Unraveling the spectral signatures of solvent ordering in K-edge XANES of aqueous Na.

The aqueous solvation structure of the Na+ ion is studied both by molecular dynamics (MD) simulations and K-edge X-ray absorption near edge spectroscopy (XANES). We present a systematic study contrasting the differences in the predicted XANES spectra, using molecular configurations generated from classical and quantum MD. Using a set of suitable order parameters, we elucidate how the spectroscopic features are influenced by the local solvation structure around the Na+ ion. Our findings suggest that XANES is sensitive to fluctuations between the first and second solvation shells and can distinguish between classical and quantum interaction representations used to generate molecular ensembles.

Revisiting the hydration structure of aqueous Na.

A combination of theory, X-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS) are used to probe the hydration structure of aqueous Na+. The high spatial resolution of the XRD measurements corresponds to Qmax = 24 Å-1 while the first-reported Na K-edge EXAFS measurements have a spatial resolution corresponding to 2k = Qmax = 16 Å-1. Both provide an accurate measure of the shape and position of the first peak in the Na-O pair distribution function, gNaO(r). The measured Na-O distances of 2.384 ± 0.003 Å (XRD) and 2.37 ± 0.024 Å (EXAFS) are in excellent agreement. These measurements show a much shorter Na-O distance than generally reported in the experimental literature (Na-Oavg ∼ 2.44 Å) although the current measurements are in agreement with recent neutron diffraction measurements. The measured Na-O coordination number from XRD is 5.5 ± 0.3. The measured structure is compared with both classical and first-principles density functional theory (DFT) simulations. Both of the DFT-based methods, revPBE and BLYP, predict a Na-O distance that is too long by about 0.05 Å with respect to the experimental data (EXAFS and XRD). The inclusion of dispersion interactions (-D3 and -D2) significantly worsens the agreement with experiment by further increasing the Na-O distance by 0.07 Å. In contrast, the use of a classical Na-O Lennard-Jones potential with SPC/E water accurately predicts the Na-O distance as 2.39 Å although the Na-O peak is over-structured with respect to experiment.

The structure of liquid water up to 360 MPa from x-ray diffraction measurements using a high Q-range and from molecular simulation.

X-ray diffraction measurements of liquid water are reported at pressures up to 360 MPa corresponding to a density of 0.0373 molecules per Å(3). The measurements were conducted at a spatial resolution corresponding to Q(max) = 16 Å(-1). The method of data analysis and measurement in this study follows the earlier benchmark results reported for water under ambient conditions having a density of 0.0333 molecules per Å(3) and Q(max) = 20 Å(-1) [J. Chem. Phys. 138, 074506 (2013)] and at 70 °C having a density of 0.0327 molecules per Å(3) and Q(max) = 20 Å(-1) [J. Chem. Phys. 141, 214507 (2014)]. The structure of water is very different at these three different T and P state points and thus they provide the basis for evaluating the fidelity of molecular simulation. Measurements show that at 360 MPa, the 4 waters residing in the region between 2.3 and 3 Å are nearly unchanged: the peak position, shape, and coordination number are nearly identical to their values under ambient conditions. However, in the region above 3 Å, large structural changes occur with the collapse of the well-defined 2nd shell and shifting of higher shells to shorter distances. The measured structure is compared to simulated structure using intermolecular potentials described by both first-principles methods (revPBE-D3) and classical potentials (TIP4P/2005, MB-pol, and mW). The DFT-based, revPBE-D3, method and the many-body empirical potential model, MB-pol, provide the best overall representation of the ambient, high-temperature, and high-pressure data. The revPBE-D3, MB-pol, and the TIP4P/2005 models capture the densification mechanism, whereby the non-bonded 5th nearest neighbor molecule, which partially encroaches the 1st shell at ambient pressure, is pushed further into the local tetrahedral arrangement at higher pressures by the more distant molecules filling the void space in the network between the 1st and 2nd shells.

Effect of standard treatment guidelines with or without prescription audit on prescribing for acute respiratory tract infection (ARI) and diarrhoea in some thana health complexes (THCs) of Bangladesh.

Inappropriate prescribing for ARI and diarrhoea is a serious health problem in many developing countries including Bangladesh. A baseline retrospective prescribing survey for ARI and diarrhoea have been conducted in randomly selected 60 thana health complexes (THCs) of Dhaka division of Bangladesh. In the 38 of 60 THCs, the prescribers did not comply with the standard treatment guidelines (STG) for ARI. They are marked as 'unsatisfactory performers'. In these THCs unnecessary antibiotics were prescribed in more than 50% of the encounters. The study further revealed that in 26 THCs, comprising 41.6% of the 38 THCs, the situation was even worse regarding the indiscriminate use of antibiotics. In these THCs antibiotics were prescribed in > or =72% of the encounters. For diarrhoea, only in 8.3% of the THCs antibiotics were prescribed in > or =50% of the encounters. Encouragingly, most of the prescribers prescribed ORS. So the diarrhoea cases were dropped from the intervention. The 24 out of 26 worse performing THCs for ARI management, were grouped into three groups: Group-I (implementing STG+ Audit), Group-II (STG) and Group-III (no intervention, control). The prescribers of the THCs belonging to Group-I and Group-II received STG+Audit and STG only respectively as intervention(s). On the contrary, the prescribers of the THCs of Group-III (control) did not receive any intervention. It was observed that after the implementation of interventions the use of the unnecessary antibiotics to treat ARI was significantly reduced (p<0.01) compared to pre-intervention period in Group-I (STG+Audit). In this group highly significant (p<0.000) reduction in antibiotics use was achieved in 6 out of 8 THCs. The average reduction in antibiotic use in terms of encounters was 23.7 and 15.2% in the Group-I and Group-II respectively owing to the intervention(s). Significant reduction in antibiotic use in terms of THCs was 3 (out of 8 THCs) and 2 (out of 8 THCs) belonging to the Group-II and Group-III respectively. When compensated for the change in the control group, the reduction of antibiotic use in terms of encounters was 15.2 and 6.9% in the THCs of the Group-I and Group-II respectively due to introduction of the interventions. The study concludes that STG supported by prescription audit are highly effective interventions to change the prescribing behaviour of the prescribers for ARI in the THCs.