Conformational properties of 1-cyano-1-silacyclohexane, C5H10SiHCN: Gas electron diffraction, low-temperature NMR and quantum chemical calculations

The conformational preference of the cyano group of the 1-cyano-1-silacyclohexane was studied experimentally by means of gas electron diffraction (GED) and dynamic nuclear magnetic resonance (DNMR) as well as by quantum chemical (QC) calculations applying high-level coupled cluster methods as well as DFT methods. According to the GED experiment, the compound exists in the gas-phase as a mixture of two conformers possessing the chair conformation of the six-membered ring and Cs symmetry while differing in the axial or equatorial position of the substituent (axial = 84(12) mol %/equatorial = 16(12) mol %) at T = 279(3) K, corresponding to an A value (Gax – Geq) of −1.0(4) kcal mol−1. Gas-phase CCSD(T) calculations predict an A value of −0.72 kcal mol−1 at 279 K. In contrast, the low-temperature 13C NMR experiments resulted in an axial/equatorial ratio of 35/65 mol % at 120 K corresponding to an A value of 0.14 kcal mol−1. An average value for ΔG#e→a = 5.6 ± 0.1 kcal mol−1 was obtained for the temperature range 110–145 K. The dramatically different conformational behaviour in the gas-phase (GED) compared to the liquid phase (DNMR) suggests a strong solvation effect. According to natural bond orbital analysis the axial conformer of the title compound is an example of stabilization of a form, which is not favored by electrostatic effects and is favored predominantly by steric and conjugation effects.A.V.B. and Yu.F.S. are grateful to the Ministry of Education and Science of Russia (State Contracts N 14.B25.31.0013) for financial support. S.A.Sh. thanks the Russian Foundation for Basic Research (Grant 14-03-0023-a). I.A., S.O.W., and N.R.J. thank the Icelandic Centre for Research (RANNIS) for financial support, Grants No 080038021 and 100040022. R.B. acknowledges support from the Icelandic Research Fund, grant no. 141218051

Plants with genetically encoded autoluminescence

Autoluminescent plants engineered to express a bacterial bioluminescence gene cluster in plastids have not been widely adopted because of low light output. We engineered tobacco plants with a fungal bioluminescence system that converts caffeic acid (present in all plants) into luciferin and report self-sustained luminescence that is visible to the naked eye. Our findings could underpin development of a suite of imaging tools for plants

Gas-Phase Structure of 3,7,9-tris(trifluoromethylsulfonyl)-3,7,9-triazabicyclo[3.3.1]nonane by GED and Theoretical Calculations

The molecular structure and conformational and rotational composition of 3,7,9-tris(trifluoromethylsulfonyl)-3,7,9-triazabicyclo[3.3.1]nonane 1 have been investigated by synchronous gas-phase electron diffraction/mass spectrometry GED/MS and theoretical calculations (B3LYP and M06-2X with cc-pVTZ and aug-cc-pVTZ basis sets) and compared to the X-ray structure. All 16 possible conformers and rotamers were calculated, differing by the conformations of the two piperazine rings, orientation of the CF3 groups relative to these rings, and non-equivalence of the two wings of the butterfly structure. The optimized geometry of the most stable 1-c-out-2-c-out conformer coincides with that in the crystal. In contrast to only one conformer determined by X-ray, the GED analysis revealed the presence of five conformers, 1-c-out-2-c-out (I), 1-c-in-2-c-out (II), 1-c-out-2-c-in (III), 1-b-out-2-c-out (IV), 1-c-out-2-b-out (V) in the ratio of I:(II + III):IV:V = 36(10):42(6):22(10):0(10). The experimental results are better reproduced by calculations performed for 428 K (the temperature of the GED experiment) than for 298 K (standard), and most satisfactorily at the M06-2X/aug-cc-pVTZ level of theory

Combined gas electron diffraction and mass spectrometric experimental setup at Bielefeld University

Vishnevskiy Y, Blomeyer S, Reuter C, Pimenov OA, Shlykov SA. Combined gas electron diffraction and mass spectrometric experimental setup at Bielefeld University. REVIEW OF SCIENTIFIC INSTRUMENTS. 2020;91(7).We have designed and constructed a combined experimental setup for synchronous measurements of electron diffraction patterns and mass-spectra of gas samples. Test measurements have been performed for acetic acid at two temperatures, 296 K and 457 K. Electron diffraction data have been analyzed taking into account mass spectra measured in the same experiments. From the diffraction intensities, molecular structures and mole fractions of the acetic acid monomer and dimer have been refined. The obtained results demonstrate the importance of measuring mass spectra in gas electron diffraction experiments. In particular, it is possible to detect the sample decomposition, which can be used for the optimization of experimental conditions and for the data interpretation. The length of the hydrogen bond in the acetic acid dimer determined in this work, r(e)(OH) = 1.657(9) angstrom, is in good agreement with modern theoretical predictions. We recommend measuring the diffraction patterns of acetic acid for the calibration of the sample pressure in the diffraction volume

Combined Gas Electron Diffraction and Mass Spectrometric Experimental Setup at Bielefeld University

We have designed and constructed a combined experimental setup for synchronous measurements of electron diffraction patterns and mass-spectra of gas samples. Test measurements have been performed for acetic acid at two temperatures, 296 and 457 K, respectively. Electron diffraction data have been analysed taking into account mass spectra measured in the same experiments. From the diffraction intensities molecular structures and mole fractions of the acetic acid monomer and dimer have been refined. The obtained results demonstrate the importance of measuring mass spectra in gas electron diffraction experiments. In particular, it is possible to detect the sample decomposition, which can be used for the optimization of experimental conditions and for the data interpretation. The determined in this work length of the hydrogen bond in the acetic acid dimer, re(O...H) = 1.657(9) Å, is in good agreement with modern theoretical predictions. We recommend to measure diffraction patterns of acetic acid for the calibration of the sample pressure in the diffraction point.<br /

Molecular Structure of Nickel Octamethylporphyrin&mdash;Rare Experimental Evidence of a Ruffling Effect in Gas Phase

The structure of a free nickel (II) octamethylporphyrin (NiOMP) molecule was determined for the first time through a combined gas-phase electron diffraction (GED) and mass spectrometry (MS) experiment, as well as through quantum chemical (QC) calculations. Density functional theory (DFT) calculations do not provide an unambiguous answer about the planarity or non-planar distortion of the NiOMP skeleton. The GED refinement in such cases is non-trivial. Several approaches to the inverse problem solution were used. The obtained results allow us to argue that the ruffling effect is manifested in the NiOMP molecule. The minimal critical distance between the central atom of the metal and nitrogen atoms of the coordination cavity that provokes ruffling distortion in metal porphyrins is about 1.96 &Aring;