No description available.

No description available.

A series of unsymmetrical meso-tetra-arylporphyrins, substituted with redox active (3,5 di-tertiary-butyl-4- hydroxyphenyl (DtB4HP» and funct'ionalisable (4-hydroxyphenyl (4HP), 3-hydroxyphenyl (3HP) and 4-nitrophenyl (4NP)) substituents were synthesised and characterized by nuclear magnetic resonance spectroscopy, elemental analysis and fast atom bombardment mass spectroscopy. Their aerial oxidation in basified dichloromethane solutions (using 1 molar potassium hydroxide in methanol (1M KOH/MeOH) and l molar tetra-n-butylammonium hydroxide in methanol (1M tnBAH/MeOH») was followed by UV/visible spectroscopy, electron spin resonance spectroscopy and cyclic voltammetry. Basification with. 1M tnBAH/MeOH produced very little aerial oxidation for all the porphyrins in this study, but basification with 1M KOH/MeOH lead to substantial aerial oxidation of the 4HP series and the mono-4NP and trans-4NP porphyrins. Little oxidation in the case of the 3HP series occurred with either base. Cyclic voltammetry showed that in basified DCM solutions, one electron oxidation becomes more difficult as the DtB4HP groups are replaced by 4HP. In contrast, the trend in oxygen reactivity for the 3HP and 4NP porphyrins was not correlated with the first half-wave potentials obtained from cyclic voltammetry. An explanation for these differences is suggested in terms of: (1) the difference in the strength of electron releasing power of the three types (DtB4HP, 4HP and 3HP) of phenolic substituent. DtB4HP groups release electron density onto the porphyrin macrocycle more effectively than 4HP groups, which in turn release electron density more effectively than 3HP groups; (2) the relative availability to oxygen of DtB4HP electron density in the various series of porphyrins¡ (3) the relative ability in certain 4NP-substituted porphyrins to stabilise unpaired electron density over the macrocycle and its substituents.

No description available.

Huang, Yingsi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 105-106). / Abstracts in English and Chinese. / Abstract --- p.i / Abstract (in Chinese) --- p.iii / Acknowledgment --- p.v / Table of Contents --- p.vii / List of Figures --- p.x / List of Schemes --- p.xv / List of Tables --- p.xv / Abbreviations --- p.xvi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Natural Photosynthesis --- p.1 / Chapter 1.1.1 --- Process of Natural Photosynthesis --- p.1 / Chapter 1.1.2 --- Chromophores of Natural Photosynthesis --- p.2 / Chapter 1.1.3 --- Mechanism of Natural Photosynthesis --- p.3 / Chapter 1.2 --- Development of Artificial Photosynthetic Models --- p.4 / Chapter 1.2.1 --- Models Based on Porphyrins and Fullerene Derivatives --- p.6 / Chapter 1.2.2 --- Models Based on Boron Dipyrromethenes (BDPs) --- p.12 / Chapter 1.2.3 --- Applications of Artificial Photosynthetic Models --- p.14 / Chapter 1.3 --- Boron Dipyrromethenes (BDPs) --- p.15 / Chapter 1.3.1 --- General --- p.15 / Chapter 1.3.2 --- Energy Transfer Systems Based on BDPs --- p.16 / Chapter 1.3.2.1 --- BDPs as Energy Donors --- p.16 / Chapter 1.3.2.2 --- BDPs as Energy Acceptors --- p.22 / Chapter 1.3.2.3 --- BDPs as both Energy Donors and Acceptors --- p.26 / Chapter 1.4 --- References --- p.30 / Chapter Chapter 2 --- "Synthesis, Characterization, and Photophysical Properties of the Triad BDP-SiPc-MSBDP as an Artificial Photosynthetic Model" --- p.35 / Chapter 2.1 --- Introduction --- p.35 / Chapter 2.2 --- Results and Discussion --- p.38 / Chapter 2.2.1 --- Preparation and Characterization --- p.38 / Chapter 2.2.2 --- Electronic Absorption and Photophysical Properties --- p.45 / Chapter 2.2.3. --- Electrochemical Properties --- p.50 / Chapter 2.3 --- Conclusion --- p.52 / Chapter 2.4 --- Experimental Section --- p.52 / Chapter 2.4.1 --- General --- p.52 / Chapter 2.4.2 --- Photophysical Studies --- p.53 / Chapter 2.4.3 --- Electrochemical Studies --- p.54 / Chapter 2.4.4 --- Synthesis --- p.54 / Chapter 2.5 --- References --- p.58 / Chapter Chapter 3 --- "Synthesis, Characterization, and Photophysical Properties of the Pentad SiPc(MSBDP-BDP)2" --- p.60 / Chapter 3.1 --- Introduction --- p.60 / Chapter 3.2 --- Results and Discussion --- p.61 / Chapter 3.2.1 --- Preparation and Characterization --- p.61 / Chapter 3.2.2 --- Ground-State Electronic Properties and Energy Transfer Processes of BDP-MSBDP 3.3 --- p.66 / Chapter 3.2.3 --- Photophysical Properties of the Pentad SiPc(MSBDP-BDP)2 (3.1) --- p.68 / Chapter 3.2.4 --- Electrochemical Properties of the Pentad SiPc(MSBDP-BDP)2 (3.1) --- p.73 / Chapter 3.3 --- Conclusion --- p.75 / Chapter 3.4 --- Experimental Section --- p.75 / Chapter 3.4.1 --- General --- p.75 / Chapter 3.4.2 --- Synthesis --- p.75 / Chapter 3.5 --- References --- p.80 / Chapter Chapter 4 --- Novel Artificial Photosynthetic Models Constructed by Supramolecular Methodology --- p.81 / Chapter 4.1 --- Introduction --- p.81 / Chapter 4.2 --- Results and Discussion --- p.83 / Chapter 4.2.1 --- Preparation and Characterization --- p.83 / Chapter 4.2.2 --- Ground-state Electronic Properties and Energy Transfer Process of Compound 4.6 --- p.86 / Chapter 4.2.3 --- Formation and Properties of Assembly 4.1 (ZnTPP.4.6) --- p.89 / Chapter 4.2.4 --- Formation and Properties of Assembly 4.2 [Ru(CO)TPP.4.6] --- p.95 / Chapter 4.2.5 --- Comparison of the Assemblies 4.1 and 4.2 --- p.100 / Chapter 4.3 --- Conclusion --- p.101 / Chapter 4.4 --- Experimental Section --- p.101 / Chapter 4.4.1 --- General --- p.101 / Chapter 4.4.2 --- Synthesis --- p.102 / Chapter 4.5 --- References --- p.105

Thesis (Ph. D.)--Oregon State University, 1963. / Typescript. Includes bibliographical references (leaves 64-69). Also available on the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 1985. / Typescript (photocopy). Includes bibliographical references (leaves 72-79). Also available on the World Wide Web.

No description available.

Ashe juniper (Juniperus ashei Bucholz) has encroached into the historical grasslands of the Edwards Plateau. This area is environmentally sensitive as it serves as the recharge zone for the Edwards aquifer, providing large municipalities such as Austin, San Antonio, and San Marcos with water. The increased tree density may impact local water budgets, but the trees may have the capability of sequestering a greater amount of carbon than the historic grasslands. An understanding of what regulates gas exchange and water relations at the leaf level of the two dominant tree species, Ashe juniper and live oak (Quercus virginiana P. Mill. Var. fusiformis), is important to assess the impact of juniper encroachment on the aquifer. Photosynthesis and transpiration were measured in four juniper and four oak trees throughout an entire year. Juniper consistently had lower carbon assimilation rates, transpiration, and conductance values than oak. Oak exhibited greater seasonal variation and seemed less dependent on precipitation to maintain gas exchange. Canopy position in live oak regulates leaf level photosynthesis to a higher degree than in Ashe juniper. Gas exchange of both species decline as water becomes limited, but juniper consistently exhibits lower and steadier rates throughout the year than oak. Juniper does not respond quickly to erratic precipitation events. The consistent low rates of gas exchange and stomatal responses in juniper could indicate shallower rooting structure and/or limitation of hydraulic conductivity, as well as photosynthetic capacity. The higher rates of photosynthesis, transpiration, and stomatal conductivity exhibited by live oak during drought suggest a deeper rooting pattern than Ashe juniper. Light response curves were computed for three juniper and three oak trees that were marked and sampled at three different seasons. Juniper light-compensation and light-saturation estimates, at different canopy positions, were poor indicators of differences in photosynthetic capacity between the two species. Patterns of light responses of juniper and oak did not follow responses of previous studies assessing differences in photosynthetic capacity through light-response curves. Computing the light curves was difficult due to low tree activity and lack of responses to changes in light, especially in juniper.

The methodology of phytoplankton production measurements in the Laurentian Great Lakes and other freshwater lakes has remained largely unchanged in the past 40 years. In most studies photosynthesis from a single water sample is measured across an in vitro light gradient usually using an artificial light source then extrapolating to the in situ environment. These traditional methods are laborious, thus limiting the amount of observations in space and time, and may not accurately represent in situ photosynthesis. Active chl a fluorescence, intrinsically linked to photosynthesis, can be measured in situ and instantaneously. Various bio-optical models that scale these fluorescence measurements to phytoplankton production are gaining widespread attention in the marine environment but have not been extensively tested in freshwater ecosystems. The methodology and efficacy of the various bio-optical models are tested in this thesis using a large dataset of active fluorescence profiles and ancillary water chemistry parameters against synchronously derived in vitro phytoplankton production collected across mixing, trophic and taxonomic gradients in Lake Erie. From this analysis, the most common bio-optical model parameterization yields photosynthetic rates that are largely incongruent with in vitro measurements. Bio-optical models are largely a function of two parameters, the absorption spectrum of photosystem II (aPSII) and the photochemical efficiency of PSII (fPSII). In Lake Erie fPSII is relatively constrained suggesting that even nutrient limited phytoplankton achieve balanced growth by adjusting the supply of energy through changes in light harvesting (aPSII) to match the demand for photosynthetic energy. This thesis goes on to demonstrate the success of bio-optical models depends largely on the formulation of aPSII. Alternative methods to derive aPSII, largely ignored in published bio-optical models, are reviewed, formulated, and when incorporated into a bio-optical model and compared to synchronous in vitro production measurements, this novel bio-optical model outperforms all other comparative studies performed across a taxonomic gradient.