NEXAFS spectroscopy and site-specific fragmentation of N -methylformamide, N,N -dimethylformamide, and N,N -dimethylacetamide

Near-edge X-ray absorption fine-structure (NEXAFS) spectra measured at the C, N, and O K-edges for three molecules containing the amide moiety, N-methylformamide (HCONHCH3), N,Ndimethylformamide (HCON(CH3)2), and N,N-dimethylacetamide (CH3CON(CH3)2) are presented. These molecules have similar structures and differ by the number of methyl groups located at the molecular ends. The fragmentation of these molecules after resonant excitation at different K-edge resonances is also investigated, using a 3D-ion imaging time-of-flight spectrometer. A comparison between the molecules with respect to the relative contributions of the fragments created upon excitation at distinct resonances reveals site-specific fragmentation. Further information about the character of the core-excitation and dissociation process is obtained from the angular distributions of the ion fragments

Single photon thermal ionization of C60

We report on experiments which show that C60 can ionize in an indirect, quasi-thermal boiloff process after absorption of a single photon. The process involves a large number of incoherently excited valence electrons and yields electron spectra with a Boltzmann distribution with temperatures exceeding 10^4 K. It is expected to be present for other molecules and clusters with a comparatively large number of valence electrons. The astrophysical consequences are briefly discussed

Structure-Specific Vibrational Modes of Isolated Biomolecules Studied with Mid- and Far-Infrared Laser Spectroscopy

Biomolecular structure elucidation is crucial for our detailed understanding of various biological processes, since there is an intimate relationship between the biomolecular function and structure. In this respect, isolated biomolecules, despite being outside of their natural environment, are perfect model systems for in-depth studies of various fundamental interactions that govern the formation of biomolecular structure. This thesis focuses on structure elucidation of isolated molecules of biological importance, with special emphasis on the development of novel infrared (IR) laser spectroscopic tools. The first part of the thesis applies far-IR spectroscopy, which excites low-frequency molecular vibrations in the IR light wavelength range of λ > 12 µm. The far-IR range provides valuable structural information complementing the well-established mid-IR (λ = 2.5 - 12 µm) spectroscopic analysis. However, routine application of far-IR spectroscopy to biomolecular structure elucidation is complicated by the limited knowledge of structure-specific far-IR spectral features, as well as poor performance of conventional theoretical approaches for the treatment of delocalized and anharmonic far-IR vibrational modes. In the attempt to fill these knowledge gaps, we applied far-IR spectroscopy to small, aromatic molecules of biological importance, which have a relatively low number of vibrational modes in the far-IR and are amenable to highly-accurate quantum-chemical calculations and detailed vibrational assignment. Isomer- and conformer-specific far-IR features of cold isolated aminophenol and methylacetanilide molecules were obtained with IR-UV ion-dip spectroscopy and assigned with the help of quantum chemical calculations. The observed far-IR transitions associated with deformation of the peptide link, an important structural unit in proteins, were found to be highly sensitive to the peptide link planarity, trans/cis configuration, and hydrogen bonding. The powerful conformer-selective IR-UV ion-dip spectroscopy technique applied in the first part of the thesis is unfortunately restricted to molecules that possess an aromatic UV-absorption chromophore. The studies presented in the second part of the thesis attempt to circumvent this limitation by introducing a novel approach that combines cooling of molecules in a supersonic jet, IR multiple photon dissociation (IRMPD), vacuum ultraviolet (VUV) ionization, and mass spectrometry. The approach was demonstrated by measuring the vibrational spectrum of the simplest peptide analog, N-methylacetamide, and its oligomers. The possibility to extract structural information from the IRMPD-VUV spectra was investigated for the Gly-Gly and Ala-Ala dipeptides, which are particularly interesting due to possible competition between their extended (β-strand like) and folded structures. The measured spectra for these dipeptides showed that the extended structure with weak hydrogen bonding interactions is strongly favored in the cold molecular beam due to its higher flexibility (larger entropy), as well as due to efficient collisional relaxation processes in the supersonic jet. The results show that even though IRMPD-VUV spectroscopy does not allow recording spectra of individual conformers, it nonetheless provides valuable structural information, especially for molecules that are not suited to conventional spectroscopy techniques

Far-ir action spectroscopy of aminophenol and ethylvanillin: experiment and theory

Investigations of molecular structure and conformational isomerism are at the forefront of today's biophysics and biochemistry. In particular, vibrations excited by far-IR radiation can be highly sensitive to the molecular 3D structure as they are delocalized over large parts of the molecule. Current theoretical predictions of vibrational frequencies in the far-IR range are not accurate enough because of the non-local character and anharmonicity of these vibrations. Therefore experimental studies in the far-IR are vital to guide theory towards improved methodology. In this work we present the conformer-specific far-IR spectra of aminophenol and ethylvanillin molecules in the range of 220-800 wn utilizing ion-dip action spectroscopy carried out at the free electron laser FELIX in Nijmegen, Netherlands. The systems studied are aromatic molecules with important functional groups such as the hydroxyl (chem{OH}) and amino (chem{NH_2}) groups in aminophenol, and the hydroxyl, ethoxy (chem{OCH_2CH_3}) and formyl (chem{CHO}) groups in ethylvanillin. The experimental spectra show well resolved conformer-specific vibrational bands. In the case of ethylvanillin only two planar conformers have been observed under supersonic jet expansion conditions. Despite the fact that these conformers differ only in the position of oxygen of the formyl group with respect to ethoxy group, they are well distinguishable in far-IR spectra. The capability of numerical methods based on density functional theory (DFT) for predicting vibrational frequencies in this spectral region within the harmonic approximation has been investigated by using several hybrid-functionals such as B3LYP, PBE0, B2PLYP and CAM-B3LYP. An anharmonic correction based on vibrational second order perturbation theory approachfootnote{V. Barone, Anharmonic vibrational properties by a fully automated second-order perturbative approach, J. Chem. Phys. 122 (2005) 014108.} was also applied. We have found that the methods we considered are well suited for the assignment of far-IR vibrational features except the modes which are strongly anharmonic, like the chem{NH_2} wagging mode in aminophenol which is likely to be due to double well potential governing this motion

Indication of 310-Helix Structure in Gas-Phase Neutral Pentaalanine

We investigate the gas-phase structure of the neutral pentaalanine peptide. The IR spectrum in the 340-1820 cm-1 frequency range is obtained by employing supersonic jet cooling, infrared multiphoton dissociation, and vacuum-ultraviolet action spectroscopy. Comparison with quantum chemical spectral calculations suggests that the molecule assumes multiple stable conformations, mainly of two structure types. In the most stable conformation theoretically found, the N-terminus forms a C5 ring and the backbone resembles that of an 310-helix with two beta-turns. Additionally, the conformational preferences of pentaalanine have been evaluated using Born-Oppenheimer molecular dynamics, showing that a nonzero simulation time step causes a systematic frequency shift.Funding Agencies|Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO); Swedish Research Council [2019-04439]</p

Indication of 310-Helix Structure in Gas-Phase Neutral Pentaalanine

We investigate the gas-phase structure of the neutral pentaalanine peptide. The IR spectrum in the 340-1820 cm-1 frequency range is obtained by employing supersonic jet cooling, infrared multiphoton dissociation, and vacuum-ultraviolet action spectroscopy. Comparison with quantum chemical spectral calculations suggests that the molecule assumes multiple stable conformations, mainly of two structure types. In the most stable conformation theoretically found, the N-terminus forms a C5 ring and the backbone resembles that of an 310-helix with two β-turns. Additionally, the conformational preferences of pentaalanine have been evaluated using Born-Oppenheimer molecular dynamics, showing that a nonzero simulation time step causes a systematic frequency shift

Analyzing glycans cleaved from a biotherapeutic protein using ultrahigh-resolution ion mobility spectrometry together with cryogenic ion spectroscopy

Glycans covalently attached to protein biotherapeutics have a significant impact on their biological activity, clearance, and safety. As a result, glycosylation is categorized as a critical quality attribute that needs an adequate analytical approach to guarantee product quality. However, the isomeric complexity and branched structure of glycans makes their analysis a significant challenge. In this work, we propose a multidimensional approach for monitoring released glycans that combines ultrahigh-resolution ion mobility spectrometry (IMS) and cryogenic vibrational spectroscopy, and we demonstrate this technique by characterizing four N-glycans cleaved from the therapeutic fusion protein etanercept that range in abundance from 1% to 22% of the total N-glycan content. The recorded vibrational spectra exhibit well-resolved transitions that can be used as a fingerprint to identify a particular glycan. This work represents an important advance in the analysis of N-linked glycans cleaved from biopharmaceutical proteins that could eventually be used as tool for monitoring biopharmaceutical glycoforms

The Importance of Outstanding Personalities in the Field of Surfing

В статті розглядаються найвідоміші серфінгісти світу та наведено найвідоміші світові школи серфінгу.The article examines the most famous surfers in the world and lists the world's most famous surfing schools