Rapid and simultaneous relaxometric methods to study paramagnetic ion complexes in solution: An alternative to spectrophotometry

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Although the Cu2+‐sorbitol complex [Cu2+‐Sorb] structure in crystalline state has been determined by X rays, it is not known in solution, where most studies of this complex are performed. Therefore, the goal of this work was to obtain information about the structure of this complex in aqueous solution using nuclear magnetic resonance and electron paramagnetic resonance spectroscopies. The magnetic resonance results indicate that the complex is formed at approximately pH 12. In this pH the sorbitol 1H relaxation times were so short (broad line) that was not possible to use standard nuclear magnetic resonance parameters (nuclear Overhauser effect and spin–spin coupling constants values) to solve the three‐dimensional structure. However, valuable structural information about the complex in solution was obtained. The relaxation results indicate that the Cu2+ ions are buried in the structure and not accessible to solvent; the 1H and 13C spectra shows strong paramagnetic shift effect indicating short distance between these nuclei and Cu2+ in the structure. No electron paramagnetic resonance signal was observed in pH 12 indicating strong Cu2+‐ Cu2+ dipolar interaction, compatible to Cu2+‐Cu2+ distances measured in crystal, from 1.148 to 1.393 Angstroms. The complex self‐diffusion coefficient (D) of 1.58 × 10−10 m2/s value, determined by Diffusion‐Ordered Spectroscopy, is compatible to a molecular weight of 3–6 KDa. Therefore, these results corroborate that the [Cu2+‐Sorb] complex is assembled in solution, at pH 12, with several structural parameters compatible to the toroidal hexadecacuprate supramolecular structure determined in solid state.

Section: Resultssupporting

confidence: 56%

Section: Resultsmentioning

confidence: 70%

Section: Resultsmentioning

confidence: 99%

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Magnetic resonance studies of copper (II) sorbitol complex, in solution, reveal a supramolecular structure compatible to the crystal structure

Kock

Higuera-Padilla

Vigatto

et al. 2019

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“…Other steady‐state sequences, such as Continous Wave Free Precession (CWFP) and Carr‐Purcell Continuous Wave Free Precession (CP‐CWFP) are able to simultaneously estimate T 1 and T 2 values with the aid of pre‐established mathematical models. These sequences are suitable in cases where T p < < T 1 , T 2 , with T p being the time between each pulse in the train.…”

Section: Introductionmentioning

confidence: 99%

Single‐shot measurement of solids and liquids T₁ values by a small‐angle flip‐flop pulse sequence

Neto

Rodrigues

Tavares

2019

We propose the small‐angle flip‐flop (SAFF) pulse sequence as an alternative procedure for the rapid measurement of the 1H spin–lattice relaxation time in the laboratory frame (T1) of solid and liquid substances, in a time‐domain NMR experiment. Based on the original flip‐flop pulse sequence, this technique allows the fast estimation of T1 values of samples that require minutes to hours of acquisition time if traditional pulse sequences are employed. We have applied SAFF to different substances, with T1 ranging from microseconds up to seconds, including natural clays, polymers, and organic and inorganic solvents. We also demonstrate the potential of the pulse sequence in the real‐time monitoring of dynamic processes, such as the conformational changes of polymeric materials during heating. The results we obtained with SAFF are comparable with those acquired with the inversion‐recovery pulse sequence, with the addition of several benefits. This pulse sequence obeys steady‐state and magnetization‐conserving principles, making it possible to dismiss the need for relaxation delay times of the order of 5T1. SAFF has shown high sensitivity in the resolution of individual components of T1 in multiexponential systems and can be easily integrated to well‐established pulse sequences, such as Magic Sandwich Echo and Carr–Purcell–Meiboom–Gill, for the single‐shot determination of T1 and T2 or T2*.

“…Time‐domain nuclear magnetic resonance (TD‐NMR) relaxometry, in low‐field spectrometers, have been widely used to obtain valuable information about physical properties and chemical composition and that evolution in homogeneous and heterogeneous materials such as raw and processed food, biological tissues, oil‐bearing rocks, cements, and among other materials …”

Section: Introductionmentioning

confidence: 99%

Enhancing signal‐to‐noise ratio and resolution in low‐field NMR relaxation measurements using post‐acquisition digital filters

Monaretto

Souza²,

Moraes

et al. 2018

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The traditional way to enhance signal‐to‐noise ratio (SNR) of nuclear magnetic resonance (NMR) signals is to increase the number of scans. However, this procedure increases the measuring time that can be prohibitive for some applications. Therefore, we have tested the use of several post‐acquisition digital filters to enhance SNR up to one order of magnitude in time domain NMR (TD‐NMR) relaxation measurements. The procedures were studied using continuous wave free precession (CWFP‐T1) signals, acquired with very low flip angles that contain six times more noise than the Carr–Purcell–Meiboom–Gill (CPMG) signal of the same sample and experimental time. Linear (LI) and logarithmic (LO) data compression, low‐pass infinity impulse response (LP), Savitzky–Golay (SG), and wavelet transform (WA) post‐acquisition filters enhanced the SNR of the CWFP‐T1 signals by at least six times. The best filters were LO, SG, and WA that have high enhancement in SNR without significant distortions in the ILT relaxation distribution data. Therefore, it was demonstrated that these post‐acquisition digital filters could be a useful way to denoise CWFP‐T1, as well as CPMG noisy signals, and consequently reducing the experimental time. It was also demonstrated that filtered CWFP‐T1 method has the potential to be a rapid and nondestructive method to measure fat content in beef and certainly in other meat samples.