Thermodynamics of the Abraham General Solvation Model: Solubility and Partition Aspects (open access)

Thermodynamics of the Abraham General Solvation Model: Solubility and Partition Aspects

Experimental mole fraction solubilities of several carboxylic acids (2-methoxybenzoic acid, 4-methoxybenzoic acid, 4-nitrobenzoic acid, 4-chloro-3-nitrobenzoic acid, 2-chloro-5-nitrobenzoic acid,2-methylbenzoic acid and ibuprofen) and 9-fluorenone, thianthrene and xanthene were measured in a wide range of solvents of varying polarity and hydrogen-bonding characteristics. Results of these measurements were used to calculate gas-to-organic solvent and water-to-organic solvent solubility ratios, which were then substituted into known Abraham process partitioning correlations. The molecular solute descriptors that were obtained as the result of these computations described the measured solubility data to within an average absolute deviation of 0.2 log units. The calculated solute descriptors also enable one to estimate many chemically, biologically and pharmaceutically important properties for the ten solutes studied using published mathematical correlations.
Date: August 2006
Creator: Stovall, Dawn Michele
System: The UNT Digital Library
The evaluation, development, and application of the correlation consistent basis sets. (open access)

The evaluation, development, and application of the correlation consistent basis sets.

Employing correlation consistent basis sets coupled with electronic structure methods has enabled accurate predictions of chemical properties for second- and third-row main group and transition metal molecular species. For third-row (Ga-Kr) molecules, the performance of the correlation consistent basis sets (cc-pVnZ, n=D, T, Q, 5) for computing energetic (e.g., atomization energies, ionization energies, electron and proton affinities) and structural properties using the ab initio coupled cluster method including single, double, and quasiperturbative triple excitations [CCSD(T)] and the B3LYP density functional method was examined. The impact of relativistic corrections on these molecular properties was determined utilizing the Douglas-Kroll (cc-pVnZ-DK) and pseudopotential (cc-pVnZ-PP) forms of the correlation consistent basis sets. This work was extended to the characterization of molecular properties of novel chemically bonded krypton species, including HKrCl, FKrCF3, FKrSiF3, FKrGeF3, FKrCCF, and FKrCCKrF, and provided the first evidence of krypton bonding to germanium and the first di-krypton system. For second-row (Al-Ar) species, the construction of the core-valence correlation consistent basis sets, cc-pCVnZ was reexamined, and a revised series, cc-pCV(n+d)Z, was developed as a complement to the augmented tight-d valence series, cc-pV(n+d)Z. Benchmark calculations were performed to show the utility of these new sets for second-row species. Finally, the correlation consistent basis …
Date: December 2006
Creator: Yockel, Scott
System: The UNT Digital Library
Computational Studies of Coordinatively Unsaturated Transition Metal Complexes (open access)

Computational Studies of Coordinatively Unsaturated Transition Metal Complexes

In this research the validity of various computational techniques has been determined and applied the appropriate techniques to investigate and propose a good catalytic system for C-H bond activation and functionalization. Methane being least reactive and major component of natural gas, its activation and conversion to functionalized products is of great scientific and economic interest in pure and applied chemistry. Thus C-H activation followed by C-C/C-X functionalization became crux of the synthesis. DFT (density functional theory) methods are well suited to determine the thermodynamic as well as kinetic factors of a reaction. The obtained results are helpful to industrial catalysis and experimental chemistry with additional information: since C-X (X = halogens) bond cleavage is important in many metal catalyzed organic syntheses, the results obtained in this research helps in determining the selectivity (kinetic or thermodynamic) advantage. When C-P bond activation is considered, results from chapter 3 indicated that C-X activation barrier is lower than C-H activation barrier. The results obtained from DFT calculations not only gave a good support to the experimental results and verified the experimentally demonstrated Ni-atom transfer mechanism from Ni=E (E = CH2, NH, PH) activating complex to ethylene to form three-membered ring products but also validated …
Date: December 2006
Creator: Vaddadi, Sridhar
System: The UNT Digital Library
General Chemistry Topic Coverage (GCTC) comparison between community colleges and universities in the United States. (open access)

General Chemistry Topic Coverage (GCTC) comparison between community colleges and universities in the United States.

This study is based on survey responses of 224 general chemistry instructors at United States (U.S.) community colleges and universities representing 46 states. The mean values of General Chemistry Topic Coverage (GCTC) score, developed by this researcher specifically for this dissertation study as a measure of course content, were statistically analyzed. The aim of this study is to answer five research questions: (a) Is there a difference in mean GCTC scores between U.S. community colleges and four-year colleges and universities? (b) If there is a difference in mean GCTC score between the two study groups, what are the observed differences in subtopics covered between community colleges and four-year colleges and universities? (c) Considering both community colleges and universities, is there a difference in mean GCTC score between the different designated U.S. regions? (d) Considering both community college and university professors, is there a difference in GCTC score for professors with a master's degree compared to those with a doctorate?, and (e) Is there a correlation between GCTC score and the percentage of students that major in science? Results indicate that there is a statistically significant difference in course content between community colleges and universities, there is a statistically significant difference …
Date: December 2006
Creator: El-Ashmawy, Amina Khalifa
System: The UNT Digital Library
Photochemical and Photophysical Properties of Gold(I) Complexes and Phosphorescence Sensitization of Organic Luminophores (open access)

Photochemical and Photophysical Properties of Gold(I) Complexes and Phosphorescence Sensitization of Organic Luminophores

Two major topics that involve synthetic strategies to enhance the phosphorescence of organic and inorganic luminophores have been investigated. The first topic involves, the photophysical and photochemical properties of the gold (I) complexes LAuIX (L = CO, RNC where R = alkyl or aryl group; X = halide or pseudohalide), which have been investigated and found to exhibit Au-centered phosphorescence and tunable photochemical reactivity. The investigations have shown a clear relationship between the luminescence energies and association modes. We have also demonstrated for the first time that aurophilic bonding and the ligand p-acceptance can sensitize the photoreactivity of Au(I) complexes. The second topic involves conventional organic fluorophores (arenes), which are made to exhibit room-temperature phosphorescence that originates from spin-orbit coupling owing to either an external or internal heavy atom effect in systematically designed systems that contain d10 metals. Facial complexation of polycyclic arenes to tris[{m-(3,4,5,6-tetrafluorophenylene)}mercury(II)], C18F12Hg3 (1) results in crystalline adducts that exhibit bright RGB (red-green-blue) phosphorescence bands at room temperature. This arene-centered phosphorescence is always accompanied by a reduction of the triplet excited state lifetime due to its sensitization by accelerating the radiative instead of the non-radiative decay. The results of both topics are significant for rational design of …
Date: August 2006
Creator: El-Bjeirami, Oussama
System: The UNT Digital Library
Electrochemical Study of Under-Potential Deposition Processes on Transition Metal Surfaces (open access)

Electrochemical Study of Under-Potential Deposition Processes on Transition Metal Surfaces

Copper under-potential deposition (UPD) on iridium was studied due to important implications it presents to the semiconductor industry. Copper UPD allows controlled superfilling on sub-micrometer trenches; iridium has characteristics to prevent copper interconnect penetration into the surrounding dielectric. Copper UPD is not favored on iridium oxides but data shows copper over-potential deposition when lower oxidation state Ir oxide is formed. Effect of anions in solution on silver UPD at platinum (Pt) electrodes was studied with the electrochemical quartz crystal microbalance. Silver UPD forms about one monolayer in the three different electrolytes employed. When phosphoric acid is used, silver oxide growth is identified due to presence of low coverage hydrous oxide species at potentials prior to the monolayer oxide region oxide region.
Date: August 2006
Creator: Flores Araujo, Sarah Cecilia
System: The UNT Digital Library
The synthesis and study of poly(N-isopropylacrylamide)/poly(acrylic acid) interpenetrating polymer network nanoparticle hydrogels. (open access)

The synthesis and study of poly(N-isopropylacrylamide)/poly(acrylic acid) interpenetrating polymer network nanoparticle hydrogels.

Homogeneous hydrogels made of an interpenetrating network of poly(N-isopropylacrylamide) (PNIPAm) and poly(acrylic acid) (PAAc) are synthesized by a two-step process; first making PNIPAm hydrogels and then interpenetrating acrylic acid throughout the hydrogel through polymerization. The kinetic growth of the IPN is plotted and an equation is fitted to the data. When diluted to certain concentrations in water, the hydrogels show reversible, inverse thermal gelation at about 34°C. This shows unique application to the medical field, as the transition is just below body temperature. A drug release experiment is performed using high molecular weight dyes, and a phase diagram is created through observation of the purified, concentrated gel at varying concentrations and temperatures.
Date: August 2006
Creator: Crouch, Stephen Wallace
System: The UNT Digital Library
Synthesis and Characterization of 2,3-Dichloropyrrolo[1,2-a]benzimidazol-1-one and Its Methylthiol Derivatives (open access)

Synthesis and Characterization of 2,3-Dichloropyrrolo[1,2-a]benzimidazol-1-one and Its Methylthiol Derivatives

Condensation of 2,3-dichloromaleic anhydride and o-phenylenediamine in refluxing toluene affords the three compounds 2,3-dichloro-N-o-C6H4(NH2)maleimide (1), N,N¢-o-C6H4-bis(2,3-dichloromaleimide) (2), and 2,3-dichloropyrrolo[1,2-a]benzimidazol-1-one (3), with compound 1 as the major product. Repeating the same reaction in the presence of added PTSA furnishes compound 3 as the major product. Treatment of 3 with methylthiol in the presence of pyridine affords monosulfide compounds 2-chloro-3-methylthiopyrrolo[1,2-a]benzimidazol-1-one (4) and and the disulfide derivatives 2,3-di(methylthio)pyrrolo[1,2-a]benzimidazol-1-one (5). The substitution of the first chlorine group in compound 3 occurs regioselectively at C-3 to produce compound 4, followed by replacement of the remaining chlorine group to furnish the disulfide compounds 5. The new compounds 1-5 have been isolated by column chromatography and characterized by IR, NMR, XRD, CV and etc.
Date: May 2006
Creator: Wu, Guanmin
System: The UNT Digital Library