FARQ y Archiprix International : una relación inspiradora

Artículo origina

Energetics and Mechanism of Drug Transport Mediated by the Lactococcal Multidrug Transporter LmrP

The gene encoding the secondary multidrug transporter LmrP of Lactococcus lactis was heterologously expressed in Escherichia coli. The energetics and mechanism of drug extrusion mediated by LmrP were studied in membrane vesicles of E. coli. LmrP-mediated extrusion of tetraphenyl phosphonium (TPP+) from right-side-out membrane vesicles and uptake of the fluorescent membrane probe 1-[4-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH) into inside-out membrane vesicles are driven by the membrane potential (Δψ) and the transmembrane proton gradient (ΔpH), pointing to an electrogenic drug/proton antiport mechanism. Ethidium bromide, a substrate for LmrP, inhibited the LmrP-mediated TPP+ extrusion from right-sideout membrane vesicles, showing that LmrP is capable of transporting structurally unrelated drugs. Kinetic analysis of LmrP-mediated TMA-DPH transport revealed a direct relation between the transport rate and the amount of TMA-DPH associated with the cytoplasmic leaflet of the lipid bilayer. This observation indicates that drugs are extruded from the inner leaflet of the cytoplasmic membrane into the external medium. This is the first report that shows that drug extrusion by a secondary multidrug resistance (MDR) transporter occurs by a “hydrophobic vacuum cleaner” mechanism in a similar way as was proposed for the primary lactococcal MDR transporter, LmrA.

High temperature dewatering of ethanol by vapour permeation and pervaporation with HybSi® membranes

Ethanol is one of the most important commodity chemicals used in a broad range of applications and can be produced by the hydrolysis of ethylene, though by far the largest fraction of ethanol is produced via fermentation mainly using 1st generation feedstock. Regardless of the source of the ethanol, from fermentation or from direct hydration of ethylene, the product is normally a dilute aqueous solution. The product is fed to a distillation system to concentrate ethanol. The separation of ethanol and water is complicated because ethanol and water form an azeotrope at 95.6 weight% ethanol. It is not possible to produce pure ethanol from an azeotropic mixture by normal distillation. Pervaporation is a method for dehydration of organics such as ethanol, which substantially avoids drawbacks of azeotropic distillation and adsorption. As the pervaporation process is not governed by thermodynamic equilibria and the selectivity is determined by the difference in permeation rates of components through the membrane, mixtures of components with close boiling points and azeotropic mixtures can be effectively separated. Pervaporation exhibits its highest efficiency in a concentration range of the ethanol-water mixture where distillation is least effective, namely, at high ethanol concentrations of 90-95 wt.%, especially in the vicinity of the azeotropic concentration. Previous studies have shown that hybrid distillation processes combined with either pervaporation or vapour permeation can be very attractive for the separation of liquid mixtures. Such a hybrid process leads to large energy savings when the membrane is used for breaking the azeotrope. At the preferred process conditions currently available commercial polymer and zeolite membranes cannot be used. In this study, the focus is on membrane stability at higher operating temperatures in a water ethanol mixture for sol–gel derived Hybsi® membranes and the membrane performance in pervaporation and vapour permeation. The stability of the membranes is one of the crucial factors of their application in industrial separation processes. A comparison between pervaporation and vapour permeation has been made in which water removal from ethanol has been used as an example. By applying higher temperatures and thus higher driving forces in the membrane unit the required membrane area and the total costs of the process are strongly reduced. The comparison was based on endurance tests, in the dehydration of ethanol at 150°C. The high hydrothermal and chemical stability of the membrane was proven in continuous measurements (24/7) that lasted for periods of over 500 days. The membrane performance was followed during this period of time by measuring the flux and membrane selectivity. Both in pervaporation and vapour permeation a good and stable membrane performance was obtained after a stabilisation period and from a flux and selectivity point of view at 150°C both membrane operation options show similar results. Detailed test results will be presented. For ethanol dehydration vapour permeation would be preferred above pervaporation as advantage can be taken of the vapour already present at the top of the distillation column which will still be used to remove major part of the water present. The presented results show that HybSi® membranes are applicable in the dehydration of ethanol by pervaporation and vapour permeation at higher temperatures. The high temperature use leads to a broadened application window and will open up markets that have so far been inaccessible for commercially available pervaporation and vapour permeation membranes

The Impact of Management Control on Employee Motivation and Performance in the Public Sector

This study examines the relations among various types of management control, intrinsic and extrinsic motivation, and performance in the public sector. We draw on motivation crowding theory and self-determination theory to argue that four different types of management control (i.e. personnel, cultural, action, and results control) are likely to have an influence on intrinsic motivation and/or extrinsic motivation. We test a structural equation model using survey data from 105 similar departments in the public sector. Our findings indicate that the use of personnel and cultural controls is positively associated with employees’ intrinsic motivation, and that the use of results controls is positively associated with employees’ extrinsic motivation. Moreover, both intrinsic motivation and extrinsic motivation are positively associated with performance. Taken together, these findings support the idea advocated by New Public Management proponents that results control can enhance employee motivation and performance in the public sector. However, the findings also highlight an essential nuance; in addition to results control, personnel and cultural controls are also important, as they enhance intrinsic motivation and performance. This implies that a sole focus on results control is too narrow and can lead to suboptimal levels of employee motivation and performance in the public sector

Lab and pilot scale pervaporation process for the purification of dimethyl carbonate

The separation of dimethyl carbonate (DMC) from methanol is of great industrial interest, as DMC can be prepared from urea (made from captured CO2 and ammonia) and methanol with methanol also acting as a solvent for the reaction. As a result relative low levels of DMC in methanol can be obtained. The purification is a very energy intensive process with the base case being a pressure swing distillation method. The use of polymeric membranes for this purpose is not recommended as the driving forces for the transport of methanol are fairly low, which asks for high operating temperatures of over 120°C. These conditions call for a ceramic membrane. Zeolitic membranes are typically not suited for the transportation of methanol and polymeric membranes are not stable under these conditions. Hybrid silica membranes, such HybSi® can combine high operation temperatures, with sufficient high selectivities and high permeances. In the current study, we have performed process simulations to assess the potential reduction in CAPEX and OPEX when a HybSi® membrane is included in the process. The costs of the separation of DMC from methanol has been assessed by Aspen Plus flow sheeting using the by ECN developed Pervatool to simulate the behavior of the membrane pervaporation process. The calculations were based on actual lab scale membrane performance data and vapor-liquid-equilibrium data originating from internal and published sources. To facilitate a transparent comparison, the total costs of the purification were calculated per ton of DMC produced. The cost saving is as high as 45% when a hybrid process is being used that combines membranes and distillation as compared to the base case with pressure swing distillation, see Table 1. Cost reductions can be found in both the OPEX and the CAPEX and range from 25 to 55%. The OPEX savings can be ascribed to a strongly reduced energy consumption, while the CAPEX reduction is ascribed to a much more compact design with smaller distillation columns. The values are dependent on the way of calculation, e.g. absolute numbers or relative to the amount of DMC produced, and on technical factors such as the DMC content in the methanol recycle and various process conditions throughout the separation train. These simulations have been supported by long term measurements at lab scale as well as a pilot testing in a fully specialized plant using about 0.7 m2 of membrane area. In the presentation all the relevant results will be discussed of the process simulations and the lab and pilot scale testing. Table 1: Purification costs per ton DMC produced taking into account both CAPEX and OPEX Relative purification costs per ton DMC produced Relative cost reduction Base case with high purity recycle 100 Base case with low purity recycle 96 4% Membrane case with high purity recycle 72 28% Membrane case with low purity recycle 55 45