Computational chemistry studies of UV induced processes in human skin

This thesis presents and uses the techniques of computational chemistry to explore two different processes induced in human skin by ultraviolet light. The first is the transformation of urocanic acid into a immunosuppressing agent, and the other is the enzymatic action of the 8-oxoguanine glycosylase enzyme. The photochemistry of urocanic acid is investigated by time-dependent density functional theory. Vertical absorption spectra of the molecule in different forms and environments is assigned and candidate states for the photochemistry at different wavelengths are identified. Molecular dynamics simulations of urocanic acid in gas phase and aqueous solution reveals considerable flexibility under experimental conditions, particularly for for the cis isomer where competition between intra- and inter-molecular interactions increases flexibility. A model to explain the observed gas phase photochemistry of urocanic acid is developed and it is shown that a reinterpretation in terms of a mixture between isomers significantly enhances the agreement between theory and experiment , and resolves several peculiarities in the spectrum. A model for the photochemistry in the aqueous phase of urocanic acid is then developed, in which two excited states governs the efficiency of photoisomerization. The point of entrance into a conical intersection seam is shown to explain the wavelength dependence of photoisomerization quantum yield. Finally some mechanistic aspects of the DNA repair enzyme 8-oxoguanine glycosylase is investigated with density functional theory. It is found that the critical amino acid of the active site can provide catalytic power in several different manners, and that a recent proposal involving a SN1 type of mechanism seems the most efficient one.

Monosyllabic Circumflexion in Lithuanian

This PhD thesis examines a phenomenon known as Monosyllabic Circumflexion (MC, hereafter) from a historical linguistics / phonological point of view. MC denotes a Lithuanian or Balto-Slavic phenomenon according to which long vowels and diphthongs in monosyllabic words exhibit a circumflex tone instead of the expected acute tone.  It is observed in the following four categories: I. 3rd person future forms of monosyllabic stems (e.g., šõks ― šókti `to jump;' vy͂s ― výti `to drive') II. reflexes of PIE root nouns (e.g., Latv. gùovs `cow;' Lith. šuõ `dog') III. prepositions/adverbs (e.g., nuõ `from' ~  nùotaka `bride;' vė͂l `again' ~ Latv. vêl `still, yet,' tė͂ (permissive particle) < *teh1) IV. pronominal forms (e.g., tuõ ~ gerúoju `the good (m.~sg.~instr.),' tie͂ ~ tíeji `id. (pl.nom)'). The unexpected circumflex tone in these categories is problematic and important for the solution of a Balto-Slavic accentological question on the etymological background of acute and non-acute tones. The aim of this thesis is to partially contribute to the solution of this problem by establishing the existence of MC and its relative chronology. The first category, the 3rd person future forms, provides a substantial number of examples and counterexamples. The examination of them has revealed the fact that the counterexamples constitute a morpho-semantic group of verbs whose future stems underwent considerable morphological changes in the prehistory, hence not exhibiting MC. This shows that the regular tonal reflex of the 3rd person future forms of monosyllabic acute stem must be circumflex, allowing for the establishment of MC as a regular phonological process, although this category does not provide much information on the relative chronology of MC. The second category, the reflexes of Proto-Indo-European root nouns, gives an important clue as to where MC is located in the relative chronology of Balto-Slavic sound changes. Next, there is a discussion of whether the results of the examinations of the first two categories can be maintained for the data of the third and fourth categories, which show an irregular distribution of the acute and circumflex tones in monosyllabic forms. It is shown that various morphological factors, such as homonymic clashes within the paradigms for pronouns, can explain why some monosyllabic forms have acute tone. Also, the linguistic feature of West Aukštaitian dialects of Lithuanian that tend to preserve the results of MC is revealed. These dialects are known to have played an important role in the formation of standard Lithuanian. In this way, the monosyllabic forms with unexpected circumflex tone in Lithuanian are explained as a combination of MC in the Proto-Balto-Slavic time and the dialectal tendency of West Aukštaitian dialects of Lithuanian.