RESUMEN
We study the rotational and translational dynamics of three small important linear molecules, namely, carbon monoxide (CO), nitric oxide (NO), and cyanide ion (CN-) in water-ethanol mixtures, at different compositions. Here, we report a detailed study of the dynamics of these diatomics in water-ethanol binary mixtures for the first time. We find multiple anomalous results, namely, (i) faster rotational motion of CO and NO than CN-, (ii) larger translational diffusion of CO and NO in pure ethanol than in water but the reverse for CN-, (iii) a pronounced anomaly in the composition dependence of translational-rotational dynamics at low ethanol composition, and (iv) a re-entrant type behavior in the viscosity dependence of orientational relaxation. We compare our simulation result-based observations with the existing experimental results wherever available and find that the simulation results are in reasonably good agreement with the experiments. We implement, for the first time, a calculation of the rotational binary friction following the sophisticated scheme of Evans and co-workers. We also calculate the hydrodynamic predictions for the solute molecules. On comparison with the simulation and experimental results, we find that neither the rotational binary friction nor the hydrodynamic expressions (both stick and slip) can reproduce the results. To rectify the situation, we develop a detailed mode-coupling theory and suggest that such an approach if completely implemented can provide a more reliable description than the hydrodynamic approach. Many of our results could be tested in experimental studies because these linear molecules are amenable to spectroscopic studies, such as 2D-IR.
RESUMEN
We study by computer simulations, and by theory, the coupled rotational and translational dynamics of three important linear diatomic molecules, namely, carbon monoxide (CO), nitric oxide (NO), and cyanide ion (CN-) in water. Translational diffusion of these molecules is found to be strongly coupled to their own rotational dynamics which, in turn, are coupled to similar motions of the surrounding water. In particular, we find that coupled orientational jump motions play an important role in all three cases. While CO and NO show similar features, CN- exhibits certain differences. Our results agree well with the known experimental values of the diffusion coefficient. We examined the validity of hydrodynamic predictions and found them to be inadequate, particularly for rotational diffusion. A mode coupling theory approach is developed and applied to understand the complexity of translation-rotation coupling.
RESUMEN
Multidrug resistant strains and fungi add to treatment conundrums in skull base osteomyelitis (SBO). Deep tissue culture in these patients is challenging due to their advanced age and co-morbidities. Besides, fungal culture positivity is seen only in 60% of invasive aspergillosis. To determine the efficacy of a minimally invasive test-Serum Galactomannan (sGM)-for diagnosing fungal SBO. Prospective observational study. Thirty- three patients, clinically diagnosed with SBO were included in this study. Baseline ESR (Erythrocyte Sedimentation Rate), CRP (C- Reactive Protein), pain score, and sGM were noted for all patients. Antifungal Voriconazole was initiated on patients if the sGM values were more than 0.8. At the 12th week of treatment, all parameters were repeated and compared with the baseline values. A significant reduction was noted in ESR, CRP, and pain scores at the 12th week of treatment compared to the baseline values in patients with raised sGM values who were started on Voriconazole. For a culture-proven fungal skull base osteomyelitis with a cut-off value of sGM > / = 0.8, the obtained sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were 81.82, 36.36, 39.13, 80 and 51.52% respectively. At a cut-off value of sGM > / = 01.6, the values of sensitivity/specificity, PPV, NPV and accuracy were 81.82/72.73%, 60%, 88.89% and 75.76%. Culture-negative patients in SBO with sGM value > 0.8 were more likely to be fungal SBO. An sGM cut-off of 1.6 was observed to give maximum accuracy for diagnosing fungal SBO.
RESUMEN
Because of the amphiphilic nature of ethanol in the aqueous solution, ions cause an interesting microheterogeneity where the water molecules and the hydroxy groups of ethanol preferentially solvate the ions, while the ethyl groups tend to occupy the intervening space. Using computer simulations, we study the dynamics of rigid monovalent cations (Li+, Na+, K+, and Cs+) in aqueous ethanol solutions with chloride as the counterion. We vary both the size of the ions and the composition of the mixture to explore size- and composition-dependent ion diffusion. The relative stability of enhanced microheterogeneous configurations makes ion diffusion slower than what would be surmised by using the bulk properties of the mixture, using the Stokes-Einstein relation. We study the structure through partial radial distribution functions and the stability through coordination number fluctuations. The ion diffusion coefficient exhibits sharp re-entrant behavior when plotted against viscosity varied by composition. Our studies reveal multiple anomalous features of ion motion in this mixture. We formulate a mode-coupling theory (MCT) that takes into account the interaction between different dynamical components; MCT can incorporate the effects of heterogeneous dynamics and nonlinearity in composition dependence that arise from the feedback between mutually dependent ion-solvent dynamics.