Mass spectrometry in the characterization of ambers. I. Studies of amber samples of different origin and ages by laser desorption ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization mass spectrometry

Amber is a fossil resin constituted of organic polymers derived through complex maturation processes of the original plant resin. A classification of eight samples of amber of different geological age (Miocene to Triassic) and geographical origin is here proposed using direct mass spectrometric techniques, i.e. laser desorption ionization (LDI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI), in order to obtain a fingerprint related to the amber origin. Differences and similarities were detected among the spectra with the four methods, showing quite complex spectra, full of ionic species in the mass range investigated (up to m/z 2000). The evaluation required statistical analysis involving multivariate techniques. Cluster analysis or principal component analysis (PCA) generally did not show a clear clustering with respect to the age of samples, except for the APPI method, which allowed a satisfying clustering. Using the total ion current (TIC) obtained by the different analytical approaches on equal quantities of the different amber samples and plotted against the age, the only significant correlation appeared to be that involving APPI. To validate the method, four amber samples from Cretaceous of Spain were analyzed. Also in this case a significant correlation with age was found only with APPI data. PCA obtained with TIC values from all the MS methods showed a fair grouping of samples, according to their age. Three main clusters could be detected, belonging to younger, intermediate and older fossil resins, respectively. This MS analysis on crude amber, either solid or extract, followed by appropriate multivariate statistical evaluation, can provide useful information on amber age. The best results are those obtained by APPI, indicating that the quantity of amber soluble components that can be photoionized decreases with increasing age, in agreement with the formation of highly stable, insoluble polymers.     

A new parameter-free correlation functional based on an average atomic reduced density gradient analysis

A new parameter-free correlation functional based on the local Ragot-Cortona approach [J. Chem. Phys. 121, 7671 (2004)] is presented. This functional rests on a single ansatz for the gradient correction enhancement factor: it is assumed to be given by a simple analytic expression satisfying some exact conditions and containing two coefficients. These coefficients are determined without implementing the functional and without using a fitting procedure to experimental data. Their values are determined by requiring that the functional gives a correct average reduced density gradient for atoms, which, to some extent, can be considered an intrinsic atomic property. The correlation functional is then coupled with the Perdew-Burke-Erzernhof (PBE) exchange and compared with the original PBE approach as well as with some other pure density or hybrid approaches. Standard tests for atomic and molecular systems show that our new functional significantly improves on PBE, showing very interesting properties.     

A primal algorithm for the weighted minimum covering ball problem in $$\mathbb {R}^n$$

The nonlinear programming problem of finding the minimum covering ball of a finite set of points in \(\mathbb {R}^n\), with a positive weight corresponding to each point, is solved by a directional search method. At each iteration, the search path is either a ray or the arc of a circle and is determined by bisectors of points. Each step size along the search path is determined explicitly. The primal algorithm is shown to search along the farthest point Voronoi diagram of the given points. We provide computational results that show the efficiency of the algorithm when compared to general convex nonlinear optimization solvers.     

Coordination in a distribution channel with decisions on the nature of incentives and share-dependency on pricing

We research the most suitable coordination mechanism for a distribution channel that is composed of one manufacturer and one retailer. Coordination is sought through a Revenue Sharing Contract (RSC) and the channel members have four coordination options in the menu: The share of revenues can be either set during the course of the game (endogenous) or preset before the game starts (exogenous); similarly, the retail price can be either share-dependent or share-independent. We seek to identify the coordination mechanism that leads to a profit-Pareto-improving situation with respect to a non-coordinated channel that implements a wholesale price contract. We compare players’ profits in the four coordination options and identify the mechanisms that firms prefer. Compared to the non-coordinated channel, our findings suggest that the manufacturer is always economically better-off through coordination, independent of the mechanism the channel uses. In contrast, the retailer is better-off with a share-dependent-pricing mechanism with the share set ex-post. The adoption of a preset share is conditionally beneficial to the parameter fraction. The economic value loss due to the double marginalization cannot be entirely eliminated, independent of the nature (exogenous or endogenous) of the sharing parameter and on the effect of RSC on pricing. In the comparison among coordination mechanisms, only a share-dependent-pricing mechanism with the share fixed over the course of the game is profit-Pareto-improving.     

Reactive oxygen species scavenging activity of flavone glycosides from Melilotus neapolitana

One new and six known flavone glycosides were isolated from the MeOH extract of Melilotus neapolitana Ten. The new compound, identified as 7-O-beta-D-glucopyranosyloxy-4',5-dihydroxy-3-[O-alpha-L-rhamnopyranosyl-(1-->6)-3-O-beta-D-glucopyranosyloxy]flavone (1) by 1D and 2D NMR techniques and mass spectra, was isolated along with kaempferol-3-O-rutinoside (2), kaempferol-3-O-glucoside (3), rutin (4), quercetin-3-O-glucoside (5), isorhamnetin-3-O-rutinoside (6), and isorhamnetin-3-O-glucoside (7). The antioxidant and radical scavenging activities of these compounds and the whole crude methanol extract were evaluated. The organic extract can inhibit MDA marker's synthesis by 57%. All the metabolites displayed good reducing power, with the kaempferol (2,3) and isorhamnetin derivatives (6,7) being less active than the corresponding quercetin derivatives 4,5.     

HPLC with diode-array detection for the simultaneous determination of di(2-ethylhexyl)phthalate and mono(2-ethylhexyl)phthalate in seminal plasma

A high-performance liquid chromatographic method for the simultaneous determination of di(2-ethylhexyl)phthalate (DEHP) and its major metabolite mono(2-ethylhexyl)phthalate (MEHP) in seminal plasma was developed and validated. The method involves liquid-liquid extraction followed by isocratic reversed-phase chromatography with diode-array detection. The recovery, selectivity, linearity, precision and accuracy of the method were evaluated from the analysis of spiked seminal plasma samples. The effect of mobile-phase composition and pH on the retention of the target analytes was investigated. The limits of detection were 0.010 and 0.015 microg/mL, for DEHP and MEHP, respectively. This method was used to analyze real samples in support of clinical studies on these potential endocrine disruptors.     

Multiphasic heterogeneous catalysis mediated by catalyst-philic liquid phases

This critical review addresses heterogeneous catalysis in systems where multiple liquid phases coexist and where one of the phases is catalyst-philic. This technique provides built-in catalyst separation, and product recovery for organic reactions. Focus is placed on the components of the multiphasic systems with emphasis on the constituents of the catalyst-philic phases (PEGs, onium salts, ionic liquids) that incorporate the catalysts, as well as on the effects on catalytic efficiency. It collects a wide body of scattered information that is often labelled with different terms.     

The intriguing case of organic impurities contained in synthetic methanol: a mass spectrometry based investigation

The role of organic impurities in the methanol-to-olefin (MTO) industrial process catalyzed by zeolites is the subject of ongoing debate. We have found that methanol (HPLC and RPE grade) purchased from different chemical companies may contain organic impurities, whose ionization is the dominant process in the positive ion atmospheric pressure chemical ionization (APCI) spectrum of commercial CH(3)OH. Such impurities produce ions with elemental formulae C(n)H(2n+1)O(+) (n = 4, 5, 6); likewise, ionization of tetradeuterated methanol (CD(3)OD) leads to the corresponding fully deuterated series C(n)D(2n+1)O(+) (n = 4, 5, 6), an outcome which represents a clear evidence of their widespread diffusion. We suggest that their formation might be inherent to the chemical process whereby methanol is synthesized on an industrial scale. Mass spectrometry (MS) experiments, gas chromatography/mass spectrometry (GC/MS) analysis and nuclear magnetic resonance (NMR) measurements allowed us to establish that commercial methanol contains dimethyl acetals of simple alkyl ketones, such as propanone, butanone and pentanone. Ab initio calculations (DFT/B3LYP) proved useful to understanding the ionization mechanisms of such impurities.