Mass spectrometric and quantum mechanical analysis of gas-phase formation, structure, and decomposition of various b2 ions and their specifically deuterated analogs

AbstractB ions represent an important type of fragment ions derived from protonated peptides by cleavage of an amide bond with N-terminal charge retention. Such species have also been discussed as key intermediates during cyclic peptide fragmentation. Detailed structural information on such ion types can facilitate the interpretation of multiple step fragmentations such as the formation of inner chain fragments from linear peptides or the fragmentation of cyclic peptides. The structure of different b2 ion isomers was investigated with collision-induced dissociations (CID) in combination with hydrogen/deuterium (H/D) exchange of the acidic protons. Special care was taken to investigate fragment ions derived from pure gas-phase processes. Structures deduced from the results of the CID analysis were compared with structures predicted on the basis of quantum chemical density functional theory (DFT) calculations to be most stable. The results pointed to different types of structures for b2 ion isomers of complementary amino acid sequences. Either the protonated oxazolone structure or the N-terminally protonated immonium ion structure were proposed on the basis of the CID results and the DFT calculations. In addition, the analysis of different selectively N-alkylated peptide analogs revealed mechanistic details of the processes generating b ions

Examination of Protonation-Induced Dinitrogen Splitting by in Situ EXAFS Spectroscopy

The splitting of dinitrogen into nitride complexes emerged as a key reaction for nitrogen fixation strategies at ambient conditions. However, the impact of auxiliary ligands or accessible spin states on the thermodynamics and kinetics of N-N cleavage is yet to be examined in detail. We recently reported N-N bond splitting of a {Mo(μ2:η1:η1-N2)Mo}-complex upon protonation of the diphosphinoamide auxiliary ligands. The reactivity was associated with a low-spin to high-spin transition that was induced by the protonation reaction in the coordination periphery, mainly based on computational results. Here, this proposal is evaluated by an XAS study of a series of linearly N2 bridged Mo pincer complexes. Structural characterization of the transient protonation product by EXAFS spectroscopy confirms the proposed spin transition prior to N-N bond cleavage

Inkjet- and flextrail-printing of silicon polymer-based inks for local passivating contacts

In this work innovative additive printing methods for formation of polycrystalline silicon (poly-Si) and polycrystalline silicon carbide (poly-SiC) layers of local tunnel oxide passivating contacts (TOPCon) is evaluated. Replacement of conventional vacuum processes and vapor-phase deposition by additive printing of Si in fabrication process of high efficiency solar cells reduces processing complexity, and, hence manufacturing costs. Reliable inkjet- and FlexTrail-printing processes are developed for liquid-phase polysilane and organic polysilazane inks that are precursors of Si and SiC, respectively. FlexTrail is introduced as a potential technology to print uniform closed thin films of polysilane free of ruptures. Moreover, from inkjet-printing of the developed polysilane ink, homogenous, closed and crack free thin films of poly-Si are obtained after high temperature annealing. The polysilane ink is formulated considering evaluation of several solvents and photoinduced polymerization conditions. Inkjet-printing process development and optimization according to high frequency rheological characterization of organic polysilazane (OPSZ) is presented. Printed thin films are characterized after high temperature annealing (T = 950 °C, t = 60 min) to be uniform and free of micro cracks

The calculation of 29Si NMR chemical shifts of tetracoordinated silicon compounds in the gas phase and in solution

Aiming at the identification of an efficient computational protocol for the accurate NMR assessment of organosilanes in low-polarity organic solvents, 29Si NMR chemical shifts of a selected set of such species relevant in organic synthesis have been calculated relative to tetramethylsilane (TMS, 1) using selected density functional and perturbation theory methods. Satisfactory results are obtained when using triple zeta quality basis sets such as IGLO-III. Solvent effects impact the calculated results through both, changes in substrate geometry as well as changes in the actual shieldings. Spin-orbit (SO) corrections are required for systems carrying more than one chlorine atom directly bonded to silicon. Best overall results are obtained using gas phase geometries optimized at MPW1K/6-31+G(d) level in combination with shielding calculations performed at MPW1K/IGLO-III level in the presence of the PCM continuum solvation model