A mutasynthesis approach with a Penicillium chrysogenum ΔroqA strain yields new roquefortine D analogues.

Penicillium chrysogenum, which lacks the roqA gene, processes synthetic, exogenously added histidyltryptophanyldiketopiperazine (HTD) to yield a set of roquefortine-based secondary metabolites also produced by the wild-type strain. Feeding a number of synthetic HTD analogues to the ΔroqA strain gives rise to the biosynthesis of a number of new roquefortine D derivatives, depending on the nature of the synthetic HTD added. Besides delivering semisynthetic roquefortine analogues, the mutasynthesis studies presented here also shed light on the substrate preferences and molecular mechanisms employed by the roquefortine C/D biosynthesis gene cluster, knowledge that may be tapped for the future development of more complex semisynthetic roquefortine-based secondary metabolites.

Structural characterization of arabinoxylans from two African plant species Eragrostis nindensis and Eragrostis tef using various mass spectrometric methods.

RATIONALE: The arabinoxylans are one of the main components of plant cell walls and are known to play major roles in plant tissues properties depending in particular on their structural features. It has been recently shown that one of the strategies developed by resurrection plants to overcome dehydration is based on cell wall composition. For this purpose, the structural characterization of arabinoxylans from desiccation-tolerant grass Eragrostis nindensis (E. nindensis) was compared with its close relative, the desiccation-sensitive Eragrostis tef (E. tef) in order to further understand mechansism of desiccation tolerance in resurrection plants. METHODS: Ion mobility spectrometry coupled to mass spectrometry (IM-MS) in combination with the conventional mass spectrometric approaches, including matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)) and gas chromatography/mass spectrometry (GC/MS), were used to characterize arabinoxylan fragments obtained after endo-xylanase digestion of leave extracts from E. nindensis and E. tef. RESULTS: Whole fingerprinting by MALDI-MS analysis showed the presence of various arabinoxylan fragments within leaves of E. nindensis and E. tef. The monosaccharide composition and some linkage information were determined by GC/MS experiments. Information regarding the branching and sequence details was obtained by ESI-MS(n) experiments after sample permethylation. The presence of structural isomeric ions with different collision cross sections was evidenced by IM-MS which could be differentiated using ESI-MS(n). CONCLUSIONS: We have shown that an orthogonal approach, and especially IM-MS associated to ESI-MS(n) (n = 2 to 4) and GC/MS allowed characterization of arabinoxylan fragments of E. nindensis and E. tef and revealed the presence of isomeric structures. The same arabinoxylan structures were identified for both species but in different relative abundance. Moreover, this work illustrated that IM-MS can efficiently separate isomeric structures and advantageously complements the conventional mass spectrometric methodologies used for arabinoxylan structural characterization.

Investigation of dendriplexes by ion mobility-mass spectrometry.

Highly branched polyamidoamine (PAMAM) dendrimers presenting biological activities have been envisaged as non-viral gene delivery vectors. They are known to associate with nucleic acid (DNA) in non-covalent complexes via electrostatic interactions. Although their transfection efficiency has been proved, PAMAMs present a significant cytotoxicity due to their cationic surface. To overcome such a drawback, different chemical modifications of the PAMAM surface have been reported such as the attachment of hydrophobic residues. In the present work, we studied the complexation of DNA duplexes with different low-generation PAMAM; ammonia-cored G0(N) and G1(N) PAMAM, native or chemically modified with aromatic residues, i.e., phenyl-modified-PAMAM G0(N) and phenylalanine-modified-PAMAM G1(N). To investigate the interactions involved in the PAMAM/DNA complexes, also called dendriplexes, we used electrospray ionization (ESI) coupled to ion mobility spectrometry-mass-spectrometry (IM-MS). ESI is known to allow the study of non-covalent complexes in native conditions while IM-MS is a bidimensional separation technique particularly useful for the characterization of complex mixtures. IM-MS allows the separation of the expected complexes, possible additional non-specific complexes and the free ligands. Tandem mass spectrometry (MS/MS) was also used for the structural characterization. This work highlights the contribution of IM-MS and MS/MS for the study of small dendriplexes. The stoichiometries of the complexes and the equilibrium dissociation constants were determined. The [DNA/native PAMAM] and [DNA/modified-PAMAM] dendriplexes were compared.

Identification of ion series using ion mobility mass spectrometry: the example of alkyl-benzothiophene and alkyl-dibenzothiophene ions in diesel fuels.

Ion mobility-mass spectrometry (IMMS) has been presented as a promising method for analysis of highly complex mixtures. This coupling adds an additional postionization separation dimension to MS. The IM separation of ions is obtained in the millisecond time scale and can be particularly helpful when chromatographic separation is not possible. For obtaining relevant information about the samples, data processing is usually the bottleneck because of the high amount of data generated with IMMS. In the current work, we present a new workflow using specific comparison software dedicated to IMMS data, which allows one to compare m/z-drift time plots to highlight differences between samples. Two diesel fuels have been compared, i.e., the feed and the product of hydrodesulfurization (HDS) process, and this approach allowed us to clearly highlight the variation of intensity of several ions distributed along the plots of both samples. Accurate mass measurements and post IM collision induced dissociation experiments allowed us to identify two series of polycyclic aromatic sulfur-containing heterocycle (PASH) compounds among the matrix ions.

Atmospheric solid analysis probe-ion mobility mass spectrometry of polypropylene.

Polyolefin, including polypropylene (PP), constitutes an important class of materials. In particular, the recent interest in recycling plastic wastes necessitates their characterization as well as their degradation mechanism being understood. PP materials characterization by mass spectrometry, including polymer and additives parts, is not direct and generally involves a pyrolysis step to produce ionizable species. In this study, we extended the use of atmospheric solid analysis probe (ASAP) in combination with traveling wave ion mobility mass spectrometry (TWIM-MS) for the characterization of PP materials, including polymer as well as additives. Different commercial PP samples, from polymer standard to plastic item, were studied. The use of ASAP allow analysis to be done without any sample preparation, while TWIM-MS permitted a clear separation of polymer ions and additive signals. Several series of polymer pyrolysis residues, similar to those produced by classic pyrolysis, were obtained. Moreover, additive characterization has been done and supported by accurate mass measurements and tandem mass spectrometry experiments. Finally, this strategy put in evidence the role of additives in polymer degradation.

Formation of unexpected ions from a first-generation polyamidoamine dendrimer by use of methanol: an artefact due to electrospray emitter corrosion?

We report the formation of unexpected ions during the analyses of a first-generation polyamidoamine dendrimer in negative ion mode using an ion trap equipped with an electrospray ionisation source. These surprising ions corresponded to an increase of 12 m/z units over those expected. The formation of the unexpected ions was dependent on the tuning of the solution flow rate and the capillary high voltage. In addition, measurements of unusual value of the current suggested that a reaction was occurring in the corona plasma. The influence of methanol in this phenomenon was demonstrated by using CD(3)OH in the sample preparation. We propose two structures to explain the observed adduct based on the results of MS(2) experiments and by referring to previous work dealing with 12 m/z units addition. We showed that a corona discharge caused by alterations taking place to the electrospray capillary emitter was the origin of these unexpected ions. Finally, we discuss the mechanism involved in the formation of the ions and we propose means to control such artefacts.

Adaptive Incremental Mixture Markov Chain Monte Carlo.

We propose adaptive incremental mixture Markov chain Monte Carlo (AIMM), a novel approach to sample from challenging probability distributions defined on a general state-space. While adaptive MCMC methods usually update a parametric proposal kernel with a global rule, AIMM locally adapts a semiparametric kernel. AIMM is based on an independent Metropolis-Hastings proposal distribution which takes the form of a finite mixture of Gaussian distributions. Central to this approach is the idea that the proposal distribution adapts to the target by locally adding a mixture component when the discrepancy between the proposal mixture and the target is deemed to be too large. As a result, the number of components in the mixture proposal is not fixed in advance. Theoretically, we prove that there exists a stochastic process that can be made arbitrarily close to AIMM and that converges to the correct target distribution. We also illustrate that it performs well in practice in a variety of challenging situations, including high-dimensional and multimodal target distributions. Finally, the methodology is successfully applied to two real data examples, including the Bayesian inference of a semiparametric regression model for the Boston Housing dataset. Supplementary materials for this article are available online.

Analysis of oxysterols and vitamin D metabolites in mouse brain and cell line samples by ultra-high-performance liquid chromatography-atmospheric pressure photoionization-mass spectrometry.

We have developed an ultra-high-performance liquid chromatography-atmospheric pressure photoionization-tandem mass spectrometric (UHPLC-APPI-MS/MS) method for the simultaneous quantitative analyses of several oxysterols and vitamin D metabolites in mouse brain and cell line samples. An UHPLC-APPI-high resolution mass spectrometric (UHPLC-APPI-HRMS) method that uses a quadrupole-time of flight mass spectrometer was also developed for confirmatory analysis and for the identification of non-targeted oxysterols. Both methods showed good quantitative performance. Furthermore, APPI provides high ionization efficiency for determining oxysterols and vitamin D related compounds without the time consuming derivatization step needed in the conventionally used electrospray ionization method to achieve acceptable sensitivity. Several oxysterols were quantified in mouse brain and cell line samples. Additionally, 25-hydroxyvitamin D3 was detected in mouse brain samples for the first time.

Traveling wave ion mobility mass spectrometry study of low generation polyamidoamine dendrimers.

We reported the use of ion mobility (IM) combined with mass spectrometry (MS) as an analytical tool to investigate low generation polyamidoanine (PAMAM) dendrimers. This analytical approach has been employed to separate ions of defective structures with different charge state but exactly the same m/z value. Tandem mass spectrometry (MS/MS) after IM separation allowed a comprehensive structural characterization of defective dendrimers. In addition, IM was used to evaluate the collision cross-sections of ions of perfect dendrimers. They showed a good correlation with calculated collision cross-sections obtained by the trajectory method (TM) and were also consistent with dimensions reported by other established analytical methods.

Detecting aircraft with a low-resolution infrared sensor.

Existing computer simulations of aircraft infrared signature (IRS) do not account for dispersion induced by uncertainty on input data, such as aircraft aspect angles and meteorological conditions. As a result, they are of little use to estimate the detection performance of IR optronic systems; in this case, the scenario encompasses a lot of possible situations that must be indeed addressed, but cannot be singly simulated. In this paper, we focus on low-resolution infrared sensors and we propose a methodological approach for predicting simulated IRS dispersion of poorly known aircraft and performing aircraft detection on the resulting set of low-resolution infrared images. It is based on a sensitivity analysis, which identifies inputs that have negligible influence on the computed IRS and can be set at a constant value, on a quasi-Monte Carlo survey of the code output dispersion, and on a new detection test taking advantage of level sets estimation. This method is illustrated in a typical scenario, i.e., a daylight air-to-ground full-frontal attack by a generic combat aircraft flying at low altitude, over a database of 90,000 simulated aircraft images. Assuming a white noise or a fractional Brownian background model, detection performances are very promising.