Apostolos Spyros

Primary and secondary marine organic aerosols over the North Atlantic Ocean during the MAP experiment

[1] The organic chemical composition of atmospheric submicron particles in the marine boundary layer was characterized over the northeast Atlantic Ocean in summer 2006, during the season of phytoplankton blooms, in the frame of the Marine Aerosol Production (MAP) experiment. First measurements of water‐insoluble organic carbon (WIOC) in marine aerosol particles by nuclear magnetic resonance (NMR) spectroscopy showed that it is structurally similar to lipids, resembling the organic fraction of sea spray formed during bubble‐bursting experiments. The composition of the water‐soluble organic carbon (WSOC) fraction was investigated by liquid chromatography – mass spectrometry and by 1D‐ and 2D‐NMR spectroscopy, and showed a less hydrophilic fraction containing traces of fatty acids and rich of alkanoic acids formed by lipid degradation, and a more hydrophilic fraction, containing more functionalized species encompassing short‐chain aliphatic acids and sulfate esters of hydroxyl‐carboxylic acids. The more oxidized fraction of WSOC accounts for the oxidized organic aerosol components, which can form by either gas‐to‐particle conversion or extensive chemical aging of lipid‐containing primary particles, as also suggested by the parallel measurements using online mass spectrometric techniques (presented in a companion paper), showing oxidized organic substances internally mixed with sea salt particles. These measurements are also compared with online measurements using an Aerosol Time‐Of‐Flight Mass Spectrometer (ATOFMS) and Aerodyne Aerosol Mass Spectrometer (AMS). Given the large variability in the chemical composition of marine organic aerosol particles, a multitechnique approach is recommended to reduce method‐dependent categorizations and oversimplifications and to improve the comparability with the results obtained in different oceanic areas.

Geographical Characterization of Greek Virgin Olive Oils (Cv. Koroneiki) Using 1H and 31P NMR Fingerprinting with Canonical Discriminant Analysis and Classification Binary Trees

This work deals with the prediction of the geographical origin of monovarietal virgin olive oil (cv. Koroneiki) samples from three regions of southern Greece, namely, Peloponnesus, Crete, and Zakynthos, and collected in five harvesting years (2001-2006). All samples were chemically analyzed by means of 1H and 31P NMR spectroscopy and characterized according to their content in fatty acids, phenolics, diacylglycerols, total free sterols, free acidity, and iodine number. Biostatistical analysis showed that the fruiting pattern of the olive tree complicates the geographical separation of oil samples and the selection of significant chemical compounds. In this way the inclusion of the harvesting year improved the classification of samples, but increased the dimensionality of the data. Discriminant analysis showed that the geographical prediction at the level of three regions is very high (87%) and becomes (74%) when we pass to the thinner level of six sites (Chania, Sitia, and Heraklion in Crete; Lakonia and Messinia in Peloponnesus; Zakynthos). The use of classification and binary trees made possible the construction of a geographical prediction algorithm for unknown samples in a self-improvement fashion, which can be readily extended to other varieties and areas.

Adsorption of organophosphates into microporous and mesoporous NaX zeolites and subsequent chemistry.

Due to the neurotoxicity of organophosphate (OP) pesticides and nerve agents synthesized as military or terror agents, their safe destruction and disposal is of considerable current importance. A representative OP, trimethyl phosphate (TMP), was adsorbed onto NaX zeolite, two mesoporous modifications, and a low-silica X zeolite. The nucleophilic chemical reactions of TMP with the zeolites were investigated by solid-state 13C and 31P nuclear magnetic resonance (NMR) and the solvent extracts by 1H, 13C, and 31P NMR. Nucleophilic substitution and subsequent hydrolysis reaction schemes are proposed. All of the zeolites have similar TMP decomposition yields, supporting the hypothesis that slow or incomplete diffusion of TMP in the microporous zeolite regions limits TMP decomposition.

NMR study of the rotational dynamics of linear homopolysaccharides in dilute solutions as a function of linkage position and stereochemistry

Abstract Variable temperature and magnetic field dependent 13 C NMR relaxation measurements ( T 1 , T 2 , and NOE) were carried out on a series of linear homopolysaccharides: α-(1→3)- d -glucan, β-(1→3)- d -glucan in Me 2 SO- d 6 , and α-(1→6)- d -glucan in D 2 O and Me 2 SO- d 6 dilute solutions. The relaxation data of the backbone carbons were analyzed quantitatively by using a variety of theoretical unimodal and bimodal time-correlation functions in an attempt to describe the main carbohydrate chain dynamics as a function of linkage position and stereochemistry. Among these, the time-correlation function developed by Dejean, Laupretre, and Monnerie (DLM) offered the best quantitative description of the segmental motion of the carbohydrate chains. The internal rotation of the hydroxymethyl groups about the exocyclic C-5–C-6 bonds superimposed on segmental motion has been described as a diffusion process of restricted amplitude. Comparison of the dynamics of polysaccharides has been extended to include amylose and inulin studied previously. On the basis of the calculated correlation times for segmental motion, the flexibility of the carbohydrate chains decreases from inulin and dextran following the order; inulin>dextran>α-(1→3)- d -glucan>β-(1→3)- d -glucan∼amylose, whereas the rate and the amplitude of the internal rotation of the hydroxymethyl groups about the exocyclic C-5–C-6 bonds showed that the restriction of the hydroxymethyl internal rotation decreases from inulin to amylose following the order; inulin>α-(1→3)- d -glucan∼β-(1→3)- d -glucan>amylose. Solvent effects on segmental dynamics and the temperature–frequency superposition of the relaxation data of the three polysaccharides have been discussed as well.

Analysis and aging of unsaturated polyester resins in contemporary art installations by NMR spectroscopy

AbstractTwo original art installations constructed from unsaturated polyester resins (UPR) and four different reference UPR products (before and after UVB aging) were analyzed by high-resolution 1D and 2D nuclear magnetic resonance (NMR) spectroscopy. Breaking strain studies were also conducted for the four UPR model products before and after different aging procedures (moisture, UVB exposure, melt/freeze). NMR analysis of the chemical composition of the UPR resin extracts showed they contain several low MW organic compounds and oligomers rich in polar –OH groups that play a significant role in the degradation behavior of the composite UPR materials. Statistical analysis of the NMR compositional data showed that styrene and benzaldehyde contents can be used to differentiate between fresh and aged UPR samples. The phthalate and propylene glycol unit speciation (esterified, primary or secondary –OH) of the extracts provided evidence that UPR resin C was used in the construction of the two art installations, and direct comparison of 1H and 13C NMR spectra verified this compositional similarity. UPR resin C was shown by both NMR and breaking strain studies to be the reference UPR most susceptible to degradation by different aging procedures, a characteristic attributed to the lower styrene content of resin C. FigureA1. NMaRt

31P NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY OF POLYPHENOL-CONTAINING OLIVE OIL MODEL COMPOUNDS

Abstract Phosphitylation of the free hydroxyl and carboxyl groups of a series of polyphenol-containing olive oil model compounds with 2-chloro-4,4,5,5-tetramethyl-dioxaphospholane allows their classification on the basis of 31P NMR chemical shifts. Unambiguous assignment of the 31P NMR chemical shifts of the dihydroxy- and polyhydroxy-phenols has been achieved by employing one and two-dimensional NMR techniques. Furthermore, integration of the appropriate signals of the hydroxyl derivatives in the corresponding 31P NMR spectra allows the quantification of these compounds. This study forms the basis for the development of a novel and sensitive method that can be used to obtain valuable information about polyphenols that are present in olive oils.

Identification and quantitative determination of carbohydrate molecules in Greek honey by employing 13C NMR spectroscopy

A methodology based on 13C NMR spectroscopy was employed to detect and quantify fourteen mono-, di- and trisaccharide molecules in authentic Greek honey samples with no prior separation. Unambiguous assignment of 13C NMR chemical shifts has been achieved by means of two-dimensional NMR techniques using sugar model compounds. The quantitative 13C NMR method was rigorously validated (accuracy, linearity, range, limit of detection, etc.) using either single sugar molecules, or artificial mixtures of isoglucose (glucopyranose and fructose) and global mixtures of fourteen model compounds. Subsequent integration of appropriate signals in the 13C NMR spectra allowed the quantification of these compounds. The present methodology has been applied to authentic Greek honey samples and provided quantitative results for 28 sugar tautomers. The observed differentials in the content of these biomarkers amongst the various honey samples of different botanical origins are expected to form the basis for the development of a sensitive method that can be used to obtain valuable information about the authenticity of honey.

Egg yolk identification and aging in mixed paint binding media by NMR spectroscopy.

NMR spectroscopy is a powerful analytical tool for the identification and quantitative analysis of organic materials in a cultural heritage context. In this report, we present an analytical NMR protocol for the identification and semiquantification of egg yolk binders and mixed binding media that also contain a drying oil, namely linseed oil. The samples studied have been artificially and/or naturally aged in order to simulate the composition of organic materials in paintings. Analysis of the 1D and 2D NMR spectra showed that egg yolk can be identified even in binding media of considerable age via signals originating from cholesterol and/or cholesterol oxidation products present in the aged binding medium. Based on cholesterol‐related and other lipid signals in the NMR spectra of egg yolk binders, a molecular marker (R/F) that suggests the presence of egg yolk in paint binders is proposed. Via this marker, the presence of egg yolk in the organic material obtained from an early 18th century Greek icon is confirmed, and this is further verified by 2D NMR spectroscopy. It is demonstrated that NMR molecular markers developed to estimate the hydrolysis/oxidation state of oil paintings are also suitable for the analysis of egg yolk and mixed medium (egg yolk–linseed oil) binders, indicating the generality of the NMR methodological approach in the analysis of organic materials in a cultural heritage context. Copyright

NMR-based metabolomics in wine quality control and authentication

A comprehensive summary of research work related to applications of NMR spectroscopy in combination with multivariate statistical analysis techniques for the analysis, quality control, and authentication of wine is presented. NMR spectroscopy is used to obtain the non-volatile metabolic profile and/or phenolic profile of wines, with the help of 2D NMR spectroscopy. Metabolomics is then used as an analytical tool to investigate the variability of the metabolic profile of wines due to a series of different factors involved during wine production, including terroir, pedoclimatic conditions, vintage, vineyard practices, wine-making, barrel maturation, and aging. The discriminating power of the NMR-obtained wine metabolome is utilized as a wholistic analytical approach in efforts to authenticate wine with respect to important economic attributes, such as cultivar, vintage, and geographical origin.Graphical abstract.

Application of NMR in food analysis

This chapter is devoted to applications of NMR in food analysis between January 2010 and June 2015, the term NMR encompassing a broad range of magnetic resonance applications, including spectroscopy, imaging and relaxation. The data included are arranged in subchapters according to food type (beverages, fats/oils fruits/vegetables, meat, dairy etc.), to help the reader locate relevant information.