Search results for "magnetic resonance spectroscopy"

Conformation of the galactose ring adopted in solution and in crystalline form as determined by experimental and DFT 1H NMR and single-crystal X-ray …

2003

The solution-state conformations of various galactose derivatives were determined by comparison of the experimental (1)H-(1)H vicinal coupling constants to those calculated using density functional theory (DFT) at the B3LYP/cc-pVTZ//B3LYP/6-31G(d,p) level of theory. The agreement between the experimental and calculated vicinal coupling constants for 1,2:3,4-di-O-isopropylidene-alpha-d-galactopyranose was good, thereby confirming an (O)S(2) skew conformation for it and its derivatives on the basis of their similar observed couplings. Single-crystal X-ray analysis of 1,2:3,4-di-O-isopropylidene-6-O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phthalimido-beta-d-glucopyranosyl)-alpha-d-galactopyranose and …

Simulated annealing with restrained molecular dynamics using a flexible restraint potential: Theory and evaluation with simulated NMR constraints

1996

A new functional representation of NMR-derived distance constraints, the flexible restraint potential, has been implemented in the program CONGEN (Bruccoleri RE, Karplus M, 1987, Biopolymers 26:137-168) for molecular structure generation. In addition, flat-bottomed restraint potentials for representing dihedral angle and vicinal scalar coupling constraints have been introduced into CONGEN. An effective simulated annealing (SA) protocol that combines both weight annealing and temperature annealing is described. Calculations have been performed using ideal simulated NMR constraints, in order to evaluate the use of restrained molecular dynamics (MD) with these target functions as implemented i…

13C nuclear magnetic resonance study of some phosphinolipids: Assignments and conformational studies

1989

13C chemical shifts and 31P, 13C spin-spin coupling constants are reported for six model phosphinates and eight synthetic phosphinolipids. The complex spectra of the synthetic phosphinolipids could be assigned from increments and couplings derived from the model compounds. Based on these investigations the 3J(PC) couplings of 7–15 Hz indicate a preferential trans orientation of the respective head-group carbon relative to the phosphorus. This behaviour is similar to that of natural phosphatidylcholine lipids.

Kinetic control in the chiral recognition of three-bladed propellers

2010

The ion pair of the stereolabile C(3)-symmetric, i(+)o proton complex [1H](+) of diaza-macropentacycle 1 and the configurationally stable Delta-TRISPHAT ([Delta-3](-)) anion exists in the form of two diastereomers, namely, [Delta-(1.H)][Delta-3] and [Lambda-(1.H)][Delta-3], the ratio of which, in terms of diastereomeric excess (de) decreases in the order [D(8)]THF (28%)CD(2)Cl(2) (22%)CDCl(3) (20%)[D(8)]toluene (16%)C(6)D(6) (7%)[D(6)]acetone (0%) at thermodynamic equilibrium. Except in the case of [D(6)]acetone, the latter is reached after a period of time that increases from 1 h ([D(8)]THF) to 24 h (CDCl(3)). Moreover, the initial value of the de of [1.H][Delta-3] in CDCl(3), before the t…

Spin Cross-Over (SCO) Complex Based on Unsymmetrical Functionalized Triazacyclononane Ligand: Structural Characterization and Magnetic Properties

2019

International audience; The unsymmetrical ligand 1-(2-aminophenyl)-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane (L6) has been prepared and characterized by NMR spectroscopy. The L6 ligand is based on the triazamacrocycle (tacn) ring that is functionalized by two flexible 2-pyridylmethyl and one rigid 2-aminophenyl groups. Reaction of this ligand with Fe(ClO4)2·xH2O led to the complex [Fe(L6)](ClO4)2 (1), which was characterized as the first Fe(II) complex based on the unsymmetrical N-functionalized tacn ligand. The crystal structure revealed a discrete monomeric [FeL6]2+ entity in which the unsymmetrical N-functionalized triazacyclononane molecule (L6) acts as hexadentate ligand. As …

1979

2D NMR spectra have been measured at variable temperatures between −100°C and +110°C in a sample of melt crystallized deuterated polyethylene (PE). The line shape could be decomposed into a central part originating from deuterons in the amorphous regions and outer parts from crystalline regions of PE. The “NMR crystallinity” determined from this separation was 72% in agreement with the X-ray crystallinity of 74%. Changes of the crystalline NMR line shape were interperted in terms of oscillations around the chain axis, the r.m.s. oscillation amplitude varying from 5° at 40°C to 12° at 110°C. The central part of the NMR line shape indicates the existence of a “narrow” and a “medium” component…

Asymmetric [N–I–N]+ halonium complexes

2020

The first asymmetric halogen-bonded iodonium complexes [I(py)(4-DMAP)]PF6 (2c) and [I(py)(4-Etpy)]PF6 (2e) were prepared via [N–Ag–N]+ → [N–I–N]+ cation exchange of their analogous 2-coordinate silver complexes. The complexes were characterised by 1H and 1H–15N HMBC NMR spectroscopy, and single crystal X-ray crystallography.

Complete assignments of1H and13C NMR spectra of four hispanane diterpenoids

2000

An NMR study of four hispanane diterpenoids is described. In addition to conventional 1D NMR methods, 2D shift-correlated experiments [1H,1H-COSY, 1H,1H-TOCSY, 1H,13C-HSQC-1J(C,H). 1H,13C-HMBC-nJ(C,H) (n = 2 and 3)] and 2D 1H,1H-NOESY were used for the complete and unambiguous 1H and 13C chemical shift assignments of these diterpenoids. Copyright © 2000 John Wiley & Sons, Ltd.

Doubly charged ions of bridged [4n] annulenes. An evaluation of diatropic ring current effects.

1985

Abstract [4n]Annulenes are transformed into doubly charged ions (dianion, dication) and characterized NMR spectroscopically. The diatropic character of the ionic (4n+2)π-systems is studied as a function of the number of π-electrons.

Reversible Dimerization of Tetraureas Derived from Calix[4]Arenes

1999

Calix[4]arene derivatives, substituted at the wider rim by four urea functions are easily available in great variety. In apolar solvents like benzene or chloroform they dimerize via NH…O=C hydrogen bonds encapsulating a single solvent molecule as guest. The exclusive formation of dimers has been proved in solution by NMR, while their shape has been characterized by single crystal X-ray analysis. The kinetic stability and the rate of the guest exchange have been studied by NOESY experiments using a derivative with lower symmetry.