scholarly journals Predicting the Crystal Structure of Decitabine by Powder NMR Crystallography: Influence of Long-Range Molecular Packing Symmetry on NMR Parameters

2016 ◽  
Vol 16 (12) ◽  
pp. 7102-7111 ◽  
Author(s):  
Jiri Brus ◽  
Jiri Czernek ◽  
Libor Kobera ◽  
Martina Urbanova ◽  
Sabina Abbrent ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Long Range ◽  
Molecular Packing ◽  
Nmr Parameters ◽  
Nmr Crystallography

scholarly journals The ambient hydration of the aluminophosphate JDF-2 to AlPO-53(A): insights from NMR crystallography

2017 ◽  
Vol 73 (3) ◽  
pp. 191-201 ◽  
Author(s):  
Daniel M. Dawson ◽  
Richard I. Walton ◽  
Stephen Wimperis ◽  
Sharon E. Ashbrook
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Frictional Heating ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Good Representation ◽  
Functional Theory ◽  
Nmr Parameters ◽  
Nmr Crystallography ◽  
Angle Spinning

The aluminophosphate (AlPO) JDF-2 is prepared hydrothermally with methylammonium hydroxide (MAH+·HO−, MAH+ = CH3NH3 +), giving rise to a microporous AEN-type framework with occluded MAH+ cations and extra-framework (Al-bound) HO− anions. Despite the presence of these species within its pores, JDF-2 can hydrate upon exposure to atmospheric moisture to give AlPO-53(A), an isostructural material whose crystal structure contains one molecule of H2O per formula unit. This hydration can be reversed by mild heating (such as the frictional heating from magic angle spinning). Previous work has shown good agreement between the NMR parameters obtained experimentally and those calculated from the (optimized) crystal structure of JDF-2. However, several discrepancies are apparent between the experimental NMR parameters for AlPO-53(A) and those calculated from the (optimized) crystal structure (e.g. four 13C resonances are observed, rather than the expected two). The unexpected resonances appear and disappear reversibly with the respective addition and removal of H2O, so clearly arise from AlPO-53(A). We investigate the ambient hydration of JDF-2 using quantitative 31P MAS NMR to follow the transformation over the course of ∼3 months. The structures of JDF-2 and AlPO-53(A) are also investigated using a combination of multinuclear solid-state NMR spectroscopy to characterize the samples, and first-principles density functional theory (DFT) calculations to evaluate a range of possible structural models in terms of calculated NMR parameters and energetics. The published structure of JDF-2 is shown to be a good representation of the dehydrated material, but modification of the published structure of AlPO-53(A) is required to provide calculated NMR parameters that are in better agreement with experiment. This modification includes reorientation of all the MAH+ cations and partial occupancy of the H2O sites.

scholarly journals Structural Changes in the Acceptor Site of Photosystem II upon Ca2+/Sr2+ Exchange in the Mn4CaO5 Cluster Site and the Possible Long-Range Interactions

Biomolecules ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 371
Author(s):  
Koua
Keyword(s):  
Crystal Structure ◽  
Photosystem Ii ◽  
Long Range ◽  
Electron Acceptor ◽  
Structural Changes ◽  
Acceptor Site ◽  
Oxygen Evolving Complex ◽  
Long Range Interactions ◽  
Structural Perturbations ◽  
Oxygen Evolving

The Mn4CaO5 cluster site in the oxygen-evolving complex (OEC) of photosystem II (PSII) undergoes structural perturbations, such as those induced by Ca2+/Sr2+ exchanges or Ca/Mn removal. These changes have been known to induce long-range positive shifts (between +30 and +150 mV) in the redox potential of the primary quinone electron acceptor plastoquinone A (QA), which is located 40 Å from the OEC. To further investigate these effects, we reanalyzed the crystal structure of Sr-PSII resolved at 2.1 Å and compared it with the native Ca-PSII resolved at 1.9 Å. Here, we focus on the acceptor site and report the possible long-range interactions between the donor, Mn4Ca(Sr)O5 cluster, and acceptor sites.

Molecular packing in N-heterocycles: a predicted crystal structure for 1,4,5,8-tetraazanaphthalene

1971 ◽  
Vol 1 (6) ◽  
pp. 401-403 ◽  
Author(s):  
M. J. Robey ◽  
M. Sterns ◽  
H. M. Morris ◽  
I. G. Ross
Keyword(s):  
Crystal Structure ◽  
Molecular Packing

Crystal structure of 3-amino-5-acetyl-4,7-dihydro-6-methyl-4-(2-nitrophenyl)-2-cyanothieno[2,3-b]-pyridine and specific features of its molecular packing in crystal

2000 ◽  
Vol 45 (1) ◽  
pp. 91-97
Author(s):  
A. E. Lysov ◽  
V. N. Nesterov ◽  
K. A. Potekhin ◽  
Yu. T. Struchkov
Keyword(s):  
Crystal Structure ◽  
Molecular Packing

Finding of Bulk Ferromagnetism in Stable Organic Radical Crystal

1992 ◽  
Vol 247 ◽  
Author(s):  
Minoru Kinoshita
Keyword(s):  
Crystal Structure ◽  
Long Range ◽  
Molecular And Crystal Structure ◽  
Organic Radical ◽  
Light Elements ◽  
Nitronyl Nitroxide ◽  
Β Phase ◽  
Phase Crystal ◽  
Iupac Nomenclature ◽  
Ordered State

ABSTRACTTransition to a ferromagnetic long range ordered state was found at 0.60 K in the orthorhombic β-phase crystal of p-nitrophenyl nitronyl nitroxide (or 2-(4′-nitrophenyl)-4, 4, 5, 5-tetramethyl-4, 5-dihydro-lH-imidazol-1-oxyl-3-N-oxide in the IUPAC nomenclature). This finding provides the first example of an organic bulk ferromagnet consisting of light elements and having a definite molecular and crystal structure.

Tris(biimidazolato)chromium(III) as a building block for hydrogen-bonded supramolecular assemblies

2006 ◽  
Vol 84 (7) ◽  
pp. 949-959 ◽  
Author(s):  
Letitia M Gruia ◽  
Fernande D Rochon ◽  
André L Beauchamp
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Porous Material ◽  
Intermolecular Interactions ◽  
Long Range ◽  
Building Block ◽  
Benzene Molecule ◽  
Methanol Solution ◽  
Solvent Molecules ◽  
Free Material

The trischelate [Cr(H2biim)3](NO3)3 complex of 2,2′-biimidazole (H2biim) was obtained by reacting CrCl3·3THF with [Ag(H2biim)](NO3) in methanol. In the solvent-free material, each ligand forms two N-H···O bonds to a nitrate ion and generates locally neutral [Cr(H2biim)3](NO3)3 units. A methanol solvate was also obtained in which intermolecular interactions involve optimal use of the hydrogen-bonding ability of the [Cr(H2biim)3]3+ cations, NO3– anions, and methanol molecules. In both cases, there is no long-range regular organization of the complex units. Deprotonation of [Cr(H2biim)3](NO3)3 with NaOCH3 yielded neutral Cr(Hbiim)3. Its powder pattern is similar to that of Ru(Hbiim)3, suggesting that it also consists of mutually perpendicular interlocked honeycomb sheets. Recrystallization by slow diffusion of diisopropyl ether into a methanol solution yielded a porous material of composition Cr(Hbiim)3·2.6C6H14O in which superposed honeycomb sheets create infinite channels (~13 Å diameter) filled with disordered solvent molecules. A totally different structure is adopted by the solvate Cr(Hbiim)3·C6H6·2H2O, where the benzene molecule is encapsulated in a cavity created by five complex molecules.Key words: chromium, biimidazole, supramolecular, crystal structure, hydrogen bonding.

Crystal structure, molecular packing, FMO, NBO, nonlinear optical and optical limiting properties of an organic imidazolium diphenylacetate diphenylacetic acid single crystal

2018 ◽  
Vol 42 (4) ◽  
pp. 2439-2449 ◽  
Author(s):  
RO. MU. Jauhar ◽  
Paavai Era ◽  
V. Viswanathan ◽  
P. Vivek ◽  
G. Vinitha ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Optical Activity ◽  
Structural Characterization ◽  
Nonlinear Optical ◽  
Optical Limiting ◽  
Molecular Packing ◽  
Optical Material ◽  
Nonlinear Optical Material ◽  
Diphenylacetic Acid

A new organic nonlinear optical material, imidazolium diphenylacetate diphenylacetic acid, with excellent structural characterization and nonlinear optical activity has been reported.

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