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Dissolution dynamic nuclear polarization (DNP) enables high‐sensitivity solution‐phase NMR experiments on long‐lived nuclear spin species such as 15N and 13C. This report explores certain features arising in solution‐state 1H NMR upon polarizing low‐γ nuclear species. Following solid‐state hyperpolarization of both 13C and 1H, solution‐phase 1H NMR experiments on dissolved samples revealed transient effects, whereby peaks arising from protons bonded to the naturally occurring 13C nuclei appeared larger than the typically dominant 12C‐bonded 1H resonances. This enhancement of the satellite peaks was examined in detail with respect to a variety of mechanisms that could potentially explain this observation. Both two‐ and three‐spin phenomena active in the solid state could lead to this kind of effect; still, experimental observations revealed that the enhancement originates from 13C→1H polarization‐transfer processes active in the liquid state. Kinetic equations based on modified heteronuclear cross‐relaxation models were examined, and found to well describe the distinct patterns of growth and decay shown by the 13C‐bound 1H NMR satellite resonances. The dynamics of these novel cross‐relaxation phenomena were determined, and their potential usefulness as tools for investigating hyperpolarized ensembles and for obtaining enhanced‐sensitivity 1H NMR traces was explored. 相似文献
3.
Athanasios Skandalis Stergios Pispas 《Journal of polymer science. Part A, Polymer chemistry》2017,55(1):155-163
The synthesis and self‐assembly properties in aqueous solutions of novel amphiphilic block copolymers composed of one hydrophobic poly (lauryl methacrylate), (PLMA) block and one hydrophilic poly (oligo ethylene glycol methacrylate) (POEGMA) block are reported. The block copolymers were prepared by RAFT polymerization and were molecularly characterized by size exclusion chromatography, NMR and FT‐IR spectroscopy, and DSC. The PLMA‐b‐POEGMA amphiphilic block copolymers self‐assemble in nanosized complex nanostructures resembling compound micelles when inserted in aqueous media, as supported by light scattering and TEM measurements. The encapsulation and release of the model, hydrophobic, nonsteroidal anti‐inflammatory drug indomethacin in the polymeric micelles is also investigated. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 155–163 相似文献
4.
5.
Saad Baaj Georges Skandalis Stefaan Vaes 《Communications in Mathematical Physics》2003,235(1):139-167
In this paper, we study C*-algebraic quantum groups obtained through the bicrossed product construction. Examples using groups of adeles are given and
they provide the first examples of locally compact quantum groups which are not semi-regular: the crossed product of the quantum
group acting on itself by translations does not contain any compact operator. We describe all corepresentations of these quantum
groups and the associated universal C*-algebras. On the way, we provide several remarks on C*-algebraic properties of quantum groups and their actions.
Received: 10 October 2002 / Accepted: 10 October 2002 Published online: 24 January 2003
Communicated by A. Connes 相似文献
6.
Saad Baaj et Georges Skandalis 《K-Theory》1989,2(6):683-721
Résumé A toute paire (A, B) de C*-algèbres, munies de coactions d'une C*-algèbre de Hopf S nous associons un groupe KK
S
(A, B) de théorie de Kasparov équivariante par S. Le produit de Kasparov se généralise à notre cadre. Dans le cas S=C
0
(G) où G est un groupe localement compact, on retrouve le groupe de Kasparov KK
G
(A, B). Nous montrons que les groupes KK
G
(A, B) et KK
C*(G)
(A × G, B × G) sont naturellement isomorphes. Nous en déduisons que si est un groupe discret moyennable, les foncteurs KK
(·,D) et KK
(D,·) sont demi-exacts.
To every pair (A, B) of C*-algebras acted upon by a Hopf C*-algebra S, we associate an S-equivariant Kasparov theory group KK S(A, B). The Kasparov product generalizes to our setting. For S=C 0(G) where G is a locally compact group, we recover Kasparov's group KK G(A, B). We show that the groups KK G(A, B) and KK C*(G) (A × G, B × G) are naturally isomorphic. We deduce that if is a discrete amenable group, the functors KK (·,D) are KK (D,·) are half-exact.相似文献
7.
Dr. Jihyun Kim Dr. Mihajlo Novakovic Prof. Dr. Sundaresan Jayanthi Dr. Adonis Lupulescu Dr. Ēriks Kupče Dr. J. Tassilo Grün Klara Mertinkus Andreas Oxenfarth Prof. Dr. Harald Schwalbe Prof. Dr. Lucio Frydman 《Chemphyschem》2022,23(4):e202100704
Hadamard encoded saturation transfer can significantly improve the efficiency of NOE-based NMR correlations from labile protons in proteins, glycans and RNAs, increasing the sensitivity of cross-peaks by an order of magnitude and shortening experimental times by ≥100-fold. These schemes, however, fail when tackling correlations within a pool of labile protons – for instance imino-imino correlations in RNAs or amide-amide correlations in proteins. Here we analyze the origin of the artifacts appearing in these experiments and propose a way to obtain artifact-free correlations both within the labile pool as well as between labile and non-labile 1Hs, while still enjoying the gains arising from Hadamard encoding and solvent repolarizations. The principles required for implementing what we define as the extended Hadamard scheme are derived, and its clean, artifact-free, sensitivity-enhancing performance is demonstrated on RNA fragments derived from the SARS-CoV-2 genome. Sensitivity gains per unit time approaching an order of magnitude are then achieved in both imino-imino and imino-amino/aromatic protons 2D correlations; similar artifact-free sensitivity gains can be observed when carrying out extended Hadamard encodings of 3D NOESY/HSQC-type experiments. The resulting spectra reveal significantly more correlations than their conventionally acquired counterparts, which can support the spectral assignment and secondary structure determination of structured RNA elements. 相似文献
8.
Cavadini S Lupulescu A Antonijevic S Bodenhausen G 《Journal of the American Chemical Society》2006,128(24):7706-7707
It is shown that nuclear magnetic resonance (NMR) spectra of nitrogen-14 (spin I = 1) can be obtained by indirect detection in powders spinning at the magic angle (MAS). The method relies on the transfer of coherence from a neighboring nucleus with S = 1/2, such as carbon-13, to single- or double-quantum transitions of nitrogen-14 nuclei. The transfer of coherence occurs through second-order quadrupole-dipole cross terms, also known as residual dipolar splittings. The two-dimensional NMR spectra reveal powder patterns determined by the second-order quadrupolar interactions of nitrogen-14. Analysis of the spectra yields the quadrupolar coupling constant, CQ, and asymmetry parameter, etaQ, of nitrogen-14. These parameters can be related to the structure of nitrogen-containing solids. 相似文献
9.
Schiff base‐functionalized boehmite nanoparticle‐supported molybdenum and vanadium complexes: efficient catalysts for the epoxidation of alkenes 下载免费PDF全文
Boehmite nanoparticles, with high surface area and high degree of surface hydroxyl groups, were prepared via hydrothermal‐assisted sol–gel processing of aluminium 2‐butoxide. The produced powder was covalently functionalized with 3‐(trimethoxysilyl)propylamine, and then, in order to support vanadium oxosulfate and molybdenum hexacarbonyl complexes, all the terminal amine groups were changed to Schiff bases by refluxing with salicylaldehyde. These catalysts were applied in the epoxidation of cis‐cyclooctene and other olefins with tert‐BuOOH in CCl4. The catalytic procedures for both catalysts were optimized for various parameters such as solvent and oxidant. Recycling experiments revealed that these heterogeneous nano‐catalysts could be repeatedly applied for the epoxidation of alkenes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
10.
Recent years have witnessed efforts geared at increasing the sensitivity of NMR experiments, by relying on the suitable tailoring and exploitation of relaxation phenomena. These efforts have included the use of paramagnetic agents, enhanced (1)H-(1)H incoherent and coherent transfers processes in 2D liquid state spectroscopy, and homonuclear (13)C-(13)C spin diffusion effects in labeled solids. The present study examines some of the opportunities that could open when exploiting spontaneous (1)H-(1)H spin-diffusion processes, to enhance relaxation and to improve the sensitivity of dilute nuclei in solid state NMR measurements. It is shown that polarization transfer experiments executed under sufficiently fast magic-angle-spinning conditions, enable a selective polarization of the dilute low-γ spins by their immediate neighboring protons. Repolarization of the latter can then occur during the time involved in monitoring the signal emitted by the low-γ nuclei. The basic features involved in the resulting approach, and its potential to improve the effective sensitivity of solid state NMR measurements on dilute nuclei, are analyzed. Experimental tests witness the advantages that could reside from utilizing this kind of approach over conventional cross-polarization processes. These measurements also highlight a number of limitations that will have to be overcome for transforming selective polarization transfers of this kind into analytical methods of choice. 相似文献