Isomer

Résumé

In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refers to the existence or possibility of isomers. Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural or constitutional isomerism, in which bonds between the atoms differ; and stereoisomerism or spatial isomerism, in which the bonds are the same but the relative positions of the atoms differ. Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different isotopologues. The depth of analysis depends on the field of study or the chemical and physical properties of interest. The English word "isomer" (ˈaɪsəməɹ) is a back-form

Source officielle

https://en.wikipedia.org/wiki/Isomer

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L'objectif de ce cours est de fournir les connaissances et le moyen de comprendre, au niveau moléculaire, le fonctionnement des réactions chimiques organiques. Pendant le cours, l'étudiant réfléchira et résoudra de nouveaux problèmes.

This course provides a basic foundation in organic chemistry and polymer chemistry, including chemical nomenclature of organic compounds and polymers, an understanding of chemical structures, chemical reaction mechanisms, as well as methods of organic and polymer synthesis.

Le cours comporte deux parties. Les bases de la thermodynamique des équilibres et de la cinétique des réactions sont introduites dans l'une d'elles. Les premières notions de chimie quantique sur les électrons et les liaisons chimiques, exemplifiées en chimie organique, sont présentées dans l'autre.

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A new approach for identifying positional isomers of glycans cleaved from monoclonal antibodies

Priyanka Bansal, Ahmed Ben Faleh, Thomas Rizzo, Stephan Warnke, Natalia Yalovenko, Vasyl Yatsyna

Glycosylation patterns in monoclonal antibodies (mAbs) can vary significantly between different host cell types, and these differences may affect mAbs safety, efficacy, and immunogenicity. Recent studies have demonstrated that glycan isomers with the terminal galactose position on either the Man alpha 1-3 arm or the Man alpha 1-6 arm have an impact on the effector functions and dynamic structure of mAbs. The development of a robust method to distinguish positional isomers of glycans is thus critical to guarantee mAb quality. In this work, we apply high-resolution ion mobility combined with cryogenic infrared spectroscopy to distinguish isomeric glycans with different terminal galactose positions, using G1F as an example. Selective enzymatic synthesis of the G1(alpha 1-6)F isomer allows us to assign the peaks in the arrival-time distributions and the infrared spectra to their respective isomeric forms. Moreover, we demonstrate the impact of the host cell line (CHO and HEK-293) on the IgG G1F gycan profile at the isomer level. This work illustrates the potential of our approach for glycan analysis of mAbs.

ROYAL SOC CHEMISTRY2021

Chargement

Identification of N-glycan positional isomers by combining IMS and vibrational fingerprinting of structurally determinant CID fragments

Priyanka Bansal, Ahmed Ben Faleh, Thomas Rizzo, Stephan Warnke

While glycans are present on the surface of cells in all living organisms and play key roles in most biological processes, their isomeric complexity makes their structural characterization challenging. Of particular importance are positional isomers, for which analytical standards are difficult to obtain. We combine ultrahigh-resolution ion-mobility spectrometry with collision-induced dissociation and cryogenic infrared spectroscopy to determine the structure of N-glycan positional isomers. This approach is based on first separating the parent molecules by SLIM-based IMS, producing diagnostic fragments specific to each positional isomer, separating the fragments by IMS, and identifying them by comparing their IR fingerprints to a previously recorded spectral database. We demonstrate this strategy using a bottom-up scheme to identify the positional isomers of the N-linked glycan G0-N, in which a terminal N-acetylglucosamine (GlcNAc) is attached to either the alpha-3 or alpha-6 branch of the common N-glycan pentasaccharide core. We then use IR fingerprints of these newly identified isomers to identify the positional isomers of G1 and G1F, which are biantennary complex-type N-glycans with a terminal galactose attached to either the alpha-3 or alpha-6 branch, and in the case of G1F a fucose attached to the reducing-end GlcNAc. Starting with just a few analytical standards, this fragment-based spectroscopy method allows us to develop a database which we can use to identify positional isomers. The generalization of this approach would greatly facilitate glycan analysis.

ROYAL SOC CHEMISTRY2022

Chargement

Identification of Mobility-Resolved N-Glycan Isomers

Priyanka Bansal, Ahmed Ben Faleh, Robert Paul Pellegrinelli, Thomas Rizzo, Stephan Warnke

ABSTRACT: Glycan analysis has evolved considerably during the last decade. The advent of high-resolution ion-mobility spectrometry has enabled the separation of isomers with only the slightest of structural differences. However, the ability to separate such species raises the problem of identifying all the mobility-resolved peaks that are observed, especially when analytical standards are not available. In this work, we report an approach based on the combination of IMSn with cryogenic vibrational spectroscopy to identify N-glycan reducing-end anomers. By identifying the reducing-end alpha and beta anomers of diacetyl-chitobiose, which is a disaccharide that forms part of the common core of all N-glycans, we are able to assign mobility peaks to reducing anomers of a selection of N-glycans of different sizes, starting from trisaccharides such as Man-1 up to glycans containing nine monosaccharide units, such as G2. By building an infrared fingerprint database of the identified N-glycans, our approach allows unambiguous identification of mobility peaks corresponding to reducing-end anomers and distinguishes them from positional isomers that might be present in a complex mixture.

AMER CHEMICAL SOC2022

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