Nonlinear optical molecular switches for alkali ion identification

This work demonstrates by means of DFT and ab initio calculations that recognition of alkali cations can be achieved by probing the variations of the second-order nonlinear optical properties along the commutation process in spiropyran/merocyanine systems. Due to the ability of the merocyanine isomer to complex metal cations, the switching between the two forms is accompanied by large contrasts in the quadratic hyperpolarizability that strongly depend on the size of the cation in presence. Exploiting the nonlinear optical responses of molecular switches should therefore provide powerful analytical tools for detecting and identifying metal cations in solution

Antigen Uptake by Langerhans Cells Is Required for the Induction of Regulatory T Cells and the Acquisition of Tolerance During Epicutaneous Immunotherapy in OVA-Sensitized Mice

The skin is a major immunologic organ that may induce protection, sensitization or tolerance. Epicutaneous immunotherapy (EPIT) has been proposed as an attractive strategy to actively treat food allergy and has been shown to induce tolerance in sensitized mice through the induction of Foxp3+ regulatory T cells (Tregs), especially CD62L+ Tregs. Among immune cells in the skin, dendritic cells are key players in antigen-specific immune activation or regulation. The role of different populations of skin DCs in tolerance induction remains to be elucidated. Using OVA-sensitized BALB/c mice, we demonstrated that the application of a patch containing OVA-A647 to the skin resulted in allergen uptake by Langerhans cells (LCs) and CD11b+ dermal cDC2 and subsequent migration into skin draining lymph nodes. These 2 populations induced Foxp3 expression in CD4+ cells in vitro. Only LCs induced LAP+ cells and CD62L+ Tregs. Using Langerin-eGFP-DTR mice, we analyzed the role of LCs in the mechanisms of tolerance induction by EPIT in vivo. Following complete depletion of LCs, a dramatic decrease in the number of OVA+ DCs and OVA+ CD11b+ dermal cDC2 was observed in skin draining lymph nodes 48 h after epicutaneous application. Likewise, 2 weeks of EPIT in non-depleted mice induced Foxp3+ Tregs, especially CD62L+, and LAP+ Tregs in skin draining lymph nodes and spleen, whereas no induction of Tregs was observed in LC-depleted mice. Following 8 weeks of treatment, EPIT-treated mice showed significant protection against anaphylaxis accompanied by a significant increase of Foxp3+ Tregs, especially CD62L+ Tregs, which was not seen in the absence of LCs. In summary, although both LCs and CD11b+ dermal cDC2s could induce regulatory T cells, the absence of LCs during EPIT impaired treatment efficacy, indicating their crucial role in skin-induced tolerance

Knot-isomers of Moebius Cyclacene: How Does the Number of Knots Influence the Structure and First Hyperpolarizability?

Four large ring molecules composed by 15 nitrogen-substituted benzene rings, named as "knot-isomers of Moebius cyclacene", i.e. non-Moebius cyclacenes without a knot (0), Moebius cyclacenes with a knot (1), non-Moebius cyclacenes with two knots (2), and Moebius cyclacenes with three knots (3), are systematically studied for their structures and nonlinear optical properties. The first hyperpolarizability (beta_0) values of these four knot-isomers structures are 4693 (0) < 10484 (2) < 25419 (3) < 60846 au (1). The beta_0 values (60846 for 1, 10484 for 2 and 25419 au for 3) of the knot-isomers with knot(s) are larger than that (4693 au for 0) of the knot-isomer without a knot. It shows that the beta_0 value can be dramatically increases (13 times) by introducing the knot(s) to the cyclacenes structures. It is found that introducing knots to cyclacenes is a new means to enhance the first hyperpolarizability.Comment: 12 pages, 4 figure

Design of molecular switches exhibiting second-order nonlinear optical responses : ab initio investigations and hyper Rayleigh scattering characterizations

Les interrupteurs moléculaires sont des composés capables de commuterréversiblement entre deux ou plusieurs états stables en réponse à un stimulusextérieur. Lʼobjectif de la thèse est la conception dʼinterrupteurs moléculairesprésentant des contrastes optiques non-linéaires (ONL) et la mise évidence desparamètres structuraux et électroniques menant à dʼimportants contrastes depremière hyperpolarisabilité (β) via une approche multidisciplinaire qui combine lasynthèse de nouveaux composés, la caractérisation de leurs réponses optiqueslinéaires et non-linéaires par spectroscopie dʼabsorption UV-visible et par diffusionhyper-Rayleigh et lʼutilisation des méthodes de la chimie théorique afin de prédire etdʼinterpréter les propriétés moléculaires. Ces phénomènes de commutationsréversibles et les changements de propriétés qui les accompagnent présentent denombreux intérêts, tant technologiques comme lʼélaboration dʼordinateursmoléculaires quʼau niveau des organismes vivants où de nombreuses fonctionsbiologiques sont basées sur un phénomène de commutation. Les principaux résultatsde nos travaux se situent au niveau de lʼinterprétation des réponses ONL et de leurscontrastes en fonction de la nature, de la position et du caractère donneur/accepteurdes substituants présents sur le squelette des interrupteurs moléculaires.Molecular switches are compounds presenting the ability to commutereversibly between two or more states in response to external stimuli. The goal of thework is the design of molecular switches exhibiting contrasts of their second-ordernonlinear optical (NLO) properties and the highlight of the structural and electronicparameters leading to large contrasts of first hyperpolarizability (β) via amultidisciplinary approach combining the synthesis of new compounds, thecharacterization of their linear (by UV-Visible absorption spectroscopy) and nonlinearoptical properties (by hyper Rayleigh scattering), and the theoretical simulations inorder to predict and interpret molecular properties. These reversible switchingprocesses and the resulting variations of molecular properties have many interests intechnological area such as the development of molecular computers or in lifesciences since many biological functions are based on commutation mechanisms.The major results of our investigations are the interpretation of the NLO responsesand contrasts as a function of the nature, the positioning, and the donor/acceptorcharacter of the substituents

Cointegration analysis among European crude oil, natural gas and coal prices between 1980 and 2015.

The beginning of cointegration theory lies in the fact that a lot of financial and macroeconomic series are non-stationary. But when common methods are applied, a problem arises and is called “spurious regression”. Spurious regression is a situation in which variables that are related appear to be statistically significant when the variables are unrelated. Non-stationarity is a property of many time series and arises when a variable doesn’t have a clear tendency to return to a constant value or linear trend. This property consequently leads to invalidate classical inference methods. Cointegration theory allows the study of such non-stationary time series which are stationary when a linear combination is applied. Then it allows specifying stable long-run relationships while analysing the short-run dynamic of variables under consideration. Two cointegration methods will be used in this thesis. The first one is the Engle-Granger (1987) method which has the characteristic to be very simple to implement but has the main limit to allow the analysis of only two variables at a time. In order to counter this limit, the multivariate Johansen’s (1991) approach will be used as the second cointegration method. In this thesis, we will apply cointegration theory among European price series of crude oil, natural gas and coal in a relative large sample of 35 years from 1980 to 2015. Such empirical research on cointegration among energy fossil fuels have already been led by Serletis and Herbet (1999), Villar and Joutz (2006), Mohammadi (2009), Bencivenga et al. (2010) and Westgaard et al. (2011). Nevertheless, none of them took as large a sample as in this thesis. Moreover, we also take into account data from the ten last years which are characterised by a high volatility, especially with the worldwide financial and economic crisis in 2008 and 2009. Based on monthly price series of Brent crude oil, natural gas and coal from European countries, and using the software R, several hypotheses are tested in this thesis: - Hypothesis n°1: There is (are) cointegration relationship(s) using the Engle- Granger (1987) method between prices of crude oil/natural gas, natural gas/coal, and coal/crude oil. - Hypothesis n°2: There is (are) cointegration relationship(s) using Johansen’s (1991) approach. - Hypothesis n°3: Considering a structural break, there is (are) cointegration relationship(s) using Johansen’s (1991) approach. Economic and financial price series exhibit, most of the time, the characteristic to be non-stationary. The problem with those kinds of series which have this property is that classical analytical methods cannot be used on them, at the risk of having as a result “spurious regression”. In order to get around this difficulty, we applied the cointegration theory on our variables in order to detect some hypothetical relationships among prices of crude oil, natural gas and coal. Two main methods were used with the first one being the Engle-Granger (1987) method which allows us to analyse the cointegration relationships between pairs of variables and the second one being the multivariate Johansen’s (1991) approach which allows us to determine the number of cointegration relationships from VAR models. The results from the Engle-Granger (1987) method (and from the Granger causality tests) show us that there are three cointegration relationships among our variables seeing that the prices of coal have an impact on the prices of crude oil and natural gas and the prices of crude oil have an impact on the prices of natural gas. After estimating their respective error correction model for each relation, it has been interpreted that all of them exhibit a long-run relationship, meaning that an error correction mechanism is present in order to compensate some potential disequilibrium. This mechanism helps to keep the evolution of the three price series on the same path in the long-run. Moreover, it seems that the growth of coal prices has a positive impact on the growth of crude oil and natural gas prices when the growth of crude oil prices has a negative impact on the growth of natural gas prices. This first step accomplished, we can say that our hypothesis n°1 is verified for those three relations. The second method used for cointegration analysis is Johansen’s (1991) approach and it allows the analysis of multiple variables at the same time and not only by pairs, as it was only possible with the Engle-Granger (1987) method. Based on the estimation of a VAR model with our three variables, the results of this second method show us the existence of one cointegration vector among the three variables which allows us the estimation of the VECM. The results from the estimated VECM show us that, like in the Engle-Granger (1987) method, there is an error correction mechanism but only in the relations relative to the crude oil prices and the natural gas prices. The relation relative to the coal prices does not have a significant error term in its relation. Concerning the short-term indicators, the results coincide with the Engle-Granger (1987) method. In fact, the growth of crude oil prices is positively dependent on the past values of the growth of coal prices and its own past growth in price values. The growth of natural gas prices are negatively linked to the past values of the growth of crude oil and coal but also to its own past growth in price values. And finally, the growth of coal prices is positively dependent on the past values of the growth of crude oil prices and on its own growth in price values. Based on those results, we can then assert that our hypothesis n°2 is verified and there is in fact a cointegration relationship among our variables. The third and final analysis used the same Johansen’s (1991) approach but with the difference that, in the estimated model, a structural break at an unknown date has been introduced. The method is based on Luetkepohl et al (2004) and allows the analysis of cointegration relationships when a structural break in our data is taken into account. The reason for this analysis is to determine if strong variations in our data have an impact on the presence of cointegration relationships we found earlier. The strong variations refer to the high volatility period resulting from the economic and financial crisis in 2008 and 2009 when the prices of our three variables experienced a huge drop. The results from this third cointegration analysis show us the existence of an additional cointegration vector in the estimated model compared to the previous analysis which gives us two cointegration vectors. The estimation of the VECM gives us the same interpretation as Johansen’s approach with an error correction mechanism in the relation relative to the crude oil and natural gas prices but not for the coal prices. With this last result, we can then validate our hypothesis n°3 and say that, despite the presence of a structural break in the model, there exist two cointegration relationships among our variables which have a long-run relationship. The fact that the presence of a structural break has a positive impact on the presence of cointegration relationships shows us that there are strong relations between crude oil, natural gas and coal prices, even if a high volatility period occurs in the prices series. In fact, such highly volatile periods, like the one from the ten last years, could have an important impact on the models’ estimations but it seems that the cointegration relationships among our variables do not react the same way and there is no decoupling effect. The results of this thesis could be particularly useful for the energy industries especially for hedgers who are looking to diminish risk during a crisis period. In fact, during high volatility periods, it is relatively difficult to reduce the risk linked to energy sources. The fact that the three prices seem to be cointegrated could be helpful to better anticipate the behaviour of energy prices during economical or financial crisis periods.Master [120] en Ingénieur de gestion, Université catholique de Louvain, 201

Conception d’interrupteurs moléculaires présentant des réponses optiques non-linéaires du deuxième ordre : étude théorique et caractérisation par diffusion hyper Rayleigh

Les interrupteurs moléculaires sont des composés capables de commuterréversiblement entre deux ou plusieurs états stables en réponse à un stimulusextérieur. Lʼobjectif de la thèse est la conception dʼinterrupteurs moléculairesprésentant des contrastes optiques non-linéaires (ONL) et la mise évidence desparamètres structuraux et électroniques menant à dʼimportants contrastes depremière hyperpolarisabilité (β) via une approche multidisciplinaire qui combine lasynthèse de nouveaux composés, la caractérisation de leurs réponses optiqueslinéaires et non-linéaires par spectroscopie dʼabsorption UV-visible et par diffusionhyper-Rayleigh et lʼutilisation des méthodes de la chimie théorique afin de prédire etdʼinterpréter les propriétés moléculaires. Ces phénomènes de commutationsréversibles et les changements de propriétés qui les accompagnent présentent denombreux intérêts, tant technologiques comme lʼélaboration dʼordinateursmoléculaires quʼau niveau des organismes vivants où de nombreuses fonctionsbiologiques sont basées sur un phénomène de commutation. Les principaux résultatsde nos travaux se situent au niveau de lʼinterprétation des réponses ONL et de leurscontrastes en fonction de la nature, de la position et du caractère donneur/accepteurdes substituants présents sur le squelette des interrupteurs moléculaires.Molecular switches are compounds presenting the ability to commutereversibly between two or more states in response to external stimuli. The goal of thework is the design of molecular switches exhibiting contrasts of their second-ordernonlinear optical (NLO) properties and the highlight of the structural and electronicparameters leading to large contrasts of first hyperpolarizability (β) via amultidisciplinary approach combining the synthesis of new compounds, thecharacterization of their linear (by UV-Visible absorption spectroscopy) and nonlinearoptical properties (by hyper Rayleigh scattering), and the theoretical simulations inorder to predict and interpret molecular properties. These reversible switchingprocesses and the resulting variations of molecular properties have many interests intechnological area such as the development of molecular computers or in lifesciences since many biological functions are based on commutation mechanisms.The major results of our investigations are the interpretation of the NLO responsesand contrasts as a function of the nature, the positioning, and the donor/acceptorcharacter of the substituents