For more than 150 years, since the synthesis of urea by Friedrich Wöhler in 1828, molecular chemistry has developed a vast array of highly sophisticated and powerful methods for the construction of more complex molecular structures. Beyond the molecular chemistry based on the covalent bond, there lies the field of supramolecular chemistry, aims to gain control over the intermolecular bond. Supramolecular species are characterized both by the spatial arrangement of their components and by the nature of the intermolecular bonds that hold these components together. They possess well-defined structural, conformational, thermodynamic and kinetic properties. Research has been focused on utilization of such confined spaces to manipulate reaction dynamics, properties of the encapsulated guest molecules. This research presented in this thesis is a consolidated account of photophysical and photochemical reactions carried in water-soluble macrocycles, cavitands and dynamic host systems such as dendrimers and micelles. With the aid of NMR (1D and 2D) spectroscopic techniques, the host-guest complex characterization is executed.

Formaldehyde (HCHO) plays a primary role in tropospheric chemistry. Its photochemical activity is an important source of radical species such as HCO, H, and subsequently HO2 as well as molecular hydrogen and carbon monoxide. As a source of hydrogen radicals (HOx = OH + HO2), HCHO plays a significant role in the oxidative capacity of the atmosphere, and an important part in the interrelated chemistries of ozone and the HOx and NOx (NO + NO2) cycles. Accurate atmospheric photolysis rates of HCHO are thus required in order to properly model tropospheric chemistry. Despite extensive studies HCHO’s spectroscopy and photochemistry remains to be well characterized. Absolute room temperature absorption cross sections for the A1A2 – X1A1 electronic transition of formaldehyde have been measured over the spectral range 30285 – 32890 cm-1 (304 – 330 nm) using ultraviolet (UV) laser absorption spectroscopy. Absorption cross sections were obtained at an instrumental resolution better than 0.09 cm-1 which is slightly broader than the Doppler width of a rotational line of HCHO at 300K (~0.07 cm-1) and so we were able to resolve all but the most closely spaced lines. Qualitative comparisons with spectral simulations show varying agreement depending on vibronic band. Refined state origins and transition dipole moments for each vibronic band have been reported. There is evidence of areas of perturbation and the need to optimize higher order spectral constants. Pressure broadening parameters have been measured and increase with the strength of intermolecular interaction between formaldehyde and the collision partner. Comparisons between the available high-resolution studies and spectral simulations indicate that the HCHO absorption cross section is still not well characterized. The relative quantum yield for the production of radical products, H+HCO, from the UV photolysis of formaldehyde (HCHO) has been measured directly using a Pulsed Laser Photolysis – Pulsed Laser Induced Fluorescence (PLP – PLIF) technique across the same spectral region. Relative yields were normalized to a value of 0.69 at 31750 cm-1 based on the current NASA-JPL recommendation. The resulting absolute radical quantum yields agree well with previous experimental studies and show more wavelength dependent behavior than the recommendation. This provides support for the complicated competition among the various HCHO dissociation pathways.

Thesis (Ph. D.)--University of Wyoming, 2005. / Includes bibliographical references. Also available online.

The focus of this dissertation is to decipher the previously unknown reaction dynamics of NO3 photodissociation. Although the NO + O2 products are known to catalyze atmospheric ozone destruction, the mechanism by which these products are formed has remained a mystery, and no energetically accessible transition state has ever been calculated. Using velocity map ion imaging experiments to carefully study the stereochemistry of the product fragments combined with theoretical calculations performed by Drs. Xiao, Maeda, and Morokuma at Kyoto University, we have determined that the reaction proceeds exclusively via the unusual "roaming mechanism," with no evidence of a competing traditional transition state pathway. Within, the significance of this discovery is discussed in regards to both the NO3 system and roaming dynamics in general, for which this system has provided new insight.

The secondary structure of peptides is of pivotal importance for their biological function. The introduction of photoswitchable moieties into the backbones of peptides provides a unique way of regulating their conformation using an external stimulus, i.e., light. This thesis addresses the design, synthesis, and conformational analysis of photoswitchable peptidomimetics (PSPM). Examples of photomodulation of their functional properties are given. PSPM were prepared by incorporation of stilbene and thioaurone chromophores (switches) into dipeptides. Synthetic schemes for preparing these chromophores have been developed. Their suitability for incorporation into peptidomimetics has been demonstrated, and the resulting PSPM have been subjected to photoisomerization as well as computational and spectroscopic conformational analysis. The chromophore’s potential as a β-hairpin inducer was particularly interesting. To investigate the factors that govern the formation of β-hairpins, a series of decapeptides were prepared. Turn regions consisting of amino acids or chromophores were combined with antiparallel peptide strands with hydrophobic side chains. Linear tryptophan zipper peptidomimetics and cyclic peptidomimetics with a second, hairpin-inducing turn region were particularly promising. Comparison between switches revealed that the more flexible stilbene is a better choice for upholding the β-hairpin conformation than the thioaurone. The catalytic properties of an artificial hydrolase with a helix-loop-helix structure can be improved by introducing a stilbene photoswitch into the loop region. Photoisomerization regulates the catalytic activity of this peptidomimetic, and provides a means to control its aggregation state. The activity of the enzyme Mycobacterium tuberculosis ribonucleotide reductase was realized by incorporating a stilbene moiety into a linear peptide. Here, one photoisomer proved to be an inhibitor at nM concentrations. A significantly lower effect was observed for the other isomer. Finally, the decomposition of thioaurones, mainly to thioflavonols and thiaindenes, under conditions used for solid-phase peptide synthesis has been mapped. These findings are expected to have implications for future use of this chromophore.

Photon energy upconversion (UC), a process that can convert two or more photons with low energy to a single photon of higher energy, has the potential for overcoming the thermodynamic efficiency limits of sunlight-powered devices and processes. An attractive route to lowering the incident power density for UC lies in harnessing energy transfer through triplet-triplet annihilation (TTA). To maximize energy migration in multicomponent TTA-assisted UC systems, triplet exciton diffusivity of the chromophores within an inert medium is of paramount importance, especially in a solid-state matrix for practical device integration. In this thesis, low-threshold sensitized UC systems were fabricated and demonstrated by a photo-induced interfacial polymerization within a coaxial-flow microfluidic channel and in combination with nanostructured optical semiconductors. Dual-phase structured uniform UC capsules allow for the highly efficient bimolecular interactions required for TTA-based upconversion, as well as mechanical strength for integrity and stability. Through controlled interfacial photopolymerization, diffusive energy transfer-driven photoluminescence in a bi-molecular UC system was explored with concomitant tuning of the capsule properties. We believe that this core-shell structure has significance not only for enabling promising applications in photovoltaic devices and photochromic displays, but also for providing a useful platform for photocatalytic and photosensor units. Furthermore, for improving photon upconverted emission, a photonic crystal was integrated as an optical structure consisting of monodisperse inorganic colloidal nanoparticles and polymer resin. The constructively enhanced reflected light allows for the reuse of solar photons over a broad spectrum, resulting in an increase in the power conversion efficiency of a dye-sensitized solar cell as much as 15-20 %.

Irradiation of 1,1-dioxo-2-phenyl-4-thiazolidinone resulted in loss of S02 and formation of a carbon-carbon bond. When (2S,5R) cis-3,5-dimethyl-l,l-dioxo-2-phenyl-4thiazolidinone was photolyzed (through a Vycor filter in t-BuOH/CH3CN) (3S,4S) cis-l,3-dimethyl-4-phenyl-2-azetidinone (i.e., optically active cis a-lactam) was obtained as a major product. The synthesis of (2S,5R) cis-3,5-dimethyl1,1-dioxo-2-phenyl-4-thiazolidinone is described. The verification of optical activity was accomplished by the use of Eu(tfc)3.In addition to the earlier data, the above results have helped us to elucidate the mechanistic pathway of S02 photoextrusion to form p-lactam rings. Sensitization experiments by M. R. Johnson and his use of triplet state quencher have shown that the photoextrusion is a singletstate reaction. Johnson's trapping experiments indicated the existence of a radical intermediate. In the work of this thesis, the observation of optical activity of the cis S-lactam product ruled out a planar diradical and a butadiene-like intermediate. Thus, it can be concluded that the S02 photoextrusion process occurs via discrete radical and diradical intermediates. The diradical is probably formed by stepwise loss of S02 and is so shortlived that optical activity along with cis stereochemistry is maintained.Ball State UniversityMuncie, IN 47306

No description available.

This work has focused on showing the differences among four different NMHC oxidation mechanisms: GT Lurmann, CBIV, RACM, and SAPRC mechanisms. This study was carried out to characterize these mechanisms using both specified NOx/NMHC gas mixtures and observational data from NASAs TRACE-P campaign. The differences among these mechanisms were found to be mainly driven by the use of different kinetic data and the specifics of each oxidation scheme. In the test runs, the differences between mechanisms were shown to be dependent on the levels of NOx and NMHC, as well as the reactivity of NMHC species used. Typically, propane had the smallest impact on all product species, whereas propene had the largest. Differences in the predicted levels of OH and HO2 were much smaller compared to those for CH3O2 and CH2O due to the fact that HOx species were generally less sensitive to the presence of NMHCs. During TRACE-P, which involved flights over only marine areas that were slightly polluted by the inflow of pollutants, the alkanes were the dominant NMHC family. Thus, most of the model runs involved relatively low levels of NMHCs and NOx. Therefore, the levels of OH, HO2, CH3O2, and CH2O predicted by the four mechanisms were not dramatically different. A net O3 increase was found only in areas where the NMHC reactivity was high. Because of the similar O3 destruction rates given by all four mechanisms, the difference in O3 tendency among these mechanisms was mainly determined by the O3 formation rate. A significantly higher (e.g., ~30%) O3 formation was found in the Lurmann mechanism than in CBIV due to the stronger contribution from the NO/RO2 channel in this mechanism. This resulted in a difference in the O3 tendency of a factor of 1.5. A major need in terms of future studies will be that of examining these same four mechanisms with a data set that enfolds observations in more polluted regions.

1. FVP of arylmethylazides (33b¡B34b) via 3,3-sigmatropic rearrangement gave nitrogen-containing heterocyclic compounds (2b¡B4b). FVP of 35 gave 3-benzyl-2-thiophenecarbaldehyde (65) by 1,2 H shift of nitrene 32 followed by hydrolysis. 2. FVP of benzoic 3-(1-propenyl)-2-thiophenecarboxylic anhydride (67) gave 7-hydroxybenzo[b]thiophene (70) and cyclopenteno[b]thiophene (71). Compound 71 is difficult to synthesize by normal organic synthetic methods. The formation of 7-hydroxybenzo[b]thiophene (70) suggesting the existence of 68. 3. FVP of arylimine gave phenanthridine (3)¡B3-methylpyrrolo[2,3-c] quinoline (69) and thieno[2,3-c]quinoline (134). Such a method can synthesize tricyclic products in one step. On the other hand, photolytic study of arylimine gave compounds 156¡B184¡B164¡B180¡B185 and 186.