Van't Hoff law for temperature dependent Langmuir constants in clathrate hydrate nanocavities

This work gives a van't Hoff law expression of Langmuir constants of different species for determining their occupancy in the nanocavities of clathrate hydrates. The van't Hoff law's parameters are derived from a fit with Langmuir constants calculated using a pairwise site-site interaction potential to model the anisotropic potential environment in the cavities, as a function of temperature. The parameters can be used for calculating clathrates compositions. Results are given for nineteen gas species trapped in the small and large cavities of structure types I and II [1]. The accuracy of this approach is based on a comparison with available experimental data for ethane and cyclo- propane clathrate hydrates. The numerical method applied in this work, was recently validated from a comparison with the spherical cell method based on analytical considerations [1]Comment: 2 figure

Trapping effects on the vibration-inversion-rotation motions of an ammonia molecule encapsulated in C60_{60} fullerene molecule

The infrared bar-spectrum of a single ammonia molecule encapsulated in nano-cage C$_{60}$ fullerene molecule is modelled using the site inclusion model successfully applied to analyze spectra of CO$_2$ isotopologues isolated in rare gas matrix. Calculations show that NH$_3$ can rotate freely on a sphere of radius 0.184 $\text{\AA}$ around the site centre of the nano-cage and spin freely about its C$_3$ symmetry axis. In the static field inside the cage degenerate $\nu_3$ and $\nu_4$ vibrational modes are blue shifted and split. When dynamic coupling with translational motion is considered, the spectral signature of the $\nu_2$ mode is modified with a higher hindering barrier (2451 cm$^{-1}$), an effective reduced mass (6.569 g.mol$^{-1}$) and a longer tunneling time (55594 ps) for the fundamental level compared to gas-phase values (2047 cm$^{-1}$), (2.563 g.mol$^{-1}$) and (20.85 ps). As a result this mode is red shifted. Moreover, simulation shows that the changes in the bar-spectrum of the latter mode can be used to probe the temperature of the surrounding media in which fullerene is observed

Investigation of the interaction of some astrobiological molecules with the surface of a graphite (0001) substrate. Application to the CO, HCN, H2O and H2CO molecules

Detailed semi-empirical interaction potential calculations are performed to determine the potential energy surface experienced by the molecules CO, HCN, H2O and H2CO, when adsorbed on the basal plane (0001) of graphite at low temperature. The potential energy surface is used to find the equilibrium site and configuration of a molecule on the surface and its corresponding adsorption energy. The diffusion constant associated with molecular surface diffusion is calculated for each molecule.Comment: 15 pages, 3 figure

The simplicity index of tournaments

An $n$-tournament $T$ with vertex set $V$ is simple if there is no subset $M$ of $V$ such that $2\leq \left \vert M\right \vert \leq n-1$ and for every $x\in V\setminus M$, either $M\rightarrow x$ or $x \rightarrow M$. The simplicity index of an $n$-tournament $T$ is the minimum number $s(T)$ of arcs whose reversal yields a non-simple tournament. M\"{u}ller and Pelant (1974) proved that $s(T)\leq\frac{n-1}{2}$, and that equality holds if and only if $T$ is doubly regular. As doubly regular tournaments exist only if $n\equiv 3\pmod{4}$, $s(T)<\frac{n-1}{2}$ for $n\not\equiv3\pmod{4}$. In this paper, we study the class of $n$-tournaments with maximal simplicity index for $n\not\equiv3\pmod{4}$

Simulating relaxation channels of CO2 in clathrate canocages

The energy levels of CO2 in the small (s) and large (l) nano-cages of cubic sI clathrates are calculated in the Born-Oppenheimer approximation using pairwise atom-atom interaction potentials. In the s cage, the centre of mass of CO2 oscillates with small amplitudes, asymmetrically about the cage center with harmonic frequencies around 100 cm-1. In the l cage, oscillations are anharmonic with large amplitude motions in a plane parallel to the hexagonal faces of the cage and the corresponding frequencies are calculated to be 55 cm-1 and 30 cm-1. Librational harmonic frequencies are calculated at 101.7 cm-1 and 56.0 cm-1 in the 5 cage and at 27.9 cm-1 and 46.4 cm-1 in the l cage. Results show that the coupling between the CO2 molecule and the nano-cage is quite different for the low frequency translational, rotational or librational modes and the high frequency vibrational modes, which consequently leads to different relaxation channels

2D- and 3D-QSRR Studies of Linear Retention Indices for Volatile Alkylated Phenols

In this study, 29 volatile alkylated phenols were subjected to a quantitative structure retention relationships (QSRR) studies; we have developed two- and three-dimensional quantitative structure retention relationships (2D- and 3D-QSRR) for this series; and these molecules were subjected to a 2D-QSRR analysis for their retention property using stepwise multiple linear regression (MLR) and 3D-QSRR analysis using partial least squares (PLS). The 28 descriptors are calculated for the 29 molecules using the ChemOffice and ChemSketch software to construct 2D-QSRR model. The 3D-QSRR models were constructed using comparative molecular field analysis (CoMFA) method. The models were used to predict the linear retention indices of the test set compounds, and agreement between the experimental and predicted values was verified. The statistical results indicate that the predicted values are in good agreement with the experimental results (r2 = 0.980; r2CV = 0.977 and r2 = 0.998; r2CV = 0.959 for MLR and CoMFA methods, respectively). To validate the predictive power of the resulting models, external validation multiple correlation coefficient was calculated; in addition to a performance prediction power, this coefficient has a favorable estimation of stability for the two methods (rtest = 0.938 and rtest = 0.955 for MLR and CoMFA methods, respectively)

QSPR Study of the Retention/release Property of Odorant Molecules in Water Using Statistical Methods

An integrated approach physicochemistry and structures property relationships has been carried out to study the odorant molecules retention/release phenomenon in the water. This study aimed to identify the molecular properties (molecular descriptors) that govern this phenomenon assuming that modifying the structure leads automatically to a change in the retention/release property of odorant molecules. ACD/ChemSketch, MarvinSketch, and ChemOffice programs were used to calculate several molecular descriptors of 51 odorant molecules (15 alcohols, 11 aldehydes, 9 ketones and 16 esters). A total of 37 molecules (2/3 of the data set) were placed in the training set to build the QSPR models, whereas the remaining, 14 molecules (1/3 of the data set) constitute the test set. The best descriptors were selected to establish the quantitative structure property relationship (QSPR) of the retention/release property of odorant molecules in water using multiple linear regression (MLR), multiple non-linear regression (MNLR) and an artificial neural network (ANN) methods. We propose a quantitative model according to these analyses. The models were used to predict the retention/release property of the test set compounds, and agreement between the experimental and predicted values was verified. The descriptors showed by QSPR study are used for study and designing of new compounds. The statistical results indicate that the predicted values are in good agreement with the experimental results. To validate the predictive power of the resulting models, external validation multiple correlation coefficient was calculated and has both in addition to a performant prediction power, a favorable estimation of stability. DOI:&nbsp;http://dx.doi.org/10.17807/orbital.v9i4.97

Density Functional Theory Based Quantitative Structure-Activity Relationship Study of Cycloguanil Derivatives Acting as Plasmodium falciparum.

This work presents a study of quantitative structure-activity relationship (QSAR) on the cycloguanil derivatives which are reported as growth inhibitors of clone of Plasmodium falciparum (T9/94 RC17) which houses A16V+S108T mutant dihydrofolate reductase (DHFR) enzyme. A set of 24 molecule-derived cycloguanil was modeled using the Gauss View software (03) using DFT B3LYP 6,6-31G-31G (d) as a base function. The obtained descriptions are purely electronic. The set constitute the inhibitory activity and the calculated electronic descriptors were statistically processed with principal component analysis (PCA), multiple linear regression (MLR), multiple nonlinear regressions (MNLR) and artificial neural network (ANN). The results obtained by the artificial neural network (ANN) show that the expected activities are in good agreement with the experimental results, with equal correlation coefficient R = 0, 912.To determine the architecture of this network, we varied the number of hidden layers, the number of neurons in the hidden layers, the transfer functions and the pairs of transfer functions. The best results were obtained with a network architecture [3-3-1], activation functions (Tansig-Purelin) and a learning algorithm of Levenberg-Marquardt.