Relaxation properties of the deuteron spin system in CD₄ and CD₃H were studied in the temperature range from 105°K - 57°K. These results show that the intra-molecular quadrupole interactions dominate and the relaxation occurs through the molecular reorientations of the molecule. The deuteron spin-lattice relaxation times are approximately temperature independent, except for a small contribution from the magnetic dipolar interactions near the melting point in CD₃H. From this data it is concluded that the reorientatlonal correlation time is temperature independent. The deuteron T₂ shows the same temperature dependence as the proton T₂; the deuteron T₂ can be accounted for on the basis of magnetic dipolar interactions alone. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Crude oil leakages often give rise to in situ contamination with both oil and salt. In this study, the biodegradation of model alkanes and of saturated hydrocarbons in whole crude oil by hydrocarbon-degrading bacteria was investigated at different salt (NaCl, KCl, Na2SO4) concentrations. Changes in cell surface hydrophobicity at different NaCl concentrations were also investigated. The results show that with increasing NaCl concentration, the lag phase for strain growth on hydrocarbons was prolonged; however, the total degradation efficiency was not influenced greatly. The formation of different sizes of cell aggregates at different salt concentrations indicated that salt could indirectly influence mass transfer of hydrocarbons from the medium to the interior of the cells. The results also showed that KCl had a less inhibitory effect on biodegradation than NaCl, and changes of Na2SO4 concentration did not greatly affect biodegradation. In addition, cell surface hydrophobicity increased with increasing NaCl concentration when the cultures were grown on hydrocarbons.

Fecal recoveries of n-alkanes were determined in three digestion balance experiments consisting of two periods each. Each experiment compared two diets in a switch-back design using eight mature Thoroughbred geldings. Horses were randomly assigned to two groups of four and offered one of two mixed grass/legume hays (Diets 1 and 2) in Exp. 1, mixed grass/legume hay and one of two concentrates (Diets 3 and 4) in Exp. 2, and mixed grass/legume pasture (Diets 5 and 6) in Exp. 3. In Exp. 1 and 2, horses were housed in stalls and in Exp. 3, two horses from each diet were housed in stalls and two horses remained on pasture. Balance periods lasted 11 days with d 1 to d 7 consisting of a dietary accommodation period, followed by 4 days of total collection. Results indicated that fecal recoveries of odd-chain alkanes (C25 to C33) were less than 100 % and similar between chain lengths. Estimates of DMD (DE) were similar to the total collection DMD (DTC) for Diet 1 in Exp. 1, but underestimated DTC for Diet 2 in Exp. 1 (P < .05) and Diets 3 and 4 in Exp. 2 (P < .05). For Diet 5 in Exp. 3, the DE for stall-fed horses using C25 and C33 was similar to DTC, whereas C27, C29, and C31 underestimated DTC (P < .05). For pastured horses, the DE using C29 and C31 were similar to DTC, whereas C25, C27, and C33 underestimated DTC (P < .05). For Diet 6 in Exp. 3, the DE for stalled horses calculated using C25 was similar to the DTC, whereas use of C27, C29, C31, and C33 underestimated DTC (P < .05). For pastured horses, the DE using C29 was similar to DTC, whereas all other alkanes underestimated DTC (P < .05). When DE was adjusted (DA1) using the mean recovery of each odd-chain alkane, DA1 was similar to DTC for Diet 2 in Exp. 1, Diets 3 and 4 in Exp. 2, and stalled horses offered Diets 5 and 6 in Exp. 3. The DA1 using C25 underestimated DTC for Diet 1 in Exp. 1 (P < .05). For pastured horses offered Diet 5, DA1 for C33 was not different from the DTC estimate, whereas all other DA1 for n-alkanes overestimated DTC (P < .05). For pastured horses offered Diet 6, DA1 for C29 and C31 overestimated, but were similar to the DTC, whereas the DA1 for C33 underestimated DTC and was similar to the DTC. The DA1 for C25 and C27 overestimated DTC (P < .05). When DE was adjusted for the mean recovery of all n-alkanes (DA2), all DA2 estimates for stalled horses in Exp. 1, 2, and 3 were similar. In pastured horses offered Diets 5 and 6 in Exp. 3, the DA2 overestimated DTC (P < .05). These results suggest that accurate mean estimates of DMD can be obtained by adjusting for mean recovery of each odd-chain alkane in a specific diet. / Master of Science

published_or_final_version / Chemistry / Master / Master of Philosophy

No description available.

“Matrix effects” in Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy are the spectroscopic changes induced by intermolecular interactions, providing sensitivity to local structure and order in solids and liquids. This project aims to identify the effect of intermolecular interactions caused by different n-alkane solid state structures on their NEXAFS spectra. Changes to the carbon 1s NEXAFS spectra are studied as a function of their solid state structure and organization. Two experimental approaches were proposed in this project. In the first approach, different n-alkane crystal structures (orthorhombic, monoclinic, etc.) are examined which arise as a function of n-alkane chain length. In the second approach, changes observed through the pre-melting point order-disorder phase transition found in n-alkanes are examined. This work will explore the characteristic spectroscopic differences observed between n-alkanes in different crystalline forms as well as in the disordered phase below the melting points. In this project, well-ordered diamond shape n-alkane single crystals were obtained by solution casting, using experimental conditions optimized for each n-alkane. As circularly polarized radiation will average the effect of molecular orientation, circularly polarized radiation was used to obtain the NEXAFS spectra of n-alkanes. However, in the analysis of the NEXAFS spectra of n-alkanes recorded with the left circularly polarized X-rays, a significant linear polarization contamination was found. Therefore, linearly polarized X-rays were used to acquire angle dependent NEXAFS spectra, where the X-ray polarization was deliberately aligned along the principal axes (X, Y) of the n-alkane crystal. It was observed that the room temperature carbon 1s NEXAFS spectrum of n-octacosane (C28H58) was different from that of the other n-alkanes, n-tetracosane (C24H50), n-tricosane (C23H48) and n-tetracontane (C40H82). This difference can be attributed due to the different crystal packing of n-octacosane (C28H58 - monoclinic) relative to the other n-alkanes (triclinic and orthorhombic), suggesting different intermolecular interactions (matrix effects) in n-octacosane (C28H58). The analysis of the temperature dependent NEXAFS spectra of n-alkanes reveals that samples of the short chain n-alkane crystals, specially n-tricosane (C23H48), n-tetracosane (C24H50) and n-octacosane (C28H58), sublimed in the STXM microscope. Changes observed in the carbon 1s NEXAFS spectra of n-tetracontane (C40H82) with temperature were attributed to the order-disorder transition. This further illustrates the existence of matrix effects in the NEXAFS spectra of n-alkanes.

Water-mediated interactions between non-polar moieties play a crucial role in driving self-assembly processes such as surfactant micellization, protein folding, and many other diverse phenomena. Among a variety of forces contributing to the self assembly, hydrophobic interactions play a dominant role. Historically, thermodynamic models describing hydrophobic effects have invariably relied on macroscopic thermodynamic properties to infer this molecular behavior. Experimental studies help to probe the spatial correlations between model hydrophobic solutes and to measure their waters of hydration in order to examine structural perturbations in the surrounding water induced by the solute, or to measure directly the attractive forces between hydrophobic surfaces. Further, molecular simulations can be used to derive entropic and enthalpic contributions to the free energy of hydrophobic hydration in terms of water structure surrounding simple, model hydrophobic solutes, such as methane. Based on the results for simple solutes, these methods can now be extended to investigate the hydrophobic hydration of more complex molecular solutes of arbitrary size and shape such as micelles. Atomistic simulations of chemical systems provide a new perspective towards testing the theories behind the ubiquitous phenomenon of hydrophobic effect, and probe the underlying thermodynamic signatures. In this context, my research work delves into the water-mediated interactions leading to the hydrophobic hydration of short chain alkanes, volumetric properties of unfolded polypeptides and self-assembly mechanism in polymer-surfactant systems. The first part of my research involves re-optimization of existing force field interaction parameters for the CHn alkane sites (n=0 to 4) to accurately reproduce the experimental hydration free energies of linear and branched chain alkanes over a range of temperatures. This Hydrophobic Hydration-Alkane (HH-Alkane) model accounts for polarization effects in the alkane hydration and can be extended to polypeptides in water. Subsequent discussions will focus on the results from extensive molecular simulations of tri- and tetrapeptides to quantify the accuracy of the simulation model in capturing the volumetric properties of unfolded polypeptides. Group additivity correlation was used to calculate the partial molar volumes of the neutral sidechains of amino acids, glycine backbone unit and both zwitterionic and N-acetyl/amide terminal units. The simulation results will be compared to the experimental results to validate these observations. In addition, the research explores the self-assembly and aggregation mechanism in anionic sodium dodecyl sulfate (SDS) surfactant- non-ionic Polyethylene Oxide (PEO) and Poly vinyl pyrrolidone (PVP) polymer systems. Potential of mean force calculations at multiple temperatures show an increasing trend in hydrophobic attractions within the polymer-micelle system. Also, these simulations provide interesting insights into the experimentally observed phenomena between the polymers and the micelles starting from pre-formed structure as well as random configurations. / 1 / Lalitanand N. Surampudi

No description available.

In the first experiment, forage samples (n = 39) were collected during 4 years (2006 ? 2009) from pastures grazed by Santa Gertrudis cattle at the King Ranch, TX. The in vitro gas production technique (IVGP) was performed to understand the pattern of fermentation parameters of the forage and obtain fractional digestion rate (kd) values to predict total digestible nutrients (TDN). The best nonlinear model to describe the IVGP values of the forages was the two-pool logistic equation. The passage rate (kp) of 4%/h was used.. The kp predicted by the Large Nutrient Ruminant System (LNRS) model was 3.66%/h. The average TDN was 55.9% compared to 53.8% using a theoretical equation. In the second experiment, Brahman bulls (n = 16) grazed Coastal bermudagrass pastures [Cynodon dactylon (L.) Pers.] and stocked at a moderate to low grazing pressure. Three periods of fecal collections were made within each period. Bulls were individually fed at 0700 and 1900 h of 400 g of corn gluten pellets containing C32 n-alkanes. Each period was divided in 2 sub periods in which fecal samples were collected 4 times a day (0700, 1100, 1500 and 1900 h). N-alkanes in the forage and feces were determined using gas chromatography. In the third experiment, four methods were used to estimate dry matter intake (DMI): C31 or C33 with or without adjustment for forage C32 (C31_0 and C33_0, respectively). There was a difference between morning (0700 and 1100 h) and afternoon fecal collections (1500 and 1900 h) on the predicted DMI using C31 (P = 0.0010), C33 (P = 0.0001), C31_0 (P = 0.0010), or C33_0 (P < 0.0001). There was no difference in average daily gain (ADG) between low and high residual feed intake (RFI) (P = 0.5709). The nonparametric analysis indicated that preranking animals for efficiency under confinement conditions does not guarantee (P < 0.0001) similar ranking under grazing conditions when using the alkane technique to determine forage DMI. In order to estimate DMI at least 5 d of fecal collection and 2 times a day of collection (0700 and 1500h) are needed to decrease the variability.

Twenty-two sediment samples were collected from Kaohsiung Harbour, and it¡¦s neighboring coastal area, Taiwan and analysed for a suite of n-C10-C35 aliphatic hydrocarbons and fifteen polycycilc aromatic hydrocarbons (PAHs). The average total concentration of n-alkanes was 4.327 £gg/g dry wt. (0.461-22.601 £gg/g dry wt.) and PAHs was 0.588 £gg/g dry wt. (0.088-1.75 £gg/g dry wt.). The highest n-alkanes and PAHs concentrations were recorded in samples from D and A stations in Kaohsiung Harbour ; stations D and A are near the outlets of Chyan-Jenn and Jen-Ai rivers, respectively. The sources of n-alkanes are probably contributed form origins of petrogenic, biogenic and higher plants according to the value of CPI (carbon preference index), chromatogram of UCM (unresolved complex materials), and n-C16 ratio etc.; while PAHs were contributed mainly from combustion in coastal areas and petrogenic in harbour areas based on the ratios of total combustion and LMW/HMW ratios. Overall, sediment concentrations of n-alkanes and PAHs in Kaohsiung coastal area were similar to literature in the world. The potential for biological effects due to PAHs is found to be low based as their individual PAHs concentrations are in general lower than effects most existed sediment quality guidelines, except Acenaphthaene, Anthracene, Benzo[a]anthracene, and Fluorene.