High-field 1H Nuclear Magnetic Resonance Research Articles

Discriminating extra virgin olive oils from common edible oils: Comparable performance of PLS-DA models trained on low-field and high-field 1H NMR data.

Olive oil, derived from the olive tree (Olea europaea L.), is used in cooking, cosmetics, and soap production. Due to its high value, some producers adulterate olive oil with cheaper edible oils or fraudulently mislabel oils as olive to increase profitability. Adulterated products can cause allergic reactions in sensitive individuals and can lack compounds which contribute to the perceived health benefits of olive oil, and its corresponding premium price. There is a need for robust methods to rapidly authenticate olive oils. By utilising machine learning models trained on the nuclear magnetic resonance (NMR) spectra of known olive oil and edible oils, samples can be classified as olive and authenticated. While high-field NMRs are commonly used for their superior resolution and sensitivity, they are generally prohibitively expensive to purchase and operate for routine screening purposes. Low-field benchtop NMR presents an affordable alternative. We compared the predictive performance of partial least squares discrimination analysis (PLS-DA) models trained on low-field 60 MHz benchtop proton (1H) NMR and high-field 400 MHz 1H NMR spectra. The data were acquired from a sample set consisting of 49 extra virgin olive oils (EVOOs) and 45 other edible oils. We demonstrate that PLS-DA models trained on low-field NMR spectra are highly predictive when classifying EVOOs from other oils and perform comparably to those trained on high-field spectra. We demonstrated that variance was primarily driven by regions of the spectra arising from olefinic protons and ester protons from unsaturated fatty acids in models derived from data at both field strengths.

Benchtop low-field 1H Nuclear Magnetic Resonance for detecting falsified medicines

Falsified medicines represent a serious threat to public health. Among the different measures to effectively combat this scourge, analytical methods play a key role in their detection and removal from the market before they reach patients. The present study evaluates for the first time the potential of a benchtop low-field (LF) Nuclear Magnetic Resonance (NMR) spectrometer for uncovering drug falsification by focusing on the analysis of fifteen erectile dysfunction and nine antimalarial medicines, the most commonly reported falsified medicines in developed and developing countries respectively. After a simple and rapid sample preparation and ≈ 5 min of spectrum recording, LF 1H NMR allows to conclude on the quality of the medicine: presence or absence of the expected active pharmaceutical ingredient (API), presence of unexpected API, absence of any API. Some 2D experiments are also described but although conclusive they are hampered by the duration of the experiments. The LF 1H NMR assay, based on the internal standard method, is validated by the determination of its accuracy, repeatability, limits of detection (LOD) and quantification (LOQ), and by comparison of the data obtained on some medicines after 45 min of spectrum recording to those measured with high-field 1H NMR. Because of its saving capabilities (cost, space, user experience), LF 1H NMR spectroscopy might become a routine screening tool in laboratories in charge of detecting falsified medicines.

Integration of high and low field 1H NMR to analyse the effects of bovine dietary regime on milk metabolomics and protein-bound moisture characterisation of the resulting mozzarella cheeses during ripening

The influence of dairy cow feeding regime was investigated using 1H nuclear magnetic resonance (NMR). Two different NMR analytical systems were deployed: high field 1H NMR to investigate the influence on milk metabolomics and low field NMR to characterise proton relaxation linked to changes in the state of mozzarella cheese moisture during ripening. The metabolomics results showed that grass-based feeding increased the concentration of a biological marker that signifies near-organic milk production conditions. On the other hand, the investigation of cheese moisture distribution showed that grass-based diets reached final moisture partitioning in a shorter time, which implied the formation of a more compact protein structure in the cheese matrix. These results indicate that pasture-based dairying may be differentiated in terms of the provenance of milk produced along with the accrual of additional benefits during ripening of the resulting mozzarella cheeses.

A 43 MHz Low-Field Benchtop 1H Nuclear Magnetic Resonance Method to Discriminate Perilla Oil Authenticity.

The aim of this study was to discriminate the authenticity of perilla oils distributed in Korea using their 1H nuclear magnetic resonance (NMR) spectra acquired by a 43 MHz low-field benchtop NMR spectrometer. Significant differences existed in the integration values of all 6 peaks found in the spectrum between authentic and adulterated perilla oil samples. The integration values of 4 peaks that signify the methylene protons present in all fatty acids (FA) and allylic or olefinic protons present in all unsaturated FA were the best variables for establishing perilla oil authenticity. The procedure for applying the range of variables found in authentic perilla oil samples correctly discriminated between the samples of perilla oils with soybean oils added at concentrations of ≥ 6 vol%. The results demonstrated that this NMR procedure is a possible cost-effective alternative to the high-field 1H NMR method for discriminating the authenticity of perilla oils.

Characterisation of Gouda cheeses based on sensory, analytical and high-field 1H nuclear magnetic resonance spectroscopy determinations: Effect of adjunct cultures and brine composition on sodium-reduced Gouda cheese

This study aimed at the interception of flavour deviations of salt-reduced Gouda-type cheeses, salted in sodium-reduced brines (NaCl + KCl brine) compared with a reference brine (NaCl brine), by the addition of adjunct strains of Lactobacillus helveticus and Lactobacillus paracasei, next to the common mixed-strain starter culture for Gouda. A multiphasic analysis of carbohydrates, organic acids, amino acids, and volatile flavour compounds was performed. After 56 days of ripening, the sensory characteristics of the cheeses were evaluated. Trained taste panel analysis determined some significant differences (P < 0.05) in saltiness, bitterness, texture and preference. The selected chemical fingerprint techniques, combined with multivariate data analysis, could be used to characterise Gouda cheeses that varied in ripening time and to which adjunct cultures were added. The variations were related to proteolysis and metabolic processes during ripening. There were no significant differences in the chemometric results between the reference NaCl-brined cheeses and the NaCl + KCl-brined cheeses.

Mobile Low-Field 1H NMR Spectroscopy Desktop Analysis of Biodiesel Production

Biodiesel produced mainly by the base-catalyzed transesterification of vegetable oils or animal fats with a short chain alcohol, has become an attractive alternative to petroleum-based diesel fuel. Even though high-field 1H nuclear magnetic resonance (NMR) is a reliable method for biodiesel quality control, it is restricted by its poor mobility and expensive superconducting coils. As an alternative, this study presents a mobile low-field 1H NMR spectrometer for the analysis of biodiesel samples derived from different feedstock oils. The low-field 1H NMR spectra of all the compounds coexisting in a typical transesterification reaction such as rapeseed oil, rapeseed biodiesel, methanol, and glycerol, could be clearly differentiated. Field-dependent characteristic parameters such as relaxation times are provided. The degree of saturation of the different biofuels samples could be reliably estimated via integration of the resolved signals of the spectra. The obtained results agreed well with those measured at high-field 1H NMR. Since this compositional information is directly related to the biodiesel properties, the presented mobile low-field 1H NMR device built from permanent magnets arrayed in a Halbach geometry, constitutes an excellent alternative tool for biodiesel quality control.

Serum Metabolic Signature of Minimal Hepatic Encephalopathy by 1H-Nuclear Magnetic Resonance

Minimal hepatic encephalopathy (MHE) reduces quality of life of cirrhotic patients, predicts overt hepatic encephalopathy, and is associated with poor prognosis. We hypothesized that MHE arises once metabolic alterations derived from the liver reach a particular threshold. Our aim was to assess whether metabolic profiling of serum samples by high-field (1)H-nuclear magnetic resonance spectroscopy ((1)H NMR) and subsequent multivariate analyses would be useful to characterize metabolic perturbations associated with MHE and to identify potential metabolic biomarkers. Metabolic serum profiles from controls (n = 69) and cirrhotic patients without MHE (n = 62) and with MHE (n = 39) were acquired using high field NMR. Supervised modeling of the data provided perfect discrimination between healthy controls and cirrhotic patients and allowed the generation of a predictive model displaying strong discrimination between patients with and without MHE (R(2)Y = 0.68, Q(2)Y = 0.63). MHE patients displayed increased serum concentrations of glucose, lactate, methionine, TMAO, and glycerol, as well as decreased levels of choline, branch amino acids, alanine, glycine, acetoacetate, NAC, and lipid moieties. Serum metabonomics by (1)H NMR offers a useful approach for characterizing underlying metabolic differences between patients with and without MHE. This procedure shows great potential as a diagnostic tool of MHE as it objectively reflects measurable biochemical differences between the patient groups and may facilitate monitoring of both disease progression and effects of therapeutic treatments.

Multiway chemometric analysis of the metabolic response to toxins monitored by NMR

For the first time, the multiway chemometric model Tucker3 was applied to nuclear magnetic resonance (NMR) time series data from studies of the metabolic response to toxins. Three data sets were analysed, each consisting of 1D high-field 1H NMR spectra of rat urine samples collected over 7 days after administration of a single dose of a model toxin in different doses. The analysis using the multiway Tucker3 model resulted in models with two to three components in each mode. The observed perturbations following administration of the toxins corresponded well to those reported in other studies using two-way chemometric methods (PCA and batch processing analysis). The advantage of the Tucker3 analysis is that the three-way structure of the data (rat, time, reduced NMR spectra) is retained and used throughout the analysis. Only the metabolic perturbations that have common time profiles are modelled, whereas random or less general changes in metabolite levels, which do not have common time profiles, are considered as noise. In the Tucker3 model, no constraints are imposed on time profiles, and thus, the models can handle effects with complex time evolution behavior.

Application of proton NMR spectroscopy to measurement of whole-body RNA degradation rates: effects of surgical stress in human patients

The urinary catabolites, N 2, N 2-dimethylguanosine (DMG), pseudouridine (PSU) and 7-methylguanine (m 7-Gua) are formed from post-transcriptional methylation of RNA bases and are not reincorporated into RNA upon its degradation. Their quantitative urinary excretion may be used to determine rates of whole body degradation of individual RNA species since DMG occurs exclusively in tRNA, PSU occurs in rRNA and tRNA and m 7-Gua occurs in all RNA species. Conventional HPLC analysis has several drawbacks since pre-analytical steps may involve selective losses and, under certain conditions, other urinary analytes may co-elute. In the present paper, we report analysis of these compounds by high-field 1H-nuclear magnetic resonance ( 1H-NMR) spectroscopy. Urinary concentrations of these metabolites were found to be in agreement with previously published HPLC and ELISA determinations. However, NMR analysis required minimal sample preparation (other than lyophilisation and reconstitution) and was capable of the simultaneous determination of other relevant analytes such as creatinine. This technique was therefore applied to urine samples from patients who had undergone surgical stress and insulin-like growth factor-I (IGF-I) therapy. Surgical stress increased the excretion of DMG and m 7-Gua. Degradation rates for tRNA and mRNA were also higher in surgically stressed subjects when compared with controls but degradation rates of rRNA decreased by approx. 30%. However, injection of IGF-I (40 μg/kg s.c.) had no significant effect on the excretion of these nucleosides. These data indicated that IGF-I therapy has no marked effects on RNA turnover following trauma. We suggest that this technique can be applied to study of RNA metabolism in any surgical or medical condition. Furthermore, since only 0.6 ml of urine is required, studies in neonates seem to be feasible.

Generation of substance P carbamate in neutral aqueous solution: Relevance to inflammatory joint diseases

High-field proton ( 1H) nuclear magnetic resonance (NMR) spectroscopy has been employed to evaluate the formation of substance P carbamate in aqueous solution. Equilibration of substance P with physiologically relevant concentrations of bicarbonate (2.50 × 10 −2 mol·dm −3) at pH 7.00 generated a new multiplet signal centred at 4.13 ppm in its NMR spectrum, characteristic of the α-proton of peptide carbamate species. High-field 1H NMR spectroscopy also demonstrated that the model dipeptide, Arg-Gly, formed a carbamate in neutral aqueous solutions containing 2.50 × 10 −2 mol·dm −3 HCO 3. The physiological significance of these results is discussed in view of the central roles of vasoactive neuropeptides in human joint diseases and the hypercapnic environment of the inflamed rheumatoid joint.

Synthesis of 6β-hydroxyaldosterone by A6 (toad kidney) cells in culture

Incubation of aldoslerone with confluent layers of A6 (toad kidney) cells leads to its hydroxylation at the 6β-position. 6β-Hydroxyaldosterone is the major metabolite when the incubation is carried out at pH 6.8, whereas the product comprises dβ-hydroxy-17-isoaldosterone accompanied by some 6β-hydroxyapoaldosterone at pH 7.4. All products were identified by high-field 1H nuclear magnetic resonance spectroscopy. Control experiments indicated that the side-chain isomerization to form the 17-iso and apo derivatives occurs after the cytochrome P 450-dependent synthesis of 6β-hydroxyaldosterone. (Steroids 55:482–487, 1990)

Monitoring the Purity of Pharmaceutical Heparin Preparations by High-Field 1H-Nuclear Magnetic Resonance Spectroscopy

High-field (300 MHz) 1H NMR spectral analyses are reported for various sodium or calcium heparin products available on the Canadian market. Dermatan sulfate (chondroitin sulfate B) was detected as a contaminant in virtually all of these products. Its content varied among the suppliers from less than 1 to 15%, and also over nearly the same range within the groups of heparin preparations of particular suppliers. No correlation was found between in vitro biological activities (potency and anti-factor Xa by the USP tests) and the levels of dermatan sulfate found. Other components, or unlisted constituents, detected in some preparations were paramagnetic metal ions, polyols, and lidocaine.

Nuclear magnetic resonance probing of binding interactions used by minor groove binding, DNA-directed ligands: assignment of the binding site of Hoechst 33258 on the self-complementary oligonucleotide, d(CGCGAATTCGCG)

The binding of Hoechst 33258 to the minor groove of the duplex formed by the self-complementary oligonucleotide d(CGCGAATTCGCG) has been shown by means of high-field 1H nuclear magnetic resonance spectroscopy to be across the central AATT region of the duplex.

Osmium tetrahydrides and their high-field 1H nuclear magnetic resonance spectra

The complexes [OsH4L3](L = PMe2Ph, PEt2Ph, PPh3, and AsPh3) are described, and the high-field n.m.r. spectra of these and some related complexes are discussed.