The multiple hybrid bootstrap — Resampling multivariate linear processes

The paper reconsiders the autoregressive aided periodogram bootstrap (AAPB) which has been suggested in Kreiss and Paparoditis (2003) [18]. Their idea was to combine a time domain parametric and a frequency domain nonparametric bootstrap to mimic not only a part but as much as possible the complete covariance structure of the underlying time series. We extend the AAPB in two directions. Our procedure explicitly leads to bootstrap observations in the time domain and it is applicable to multivariate linear processes, but agrees exactly with the AAPB in the univariate case, when applied to functionals of the periodogram. The asymptotic theory developed shows validity of the multiple hybrid bootstrap procedure for the sample mean, kernel spectral density estimates and, with less generality, for autocovariances.     

Two Novel Thermal Biradical Cyclizations in Theory and Experiment: New Synthetic Routes to 6H-Indolo[2,3-b]quinolines and 2-Aminoquinolines from Enyne-Carbodiimides

The regioselectivity of the biradical cyclization of enyne-carbodiimides 1 can easily be controlled by variation of R¹ at the alkyne terminus. Attachment of a hydrogen atom (R¹=H) leads to C²–C⁷ cyclization and formation of biradical 2 , whereas C²–C⁶ cyclization to provide biradical 3 is observed with R¹=Me₃Si or Ph.     

Two Novel Thermal Biradical Cyclizations of Enyne-Ketenimines: Theory,Experiment, and Synthetic Potential

Both benzocarbazoles and quinolines can be synthesized from enyne ketenimines 1 generated in situ via biradical intermediates (see reaction below). Which of the heterocyclic ring systems is formed depends on the choice of the substituent R¹ at the alkyne terminus.     

Laminare Wolframsäure

Ohne Zusammenfassung     

MALDI imaging in human skin tissue sections: focus on various matrices and enzymes

Matrix-assisted laser/desorption ionization (MALDI) mass-spectrometric imaging (MSI), also known as MALDI imaging, is a powerful technique for mapping biological molecules such as endogenous proteins and peptides in human skin tissue sections. A few groups have endeavored to apply MALDI-MSI to the field of skin research; however, a comprehensive article dealing with skin tissue sections and the application of various matrices and enzymes is not available. Our aim is to present a multiplex method, based on MALDI-MSI, to obtain the maximum information from skin tissue sections. Various matrices were applied to skin tissue sections: (1) 9-aminoacridine for imaging metabolites in negative ion mode; (2) sinapinic acid to obtain protein distributions; (3) α-cyano-4-hydroxycinnamic acid subsequent to on-tissue enzymatic digestion by trypsin, elastase, and pepsin, respectively, to localize the resulting peptides. Notably, substantial amounts of data were generated from the distributions retrieved for all matrices applied. Several primary metabolites, e.g. ATP, were localized and subsequently identified by on-tissue postsource decay measurements. Furthermore, maps of proteins and peptides derived from on-tissue digests were generated. Identification of peptides was achieved by elution with different solvents, mixing with α-cyano-4-hydroxycinnamic acid, and subsequent tandem mass spectrometry (MS/MS) measurements, thereby avoiding on-tissue MS/MS measurements. Highly abundant peptides were identified, allowing their use as internal calibrants in future MALDI-MSI analyses of human skin tissue sections. Elastin as an endogenous skin protein was identified only by use of elastase, showing the high potential of alternative enzymes. The results show the versatility of MALDI-MSI in the field of skin research. This article containing a methodological perspective depicts the basics for a comprehensive comparison of various skin states.

Energy dependence of the total reaction cross section for Br− + CH4

The energy dependence of the total cross section for the reaction Br^? + CH₄ → CH₂Br^? + H₂ was measured in a beam experiment. From the threshold energy it can be assumed that the above reaction proceeds via the same transition state as the nucleophilic substitution leading to the also observed H^?. Thus we propose Br^? + CH₄ → [CH₄Br^?]

     

Raman spectroscopy of carbonization films and carbonaceous limiters in fusion vessels

The Raman signal of hydrogenated and deuterated amorphous carbon-films, respectively, is dominated by the resonance Raman spectrum of clusters. Loss of H and D by thermal annealing sharpens and shifts Raman bands analogous to the case of annealing of amorphous carbon and ion bombarded graphite. H ₂ ⁺ and D ₂ ⁺ bombarded graphite displays a weak signal assigned to diamond clusters.     

Thermal C2-C6 cyclization of enyne-carbodiimides: experimental evidence contradicts a diradical and suggests a carbene intermediate

Mechanistic details of the thermal C2-C6 cyclization of enyne-carbodiimides are investigated. A variety of product and kinetic studies on solvent and substituent effects open the way for a deeper mechanistic understanding. Nonlinear Hammett correlations suggest that a change of mechanism takes place: the thermal C2-C6 cyclization of enyne-carbodiimides with electron-withdrawing substituents may be best described as a coarctate cyclization to a carbene and with electron-donating substituents as a polar cyclization to a carbene with strong zwitterionic character. Theoretical investigations had originally suggested a diradical intermediate. DFT computations and NBO analysis for the parent diazafulvenediyl are in agreement with a carbene intermediate. While any intermolecular trapping of the intermediate failed, the formation of the C-H insertion product 19 strongly supports the carbene hypothesis.