Relaxation Processes in Aromatic Methyl Groups. II. Methyl-Methyl Nuclear Overhauser Enhancements

1990 ◽  
Vol 43 (4) ◽  
pp. 741 ◽  
Author(s):  
ML Baron ◽  
LL Martin ◽  
ID Rae ◽  
PM Simmonds ◽  
ML Woolcock
Keyword(s):  
Methyl Groups ◽  
Relaxation Processes ◽  
Methyl Methyl ◽  
Nuclear Overhauser

A range of compounds with methyl groups disposed ortho and peri on heteroaromatic frameworks have been prepared, and T1 values and methyl-methyl Overhauser effects measured for them. Most of the n.O.e . Values were ≤6%, but two examples of methyls flanked by two others exhibited values of 9% (6-hydroxy-4,4,5,7-tetramethyl-3,4-dihydro-2H-benzopyran-2-one) and 15% (1,4,5,8,9-pentamethylcarbazole).

Relaxation Processes in the N-Methyl Group of 1,2,2,6,6-Pentamethylpiperidine

1990 ◽  
Vol 43 (2) ◽  
pp. 447 ◽  
Author(s):  
ID Rae ◽  
ML Woolcock
Keyword(s):  
Relaxation Times ◽  
Spin Rotation ◽  
Relaxation Processes ◽  
Methyl Group ◽  
Methyl Methyl ◽  
Overhauser Effect ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Relaxation times (T1) and methyl-methyl nuclear Overhauser effects were measured for 1H, 13C and 2H nuclei in 1,2,2,6,6-pentamethylpiperidine and its N-CHD2 analogue which was synthesized by LiAlD4 reduction of the N-CHO compound. The relaxation pathways for hydrogens of the N-CH3 group were estimated to be as follows: spin-rotation 0.046 s-1, dipole-dipole within N-methyl 0.069 s-1, and dipole-dipole with the hydrogens of the C- methyls 0.027 s-1. The 1H{1H) Overhauser effect at the N-CH3 was 7.6%.

scholarly journals Crystal structures of titanium–aluminium and –gallium complexes bearing twoμ2-CH3units

2017 ◽  
Vol 73 (5) ◽  
pp. 691-693 ◽  
Author(s):  
Tim Oswald ◽  
Mira Diekmann ◽  
Annika Frey ◽  
Marc Schmidtmann ◽  
Rüdiger Beckhaus
Keyword(s):  
Single Crystal ◽  
Crystal Structures ◽  
Lewis Acids ◽  
Methyl Groups ◽  
X Ray Diffraction ◽  
X Ray ◽  
Methyl Methyl ◽  
Low Valent ◽  
Titanium Aluminium ◽  
Gallium Complexes

The isotypic crystal structures of two titanocene complexes containing anEMe3unit (E =Al, Ga; Me = methyl) with twoμ2-coordinating methyl groups, namely [μ-1(η5)-(adamantan-1-yl-2κC1)cycylopentadienyl]di-μ2-methyl-methyl-2κC-[1(η5)-pentamethylcyclopentadienyl]aluminiumtitanium(III), [AlTi(CH3)3(C10H15)(C15H18)], and [μ-1(η5)-(adamantan-1-yl-2κC1)cycylopentadienyl]di-μ2-methyl-methyl-2κC-[1(η5)-pentamethylcyclopentadienyl]galliumtitanium(III), [GaTi(CH3)3(C10H15)(C15H18)], are reported. Reacting a dinuclear nitrogen-bridged low-valent titanium(III) complex with the Lewis acids AlMe3or GaMe3results in the loss of molecular dinitrogen and the formation of two monomeric titanocene(III) fragments bearing twoμ2-bridging methyl groups. Single crystal X-ray diffraction reveals the formation of a newE—C bond involving the pentafulvene ligand while the bridging and terminal methyl groups remain intact.

Relaxation Processes in Aromatic Methyl-Groups. I. 2-Chloro-Toluene and 2,6-Dichloro-Toluene

1986 ◽  
Vol 39 (12) ◽  
pp. 2049 ◽  
Author(s):  
DJ Craik ◽  
RM Drew ◽  
I Kyratzis ◽  
ID Rae ◽  
JA Weigold
Keyword(s):  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Methyl Groups ◽  
Relaxation Processes ◽  
Molecular Orbital Calculations ◽  
Relaxation Rates ◽  
Methyl Group ◽  
Spin Lattice ◽  
Group Rotation ◽  
Methyl Group Rotation

Three series of selectively deuterated toluenes, 2-chlorotoluenes and 2,6-dichlorotoluenes have been synthesized, and their methyl group 1H n.m.r. relaxation pathways have been determined by 1H, 2H and 13C n.m.r. spin-lattice relaxation time measurements. 1H spin-lattice relaxation in the methyl groups of these series occurs predominantly through an intramethyl H-H dipolar mechanism as well as through the spin-rotation mechanism. Dipolar spin-lattice relaxation rates for intramethyl H-H pairs are 0.012, 0.020 and 0.025 s-1 for toluene, 2,6-dichlorotoluene and 2-chlorotoluene respectively, suggesting a decrease in the rate of methyl group rotation in this order. Ab initio molecular orbital calculations on the same compounds show that the theoretically predicted barrier to methyl group rotation increases in the order toluene < 2,6-dichlorotoluene < 2-chlorotoluene, supporting the experimentally derived results.

scholarly journals Structure-based methyl resonance assignment with MethylFLYA

2019 ◽  
Author(s):  
Iva Pritišanac ◽  
Julia Würz ◽  
T. Reid Alderson ◽  
Peter Güntert
Keyword(s):  
Resonance Assignment ◽  
Nmr Spectra ◽  
Isotope Labeling ◽  
Nuclear Overhauser Effect ◽  
Average Error ◽  
Methyl Groups ◽  
Automatic Picking ◽  
Complete Automation ◽  
Nuclear Overhauser ◽  
Methyl Resonance Assignment

AbstractMethyl groups provide crucial NMR probes for investigating protein structure, dynamics and mechanisms in systems that are too large for NMR with uniform isotope labeling. This requires the assignment of methyl signals in the NMR spectra to specific methyl groups in the protein, an expensive and time-consuming endeavor that limits the use of methyl-based NMR for large proteins. To resolve this bottleneck, several methyl resonance assignment methods have been developed. These approaches remain limited with regard to complete automation and/or the extent and accuracy of the assignments. Here, we present the completely automated MethylFLYA method for the assignment of methyl groups. MethylFLYA requires as input exclusively methyl-methyl nuclear Overhauser effect spectroscopy (NOESY) peak lists. The algorithm was applied to five proteins of 28–358 kDa mass with a total of 708 isotope-labeled methyl groups. Manually made 1H/13C reference assignments were available for 674 methyls. The available experimental peak lists contained NOESY cross peaks for 614 methyls. MethylFLYA confidently assigned 488 methyls, i.e. 79% of those with NOESY data. Of these assignments, 460 agreed with the reference, 5 were different (and 23 concerned methyls without reference assignment). For three proteins of 28, 81, and 358 kDa, all confident assignments by MethylFLYA were correct. We furthermore show that, for high-quality NOESY spectra, automatic picking of NOE signals followed by resonance assignment with MethylFLYA can yield results that are comparable to those obtained for manually prepared peak lists, indicating the feasibility of unbiased, fully automatic methyl resonance assignment starting directly from the NMR spectra. This renders MethylFLYA an advantageous alternative to existing approaches for structure-based methyl assignment. MethylFLYA assigns, for most proteins, significantly more methyl groups than other algorithms, has an average error rate of 1%, modest runtimes of 0.4–1.2 h for the five proteins, and flexibility to handle arbitrary isotope labeling patterns and include data from other types of NMR spectra.

Sign in / Sign up

Export Citation Format

Share Document