In this work, a comparative electrochemical study has been performed to evaluate corrosion inhibition property of several film-forming corrosion inhibitors provide by Akzo Nobel on carbon steel in a chloride solution. For carbon steel exposed to 1 M NaCl solution with and without added inhibitor, electrochemical measurements including electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) at different exposure time intervals, and potentiodynamic polarization at the termination of the exposure, have been performed to investigate the film forming process and to evaluate corrosion inhibition efficiency of the inhibitors, as well as its evolution with time. The corrosion resistance data obtained from the EIS and LPR measurements are in good agreement. The results indicate different inhibition properties of the inhibitors tested. The inhibition effect of SSF CI-1 is negligible in the first hour of exposure, but it increases steadily with time for 1 day, and then remains the same level during the exposure up to one week. SSF CI-2 exhibits a good inhibition effect in the first hour, but the effect decreases with time to a low level after 8 hours, and then increases again with prolonged exposure. SSF CI-4 shows a low inhibition effect during the first day, and then increases to a maximum level after three days’ exposure. For SSF CI-5 and SSF CI-6, the inhibition effect within 8 hours is relative low but higher than that of SSF CI-4, and the effect increases with time during prolonged exposure. The SSF CI-5 seems to be better than SSF CI-6 because of a more stable inhibition effect. The EIS results indicate that most of the inhibitors form a resistive surface film on carbon steel, which becomes more resistive and protective after several days’ of exposure. However, in the initial stage of exposure, the SSF CI-6 does not show an effect of formation of a resistive film on the surface. The potentiodynamic polarization measurements suggest that, SSF CI-1 and SSF CI-2 are anodic type inhibitor, SSF CI-4 is cathodic type inhibitor, and SSF CI-5 and SSF CI-6 are mix type inhibitor. Moreover, the inhibitors tested show a similar corrosion inhibition effect as mussel adhesive protein (MAP) at the low dosage level.

Les inhibiteurs des protéases à sérine (Serpins) constituent une classe d'enzymes très peu étudiée chez les bactéries. Dans ce travail de thèse nous nous sommes intéressés à l'étude des serpins provenant du microbiote intestinal et l'investigation de leur potentiel anti-inflammatoire pour le traitement des maladies inflammatoires chroniques de l'intestin (MICI) chez l'homme. Pour cela nous avons identifié les serpins provenant du microbiote intestinal humain et analysé leur diversité ainsi que leur distribution entre les individus malades et sains. Ces données nous ont permis d'isoler les serpins significativement associées aux MICI. La purification de quarte d'entre elles nous a amené à démontrer qu'elles inhibent les protéases humaines impliquées dans les MICI. L'analyse biochimique et cinétique approfondie de ces protéines a montré qu'elles possèdent des propriétés originales notamment leur efficacité d'inhibition élevée. L'étude de l'effet protecteur de trois serpins chez un modèle animal de colite a démontré pour la première fois l'efficacité des serpins in vivo démontrant ainsi leur potentiel thérapeutique. / Serine protease inhibitors (Serpins) are a class of proteins that reamin poorly studied in bacteria. In this thesis we are interested in the study of serpins originating from the intestinal microbiota and the investigation of their anti-inflammatory potential for the treatment of inflammatory bowel diseases (IBD) in humans. For this we have identified serpins from the human gut microbiota and analyzed their diversity as well as their distribution between healthy and IBD patients. These data allowed isolating serpins significantly associated with IBD. The purification of four of them led us to demonstrate that they inhibit human proteases involved in IBD. Biochemical and kinetic analysis of these proteins showed that they exhibit original properties, in particular their high inhibition efficiency. The study of the protective effect of three serpins in an animal model of colitis demonstrated for the first time the efficacy of serpins in vivo demonstrating thus their therapeutic potential.

In our pervious study, the ethanol extracts from Eupatorium fortunei Turcz at concentrations of 200 ÷ 500 mg L-1 significantly inhibited the growth of Microcystis aeruginosa, which is the most common species, responsible for toxic cyanobacteria blooming in fresh water. o-Coumaric acid (or 2-hydroxy-cinnamic acid) isolated from E. fortunei was tested its growth-inhibitory effect on M. aeruginosa and Chlorella vulgaris at the concentrations of 1.0, 10.0 and 100.0 mg L-1 in the 96- hour experiment by the optical density and the analytical method of chlorophyll a concentration. Results indicated that the compound strongly affected towards M. aeruginosa at the concentration of 100.0 mg L-1 with the inhibition efficiency (IE) values of 76.76 % and 84.66 %, respectively while those for C. vulgaris were lower just of 60.59%, and 74.53 %, respectively. The obtained data demonstrated that two methods were highly consistent and o- coumaric acid was more toxic to M. aeruginosa than C. vulgaris at all tested concentrations (p<0.05). The images of M. aeruginosa and C. vulgaris cells under the light microscope clearly showed the damage of these cells under the attck of o-coumaric acid. Although o-coumaric compound was widely demonstrated antibacterial properties in previous reports, to the best of our knowledge, our study was the first report about effect of o- coumaric acid on the growth of M. aeruginosa and C. vulgaris. / Những nghiên cứu trước đây đã chỉ ra rằng cao chiết etanol từ cây Mần tưới Eupatorium fortune Turcz tại dải nồng độ 200 ÷ 500 μg mL-1 ức chế mạnh sinh trưởng của Microcystis aeruginosa, - loài phổ biến nhất gây nên sự bùng nổ tảo độc trong hệ sinh thái nước ngọt. o-Coumaric axit (hay 2-hydroxy-cinnamic axit) phân lập từ E. fortune được tiến hành đánh giá ảnh hưởng lên sinh trưởng của hai loài M. aeruginosa và Chlorella vulgaris tại ba nồng độ là 1.0, 10.0 and 100.0 mg L-1 trong thời gian 96 giờ thực nghiệm theo phương pháp đo mật độ quang và phân tích hàm lượng chlorophyll a. Kết quả nghiên cứu cho thấy sau 96 giờ phơi nhiễm tại nồng độ 100 mg L-1 hoạt chất ức chế mạnh tới M. aeruginosa với giá trị ức chế sinh trưởng (IE) tương ứng là 76.76 và 84.66%. Giá trị IE đối với C.vulgaris ghi nhận thấp hơn chỉ là 60.65 và 74.53%, tương ứng. Hai phương pháp phân tích trên có tính nhất quán cao và o-coumaric ức chế sinh trưởng lên loài M.aeruginosa mạnh hơn so với loài C.vulgaris tại tất cả các nồng độ nghiên cứu (p<0.05). Ảnh chụp các tế bào M.aeruginosa và C.vulgaris dưới kính hiển vi điện tử đã chứng minh những tổn thương của tế bào dưới tác động của o-coumaric axit. Mặc dù o- coumaric cho thấy đặc tính chống khuẩn cao trong các công bố trước đây, nhưng theo hiểu biết của chúng tôi đây là nghiên cứu đầu tiên công bố về ảnh hưởng của hoạt chất o-coumaric axit lên sinh trưởng của M. aeruginosa và C. vulgaris.