Modeling of non-isothermalvapor membrane separation with thermodynamic models and generalized mass transfer equations

A rigorous unit operation model is developed for vapor membrane separation. The new model is able to describe temperature, pressure, and concentration dependent permeation as wellreal fluid effects in vapor and gas separation with hydrocarbon selective rubbery polymeric membranes. The permeation through the membrane is described by a separate treatment of sorption and diffusion within the membrane. The chemical engineering thermodynamics is used to describe the equilibrium sorption of vapors and gases in rubbery membranes with equation of state models for polymeric systems. Also a new modification of the UNIFAC model is proposed for this purpose. Various thermodynamic models are extensively compared in order to verify the models' ability to predict and correlate experimental vapor-liquid equilibrium data. The penetrant transport through the selective layer of the membrane is described with the generalized Maxwell-Stefan equations, which are able to account for thebulk flux contribution as well as the diffusive coupling effect. A method is described to compute and correlate binary penetrant¿membrane diffusion coefficients from the experimental permeability coefficients at different temperatures and pressures. A fluid flow model for spiral-wound modules is derived from the conservation equation of mass, momentum, and energy. The conservation equations are presented in a discretized form by using the control volume approach. A combination of the permeation model and the fluid flow model yields the desired rigorous model for vapor membrane separation. The model is implemented into an inhouse process simulator and so vapor membrane separation may be evaluated as an integralpart of a process flowsheet.

Role of Membrane Transporters, P-Glycoprotein and Mrp1, in The Placental Transfer of Drugs With Special Reference to Saquinavir and Quetiapine

Drug transporting membrane proteins are expressed in various human tissues and blood-tissue barriers, regulating the transfer of drugs, toxins and endogenous compounds into or out of the cells. Various in vitro and animal experiments suggest that P-glycoprotein (P-gp) forms a functional barrier between maternal and fetal blood circulation in the placenta thereby protecting the fetus from exposure to xenobiotics during pregnancy. The multidrug resistance-associated protein 1 (MRP1) is a relatively less studied transporter protein in the human placenta. The aim of this study series was to study the role of placental transporters, apical P-gp and basal MRP1, using saquinavir as a probe drug, and to study transfer of quetiapine and the role of P-gp in its transfer in the dually perfused human placenta/cotyledon. Furthermore, two ABCB1 (encoding P-gp) polymorphisms (c.3435C>T, p.Ile1145Ile and c.2677G>T/A, p.Ala893Ser/Thr) were studied to determine their impact on P-gp protein expression level and on the transfer of the study drugs. Also, the influence of the P-gp protein expression level on the transfer of the study drugs was addressed. Because P-gp and MRP1 are ATP-dependent drug-efflux pumps, it was studied whether exogenous ATP is needed for the function of ATP-dependent transporter in the present experimental model. The present results indicated that the addition of exogenous ATP was not necessary for transporter function in the perfused human placental cotyledon. Saquinavir and quetiapine were both found to cross the human placenta; transplacental transfer (TPTAUC %) for saquinavir was <0.5% and for quetiapine 3.7%. Pharmacologic blocking of P-gp led to disruption of the blood-placental barrier (BPB) and increased the placental transfer of P-gp substrate, saquinavir, into the fetal circulation by 6- to 8-fold. In reversed perfusions P-gp, MRP1 and possibly OATP2B1 had a negligible role in the fetal-to-maternal transfer of saquinavir. The TPTAUC % of saquinavir was about 100-fold greater from the fetal side to the maternal side compared with the maternal-to-fetal transfer. P-gp activity is not likely to modify the placental transfer of quetiapine. Higher P-gp protein expression levels were associated with the variant allele 3435T, but no correlation was found between the TPTAUC % of saquinavir and placental P-gp protein expression. The present results indicate that P-gp activity drastically affects the fetal exposure to saquinavir, and suggest that pharmacological blockade of the P-gp activity during pregnancy may pose an increased risk for adverse fetal outcome. The blockade of P-gp activity could be used in purpose to obtain higher drug concentration to the fetal side, for example, in prevention (to decrease virus transfer to fetal side) or in treating sick fetus.

Utilisation of magnetic field in membrane filtration

As it is known, the major problem of membrane filtration is fouling of membrane during the filtration process. There are a lot of methods to prevent or reduce fouling. One very little studied method is applying of magnetic field in membrane filtration. Magnetic field has such advantages as bulk, contact free, nondestructive impact on the sample, thus it can be combined with different types of processes. In addition, the use of magnetic fields has given positive results in various areas of science and life. So, the present thesis is devoted to the research of influence of magnetic field on performances of nanofiltration. In the literature part of the thesis a short description of membrane process and mechanism of reorientation of nanoparticals in magnetic field is presented. The utilization of magnetic field in different spheres of life, in general, and membrane area, in particular, is represented. In the experimental part the influence of magnetic field created by two permanent magnets on filtration of two solutions (citric acid and sodium dodecyl sulfate) was investigated. Factors, which affect on the impact of magnetic field was estimated. The effect of magnetic field was evaluated by measuring a change of pure water permeability after the filtration of model solution. This work demonstrated that direction of magnetic field and the type of molecules of filtered solution has significant effect to the efficiency of nanofiltration. Utilization of magnetic field might increase retention of membrane and flux through membrane and reduce fouling.

Identification of extractives and polysaccharides as foulants in membrane filtration of pulp and paper mill effluents

The search for new renewable materials has intensified in recent years. Pulp and paper mill process streams contain a number of potential compounds which could be used in biofuel production and as raw materials in the chemical, food and pharmaceutical industries. Prior to utilization, these compounds require separation from other compounds present in the process stream. One feasible separation technique is membrane filtration but to some extent, fouling still limits its implementation in pulp and paper mill applications. To mitigate fouling and its effects, foulants and their fouling mechanisms need to be well understood. This thesis evaluates fouling in filtration of pulp and paper mill process streams by means of polysaccharide model substance filtrations and by development of a procedure to analyze and identify potential foulants, i.e. wood extractives and carbohydrates, from fouled membranes. The model solution filtration results demonstrate that each polysaccharide has its own fouling mechanism, which also depends on the membrane characteristics. Polysaccharides may foul the membranes by adsorption and/or by gel/cake layer formation on the membrane surface. Moreover, the polysaccharides interact, which makes fouling evaluation of certain compound groups very challenging. Novel methods to identify wood extractive and polysaccharide foulants are developed in this thesis. The results show that it is possible to extract and identify wood extractives from membranes fouled in filtration of pulp and paper millstreams. The most effective solvent was found to be acetone:water (9:1 v/v) because it extracted both lipophilic extractives and lignans at high amounts from the fouled membranes and it was also non-destructive for the membrane materials. One hour of extraction was enough to extract wood extractives at high amounts for membrane samples with an area of 0.008 m2. If only qualitative knowledge of wood extractives is needed a simplified extraction procedure can be used. Adsorption was the main fouling mechanism in extractives-induced fouling and dissolved fatty and resin acids were mostly the reason for the fouling; colloidal fouling was negligible. Both process water and membrane characteristics affected extractives-induced fouling. In general, the more hydrophilic regenerated cellulose (RC) membrane fouled less that the more hydrophobic polyethersulfone (PES) and polyamide (PA) membranes independent of the process water used. Monosaccharide and uronic acid units could also be identified from the fouled synthetic polymeric membranes. It was impossible to analyze all monosaccharide units from the RC membrane because the analysis result obtained contained degraded membrane material. One of the fouling mechanisms of carbohydrates was adsorption. Carbohydrates were not potential adsorptive foulants to the sameextent as wood extractives because their amount in the fouled membranes was found to be significantly lower than the amount of wood extractives.

Muscarinic toxins : characterization of adrenoceptor binding and applicability of membrane anchoring via glycosylphosphatidylinositol tail

Adrenoceptors (ARs), G-protein coupled receptors (GPCRs) at the plasma membrane, respond to endogenous catecholamines noradrenaline and adrenaline. These receptors mediate several important physiological functions being especially important in the cardiovascular system and in the regulation of smooth muscle contraction. Impairments in the function of these receptors can thus lead to severe diseases and disorders such as to cardiovascular diseases and benign prostatic hyperplasia. The Eastern green mamba (Dendroaspis angusticeps) venom has been shown to contain toxins that can antagonize the functions of GPCRs. The most well-known are muscarinic toxins (MTs) targeting muscarinic acetylcholine receptors (mAChRs) with high affinity and selectivity. However, some reports have indicated that these toxins might also act on the α1- and α2-ARs which can be divided into various subtypes; the α1-ARs to α1A-, α1B- and α1D-ARs and α2-ARs to α2A-, α2B- and α2C-ARs. In this thesis, the interaction of four common MTs (MT1, MT3, MT7 and MTα) with the adrenoceptors was characterized. It was also evaluated whether these toxins could be anchored to the plasma membrane via glycosylphosphatidylinositol (GPI) tail. Results of this thesis reveal that muscarinic toxins are targeting several α-adrenoceptor subtypes in addition to their previously identified target receptors, mAChRs. MTα was found to interact with high affinity and selectivity with the α2B-AR whereas MT7 confirmed its selectivity for the M1 mAChR. Unlike MTα and MT7, MT1 and MT3 have a broad range of target receptors among the α-ARs. All the MTs characterized were found to behave as non-competitive antagonists of receptor action. The interaction between MTα and the α2B-AR was studied more closely and it was observed that the second extracellular loop of the receptor functions as a structural entity enabling toxin binding. The binding of MTα to the α2B-AR appears to be rather complex and probably involves dimerized receptor. Anchoring MTs to the plasma membrane did not interfere with their pharmacological profile; all the GPI-anchored toxins created retained their ability to block their target receptors. This thesis shows that muscarinic toxins are able to target several subtypes of α-ARs and mAChRs. These toxins offer thus a possibility to create new subtype specific ligands for the α-AR subtypes. Membrane anchored MTs on the other hand could be used to block α-AR and mAChR actions in disease conditions such as in hypertension and in gastrointestinal and urinary bladder disorders in a cell-specific manner and to study the physiological functions of ARs and mAChRs in vivo in model organisms.

Membrane properties of structurally modified ceramides : effects on lipid lateral distribution and sphingomyelin-interactions in artificial bilayer membranes

Ceramides comprise a class of sphingolipids that exist only in small amounts in cellular membranes, but which have been associated with important roles in cellular signaling processes. The influences that ceramides have on the physical properties of bilayer membranes reach from altered thermodynamical behavior to significant impacts on the molecular order and lateral distribution of membrane lipids. Along with the idea that the membrane physical state could influence the physiological state of a cell, the membrane properties of ceramides have gained increasing interest. Therefore, membrane phenomena related to ceramides have become a subject of intense study both in cellular as well as in artificial membranes. Artificial bilayers, the so called model membranes, are substantially simpler in terms of contents and spatio-temporal variation than actual cellular membranes, and can be used to give detailed information about the properties of individual lipid species in different environments. This thesis focuses on investigating how the different parts of the ceramide molecule, i.e., the N-linked acyl chain, the long-chain sphingoid base and the membrane-water interface region, govern the interactions and lateral distribution of these lipids in bilayer membranes. With the emphasis on ceramide/sphingomyelin(SM)-interactions, the relevance of the size of the SMhead group for the interaction was also studied. Ceramides with methylbranched N-linked acyl chains, varying length sphingoid bases, or methylated 2N (amide-nitrogen) and 3O (C3-hydroxyl) at the interface region, as well as SMs with decreased head group size, were synthesized and their bilayer properties studied by calorimetric and fluorescence spectroscopic techniques. In brief, the results showed that the packing of the ceramide acyl chains was more sensitive to methyl-branching in the mid part than in the distal end of the N-linked chain, and that disrupting the interfacial structure at the amide-nitrogen, as opposed to the C3-hydroxyl, had greater effect on the interlipid interactions of ceramides. Interestingly, it appeared that the bilayer properties of ceramides could be more sensitive to small alterations in the length of the long-chain base than what was previously reported for the N-linked acyl chain. Furthermore, the data indicated that the SM-head group does not strongly influence the interactions between SMs and ceramides. The results in this thesis illustrate the pivotal role of some essential parts of the ceramide molecules in determining their bilayer properties. The thesis provides increased understanding of the molecular aspects of ceramides that possibly affect their functions in biological membranes, and could relate to distinct effects on cell physiology.

Cell Model Systems in Characterizing Alpha2-Adrenoceptors as Drug Targets.

The three alpha2-adrenoceptor (alpha2-AR) subtypes belong to the G protein-coupled receptor superfamily and represent potential drug targets. These receptors have many vital physiological functions, but their actions are complex and often oppose each other. Current research is therefore driven towards discovering drugs that selectively interact with a specific subtype. Cell model systems can be used to evaluate a chemical compound's activity in complex biological systems. The aim of this thesis was to optimize and validate cell-based model systems and assays to investigate alpha2-ARs as drug targets. The use of immortalized cell lines as model systems is firmly established but poses several problems, since the protein of interest is expressed in a foreign environment, and thus essential components of receptor regulation or signaling cascades might be missing. Careful cell model validation is thus required; this was exemplified by three different approaches. In cells heterologously expressing alpha2A-ARs, it was noted that the transfection technique affected the test outcome; false negative adenylyl cyclase test results were produced unless a cell population expressing receptors in a homogenous fashion was used. Recombinant alpha2C-ARs in non-neuronal cells were retained inside the cells, and not expressed in the cell membrane, complicating investigation of this receptor subtype. Receptor expression enhancing proteins (REEPs) were found to be neuronalspecific adapter proteins that regulate the processing of the alpha2C-AR, resulting in an increased level of total receptor expression. Current trends call for the use of primary cells endogenously expressing the receptor of interest; therefore, primary human vascular smooth muscle cells (SMC) expressing alpha2-ARs were tested in a functional assay monitoring contractility with a myosin light chain phosphorylation assay. However, these cells were not compatible with this assay due to the loss of differentiation. A rat aortic SMC cell line transfected to express the human alpha2B-AR was adapted for the assay, and it was found that the alpha2-AR agonist, dexmedetomidine, evoked myosin light chain phosphorylation in this model.