Reaktionen von Glutaminsäuredimethylester im Massenspektrometer. 21. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen

The mass spectral fragmentation of dimethyl glutamate ( 1 ) and its deuterated derivatives 1a , 1b and 1c has been investigated. By loss of a methoxycarbonyl group from the molecular ion an ion of m/e 116 is generated. The latter splits off methanol (m*), the resulting fragment of m/e 84 giving raise to the base peak of the spectrum. Only part of the hydrogen transferred to the leaving group originates from thc amino group, as was suggested earlier [2] [3]. Basing on experiments with deuterated compounds we propose an additional mechanism for the reaction, i.e. hydrogen transfer from C(3) to methoxyl. The fragment generated by both processes is most likely to be a pyrrolinonium ion. Thermal side reactions in the mass spectrometer (formation of pyroglutamic acid ester) followed by fragmentation may lead to the same ion. – The mechanisms discussed are supported by the mass spectral fragmentation of N-acetyl-glutamic acid diesters 3 , 3a , 3b and 3d and of the N, N-dimethyl derivatives 4 and 4a . – The fragmentation reactions investigated are similar to some of 1,3-trimethylenediamine derivatives [7]. This means that there are parallels in the mass spectral fragmentation of difunctional compounds irrespective of the nature of the functional groups.     

Reversed-phase liquid-chromatographic mass spectrometric N-glycan analysis of biopharmaceuticals

N-Glycosylation is a common post-translational modification of monoclonal antibodies with a potential effect on the efficacy and safety of the drugs; detailed knowledge about this glycosylation is therefore crucial. We have developed a reversed-phase liquid chromatographic–mass spectrometric method, with different fluorescent labels, for analysis of N-glycosylation, and compared the sensitivity and selectivity of the methods. Our work demonstrates that anthranilic acid as fluorescent label in combination with reversed-phase liquid chromatography–mass spectrometry is an advantageous method for identification and quantification of neutral and acidic N-glycans. Our results show that mass spectrometry-based quantification correlates with quantification by fluorescence. Chromatographic discrimination between several structural glycan isomers was achieved. The sharp peaks of the eluting anthranilic acid-labeled N-glycans enabled on-line mass spectrometric analysis of even low-abundance glycan species. The method is broadly applicable to N-glycan analysis and is an orthogonal analytical method to the widely established hydrophilic-interaction liquid chromatography of 2-aminobenzamide-labeled N-glycans for characterization of N-glycans derived from biopharmaceuticals.     

Template-induced formation of heterobidentate ligands and their application in the asymmetric hydroformylation of styrene

We report the template-induced formation of chelating heterobidentate ligands by the selective self-assembly of two different monodentate ligands on a rigid bis-zinc(II)-salphen template with two identical binding sites; these templated heterobidentate ligands induce much higher enantioselectivities (up to 72% ee) in the rhodium-catalyzed asymmetric hydroformylation of styrene than any of the corresponding homobidentate ligands or non-templated mixed ligand combinations (up to 13% ee).     

Protein structure information from mass spectrometry? Selective titration of arginine residues by sulfonates

Noncovalently bound complexes between basic sites of peptides/proteins and sulfonates are studied using Matrix Assisted Laser Desorption/Ionization (MALDI) Mass Spectrometry. Reactive sulfonate dyes such as Cibacron Blue F3G-A are known to bind to protonated amino groups on the exterior of a protein. In this work, we examine a wide range of other sulfonates with distinctly simpler structure and more predictable reactivity. Naphthalene-sulfonic acid derivatives were found to bind to arginine only, as opposed to expected binding to all basic sites (Arg, Lys and His). Detailed control experiments were designed to unambigously confirm this selectivity and to rule out nonspecific adduct formation in the gas phase. The data show that the number of complex adducts found equals the number of accessible arginine sites on the surface of folded peptides and proteins, plus the N-terminus. Lys and His are not complexed nor are buried residues with hindered access. MALDI-MS can therefore provide fast information related to the exposed surface of these biomolecules. Additional titration experiments with 1-anilino-naphthalene-8-sulfonic acid (ANS) revealed that this fluorescent dye, which was often hypothesized to bind to so-called molten globule states of proteins, behaved exactly like all other naphthalene-sulfonic acids. ANS binding thus occurs largely through the sulfonate group.     

A new sorption model with a dynamic correction for the determination of diffusion coefficients

This paper describes an improvement to the method used for the calculation of diffusion coefficients from data obtained by the measurement of vapor sorption kinetics in a flat, non-porous polymeric membrane. The advantage of our corrected model is that it can be applied to systems displaying both fast and slow sorption kinetics, as is demonstrated using cellulose myristate – hexane and cellulose acetovalerate – ethanol systems at a temperature of 298 K. Experiments were conducted on a specially developed sorption apparatus equipped with McBain’s spiral quartz balances. Sorption kinetics are generally described by the solution of Fick’s second law, the solution of which assumes relative pressure in the form of the unit step function. Our correction involves modifying this solution so that a more realistic relative pressure increase is assumed in terms of the Laplace transform.     

Graphen,worin je zwei Gerüste isomorph sind

Ohne Zusammenfassung