In vacuo trimethylation of the N-terminus of a lyophilized peptide with methyl iodide was previously reported to enhance the peptide's signal in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and to suppress alkali adduct formation in electrospray ionization mass spectrometry (ESI-MS). Both the signal enhancement and alkali adduct suppression observed for methylated peptides are believed to be due to the permanent positive charge on the N-terminus of the peptide resulting from the formation of a quaternary ammonium moiety. The present work evaluates the general utility of the in vacuo methylation procedure for the MS analysis of peptides, and specifically addresses the issue of whether the methylation of nucleophilic sites other than the N-terminal amine affects the MALDI signal of modified peptides. This work establishes that, although certain side-chain modifications are inevitable using present reaction conditions, the derivatization leads to significant MALDI-MS signal improvement. The experimental results demonstrate that the N-terminal trimethylammonium derivatives of peptides exhibit MALDI signals comparable to or exceeding those of arginine-containing standards such as angiotensin I. The advantages and limitations of the in vacuo methylation procedure are discussed.

The structure of the title compound, [RuCl(C23H21N5)]ClO4·CH4O, has been determined at 113 K, revealing a mononuclear six‐coordinate structure with a 0.263 (2) Å displacement of the RuII atom from the N4 equatorial plane.

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Laser material deposition (LMD) is a process in which a laser beam creates a melt pool on the surface of a substrate while a powder nozzle delivers a powdered additive into the melt pool, where the powder material then melts. A dense, metallurgically bonded layer forms once the melt solidifies. The velocity of powder particles in LMD is one of the key factors that influence the amount of particles’ energy absorption (along their individual trajectories) through the laser beam on the way between the powder nozzle and the substrate. The amount of energy that is absorbed by the powder particles above the melt pool determines the temperature on the substrate surface and, hence, influences the formation of the melt pool and the deposition of the powder material. Data about the particle velocity are, therefore, essential for modeling the LMD process—not only for physical simulation where a particle’s energy input can be integrated along its trajectory, but also in an experimental environment of process parameter studies, where understanding the interdependencies between the process parameters is crucial. In this study, a setup using a high-speed camera and an illumination laser is used to measure the velocity of powder particles in the powder gas jet of a coaxial powder nozzle. Several parameters that are known to influence the particle velocity are varied: Feed gas rate, shielding gas rate, nozzle geometry (width of annular gap), and powder mass flow rate. In this study, four different powder types are used. The influence of these process parameters on the particle velocity is measured. Four different methods for tracking individual particles and calculating the velocity distribution within the powder gas jet are used and compared: Manual frame-by-frame particle tracking and manual evaluation from multiple exposures in single frames, as well as particle tracking velocimetry and particle image velocimetry (PIV), which incorporate region-of-interest boxes into the algorithm. Sufficient accordance as to the measurement results is found in comparing the four methods. Further, using the highly automatable PIV method, the influence of main process parameters on particle velocity is measured. Out of the examined parameters, the feed gas rate is found to have the most immediate impact with a linear correlation to particle velocity. A correlation between different powder particle size distributions and measured particle velocities is shown as well.

The structure of the title compound, [ZnCl(C23H21N5)]ClO4·H2O, has been determined at 113 K, revealing a discrete mononuclear six‐coordinate ZnII structure with a fairly large displacement [0.502 (2) Å] of ZnII from the equatorial plane of N atoms.