Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 177-202). Also available on the World Wide Web.

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The effect of steric strain on the esr hyperfine coupling constants of several free-radical adducts of perfluoropropene and perfluoro-2-butene were investigated. Silyl, hydroxyalkyl, thiyl and alkoxy free radicals, which were generated by photo-irradiation, reacted with these olefins to form free-radical adducts. Trends in the esr hfs were then looked for in each class of adducts. The thiyl and alkoxy radicals were found to be unsuitable for this type of study due to the low degree of steric strain produced by these species in the adducts. Trends toward higher a-Fβ/CF₃ hfs and lower a^Fα hfs were observed for the silyl and hydroxyalkyl radical adducts as the steric strain in the adduct was increased. The ratio of the ^Fα to a-Fβ/CF₃ hfs was shown to be a good measure of the degree of steric strain in these radical adducts. The possibility that the (Me₃Si)₂CHC(SiMe₃)₂ free radical, which has been reported to contain an "esr invisible" β-H, might be misidentified was investigated. Our conclusion was that the β-H is present and has not been replaced by a t-butoxy group. / Ph. D.

The results of our studies demonstrate a link between selectivity in free radical brominations and the internal pressure of solvent. The study encompassed l8 solvents and/or mixtures over which the rate constant ratio for SH2 ring opening of cyclopropylbenzene (kC) vs hydrogen abstraction from toluene (kH) by bromine atom was found to vary by nearly a factor of twenty as a function of solvent. The observed rate constant ratios correlate with the cohesive energy density of the solvent, which is approximately equal to the internal pressure (kC/kH is found to increase with increasing solvent pressure) for the solvents used in this study. A similar competition pitting cyclopropylbenzene against p-chlorotoluene shows the same solvent effect. It is suggested that the observed variation in selectivity "with solvent pressure occurs because the volume of activation with kC is more negative than for kH by about 20 cm3/mol. / Master of Science

Experiments were conducted to investigate the role of free radicals in exercise induced cardiac adaptations and to determine if statin administration would adversely affect cardiac adaptations to exercise. In the first experiment myocardial antioxidant enzymes, cardiac function and cardiac hypertrophy were assessed following a chronic exercise protocol previously used by our lab. MPG effectively reduced myocardial oxidative stress and activation of the signaling proteins Akt and S6 following an exercise bout. Skeletal muscle mitochondria content increased to similar levels in E and E+MPG. Similar increases (P<0.05) in both exercised groups were observed for heart wt and heart wt to body wt ratio. Cardiac function at the high workload improved in E vs S as indicated by higher (P<0.05) peak systolic pressure (SP), cardiac output (CO), coronary flow, COxSP and mechanical efficiency (COxSP/VO2). MPG prevented these exercise-induced functional improvements. This study provides evidence that free radicals do not play a role in the development of exercise-induced cardiac hypertrophy, however, they are involved in functional cardiac adaptations, which may be mediated through the PI3K/Akt pathway. In the second experiment a similar exercise protocol was used to determine if statins which have been shown to prevent pathological forms of cardiac hypertrophy, would be detrimental to exercise induced cardiac adaptations. In addition to the sedentary and exercise groups sedentary+statin and exercise+statin groups were assessed. Hearts were isolated and perfused and assessed for function at low and high workloads. Exercise treatment resulted in cardiac hypertrophy in absolute and relative terms to a similar extent in statin-treated and untreated exercised rats. Additionally it resulted in significant functional increases for SP, CO, COxSP, VO₂, and EFF in both exercised groups. In conclusion, these studies provide evidence that exercise in the cold is a valid model for physiological cardiac hypertrophy and that pathological and physiological cardiac hypertrophy signal through different pathways due to the fact that two well established treatments (mpg and statins) that prevent pathological cardiac hypertrophy did not affect exercise induced cardiac hypertrophy. / text

Thesis (MSCMedSc (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2006. / In this study, we presented data on the role of free radicals in human spermatozoa, particularly in the context of centrifugation and the potential development of defective sperm function. In order to achieve this, methods were developed to directly measure intracellular free radicals in human sperm and the effects of exogenously applied free radicals on sperm function were established. The role of brief and prolonged centrifugation and the associated generation of free radicals was also investigated.

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Chemical and molecular tagging agents have illustrated their diversity in a number of different applications. One of the most significant applications includes the use of chemical tagging agents for product registration in industry. Industrial enterprises producing good products need to ensure product authenticity to prevent duplication through piracy and unscrupulous industrialists. Fluorescent probes are chemical compounds that satisfy most of the technical and commercial aspects that are required to be excellent tagging agents. They are generally quick to synthesize, do not affect the product integrity, display little or no impact on the uses of the product or the environment and they can be identified by relatively simple detection procedures. The aim of the present study was to synthesize fluorescent polymers as tagging agents for the paint industry. 7-Hydroxy-2H-chromen-2-one (A1) and 7-hydroxy-4-methyl-2H-chromen-2-one (B1), commercially available fluorescent hydroxyl compounds, were selected as the starting materials. An esterification reaction resulted in the production of 2-oxo-2H-chromen-7-yl acrylate (A2) and 4-methyl-2-oxo-2H-chromen-7-yl acrylate (B2), which are acrylic-type monomers that were required for polymerisation. Studies showed that fluorescence was maintained during the esterification. Copolymers poly(MMA-co-A2), poly(MMA-co-B2), poly(BA-co-A2) and poly(BA-co-B2), synthesized via homogeneous free radical initiated copolymerisation, revealed how copolymer compositions were affected by the feed compositions and the pattern of monomer incorporation over time. This was investigated by following individual monomer consumption rates by 1H-NMR spectroscopy. Fluorescence studies revealed that the fluorescence behaviour of A2 and B2 was maintained during the copolymerisation. Latex particles, with fluorescent behaviour, were synthesized via in situ miniemulsion polymerisation. High molecular weight copolymers with monodisperse particle sizes (nm range) were obtained. A bench-top UV lamp and UV-reflectance studies confirmed the fact that fluorescent latex particles can be identified and quantified respectively, when dispersed in paints that are either free of titanium dioxide or paints that contain titanium dioxide. / AFRIKAANSE OPSOMMING: Die diversiteit van chemiese en molekulêre merkers in ‘n verskeidenheid van toepassings is al telkemale geïllustreer. Een van die mees belangrike toepassings in die industrie is die gebruik van chemiese merkers vir produkregistrasie. Industrieë wat goeie produkte verskaf moet die egtheid van hul produkte kan verseker deur duplikasie via nadruk (Eng: piracy) deur ander te voorkom. Fluoresserende merkers is chemiese stowwe wat aan die meeste van die tegniese en kommersiële vereistes voldoen om as uitstekende merkers te dien. Die sintese van die merkers is gewoonlik nie tydrowend nie, beïnvloed nie die integriteit van die produk nie, het min of geen impak op die gebruike van die produk of die omgewing en kan deur relatief eenvoudige prosedures bepaal word. Die doel van hierdie studie was die sintese van fluoresserendepolimere om as merkers in die verfindustrie te dien. 7-Hidroksie-2H-chromen-2-oon (A1) en 7-hidroksie-4-metiel-2H-chromen-2-oon (B1), fluoresserende hidroksielverbindings wat kommersieël beskikbaar is, is gekies as uitgangstowwe vir die bereiding van die merkers in hierdie studie. ‘n Esterifikasie-reaksie het gelei tot die produksie van 2-okso-2H-chromen-7-ielakrilaat (A2) en 4-metiel-2-okso- 2H-chromen-7-ielakrilaat (B2). Hierdie produkte is tipiese akrilaat-tipe monomere wat benodig word vir polimerisasie. Ondersoeke het getoon dat fluoressensie behoue tydens esterifikasie gebly het. Die kopolimere poli(MMA-ko-A2), poli(MMA-ko-B2), poli(BA-ko-A2) en poli(BA-ko-B2) is deur homogene vry-radikaal-geïnisieerde kopolimerisasie gesintetiseer. Daar is vasgestel hoe die kopolimeersamestelling geaffekteer is deur die samestelling van die reagense (Eng: feed composition) en die patroon van monomeer inkorporasie met tyd. Dit was ondersoek deur die tempo van verbruik van die individuele monomere d.m.v. 1H-KMR spektroskopie te bepaal. Daar is verder vasgestel dat die fluoressensie van A2 en B2 gedurende kopolimerisasie behoue gebly het. Latekspartikels, met fluoressensie gedrag, is via in-situ mini-emulsie-polimerisasie gesintetiseer. Hoë molekulêre massa kopolimere met monodisperse partikelgroottes (in die order van nanometers) is verkry. Deur van ‘n UV-lamp en UV-refleksie studies gebruik te maak is daar bepaal dat fluoresserende latekspartikels in polimere, in verf - wat of titaniumdioksied bevat of geen titaniumdioksied bevat nie -, beide geïdentifiseer and gekwantifiseer kan word.

Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: To comply with the ever growing demands for materials with better properties and complex architectures, polymer chemistry has resorted to the use of living free radical polymerization techniques. Despite the structural control some of these techniques offer, major disadvantages do exist. For example, most require ultra-pure reagents, hence only a small fraction of the monomers used in industry can be polymerized in this way. This rendered these new living techniques less advantageous from a commercial point of view. Recently, a revolutionary new living free radical process, namely the reversible addition-fragmentation chain transfer process, or RAFT process, was developed that combines the control over the polymer produced with the robustness and versatility of a free radical process. However, the RAFT process is not without its problems. In some dithioester mediated polymerizations, significant inhibition and rate retardation effects have been observed. Two main opposing opinions have been proposed in recent literature to explain these phenomena observed. The main point of difference between these two groups is the fate of the formed intermediate RAFT radicals, i.e., slow fragmentation of the formed intermediate radicals together with possible reversible intermediate RAFT radical termination, or fast fragmentation of the formed intermediate radicals together with possible irreversible intermediate RAFT radical termination. Between these opposing two groups, there is a difference of six orders of magnitude for the rate of fragmentation of the formed intermediate RAFT radicals. The work presented in this thesis is an attempt to clarify some of the mysteries, i.e., inhibition and rate retardation observed in some RAFT polymerizations. Experimental evidence to support or contradict the theories of the above mentioned two opposing groups was investigated. The concentration-time evolution of the intermediate radical concentration (cy), for styrene and butyl acrylate polymerizations mediated by cumyl dithiobenzoate (COB) at 70°C and 90 °C, was followed via in situ electron spin resonance spectroscopy (ESR). The concentration-time evolution profiles observed were ascribed to the formation of very short chains during the early stages of the reaction. It was also found that the RAFT process is not particularly sensitive to oxygen. The intermediate and propagating radical (cp) concentrations (and their ratio) for the cumyl dithiobenzoate mediated styrene polymerizations were examined by ESR spectroscopy and kinetics. The system showed strong chain length effects in kinetics, assuming all chains were of similar number average molar mass (Mn). However, unusual behavior with respect to existing mechanistic knowledge was observed in other aspects of the system. The central equilibrium "constant" (Keq) was found to be dependent on both temperature and initial reactant concentrations. The observed intermediate radical concentrations were not consistent with predictions based on existing literature models. It was also found that the time dependence of the intermediate radical concentration varies significantly with the type of RAFT agent used. Unexpectedly, intermediate radicals were detected at very long reaction times in the virtual absence of initiator, enhancing the belief of possible reversible termination reactions involving the intermediate radicals. An extra radical (nonpropagating or intermediate) species was observed (via ESR spectroscopy) to form during some reactions. Its concentration increased with time. The combination of data from several analytical techniques provided evidence for the formation of dead chains by the termination of intermediate radicals in the free radical polymerization of styrene, mediated by a cumyl dithiobenzoate RAFT agent, at 84°C. Experiments done focused on the early stages of the reactions, targeting very low final number average molar mass values, with high initiator concentrations. The formation of these terminated chains did not occur to a significant extent until a large fraction of the chains reached a degree of polymerization greater than unity. This corresponded to the occurrence of a maximum in intermediate radical concentration. In situ 1H nuclear magnetic resonance (NMR) and electron spin resonance spectroscopy was used to directly investigate the processes that occur during the early stages (typically the first few monomer addition steps) of an AIBN-initiated reversible addition fragmentation chain transfer polymerization of styrene, in the presence of a cyanoisopropyl dithiobenzoate and cumyl dithiobenzoate RAFT agent, at 70°C and 84 °C respectively. 1H NMR spectroscopy allowed the investigation of the change in concentration of important dithiobenzoate species as a function of time. Identification and concentrations of the radicals present in the system could be inferred from corresponding ESR spectroscopy data. An apparent "inhibition" effect was observed in both the cyanoisopropyl and cumyl dithiobenzoate mediated polymerizations. This effect could be reduced by increasing the reaction temperature to 84 °C. However, the use of cumyl dithiobenzoate as RAFT agent prolonged this effect. This apparent "inhibition" effect was attributed to selective fragmentation of the formed intermediate radicals during the early stages of the reaction, and to different propagation rate coefficients (kp) of the resulting (different) radicals. A change in the equilibrium coefficient for the systems investigated was ascribed to possible progressively decreasing addition and fragmentation rate coefficients of propagating and intermediate radicals formed during the reaction. The increase in intermediate radical concentration, and thus possible intermediate radical termination, was shown to also be a probable cause of the rate retardation observed in the RAFT mediated systems investigated. To conclude, probable causes of the observed inhibition and rate retardation in some dithiobenzoate mediated systems were investigated. It was found that intermediate RAFT radical termination does occurs, albeit reversibly or irreversibly. A maximum in the intermediate radical concentration, and thus possible intermediate radical termination, was seen to occur during the observed rate retardation. An apparent inhibition effect observed was ascribed to a possible change in termination kinetics, the formation of terminated intermediate radical products and a rapidly changing kp of the propagating radicals. / AFRIKAANSE OPSOMMING: Om te voldoen aan die ewig groeiende aanvraag vir materiale met beter eienskappe en komplekse samestellings, is in die polimeerchemie lewende vry-radikaal polimerisasietegnieke ontwikkel. Ten spyte van die feit dat party van die polimerisasie tegnieke die strukuur van die gevormende polimere kan beheer, bestaan daar tog nadele. Die meeste polimerisasie tegnieke benodig ultra suiwer reagense, dus kan net 'n klein fraksie van die monomere wat deur die industrie gebruik word op so 'n manier gepolimeriseer word. Dus, vanuit 'n komersieële oogpunt, is die nuwe lewende polimerisasietegnieke minder voordelig. Onlangs is 'n revolusionere nuwe lewende vry-radikaal polimerisasieproses, naamlike die RAFT-(eng. reversible addition-fragmentation chain transfer process) proses ontwikkel, wat die beheer oor die geproduseerde polimere, kombineer met die robuustheid en veelsydigheid van 'n vry-radikaalproses. Die RAFT proses is egter nie sonder probleme nie. Beduidende inhibisie en vertraging van die polimerisasie tempo is in sommige dithioester-bemiddelde polimerisasies opgemerk. Daar is hoofsaaklik twee opponerende opinies oor die redes vir die inhibisie en vertragings effekte. Die grootste verskil tussen die twee groepe lê in die lot van die gevormde intermediêre radikaal, m.a.w. stadige fragmentasie van die gevormende intermediêre radikale tesame met moontlike onveranderlike intermediêre radikaalterminasie, of vinnige fragmentasie tesame met moontlike omkeerbare intermediêre radikaalterminasie. Tussen die twee groepe, is daar 'n verskil van ses ordegrotes vir die groote van die tempo van fragmentasie van die gevormende intermediêre radikaal. Die werk wat in die tesis weergee word, is 'n poging om sommige van die geheime van die RAFT proses, m.a.w. inhibisie en vertraging van die polimerisasietempo, op te los. Die ondersoek was gerig op eksperimetele bewyse om die teorieë van die twee opponerede groepe of te bevestig of teen te spreek. Die konsentrasie tyd-verandering van die intermediêre radikaal konsentrasie vir stireen- en butielakrilaatpolimerisasie, bemiddeled deur CDB (eng cumyl dithiobenzoate) by 70 oe and 90 oe, is gevolg deur middel van in situ (lat. vir in die oorspronklike plek, m.a.w. binne-in die ESR masjien) elektronspin-resonans (ESR) spektroskopie. Die vorm van die konsentrasie tyd-profiele is toegeskryf aan die vorming van baie kort polimeerkettings gedurende die vroeë reaksietye. Dit is ook bepaal dat die RAFT-proses nie besonder sensitief was vir suurstof nie. Die intermediêre en die propagerende radikaalkonsentrasie (en hulle verhouding) vir die CDB bemiddelde stireen polimerisasies, is bepaal deur middel van elektronspin-resonans spektroskopie en die kinetika van die sisteem. Die kinetika van die sisteem toon 'n sterk afhanklikheid teenoor die lengte van die polimeerkettings, as aanvaar word dat al die kettings dieselfde numeriese gemiddelde molêre massa het. Des nieteenstaande, is egter onverwagte gedrag in ander aspekte van die sisteem opgemerk. Dit was ook gevind dat die sentrale ewewigs-"konstante" (Keq) afhanklik was van die temperatuur en die oorspronklike reaktant konsentrasie. Die bepaalde intermediêre radikaalkonsentrasie het verskil van voorspelde waardes gebaseer op literatuur modelle. Dit is ook gevind dat die intermediêre radikaalkonsentrasie afhanklik is van die tipe RAFT agent wat in die polimerisasie reaksies gebruik word. Intermediêre radikale is onverwags gevind na baie lang reaksietye, wanner verwag is dat die konsentrasie van die afsetter, en dus ook die intermediêre radikale, baie klein sou wees. Dit het die verwagting dat omkeerbare intermediêre radikaalterminasie kan plaasving, versterk. 'n Ekstra radikale spesie, wat gedurende die reaksie vorm en waarvan die konsentrasie groter word met tyd, is ook deur ESR-spektroskopie geidentifiseer. 'n Kombinasie van verskillende skeikundige tegnieke is gebruik om bewyse te kry vir die vorming van dooie kettings wat ontstaan deur middel van intermediêre radikale terminasiereaksies, in die vry-radikaalpolimerisasie van stireen, wat deur 'n CDB RAFT-agent bemiddeled word by 84°C. Eksperimente is gedoen om die reaksie tydens vroeë reaksietye te ondersoek. Baie hoë afsetter konsentrasies is ook gebruik, wat tot uiters lae numeriese gemiddelde molêre massas van die polimeerkettings gelei het. Beduidende konsentrasies van die dooie kettings is eers gevind nadat 'n graad van polimerisasie van groter as een bereik is. Dit het ooreengestem met 'n maksimum in die konsentrasie van die intermediêre radikale. In situ 1H kern magnetiese-resonans (KMR) en electronspin-resonans spektroskopie was gebruik om 'n RAFT proses, wat gedurende die vroeë reaksie tye (tipies gedurende die eerste paar monomeer toevoegingstappe) te bestudeer, wat deur AIBN (eng azo bis(isobutyronitrile)) afgeset word en bestaan uit stireen en CIDB (eng cyanoisopropyl dithiobenzoate) en CDB RAFT agente onderskeidelik, en by 70°C and 84 °C reageer. 1H KMRspektroskopie was gebruik om die veranderinge in die konsentrasie van die belangrike spesies te bepaal. Die identifikasie en konsentrasie van die radikale kon bepaal word deur middel van ESR data. 'n Skynbare 'inhibisie-effek' is waargeneem in die reaksies wat bemiddeled word deur CIDB en CDB. Die effek is verminder toe die reaksietemperatuur verhoog is na 84°C. Die gebruik van CDB as RAFT agent het egter die effek vergroot. Die skynbare 'inhibisie effek' was toegeskryf aan die selektiewe fragmentasie van die intermediêre radikale gedurende die vroeë reaksietye, en aan verskillende propagasie tempokoëffisiënte (kp) van die verskillende radikale. Die veranderlike sentrale ewewigskoëffisiënte is toegeskryf aan die toevoegings en fragmentasie tempokoëffisiënte van die propagerende en intermediêre radikale wat toenemend afneem. Die is ook getoon dat die toename in die konsentrasie van die intermediêre radikale en dus moontlike intermediêre radikale terminasie, 'n oorsaak kan wees van die vertraging van die polimerisasietempo in die RAFT-bemiddelde reaksies. Ter samevatting, die waarskynlike oorsake vir inhibisie en die polimerisasietempo vertraging opgemerk in sekere dithiobenzoaat-bemiddelde sisteme, is ondersoek. Dit was gevind dat intermediêre radikaalterminasie wel kan gebeur, of dit nou omkeerbaar of onveranderlik gebeur. 'n Maksimum in die konsentrasie van die intermediêre radikale, en dus moontlike intermediêre radikaalterminasie, het voorgekom tesame met 'n vertraging in die polimerisasietempo. Die skynbare inhibisie-effek wat opgemerk was kan toegeskryf word aan 'n moontlike verandering in die terminasie kinetika, die formasie van getermineerde intermediêre radikale en 'n vinnig veranderende propagasie tempokoëffisiënt.