High field (400 and 600 MHz) proton NMR spectroscopy has been employed to investigate the thermally-induced autoxidation of glycerol-bound polyunsaturated fatty acids present in intact culinary frying oils and fats. Heating of these materials at 180 degrees C for periods of 30, 60 and 90 min. generated a variety of peroxidation products, notably aldehydes (alkanals, trans-2-alkenals and alka-2,4-dienals) and their conjugated hydroperoxydiene precursors. Since such aldehydes appear to be absorbed into the systemic circulation from the gut in vivo, the toxicological significance of their production during standard frying practices is discussed.

The oxidative deterioration of glycerol-bound polyunsaturated fatty acids (PUFAs) in culinary oils and fats during episodes of heating associated with normal usage (30-90 min at 180°C) has been monitored by high field 'H NMR spectroscopy. Thermal stressing of PUFA-rich culinary oils generated high levels of n-alkanals, truna-2alkenals, alka-2,rl-dienals and 4-hydroxy-trans-2-alkenals via decomposition of their conjugated hydroperoxydiene precursors, whereas only low concentrations of selected aldehydes were produced in oils with a low PUFA content, lard and dripping when subjected to the above heating episodes. Samples of repeatedly used, PUFA-rich culinary oils obtained from restaurants also contained high levels of each class of aldehyde. The dietary, physiological and toxicological ramifications of the results obtained are discussed.

SUMMARY The different forms of phosphorus (P) in 0.5 m sodium hydroxide extracts of soils from long‐term field experiments at Rothamsted were characterized by 31P‐nuclear magnetic resonance spectroscopy (NMR). The extract from an old grassland soil (pH 4.6) from a plot of the Park Grass Continuous Hay Experiment that had received no fertilizer or lime for at least 125 years contained the following forms of P: inorganic orthophosphate (22% of the extracted P), orthophosphate monoesters (49%), orthophosphate diesters (14%), phosphonates (3%), pyrophosphate (4%) and two unidentified forms of P (7%). The soil extract from a Park Grass plot given inorganic phosphate fertilizer (35 kg P ha−1) annually for 121 years contained the same forms of P and, in addition, a small amount of polyphosphate. There was also evidence of an increase in the orthophosphate monoester fraction. Another old grassland soil, of pH 6.1, contained more total and organic P than Park Grass but the extract contained fewer forms of P: inorganic orthophosphate (14% of the extracted P), orthophosphate monoesters (39%), orthophosphate diesters (34%) and an unidentified form (13%). An area of this grassland that had been ploughed up 20 years previously, and kept bare since, contained less organic P. The extract contained less of the phosphate diesters but the more stable monoesters remained relatively unchanged.

The use of 13C nmr (cmr) spectra for the determination of configurations of oximes is described. The problems of quantitative analysis of syn-anti mixtures of oximes by cmr, because of differential Ti and Overhauser effects, are considered. Chemical shifts for the cmr resonances of a number of aldehydes and ketones are reported.

High resolution 'H NMR spectroscopy has been employed to investigate the metabolic profile of heatlhy human knee-joint synovial fluid (SF) and the biochemical data acquired have been compared with those of matched serum, and inflammatory knee-joint SF samples. Results obtained indicate that the healthy human knee-joint has a hypoxic status (high lactate level when expressed relative to that of paired serum) that is milder than that of the inflamed human knee-joint. Moreover, normal SF differs from that of inflammatory SF in that it contains little or no NMRdetectable lipoprotein-associated fatty acids and 'acute-phase' glycoproteins, an observation reflecting the limited passage of these macromolecules from plasma into the synovial space in healthy subjects.

Keywords Lignin Lignin model compounds Aspen lignin Sulfite spruce lignin Phenol pulping sulfite lignin Eucalyptus kraft lignin Solid state 13 C NMR SummaryThe solution and magic angle spinning (MAS) 13 C NMR spectra of a comprehensive series of monomer and dimer lignin model compounds are reported. Most chemical shifts from solid state spectra are similar to those from the solution state, however a significant number of resonances do have substantial (4 to 9 ppm) solution-solid state chemical shift differences. The large differences are most likely the result of conformational changes on passing from the solid to the solution state. From the solid state spectra of the model compounds a table is presented of selected chemical shift ranges for selected carbon environments. It was found that under a standard set of experimental conditions the non-protonated carbon resonances from model sompound spectra gave reliable integrations. The same technique was applied to the spectra of 5 lignins from different sources and the degree of condensation and the syringyl/guaiacyl ratio of the lignins is discussed.

A reproducible method for the reconstitution of rabbit liver metallothionein (MT) containing seven cadmium atoms per mole of protein is described. This protein was studied in detail by 113Cd NMR at 88-, 55-, and 44-MHz frequencies, including the effects of pH, temperature, and ionic strength on the spectra. Our results differ significantly from previous reports of 113Cd NMR on similar samples. Thus, the spectra of both chromatographically distinguishable isoforms MT1 and MT2 were not identical, and neither could be interpreted in terms of a unique static model with the seven Cd ions forming two independent clusters of four and three Cd ions. Large differential shifts of 113Cd resonances were observed with changes in temperature over the range 277-320 K and ionic strength (0.02-0.5 M). At low temperature a slow structural change (half-life of several minutes) was detected. The structure was more rigid at high ionic strength. The frequency dependence and two-dimensional J-resolved spectra revealed that 113Cd resonances were composed of several overlapping peaks, complicating the interpretation of fine structure in one-dimensional spectra. A new flexible model of the Cd cluster in metallothionein is proposed. This model incorporates dynamic thiolate exchange reactions and involves several configurational substates of the protein. The possible relationship of such flexibility to the function of metallothionein is discussed.

Borate is an antibacterial preservative widely used in clinical and large scale epidemiological studies involving urine sample analysis. Since it readily forms covalent adducts and reversible complexes with hydroxyl and carboxylate groups, the effects of borate preservation in 1 H NMR spectroscopybased metabolic profiling of human urine samples have been assessed. Effects of various concentrations of borate (range 0-30 mM) on 1 H NMR spectra of urine were observed at sequential time points over a 12 month period. Consistent with known borate chemistry, the principal alterations in the 1 H resonance metabolite patterns were observed for compounds such as mannitol, citrate and α-hydroxyisobutyrate and confirmed by ESI-MS analysis. These included line-broadening, T 1 and T 2 relaxation and chemical shift changes consistent with complex formation and chemical exchange processes. To further investigate complexation behavior in the urinary metabolite profiles, a new tool for visualization of multi-component relaxation variations in which the spectra were color-coded according to the T 1 and T 2 proton relaxation times respectively (T 1 or T 2 Ordered Projection SpectroscopY, TOPSY) was also developed and applied. Addition of borate caused a general decrease in 1 H T 1 values consistent with non-specific effects such as solution viscosity changes. Minor changes in proton T 2 relaxation rates were observed for the most strongly complexing metabolites. From a molecular phenotyping and epidemiologic viewpoint, typical interpersonal biological variation was shown to be vastly greater than any variation introduced by the borate complexation which had a negligible effect on the metabolic mapping and classification of samples. Whilst caution is indicated in the assignment of biomarker signals where metabolites have diol groupings or where there are adjacent hydroxyl and carboxylate functions, it is concluded that borate preservation is "fit-forpurpose" for 1 H NMR-based epidemiological studies since the essential biochemical classification features of the samples are robustly maintained.*To whom correspondence should be addressed -Professor Jeremy K. Nicholson. Phone +44 (0) 20 Metabolic profiling of biofluids is now widely accepted as a tool for identifying biomarkers in disease diagnosis and toxicology, 1-4 and the application of spectroscopic methods, based on either NMR spectroscopy or mass spectrometry, are now well validated for metabolic profiling of animal studies and for small scale human clinical studies. [5][6][7] Understanding the variation in metabolic phenotypes of is of importance in molecular epidemiology studies on diverse human populations. [8][9][10] The development of the concept of the Metabolome-Wide Association Studies (MWAS) involving the broad, non-selective analysis and statistical characterization of metabolic phenotypes in relation to disease outcomes and risk factors in epidemiologic studies provides a framework for generating testable physiological hypotheses. 11,12 However, the analytic...