| 1. |
- Barreiro-Lage, Darío, et al.
(author)
-
"Smart Decomposition" of Cyclic Alanine-Alanine Dipeptide by VUV Radiation : A Seed for the Synthesis of Biologically Relevant Species
- 2021
-
In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:30, s. 7379-7386
-
Journal article (peer-reviewed)abstract
- A combined experimental and theoretical study shows how the interaction of VUV radiation with cyclo-(alanine-alanine), one of the 2,5-diketopiperazines (DKPs), produces reactive oxazolidinone intermediates. The theoretical simulations reveal that the interaction of these intermediates with other neutral and charged fragments, released in the molecular decomposition, leads either to the reconstruction of the cyclic dipeptide or to the formation of longer linear peptide chains. These results may explain how DKPs could have, on one hand, survived hostile chemical environments and, on the other, provided the seed for amino acid polymerization. Shedding light on the mechanisms of production of such prebiotic building blocks is of paramount importance to understanding the abiotic synthesis of relevant biologically active compounds.
|
|
| 2. |
- Bull, James N., et al.
(author)
-
Action spectroscopy of deprotomer-selected hydroxycinnamate anions
- 2021
-
In: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 75:2
-
Journal article (peer-reviewed)abstract
- Tandem ion mobility mass spectrometry-coupled laser excitation is used to record photodetachment, photoisomerization and photodepletion action spectra for a series of deprotomer-selected hydroxycinnamate anions, including deprotonated caffeic, ferulic and sinapinic acids. This molecular series accounts for most hydroxycinnainic moieties found in nature. Phenoxide deprotomers for para and ortho structural isomers have similar photodetachment action spectra that span the 350-460nm range with the maximum response occurring between 420 and 440 nm. None of the phenoxide deprotomers showed evidence for E -> Z photoisomerization. In contrast, photoexcitation of the carboxylate deprotomers of caffeic and ferulic acids and the meta-phenoxide deprotomer of caffeic acid initiates intramolecular proton transfer to give the para-phenoxide deprotomer. Photoexcitation of the carboxylate deprotomer of sinapinic acid and ortho-coumaric acid does not result in intramolecular proton transfer, presumably due to substantial barriers for rearrangement. For deprotonated meta-coumaric acid, interconversion between the phenoxide and carboxylate deprotomers occurs in the ion mobility spectrometer drift region where the effective ion temperature is T-eff approximate to 299 K.
|
|
| 3. |
- Bull, James N., et al.
(author)
-
Nonadiabatic Dynamics between Valence, Nonvalence, and Continuum Electronic States in a Heteropolycyclic Aromatic Hydrocarbon
- 2021
-
In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:49, s. 11811-11816
-
Journal article (peer-reviewed)abstract
- Internal conversion between valence-localized and dipole-bound states is thought to be a ubiquitous process in polar molecular anions, yet there is limited direct evidence. Here, photodetachment action spectroscopy and time-resolved photoelectron imaging with a heteropolycyclic aromatic hydrocarbon (hetero-PAH) anion, deprotonated 1-pyrenol, is used to demonstrate a subpicosecond (τ1 = 160 ± 20 fs) valence to dipole-bound state internal conversion following excitation of the origin transition of the first valence-localized excited state. The internal conversion dynamics are evident in the photoelectron spectra and in the photoelectron angular distributions (β2 values) as the electronic character of the excited state population changes from valence to nonvalence. The dipole-bound state subsequently decays through mode-specific vibrational autodetachment with a lifetime τ2 = 11 ± 2 ps. These internal conversion and autodetachment dynamics are likely common in molecular anions but difficult to fingerprint due to the transient existence of the dipole-bound state. Potential implications of the present excited state dynamics for interstellar hetero-PAH anion formation are discussed.
|
|
| 4. |
- Coughlan, Neville J. A., et al.
(author)
-
Action spectroscopy of the isolated red Kaede fluorescent protein chromophore
- 2021
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 155:12
-
Journal article (peer-reviewed)abstract
- Incorporation of fluorescent proteins into biochemical systems has revolutionized the field of bioimaging. In a bottom-up approach, understanding the photophysics of fluorescent proteins requires detailed investigations of the light-absorbing chromophore, which can be achieved by studying the chromophore in isolation. This paper reports a photodissociation action spectroscopy study on the deprotonated anion of the red Kaede fluorescent protein chromophore, demonstrating that at least three isomers–assigned to deprotomers–are generated in the gas phase. Deprotomer-selected action spectra are recorded over the S1 ← S0 band using an instrument with differential mobility spectrometry coupled with photodissociation spectroscopy. The spectrum for the principal phenoxide deprotomer spans the 480–660 nm range with a maximum response at ≈610 nm. The imidazolate deprotomer has a blue-shifted action spectrum with a maximum response at ≈545 nm. The action spectra are consistent with excited state coupled-cluster calculations of excitation wavelengths for the deprotomers. A third gas-phase species with a distinct action spectrum is tentatively assigned to an imidazole tautomer of the principal phenoxide deprotomer. This study highlights the need for isomer-selective methods when studying the photophysics of biochromophores possessing several deprotonation sites.
|
|
| 5. |
- Gatchell, Michael, et al.
(author)
-
Survival of polycyclic aromatic hydrocarbon knockout fragments in the interstellar medium
- 2021
-
In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
-
Journal article (peer-reviewed)abstract
- Laboratory studies play a crucial role in understanding the chemical nature of the interstellar medium (ISM), but the disconnect between experimental timescales and the timescales of reactions in space can make a direct comparison between observations, laboratory, and model results difficult. Here we study the survival of reactive fragments of the polycyclic aromatic hydrocarbon (PAH) coronene, where individual C atoms have been knocked out of the molecules in hard collisions with He atoms at stellar wind and supernova shockwave velocities. Ionic fragments are stored in the DESIREE cryogenic ion-beam storage ring where we investigate their decay for up to one second. After 10 ms the initially hot stored ions have cooled enough so that spontaneous dissociation no longer takes place at a measurable rate; a majority of the fragments remain intact and will continue to do so indefinitely in isolation. Our findings show that defective PAHs formed in energetic collisions with heavy particles may survive at thermal equilibrium in the interstellar medium indefinitely, and could play an important role in the chemistry in there, due to their increased reactivity compared to intact or photo-fragmented PAHs. Ion storage rings allow reactions to be studied over orders of magnitude in time, bridging the gap between typical experimental and astronomical timescales. Here the authors observe that polycyclic aromatic hydrocarbon fragments produced upon collision with He atoms at velocities typical of stellar winds and supernova shockwaves remain intact up to second timescales, thus may play an important role in interstellar chemistry.
|
|
| 6. |
- Giacomozzi, Linda, 1986-, et al.
(author)
-
Non-statistical fragmentation in photo-activated flavin mononucleotide anions
- 2021
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 155:4
-
Journal article (peer-reviewed)abstract
- The spectroscopy and photo-induced dissociation of flavin mononucleotide anions in vacuo are investigated over the 300-500 nm wavelength range. Comparison of the dependence of fragment ion yields as a function of deposited photon energy with calculated dissociation energies and collision-induced dissociation measurements performed under single-collision conditions suggests that a substantial fraction of photo-activated ions decompose through non-statistical fragmentation pathways. Among these pathways is the dominant photo-induced fragmentation channel, the loss of a fragment identified as formylmethylflavin. The fragment ion specific action spectra reveal electronic transition energies close to those for flavins in solution and previously published gas-phase measurements, although the photo-fragment yield upon excitation of the S-2 <- S-0 transition appears to be suppressed.
|
|
| 7. |
- Kjær, Christina, et al.
(author)
-
A new setup for low-temperature gas-phase ion fluorescence spectroscopy
- 2021
-
In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 92:3
-
Journal article (peer-reviewed)abstract
- Here, we present a new instrument named LUNA2 (LUminescence iNstrument in Aarhus 2), which is purpose-built to measure dispersed fluorescence spectra of gaseous ions produced by electrospray ionization and cooled to low temperatures (<100 K). LUNA2 is, as an earlier room-temperature setup (LUNA), optimized for a high collection efficiency of photons and includes improvements based on our operational experience with LUNA. The fluorescence cell is a cylindrical Paul trap made of copper with a hole in the ring electrode to permit laser light to interact with the trapped ions, and one end-cap electrode is a mesh grid combined with an aspheric condenser lens. The entrance and exit electrodes are both in physical contact with the liquid-nitrogen cooling unit to reduce cooling times. Mass selection is done in a two-step scheme where, first, high-mass ions are ejected followed by low-mass ions according to the Mathieu stability region. This scheme may provide a higher mass resolution than when only one DC voltage is used. Ions are irradiated by visible light delivered from a nanosecond 20-Hz pulsed laser, and dispersed fluorescence is measured with a spectrometer combined with an iCCD camera that allows intensification of the signal for a short time interval. LUNA2 contains an additional Paul trap that can be used for mass selection before ions enter the fluorescence cell, which potentially is relevant to diminishing RF heating in the cold trap. Successful operation of the setup is demonstrated from experiments with rhodamine dyes and oxazine-4, and spectral changes with temperature are identified.
|
|
