Spectroscopic characterization of radicals formed by hydrogen-atom abstraction from γ-valerolactone and γ-butyrolactone.

γ-valerolactone (GVL) and its unmethylated counterpart, γ-butyrolactone (GBL), are important compounds with a wide range of potential uses. For example, GVL is proposed as an ideal alternative renewable energy source, while GBL can be utilized as an electrolyte. Understanding the combustion mechanisms of these compounds is crucial for optimizing their use as energy sources and monitoring the products formed during combustion.

UV photolysis of thiourea and its -methylated derivative in cryogenic matrices.

Exploration of the photolytic dynamics of sulfurous compounds is essential, eventually contributing not only to our comprehension of their fundamental organic chemistry but also shedding light on astrophysical implications. This study aims to investigate two astrochemically relevant sulfur-containing molecules, namely, thiourea (TU) and its -methylated counterpart, -methyl thiourea (NMTU), in cryogenic matrices. These molecules were deposited both in solid Ar and in a quantum host, specifically in solid -H matrices, with the latter exhibiting unique properties.

Energetic processing of thioacetamide in cryogenic matrices.

There is an ongoing debate on the apparent depletion of sulfur in the interstellar medium (ISM) compared to its universal abundance; therefore, the investigation of sulfurous compounds at low temperatures is of utmost importance. This work aims to study thioacetamide, H3C-C(=S)-NH2, in low-temperature inert Ar and para-H2 matrices by IR spectroscopy. The samples have been exposed to various sources of irradiation, such as Lyman-α or laser UV photons as well as energetic electrons.

Infrared spectroscopy of the α-hydroxyethyl radical isolated in cryogenic solid media.

The α-hydroxyethyl radical (CH3·CHOH, 2A) is a key intermediate in ethanol biochemistry, combustion, atmospheric chemistry, radiation chemistry, and astrochemistry. Experimental data on the vibrational spectrum of this radical are crucially important for reliable detection and understanding of the chemical dynamics of this species. This study represents the first detailed experimental report on the infrared absorption bands of the α-hydroxyethyl radical complemented by ab initio computations.

Oxygen Isotope Exchange between Carbon Dioxide and Iron Oxides on Mars' Surface.

An investigation of the fundamental processes leading to the incorporation of O isotopes in carbon dioxide and in iron oxides is critical to understanding the atmospheric evolution and geochemistry of Mars. Whereas signatures of O have been observed by the Phoenix Lander and the sample analysis at Mars for carbon dioxide, the underlying isotopic exchange pathways with minerals of the crust of Mars are still elusive. Here, we reveal that reactions of gaseous O-carbon dioxide over goethite (FeO(OH)) and hematite (FeO) lead to an O transfer from the atmosphere that enriches the O content of the iron oxides in the absence of water and light.

UV-induced -OCH rotamerization in a matrix-isolated methoxy-substituted ortho-hydroxyaryl Schiff base.

A new methoxy-substituted ortho-hydroxyaryl Schiff base, 4-(3-methoxy-2-hydroxybenzylidene-amino) phenol was synthesized from 4-aminophenol and 2-hydroxy-3-methoxybenzaldehyde in methanol solution and characterized by H-NMR, C-NMR and infrared spectroscopies and elemental analysis. The compound was isolated in a cryogenic (10 K) argon matrix, and the analysis of the infrared spectrum of the matrix-isolated compound revealed that it corresponds to the E-enol-imine isomeric form, with 3 different conformers being present in the matrix. These conformers share as common structural features the conformation of the free hydroxyl group (trans relatively to the para-substituent of the ring) and the presence of an OHN intramolecular H-bond involving the methoxy-substituted phenol ring and the azomethine bridge, while they differ in the orientation of the methoxy-substituent group.

VIZSLA-Versatile Ice Zigzag Sublimation Setup for Laboratory Astrochemistry.

In this article, a new multi-functional high-vacuum astrophysical ice setup, VIZSLA (Versatile Ice Zigzag Sublimation Setup for Laboratory Astrochemistry), is introduced. The instrument allows for the investigation of astrophysical processes both in a low-temperature para-H matrix and in astrophysical analog ices. In the para-H matrix, the reaction of astrochemical molecules with H atoms and H ions can be studied effectively.

Non-energetic, Low-Temperature Formation of C-Glycyl Radical, a Potential Interstellar Precursor of Natural Amino Acids.

The reaction of H atoms with glycine was investigated at 3.1 K in -H, a quantum-solid host. The reaction was followed by IR spectroscopy, with the spectral analysis aided by quantum chemical computations.

Selective conformational control by excitation of NH imino vibrational antennas.

An imino group was used for the first time as a vibrational antenna to manipulate molecular conformations. Imino-thiol isomers of thioacetamide were generated upon UV-irradiation of its amino-thione tautomer isolated in argon matrices at 11 K. Selective and reversible conformational isomerizations were induced by narrowband near-IR irradiation tuned at the frequencies of the 2ν(NH) first stretching overtone of each imino-thiol isomer.

S-H rotamerization via tunneling in a thiol form of thioacetamide.

Rotamerization of a hydroxyl (O-H) group by tunneling is well-known and has been extensively studied. On the other hand, similar tunneling processes for the thiol (S-H) group have not been reported yet. In this work, the imino-thiol forms of thioacetamide were studied in cryogenic matrices (Ar, Xe) after UV-irradiation of the common amino-thione form of the compound.

An interstellar synthesis of phosphorus oxoacids.

Phosphorus signifies an essential element in molecular biology, yet given the limited solubility of phosphates on early Earth, alternative sources like meteoritic phosphides have been proposed to incorporate phosphorus into biomolecules under prebiotic terrestrial conditions. Here, we report on a previously overlooked source of prebiotic phosphorus from interstellar phosphine (PH) that produces key phosphorus oxoacids-phosphoric acid (HPO), phosphonic acid (HPO), and pyrophosphoric acid (HPO)-in interstellar analog ices exposed to ionizing radiation at temperatures as low as 5 K. Since the processed material of molecular clouds eventually enters circumstellar disks and is partially incorporated into planetesimals like proto Earth, an understanding of the facile synthesis of oxoacids is essential to untangle the origin of water-soluble prebiotic phosphorus compounds and how they might have been incorporated into organisms not only on Earth, but potentially in our universe as well.

On the formation and the isomer specific detection of methylacetylene (CHCCH), propene (CHCHCH), cyclopropane (c-CH), vinylacetylene (CHCHCCH), and 1,3-butadiene (CHCHCHCH) from interstellar methane ice analogues.

Pure methane (CH4) ices processed by energetic electrons under ultra-high vacuum conditions to simulate secondary electrons formed via galactic cosmic rays (GCRs) penetrating interstellar ice mantles have been shown to produce an array of complex hydrocarbons with the general formulae: CnH2n+2 (n = 4-8), CnH2n (n = 3-9), CnH2n-2 (n = 3-9), CnH2n-4 (n = 4-9), and CnH2n-6 (n = 6-7). By monitoring the in situ chemical evolution of the ice combined with temperature programmed desorption (TPD) studies and tunable single photon ionization coupled to a reflectron time-of-flight mass spectrometer, specific isomers of C3H4, C3H6, C4H4, and C4H6 were probed. These experiments confirmed the synthesis of methylacetylene (CH3CCH), propene (CH3CHCH2), cyclopropane (c-C3H6), vinylacetylene (CH2CHCCH), 1-butyne (HCCC2H5), 2-butyne (CH3CCCH3), 1,2-butadiene (H2CCCH(CH3)), and 1,3-butadiene (CH2CHCHCH2) with yields of 2.

Accessing the Nitromethane (CHNO) Potential Energy Surface in Methanol (CHOH)-Nitrogen Monoxide (NO) Ices Exposed to Ionizing Radiation: An FTIR and PI-ReTOF-MS Investigation.

(D-)Methanol-nitrogen monoxide (CHOH/CDOH-NO) ices were exposed to ionizing radiation to facilitate the eventual determination of the CHNO potential energy surface (PES) in the condensed phase. Reaction intermediates and products were monitored via infrared spectroscopy (FTIR) and photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) during the irradiation and temperature controlled desorption (TPD) phase, respectively. Distinct photoionization energies were utilized to discriminate the isomer(s) formed in these processes.

On the Synthesis of Chocolate Flavonoids (Propanols, Butanals) in the Interstellar Medium.

Complex organic molecules are ubiquitous in star- and planet-forming regions as well as on comets such as on 67P/Churyumov-Gerasimenko, but their origins have remained largely unexplained until now. Here, we report the first laboratory detection of distinct C H O (propanol, methyl ethyl ether) and C H O (n-butanal, i-butanal) isomers formed within interstellar analog ices through interaction with ionizing radiation. This study reveals that complex organics with propyl (C H ) and butyl (C H ) groups can be synthesized easily in deep space and may act as key evolutionary tracers of a cosmic ray driven non-equilibrium chemistry in low temperature interstellar ices at 10 K.

Formation of Hydroxylamine in Low-Temperature Interstellar Model Ices.

We irradiated binary ice mixtures of ammonia (NH) and oxygen (O) ices at astrophysically relevant temperatures of 5.5 K with energetic electrons to mimic the energy transfer process that occurs in the track of galactic cosmic rays. By monitoring the newly formed molecules online and in situ utilizing Fourier transform infrared spectroscopy complemented by temperature-programmed desorption studies with single-photon photoionization reflectron time-of-flight mass spectrometry, the synthesis of hydroxylamine (NHOH), water (HO), hydrogen peroxide (HO), nitrosyl hydride (HNO), and a series of nitrogen oxides (NO, NO, NO, NO, NO) was evident.

Electron Radiolysis of Ammonium Perchlorate: A Reflectron Time-of-Flight Mass Spectrometric Study.

Thin films of ammonium perchlorate (NHClO) were exposed to energetic electrons at 5.5 K to explore the radiolytic decomposition mechanisms. The effects of radiolysis were monitored on line and in situ via Fourier transform infrared spectroscopy (FTIR) in the condensed phase along with electron impact ionization quadrupole mass spectrometry (EI-QMS) and single-photon photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) during the temperature-programmed desorption (TPD) phase to probe the subliming molecules.

Synthesis of the Smallest Member of the Silylketene Family: H SiC(H)=C=O.

Exploiting photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) combined with electronic structure calculations, it is shown that the hitherto elusive silylketene molecule (H SiC(H)=C=O)-the isovalent counterpart of the well-known methylketene molecule-is forming via interaction of energetic electrons with low-temperature silane-carbon monoxide ices. In combination with the infrared spectroscopically detected triplet dicarbon monoxide reactant, electronic structure calculations suggest that dicarbon monoxide reacts with silane via a de facto insertion of the terminal carbon atom into a silicon-hydrogen single bond. This is followed by non-adiabatic reaction dynamics triggered by the heavy silicon atom intersystem crossing from the triplet to the singlet manifold, eventually leading to the formation of silylketene.

VCD Robustness of the Amide-I and Amide-II Vibrational Modes of Small Peptide Models.

The rotational strengths and the robustness values of amide-I and amide-II vibrational modes of For(AA)n NHMe (where AA is Val, Asn, Asp, or Cys, n = 1-5 for Val and Asn; n = 1 for Asp and Cys) model peptides with α-helix and β-sheet backbone conformations were computed by density functional methods. The robustness results verify empirical rules drawn from experiments and from computed rotational strengths linking amide-I and amide-II patterns in the vibrational circular dichroism (VCD) spectra of peptides with their backbone structures. For peptides with at least three residues (n ≥ 3) these characteristic patterns from coupled amide vibrational modes have robust signatures.

Exploring the conformational space of cysteine by matrix isolation spectroscopy combined with near-infrared laser induced conformational change.

Six conformers of α-cysteine were identified by matrix isolation IR spectroscopy combined with NIR laser irradiation. Five of these conformers are identical with the five out of six conformers that have recently been identified by microwave spectroscopy. The sixth conformer observed in the present study is a short-lived conformer, which decays by H-atom tunneling; its half-life in a 12 K N2 matrix is (1.

Near-infrared radiation induced conformational change and hydrogen atom tunneling of 2-chloropropionic acid in low-temperature Ar matrix.

Former assignments of the matrix-isolation infrared (MI-IR) spectrum of 2-chloropropionic acid are revised with the help of near-infrared (NIR) laser irradiation induced change in conformer ratios. This method allows not only the unambiguous assignment of each band in the MI-IR spectrum to the two trans (Z) and the cis (E) conformers but also the assignment of the spectral bands to different matrix sites. The tunneling decay of the higher-energy cis conformer prepared from both trans conformers in different sites is also investigated.

Reliability of computed signs and intensities for vibrational circular dichroism spectra.

We present in detail a novel measure that improves the reliability of the assignment procedure for vibrational circular dichroism (VCD) spectra extending the useful robustness concept introduced by Nicu and Baerends. This measure enables spectroscopists to single out bands with unreliable VCD intensities that can be disregarded during analysis and determination of absolute configuration. The previously proposed robustness criterion is shown to be gauge dependent and less reliable than the one proposed here.

Effects of strong and weak hydrogen bond formation on VCD spectra: a case study of 2-chloropropionic acid.

The vibrational circular dichroism (VCD) spectrum of S-(-) and R-(+)-2-chloropropionic acid is thoroughly analyzed. Besides the VCD spectrum of the monomer, the dimers (stabilized by strong hydrogen bonds) and the 2-chloropropionic acid-CHCl(3) complexes (stabilized by a weak hydrogen bond) are studied both experimentally (in solution and in low-temperature Ar matrix) and by quantum chemical computations. It is shown that dimer formation drastically changes, and even weak complex formation can also substantially affect the overall shape of the VCD spectrum.

Is β-homo-proline a pseudo-γ-turn forming element of β-peptides? An IR and VCD spectroscopic study on Ac-β-HPro-NHMe in cryogenic matrices and solutions.

In order to test the pseudo-γ-turn forming capability of β-homo-proline (β(3)-HPro) 2-[(2S)-1-acetylpyrrolidin-2-yl]-N-methylacetamide (Ac-β(3)-HPro-NHMe) was synthesized and its potential energy landscape was investigated by infrared (IR) and vibrational circular dichroism (VCD) spectroscopy combined with density functional calculations. Based upon a comparison between experimental and computed spectra three different pseudo-γ-turn-like trans conformers and a cis conformer were identified in low-temperature Ar and Kr matrices. The computations in agreement with the observations reveal that, in contrast to its α-Pro analogue, the room-temperature abundance of the cis conformer is significant, falling above 10% in the isolated phase.