BACKGROUND: Proper thyroid function is critical for normal fetal growth and neurodevelopment, as well as regulation of multiple systems in adults. There is growing evidence indicating that exposure to environmental chemicals may disrupt human thyroid function. Organophosphate flame retardants (PFRs) and per- and polyfluoroalkyl substances (PFASs) are two classes of potential thyroid disrupting chemicals commonly used in consumer products. OBJECTIVES: We characterized exposures to triphenyl phosphate (TPHP), a common PFR, and PFASs in two different U.S. populations. We assessed associations between TPHP and thyroid hormones in adults, as well as individual and joint associations of prenatal PFASs with maternal and neonatal thyroid hormones. METHODS: Analyses were conducted in two Boston, Massachusetts cohort studies: the Flame Retardant Exposure Study (FlaRE) and Project Viva, a longitudinal pre-birth cohort. In FlaRE, we used linear mixed effects models to assess covariate-adjusted associations between urinary DPHP concentrations and serum thyroid hormone levels in repeated samples from male and female adults (n=51). In Project Viva, we used both linear regression and weighted quantile sum regression to assess covariate-adjusted individual and joint associations of prenatal plasma PFAS concentrations measured in early pregnancy with maternal (n=726) and neonatal (n=465) thyroid hormone levels. RESULTS: In FlaRE, higher urinary DPHP was associated with higher total thyroxine (T4) levels in female but not male participants. We saw no associations between DPHP and free T4, total triiodothyronine, or thyroid stimulating hormone (TSH). In Project Viva, we found that higher prenatal exposure to PFASs was associated with lower maternal Free T4 Index (FT4I) and lower neonatal T4 in male infants, but was not associated with maternal T4 or TSH. Combined exposure to multiple PFASs was associated with lower maternal FT4I and neonatal T4 levels, but the relative contributions varied by individual PFAS. CONCLUSIONS: Exposures to both DPHP and PFASs were associated with altered thyroid hormone levels in these populations. Observed associations of DPHP and PFASs with thyroid hormone levels varied by sex, suggesting potential differences in susceptibility or mechanism of action. Associations between PFASs and thyroid hormones also differed across chemicals, suggesting potential differences in toxicological mechanism or potency. / 2019-11-08T00:00:00Z

<p> Quantitation by nuclear magnetic resonance (NMR) has been frequently done with integrals. The use of peak heights has been thought to be unreliable. The aim of this thesis is to examine the reliability of peak height method in achieving quantitative NMR measurements for small molecules such as water and sucrose.</p> <p> Isotope measurements have been traditionally done by isotope-ratio mass spectrometry. This is no doubt a highly sensitive technique for analyzing pure samples but the analysis of mixtures is not as straight-forward as it would be for the former. Ontario Hydro has encountered problems in measuring deuterium in DMSO/water mixtures. To solve the problem with NMR, an analytical method has been established to measure the deuterium content in waters and in DMSO/water mixtures. This involved testing a linear model for analyzing waters which were enriched or depleted with deuterium as well as applying the model to quantify DMSO/water mixtures. Both 1H and 2H NMR were employed. Satisfactory accuracy and precision of the results were obtained.</p> <p> For quantitative 13C work, the peak height method is often not recommended due to the variations in signal width, which is a result of varied T2 values and nuclear Overhauser enhancement (NOE). Sucrose molecules in cane sugar and beet sugar have different 13C isotopic ratios because they are synthesized by different photosynthetic pathways. To see the usefulness and limitation of the peak height method, 13C spectra of sucrose were acquired and the carbon peaks were quantified. Good precision was achieved but no predictable trend in the isotope difference could be found.</p> / Thesis / Master of Science (MSc)

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We study the formation of novel bicontinuous phases in binary mixtures of AB diblock copolymers (DBCP) using the polymeric self-consistent field theory. We predict that the bicontinuous double-diamond (DD) and plumber’s nightmare (P) phases, which are metastable phases of neat diblock copolymers, could be stablized in gyroid-forming A-minority DBCPs via the blending of specifically designed A-majority DBCPs. The mechanisms of stabilizing different bicontinuous phases are revealed by analyzing the spatial distribution of the different DBCPs. It is found that the A-majority DBCPs residing mainly in the nodes of the structure, thus alleviating the packing frustration of the A-blocks. Furthermore, a local segregation of the two DBCPs occurs at the AB interface, thus regulating the local curvature of the interfaces. A synergetic interplay of these two mechanisms results in a larger stable region of the DD and P phases via the addition of tailored A-majority DBCPs. The theoretical study provides an efficient route to obtain novel bicontinuous phases. / Thesis / Master of Science (MSc)

No / Spherical crystallization involves crystallization and simultaneous agglomeration of a crystalline particle using an immiscible phase, which has preferential affinity for the crystal surface. Here, we report application of a spherical crystallization technique to the field of co-crystallization. Carbamazepine/saccharin (CBZ/SAC) co-crystals were generated using reverse antisolvent addition and agglomerated using different bridging liquids. Two crystal forms of CBZ/SAC co-crystals were formed, depending on the levels of supersaturation achieved during processing. The selective agglomeration of co-crystal occurred during the agglomeration stage, depending on the relative interaction between bridging liquid and the crystal surfaces. The computational investigation of isosteric heats of adsorption of the bridging liquids at the prominent crystal surfaces proved to be a useful tool in understanding the surface interactions. The spherical crystallization technique shows opportunity to generate co-crystals and its purification through selective agglomeration.

<p>  </p> <p>From applications in nanoscale electronics to regenerative medicine, there is a strong need for control assembly processes at nanometer length scales.1,2 In this work, we investigate the application of microscale droplet delivery as a rapid and scalable approach to pattern the molecular assembly of nanoscale chemical patterns on highly oriented pyrolytic graphite (HOPG). Furthermore, it was also observed that variations in the blend of alkyl impurities present in technical-grade OLAm reagents influenced the temperature-dependent assembly behavior.13 This suggests a likely role of alkyl chain phase transitions in the ligand shell, particularly in more complex mixtures and for anisotropic nanocrystals.</p> <p>Oleylamine (OLAm) is a common technical-grade reagent used in nanocrystal synthesis. Most nanocrystal synthesis is done using technical grade Oleylamine (70% purity). Higher purity reagents are not readily available because in certain instances, technical grades are obtained from natural substances, resulting in differing impurities compared to those generated during preparative reactions using pure raw materials.3 Technical grade reagents of OLAm contain 70% of the cis chain OLAm and 30% of an unspecified mixture of Elaidylamine (ELAm) , Octadecylamine (ODAm) and segments of various lengths and saturated alkyl chains.4,5 Here, we use Differential Scanning Calorimetry thermograms to investigate the miscibility of binary mixtures of OLAm/ELAm, OLAm/ODAm, and ELAm/ODAm. Ternary mixtures of the lipids showed clear peaks for the trans and saturated impurities.</p> <p>We patterned graphite surfaces with amphiphiles via inkjet printing to quickly generate 1-nm-wide functional patterns. Inkjet printing allowed for long-scale hierarchical patterning. We investigated various ink formulations and the resulting printing quality of functional monolayers on 2D crystalline materials. </p>

Binary mixtures of polymers and soft nanocolloids, also called as polymer nanocomposites are well known and studied for their enormous potentials on various technological fronts. In this thesis blends of polystyrene grafted gold nanoparticles (PGNPs) and polystyrene (PS) are studied experimentally, both in bulk and in thin films. This thesis comprises three parts; 1) evolution of microscopic dynamics in the bulk(chapter-3),2) dispersion behavior of PGNPs in thin and ultra thin polymer matrices (chapter-4) 3) effect of dispersion on the glass transition behavior (chapter-5). In first part, the state of art technique, x-ray photon correlation spectroscopy is used to study the temperature and wave vector dependent microscopic dy¬namics of PGNPs and PGNP-PS mixtures. Structural similarities between PGNPs and star polymers (SPs) are shown using small angle x-ray scatter¬ing and scaling relations. We find unexpected (when compared with SPs) non-monotonic dependence of the structural relaxation time of the nanoparticles with functionality (number of arms attached to the surface). Role of core-core attractions in PGNPs is shown and discussed to be the cause of anomalous behavior in dynamics. In PGNP-PS mixtures, we find evidence of melting of the dynamically arrested state of the PGNPs with addition of PS followed by a reentrant slowing down of the dynamics with further increase in polymer frac¬tion, depending on the size ratio(δ)of PS and PGNPs. For higher δ the reen¬trant behavior is not observed with polymer densities explored here. Possible explanation of the observed dynamics in terms of the presence of double-glass phase is provided. The correlation between structure and reentrant vitrifica¬tion in both pristine PGNPs and blends are derived rather qualitatively. In the second part, the focus is shifted to miscibility between PGNPs and polymers under confinement i.e., in thin films. This chapter provide a compre¬hensive study on the different parameters affecting dispersion viz., annealing conditions, fraction of the added particles, polymer-particle interface and more importantly the thickness of the films. Changes in the dispersion behavior with annealing is shown and the need for annealing the films at temperatures higher than the glass transition temperature of the matrix polymers is clearly elucidated. Irrespective of the thickness of the films( 20 and 65 nm) studied, immiscible particle-polymer blends unequivocally prove the presence of gradi¬ent in dynamics along the depth of the films. To our knowledge for the first time, we report results on confinement induced enhancement in the dispersion of the nanoparticles in thin polymer films. The enhanced dispersion is argued to be facilitated by the increased free volume in the polymer due to confinement as shown by others. Based on these results we have proposed a phase diagram for dispersibility of the nanoparticles in polymer films. The phase diagram for ultra thin films highlights an important point: In ultra thin films the particles are dispersed even with grafting molecular weight less than matrix molecular weight. In the third part, we have studied the glass transition of the thin films whose structure has been studied earlier in the earlier part. Non-monotonic variation in glass transition with the fraction of particles in thin films has increased our belief on the gradient in the dynamics of thin polymer films. En¬hanced dispersion with confinement is captured with the enhanced deviation in glass transition temperature of ultra thin films. Effect of miscibility param¬eter on Tgis studied and the results are explained with the subtle interplay of polymer-particle interface and confinement.