrin-related neuroprotection and attenuation of neuroinflammation can be detected in vivo...
April 25, 2017: Brain, Behavior, and Immunity
https://www.readbyqxmd.com/read/28453291/amide-group-directed-protonolysis-of-cyclopropane-an-approach-to-2-2-disubstituted-pyrrolidines
#4
Marija Skvorcova, Aigars Jirgensons
Regioselective protonolytic C-C bond cleavage of acylated aminomethyl cyclopropanes can be achieved using trifluoroacetic acid. The intermediate tertiary carbenium ion undergoes an intramolecular amination to give 2,2-substituted pyrrolidines. The strength of the acid and the amine substituent are important factors to achieve high regioselectivity, suggesting intramolecular proton transfer from the protonated amide function. Preliminary mechanistic studies revealed that cyclopropane cleavage proceeds with retention of configuration at the carbon to which the proton is attached...
April 28, 2017: Organic Letters
https://www.readbyqxmd.com/read/28436068/dinitrogen-splitting-coupled-to-protonation
#5
Gleb A Silantyev, Moritz Förster, Bastian Schluschaß, Josh Abbenseth, Christian Würtele, Christian Volkmann, Max C Holthausen, Sven Schneider
The coupling of electron- and proton-transfer steps provides a general concept to control the driving force of redox reactions. N2 splitting of a molybdenum dinitrogen complex into nitrides coupled to a reaction with Brønsted acid is reported. Remarkably, our spectroscopic, kinetic, and computational mechanistic analysis attributes N-N bond cleavage to protonation in the periphery of an amide pincer ligands rather than the {Mo-N2 -Mo} core. The strong effect on electronic structure and ultimately the thermochemistry and kinetic barrier of N-N bond cleavage is an unusual case of a proton-coupled metal-to-ligand charge transfer process, highlighting the use of proton-responsive ligands for nitrogen fixation...
April 24, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28433532/exci-cest-exploiting-pharmaceutical-excipients-as-mri-cest-contrast-agents-for-tumor-imaging
#6
Dario Livio Longo, Fatima Zzahra Moustaghfir, Alexandre Zerbo, Lorena Consolino, Annasofia Anemone, Martina Bracesco, Silvio Aime
Chemical Exchange Saturation Transfer (CEST) approach is a novel tool within magnetic resonance imaging (MRI) that allows visualization of molecules possessing exchangeable protons with water. Many molecules, employed as excipients for the formulation of finished drug products, are endowed with hydroxyl, amine or amide protons, thus can be exploitable as MRI-CEST contrast agents. Their high safety profiles allow them to be injected at very high doses. Here we investigated the MRI-CEST properties of several excipients (ascorbic acid, sucrose, N-acetyl-d-glucosamine, meglumine and 2-pyrrolidone) and tested them as tumor-detecting agents in two different murine tumor models (breast and melanoma cancers)...
April 20, 2017: International Journal of Pharmaceutics
https://www.readbyqxmd.com/read/28374993/removable-backbone-modification-method-for-the-chemical-synthesis-of-membrane-proteins
#7
Jia-Bin Li, Shan Tang, Ji-Shen Zheng, Chang-Lin Tian, Lei Liu
Chemical synthesis can produce water-soluble globular proteins bearing specifically designed modifications. These synthetic molecules have been used to study the biological functions of proteins and to improve the pharmacological properties of protein drugs. However, the above advances notwithstanding, membrane proteins (MPs), which comprise 20-30% of all proteins in the proteomes of most eukaryotic cells, remain elusive with regard to chemical synthesis. This difficulty stems from the strong hydrophobic character of MPs, which can cause considerable handling issues during ligation, purification, and characterization steps...
April 4, 2017: Accounts of Chemical Research
https://www.readbyqxmd.com/read/28374764/amide-proton-transfer-magnetic-resonance-imaging-in-detecting-intracranial-hemorrhage-at-different-stages-a-comparative-study-with-susceptibility-weighted-imaging
#8
Xiaoyue Ma, Yan Bai, Yusong Lin, Xiaohua Hong, Taiyuan Liu, Lun Ma, E Mark Haacke, Jinyuan Zhou, Jian Wang, Meiyun Wang
Amide proton transfer (APT) imaging is a noninvasive molecular magnetic resonance imaging (MRI) technique based on the chemical exchange-dependent saturation transfer mechanism. The purpose of this study was to investigate the diagnostic performance of APT MRI in detecting intracranial hemorrhage (ICH) at hyperacute, acute and subacute stages by comparing with susceptibility weighted imaging (SWI). APT MRI and SWI were performed on 33 included patients with ICH by using a 3-T MRI unit. A two-sided Mann-Whitney U test was used to detect differences in APT-weighted (APTw) and SWI signal intensities of ICH at hyperacute, acute and subacute stages...
April 4, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28358208/imidazole-appended-macrocyclic-complexes-of-fe-ii-co-ii-and-ni-ii-as-paracest-agents
#9
Patrick J Burns, Jordan M Cox, Janet R Morrow
The solution chemistry and solid state structures of the Co(II), Fe(II), and Ni(II) complexes of N,N'-bis(imidazole-2-ylmethyl)-4,10-diaza-15-crown-5 (HINO) are reported. The Co(II) and Ni(II) complexes of HINO are the first examples of paraCEST agents (paramagnetic chemical exchange saturation transfer) that feature exchangeable imidazole NH protons. The crystal structures of [Co(HINO)]CoCl4·H2O and [Fe(HINO)](CF3SO3)2 have the metal ions coordinated to four nitrogen and three oxygen donor atoms of the macrocyclic ligand in a distorted pentagonal bipyramidal geometry...
March 30, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28357518/longitudinal-relaxation-optimized-amide-1-h-cest-experiments-for-studying-slow-chemical-exchange-processes-in-fully-protonated-proteins
#10
Tairan Yuwen, Lewis E Kay
Chemical Exchange Saturation Transfer (CEST) experiments are increasingly used to study slow timescale exchange processes in biomolecules. Although (15)N- and (13)C-CEST have been the approaches of choice, the development of spin state selective (1)H-CEST pulse sequences that separate the effects of chemical and dipolar exchange [T. Yuwen, A. Sekhar and L. E. Kay, Angew Chem Int Ed Engl 2016 doi: 10.1002/anie.201610759 (Yuwen et al. 2017)] significantly increases the utility of (1)H-based experiments. Pulse schemes have been described previously for studies of highly deuterated proteins...
March 29, 2017: Journal of Biomolecular NMR
https://www.readbyqxmd.com/read/28303115/evolution-of-cerebral-ischemia-assessed-by-amide-proton-transfer-weighted-mri
#11
Guodong Song, Chunmei Li, Xiaojie Luo, Xuna Zhao, Shuai Zhang, Yi Zhang, Shanshan Jiang, Xianlong Wang, Yuhui Chen, Haibo Chen, Tao Gong, Jinyuan Zhou, Min Chen
Amide proton transfer-weighted (APTW) magnetic resonance imaging (MRI) has recently become a potentially important tool for evaluating acidosis in ischemic stroke. The purpose of this study was to evaluate the dynamic pH-related changes in the lesions in patients with ischemia. Thirty-nine patients with ischemic stroke (symptom onset to imaging time ranging 2 h-7 days) were examined with a 3.0-T MRI system. Patients were divided into four groups: at the hyperacute stage (onset time ≤ 6 h), at the acute stage (6 h < onset time ≤ 48 h), at the early subacute stage (48 h < onset time ≤ 96 h), and at the late subacute stage (96 h < onset time ≤ 168 h)...
2017: Frontiers in Neurology
https://www.readbyqxmd.com/read/28273886/quantitative-chemical-exchange-saturation-transfer-cest-mri-of-glioma-using-image-downsampling-expedited-adaptive-least-squares-ideal-fitting
#12
Iris Yuwen Zhou, Enfeng Wang, Jerry S Cheung, Xiaoan Zhang, Giulia Fulci, Phillip Zhe Sun
Chemical Exchange Saturation Transfer (CEST) MRI is sensitive to dilute metabolites with exchangeable protons, allowing tissue characterization in diseases such as acute stroke and tumor. CEST quantification using multi-pool Lorentzian fitting is challenging due to its strong dependence on image signal-to-noise ratio (SNR), initial values and boundaries. Herein we proposed an Image Downsampling Expedited Adaptive Least-squares (IDEAL) fitting algorithm that quantifies CEST images based on initial values from multi-pool Lorentzian fitting of iteratively less downsampled images until the original resolution...
December 2017: Scientific Reports
https://www.readbyqxmd.com/read/28272761/accuracy-in-the-quantification-of-chemical-exchange-saturation-transfer-cest-and-relayed-nuclear-overhauser-enhancement-rnoe-saturation-transfer-effects
#13
Xiao-Yong Zhang, Feng Wang, Hua Li, Junzhong Xu, Daniel F Gochberg, John C Gore, Zhongliang Zu
Accurate quantification of chemical exchange saturation transfer (CEST) effects, including dipole-dipole mediated relayed nuclear Overhauser enhancement (rNOE) saturation transfer, is important for applications and studies of molecular concentration and transfer rate (and thereby pH or temperature). Although several quantification methods, such as Lorentzian difference (LD) analysis, multiple-pool Lorentzian fits, and the three-point method, have been extensively used in several preclinical and clinical applications, the accuracy of these methods has not been evaluated...
March 8, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28252822/diagnostic-performance-between-contrast-enhancement-proton-mr-spectroscopy-and-amide-proton-transfer-imaging-in-patients-with-brain-tumors
#14
Akihiko Sakata, Yasutaka Fushimi, Tomohisa Okada, Yoshiki Arakawa, Takeharu Kunieda, Sachiko Minamiguchi, Aki Kido, Naotaka Sakashita, Susumu Miyamoto, Kaori Togashi
PURPOSE: To explore the relationship among parameters of magnetic resonance spectroscopy (MRS) and amide proton transfer (APT) imaging, and to assess the diagnostic performance of MRS and APT imaging for grading brain tumors in comparison with contrast enhancement of conventional MRI for preoperative grading in patients with brain tumor. MATERIALS AND METHODS: Institutional Review Board approval and written informed consent were obtained. Forty-one patients with suspected brain tumors were enrolled in the study...
March 2, 2017: Journal of Magnetic Resonance Imaging: JMRI
https://www.readbyqxmd.com/read/28155086/near-uv-photodissociation-of-tryptic-peptide-cation-radicals-scope-and-effects-of-amino-acid-residues-and-radical-sites
#15
Huong T H Nguyen, František Tureček
Peptide cation-radical fragment ions of the z-type, [(●)AXAR(+)], [(●)AXAK(+)], and [(●)XAR(+)], where X = A, C, D, E, F, G, H, K, L, M, N, P, Y, and W, were generated by electron transfer dissociation of peptide dications and investigated by MS(3)-near-ultraviolet photodissociation (UVPD) at 355 nm. Laser-pulse dependence measurements indicated that the ion populations were homogeneous for most X residues except phenylalanine. UVPD resulted in dissociations of backbone CO─NH bonds that were accompanied by hydrogen atom transfer, producing fragment ions of the [yn](+) type...
February 2, 2017: Journal of the American Society for Mass Spectrometry
https://www.readbyqxmd.com/read/28154122/measurement-of-lactate-content-and-amide-proton-transfer-values-in-the-basal-ganglia-of-a-neonatal-piglet-hypoxic-ischemic-brain-injury-model-using-mri
#16
Y Zheng, X-M Wang
BACKGROUND AND PURPOSE: As amide proton transfer imaging is sensitive to protein content and intracellular pH, it has been widely used in the nervous system, including brain tumors and stroke. This work aimed to measure the lactate content and amide proton transfer values in the basal ganglia of a neonatal piglet hypoxic-ischemic brain injury model by using MR spectroscopy and amide proton transfer imaging. MATERIALS AND METHODS: From 58 healthy neonatal piglets (3-5 days after birth; weight, 1-1...
February 2, 2017: AJNR. American Journal of Neuroradiology
https://www.readbyqxmd.com/read/28145121/redox-driven-conformational-dynamics-in-a-photosystem-ii-inspired-%C3%AE-hairpin-maquette-determined-through-spectroscopy-and-simulation
#17
Hyea Hwang, Tyler G McCaslin, Anthony Hazel, Cynthia V Pagba, Christina M Nevin, Anna Pavlova, Bridgette A Barry, James C Gumbart
Tyrosine-based radical transfer plays an important role in photosynthesis, respiration, and DNA synthesis. Radical transfer can occur either by electron transfer (ET) or proton coupled electron transfer (PCET), depending on the pH. Reversible conformational changes in the surrounding protein matrix may control reactivity of radical intermediates. De novo designed Peptide A is a synthetic 18 amino-acid β-hairpin, which contains a single tyrosine (Y5) and carries out a kinetically significant PCET reaction between Y5 and a cross-strand histidine (H14)...
April 20, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28128026/amide-proton-transfer-weighted-mri-detection-of-traumatic-brain-injury-in-rats
#18
Hong Zhang, Wenzhu Wang, Shanshan Jiang, Yi Zhang, Hye-Young Heo, Xianlong Wang, Yun Peng, Jian Wang, Jinyuan Zhou
The purpose of this study was to explore the capability and uniqueness of amide proton transfer-weighted (APTw) imaging in the detection of primary and secondary injury after controlled cortical impact (CCI)-induced traumatic brain injury (TBI) in rats. Eleven adult rats had craniotomy plus CCI surgery under isoflurane anesthesia. Multi-parameter MRI data were acquired at 4.7 T, at eight time points (1, 6 h, and 1, 2, 3, 7, 14, and 28 days after TBI). At one and six hours post-injury, average APTw signal intensities decreased significantly in the impacted and peri-lesional areas due to tissue acidosis...
January 1, 2017: Journal of Cerebral Blood Flow and Metabolism
https://www.readbyqxmd.com/read/28116517/amide-proton-transfer-imaging-to-discriminate-between-low-and-high-grade-gliomas-added-value-to-apparent-diffusion-coefficient-and-relative-cerebral-blood-volume
#19
Yoon Seong Choi, Sung Soo Ahn, Seung-Koo Lee, Jong Hee Chang, Seok-Gu Kang, Se Hoon Kim, Jinyuan Zhou
OBJECTIVES: To evaluate the added value of amide proton transfer (APT) imaging to the apparent diffusion coefficient (ADC) from diffusion tensor imaging (DTI) and the relative cerebral blood volume (rCBV) from perfusion magnetic resonance imaging (MRI) for discriminating between high- and low-grade gliomas. METHODS: Forty-six consecutive adult patients with diffuse gliomas who underwent preoperative APT imaging, DTI and perfusion MRI were enrolled. APT signals were compared according to the World Health Organization grade...
January 23, 2017: European Radiology
https://www.readbyqxmd.com/read/28103693/the-logic-behind-a-physical-organic-chemist-s-research-topics
#20
Charles L Perrin
Although my research has no common theme or defining area, a coherence connects the diverse topics insofar as one project leads logically to another. Thus, studies on mechanisms of hydrogen exchange in amides and amidines led to the influence of hydrogen bonding and to NMR methods for chemical kinetics, including 2D-EXSY spectroscopy. Another connection was the OH(-)-catalyzed NH exchange in amines that had supported the hypothesis of stereoelectronic control. We therefore analyzed that hypothesis critically, tested it, found counterexamples, and proposed an alternative hypothesis...
January 20, 2017: Journal of Organic Chemistry
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