XnRelevant articles and documents
All total 113 Articles be found
All total 113 Articles be foundHetero-NMR enhancement via parahydrogen labeling
Barkemeyer, Jens,Haake, Mathias,Bargon, Joachim
, p. 2927 - 2928 (1995)
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Long-lived 1H nuclear spin singlet in dimethyl maleate revealed by addition of thiols
Zhang, Yuning,Soon, Pei Che,Jerschow, Alexej,Canary, James W.
, p. 3396 - 3399 (2014)
Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) have become important techniques in many research areas. One major limitation is the relatively low sensitivity of these methods, which recently has been addressed by hyperpolarization. However, once hyperpolarization is imparted on a molecule, the magnetization typically decays within relatively short times. Singlet states are well isolated from the environment, such that they acquire long lifetimes. We describe herein a model reaction for read-out of a hyperpolarized long-lived state in dimethyl maleate using thiol conjugate addition. This type of reaction could lend itself to monitoring oxidative stress or hypoxia by sensitive detection of thiols. Similar reactions could be used in biosensors or assays that exploit molecular switching. Singlet lifetimes of about 4.7 min for 1H spins in [D4]MeOH are seen in this system. Hyperpolarized singlet states are well isolated from the environment, such that they acquire long lifetimes. Here, we used the thiol conjugate addition to unveil the hyperpolarized long-lived singlet state in deuterated dimethyl maleate (see picture). Singlet lifetimes of 4.7 min for 1H spins in [D4]MeOH are seen in this system.
Cu(OAc)2-2,4-lutidine-ZnCl2 as an effective catalyst of functionalization of isobutylene oligomers and 1,2-polybutadiene with methyl diazoacetate
Gareev,Yangirov,Volodina,Sultanova,Biglova,Dokichev
, p. 1305 - 1309 (2009)
The possibility of [1+2]-cycloaddition of methoxycarbonylcarbene generated by catalytic decomposition of methyl diazoacetate in the presence of the Cu(OAc)2-2,4-lutidine-ZnCl2 system to the carbon-carbon double bound in isobutylene o
Limits in Proton Nuclear Singlet-State Lifetimes Measured with para-Hydrogen-Induced Polarization
Zhang, Yuning,Duan, Xueyou,Soon, Pei Che,Canary, James W.,Jerschow, Alexej,Sychrovsky, Vladimír
, p. 2967 - 2971 (2016)
The synthesis of a hyperpolarized molecule was developed, where the polarization and the singlet state were preserved over two controlled chemical steps. Nuclear singlet-state lifetimes close to 6 min for protons are reported in dimethyl fumarate. Owing to the high symmetry (AA′X3X3′ and A2 systems), the singlet-state readout requires either a chemical desymmetrization or a long and repeated spin lock. Using DFT calculations and relaxation models, we further determine nuclear spin singlet lifetime limiting factors, which include the intramolecular dipolar coupling mechanism (proton–proton and proton–deuterium), the chemical shift anisotropy mechanism (symmetric and antisymmetric), and the intermolecular dipolar coupling mechanism (to oxygen and deuterium). If the limit of paramagnetic relaxation caused by residual oxygen could be lifted, the intramolecular dipolar coupling to deuterium would become the limiting relaxation mechanism and proton lifetimes upwards of 26 min could become available in the molecules considered here (dimethyl maleate and dimethyl fumarate).
Self-Assembled Open Porous Nanoparticle Superstructures
Liu, Rongjuan,Wei, Jingjing,Wei, Yanze,Yang, Zhijie,Zhang, Fenghua
supporting information, (2021/08/20)
Imparting porosity to inorganic nanoparticle assemblies to build up self-assembled open porous nanoparticle superstructures represents one of the most challenging issues and will reshape the property and application scope of traditional inorganic nanoparticle solids. Herein, we discovered how to engineer open pores into diverse ordered nanoparticle superstructures via their inclusion-induced assembly within 1D nanotubes, akin to the molecular host-guest complexation. The open porous structure of self-assembled composites is generated from nonclose-packing of nanoparticles in 1D confined space. Tuning the size ratios of the tube-to-nanoparticle enables the structural modulation of these porous nanoparticle superstructures, with symmetries such as C1, zigzag, C2, C4, and C5. Moreover, when the internal surface of the nanotubes is blocked by molecular additives, the nanoparticles would switch their assembly pathway and self-assemble on the external surface of the nanotubes without the formation of porous nanoparticle assemblies. We also show that the open porous nanoparticle superstructures can be ideal candidate for catalysis with accelerated reaction rates.
A Br?nsted acidic, ionic liquid containing, heteropolyacid functionalized polysiloxane network as a highly selective catalyst for the esterification of dicarboxylic acids
Rajabi, Fatemeh,Wilhelm, Christian,Thiel, Werner R.
supporting information, p. 4438 - 4444 (2020/08/10)
A Br?nsted acidic, ionic liquid containing, heteropolyanion functionalized polysiloxane network was formed by self-condensation of dodecatungstophosphoric acid and a zwitterionic organosilane precursor containing both imidazolinium and sulfonate groups. The resulting hybrid material POS-HPA-IL was investigated as a catalyst for the selective esterification of dicarboxylic acids.
