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The Superposing Significant Interaction Rules (SSIR) Method
Published in A. K. Haghi, Lionello Pogliani, Eduardo A. Castro, Devrim Balköse, Omari V. Mukbaniani, Chin Hua Chia, Applied Chemistry and Chemical Engineering, 2017
Emili Besalú, Lionello Pogliani, J. Vicente Julian-Ortiz
Once the selected rules (and their votes) are known, each molecular structure will cumulate the votes for all the significant variables condensing it. The ultimate goal is to apply this voting scheme also over new compounds not present in the sublibrary in order to rank them properly. For ranked or continuous molecular property values, the resulting series of votes per molecule is expected to be correlated with them. For categorical or pure dichotomic properties, it is assumed that the higher the number of votes a structure is collecting, the higher probability of being of a particular group.
Investigations on asphaltene aggregate formation by high-field diffusion NMR and low-field ghost solvent NMR relaxometry
Published in Journal of Dispersion Science and Technology, 2022
Salim Ok, Michael Fernandes, Mohamed A. Sabti
The diffusion coefficient (D), an important molecular property giving information on molecular dimensions, association, and aggregation states of molecules, relies on various properties such as the size and shape of the molecule of interest and the surrounding fluid. For a hard-sphere in a solvent with viscosity ηs, the Einstein–Stokes equation correlates the diffusion coefficient to the viscosity as follows:[20] where kB is the Boltzmann’s constant, T is the absolute temperature, and r is the sphere’s radius. When the solvent’s viscosity is known, the determination of the diffusion constant gives the molecule’s radius. Association followed by aggregation makes it challenging to calculate the mean molecular weights of asphaltenes by conventional approaches, including the standard chromatography method of size exclusion.[21] Among different techniques, PFG 1H NMR is used to study natural organic compounds, complicated representative mixtures, and polydisperse probes.[22,23]
Lennard–Jones Lecture 2017* *
Published in Molecular Physics, 2018
RIKES spectroscopy explores the intermolecular motion in liquids through the spectrum of fluctuations in the anisotropic polarisability of the sample. It is complementary to dielectric spectroscopy which measures the spectrum of fluctuations in the dipole moment of the sample; both spectroscopies probe intermolecular motion in the liquid. CS2 is a small molecule with a large anisotropic susceptibility and, in solution, is particularly useful as a probe for the local environment of a solvent [24]. Although it is possible to obtain the RIKES spectra from simulations [25], it is expensive as a large matrix must be diagonalised at each step and, being a collective property rather than a molecular property the simulation must be run for times as long as to obtain the same signal to noise ratio as for a single molecule property. Here N is the number of molecules in the molecular dynamics cell. However, the low frequency molecular vibrational density of states provides another measure of intermolecular motion, and is cheaper to calculate being a single molecule property. Although we would not expect quantitative agreement between the vibrational density of states and the experimental RIKES spectra, we can expect that the effects of changes in the environment would be similar and that the simulation could help give a molecular explanation of these changes.
Laboratory evaluation of species-dependent relative ionization efficiencies in the Aerodyne Aerosol Mass Spectrometer
Published in Aerosol Science and Technology, 2018
Wen Xu, Andrew Lambe, Philip Silva, Weiwei Hu, Timothy Onasch, Leah Williams, Philip Croteau, Xuan Zhang, Lindsay Renbaum-Wolff, Edward Fortner, Jose L. Jimenez, John Jayne, Douglas Worsnop, Manjula Canagaratna
IE is the probability of a molecule being ionized when passing through the electron beam; σ is the EI ionization cross-section (m2), a molecular property of the analyte that varies with electron energy; lm is the width (m) of the electron beam; vm is the velocity of the molecule (m s−1); ve (ve >> vm) is the velocity of the electrons (m s−1); ne is the density of electrons in the electron beam (m−3); Je is the flux of electrons (m−2 s−1), and tm is the residence time of the molecule in the electron beam. For a given ionization source, Je is fixed, only σ and tm vary with the molecular properties. The value of tm varies with the molecular weight of the gas phase component that is undergoing ionization and σ is estimated theoretically using the Binary-Encounter-Bethe (BEB) model (Hwang et al. 1996) as briefly described below.