Variable-temperature 27Al and 29Si NMR studies of synthetic forsterite and Fe-bearing Dora Maira pyrope garnet: Temperature dependence and mechanisms of paramagnetically shifted peaks

2011 ◽  
Vol 96 (7) ◽  
pp. 1090-1099 ◽  
Author(s):  
A. C. Palke ◽  
J. F. Stebbins
Keyword(s):  
Temperature Dependence ◽  
Variable Temperature ◽  
29Si Nmr ◽  
Nmr Studies

29Si NMR Studies of Zeolite Precursor Solutions

2006 ◽  
Vol 110 (1) ◽  
pp. 313-318 ◽  
Author(s):  
Chil-Hung Cheng ◽  
Daniel F. Shantz
Keyword(s):  
29Si Nmr ◽  
Nmr Studies

Chiral "basket handle" binaphthyl porphyrins: synthesis, catalytic epoxidation and NMR conformational studies

2010 ◽  
Vol 14 (07) ◽  
pp. 646-659 ◽  
Author(s):  
Eric Rose ◽  
Emma Gallo ◽  
Nicolas Raoul ◽  
Léa Bouché ◽  
Ariane Pille ◽  
...  
Keyword(s):  
Time Scale ◽  
Room Temperature ◽  
Conformational Equilibrium ◽  
Variable Temperature ◽  
Conformational Exchange ◽  
Iron Catalysts ◽  
Nmr Studies ◽  
Conformational Studies ◽  
H Nmr ◽  
Catalytic Epoxidation

Three "basket handle" porphyrins have been prepared by condensation of tetrakis-(α,β,α,β-2-aminophenyl)porphyrin atropoisomer with 1,1′-binaphthyl, 2,2′-dimethoxy, -3,3′-dicarbonylchloride, -3,3′-diacetylchloride and -3,3′-dipropanoylchloride. The epoxidation of styrene with the three iron catalysts, obtained after metalation of the free porphyrins, occurs with good yields and moderate ee up to 54%. These porphyrins showed unexpected conformational differences, as revealed by NMR spectroscopy. In particular, variable temperature NMR studies showed that the methoxy group in one of them undergoes intermediate conformational exchange on the 1H NMR time scale at room temperature. Lowering the temperature to -50 °C revealed the presence of four states in slow exchange on the NMR time scale. These results evidence a dynamic conformational equilibrium of the binaphthyl handles that adopt different, asymmetric positions with respect to the porphyrin plane.

1H and13C NMR Studies of Etidocaine Free Base and Hydrochloride Salt. Solvent and Temperature Dependence

1992 ◽  
Vol 25 (1) ◽  
pp. 133-161
Author(s):  
Laurine A. LaPlanche ◽  
Robert Rothchild ◽  
Yangdong Xu
Keyword(s):  
Temperature Dependence ◽  
Free Base ◽  
Nmr Studies ◽  
1H And13c Nmr ◽  
Hydrochloride Salt

scholarly journals Variable temperature 1H NMR studies on Grubbs catalysts

2008 ◽  
Vol 693 (7) ◽  
pp. 1252-1260 ◽  
Author(s):  
Margaret M. Gallagher ◽  
A. Denise Rooney ◽  
John J. Rooney
Keyword(s):  
1H Nmr ◽  
Variable Temperature ◽  
Nmr Studies ◽  
Grubbs Catalysts

scholarly journals 2H NMR Studies on Water Dynamics in Functionalized Mesoporous Silica

2018 ◽  
Vol 232 (7-8) ◽  
pp. 1041-1058 ◽  
Author(s):  
Max Weigler ◽  
Martin Brodrecht ◽  
Hergen Breitzke ◽  
Felix Dietrich ◽  
Matthias Sattig ◽  
...  
Keyword(s):  
Mesoporous Silica ◽  
Temperature Dependence ◽  
Liquid Water ◽  
Water Dynamics ◽  
Spin Lattice Relaxation ◽  
Nmr Studies ◽  
Solid Water ◽  
Water Species ◽  
Mcm 41 ◽  
Dynamic Crossover

AbstractMesoporous silica MCM-41 is prepared, for which the inner surfaces are modified by 3-(aminopropyl)triethoxysilane (APTES) in a controlled manner. Nitrogen gas adsorpition yields a pore diameter of 2.2 nm for the APTES functionalized MCM-41.2H nuclear magnetic resonance (NMR) and broadband dielectric spectroscopy (BDS) provide detailed and consistent insights into the temperature-dependent reorientation dynamics of water in this confinement. We find that a liquid water species becomes accompanied by a solid water species when cooling through ~210 K, as indicated by an onset of bimodal2H spin-lattice relaxation. The reorientation of the liquid water species is governed by pronounced dynamical heterogeneity in the whole temperature range. Its temperature dependence shows a mild dynamic crossover when the solid water species emerges and, hence, the volume accessible to the liquid water species further shrinks. Therefore, we attribute this variation in the temperature dependence to a change from bulk-like behavior towards interface-dominated dynamics. Below this dynamic crossover,2H line-shape and stimulted-echo studies show that water reorientation becomes anisotropic upon cooling, suggesting that these NMR approaches, but also BDS measurements do no longer probe the structural (α) relaxation, but rather a secondary (β) relaxation of water at sufficiently low temperatures. Then, another dynamic crossover at ~180 K can be rationalized in terms of a change of the temperature dependence of theβrelaxation in response to a glassy freezing of theαrelaxation of confined water. Comparing these results for APTES modied MCM-41 with previous findings for mesoporous silica with various pore diameters, we obtain valuable information about the dependence of water dynamics in restricted geometries on the size of the nanoscopic confinements and the properties of the inner surfaces.

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