DOSY NMR applied to analysis of flavonoid glycosides from Bidens sulphurea

2D DOSY ¹H NMR has proved to be a useful technique in the identification of the molecular skeleton of the four major compounds of ethyl acetate extract of aerial parts of Bidens sulphurea (Asteraceae). The combination of this technique with HPLC, mass spectrometry and other NMR techniques enabled the identification of four flavonoid glycosides: quercetin‐3‐O‐β‐D ‐galactopyranoside, quercetin‐3‐O‐β‐D ‐glycopyranoside, quercetin‐3‐O‐α‐L ‐arabinofuranoside and quercetin‐3‐O‐β‐D ‐rhamnopyranoside. Copyright © 2009 John Wiley & Sons, Ltd.     

A fast method for the measurement of diffusion coefficients: one‐dimensional DOSY

A new experiment for the single‐scan measurement of diffusion coefficients is presented. The principle is to introduce a spatial variation in the parameters of a conventional pulse sequence, so that all of the scans required to determine some physical parameter can be recorded simultaneously from different parts of the sample. The spectrum is acquired in the presence of a weak read gradient so that the resulting lineshapes contain the information required. The pulse sequence is described in detail and demonstrated on a sample containing three components; its advantages and limitations are discussed in relation to those of existing techniques. For uncrowded spectra with high signal‐to‐noise ratio, this experiment provides an order of magnitude reduction in experiment time compared with conventional methods and is likely to be of most benefit where samples are changing rapidly with time or where a long period of polarization, which may be difficult to reproduce accurately, prohibits the use of multiple‐scan techniques. Copyright © 2003 John Wiley & Sons, Ltd.     

Enhanced chromatographic NMR with polyethyleneglycol. A novel resolving agent for diffusion ordered spectroscopy

NMR analysis of complex mixtures can be significantly simplified using polyethyleneglycol (PEG) as resolving additive in DOSY NMR technique, which allows the extraction of individual spectra of mixture components with differing polarity. Resolving power of PEG‐assisted DOSY was demonstrated with natural product mixtures. Copyright © 2010 John Wiley & Sons, Ltd.     

Generic applications of 13C‐detected NMR diffusion to formulated systems with suppression of thermal convection induced by proton decoupling

Fast and effective structural/compositional analysis on formulated systems represents one of the major challenges encountered in analytical science. ¹³C‐detected diffusion represents a promising tool to tackle the aforementioned challenges, particularly in industry. Toward exploring the generic applications of ¹³C‐detected diffusion, thermal convection induced by ¹H decoupling has been identified as a key factor that resulted in significantly reduced resolution in the diffusion dimension. Optimization of experimental parameters and utilization of double‐stimulated echo‐based pulse sequence both can effectively suppress the thermal convection caused by the ¹H decoupling, the success of which allows robust and generic applications of ¹³C‐detected diffusion to systems from mixtures of small molecules, polymer blends, and copolymers to actual complex formulated systems. The method is particularly powerful in differentiating small molecules from polymers, polymer blends from copolymers, and end‐group analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

ERETIC implemented in diffusion-ordered NMR as a diffusion reference: a clarification

Additional information as to the objectives of our previous paper entitled 'ERETIC implemented in diffusion-ordered NMR as a diffusion reference' (Magn. Reson. Chem. 2008, 46, S63) is provided. The need for an optimal instrumental stability for the method proposed to be reliably applicable in view of these objectives is emphasized and illustrated.     

Structure elucidation of the intermediate in triethylborane-mediated radical addition of oxime ethers with 2D- and 3D-DOSY NMR

The structures of the components in the triethylborane-mediated radical addition reaction of oxime ether were investigated by 1H- and 3D-DOSY NMR methods. It has been impossible to physically separate the unstable intermediates; therefore, the structures were thus far unidentified. It has been possible to elucidate the structures of these unstable intermediates using Diffusion-Ordered Spectroscopy (DOSY) methods for the reaction in an NMR tube. The DOSY methods resolved the spectra of each starting compound, intermediate and product having different diffusion coefficients. The structure of the intermediate was shown to be due to the bonding of diethylborane to the nitrogen atom of the alkoxyamino group.     

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. Copyright © 2008 John Wiley & Sons, Ltd.     

Matrix‐assisted diffusion‐ordered spectroscopy: mixture resolution by NMR using SDS micelles

Diffusion‐ordered spectroscopy (DOSY) is a powerful technique for mixture analysis, but in its basic form it cannot separate the component spectra for species with very similar diffusion coefficients. It has been recently demonstrated that the component spectra of a mixture of isomers with nearly identical diffusion coefficients (the three dihydroxybenzenes) can be resolved using matrix‐assisted DOSY (MAD), in which diffusion is perturbed by the addition of a co‐solute such as a surfactant [R. Evans, S. Haiber, M. Nilsson, G. A. Morris, Anal. Chem. 2009, 81, 4548–4550]. However, little is known about the conditions required for such a separation, for example, the concentrations and concentration ratios of surfactant and solutes. The aim of this study was to explore the concentration range over which matrix‐assisted DOSY using the surfactant SDS can achieve diffusion resolution of a simple model set of isomers, the monomethoxyphenols. The results show that the separation is remarkably robust with respect to both the concentrations and the concentration ratios of surfactant and solutes, supporting the idea that MAD may become a valuable tool for mixture analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

New validation of molecular mass measurements by means of 2D DOSY 1H NMR experiments: Application to surfactants

This study proposes a new correlation equation between surfactant diffusion coefficients and molecular mass using 2D DOSY ¹H NMR experiment. Indeed, DOSY is a suitable NMR technique to discriminate the different components in a mixture. Using Inverse Laplace Transform (ILT), all chemical shifts in the direct dimension are dispersed along the second dimension in relation to the diffusion coefficient. This approach does not make any assumption about the number of exponential components. The empiric equation was determined for anionic and non-ionic surfactants dissolved in dimethylsulfoxide (DMSO). The parameters, K = C_r = 5.18 ± 0.70 and a shape factor α = 0.45 ± 0.02 that is related to the molecular family fractal dimension constant δ_F = 2.21 ± 0.11, have been extracted from the data. The equation validity was checked for simple commercial raw material and a simple mixture composed of three surfactants classically used in detergent formulations. This equation, which describes quite satisfactorily the diffusion phenomenon of surfactants, could be used for deformulation purpose to check commercial products in case of quality control or adulteration assessment.     

Combined use of Overhauser spectroscopy and NMR diffusion experiments for mapping the hydration structure of nucleosides: structure and dynamics of uridine in water

Complementary results from 13C intermolecular nuclear Overhauser effects (NOE), 1H-13C heteronuclear Overhauser spectroscopy (HOSEY) and 1H-NMR diffusion measurements were used for probing the structure of the first solvation shell of uridine in water. It is demonstrated that a cyclic dihydrate is formed. The two water molecules produce two hydrogen bonds with the two oxygen atoms from the pyrimidine ring and accept only one hydrogen bond from the amide proton. The dihydrate has only a short lifetime as compared with the rotational correlation time of the free nucleoside. The chemical exchange constant of the amide proton with water is then estimated by diffusion experiments. The results are consistent with previous data obtained for uracil in water and provide interesting information about water accessibility in nucleic acid bases.     

NMR measurements of diffusion in concentrated samples: avoiding problems with radiation damping

Pulsed field gradient spin echo NMR is generally the method of choice for diffusion measurements on liquid samples. With modern high field instruments, however, severe problems can arise when it is applied to samples with very high proton concentrations because of the presence of radiation damping. The problems may be greatly reduced by a suitable choice of experimental parameters, in particular the use of modified stimulated echo pulse sequences with a reduced flip angle for the first pulse.     

Measurement of the hydrodynamic radii of PEE-G dendrons by diffusion spectroscopy on a benchtop NMR spectrometer

Benchtop nuclear magnetic resonance (NMR) spectroscopy is a useful tool for the rapid determination of the self-diffusion coefficient and the hydrodynamic radius of dendrons. The self-diffusion coefficients of the first four generations of poly ethoxy ethyl glycinamide (PEE-G) dendrons are measured by diffusion-ordered spectroscopy (DOSY) on a benchtop NMR equipped with diffusion gradient coils. The hydrodynamic radii of the dendrons are calculated via the Stokes–Einstein equation. The effects of solvent and pH are determined with the hydrodynamic radius increasing with generation and decreasing upon neutralization of an acidic solution. These measurements provide valuable information for biological and pharmaceutical applications of dendrons.     

Prilocaine-cyclodextrin-liposome: effect of pH variations on the encapsulation and topology of a ternary complex using 1H NMR

A better comprehension of the prilocaine (PLC)-β-cyclodextrin (β-CD) complex liberation to membranes was provided by studying the architectural supramolecular arrangements of PLC, β-CD and egg phosphatidylcholine (EPC) liposomes, a membrane model. The topologies and possible interactions of mixtures of PLC, β-CD and EPC liposomes were investigated by nuclear magnetic resonances combining experimental (1)H-NMR (1D ROESY, STD and DOSY) at different pHs. The results indicate that in the mixture PLC/β-CD/EPC at pH 10 the PLC molecules are almost totally embedded into the liposomes and little interaction was observed between PLC and β-CD. However, at pH 5.5 not only was PLC imbedded in the EPC bilayer, but PLC was also interacting with β-CD. These results were rationalized as a spontaneous PLC release from β-CD to liposomes vesicles, whereas the PLC/EPC complex formation was higher at pH 10 than pH 5.5.     

Real-life applications of the MULVADO software package for processing DOSY NMR data

MULVADO is a newly developed software package for DOSY NMR data processing, based on multivariate curve resolution (MCR), one of the principal multivariate methods for processing DOSY data. This paper will evaluate this software package by using real-life data of materials used in the printing industry: two data sets from the same ink sample but of different quality. Also a sample of an organic photoconductor and a toner sample are analysed. Compared with the routine DOSY output from monoexponential fitting, one of the single channel algorithms in the commercial Bruker software, MULVADO provides several advantages. The key advantage of MCR is that it overcomes the fluctuation problem (non-consistent diffusion coefficient of the same component). The combination of non-linear regression (NLR) and MCR can yield more accurate resolution of a complex mixture. In addition, the data pre-processing techniques in MULVADO minimise the negative effects of experimental artefacts on the results of the data. In this paper, the challenges for analysing polymer samples and other more complex samples will also be discussed.     

一些高级NMR技术介绍

对一些二维NMR技术,例如^1H-^1H相关谱（^1H-^1H COSY),^1H-^13C杂核化学位移相关谱（^1H-C^13 COSY）,奥氏核效应交换相关谱（NOESY）作了介绍,列举了一些典型谱图。     

1H‐19F REDOR‐filtered NMR spin diffusion measurements of domain size in heterogeneous polymers

Solid state NMR spectroscopy is inherently sensitive to chemical structure and composition and thus makes an ideal method to probe the heterogeneity of multicomponent polymers. Specifically, NMR spin diffusion experiments can be used to extract reliable information about spatial domain sizes on multiple length scales, provided that magnetization selection of one domain can be achieved. In this paper, we demonstrate the preferential filtering of protons in fluorinated domains during NMR spin diffusion experiments using ¹H‐¹⁹F heteronuclear dipolar dephasing based on rotational echo double resonance (REDOR) MAS NMR techniques. Three pulse sequence variations are demonstrated based on the different nuclei detected: direct ¹H detection, plus both ¹H?¹³C cross polarization and ¹H?¹⁹F cross polarization detection schemes. This ¹H‐¹⁹F REDOR‐filtered spin diffusion method was used to measure fluorinated domain sizes for a complex polymer blend. The efficacy of the REDOR‐based spin filter does not rely on spin relaxation behavior or chemical shift differences and thus is applicable for performing NMR spin diffusion experiments in samples where traditional magnetization filters may prove unsuccessful. This REDOR‐filtered NMR spin diffusion method can also be extended to other samples where a heteronuclear spin pair exists that is unique to the domain of interest.     

一种金属洗涤剂的NMR分析

由于精细化工行业的迅速发展,作为“工业味精”的表面活性剂,已广泛进入日化、轻工、纺织、建筑、石化、金属加工等生产领域,对其的分析也显得日益重要。表面活性剂的分析历来是比较困难的课题之一,而通过核磁共振(NMR)进行定性和定量的文献则更少[1]。本文利用NMR为多种表面活     

NMR定量测定片剂中的对乙酰氨基酚

以基准试剂邻苯二甲酸氢钾为内标,采用1H NMR法建立了对乙酰氨基酚片剂中对乙酰氨基酚含量的测定方法。考察了延迟时间、脉冲宽度和采样次数对测定结果的影响。选定核磁共振参数延迟时间1 s、脉冲宽度3μs、采样次数16次。结果显示,测定内标与标样的NMR峰面积比均小于0.4%,方法具有很好的重复性。将内标与标样的NMR峰面积比对其质量比绘制标准曲线,相关系数为1.000 0,内标的质量浓度为6 g/L时,对乙酰氨基酚的线性范围为2～10 g/L。用标准曲线法和绝对定量模式(内标法)测定了3种不同厂家的片剂中对乙酰氨基酚的含量。结果表明此方法与紫外分光光度法的测定结果一致,方法简单易行、结果准确。