Koffi Fiaty

ATP-dependent active transport simulations based on a phosphatase-channel-kinase membrane structure.

Simulations of coupled interactions involving enzymatic reaction diffusion and electrostatic interactions were conducted under a fixed phosphatase–channel–kinase (PCK) topology oriented from the outside to the inside of a charged membrane structure. Depending on the phosphatase and kinase locations, we recently demonstrated that active transport of a phosphorylated substrate may occur via this PCK topology. The present analysis demonstrates that, if in addition to this topology, a phosphatase activity (P1) is also present on the inner side of the membrane, but outside the unstirred layer surrounding the inner membrane surface, then active transport of the corresponding unphosphorylated substrate may also occur. Therefore, this PCK membrane topology, which behaves as a specific ATP‐dependent transporter, appears as a general topology permitting; first, on its own the active transport of a phosphorylated substrate; second, when associated with a phosphatase acting in the bulk of the receiver compartment, the active transport of the corresponding unphosphorylated substrate, that is, in most cases, the transport of an uncharged substrate. The general mathematical model given permits the active transport of a phosphorylated substrate to be analyzed (in the absence of P1), the active transport of an unphosphorylated substrate (in the presence of P1), whatever the charge distributions on both sides of the membrane surface and whatever the positions of the membrane‐bound phosphatase and the membrane‐bound kinase. This general model also takes into account the consumption of ATP occurring into the receiver compartment during the time course of these transport phenomena. A broad analysis of the role played by the main parameters taken into account in the model was conducted to precisely define the physicochemical conditions and the membrane topology needed for the highest active transports within the shortest time.

Effect of geometry and scale for axial and radial flow membrane chromatography—Experimental study of bovin serum albumin adsorption

During the last 10 years, membrane chromatography (MC) has been increasingly reported for biomolecule purification at both small and large scales. Although, several axial and radial flow MC devices are commercialized, the effect of the device dimensions on the adsorption performance has not been fully investigated. In this study, axial and radial flow anion ion-exchange MC devices were used for bovine serum albumin (BSA) adsorption. For both axial and radial flow, three devices at different scales were compared, two having similar diameter and two similar bed height. The pressure drop and the flow distribution using acetone as a non-binding solute were measured, as well as BSA breakthrough curves at different flow rates and BSA loading concentrations. For all devices, it was observed that the flow rate had no effect on the breakthrough curve, which confirms the advantage of MC to be used at high flow rates. In addition, the BSA binding capacity increased with increasing BSA concentration, which suggests that it could be preferable to work with concentrated solutions rather than with very dilute solutions, when using buffer at high phosphate concentration. For both axial and radial flow, the bed height had a negative impact on the binding capacity, as the lowest binding capacities per membrane volume were obtained with the devices having the highest bed height. Radial flow MC has potential at large-scale applications, as a short bed thickness can be combined with a large inlet surface area.

Use of electrocatalytic membrane reactor for synthesis of sorbitol

The strategy of paired electrochemical synthesis of organic compounds in undivided cell process in which the reaction product at the anode and the reaction product at the cathode are simultaneously separated was performed. In order to evaluate the feasibility of the process the electrochemical oxidation of fructose to gluconic acid and the reduction of fructose to sorbitol and mannitol were paired in an electrocatalytic membrane reactor. However, only the results obtained on the electrochemical reduction are described in this work as it required catalysis to be performed successfully. The reactor is made with two coaxial tubes of membrane support. Some parameters which modify the electrocatalytic activity of the electrode are studied.

Simulations of the active transport of a neutral solute based on a kinase-channel-phosphatase topology

Simulations of coupled interactions involving two opposite enzymatic reactions, solute diffusions, and electrostatic interactions between membrane charges and charged solutes were conducted under a fixed kinase‐channel‐phosphatase (KCP) topology oriented from the outside to the inside of a porous membrane structure. Depending on the kinase and phosphatase locations, we recently demonstrated that an active transport of a phosphorylated substrate may occur via the opposite topology, that is, a PCK topology. The present analysis demonstrates that, under a KCP membrane topology, which also behaves as a specific ATP‐dependent transporter, the active transport of a neutral substrate may occur. This analogous active transport appears to be dependent on the phosphatase location and on the membrane surface potentials. A broad analysis of the role played by the main parameters taken into account in the model was conducted in order to define precisely the physico‐chemical conditions and the membrane topology needed for the highest active transports within the shortest time.

A nonlinear high gain observer for an olive oil waste esterification in a continuous stirred tank reactor

In this paper, a nonlinear high gain observer is developed to reconstruct the full state of an olive oil waste esterification process. This operation is taking place in a semi-continuous stirred tank reactor. The plant model, as most of the chemical processes, presents a high level of non linearities and interconnections between states. Most of the works developed around such model are based on a canonical form of the model or in single input single output structure. We show, in this work, that it is possible to synthesis a high gain based full observer for a multi input multi output system and to ensure good applicability of a such observer. The results are validated on real measurements of the plant. The second part is devoted to performances comparison between our observer and the well used observer for such nonlinear systems, the Extended Kalman Filter. The comparison shows that the high gain observer presents better results in precision and application limitations.

Enzymatic membranes for the selective transport of neutral molecules by electrophoresis

The active and selective transport of glucose and glycerol was carried out using electrophoresis and artificial enzymatic membranes. These positively charged composite membranes carry, on the face adjacent to the donor compartment of an electrophoresis module, a specific kinase (hexokinase or glycerokinase) and, on the opposite face, an alkaline phosphatase (ALP). Phosphorylation of the neutral substrate (glucose or glycerol) on the donor side by the kinase generates a negatively charged phosphorylated substrate, whose transmembrane migration is promoted by an electric field and by the membranes positive charge. Dephosphorylation ofu2002the phosphorylated substrate by ALP on the opposite face regenerates the neutral substrate, which accumulates in the receiver compartment of the electrophoresis module. Using an electrophoresis module specifically designed for this study, our experiments were carried out enabling glucose and glycerol to be concentrated approximately eight‐ and twelve‐fold, respectively, in 8u2005h.

Kinetic Investigation of the Curing and Pyrolysis Procedures Used for the Preparation of Polymer-Derived Boron Nitride Fibres

The kinetic investigation of the solid-state decomposition of a typical melt-spinnable poly[B-(methylamino)borazine] into boron nitride fibers was carried out at various heating rates. It was shown that the two-step weight loss associated with the polymer-to-ceramic conversion is governed by two major diffusion-type transport mechanisms which are independent of the applied heating schedule. The application of the Kissinger and Friedman methods to dynamic TG data allowed us to measure the Ea and lnA values which are seen to increase with the extent of the ceramic conversion from region one (Ea=46.3kJ/mol, lnA=3.85; Friedman method) in going to region two (Ea=122.6J/mol, lnA=12.18; Friedman method). Kissinger and Friedman results are in good agreement. It was shown that the cross-linking process of the polymer is mainly governed by a poorly energetic mechanism indicating the occurrence of simple reactions, whereas the mineralization and ceramization steps are majoritarly represented by a highly energetic mechanism suggesting the occurrence of complex and multi-step mechanisms.

Nonlinear high ga in observers for a Semi Continuous stirred tank reactor

In this paper, two versions of nonlinear high gain observer are developed to reconstruct the full state of an olive oil waste esterification process. This operation is taking place in a Semi Continuous stirred Tank Reactor (SCSTR). The plant model, is one of the most important plants in chemical processes, presents a high level of non linearities and interconnections between states. We will show the necessary steps required to move from differential algebraic model to a differential model. We show in this work that it is possible to synthesis a two versions of high gain observer for a multi input multi output system and ensure good applicability of a such observer. The results are validated on a real measurements of the plant. The second part is devoted to performances comparison between there.

Actuator fault detection identification and isolation via high-gain observer for an olive oil waste esterification in a Semi Continuous Stirred Tank Reactor

In this study, we have developed a method of diagnosis based on high gain observers, for detecting faults of the actuators in a semi continuous chemical reactor. This algorithm has the advantage of detecting multiple faults simultaneously. The observer is constructed from a sub-model, one needs two observers which related to the number of actuator. The signals used in our study derived from a real system. This diagnostic strategy has two levels, to detect and identify defects actuators, feed rate and the warming system in order to improve the reaction rate.

Shunt Concept for Specific Active Transport Using Enzymatic Membranes: Review and Prospects

Artifical enzymatic membranes (AEMs) were conceived with the aim of replicating the active transport found in vivo. The shunt concept has recently emerged from the use of two enzymes catalysing two opposite reactions occurring on both parts of a porous charged membrane (+ oru2009−) and able to specifically add/remove (or the contrary) a charged group (+ oru2009−) on the selected molecule to be transported. Historically, the Phosphatase (P)/Kinase (K) couple (or its inverse), frequently found in nature, was selected for creating these shunts. Modelling of these transports was realized using the Nernst-Planck equation. In parallel, experimental studies were conducted proving that these shunt topologies, involving enzymatic membranes, lead to specific and active solute transports at physiological temperature and pressure. Issuing from this concept, recent technological prospects, such as the specific separation and concentration of (L) substrate from the (D/L) racemic mixture and the selective transport of neutral molecules by electrophoresis, are presented. This review presents the main results obtained using polymeric membranes linked to enzymes with the aim of replicating the active transport found in vivo.