Diffusion-ordered Spectroscopy Technique Research Articles

Matrix-Assisted DOSY for Analysis of Indole Alkaloid Mixtures.

Diffusion-ordered spectroscopy (DOSY) is a powerful tool for investigating mixtures and identifying peaks of chemical components. However, similar diffusion coefficients of the components, particularly for complex mixtures that contain crowded resonances, limit resolution and restrict application of the DOSY technique. In this paper, matrix-assisted DOSY were used to explore whether the diffusion resolution of a complex model involving indole alkaloid mixtures can be realized. Furthermore, we investigated the influence of different factors on the separation effect. The results showed that the changes in diffusion coefficient differences were achieved more obviously when using sodium dodecyl sulfate (SDS) micelles as the matrix. In addition, we also found that increasing the concentration of SDS can improve the resolution of the DOSY spectrum. Finally, after investigating the influence factors and NMR conditions, we demonstrated the applications of the SDS-assisted DOSY on analyzing the total alkaloid extract of Alstonia Mairei, and the virtual separation of mixtures was achieved.

NMR analysis of the Fischer-Tropsch wastewater: Combination of 1D selective gradient TOCSY, 2D DOSY and qNMR

The Fischer–Tropsch (FT) process is a practical approach to convert synthesis gas (CO and H2) into hydrocarbons and oxygenates, and these product mixtures are usually well-characterized. However, the analysis of Fischer–Tropsch waste water (FTW) is still somewhat underdeveloped and the exact composition of FTW remains unclear. Herein, various qualitative NMR techniques, especially diffusion-ordered spectroscopy (DOSY) and one dimension (1D) selective gradient total correlation spectroscopy (SelTOCSY) were strategically applied in the analysis of FTW. The NMR results show that the DOSY technique can pseudo-separate most of components in complex mixtures over the diffusion dimension. The SelTOCSY technique is used as a supporting method in the cases where the DOSY technique cannot clearly distinguish overlapped signals. Moreover, the quantitative 1H NMR (qNMR) was further used to quantify the components of the sample. These routine and advanced qualitative and quantitative NMR technique utilized here provide a fast, effective and feasible method for the identification of complex mixtures in FTW, which might be a powerful and fast alternative to gas chromatography or high performance liquid chromatography for FTW research.

DOSY Plus Selective TOCSY: An Efficient NMR Combination for Analyzing Hydrogenation/Hydrogenolysis Mixtures of Biomass-Derived Platform Compounds

Analyzing the mixtures obtained from hydrogenation or hydrogenolysis reactions of biomass-derived platform chemicals is challenging work. With the development and improvement of NMR techniques, the NMR spectrometer proves to be an alternative and highly efficient piece of equipment for the rapid analysis of complex mixtures without the need for tedious purification. Herein, diffusion-ordered spectroscopy (DOSY) is applied in analyzing four model mixtures, which consist of the reactants and products from hydrogenation/hydrogenolysis reactions of biomass-derived platform chemicals. The results show that the DOSY technique can pseudoseparate most components in the model mixtures. The 1D selective gradient TOCSY technique is used as a supporting tool in the cases where the DOSY technique cannot clearly distinguish between the components of the mixtures. This is generally a problem when components in the mixture have very similar diffusion coefficients or severe overlap of peaks. The results show that DOSY and...

L-Lactide polymerization studied by 1H NMR with diffusion-ordered spectroscopy (DOSY): a “One NMR Tube Experiment” providing data on monomer conversion, polymer structure, Mn and Mw

The standard NMR and DOSY techniques allowed for the first time the on-line study of the polymerization kinetics together with the determination of number average molar mass Mn and mass average molar mass Mw.

Using perdeuterated surfactant micelles to resolve mixture components in diffusion‐ordered NMR spectroscopy

Diffusion-ordered NMR spectroscopy resolves mixture components on the basis of differences in their respective diffusion coefficients or molecular sizes. However, when components have near-identical diffusion coefficients, they are not resolved in the diffusion dimension of a diffusion-ordered spectroscopy (DOSY) spectrum. Adding surfactant micelles to these mixtures has been shown to enhance resolution when the component molecules interact differentially with the micelles. This approach is similar to that used in electrokinetic chromatography (EKC) where modifiers like micelles or polymers are used to enhance the separation of mixture components. In this study, perdeuterated surfactants are added to analyte mixtures studied with the DOSY technique. Since no micelle resonances appear in the mixture spectra, the difficulty associated with performing biexponential analyses in spectral regions where analyte and surfactant resonances overlap is avoided. The approach is demonstrated using mixtures of peptides with near-identical diffusion coefficients.

DOSY technique applied to palladium nanoparticles in ionic liquids

Multinuclear ((1)H, (31)P, (19)F and (11)B) diffusion ordered spectroscopy (DOSY) technique has been applied to palladium nanoparticles systems dispersed in ionic liquids (ILs). Even if the nanoparticles themselves cannot be detected through NMR, observation of the solvent (methanol) and the IL ([BMI][PF(6)] or [BMI][NTf(2)]), their diffusion coefficients and their changes in the presence of nanoparticles allow us to draw significant assumptions about the organisation of palladium nanoparticles in the IL. For comparison, the corresponding molecular precursors ([PdCl(2)(cod)] or [Pd(2)(dba)(3)]) have been also studied.

1H Diffusion-Ordered Spectroscopy (DOSY) Nuclear Magnetic Resonance (NMR) as a Powerful Tool for the Analysis of Hydrocarbon Mixtures and Asphaltenes

Heavy crude oils are more and more of interest for the oil industry to meet the growing worldwide energy demand. Asphaltenes, which are the heaviest and least reactive molecules in crude oils, have received great attention over the last few decades, because they are responsible for many problems occurring during hydrotreatment and hydroconversion. 1H diffusion-ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR) based on pulsed field gradient (PFG) sequences is a powerful tool to analyze polydisperse samples. The key advantage of such a technique compared to traditional NMR diffusion sequences, such as pulsed field gradient spin−echo (PFGSE), is to obtain both physical and chemical information in a single experiment. 1H DOSY NMR has been carried out on different types of samples to obtain a deeper insight into the physicochemical properties of petroleum samples, because diffusion coefficients are both sensitive to molecular weights and sizes. The application of DOSY NMR to analyze hydrocarbon mixtures and asphaltenes is assessed. It is shown that both solute and solvent diffusion coefficients decrease with an increasing concentration of solute. Different types of intermolecular interactions were observed on petroleum samples depending upon the sample concentration. Dilute and semi-dilute regimes have also been detected. 1H DOSY spectra applied to diesel and asphaltene samples in toluene are presented and interpreted to demonstrate the potential of DOSY techniques to analyze heterogeneous petroleum samples. The data obtained for the diesel sample enable us to establish that monoaromatics were connected to long alkyl chains, whereas di- or triaromatic molecules were linked to shorter hydrocarbon chains. However, a clear conclusion could not be reached for the asphaltene sample because there were only a few aromatic protons that were not detected. This observation is most consistent with a continental model of these asphaltenes.

Probing Paeonol−Pluronic Polymer Interactions by 1H NMR Spectroscopy

By using a combination of 1H NMR spectroscopy, two-dimensional heteronuclear single-quantum coherence-resolved (1)H{(13)C} and homonuclear rotating-frame Overhauser enhancement NMR correlation experiments with diffusion ordered spectroscopy (DOSY), the location and distribution of a hydrophobic drug, paeonol, have been established with respect to the methyl groups of the poly(ethylene oxide)-poly(propylene oxide) -poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer. The interaction between them is adjustable according to the different temperature-dependent hydrophilicities or hydrophobicities of the triblock copolymer components. On the other hand, such interactions influence the self-assembly properties of the block copolymer amphiphiles in solution. The amount of anhydrous methyl groups of PPO segments shows an increase with increasing paeonol concentration. It was also demonstrated that the shell-crosslinking of the Pluronic polymer has an effect in increasing the amount of anhydrous methyl groups and thus increasing the hydrophobicity of Pluronic micelles. This might be the deeper reason underlying the increase in drug-loading capacity and prolongation in release time of Pluronic micelles for drug delivery after the shell-crosslinking. Changes in self-diffusion coefficients of paeonol with varying copolymer concentrations and types were also determined by the diffusion-based NMR DOSY technique, and values of K(a), DeltaG, and n were calculated.