179,804 research outputs found
Using X-ray derived charge densities to detect electron delocalization effects and non-covalent interactions
No full textBeing based on a quantum observable and measurable quantity, the Electron Density (ED) based descriptors retain the advantage of enabling a direct comparison of theoretical predictions with experimental results. We review here our most recent work aimed at evaluating whether two of such descriptors, the Source Function, SF, [1] and the Reduced Density Gradient (RDG), are able to unveil electron delocalization effects (EDEs) and non covalent interactions (NCI), respectively.
Making use of ab-initio EDs, we recently proved that the SF clearly detects EDEs in a series of supposedly electron-conjugated compounds [2]. That study is here extended to molecular crystals (benzene, a substituted binaphtyl-2-ol, citrinin), whose ED is derived from X-ray diffraction data. Regardless of the ED origin, the SF appears a useful tool to study fine details of EDEs, and independently from any symmetry constraint (e.g. / separation of the ED).
A novel NCI descriptor, based on the RDG and enabling an easy-to-catch image of either the supposedly attractive (dispersive, hydrogen bonding) or allegedly repulsive (steric) interactions, was recently proposed [3]. We have applied [4] this same tool to experimentally-derived ED’s of molecular solids (austdiol, benzene, famotidine), and discussed its performance in synergy with Bader’s analysis. We have also explored [5] the amount and type of information that is lost when the IAM replaces the “true” ED in evaluating the RDG.
References
[1] R.F.W. Bader, C. Gatti, Chem. Phys. Lett. 287 (1998) 233-238.
[2] E. Monza, C. Gatti, L. Lo Presti, E. Ortoleva, J. Phys. Chem. A 115 (2011) 12864-12878.
[3] E.R. Johnson, S. Keinan, P. Mori-Sanchez, J. Contreras-Garcia JACS 132 (2010), 6498.
[4] G. Saleh, C. Gatti, L. Lo Presti, J. Contreras-Garcia, submitted (2012)
[5] G. Saleh, C. Gatti, L. Lo Presti, submitted (2012
CLPdyn: a cheap and reliable tool for molecular dynamics studies of organic molecules in condensed phase
Full text linkWe present CLPdyn, a freely available code intended to perform Molecular Dynamics simulations of organic molecules in condensed phase.[1–3] CLPdyn can handle both continuous phases (liquids, crystals) and finite-size clusters (liquid droplets, nanoparticles), and exploits the thoroughly tested Coulomb-London-Pauli atom-atom intermolecular potential[4,5]. The implementation relies on standard MD algebra, but also includes new algorithms, specifically designed to deal with isolated clusters, to (i) suppress net overall translational and rotational momenta, (ii) handle the evaporation of molecules from the cluster surface, and (iii) measure the amount of residual symmetry from the number and kind of isometries present in the cluster. Application to organic solvents (benzene, chloroform, methanol and pyridine) [2] and crystals spanning very different intermolecular recognition patterns (maleic/succinic anhydrides, alanine/glutamic acid, methylurea, 1,4-cyclohexadiene and methyl-2-amino-5-hydroxybenzoate) [3], shows that CLPdyn reliably reproduces macroscopic thermodynamic quantities, and highlights the effect of the relative strengths of intermolecular forces on rotational correlation times, self-diffusion coefficients and pair distribution functions. Possible applications of CLPdyn to the molecular–level study of non–equilibrium solution chemistry, including the early stages of crystal nuclei formation, are also discussed.
[1] A. Gavezzotti, CLPdyn, Monte Carlo and Molecular Dynamics modules, Description and user manual, www.angelogavezzotti.it (2018).
[2] A. Gavezzotti, L. Lo Presti, New J. Chem., 2019,43, 2077-2084.
[3] A. Gavezzotti, L. Lo Presti, in preparation
[4] A. Gavezzotti, New J. Chem. 2011, 35, 1360–1368.
[5] A. Gavezzotti and L. Lo Presti, Crystal Growth Des. 2016, 16, 2952–2962
New descriptors for an “unbiased” and chemically insightful comparison of ab-initio and X-ray derived charge densities
No full textThe results of modelling always need to be compared and validated against the experiment. To be meaningful, the comparison should be as much as possible unbiased, and, hopefully, should use tools also able to provide chemical insight. Being based on a quantum observable and measurable quantity, the Electron Density (ED) based descriptors enable a direct comparison of ab-initio and X-ray derived EDs. They also provide a description of chemical paradigms which is, in principle, freed at the outset from any model preconception or arbitrariness. Furthermore, as for their nature rooted in physics, they are ideally suited to validate or reject the interpretive models of chemistry based on useful, but arbitrary objects. In this lecture, we will discuss the capability of two of such descriptors, the Source Function (SF) [1] and the Reduced Density Gradient (RDG), to unveil electron delocalization effects and to detect non covalent interactions, respectively. The SF enables one to view chemical bonding and other chemical paradigms under a new perspective [1,2]. We recently addressed the question of whether the SF is also capable to reveal electron delocalization effects (EDEs) in a series of supposedly electron-conjugated compounds, investigated through ab-initio methods [2]. The study is here extended to various molecular crystals (benzene, naphtalene and a substituted binaphtyl-2-ol), whose ED and SF results were obtained from X-ray diffraction data. Regardless of the derivation of the ED, the answer to the question above is convincingly positive. The capability of the SF to reveal EDEs is independent from a / separation and EDEs may be recovered even when such separation is unfeasible or when symmetry reasons would preclude it. Use of the SF to test the concept of hypervalency in the K2SO4 crystal [4] will also be discussed. A novel non covalent interaction (NCI) descriptor, based on the RDG and enabling an easy-to-catch pictorial visualization of either the supposedly attractive (dispersive, hydrogen bonding) or allegedly repulsive (steric) intermolecular interactions, was recently developed [5]. We apply for the first time [6] this same tool to experimentally-derived ED’s of molecular solids (austdiol, benzene, famotidine) discussing its performance in synergy with Bader’s analysis and using our software code, NCI-Milano [7], purposedly developed for such an extension.
[1] R.F.W. Bader, C. Gatti Chem Phys. Lett. 1998, 287, 233-238.
[2] C. Gatti Struct. Bond. 2012, 147, 193-286.
[3] E. Monza, C. Gatti, L. Lo Presti, E. Ortoleva J. Phys. Chem. A 2011, 115, 12864-12878.
[4] M.S. Schmøkel, S. Cenedese, J. Overgaard, M.R.V. Jørgensen, Y-S Chen, C. Gatti, D. Stalke, B.B. Iversen Inorg. Chem. 2012, 51, 8607-8616.
[5] E.R. Johnson, S. Keinan, P. Mori-Sanchez, J. Contreras-Garcia, A.J. Cohen, W. Yang J. Am. Chem. Soc 2010, 132, 6498-6506.
[6] G. Saleh, C. Gatti, L. Lo Presti, J. Contreras-Garcia Chem. Eur. J. 2012,18,15523-15536.
[7] G. Saleh, L. Lo Presti, C. Gatti, D. Ceresoli J. Appl. Cryst. 2013, 46, 1513-1517
[Letter from Arthur S. Rosichan to J. L. Zuber - August 11, 1944]
No full textLetter from Arthur S. Rosichan to J. L. Zuber: August 11, 1944. Subject of the letter is the author moving to Houston to work for the Jewish Community Council
The relationship between daily occupational affective experiences and subjective well-being.
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Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of meson decays to J/ψη and J/ψη′
Full text linkFirst evidence of the B 0 → J / ψ ω decay is found and the B s 0 → J / ψ η and B s 0 → J / ψ η ′ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb -1 collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The branching fractions of these decays are measured relative to that of the B 0 → J / ψ ρ 0 decay:frac(B (B 0 → J / ψ ω), B (B 0 → J / ψ ρ 0)) = 0.89 ± 0.19 (stat) - 0.13 + 0.07 (syst),frac(B (B s 0 → J / ψ η), B (B 0 → J / ψ ρ 0)) = 14.0 ± 1.2 (stat) - 1.5 + 1.1 (syst) - 1.0 + 1.1 (frac(f d, f s)),frac(B (B s 0 → J / ψ η ′), B (B 0 → J / ψ ρ 0)) = 12.7 ± 1.1 (stat) - 1.3 + 0.5 (syst) - 0.9 + 1.0 (frac(f d, f s)), where the last uncertainty is due to the knowledge of f d / f s, the ratio of b-quark hadronization factors that accounts for the different production rate of B 0 and B s 0 mesons. The ratio of the branching fractions of B s 0 → J / ψ η ′ and B s 0 → J / ψ η decays is measured to befrac(B (B s 0 → J / ψ η ′), B (B s 0 → J / ψ η)) = 0.90 ± 0.09 (stat) - 0.02 + 0.06 (syst)
Sex differences in the correlations of daily affective occupational experiences and subjective well-being measures.
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