The Effect of a Para Substituent on the Conformational Preference of 2,2-Diphenyl-1,3-dioxanes:  Evidence for the Anomeric Effect from X-ray Crystal Structure Analysis1

1999 ◽  
Vol 64 (5) ◽  
pp. 1436-1441 ◽  
Author(s):  
Fumiaki Uehara ◽  
Masayuki Sato ◽  
Chikara Kaneko ◽  
Hiroyuki Kurihara
Keyword(s):  
Crystal Structure ◽  
Anomeric Effect ◽  
Conformational Preference ◽  
X Ray

Synthese, Kristallstruktur und Eigenschaften von Tetraaminophosphoniumchlorid [P(NH2)4]Cl / Synthesis, Crystal Structure, and Properties of Tetraaminophosphonium Chloride [P(NH2)4]Cl

1996 ◽  
Vol 51 (1) ◽  
pp. 127-132 ◽  
Author(s):  
Stefan Horstmann ◽  
Wolfgang Schnick
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Phosphorus Pentachloride ◽  
Mean Value ◽  
Acetonitrile Solution ◽  
Anomeric Effect ◽  
Electron Pairs ◽  
X Ray ◽  
Hydrogen Bonding Interactions ◽  
Ray Methods

Abstract [P(NH2)4]Cl has been prepared by ammonolysis of phosphorus pentachloride in liquid ammonia. The product was purified by reacting the byproduct, ammonium chloride, with diethylamine and removing the diethylamine hydrochloride. Suitable single crystals were obtained from an acetonitrile solution in a temperature gradient between 60 °C and room temperature. The crystal structure of [P(NH2)4]Cl has been determined by single crystal X-ray methods (Pbcn, a = 470.8(2), b = 1622.3(3), c = 756.3(2) pm, Z = 4). In the solid, [P(NH2)4]+ and Cl- ions are found, resembling a TlI-analogous structure. The N-H···Cl distances indicate N-H···Cl hydrogen bonding interactions. The distortion of the P-N sceleton of the cation and the very short P-NH2 distances (mean value: 161.2 pm) have been confirmed by ab initio calculations, which show a generalized anomeric effect of the electron pairs at nitrogen and pπdπ bonding.

2-Thiozebularine: base modified nucleoside fully constrained in C3′-endo conformation in solution

2011 ◽  
Vol 76 (9) ◽  
pp. 1103-1119
Author(s):  
Katarzyna Ebenryter ◽  
Stefan Jankowski ◽  
Janina Karolak-Wojciechowska ◽  
Andrzej Fruziński ◽  
Julia Kaźmierczak-Baranska ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Aqueous Solution ◽  
Steric Effect ◽  
Bond Formation ◽  
Glycosidic Bond ◽  
Anomeric Effect ◽  
X Ray ◽  
Additive Action ◽  
Cancerous Cells ◽  
Carbonyl Function

2-Thiopyrimidinone ribofuranoside (2-thiozebularine, s2zeb) was synthesized by the adaptation of silyl method of N-glycosidic bond formation and using thionation of protected 2-oxonucleoside derivative (zebularine, zeb) with Lawesson reagent. The X-ray crystal structure of s2zeb and NMR determined conformations of s2zeb and zeb in solution were compared with structures of 2-thiouridine (s2U) and uridine (U). In the solid state s2zeb molecule adopts conformation typical for ribonucleosides: C3′-endo C2′-exo twist type of ribofuranose pucker, anti of N-glycosidic bond and trans around C4′–C5′ bond. In aqueous solution, however, almost 100% population of s2zeb exhibits C3′-endo ribofuranose pucker. The population of N-conformer of s2zeb is about 20% higher than for zeb (analogously to pair of s2U and U nucleosides) indicating similar influence of steric effect of bulky sulfur atom on stabilization of N-type ribose conformation. Interestingly, the absence of 4-carbonyl function in zeb and s2zeb raises the population of C3′-endo conformation by about 30% in comparison to U and s2U as a result of significant anomeric effect. Additive action of both effects makes the 2-thiozebularine almost fully constrained in C3′-endo conformation in aqueous solution. Cytotoxic properties of s2zeb are less pronounced in comparison to zebularine, with IC50 > 100 mM for HeLa and K562 cancer cells and for HUVEC non-cancerous cells.

A study on α-RuCl3 crystal structure by scanning tunneling microscopy

1989 ◽  
Vol 47 ◽  
pp. 30-31
Author(s):  
H.-J. Cantow ◽  
H. Hillebrecht ◽  
S. Magonov ◽  
H. W. Rotter ◽  
G. Thiele
Keyword(s):  
Crystal Structure ◽  
Density Distribution ◽  
Scanning Tunneling Microscopy ◽  
Electron Density ◽  
Structure Determination ◽  
Electron Density Distribution ◽  
Scanning Tunneling ◽  
Monoclinic Space Group ◽  
Tunneling Microscopy ◽  
X Ray

From X-ray analysis, the conclusions are drawn from averaged molecular informations. Thus, limitations are caused when analyzing systems whose symmetry is reduced due to interatomic interactions. In contrast, scanning tunneling microscopy (STM) directly images atomic scale surface electron density distribution, with a resolution up to fractions of Angstrom units. The crucial point is the correlation between the electron density distribution and the localization of individual atoms, which is reasonable in many cases. Thus, the use of STM images for crystal structure determination may be permitted. We tried to apply RuCl3 - a layered material with semiconductive properties - for such STM studies. From the X-ray analysis it has been assumed that α-form of this compound crystallizes in the monoclinic space group C2/m (AICI3 type). The chlorine atoms form an almost undistorted cubic closed package while Ru occupies 2/3 of the octahedral holes in every second layer building up a plane hexagon net (graphite net). Idealizing the arrangement of the chlorines a hexagonal symmetry would be expected. X-ray structure determination of isotypic compounds e.g. IrBr3 leads only to averaged positions of the metal atoms as there exist extended stacking faults of the metal layers.

X-ray Crystal Structure of ?9-THC-tosylate

Planta Medica ◽  
2008 ◽  
Vol 74 (03) ◽  
Author(s):  
W Gul ◽  
P Carvalho ◽  
D Slade ◽  
M Avery ◽  
JR Duchek ◽  
...  
Keyword(s):  
Crystal Structure ◽  
X Ray

Crystal structure of an inclusion complex between chiral monoaza-15-crown-5 and S(–)-1-phenyl-ethyl ammonium percholorate

2003 ◽  
Vol 218 (5) ◽  
Author(s):  
Süheyla Özbey ◽  
F. B. Kaynak ◽  
M. Toğrul ◽  
N. Demirel ◽  
H. Hoşgören
Keyword(s):  
Crystal Structure ◽  
Inclusion Complex ◽  
Single Crystal ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
New Type

AbstractA new type of inclusion complex, S(–)-1 phenyl ethyl ammonium percholorate complex of R-(–)-2-ethyl - N - benzyl - 4, 7, 10, 13 - tetraoxa -1- azacyclopentadecane, has been prepared and studied by NMR, IR and single crystal X-ray diffraction techniques. The compound crystallizes in space group

Single Crystal Growth of High-Pressure Phases of Ice and Salt Hydrate Far Below the Original Melting Point by Mixing Alcohol: Crystal Structure Determination of Magnesium Chloride Heptahydrate

2020 ◽  
Author(s):  
Keishiro Yamashita ◽  
Kazuki Komatsu ◽  
Hiroyuki Kagi
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Crystal Growth ◽  
Single Crystal ◽  
Room Temperature ◽  
Growth Technique ◽  
Salt Hydrate ◽  
X Ray

An crystal-growth technique for single crystal x-ray structure analysis of high-pressure forms of hydrogen-bonded crystals is proposed. We used alcohol mixture (methanol: ethanol = 4:1 in volumetric ratio), which is a widely used pressure transmitting medium, inhibiting the nucleation and growth of unwanted crystals. In this paper, two kinds of single crystals which have not been obtained using a conventional experimental technique were obtained using this technique: ice VI at 1.99 GPa and MgCl<sub>2</sub>·7H<sub>2</sub>O at 2.50 GPa at room temperature. Here we first report the crystal structure of MgCl2·7H2O. This technique simultaneously meets the requirement of hydrostaticity for high-pressure experiments and has feasibility for further in-situ measurements.

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