Methyl Thionitrite Research Articles

Toward reliable modeling of S-nitrosothiol chemistry: Structure and properties of methyl thionitrite (CH3SNO), an S-nitrosocysteine model.

Methyl thionitrite CH3SNO is an important model of S-nitrosated cysteine aminoacid residue (CysNO), a ubiquitous biological S-nitrosothiol (RSNO) involved in numerous physiological processes. As such, CH3SNO can provide insights into the intrinsic properties of the -SNO group in CysNO, in particular, its weak and labile S-N bond. Here, we report an ab initio computational investigation of the structure and properties of CH3SNO using a composite Feller-Peterson-Dixon scheme based on the explicitly correlated coupled cluster with single, double, and perturbative triple excitations calculations extrapolated to the complete basis set limit, CCSD(T)-F12/CBS, with a number of additive corrections for the effects of quadruple excitations, core-valence correlation, scalar-relativistic and spin-orbit effects, as well as harmonic zero-point vibrational energy with an anharmonicity correction. These calculations suggest that the S-N bond in CH3SNO is significantly elongated (1.814 Å) and has low stretching frequency and dissociation energy values, νS-N = 387 cm-1 and D0 = 32.4 kcal/mol. At the same time, the S-N bond has a sizable rotation barrier, △E0≠ = 12.7 kcal/mol, so CH3SNO exists as a cis- or trans-conformer, the latter slightly higher in energy, △E0 = 1.2 kcal/mol. The S-N bond properties are consistent with the antagonistic nature of CH3SNO, whose resonance representation requires two chemically opposite (antagonistic) resonance structures, CH3-S+=N-O- and CH3-S-/NO+, which can be probed using external electric fields and quantified using the natural resonance theory approach (NRT). The calculated S-N bond properties slowly converge with the level of correlation treatment, with the recently developed distinguished cluster with single and double excitations approximation (DCSD-F12) performing significantly better than the coupled cluster with single and double excitations (CCSD-F12), although still inferior to the CCSD(T)-F12 method that includes perturbative triple excitations. Double-hybrid density functional theory (DFT) calculations with mPW2PLYPD/def2-TZVPPD reproduce well the geometry, vibrational frequencies, and the S-N bond rotational barrier in CH3SNO, while hybrid DFT calculations with PBE0/def2-TZVPPD give a better S-N bond dissociation energy.

Multiconfigurational second-order perturbation study of the photochemical decomposition of methyl thionitrite

The photodissociation of methyl thionitrite (CH3SNO) has been computationally studied by means of CAS-SCF and MS-CASPT2 methods. The analysis of the multiconfigurational wavefunction corroborates the assignments of the absorption spectra, the visible and UV bands assigned to S0→S1(n, π∗) and S0→S2(π, π∗) transitions correspond to 1A′→1A″(nσ, π∗) and 1A′→2A′(nπ, π∗) excitations, respectively. With respect to the photochemistry of CH3SNO, it is found that the potential energy surfaces associated with the low-lying excited states of this molecule (11A″, 21A′, and 21A″) are repulsive along the NO elimination coordinates. For this reason, population of such excited states leads to NO extrusion as the primary process, in agreement with experiments.

The 355 nm photodissociation of jet-cooled CH 3SNO: alignment of the NO photofragment

The photodissociation dynamics of jet-cooled methyl thionitrite (CH 3SNO) have been studied using 355 nm polarised laser photolysis and probing of the NO photofragment by polarised laser-induced fluorescence. The alignment A 0 (2) between the electronic transition dipole moment involved in the absorption of the parent molecule and the rotational angular momentum J of the nascent NO ( v″=0 and v″=1) photofragment has been measured as a function of J up to J=44.5. The A 0 (2) values found are negative and approach the high- J limit confirming that the S 2←S 0 continuum transition of CH 3SNO in the near-UV arises from a π *←π transition to a repulsive excited state.

The Photodissociation of Jet‐cooled Methyl Thionitrite in the Visible

AbstractThe Dynamics of the photodissociation of jet‐cooled CH3SNO from the S1 (n,π*) state in the visible spectral range has been studied for the first time by pulsed laser photolysis and laser‐induced fluorescence probing of the nascent NO fragment. NO is formed vibrationally cold and rotationally hot confirming that the dissociation is a direct process, and that the structure in the S1 (n,π*) ← S0 absorption does not arise from predissociation. Scalar and some vector properties have been measured, and the fine structure selectivities of the NO fragment have been evaluated. NO is aligned strongly (A(2)0 = +0.75) with the E‐vector of the dissociation light and recoils perpendicularly to the transition dipole μ confirming the symmetry of the S1‐state as A″ and the electronic character as (n,π*). The observed dissociation dynamics of CH3SNO are compared with that of CH3ONO and with recent calculations by Schinke et al.

Diffuse vibrational structures in photoabsorption spectra: A comparison of CH3ONO and CH3SNO using two-dimensional a b i n i t i o potential energy surfaces

We investigated the photodissociation of methyl nitrite (CH3 ONO) and methyl thionitrite (CH3 SNO) within the first absorption band (S1 ←S0 ). The calculations were based on a two-dimensional model including the O–NO/S–NO and N=O bond distances as active coordinates. The S1 -potential energy surfaces were calculated with quantum chemical methods and the dynamical calculations were performed exactly within the time-independent approach. The main emphasis is on the origin of diffuse vibrational structure in the photoabsorption spectrum of both molecules. A low potential barrier of 0.086 eV along the O–NO dissociation coordinate in CH3 ONO prevents immediate dissociation and leads to an initial state dependent lifetime for the excited complex of 100–250 fs corresponding to 3–8 NO vibrational periods. CH3 ONO decays nonadiabatically via vibrational predissociation. The absorption spectrum of CH3 ONO is dominated by narrow Feshbach-like scattering resonances which can be characterized by two quantum numbers, m and n*: m=0 and 1 specifies the quanta of excitation in the O–NO bond and n*=0,1,2,... specifies the excited vibrational level of the N=O bond. The potential barrier is absent in CH3 SNO and the dissociation is direct on the time scale of about 10 fs corresponding to only one third of a NO vibrational period. Nevertheless, the absorption spectrum exhibits diffuse vibrational structures. The shape of the individual absorption peaks is determined by the classical Franck–Condon reflection principle. The dissociation of CH3 SNO is primarily adiabatic which leads to a pronounced energy dependence of the final NO vibrational state distribution. The diffuse structures originate in both cases from excitation of the NO stretching vibration. In order to make contact with time-dependent theory we calculated the autocorrelation function of the time-dependent wave function by inverse Fourier transformation of the energy-dependent spectra. The agreement with available experimental data for both molecules is quite satisfactory. This includes the energy spacing of the vibrational structure, the overall shape of the absorption spectrum, and the lifetime of the excited complex.

ChemInform Abstract: TWO ROTATIONAL ISOMERS OF METHYL THIONITRITE: LIGHT‐INDUCED, REVERSIBLE ISOMERIZATION IN AN ARGON MATRIX

Chemischer InformationsdienstVolume 15, Issue 31 Physical Organic Chemistry ChemInform Abstract: TWO ROTATIONAL ISOMERS OF METHYL THIONITRITE: LIGHT-INDUCED, REVERSIBLE ISOMERIZATION IN AN ARGON MATRIX R. P. + MUELLER, R. P. + MUELLERSearch for more papers by this authorJ. R. HUBER, J. R. HUBERSearch for more papers by this author R. P. + MUELLER, R. P. + MUELLERSearch for more papers by this authorJ. R. HUBER, J. R. HUBERSearch for more papers by this author First published: July 31, 1984 https://doi.org/10.1002/chin.198431044AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume15, Issue31July 31, 1984 RelatedInformation

Two rotational isomers of methyl thionitrite: light-induced, reversible isomerization in an argon matrix

Spectre IR du thionitrite de methyle en matrice d'Ar a 12 K indiquant une conformation cis et trans; Par irradiation a 485-590 nm isomerisation cis⇄trans selectivement induite. DG 298 0 (cis→trans)=5,56±0,76 kJ mole −1

Vibrational Spectra, Assignments, and Valence Force Field for S-nitrosocysteine and Isotopic Analogs

S-nitrosocysteine and the isotopically-substituted S15NO and N- d3 analogs have been prepared. FT-IR spectra have been obtained on the normal molecule and the 15N isotopomer. Spectra of the N- d3 analog were obtained with a dispersive instrument. The fundamental frequencies of the three isotopomers were calculated by using force constants previously obtained through overlay calculations on amino acids and from a normal coordinate analysis of methyl thionitrite. The average computational error between the observed and calculated frequencies using the transferred force constants was 11 cm−1. This difference was decreased to 7 cm−1 by slightly modifying some of the force constant values by a least-squares refinement. Vibrational assignments are made for all three isotopic analogs by utilizing the potential energy distribution. Out of a total of 96 fundamentals occurring above 300 cm−1, 65 may be classified as group vibrations by the potential energy criterion.

An FTIR study of the mechanism for the reaction HO + CH3SCH3

AbstractProduct studies were made using the Fourier transform infrared method in the uv (300–400‐nm) photolysis of mixtures containing CH3SCH3, C2H5ONO, and NO in ppm concentrations in 700 torr of O2–N2 diluent. Methyl thionitrite, CH3SNO, arising from the reaction CH3S + NO, was detected as an intermediate product. In addition, the yields of the major sulfur‐containing products SO2 and CH3SO3H coincided with those of the oxidation of the CH3S radicals generated directly by the photodissociation of CH3SNO. The formation of CH3S in the HO‐initiated oxidation of CH3SCH3 in the presence of NO suggests a reaction scheme involving the H‐abstraction reaction HO + CH3SCH3 → CH3SCH2 + H2O as the primary step.

Spectroscopic and photochemical properties of methyl thionitrite (CH3SNO)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSpectroscopic and photochemical properties of methyl thionitrite (CH3SNO)H. Niki, P. D. Maker, C. M. Savage, and L. P. BreitenbachCite this: J. Phys. Chem. 1983, 87, 1, 7–9Publication Date (Print):January 1, 1983Publication History Published online1 May 2002Published inissue 1 January 1983https://doi.org/10.1021/j100224a003RIGHTS & PERMISSIONSArticle Views129Altmetric-Citations29LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (327 KB) Get e-Alerts

Vibrational spectra and normal coordinate analysis of methyl thionitrite and isotopic analogs

The observed gas-phase IR frequencies for forty-four fundamentals of methyl thionitrite (CH 3SNO) and its d 3-, 13C-, and 15N-substituted analogs have been used to calculate a nineteen-parameter symmetry valence force field. The final refinement resulted in an average error of less than 4 cm −1 (~0.5%) between the calculated and observed frequencies for the four isotopomers. Contrary to earlier reports, relative intensities, isotopic frequency shifts, as well as the calculated potential-energy distribution, all support the assignment of v(CS) to a higher frequency than that of v(SN). For the normal molecule, v(CS) is observed as a weak band at 735 cm −1; by contrast, v(SN) absorbs strongly at 646 cm −1. The NO stretching fundamental occurs at 1535 cm −1 in the gas-phase spectrum of the unsubstituted molecule but shifts to 1507 cm −1 when 15N replaces the normal isotope. The five fundamental bands associated with the skeletal vibrations of CH 3SNO are compared with the analogous absorptions in the spectra of CF 3SNO and CH 3ONO.

Reactions of thiyl radicals. II. The photolysis of methyl disulfide vapor

The photolysis of methyl disulfide vapor in the pressure range 2–25 Torr at wavelengths between 2 300 and 2 800 and at 2 288 Å has been examined and the effect of temperature, pressure, added inert gases, ethyl disulfide, and nitric oxide determined.The primary process is a direct production of two CH3S radicals which have excess energy and which can be observed as methyl thionitrite when NO is present during the decomposition. When pure disulfide is photolyzed the major observable product is methanethiol, although this material accounts for only a small fraction of the primarily produced thiyl radicals whose principal fate is recombination in a substrate-reforming reaction producing excited disulfide molecules. The latter species are deactivated by added gases, or by the substrate itself. The mode of mercaptan formation is by abstraction of H atoms from the substrate by excited CH3S radicals with an apparent activation energy of 1.5 kcal.

Force constants and normal vibrational modes of a simplified molecular model of methyl thionitrite

With a potential function based on the valence force field approximation, Wilson's G- F matrix method was used to determine the force constants of a simplified molecular model of methyl thionitrite (CH 3SNO). The derivation of the model's Lagrangian function in Cartesian coordinates was used as a check of the numerical calculations performed with the aid of the G- F matrix method. The model's normal modes of vibration and their normalized energy distribution among the internal coordinates were calculated. These results led to the reassignment of two fundamental frequencies of methyl thionitrite.

The infrared spectrum of methyl thionitrite

A new reaction has been used to prepare methyl thionitrite and the infrared spectrum of its vapor phase was analyzed. By comparison with the infrared spectra of gaseous nitrous acid and methyl nitrite, most of the observed absorption bands of methyl thionitrite have been assigned to fundamental, harmonic or combination frequencies. The spectra of nitrous acid and of methyl nitrite show evidence of rotational isomerism whereas no such restriction in internal free rotation is suggested for the methyl thionitrite molecule.