There is a strong link between solubility, and thus crystallisation, and the molecular interactions of proteins in dilute salt solutions. Such molecular interactions are governed by the weak interaction forces (electrostatic, hydration and hydrophobic). Such forces can be quantitatively estimated in terms of a second virial self-coefficient (B22) and a second virial cross-coefficient (B23) for a single and a binary protein system, respectively. Previous studies confirmed the relation between a value of the second virial coefficient and a type of interaction (attractive or repulsive). The aim of this thesis is to correlate the second virial coefficient with the solubility and nucleation for single and binary protein systems. Model proteins used in this work are lysozyme and ovalbumin from egg-white, and α-amylase from Bacillus Licheniformis (BLA). The measurements are performed for sodium chloride and ammonium sulphate solutions in an acidic pH at 20 oC. Interaction chromatography is used in this work to estimate the B22 and B23 values for the model proteins in salt solutions. From the measured values of B22 and B23, the type of interaction is generalised as a function of the salt type, salt concentration, pH and protein type. For the single protein systems, in ammonium sulphate solutions (0.1 - 2.4 M) at pH 4.0 and 7.0, repulsion or no interactions are observed below 0.8 M and, as the salt concentrations are increased attractive self-interactions are observed for the model proteins. However, for the sodium chloride solutions (0.1 - 2.0 M) at pH 4.0 and 7.0, the interaction patterns vary with the salt concentration, the pH and the type of protein studied. A common feature of the self-interaction for all the model proteins is the attractive interactions close to the isoelectric point. For the binary protein systems, three distinct regions are observed in the ammonium sulphate solutions (0.1 - 1.6 M) at pH in the range 4.0 - 7.0. Attractive or no cross-interactions are observed at low salt concentrations (< 0.5 M). At the intermediate salt concentrations (0.5 - 1.0 M), the cross-interactions are constant and near zero. This is followed by a sharp increase in the attractive interactions above 1.0 M ammonium sulphate concentrations. However, for sodium chloride solutions (0.1 - 1.6 M) at pH 4.0 - 7.0, two distinct regions are observed. Attraction or no interactions are observed at low salt concentrations (< 0.5 M) and above 0.5 M concentrations of sodium chloride, negligible cross-interactions are observed between model proteins. For the single protein system, an overall increase in the solubility of three model proteins is observed with an increase in the concentrations of ammonium sulphate and also for sodium chloride solutions except for BLA, where a salting-in behaviour is observed. Linear regression is used on the solubility data to determine the parameters of the Cohn equation (β and Ks) where the values of β vary with solution pH, protein type and salt type. The values of Ks vary with protein type and salt type. However, it is insensitive to the solution pH for lysozyme in ammonium sulphate, ovalbumin in sodium chloride and BLA in ammonium sulphate solutions. For the binary protein system, the presence of ovalbumin had a measurable effect on lysozyme solubility at pH < 5.0 in both salts. In low concentration sodium chloride solutions (< 0.3 M), a decrease in the solubility of lysozyme was observed with the presence of ovalbumin at acidic pH < 5.0. However, in ammonium sulphate solutions, the lysozyme solubility increases with the addition of ovalbumin in the salt concentration range 1.6 - 2.0 M and at pH < 4.0. The primary nucleation threshold values are also determined for lysozyme in sodium chloride and ammonium sulphate solutions. In sodium chloride solutions (0.2 - 1.0 M), the critical supersaturation values increase as the solution pH is raised from 4.0 to 7.0; however in ammonium sulphate solutions (1.0 - 2.0 M), the reverse effect is observed. The critical supersaturation required to nucleate lysozyme in ammonium sulphate solutions is approximately three times higher than in sodium chloride solutions. For the single protein systems, the measured values of solubility and B22 were correlated using published models (RSL and HDW). For each protein-salt combination, a reasonable single correlation between solubility and B22 is possible as the salt concentrations and pH are varied. There are separate correlations for sodium chloride and ammonium sulphate solutions. Based on the correlation curve of solubility and B22, it is proposed that the acidic pH range (4.0 - 5.0) is better for crystallising and precipitating globular proteins from these salt solutions. If the values of solubility and B22 are converted into a non-dimensional quantity, the data derived from the different protein-salt systems collapse onto a single curve for the same salt type. The B22 values are also correlated with the critical supersaturation (ln(c*/S)) for the primary nucleation of lysozyme in salt solutions. The values of the critical supersaturation increase as the values of the second virial coefficient become negative or reduce. The ideal critical supersaturation required to create nuclei of lysozyme in salt solutions is between 0.1 and 1.4. For the binary protein systems, B23 values were related to the slope of the lysozyme and ovalbumin plot at same salt concentration and solution pH. Further work is required for binary protein systems to generalise such correlations as a function of the salt concentration and pH. The correlations derived in this thesis are useful generally to predict the solubility and primary nucleation of globular protein in salt solutions. This work reinforces the importance of the second virial coefficient in predicting the crystallisation of protein in salt solutions.

Les travaux présentés s’inscrivent dans le cadre d’une thèse financée par le ministère de la recherche. L’objectif du travail est d’élaborer un papier contenant un charge composite(TiO2/SiO2) photocatalytique permettant d’éliminer des composés volatils organiques issus des procédés d’imprimerie. Le composé organique volatil ciblé lors de ce travail de recherche est l’éthanol. Des particules de silice creuse ont été synthétisées et utilisées comme support pour desnano particules d’oxyde de titane élaborées par méthode sol-gel. Un réacteur continu a été conçuet utilisé pour traiter le flux gazeux pollué. Le gaz à traiter passe à travers le papierphotocatalytique irradié sous UV. Plusieurs supports ont été fabriqués et caractérisés parplusieurs techniques (MEB, Spectroscopie Raman, DRX). L’étude photocatalytique a permisd’optimiser la composition de ces supports. Une modélisation du réacteur et du support (papierphotocatalytique) a été développée et proposée. Cette modélisation intègre la cinétiquephotocatalytique (de type Langmuir–Hinshelwood), la diffusion de la lumière au sein du papiersuivant le modèle de Kublka-Munk et l’hydrodynamique du réacteur. / This study corresponds to a PhD thesis with financial of the Ministry of Research. The objectiveof this work is to elaborate a based-paper titanium/silica photocatalysis for on stream flue gasdepollution (volatile organic compounds) stemming from processes of printing. The volatileorganic compound used in this study is the Ethanol. Particles of hollow silica were synthesizedand used as a support for nano particles of titanium dioxide, which were elaborated by sol-gelmethod. A continuous reactor was designed and used to treat the polluted gaseous flow. Theethanol passes through the photocatalytic paper irradiated by a UV lamp. Several photocatalyticspapers were elaborated and characterized by several techniques (MEB, Spectroscopy Raman,DRX).A modeling of the reactor and the support (photocatalytic paper) was developed and proposed.This modeling integrates the Langmuir – Hinshelwood kinetic and the variation of the intensitywith position in layer’s paper using the Kublka-Munk model.

L’objectif a été d’étudier le procédé de cristallisation en émulsion d’un ingrédient cosmétique hydrophobe (EGDS) dispersé en phase aqueuse. La première étape consiste à émulsifier à chaud l’EGDS en présence d’un émulsifiant afin d’obtenir une émulsion stable huile dans eau. La cristallisation par refroidissement de l’émulsion est la seconde étape. Deux sondes optiques ont été mises au point pour permettre le suivi vidéo in situ en temps réel du procédé. A partir des séquences vidéo, la mesure de la distribution en taille des gouttes (DTG) a été faite automatiquement, celles des particules par un opérateur. La croissance des cristaux dans les gouttes a été observée au moyen d’une platine thermostatée sous microscope. Par son action sur le mécanisme de brisure la puissance spécifique d’agitation est le paramètre de premier ordre sur la DTG. La concentration en émulsifiant a un impact de second ordre sur la DTG (coalescence et stabilisation). L’emploi d’une hélice à pales minces au lieu d’une turbine Rushton est préférable (DTG étroite et polyvalence du mobile). La mesure in situ a permis de déterminer que le temps d’obtention d’une DTG stable est 3 à 4 fois supérieur aux données de la littérature. La cristallisation des gouttes est progressive, des plus grosses aux plus petites. Une goutte donne naissance à une particule dans les conditions expérimentales choisies. La fréquence de nucléation primaire a été calculée à partir de l’évolution temporelle des DTG, en supposant un mécanisme mononucléaire dans chaque goutte. Le mécanisme est hétérogène. La localisation de la nucléation primaire dans le volume de la goutte ou à sa surface interne n’a pas été possible / The aim was to study the crystallization in emulsion process of a hydrophobic cosmetic ingredient (EGDS). The emulsification of the molten EGDS in a continuous phase with the use of an emulsifier in order to obtain a stable droplet size distribution (DSD) is the first stage. The crystallization upon cooling is the second stage. Two optical probes were developed to allow the in situ video monitoring of each stage of the process in real time. From the video sequences recorded the measurement of the DSD was carried out automatically, and by an operator for the PSD. The growth of crystals in motionless droplets was observed under microscope thanks to a thermostated well. The specific power input of stirring was the main parameter acting on the reduction of DSD owing to its action on the droplet break-up mechanism. The surfactant concentration was a parameter of secondary relevance on the DSD (coalescence and stability). The use of a flat blade propeller instead of a Rushton turbine was preferable for the production of a narrower DSD. Finally the time required to reach equilibrium was found higher by a factor of 3-4 than predicted in the literature. It was shown that the droplets crystallized very progressively during cooling, from the biggest to the smallest droplets. With the experimental conditions, one drop gave birth to one particle. The primary nucleation rate was obtained from the analysis of the temporal evolution of the DSD with the hypothesis of a mononuclear mechanism in each droplet. The nature of the mechanism seems to be heterogeneous. Nevertheless its localization in the droplet volume or at the inner interfacial surface was not possible

The Ph.D. project compiled in this thesis has focused on the role of the solvent in solid-liquid phase equilibria and in nucleation kinetics. Six organic substances have been selected as model compounds, viz. ortho-, meta- and para-hydroxybenzoic acid, salicylamide, meta- and para-aminobenzoic acid. The different types of crystal phases of these compounds have been explored, and their respective solid-state properties have been determined experimentally. The solubility of these crystal phases has been determined in various solvents between 10 and 50 oC. The kinetics of nucleation has been investigated for salicylamide by measuring the metastable zone width, in five different solvents under different experimental conditions. A total of 15 different crystal phases were identified among the six model compounds. Only one crystal form was found for the ortho-substituted compounds, whereas the meta-isomeric compounds crystallized as two unsolvated polymorphs. The para-substituted isomers crystallized as two unsolvated polymorphs and as several solvates in different solvents. It was discovered that the molar solubility of the different crystal phases was linked to the temperature dependence of solubility. In general, a greater molar solubility corresponds to a smaller temperature dependence of solubility. The generality of this relation for organic compounds was investigated using a test set of 41 organic solutes comprising a total of 115 solubility curves. A semi-empirical solubility model was developed based on how thermodynamic properties relate to concentration and temperature. The model was fitted to the 115 solubility curves and used to predict the temperature dependence of solubility. The model allows for entire solubility curves to be constructed in new solvents based on the melting properties of the solute and the solubility in that solvent at a single temperature. Based on the test set comprising the 115 solubility curves it was also found that the melting temperature of the solute can readily be predicted from solubility data in organic solvents. The activity of the solid phase (or ideal solubility) of four of the investigated crystal phases was determined within a rigorous thermodynamic framework, by combining experimental data at the melting temperature and solubility in different solvents and temperatures. The results show that the assumptions normally used in the literature to determine the activity of the solid phase may give rise to errors up to a factor of 12. An extensive variation in the metastable zone width of salicylamide was obtained during repeated experiments performed under identical experimental conditions. Only small or negligible effects on the onset of nucleation were observed by changing the saturation temperature or increasing the solution volume. The onset of nucleation was instead considerably influenced by different cooling rates and different solvents. A correlation was found between the supersaturation ratio at the average onset of nucleation and the viscosity of the solvent divided by the solubility of the solute. The trends suggest that an increased molecular mobility and a higher concentration of the solute reduce the metastable zone width of salicylamide. / QC 20100831