![]() These results suggest that the increase in HA particle sizes depends on the length of aliphatic groups and the bond of methoxyl groups, and HAs were composed of HA molecules of homologous series. In addition, with increasing particle size, the percentage of aromatic protons decreased. Such a negative linear correlation was also observed between Har and Hbeta. Based on the 1H NMR data in UA, there was a significantly negative linear correlation between Har and Hco. With increasing particle sizes, the absorption of methylene groups and amide of peptides increased in the IR spectra of both HAs and that of carboxylic groups decreased in the IR spectra of UA, the HA obtained from an Umbric Andosol. off-resonance ROESY or Tilted ROESY in the Bruker's nomenclature.Humic acids (HAs) extracted from an Umbric Andosol (UA) and a Dystric Cambisol (DC) wee fractionated into 7 fractions by successive gel permeation chromatography (GPC) and their fractions were studied by spectral analysis. This remark has allowed us to propose the most reliable pulse sequence to study cross-relaxation between protons in small to medium size molecule, i.e. However in term of in-phase coherence transfer due to scalar couplings J (Homonuclear Hartmann-Hahn transfer or TOCSY) the difference of chemical shifts between two protons remains non small relative to J, preventing this type of transfer. Indeed a large offset D induces that chemical shift variation along the spectrum becomes negligible relative to this offset. In term of implementation the two drawbacks of on-resonance rf irradiation studies disappear.This allows the exploration of very slow overall dynamics or fast chemical exchange appearing in the micro to millisecond time scale, and in fact using this approach we had reported the fastest chemical exchange rate or the determination of the whole chemical exchange spectral density function. By increasing the offset Δ it becomes possible to probe molecular dynamics at a scale on the order of 1/Ω which means about two orders of magnitude larger than what can be achieved by on-resonance rf irradiation.The precision on their determination is nevertheless increased since it benefits from the absolute relation between the measured rates and these two limit values which is dependent in a perfectible predictable way of the angle θ. Usually only two, the longitudinal and transverse relaxation rates, which correspond to θ=0 and θ = 90°. Depending on the relaxation mechanisms considered two or more dynamic pieces of information can be obtained. Obviously a large number of relaxation rates correlated by the θ and Δ values can be experimentally determined. Δ and ω 1, the direction of the effective field continuously varies from the longitudinal case to the transverse one. This effective field makes an angle Θ=atan(ω 1/Δ) with the static magnetic field direction and its amplitude Ω is defined by Ω 2= ω 1 2+Δ 2. In the frame rotating at the rf field frequency this defines an effective field and we can study the relaxation along this field. Principle: The key point consists in applying the rf irradiation of amplitude ω 1 not on-resonance as usual but off-resonance at a distance Δ in Hz from the spectrum centre. What we have studied for a while has led to the definition of a general unified view which links longitudinal relaxation along the static magnetic field direction and transverse one performed in the presence of rf irradiation. This obviously needs to be extended in a first step to dipolar cross relaxation as explored by NOESY or ROESY experiments and in a further step to any mechanism involving cross-correlation induced relaxation. ![]() Aim: The classical way to see relaxation in liquids is strongly associated to Bloch's equations, characterized by a longitudinal T1 and a transverse T2.
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