Halogenation of Tris(amido)tantalacarboranes with Dihalomethanes CH2X2 (X = Cl, Br)

2002 ◽  
Vol 67 (6) ◽  
pp. 791-807 ◽  
Author(s):  
Mark A. Fox ◽  
Andrés E. Goeta ◽  
Andrew K. Hughes ◽  
John M. Malget ◽  
Ken Wade
Keyword(s):  
Single Crystal ◽  
Prolonged Exposure ◽  
Chemical Shifts ◽  
Amide Group ◽  
The Other ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Hydrolysis Of

Slow reactions of isomeric metallacarboranes of general formulae [(NMe2)3TaC2B9H11] (3 isomers) and [(NMe2)3TaC2B9H10Me] (3 isomers) with CD2Cl2 afford quantitative yields of monochloro complexes [Cl(NMe2)2TaC2B9H11] and [Cl(NMe2)2TaC2B9H10Me]. Exposure to CD2Cl2 for months leads to solutions containing about 70% of the dichlorides in three cases. More prolonged exposure of these and the other monochlorides leads to a mixture of boron-substituted complexes. Hydrolysis of [3,3,3-(NMe2)3-3,1,2-TaC2B9H11] by moist toluene results in the formation of the oxo-bridged complex 3,3'-[3,3-(NMe2)2-3,1,2-TaC2B9H11]2(μ-O), characterised by single-crystal X-ray crystallography. The limited solubility of the latter complex in CD2Cl2 eliminates the presence of this compound in the reaction of [3,3,3-(NMe2)3-3,1,2-TaC2B9H11] with CD2Cl2. The reaction of [2,2,2-(NMe2)3-2,1,12-TaC2B9H11] with CH2Br2 in C6D6 quantitatively yields the monobromide [2-Br-2,2-(NMe2)2-2,1,12-TaC2B9H11]. Prolonged reaction with CH2Br2 leads directly to isomeric boron-substituted complexes with no evidence for dibromides. The influence on 11B, 13C and 1H NMR chemical shifts of replacing an amide group in [(NMe2)3TaC2B9H11] with chloride to give [Cl(NMe2)2TaC2B9H11] is also discussed.

Conformation of a Fluorochrome from Aniline Blue

1997 ◽  
Vol 50 (10) ◽  
pp. 987
Author(s):  
Maureen F. Mackay, ◽  
Michael J. McTigue ◽  
Maruse Sadek
Keyword(s):  
Solid State ◽  
Single Crystal ◽  
Dimethyl Sulfoxide ◽  
Chemical Shifts ◽  
Deuterium Oxide ◽  
Sodium Ion ◽  
Space Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Solid State Conformation

The solid-state conformation of the fluorochrome sodium 4,4′-[carbonylbis(benzene-4,1-diyl)bis(imino)]-bisbenzenesulfonate has been defined by single-crystal X-ray crystallography. Monoclinic crystals belong to the space group C 2/c with a 11·732(1), b 6·185(1), c 37·179(3) Å, β 94·40(1)° and Z 8. The structure was refined to a final R0·042 for all 2271 unique terms. In the crystal six oxygen atoms form an octahedral grouping around the sodium ion and these octahedra are linked into layers sandwiched between the layers of organic anions which adopt an extended conformation. The n.m.r. spectra indicate that in solution the fluorochrome is flexible and averages to an extended structure that maintains symmetry about its longitudinal and carbonyl axes. Chemical shifts have been measured in water, deuterium oxide and (D6)dimethyl sulfoxide

Tris-triphenylsiloxy compounds of aluminium

1992 ◽  
Vol 70 (3) ◽  
pp. 771-778 ◽  
Author(s):  
Allen W. Apblett ◽  
Alison C. Warren ◽  
Andrew R. Barron
Keyword(s):  
Variable Temperature ◽  
Molecular Structures ◽  
Water Ligand ◽  
X Ray ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Phenyl Rings ◽  
Coordinated Water ◽  
Hydrolysis Of ◽  
Solvent Complex

The reaction of AlMe3 with three equivalents of HOSiPh3 in THF results in the formation of the solvent complex Al(OSiPh3)3(THF) (1). Hydrolysis of 1 yields the stable water complex Al(OSiPh3)3(H2O)(THF)2 (2) in which the THF molecules are hydrogen bonded to the coordinated water ligand. Compounds 1 and 2 have been fully characterized by 1H, 13C, 17O, 27Al, and 29Si NMR and IR spectroscopy. In addition, variable temperature 1H NMR of 2 has been employed to investigate the steric interactions between the phenyl rings of adjacent siloxide ligands. The molecular structures of the solvates 1•(THF) and 2•(THF)1.25 have been determined by X-ray crystallography. 1•(THF): monoclinic P21/c, a = 10.03 (1), b = 23.758 (6), c = 23.294 (7) Å, β = 101.13 (6)°, Z = 4, R = 0.084, Rw = 0.094. 2•(THF)1.25: cubic [Formula: see text], a = 23.034 (3) Å, Z = 4, R = 0.093, Rw = 0.099. Keywords: aluminium, siloxide, hydrolysis, complex, NMR spectroscopy.

Assigning structures to diastereomeric aliphatic α,α'-dibromo ketones

2002 ◽  
Vol 80 (4) ◽  
pp. 413-417 ◽  
Author(s):  
Masood Parvez ◽  
SM Humayan Kabir ◽  
Ted S Sorensen ◽  
Fang Sun ◽  
Brian Watson
Keyword(s):  
Liquid Chromatography ◽  
Key Words ◽  
Crystal Structures ◽  
Chemical Shifts ◽  
Gas Liquid Chromatography ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
H Nmr ◽  
Dibromo Ketones

X-ray crystal structures are reported for two symmetrical aliphatic α,α'-dibromo ketones: a meso diastereomer of 3,5-dibromo–2,2,6,6-tetramethylheptan-4-one, and a rac isomer of 4,6-dibromo–2,2,3,3,7,7,8,8-octamethylnonan-5-one. Using these secure assignments and a previously confirmed structure for the diastereomers of 2,4-dibromopentan-3-one, we show in this study that gas-liquid chromatography (GLC) retention times (meso > rac) can be used to confidently assign the diastereomers for a range of symmetrical and unsymmetrical aliphatic α,α'-dibromo ketones. 1H NMR chemical shifts for the >CHBr hydrogen(s) can also be corroboratively used for assignment purposes (δracH > δmesoH).Key words: α,α'-dibromo ketones, X-ray crystal structures, GLC retention times, isomer assignment

scholarly journals Informing NMR experiments with molecular dynamics simulations to characterize the dominant activated state of the KcsA ion channel

2020 ◽  
Author(s):  
Sergio Perez-Conesa ◽  
Eric G. Keeler ◽  
Dongyu Zhang ◽  
Lucie Delemotte ◽  
Ann E McDermott
Keyword(s):  
Molecular Dynamics ◽  
Chemical Shifts ◽  
Md Simulations ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
X Ray Crystallography ◽  
Activated State ◽  
State Present ◽  
Dynamics Simulations ◽  
Inference Techniques

As the first potassium channel with a X-ray structure determined, and given its homol- ogy to eukaryotic channels, the pH-gated prokaryotic channel KcsA has been extensively studied. Nevertheless, questions related in particular to the allosteric coupling between its gates remain open. The many currently available X-ray crystallography structures appear to correspond to various stages of activation and inactivation, offering insights into the molecular basis of these mechanisms. Since these studies have required mutations, com- plexation with antibodies, and substitution of detergents for lipids, examining the channel under more native conditions is desirable. Solid-state NMR (SSNMR) can be used to study the wild-type protein under activating conditions (low pH), at room temperature, and in bacteriomimetic liposomes. In this work, we sought to structurally assign the acti- vated state present in SSNMR experiments. We used a combination of molecular dynamics (MD) simulations, chemical shift prediction algorithms, and Bayesian inference techniques to determine which of the most plausible X-ray structures resolved to date best represents the activated state captured in SSNMR. We first identified specific nuclei with simulated NMR chemical shifts that differed significantly when comparing partially open vs. fully open ensembles from MD simulations. The simulated NMR chemical shifts for those spe- cific nuclei were then compared to experimental ones, revealing that the simulation of the partially open state was in good agreement with the SSNMR data. Nuclei that discrimi- nate effectively between partially and fully open states belong to residues spread over the sequence and provide a molecular level description of the conformational change.

Refinement of labile hydrogen positions based on DFT calculations of 1H NMR chemical shifts: comparison with X-ray and neutron diffraction methods

2017 ◽  
Vol 15 (21) ◽  
pp. 4655-4666 ◽  
Author(s):  
Michael G. Siskos ◽  
M. Iqbal Choudhary ◽  
Ioannis P. Gerothanassis
Keyword(s):  
High Resolution ◽  
Hydrogen Bonds ◽  
Neutron Diffraction ◽  
Dft Calculations ◽  
Energy Minimization ◽  
Chemical Shifts ◽  
Labile Hydrogen ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
H Nmr

High resolution structures of hydrogen bonds: experimental (δexp) and GIAO calculated 1H NMR chemical shifts, δcalc, in combination with DFT energy minimization, are an excellent means for obtaining high resolution structures of labile protons.

Selective chemistry of tripentaerythritol — Synthesis of acetals and their derivatives

2006 ◽  
Vol 84 (4) ◽  
pp. 516-521 ◽  
Author(s):  
Hussein Al-Mughaid ◽  
T Bruce Grindley
Keyword(s):  
Lewis Acid ◽  
Chemical Shifts ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
X Ray Crystallography ◽  
Catalysed Reaction ◽  
Toluenesulfonic Acid ◽  
C Nmr

Tripentaerythritol was converted efficiently into 2′,2′′:6′,6′′:10′,10′′-tri-O-cyclohexylidene-2,2,6,6,10,10-hexakis(hydroxymethyl)-4,8-dioxa-1,11-undecandiol (4) by the toluenesulfonic acid catalysed reaction with cyclohexanone in a mixture of N,N-dimethylformamide and benzene. Reaction of tripentaerythritol with benzaldehyde under similar conditions gave an easily separated mixture of the four possible stereoisomers. Structures of these stereoisomers were assigned based on 1H and 13C NMR chemical shifts using trends previously observed for the dibenzylidene acetals of dipentaerythritol, whose structures had been established unambiguously by X-ray crystallography. It was found that reduction of the mixture of benzylidene acetals to 2,6,10-tris(benzyloxymethyl)-4,8-dioxa-1,11-undecanediol could be accomplished using triethylsilane with ethylaluminium dichloride as the Lewis acid after a number of commonly used conditions for this transformation failed.Key words: pentaerythritol, tripentaerythritol, dipentaerythritol, acetals, benzylidene acetals, reduction.

Mixed behavior of p-phenylenediaminium guest binding with the inverted cucurbit[6]uril host

2015 ◽  
Vol 13 (30) ◽  
pp. 8330-8334 ◽  
Author(s):  
De-Qing Zhang ◽  
Rui-Lian Lin ◽  
Wen-Qi Sun ◽  
Zhu Tao ◽  
Qian-Jian Zhu ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Sandwich Structure ◽  
The Other ◽  
Binding Interaction ◽  
X Ray ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Guest Binding ◽  
Different Types ◽  
Inclusion Structure

The binding interaction between inverted cucurbit[6]uril (iQ[6]) and p-phenylenediaminium has been investigated by X-ray crystallography, 1H NMR spectroscopy and ITC. Our data indicate that the host and the guest can form two different types of complexes: one is an inclusion structure and the other is a sandwich structure.

Reaction between Yttrium Nitrate and 2,2':6',2"-Terpyridine (terpy) in MeCN: Preparation, Crystal Structures and Spectroscopic Characterization of [Y (NO3)3(terpy)(H2O )] and [Y(NO3)3(terpy)(H2O )] · terpy · 3 MeCN

2001 ◽  
Vol 56 (2) ◽  
pp. 122-128 ◽  
Author(s):  
Athanassios K. Boudalis ◽  
Vassilios Nastopoulos ◽  
Aris Terzis ◽  
Catherine P. Raptopoulou ◽  
Spyros P. Perlepes
Keyword(s):  
Oxygen Atom ◽  
Single Crystal ◽  
Crystal Structures ◽  
Spectroscopic Characterization ◽  
Yttrium Nitrate ◽  
X Ray ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Tricapped Trigonal Prism

Abstract The reaction of Y(NO3)3 · 5H2O and 2,2':6',2"-terpyridine (terpy) in MeCN leads to [Y(N03 )3(terpy)(H2O )] (1) and [Y(N03 )3(terpy)(H2O )] terpy-3MeCN (2) in good yields depending on the isolation conditions. The structures of both complexes were determined by single-crystal X-ray crystallography. The YIII atom in 1 is 9-coordinate and ligation is provided by one terdentate terpy molecule, two chelating nitrates, one monodentate nitrate and one terminal H2O molecule; the coordination polyhedron about the metal may be viewed as a tricapped trigonal prism. The YIII atom in 2 is 10-coordinate and its coordination sphere consists of three nitrogen atoms from the terdentate terpy, six oxygen atoms from the three chelating nitrates (one of them being “anisobidentate”) and one oxygen atom from a terminal H2O molecule; the polyhedron about the metal may be viewed as a distorted sphenocorona. The interstitial terpy is strongly hydrogen-bonded to the O atom of the coordinated H2O molecule to form [Y(NO3 )3(terpy)(H20)] ··· terpy pairs. The new complexes were characterized by IR and 1H NMR spectroscopies. The YIII/NO3-/terpy chemistry is compared to the already well-developed LnIII/NO3-/terpy chemistry (Ln = lanthanide).

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