In the present paper, we report a molecular dynamics (MD) simulation study for the structure and dynamics of H + ions in non-rigid dehydrated H12-A zeolite framework at 298.15 K, using the same method we used in our previous studies of rigid and non-rigid zeolite-A frameworks. It is found that two different structures appear, depending on the choice of the Lennard-Jones parameter (σ) for the H + ion, as is also observed in the study of rigid dehydrated H12-A zeolite framework, but the ranges of σ are different for the two structures. It is also found that some of the H + ions exchanged their sites without changing the number of H + ions at each site. The agreement between experimental and calculated structural parameters for non-rigid dehydrated H12-A zeolite is generally quite good. The calculated IR spectrum by Fourier transform of the total dipole moment auto-correlation function shows two major peaks, one around 2700 cm -1 and the other around 7000 cm -1 . The former appears in the calculated IR spectra of non-rigid zeolite-A framework only system and the latter remains unexplained except, perhaps, as an indication of a new formation of a vibrational mode of the framework due to the adsorption of the H + ions.

In recent papers C1-31 we reported molecular dynamics simulation studies of ions and water molecules adsorbed in a rigid zeolite-A framework using a simple Lennard-Jones potential plus Coulomb potential with Ewald summation to investigate the structure and dynamics of the adsorbates. In the present paper the same technique is applied to study the local structure and dynamics of NH: ions in a rigid dehydrated zeolite-A. During the preliminary equilibration, the unstable NH,(4) type ion (the 12th ion) is pushed down to near a more stable 6-ring position in the a-cage that is already associated with an NH,(l) type ion (the 1st) in the 8-cage, which moves to another 6-ring position in the 8-cage that is already associated with an NH,(2) type ion (the 7th) in the cc-cage. Calculated x, y, and z coordinates of some NHf ions are in good agreement with those obtained from an X-ray diffraction experiment except that no NH,(4) type ion is found and there are six NH4(2) type ions instead of 0.5 and 5.5 occupancy. The analyses of calculated interatomic distances and time correlation functions of these ions indicate that the NH4(l -1) and NH4(3) type ions are associated loosely with only one 0 (3) atom of the 6-ring and with only one O(1) atom of the 8-ring windows, respectively, while the NH,(l-2) and NH,(2) type ions are associated strongly with two or three 0 ( 3 ) atoms of the 6-ring windows in the a-and 8-cages, respectively. The analysis of hydrogen bond time correlation functions of these ions indicate that about one, two or three, three, and one hydrogen bond of each NH,(l-I), NH,(l-2), NH,(2) and NH4(3) type ion is kept for 1.4, 21, 75, and 1.4 ps, respectively, before breakup of the hydrogen bond occurs and significant exchange of 0 atom hydrogen-bonded to the ion.

In the present paper a molecular dynamics simulation technique is applied to study the local structure and dynamics of H+, CH3NH3 +, and Na+ ions in rigid dehydrated zeolite-A frameworks using a simple Lennard-Jones potential plus Coulomb potential with Ewald summation. In the H12-A zeolite system, two structures appear, depending upon the choice of the Lennard-Jones parameter, σ, for the H+ ion. For the smaller values of σ, the 12th H+ ion is located on one of the 8-ring window sites which are already occupied by three H+ ions; for the larger values of σ, it is at one of the opposite-4-ring sites with the remaining 11 H+ ions almost fixed near their initial positions. In the (CH3NH3)10Na2-A zeolite system, the main structural differences from an X-ray crystallographic report are 4-fold:  no facing CH3NH3 + ions through a 6-ring window, two ions in the β-cage, the appearance of a CH3NH3 + ion on one of the opposite-4-ring sites, and the lying of CH3NH3 + ions on the planes of the 8-ring window sites. Four kinds of time correlation functions for the CH3NH3 + ions show the dynamics of the ions, reflecting the different structural arrangements of the ions well. The analyses of hydrogen bond time correlation functions for the four nonequivalent CH3NH3 + ions indicate that about 0.8, 2.9, 0.6, 2.9, 1.6, 0.9, 1.7, and 2.0 hydrogen bonds formed between I and O(2), I and O(3), II and O(2), II and O(3), III and O(1), III and O(2), IV and O(1), and IV and O(3) are retained for 0.83, 1.89, 0.63, 1.61, 0.42, 0.31, 1.11, and 1.26 ps, respectively, before a breaking of the hydrogen bond occurs, leading to a significant exchange of O atoms hydrogen-bonded to the ion.

Background: There are many reports showing that a thoracic paravertebral block (TPB) can be used for post-thoracotomy pain control. However, the proper concentration of local anesthetics for TPB has not been established. The aim of this study was to define the proper concentration of bupivacaine for TPB after a thoracotomy.Methods: Sixty patients were allocated randomly into one of the following three groups: thoracic paravertebral 0.5%, 0.25%, or 0.125% bupivacaine at a rate of 0.1 ml/kg/h (kg: ideal body weight). The resting and coughing visual analogue scale (VAS) score, cumulative dose of fentanyl, and the 5 point satisfaction scale were checked.Results: 0.5% and 0.25% bupivacaine showed lower VAS score and cumulative dose of fentanyl than 0.125%. There was no difference in the satisfaction scale between the 3 groups. There was no difference between the 0.5% and 0.25% bupivacaine in all parameters measured. Conclusions: 0.25% bupivacaine used for TPB is more effective when used for pain control after a thoracotomy than 0.5% and 0.125% bupivacaine.