Direct mass spectrometry of polymers. VII. Primary thermal fragmentation processes in polycarbonates

The primary fragmentation mechanisms in the thermal decomposition of several polycarbonates were studied by direct pyrolysis into the mass spectrometer. Our results indicate that ester exchange reactions predominate in the primary thermal fragmentation process of polycarbonates, causing the formation of cyclic oligomers.     

Epoxycarotenoids esters analysis in intact orange juices using two‐dimensional comprehensive liquid chromatography

In this work, the native carotenoid pattern of different orange juices was studied by LC×LC‐DAD/APCI‐IT‐TOF‐MS for the first time. Special attention was given to the epoxycarotenoids components. It has been already proposed that the relative proportions and composition of these epoxycarotenoids can be used to estimate the age and freshness of an orange juice. Re‐arrangements from 5,6‐ to 5,8‐epoxides can occur with time, partially due to the natural acidity of the juices. Thus, the study of these carotenoids in their intact form, that is, esterified with fatty acids, is of great interest. Besides, other free carotenoid and carotenoids esters were identified in seven different monovarietal orange juices and a commercial orange juice. Moreover, the higher separation power of the present LC×LC approach allowed a clearer identification of the compounds contained in the sample compared to the more commonly used approach which uses C₃₀ stationary phases in conventional LC, thanks to the attainment of clearer MS spectra due to the higher resolution and separation degree obtained in LC×LC. This method could also be used to establish authenticity markers among orange varieties that could be potentially used to prevent or detect adulterations or to establish ripeness indexes.     

Hemispherodextrins, a new class of cyclodextrin derivatives, in capillary electrophoresis

A capped cyclodextrin derivative (THCMH), called hemispherodextrin, was observed to behave as a very efficient chiral selector for a variety of phenoxyacid enantiomeric pairs, both at pH 6 and pH 9. The very low concentration necessary to obtain separation was particularly impressive. The behaviour of THCMH was compared with that of other hemispherodextrins and cyclodextrin derivatives and the conclusions are reported. Some interesting conclusions are drawn by comparing the behaviour of THCMH with that of other hemispherodextrins reported elsewhere.     

The Hilbert function of a curve lying on a smooth cubic surface

Summary Let C be any reduced and irreducible curve, lying on a smooth cubic surface S P ³. In this paper we determine the Hilbert function of C. Moreover we characterize some kinds of curves on S: the arithmetically Cohen-Macaulay curves, the maximal rank curves and the extremal ones.Work done with financial support of M.P.I., while the author was a member of C.N.R.     

Characterization of the pigment fraction in sweet bell peppers (Capsicum annuum L.) harvested at green and overripe yellow and red stages by offline multidimensional convergence chromatography/liquid chromatography–mass spectrometry

Offline multidimensional supercritical fluid chromatography combined with reversed‐phase liquid chromatography was employed for the carotenoid and chlorophyll characterization in different sweet bell peppers (Capsicum annuum L.) for the first time. The first dimension consisted of an Acquity HSS C₁₈ SB (100 × 3 mm id, 1.8 μm particles) column operated with a supercritical mobile phase in an ultra‐performance convergence chromatography system, whereas the second dimension was performed in reversed‐phase mode with a C₃₀ (250 × 4.6 mm id, 3.0 μm particles) stationary phase combined with photodiode array and mass spectrometry detection. This approach allowed the determination of 115 different compounds belonging to chlorophylls, free xanthophylls, free carotenes, xanthophyll monoesters, and xanthophyll diesters, and proved to be a significant improvement in the pigments determination compared to the conventional one‐dimensional liquid chromatography approach so far applied to the carotenoid analysis in the studied species. Moreover, the present study also aimed to investigate and to compare the carotenoid stability and composition in overripe yellow and red bell peppers collected directly from the plant, thus also evaluating whether biochemical changes are linked to carotenoid degradation in the nonclimacteric investigated fruits, for the first time.     

Direct mass spectrometry of polymers. XII. Thermal fragmentation processes in poly-α-aminoacids

The thermal fragmentation processes in poly-α-aminoacids have been investigated by direct pyrolysis–Mass Spectrometry. The mass spectral data show that the pyrolytic breakdown of polyglycine, polysarcosine, and polyproline leads to the formation of cyclic oligomers. Polyalanine, polyphenylalanine, and polytyrosine decompose yielding compounds with olefin and nitrile end-groups. Finally, in the case of poly-α-methylglutamate, the primary thermal process is the loss of methanol with consequent formation, along the polymer chain, of pyroglutamic units, which yield cyclic dimer as main pyrolysis product.     

Analysis of native carotenoid composition in orange juice using C30 columns in tandem

In the present contribution, a novel analytical approach based on using serial coupled conventional LC columns is proposed to the study of the native carotenoid composition of orange juice. The great difficulties that are found when analyzing complex carotenoid samples, due to the high natural variability of these compounds as well as to the presence of carotenoid esters are well documented. To overcome some of these limitations, we have developed a methodology including the study of both the saponified and the intact sample by means of two different LC-DAD/APCI-MS methods. The increase in the resolution and separation power obtained when using two serial coupled C(30) columns is demonstrated, and significant increases in peak capacity have been achieved. By using this new methodology, 44 different carotenoids have been tentatively identified. Among them, several violaxanthin diesters have been directly identified in orange juice for the first time. The main carotenoids in orange juice were violaxanthin, lutein, luteoxanthin, 9-cis-antheraxanthin, and beta-cryptoxanthin. Some of them were found in both their free and esterified forms. To the best of our knowledge, this is the first application of serial couplings of C(30) columns for the identification of the native carotenoid composition of natural matrices.     

Combined cup loading, bis(2-hydroxyethyl) disulfide, and protein precipitation protocols to improve the alkaline proteome of Lactobacillus hilgardii

Despite the large number of papers dealing with bacterial proteomes, very few include information about proteins with alkaline pI's, because of the limits inherent in 2-DE technology. Nonetheless, analyses of in silico proteomes of many prokaryotes show a bimodal distribution of their proteins based on their pI's; the most crowded areas lying between pI 4-7 and 9-11. The aim of the present research was to set up a general, simple, and standardizable 2-DE protocol suitable for studying the alkaline proteome of Lactobacillus hilgardii, a Gram-positive bacillus isolated from wine. The method has also been tested on a Gram-negative bacterium able to degrade aromatic pollutants, Acinetobacter radioresistens S13. Optimization of the method was mainly focused on improving protein extraction and IEF (pI 6-11) separation protocols. Concerning IEF, different methods for sample loading (in-gel rehydration and cup loading), and different reducing agents (DTT and bis(2-hydroxyethyl) disulfide (HED)) were tested and compared. The proposed protocol was found to resolve efficiently alkaline proteins from both of our Lactobacillus and Acinetobacter strains, in spite of their different external layers, thus, enabling a more comprehensive study of their proteomes.     

IDEA: interface dynamics and energetics algorithm

IDEA, interface dynamics and energetics algorithm, was implemented, in FORTRAN, under different operating systems to mimic dynamics and energetics of elementary events involved in interfacial processes. The code included a parallel elaboration scheme in which both the stochastic and the deterministic components, involved in the developed physical model, worked simultaneously. IDEA also embodied an optionally running VISUAL subroutine, showing the dynamic energy changes caused by the surface events, e.g., occurring at the gas-solid interface. Monte Carlo and ordinary differential equation system subroutines were employed in a synergistic way to drive the occurrence of the elementary events and to manage the implied energy flows, respectively. Biphase processes, namely isothermal and isobaric adsorption of carbon monoxide on nickel, palladium, and platinum surfaces, were first studied to test the capability of the code in modeling real frames. On the whole, the simulated results showed that IDEA could reproduce the inner characteristics of the studied systems and predict properties not yet experimentally investigated.     

Comparison of available analytical methods to measure trans-octadecenoic acid isomeric profile and content by gas-liquid chromatography in milk fat

Accurate quantification of trans-fatty acids (TFAs) could be achieved by infrared spectroscopy or by gas-liquid chromatography (GLC). Accurate quantification by GLC should be achieved using specific highly polar capillary columns such as 100 m CP-Sil 88 or equivalent. A pre-fractionation of cis and trans-fatty acids could be performed by silver-ion thin-layer chromatography (Ag-TLC), silver-ion solid-phase extraction (Ag-SPE), or by high-performance liquid-chromatography (HPLC). A pre-fractionation step allows accurate determination of the isomeric profile but it is not essential to achieve quantification of total trans-18:1 isomers nor to determine the level of vaccenic (trans-11 18:1) acid in dairy fat. TFA content could also be calculated in milk fat based on the TAG profile determined by GLC. In this paper, different GLC methods suitable to measure the total of trans-18:1 isomers, vaccenic acid and trans-18:1 acid isomeric distribution in milk fat were compared. Pre-separation of cis- and trans-18:1 isomers by Ag-TLC followed by GLC analysis under optimal conditions was selected as the reference method. Results obtained using alternative methods including pre-separation by HPLC followed by GLC analysis, direct quantification by GLC or calculation from the triacylglycerol (TAG) profile were compared to data acquired using the reference method. Results showed that accurate quantification of total trans-18:1 isomers and vaccenic acid could be achieved by direct quantification by GLC under optimal chromatographic conditions. This method represents a very good alternative to Ag-TLC followed by GLC analysis. On the other hand, we showed that pre-fractionation of fatty acid methyl esters (FAMEs) by HPLC represents a good alternative to Ag-TLC, even if some minor isomers are not selectively purified using this procedure.