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1. Comment on “The chemical reactions in electrosprays of water do not always correspond to those at the pristine air–water interface” by A. Gallo Jr, A. S. F. Farinha, M. Dinis, A.-H. Emwas, A. Santana, R. J. Nielsen, W. A. Goddard III and H. Mishra, Chem. Sci. , 2019, 10 , 2566

   https://doi.org/10.1039/c9sc00991d  

   Colussi, Agustín J. ; Enami, Shinichi ( September 2019 , Chemical Science)

   null (Ed.)

   Recently, Gallo et al. ( Chem. Sci., 2019, 10, 2566) investigated whether the previously reported oligomerization of isoprene vapor on the surface of pH < 4 water in an electrospray ionization (ESI) mass spectrometer ( J. Phys. Chem. A, 2012, 116, 6027 and Phys. Chem. Chem. Phys., 2018, 20, 15400) would also proceed in liquid isoprene–acidic water emulsions. Gallo et al. hypothesized that emulsified liquid isoprene would oligomerize on the surface of acidic water because, after all, isoprene, liquid or vapor, is always a hydrophobe. In their emulsion experiments, isoprene oligomers were to be detected by ex situ proton magnetic resonance ( 1 H-NMR) spectrometry. 

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2. Experimental and theoretical assessment of protonated Hoogsteen 9-methylguanine–1-methylcytosine base-pair dissociation: kinetics within a statistical reaction framework

   https://doi.org/10.1039/d0cp06682f  

   Moe, May Myat ; Benny, Jonathan ; Sun, Yan ; Liu, Jianbo ( April 2021 , Physical Chemistry Chemical Physics)

   null (Ed.)

   We investigated the collision-induced dissociation (CID) reactions of a protonated Hoogsteen 9-methylguanine–1-methylcytosine base pair (HG-[9MG·1MC + H] + ), which aims to address the mystery of the literature reported “anomaly” in product ion distributions and compare the kinetics of a Hoogsteen base pair with its Watson-Crick isomer WC-[9MG·1MC + H] + (reported recently by Sun et al. ; Phys. Chem. Chem. Phys. , 2020, 22 , 24986). Product ion cross sections and branching ratios were measured as a function of center-of-mass collision energy using guided-ion beam tandem mass spectrometry, from which base-pair dissociation energies were determined. Product structures and energetics were assessed using various theories, of which the composite DLPNO-CCSD(T)/aug-cc-pVTZ//ωB97XD/6-311++G(d,p) was adopted as the best-performing method for constructing a reaction potential energy surface. The statistical Rice–Ramsperger–Kassel–Marcus theory was found to provide a useful framework for rationalizing the dominating abundance of [1MC + H] + over [9MG + H] + in the fragment ions of HG-[9MG·1MC + H] + . The kinetics analysis proved the necessity for incorporating into kinetics modeling not only the static properties of reaction minima and transition states but more importantly, the kinetics of individual base-pair conformers that have formed in collisional activation. The analysis also pinpointed the origin of the statistical kinetics of HG-[9MG·1MC + H] + vs. the non-statistical behavior of WC-[9MG·1MC + H] + in terms of their distinctively different intra-base-pair hydrogen-bonds and consequently the absence of proton transfer between the N1 position of 9MG and the N3′ of 1MC in the Hoogsteen base pair. Finally, the Hoogsteen base pair was examined in the presence of a water ligand, i.e. , HG-[9MG·1MC + H] + ·H 2 O. Besides the same type of base-pair dissociation as detected in dry HG-[9MG·1MC + H] + , secondary methanol elimination was observed via the S N 2 reaction of water with nucleobase methyl groups. 

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3. Correction: High pressure single-molecule FRET studies of the lysine riboswitch: cationic and osmolytic effects on pressure induced denaturation

   https://doi.org/10.1039/d0cp90155e  

   Sung, Hsuan-Lei ; Nesbitt, David J. ( July 2020 , Physical Chemistry Chemical Physics)

   Correction for ‘High pressure single-molecule FRET studies of the lysine riboswitch: cationic and osmolytic effects on pressure induced denaturation’ by Hsuan-Lei Sung et al. , Phys. Chem. Chem. Phys. , 2020, DOI: 10.1039/d0cp01921f. 

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4. Classical and nonclassical effects in surface hopping methodology for simulating coupled electronic-nuclear dynamics

   https://doi.org/10.1039/C9FD00042A  

   Martens, Craig C. ( January 2019 , Faraday Discussions)

   In this paper, we analyze the detailed quantum-classical behavior of two alternative approaches to simulating molecular dynamics with electronic transitions: the popular fewest switches surface hopping (FSSH) method, introduced by Tully in 1990 [Tully, \textit{J.~Chem.~Phys.}, 1990, \textbf{93}, 1061] and our recently developed quantum trajectory surface hopping (QTSH) method [Martens, \textit{J.~Phys.~Chem.~A}, 2019 \textbf{123}, 1110]. Both approaches employ an independent ensemble of trajectories that undergo stochastic transitions between electronic surfaces. The methods differ in their treatment of energy conservation, with FSSH imposing conservation of the classical kinetic plus potential energy by rescaling of the classical momenta when a surface hop occurs, while QTSH incorporates quantum forces throughout the dynamics which lead naturally to the conservation of the full quantum-classical energy. We investigate the population transfer and energy budget of the surface hopping methods for several simple model systems and compare with exact quantum result. In addition, the detailed dynamics of the trajectory ensembles in phase space are compared with the quantum evolution in the Wigner representation. Conclusions are drawn. 

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5. Tuning the melting point of selected ionic liquids through adjustment of the cation's dipole moment

   https://doi.org/10.1039/D0CP01214A  

   Rabideau, Brooks D. ; Soltani, Mohammad ; Parker, Rome A. ; Siu, Benjamin ; Salter, E. Alan ; Wierzbicki, Andrzej ; West, Kevin N. ; Davis, James H. ( June 2020 , Physical Chemistry Chemical Physics)

   In previous work with thermally robust salts [Cassity et al., Phys. Chem. Chem. Phys. , 2017, 19 , 31560] it was noted that an increase in the dipole moment of the cation generally led to a decrease in the melting point. Molecular dynamics simulations of the liquid state revealed that an increased dipole moment reduces cation–cation repulsions through dipole–dipole alignment. This was believed to reduce the liquid phase enthalpy, which would tend to lower the melting point of the IL. In this work we further test this principle by replacing hydrogen atoms with fluorine atoms at selected positions within the cation. This allows us to alter the electrostatics of the cation without substantially affecting the sterics. Furthermore, the strength of the dipole moment can be controlled by choosing different positions within the cation for replacement. We studied variants of four different parent cations paired with bistriflimide and determined their melting points, and enthalpies and entropies of fusion through DSC experiments. The decreases in the melting point were determined to be enthalpically driven. We found that the dipole moment of the cation, as determined by quantum chemical calculations, is inversely correlated with the melting point of the given compound. Molecular dynamics simulations of the crystalline and solid states of two isomers showed differences in their enthalpies of fusion that closely matched those seen experimentally. Moreover, this reduction in the enthalpy of fusion was determined to be caused by an increase in the enthalpy of the crystalline state. We provide evidence that dipole–dipole interactions between cations leads to the formation of cationic domains in the crystalline state. These cationic associations partially block favourable cation–anion interactions, which are recovered upon melting. If, however, the dipole–dipole interactions between cations is too strong they have a tendency to form glasses. This study provides a design rule for lowering the melting point of structurally similar ILs by altering their dipole moment. 

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