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Podisus nigrispinus Dallas (Hemiptera: Pentatomidae) is a zoophytophagous insect that has a potential in biological control because its nymphs and adults prey on various insects. They insert their mouthparts and inject the contents of their salivary glands in their prey to kill them. Although it is understood that the saliva of this predator is toxic, the toxic compounds responsible for the prey death remains unknown. To identify the components of the saliva of P. nigrispinus, we evaluated the ultrastructure and cytochemistry of the salivary glands of this insect. Cytochemistry evaluation identified the compounds of the saliva of P. nigrispinus responsible for the death of Anticarsia gemmatalis prey. The salivary system of P. nigrispinus has consists of a pair of principal salivary glands, which are bilobed with a short anterior and a long posterior lobe, and a pair of tubular accessory glands. The cells of both the glands are well developed with a predominance of mitochondria and rough endoplasmic reticulum and with basal plasma membrane infoldings, indicating that both the glands play a role in the transport of hemolymph substances and protein synthesis. The cytochemical tests demonstrated positive reactions for carbohydrate, protein, and acid phosphatase in the cells of both the salivary glands. An injection of the saliva of P. nigrispinus exposed to enzyme inhibitors and proteases and extracted at the ether phase caused mortality of A. gemmatalis larvae, with LD50 = 1.91 and LD90 = 4.34 μL. These saliva fractions were identified as N,N-dimethylaniline and 1,2,3-trithiepane, and the injection of the first compound showed an LC50 = 136.1 nL and LC90 = 413.8 nL, suggesting that these non- proteineous compound is responsible for the saliva toxicity of P. nigrispinus. The ultrastructural and cytochemical features suggested participation of the principal and accessory salivary glands in the secretion of proteinaceous and non-proteinaceous toxic substances in the saliva of this insect. This was further confirmed by identification of N,N-dimethylaniline and 1,2,3-trithiepane responsible for the death of A. gemmatalis. This is the first study reporting the toxic compounds of the saliva of this insect.

Podisus nigrispinus Dallas (Hemiptera: Pentatomidae) é um inseto zoofitófago com potencial para controle biológico, pois ninfas e adultos predam diversos insetos, inserindo o aparelho bucal e injetando o conteúdo das glândulas salivares no interior das presas, causando a morte das mesmas. Entretanto, os compostos tóxicos da saliva desse inseto, responsáveis pela morte das presas são ainda desconhecidos. Como primeira etapa para a identificação das possíveis substâncias presentes na saliva de P. nigrispinus, este estudo avaliou a ultraestrutura e citoquímica das…

Advisors/Committee Members: Zanuncio, José Cola, Fialho, Maria do Carmo Queiroz, Serrão, José Eduardo, Alves, Stênio Nunes, Lemos, Walkymário de Paulo, Oliveira, Leandro Licursi de, Oliveira, Eugenio Eduardo de.

The critically important nature of radical and radical ion mechanisms in biology and chemistry continues to be recognized as our understanding of these unique transient species grows. The work presented herein demonstrates the versatility of kinetic studies for understanding the elementary chemical reactions of radicals and radical ions. Chapter 2 discusses the use of direct ultrafast kinetics techniques for investigation of crucially important enzymatic systems; while Chapter 3 demonstrates the value of indirect competition kinetics techniques for development of synthetic methodologies for commercially valuable classes of compounds. The mechanism of decay for aminyl radical cations has received considerable attention because of their suspected role as intermediates in the oxidation of tertiary amines by monoamine oxygenases and the cytochrome P450 family of enzymes. Radical cations are believed to undergo deprotonation as a key step in catalysis. KIE studies performed by previous researchers indicate N,N-dimethylaniline radical cations deprotonate in the presence of the bases acetate and pyridine. By studying the electrochemical kinetics of the reaction of para substituted N,N-dimethylaniline radical cations with acetate anion, we have produced compelling evidence to the contrary. Rather than deprotonation, acetate reacts with N,N-dimethylaniline radical cation by electron transfer, generating the neutral amine and acetoxyl radical. Transport properties of reactants and solvent polarity changes were investigated and confirmed not to influence the electrochemical behavior forming the basis for our mechanistic hypothesis. To reconcile our conclusion with earlier results, KIEs were reinvestigated electrochemically and by nanosecond laser flash photolysis. Rather than a primary isotope effect (associated with C-H bond cleavage), we believe the observed KIEs are secondary, and can be rationalized on the basis of a quantum effect due to hyperconjugative stabilization in aromatic radical cations during an electron transfer reaction. Product studies performed by constant potential coulometry indicate N,N-dimethylaniline radical cations are catalytic in carboxylate oxidations. Collectively, our results suggest that aminyl radical cation deprotonations may not be as facile as was previously thought, and that in some cases, may not occur at all. Interest in design and synthesis of selenium containing heterocycles stems from their ability to function as antioxidants, anti-virals, anti-inflammatories, and immunomodulators. To establish synthetic feasibility of intramolecular homolytic substitution at selenium for preparation of selenocycles, we set out to determine what factors influence cyclization kinetics. A series of photochemically labile Barton and Kim esters have been syntheisized and employed as radical precursors. The effect of leaving radical stability on kinetics has been investigated through determination of rate constants and activation parameters for intramolecular homolytic substitution of the corresponding… Advisors/Committee Members: Tanko, James M. (committeechair), Marand, Hervé L. (committee member), Marand, Hervé L. (committee member), Long, Timothy E. (committee member), Madsen, Louis A. (committee member), Troya, Diego (committee member).