Cardiac contraction at the level of the sarcomere is regulated by the thin filament (TF) composed of actin, alpha tropomyosin (TPM), and the troponin (Tn) complex (cTnT: cTnC: cTnI). The "gate-keeper" protein, α-TPM, is a highly conserved α-helical, coiled-coil dimer that spans actin and regulates myosin-actin interactions. The N-terminus of one α-TPM dimer inter-digitates with the C-terminus of the adjacent dimer in a head-to-tail fashion forming the flexible and cooperative TPM-overlap that is necessary for myofilament activation. Two dilated cardiomyopathy (DCM) causing mutations in TPM (D84N and D230N) and one hypertrophic cardiomyopathy (HCM) causing mutation (E62Q), all identified in large, unrelated, multigenerational families, were utilized to study how primary alterations in protein structure cause functional deficits. We hypothesize that structural changes from a single point mutation propagate along the -helical coiled-coil of TPM, thus affecting its regulatory function. Structural effects of the mutations studied via differential scanning calorimetry (DSC) on TPM alone revealed significant changes in the thermal unfolding temperatures of both the C- and N-termini for all mutants compared to WT, indicating that mutational effects propagate to both ends of TPM, thus affecting the overlap region. Although, of note, the proximal termini to the mutation has shown more significant structural changes compared to WT. DSC analysis on fully reconstituted TF’s (Tn:TPM:Actin) revealed effects on the TPM-Actin cooperativity of activation, affecting interaction strength (thermal stability), and the rigidity of TPM moving along actin (FWHM). To characterize the resultant functional effect of these discrete changes in thermal stability and TPM rigidity, ATPase assays were used to measure actomyosin activation in the presence and absence of Ca2+. Together, these data will provide a molecular level understanding of the structural and functional deficits caused by these mutations to help elucidate the mechanisms leading to disease.

Les fluides de forage à base d'huile sont utilisés lors d'opérations de forage off-shore. Ils permettent de lubrifier l'outil de forage, d'évacuer les déblais ainsi que de maintenir une pression hydrostatique dans le puits. Avec des forages off-shore de plus en plus profonds, les conditions thermodynamiques sont réunies (haute pression et basse température) pour la formation d'hydrates de gaz dans les fluides de forage. L'analyse calorimétrique différentielle sous haute pression est une technique qui a fait ses preuves pour l'étude de l'équilibre thermodynamique du système triphasique gaz - eau - hydrate. Elle a été retenue pour étudier la cinétique de formation d'hydrates car elle est particulièrement bien adaptée aux milieux dispersés complexes. Une étude a été menée en faisant varier la pression de 11 à 40 MPa, le degré de sous-refroidissement de 14 à 30 K et en étudiant la formation d'hydrates dans trois fluides de composition différente. L'étude expérimentale a mis en évidence l'effet des paramètres cinétiques étudiés. L'utilisation de modèles classiques a permis de représenter les résultats expérimentaux pour des faibles et des fortes forces motrices. On a ensuite développé un modèle cinétique qui combine la théorie de la cristallisation, l'aspect statistique de la nucléation et les bilans de matière sur les espèces présentes dans le système.

Depression is one of the most commonly seen psychiatric diseases in the population in recent years. Treatment of depression is mainly carried out by psychiatric drugs. In the past few years, agomelatine which is released to the market with a trade name, Valdoxane, has been thought to have far less side effects due to its non-addictive nature, not having trouble when the drug is quitted, and also due to its property of binding only to the specific receptor that the drug interacts with. The action mechanism of agomelatine on the membrane structure has not been clarified yet, for instance, no study has been found in the literature about the interaction of agomelatin with the lipids of biological membranes. In this current study, the interaction of agomelatine with the model membranes of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylgylcerol (DPPG) and sphingomyelin (SM) is examined by Fourier transform infrared spectroscopy (FTIR) and Differential scanning calorimetry (DSC). DSC and FTIR studies show that, agomelatine shifts the phase transition temperature of DPPC and DPPG multilamellar membrane to the lower degrees, however, it shifts the phase transition temperature of SM membrane to the higher degrees. Agomelatine addition increases the lipid order of the DPPC and SM liposome, whereas, it decreases the lipid order of DPPG liposome. Moreover this drug enhances the membrane fluidity among all types of liposome studied. The increase of v lipid order and increase of fluidity at DPPC and SM liposome indicates domain formation upon drug addition (Vest et al., 2004). This was also confirmed by DSC studies. Agomelatine enhances H bonding capacity of all types of liposomes have been studied. However it has different effects on glycerol backbones of the DPPC and DPPG liposomes. At low agomelatine concentrations the increase in the frequency values indicates a decrease in the hydrogen bonding capacity of the glycerol skeleton of DPPC. In contrast, at high concentrations of agomelatine, a decrease in the frequency values was observed as an indicator of the enhancement of the hydrogen bonding capacity. So it enhances H-bonding capacity at gel phase but lowers it at liquid chrystalline phases. A progressive decreases in Tm was observed at DPPG and DPPC liposomes where it increased the Tm at SM. The pretransition peak is abolished and the Tm peak becomes broad, indicating a larger perturbation to the membrane. These observations indicate the possible interaction of agomelatine with the head group as well. The shoulder seen at the thermograms of DPPC and DPPC liposomes at high doses may indicate the lateral phase separation in to drug-rich and drug-poor domains (D&rsquo / Souza et al., 2009). These results may indicate that agomelatine is partially buried in the hydrocarbon core of the bilayer, interacting primarily with the C2-C8 methylene region of the hydrocarbon chains. All these results highlight the fact that agomelatine interacts around the head group in such a manner that it destabilizes the membrane architecture to a large extent.

The purpose of this work was to provide a better understanding of urea’s decomposition and byproduct formation in an SCR system on heavy trucks. In my experimental setup with TGA-DSC-FTIR (a combination of two thermal analysis methods and a method for gas phase detection), an FTIR method for urea in the gas phase was developed for the qualitative and quantitative determination of urea and its decomposition products. Chemicals such as urea, biuret, cyanuric acid and melamine of p.a. quality were used in this method development. Beforehand, there was no FTIR method available to detect these substances; hence, the aim of this work was to develop an FTIR method to understand the degradation chain of urea.  The combination of TGA and DSC was used for analysis of different samples, where urea, biuret, cyanuric acid and melamine in varying amounts have been weighted in for various experiments in order to study the temperature at which a phase transition or reaction occurs, i.e. the temperature at which substances begin to melt, vaporize, decompose and react. In combination with FTIR, information was obtained for the appearance of substances at various temperatures. With FTIR, we have been able to develop unique infrared spectra of substances and along with weight loss in TGA the calibration of different substances has been achieved. These calibrations have been combined together to develop an FTIR method, which has been used for detection of the substances in the ongoing study of the reaction pathways. In this study we also investigated the degradation chain of urea in the presence of metals. Austenitic and ferritic silencer materials with different surface roughness were analyzed to study whether the metals have a catalytic function or effect on the byproduct formation. Those experiments have shown that a higher amount of urea was decomposed in contact with metal surface, i.e. a larger amount of NH3 and HNCO was formed. Biuret studies in the presence of metals appeared to give a higher formation of urea over the rougher surfaces (a larger amount of biuret was decomposed over the rougher surfaces), while experiments with cyanuric acid revealed a higher HNCO formation over ferrite than over austenite, i.e. a larger amount of cyanuric acid was decomposed. By the chosen method, used in FTIR in combination with TGA-DSC, the following important reactions have been demonstrated:  Biuret decomposed to urea and HNCO; Urea decomposed into HNCO and NH3; formation of cyanuric acid from the decompositions of urea and biuret and finally decomposition of cyanuric acid into HNCO at a higher temperature.

As a non-invasive method, functional MRI (fMRI) has been widely used for human brain mapping. Although many applications have been done, there are still some critical issues associated with fMRI. Perfusion-weighted fMRI (PWI) with exogenous contrast agent suffered from the problems of recirculation, which could contaminate the cerebral blood flow (CBF) estimation and make its ability of prediction "tissue-at-risk" in debate. We propose a rapid and effective method that combines matched-filter-fitting (MFF) and ICA where ICA was used for regions with a prolonged TTP and MFF was utilized for the remaining areas. The calculation of cerebral hemodynamics afterwards demonstrates that the proposed method may lead to a more accurate estimation of CBF. The extent to which CBF is reduced in relationship to normal values has been utilized as an indicator to discern ischemic injury. However, despite the well known difference in CBF between gray and white matter, relatively little attention has been given as to how CBF may be differently altered in gray and white matter during ischemia due to the inability to accurately separate gray and white matter. To this end, we propose a robust clustering method for automatic classification of perfusion compartments. The method is first to apply a robust principal component analysis to reduce dimension and then to use a mixture model of multivariate T distribution for clustering. Our results in ischemic stroke patients at the hyperacute phase show the clear advantage over the conventional technique. BOLD fMRI, as a feasible and preferred method for developmental neuroimaging, is seldom conducted in pediatric subjects and therefore the information about brain functional development in the early age is somewhat lacking. To this end, this dissertation also focuses on how functional brain connectivity may be present in pediatric subjects in a sleeping condition. We propose a statistical method to delineate frequency-dependent brain connectivity among brain activation regions, and an automatic procedure combined with spatial ICA approach to determine the brain functional connectivity. Our results suggest that functional connectivity exists as young as two weeks old for both sensorimotor and visual cortices and that functional connectivity is highly age-dependent. / Dissertation

Nanoporous polymer hydrogels offer a desirable combination of mechanical, optical, and transport characteristics that have placed them at the core of a variety of biomedical technologies including engineered tissue scaffolds, substrates for controlled release of pharmaceutical compounds, and sieving matrices for electrophoretic separation of DNA and proteins. Ultimately, we would like to obtain a detailed picture of the nanoscale pore morphology and understand how it can be manipulated so that we can rationally identify gel formulations best suited for a specific application. But this goal has proven elusive because the most fundamental descriptors of the pore network architecture (e.g., the average pore size and its polydispersity) are particularly difficult to measure in polymer hydrogels. Here we introduce an approach that enables both the mean pore size and the pore size distribution to be quantitatively determined without prior knowledge of any physical material parameters A novel technique to prepare TEM samples was developed so that the nanoscale hydrogel pore size, pore shape and distribution are clearly visualized and quantitatively studied for the first time. The pore sizes of the hydrogel are also estimated with rheology. A new fixture is used in the rheometer and the whole polymerization process can be directly studied using an in-situ rheology experiment. A series of thermoporometry experiments are also conducted, and suitable methods and equations to study hydrogel pore size and distribution are chosen. The pore size derived from TEM, rheology, DSC is compared and their values are self-consistent. These techniques help us understand how the nanoporous morphology of crosslinked polyacrylamide hydrogels is influenced by their chemical composition and polymerization conditions. It is interesting to find hydrogels with similar pore size but different distribution. For two hydrogels with similar pore size, the broader the distribution, the faster the release rate and the higher the accumulated release percentage. So we can control the release of trapped molecules by simply varying the hydrogel pore size distribution. This discovery would have a very promising potential in the application of pharmaceuticals.

The interactions of the non steroidal anti-inflammatory drug celecoxib with pure and cholesterol containing distearoyl phosphatidylcholine multilamellar vesicles were studied using Fourier transform infrared spectroscopy, differential scanning calorimetry and turbidity technique at 440 nm. The results reveal that celecoxib exerts opposing effects on membrane order in a concentration dependent manner while cholesterol disorders and orders the membrane in the gel and liquid crystalline phase, respectively. Ternary mixtures of DSPC/Cholesterol/celecoxib behave similar to cholesterol with a small effect of celecoxib. While celecoxib decreases fluidity of the DSPC membranes, cholesterol shows an opposite effect, and in ternary mixtures, a dominant effect of cholesterol is observed. Celecoxib induces opposite effects on the hydration status of the carbonyl groups in the binary system whereas / cholesterol induces hydrogen bonding around this group. An evidence of phase separation has also been observed for all three systems (DSPC/celecoxib, DSPC/Chol, and DSPC/Chol/celecoxib). In addition, a possible location of celecoxib in the interfacial region of the membrane has been proposed. Finally, penetration of celecoxib into the hydrophobic core of the ternary system at high cholesterol concentrations and formation of a new phase has also been suggested. Thus, depending on the concentration used, celecoxib induces significant changes in the biophysical properties of membranes that may aid in understanding its mechanism of action. Furthermore, highly complex interactions take place in ternary membrane systems and further investigations are needed to explore them in detail.

In recent years, tissue engineering has shown great potential in treatment of injured tissues which aims to create artificial structures for cells to regenerate new tissues for replacing the damaged and diseased ones. The selection of scaffold materials is one of the critical factors affecting tissue healing process. Among a wide range of scaffold materials, chitosan (CS) has been demonstrated as an ideal material due to its biocompatibility, nontoxicity, biodegradability, antibacterial activity and favorable strength and stiffness. However, its insufficient mechanical properties limits its feasibility and scope for clinical application, especially for bone scaffolds. The main purpose of the study is to explore the potential of incorporation of nanofillers into CS to enhance the mechanical properties for tissue engineering. In this work, nanodiamond (ND) is applied and studied due to its high surface to volume ratio, rich surface chemistry, high mechanical strength, and excellent biocompatibility. ND/CS nanocomposites with different diamond concentration from 1wt. % to 5wt. % were synthetized through a solution casting method. The microstructure and mechanical properties of the composites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), and nanoindentation. Compared with pristine CS, the addition of ND resulted in a dramatic improvement of mechanical properties, including a 239%, 276%, 321%, 333%, and 343% increase in Young’s modulus and 68%, 96%, 114%, 118%, and 127% increase in hardness when ND amount is 1wt. %, 2wt. %, 3wt. %, 4wt. %, and 5wt. %, respectively. The strong interaction between ND surface groups and chitosan matrix is of great importance in changing polymer structure and improving mechanical properties. The cell viability and cytotoxicity of the nanocomposite were also studied using MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay. The results show that the addition of ND has no negative effect on cell viability and the nanocomposites have no cytotoxicity.

Understanding when hydrates will nucleate has notable importance in the area of flow assurance. Attempts to model hydrate formation in subsea pipelines currently requires an arbitrary assignment of a nucleation subcooling. Previous studies showed that sII hydrate containing a model water-soluble former, tetrahydrofuran, would nucleate over a narrow temperature range of a few degrees with constant cooling. It is desirable to know if gas phase hydrate formers, which are typically more hydrophobic and hence have a very low solubility in water, also exhibit this nucleation behavior. In this study, differential scanning calorimetry has been applied to determine the hydrate nucleation point for gas phase hydrate formers. Constant cooling ramps and isothermal approaches were combined to explore the probability of hydrate nucleation. In the temperature ramping experiments, methane and xenon were used at various pressures and cooling rates. In both systems, hydrate nucleation occurred over a narrow temperature range (2-3°C). Using methane at lower pressures, ice nucleated before hydrate; whereas at higher pressures, hydrate formed first. A subcooling driving force of around 30°C was necessary for hydrate nucleation from both guest molecules. The cooling rates (0.5-3°C/min) did not show any statistically significant effect on the nucleation temperature for a given pressure. The isothermal method was used for a methane system with pure water and a water-in-West African crude emulsion. Two isotherms (-5 and -10°C) were used to determine nucleation time. In both systems, the time required for nucleation decreased with increased subcooling.

Gas hydrates are known to form plugs in pipelines. Hydrate plug dissociation times can be predicted using the CSMPlug program. At high methane mole fractions of a methane + ethane mixture the predictions agree with experiments for the relative dissociation times of structure I (sI) and structure II (sII) plugs. At intermediate methane mole fractions the predictions disagree with experiment. Enthalpies of dissociation were measured and predicted with the Clapeyron equation. The enthalpies of dissociation for the methane + ethane hydrates were found to vary significantly with pressure, the composition, and the structure of hydrate. The prediction and experimental would likely agree if this variation in the enthalpy of dissociation was taken in to account. In doing the plug dissociation studies at high methane mole fraction a discontinuity was observed in the gas evolution rate and X-ray diffraction indicated the possibility of the presence of both sI and sII hydrate structures. A detailed analysis by step-wise modelling utilising the hydrate prediction package CSMGem showed that preferential enclathration could occur. This conclusion was supported by experiment. Salts such as tetraisopentylammonium fluoride form semi-clathrate hydrates with melting points higher than 30 ℃ and vacant cavities that can store cages such as methane and hydrogen. The stability of this semi-clathrate hydrate with methane was studied and the dissociation phase boundary was found to be at temperatures of about (25 to 30) K higher than that of methane hydrate at the same pressure.