Profiling food volatiles by comprehensive two-dimensional ga schromatography coupled with mass spectrometry: Advanced fingerprinting approaches for comparative analysis of the volatile fraction of roasted hazelnuts (Corylus avellana L.) from different origins

This study examined how advanced fingerprinting methods (i.e., non-targeted methods) provide reliable and specific information about groups of samples based on their component distribution on the GC × GC chromatographic plane. The volatile fractions of roasted hazelnuts (Corylus avellana L.) from nine different geographical origins, comparably roasted for desirable flavor and texture, were sampled by headspace-solid phase micro extraction (HS-SPME) and then analyzed by GC × GC-qMS. The resulting patterns were processed by: (a) “chromatographic fingerprinting”, i.e., a pattern recognition procedure based on retention-time criteria, where peaks correspondences were established through a comprehensive peak pattern covering the chromatographic plane; and (b) “comprehensive template matching” with reliable peak matching, where peak correspondences were constrained by retention time and MS fragmentation pattern similarity criteria. Fingerprinting results showed how the discrimination potential of GC × GC can be increased by including in sample comparisons and correlations all the detected components and, in addition, provide reliable results in a comparative analysis by locating compounds with a significant role. Results were completed by a chemical speciation of volatiles and sample profiling was extended to known markers whose distribution can be correlated to sensory properties, geographical origin, or the effect of thermal treatment on different classes of compounds. The comprehensive approach for data interpretation here proposed may be useful to assess product specificity and quality, through measurable parameters strictly and consistently correlated to sensory properties and origin.     

Optimized use of a 50 μm ID secondary column in comprehensive two-dimensional gas chromatography–mass spectrometry

The objective of the present research is directed towards the optimized use of a 50 μm ID secondary column, in a comprehensive two-dimensional gas chromatography–quadrupole mass spectrometry (GC × GC–qMS) system. The analytical aim was achieved by exploiting a split-flow GC × GC approach, and a rapid-scanning qMS instrument. The stationary phase combination consisted of an apolar (silphenylene polymer) 30 m × 0.25 mm ID column, linked by means of a Y-union, to an MS-connected 1 m × 0.05 mm ID polar one [poly(ethyleneglycol)], and to a 0.20 m × 0.05 mm ID uncoated capillary segment; the latter was connected to a manually operated split-valve. It will be herein demonstrated that the split-flow GC × GC approach, successfully employed in previous H₂-based, flame ionization detection experiments, provides equally satisfactory results using mass spectrometric detection and helium as carrier gas. An optimized split-flow GC × GC–qMS method was developed and exploited for the analysis of a perfume sample. The results attained were compared with those observed using the same analytical column combination, but with no flow-splitting. It was found that it is not convenient to employ a 50 μm ID secondary column in a conventional GC × GC–MS instrument. On the contrary, the use a 50 μm ID secondary column, in a split-flow, twin-oven system, provided a good performance. A recently developed comprehensive chromatography software was used for data processing.     

Determination of synthetic phenolic antioxidants and their metabolites in water samples by downscaled solid-phase extraction,silylation and gas chromatography–mass spectrometry

The development and performance evaluation of an analytical method dedicated to the comprehensive determination of the most relevant antioxidants and their metabolites in aqueous environmental samples is presented. This was achieved by a miniaturised solid-phase extraction (SPE) with 10 mg Oasis HLB cartridges, which allow to achieve a concentration factor of 200, reducing organic solvent wastes (1 mL of ethyl acetate suffices for complete elution) and SPE costs and eliminating the need for solvent evaporation that otherwise compromises the recoveries of butylated hydroxytoluene (BHT) and 2,6-di-tert-butylcyclohexa-2,5-diene-1,4-dione (BHT-Q). Analytes were then determined by gas chromatography–mass spectrometry (GC–MS) after derivatisation with N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA) in a single run. BHT-d₇ and n-propyl-paraben-d₄ (PrP-d₄) were used as surrogate internal standards. These surrogates allowed obtaining relative recoveries in the 80–110% range for all analytes even with complex wastewater samples and LODs at the 2–44 ng L⁻¹ level taking into account blank issues often associated to antioxidants analysis. The method was applied to sewage and river waters, showing that the seven analytes could be detected in raw wastewater. BHT and BHT-Q were the most concentrated species in that type of sample (in the 275–871 ng L⁻¹ range). On the other hand two metabolites of BHT, 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO) and 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHT-COOH) appeared to be the most ubiquitous species, being found in all samples in the 10–150 ng L⁻¹ concentration range.     

Magnetostructural Correlations in Tetrairon(III) Single‐Molecule Magnets

Tunable single‐molecule magnets : The spin‐level landscape in a series of Fe^III₄ single‐molecule magnets with propeller‐like structure was analyzed by means of high‐frequency EPR spectroscopy. The zero‐field splitting parameter D of the ground S=5 spin state correlates strongly with the pitch of the propeller γ (see picture), and thus provides a simple link between molecular structure and magnetic behavior.

     

Electrostatically immobilised BOX and PYBOX metal catalysts: application to ene reactions

Copper(I), copper(II) and scandium(III) triflate complexes of BOX and PYBOX ligands have been electrostatically immobilised on silica. The performance of the immobilised catalysts, in the two carbonyl-ene reactions studied, compares very well with that of their homogeneous equivalents. The immobilised catalysts were successfully reused a number of times. In the case of a scandium complex, a variation in enantioselectivity of up to 73% was observed on immobilisation compared to its use homogeneously. The reason for this variation in enantioselectivity is explored with the aid of molecular modelling.     

Multifractal rainfall extremes: Theoretical analysis and practical estimation

We study the extremes generated by a multifractal model of temporal rainfall and propose a practical method to estimate the Intensity–Duration–Frequency (IDF) curves. The model assumes that rainfall is a sequence of independent and identically distributed multiplicative cascades of the beta-lognormal type, with common duration D. When properly fitted to data, this simple model was found to produce accurate IDF results [Langousis A, Veneziano D. Intensity–duration–frequency curves from scaling representations of rainfall. Water Resour Res 2007;43. doi:10.1029/2006WR005245]. Previous studies also showed that the IDF values from multifractal representations of rainfall scale with duration d and return period T under either d → 0 or T → ∞, with different scaling exponents in the two cases. We determine the regions of the (d, T)-plane in which each asymptotic scaling behavior applies in good approximation, find expressions for the IDF values in the scaling and non-scaling regimes, and quantify the bias when estimating the asymptotic power-law tail of rainfall intensity from finite-duration records, as was often done in the past. Numerically calculated exact IDF curves are compared to several analytic approximations. The approximations are found to be accurate and are used to propose a practical IDF estimation procedure.     

Highly Emissive Nanostructured Thin Films of Organic Host–Guests for Energy Conversion

All‐organic nanostructured host–guest materials (see picture) show enhanced, tunable fluorescence due to a high concentration of dyes with controlled spatial and geometrical organization that allows controlled resonant energy transfer. Homogeneous films of deoxycholic acid host–guests, provide coatings that convert near‐UV light into blue light with an efficiency higher than that of the standard polymeric blends.

     

RP–HPLC–ESI–MS characterization of novel peptide fragments related to rat parotid secretory protein in parasympathetic induced saliva

Two peptides (MW 1211.7 and 928.5 Da) were detected by RP–HPLC–ESI–MS analysis of parotid saliva secreted upon continuous parasympathetic stimulation. The peptide with the higher mass (PSPFr‐A) corresponded to the N‐terminal dodecapeptide (Fragment 1–12) of rat parotid secretory protein (PSP), while the peptide with the lower mass (PSPFr‐B) corresponded to the 4–12 fragment of the same protein. During stimulation, the PSPFr‐A secretion increased, while the PSPFr‐B secretion decreased (HPLC–ESI–MS). In the presence of cycloheximide, PSPFr‐A was not demonstrated, while the PSPFr‐B secretion decreased. In the presence of aprotinin, the PSPFr‐B secretion was almost abolished, while the PSPFr‐A secretion increased to higher levels than those observed in the absence of the inhibitor. In vitro perfusion, with artificial solution, of stimulated rat parotid glands excluded that the fragments were derived from the circulation. Neither peptide occurred in enriched granule preparations from unstimulated glands. The results suggest that at least two pathways – granular and vesicular – are responsible for the generation of the two peptides. PSPFr‐A is the first cleavage product in both pathways. PRPFr‐B is probably generated from granular PSPFr‐A only and, at the end of the granule mediated pathway, by the action of an enzyme of the serine protease class.     

Combined liquid chromatography-coulometric detection and microextraction by packed sorbent for the plasma analysis of long acting opioids in heroin addicted patients

The sublingual combination of buprenorphine and naloxone (Suboxone^®) and Methadone Maintenance Therapy have been found effective in treating heroin addiction. A new analytical method suitable for the simultaneous determination of buprenorphine, norbuprenorphine, methadone and naloxone in human plasma by means of liquid chromatography with coulometric detection has been developed. The chromatographic separation was achieved with a phosphate buffer–acetonitrile mixture as the mobile phase on a cyano column. The monitoring cell of the coulometric detector was set at an oxidation potential of +0.600 V. A rapid clean-up procedure of the biological samples using a microextraction by packed sorbent technique has been implemented, employing a C8 sorbent inserted into a syringe needle. The extraction yield values were satisfactory for all analytes (>85%). The calibration curves were linear over a range of 0.25–20.0 ng mL⁻¹ for buprenorphine and norbuprenorphine, 3.0–1000.0 ng mL⁻¹ for methadone and 0.13–10.0 ng mL⁻¹ for naloxone. The sensitivity was also high with limits of detection of 0.08 ng mL⁻¹ for both buprenorphine and norbuprenorphine, 0.9 ng mL⁻¹ for methadone and 0.04 ng mL⁻¹ for naloxone. The intraday and interday precision data were always satisfactory.The method was successfully applied to plasma samples obtained from former heroin addicts treated with opioid replacement therapy.     

Zn2+'s ability to alter the distribution of Cu2+ among the available binding sites of Aβ(1-16)-polyethylenglycol-ylated peptide: implications in Alzheimer's disease

The formation of mixed copper(II) and zinc(II) complexes with Aβ(1-16)-PEG has been investigated. The peptide fragment forms stable mixed metal complexes at physiological pH in which the His13/His14 dyad is the zinc(II)'s preferred binding site, while copper(II) coordination occurs at the N-terminus also involving the His6 imidazole. Copper(II) is prevented by zinc(II) excess from the binding to the two His residues, His13 and His14. As the latter binding mode has been recently invoked to explain the redox activity of the copper-Aβ complex, the formation of ternary metal complexes may justify the recently proposed protective role of zinc(II) in Alzheimer's disease. Therefore, the reported results suggest that zinc(II) competes with copper for Aβ binding and inhibits copper-mediated Aβ redox chemistry.