Impact Of Packing Research Articles

Aromatic ring flips in differently packed ubiquitin protein crystals from MAS NMR and MD

Probing the dynamics of aromatic side chains provides important insights into the behavior of a protein because flips of aromatic rings in a protein’s hydrophobic core report on breathing motion involving a large part of the protein. Inherently invisible to crystallography, aromatic motions have been primarily studied by solution NMR. The question how packing of proteins in crystals affects ring flips has, thus, remained largely unexplored. Here we apply magic-angle spinning NMR, advanced phenylalanine 1H-13C/2H isotope labeling and MD simulation to a protein in three different crystal packing environments to shed light onto possible impact of packing on ring flips. The flips of the two Phe residues in ubiquitin, both surface exposed, appear remarkably conserved in the different crystal forms, even though the intermolecular packing is quite different: Phe4 flips on a ca. 10–20 ns time scale, and Phe45 are broadened in all crystals, presumably due to µs motion. Our findings suggest that intramolecular influences are more important for ring flips than intermolecular (packing) effects.

Experimental investigation of terminal velocity and Sherwood number of rising droplet in an extraction column

Mass transfer and terminal velocity of toluene drops rising in an extraction column was studied experimentally. The impact of packing was investigated by inserting a structured packing in three different heights of 10, 25 and 40 cm inside the column. The effect of packing height, flow rate and drop size on terminal velocity and Sherwood number were investigated and the results were also compared with the case of non-packed column. It was discussed that a 30% increase in Sherwood number could be achieved using the packing with 40 cm in height. It was also found that for Eotvos number, Eo, higher than 0.4, the deformation of drops and velocity oscillation appeared, which affected the terminal velocity. Finally, two correlations were proposed, which permitted the prediction of deformation and extraction ratio versus the dimensionless numbers of Reynolds, Eotvos and the packing height ratio.

Impact of Packing and Processing Technique on Mechanical Properties of Acrylic Denture Base Materials

The fracture resistance of polymethylmethacrylate (PMMA) as the most popular denture base material is not satisfactory. Different factors can be involved in denture fracture. Among them, flexural fatigue and impact are the most common failure mechanisms of an acrylic denture base. It has been shown that there is a correlation between the static strength and fatigue life of composite resins. Therefore, the transverse strength of the denture base materials can be an important indicator of their service life. In order to improve the fracture resistance of PMMA, extensive studies have been carried out; however, only a few promising results were achieved, which are limited to some mechanical properties of PMMA at the cost of other properties. This study aimed at optimizing the packing and processing condition of heat-cured PMMA as a denture base resin in order to improve its biaxial flexural strength (BFS). The results showed that the plain type of resin with a powder/monomer ratio of 2.5:1 or less, packed conventionally and cured in a water bath for 2 h at 95 °C provides the highest BFS. Also, it was found that the performance of the dry heat processor is inconsistent with the number of flasks being loaded.

Packing of Intervertebral Spaces with Oxidized Regenerated Cellulose to Prevent the Recurrence of Lumbar Disc Herniation

Abstract OBJECTIVE To investigate the impact of packing of intervertebral spaces with oxidized regenerated cellulose (ORC) on the incidence of recurrence of lumbar disc herniation (LDH). METHODS We retrospectively reviewed 158 consecutive patients who underwent surgery for a newly diagnosed LDH and had a minimum of 18 months of follow-up. Single-level (151 patients) and two-level (7 patients) procedures accounted for 165 microdiscectomies. After microsurgical removal of disc herniation and curettage, the interspaces were tightly packed with ORC. RESULTS The average hospital stay was 1.47 days, without any relevant and permanent complications. In particular, complications related to intervertebral ORC packing were never observed. At a median follow-up of 29 months (range, 18–51 mo), the pain decreased or disappeared in almost all patients and the patient satisfaction rate was very high. A recurrence of LDH was observed in two patients (1.34%), both of whom needed a second operation. Three patients (2.01%) experienced a disc herniation involving another intervertebral space. CONCLUSION Our preliminary results suggest that the packing of intervertebral spaces with ORC at the end of microdiscectomy is a safe technique that may reduce the incidence of recurrent LDHs, although the true impact of this technique on long-term follow-up is still unclear. At the moment, it seems reasonable to assume that this technique should be used only under the auspices of large clinical investigations with prospective and randomized protocols.