Microwave spectroscopy

Résumé

Microwave spectroscopy is the spectroscopy method that employs microwaves, i.e. electromagnetic radiation at GHz frequencies, for the study of matter. History The ammonia molecule NH3 is shaped like a pyramid 0.38 Å in height, with an equilateral triangle of hydrogens forming the base.The nitrogen situated on the axis has two equivalent equilibrium positions above and below the triangle of hydrogens, and this raises the possibility of the nitrogen tunneling up and down, through the plane of the H-atoms. In 1932 Dennison et al. ... analyzed the vibrational energy of this molecule and concluded that the vibrational energy would be split into pairs by the presence of these two equilibrium positions. The next year Wright and Randall observed ... a splitting of 0.67 cm–1 in far infrared lines, corresponding to ν = 20 GHz, the value predicted by theory.In 1934 Cleeton and Williams ... constructed a grating echelette spectrometer in order to measure this splitting directly, ther

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

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Analyzing glycans cleaved from a biotherapeutic protein using a combination of ion mobility spectrometry and cryogenic ion spectroscopy

Natalia Yalovenko

The characterization of biomolecules plays a central role in biomedical research. The development of state-of-the-art technologies is needed to make such analyses faster, more sensitive, and more accurate. While mass spectrometry continues to play a central role in biomolecular analysis, the use of multidimensional approaches that combine mass spectrometry, ion mobility spectrometry, and ion spectroscopy have been rapidly developing. This thesis investigates the application of such an approach for the routine analysis of glycans. The first part of this thesis describes combining ultrahigh-resolution ion mobility with cryogenic IR spectroscopy and mass spectrometry for analysis of N-linked glycans. This approach is demonstrated by characterizing four N-glycans cleaved from the therapeutic fusion protein Etanercept that differ in abundance from 1% to 22% of the total N-glycan content. Our results demonstrate that the sensitivity, speed, and resolution of vibrational spectra are sufficient for large-scale N-glycan characterization and identification. In addition to the successful demonstration of our approach for identifying known N-glycans, we developed a strategy to synthesize and identify commercially unavailable positional isomers of N-glycans. This work demonstrates the potential of the technique to become a broadly accessible analytical tool for glycan analysis. In the following part, the ability of our approach to quantify the glycan mixtures is investigated. Spray instability, different ionization efficiency of analytes, and their tagging efficiency complicate the process of quantification. Proposed solutions to these issues are discussed. We also present a study demonstrating that cryogenic infrared spectra of alkali metal complexes of carbohydrates of different complexity, including disaccharides and N-glycans can serve as fingerprints. We showed that the identity of the metal cation has no effect on the IR spectral complexity. In the last part, cryogenic infrared spectroscopy with isotopic substitution in positive and negative ion modes was used for structural characterization of the reverse peptides GRGDS and SDGRG. The recorded cryogenic spectra represent a useful benchmark for theoretical structural predictions due to their sharp and distinct features. This work represents the first step towards the structural determination of these peptides, with ongoing efforts focused on quantum chemical calculations.

EPFL2021

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In this report, spectroscopy was used to track the energy of different states in a LiHoF4 sample around its critical temperature. The experimental setup consist of a Cooper cavity with the sample, an antenna and a resonator inside. This cavity is attached to a probe and put inside a cooled well and a transverse magnetic field. Two different frequency ranges were examined around, f0 = (1.18732 0.00001) Ghz and f0 = (3.32940 0.00001) Ghz. The energy difference between states was successfully tracked for different temperatures thanks to the Q factor plots. However, the lack of sufficient data points and the unexpected behaviour around Tc (there are no gaps and no discontinuities), implies that this is only the beginning of this experiment and more time and measurements is needed to claim reasonable results.

2022

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The isomeric heterogeneity of glycans poses a great challenge for their analysis. While combining ion mobility spectrometry (IMS) with tandem mass spectrometry is a powerful means for identifying and characterizing glycans, it has difficulty distinguishing the subtlest differences between isomers. Cryogenic infrared spectroscopy provides an additional dimension for glycan identification that is extremely sensitive to their structure. Our approach to glycan analysis combines ultrahigh-resolution IMS-IMS using structures for lossless ion manipulation (SLIM) with cryogenic infrared spectroscopy. We present here the design of a SLIM board containing a series of on-board traps in which we perform collision-induced dissociation (CID) at pressures in the millibar range. We characterize the on-board CID process by comparing the fragments generated from a pentapeptide to those obtained on a commercial tandem mass spectrometer. We then apply our new technique to study the mobility and vibrational spectra of CID fragments from two human milk oligosaccharides. Comparison of both the fragment drift times and IR spectra with those of suitable reference compounds allows us to identify their specific isomeric form, including the anomericity of the glycosidic linkage, demonstrating the power of this tool for glycan analysis.

AMER CHEMICAL SOC2020

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Analyzing glycans cleaved from a biotherapeutic protein using a combination of ion mobility spectrometry and cryogenic ion spectroscopy

Natalia Yalovenko

EPFL2021