Damage to primary photosynthetic reactions caused by environmental stress can be assessed by measurement of chlorophyll fluorescence induction in intact leaves. This approach was applied in studies of ultraviolet-B photoinhibition of photosynthesis in Pisum sativum L. and Rumex patientia L. leaves. At ultraviolet-B dose rates insufficient to cause inhibition of net photosynthesis, changes in the magnitude of fluorescence transients did occur, which suggested direct effects on chloroplast pigments in Pisum and inhibition of photosynthetic electron transport between the photosystems in both species. Leaves of these two species subjected to a much higher dose rate had a significant reduction of net photosynthesis and changes in the magnitude of fluorescence transients that indicated partial loss of water-splitting capability and direct effects on chloroplast pigments. Ultraviolet radiation-induced changes of photosynthetic thylakoid membranes may be ultimately responsible for these disruptions of the primary photosynthetic reactions.

The requirements of information storage exclusively continue to increase in our daily lives and future, will need even more memory space which should be very small in size but hold the capacity to store a huge volume of information. For that reason, modern research is focusing on molecular memory or optical switches devices where nanoparticles undergoing light-induced transformations (e.g. photodimerization) between structural phases with different optical properties are key components. Hence, the UV reversible photodimerization of the cinnamate groups have the potential to be used as switching segments in optical memory devices. The dissertation deals with the solid state NMR investigation on the influence of alkali cations on the photodimerization of cinnamate salts and cinnamic acid derivatives intercalated in hydrotalcite LDH (layered double hydroxides). The packing of molecules determines reactivity and stereo product, so the motivation is to modify molecular packing through noncovalent interactions by using different cations to influence packing and photodimerization products as well as photodimerization kinetics. The alkali metal salts of m-bromo/chloro cinnamic acid and their photodimerization products are analyzed by solid-state NMR. Cesium, rubidium, and potassium salts show well resolved signals in the 13C CPMAS spectra, whereas for ammonium and sodium salts broader lines are obtained. The size of the cation and with that the packing arrangement in the crystal has a significant influence on the resulting spectra. Cesium, rubidium, and potassium salts photoreact to the corresponding truxinates with a non-planar cyclobutane ring but disorder and lower crystallinity are found in the ammonium and sodium photoproducts. In case of divalent cations, both show good crystal packing in the reactant but Ca di-trans cinnamate shows better photoreaction than Mg di-trans cinnamate. Analysis of the kinetics by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation shows that the reaction rate is faster with smaller catcationsd in general chlorine salts react faster than the corresponding bromine salts. Furthermore, dethe termination of the chemical shift anisotropy (CSA) tensor for reactant and product provides information for required atomic reorientations in consequence of photoreaction. Results are explained based on these necessary movements of atoms betweethe n reactant and product. Finally, m-bromo cinnamate and K m-bromo cinnamate are successfully incorporated into the LDH to investigate photoreactivity in a confine system. These samples also undergo [2+2] photodimerization upon irradiation with UV light to yield truxinates the , but high degree of disorder in the ipso, cyclobutane and carboxylate spectral region of the photoproduct is found which indicates low crystallinity in both samples.:Bibliographische Beschreibung III Table of contents V List of Figures VII List of Tables XIX Abbreviations XXI 1 Motivation 1 2 Introduction 4 2.1 [2+2] photodimerization of cinnamic acid 5 2.2 Cinnamic acid as optical memory or molecular switches 7 2.3 Layered Double Hydroxide (LDH) 9 2.4 Previous studies of cinnamic acid derivatives by SSNMR 10 3 Experimental 12 3.1 NMR techniques 12 3.1.1 NMR interactions in Solid State NMR 12 3.1.2 Chemical Shift: 13 3.1.3 Dipole-Dipole Interaction: 13 3.1.4 Magic-angle spinning (MAS) 14 3.1.5 Relaxation times 15 3.2 Pulse sequences 16 3.2.1 13C CP (Cross polarization) 16 3.2.2 Dipolar decoupling 17 3.2.3 13C cross polarization dephasing experiment 17 3.2.4 Dipolar coupling 18 3.2.5 2D PASS 19 3.2.6 FSLG 13C-1H CP HETCOR 20 3.3 Typical measurement parameters 20 3.4 Sample preparation 22 3.4.1 Preparation of different cinnamate salt 22 3.4.2 Incorporation of cinnamic compounds into LDH 24 3.5 Sample irradiation by an UV lamp 24 3.6 Computational methods 28 3.7 Single crystal structure data 28 4 Results and discussion 30 4.1 m-Br cinnamate salts of different cations 30 13C CPMAS Spectra of Truxinates 42 Summary 57 4.2 m-Cl cinnamate salts of different cations 57 13C CPMAS Spectra of Truxinates 69 Summary 83 4.3 Influence of divalent cation on cinnamic acid 84 Ca di-trans-cinnamate 84 Mg di-trans-cinnamate 91 Summary 95 4.4 Photoreaction kinetics of cinnamate salts 96 Analysis of reaction kinetics 96 Summary 119 4.5 Intercalation of cinnamic acid derivatives in LDH 120 5 Conclusion 131 6 Outlook 135 7 Appendix 136 8 References 146

No description available.

No description available.

The kinetics of drugs photodegradation have traditionally been treated using thermal kinetic analysis methods consisting most commonly in zero and first order kinetics. These treatment strategies were shown to lack specificity and present a number of limitations when applied to photoreactions kinetics. Nevertheless, these methods have widely been used due to a lack of integrated rate-laws for the majority of photoreactions types, in turn, due to the presence of a variable time-dependent factor in most photoreactions rate-laws that prevents their mathematical integration. To address these limitations, a new methodology for the development and validation of semi-empirical integrated rate-laws that faithfully describe photoreactions kinetics and photoreactions simulated cases generated by numerical integration methods (NIMs), is hereby presented. Using this methodology, a new kinetic order was ascribed to photoreactions namely the Φ-order kinetics. Semi-empirical integrated rate-laws were, thus, developed for three photoreaction types namely, unimolecular, AB(1Φ), photoreversible ,AB(2Φ), and consecutive, AB4(4Φ), photoreactions. The proposed models were further tested experimentally on drugs following these photodegradation mechanisms using; nifedipine and nisoldipine for unimolecular photoreactions; montelukast and fluvoxamine for photoreversible reactions; and riboflavin for consecutive photoreactions. The developed models not only accurately described the photoreaction kinetics of these drugs but also allowed the determination of all the kinetic parameters that characterise them. Furthermore, the above studied drugs were shown to act as precise and simple actinometers when analytically treated with the Φ-order kinetic methods, hereby presented. A universal standard method for the precise and worldwide reproducible study of drugs stability and compounds photoreactions, based on monochromatic irradiation and Φ-kinetics data analysis, is also detailed and adopted throughout the thesis. Finally, two new kinetic parameters namely, the pseudo-rate-constant and pseudo-initial velocity have been identified and shown to be more reliable and accurate in the description and universal comparison of photoreactions kinetics.