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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Studies on the active site modification of pyridoxal and flavin dependent enzymes with acetylenic and olefinic substrate analogues.

Marcotte, Patrick Allen. January 1977 (has links)
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 1977 / Vita. / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Chemistry
22

Syntéza rozpustných prírodou inšpirovaných N, N-alkylovaných riboflavínových derivátov, štúdium efektu alkylových skupín / Synthesis of soluble nature-inspired N, N-alkylated riboflavin derivatives, study of the effect of alkyl groups

Ivanová, Lucia January 2021 (has links)
By flavin's unique structure, nature predestined riboflavin and its derivatives to the participation in redox processes within the bodies of all the living organisms. These biomolecules draw attention with intriguing optical properties and photosensitising abilities. Nature-inspired flavin derivatives share these qualities, and there is also a possibility of fine-tuning for the particular application from the chemical point of view. The thesis deals with two main aims. The first aim handles the synthesis of the trimer heteroaromatic precursor and 1,2-diketone. These key intermediates are essential for the future synthesis of the central aromatic core of the novel NH-free non-fused flavin derivative. The thesis introduces and verifies three approaches, including oxidation of diarylalkynes, nucleophilic addition of a corresponding organolithium compound to a Weinreb amide and benzoin condensation. The second aim covers the properties customization of NH-free fused systems by implementation of linear and bulky alkyl side-chains on the nitrogen atoms N1 and N3 of the alloxazine dilactam. N,N-alkylation introduced an increase in solubility in common organic solvents dichloromethane and chloroform. For the derivatives with 2-(adamantan-1-yl)ethyl substituents, high thermal stability was observed via TGA.
23

Elucidation of the quinone methide tautomer of riboflavin and generation of a flavin nitroxyl radical

Frost, John Wesley January 1981 (has links)
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by John Wesley Frost. / Ph.D.
24

Antioxidative and vascular relaxing effects of black tea theaflavins. / CUHK electronic theses & dissertations collection

January 2003 (has links)
by Su Ya Lun. / "August 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 163-181). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.
25

Aspectos da reatividade de vitaminas do complexo B frente ao estado tripleto excitado de flavinas / Aspects of the reactivity of B vitamins towards flavins triplet excited state

Arrivetti, Leandro de Oliveira Rodrigues 14 September 2012 (has links)
Dentre os diversos fatores responsáveis pela instabilidade química das vitaminas nos alimentos, a exposição à radiação luminosa é determinante, principalmente em alimentos contendo vitamina B2. O presente trabalho investigou a degradação fotossensibilizada das vitaminas do complexo B (ácido fólico, piridoxal, biotina e niacina) por flavinas. O piridoxal-5\'-fosfato (PLP) mostrou-se reativo frente aos estados singleto e tripleto excitado das flavinas com constante de desativação de 1,03 1011 L mol-1 s-1 para o estado singleto, valor este superior ao valor esperado para reações bimoleculares controladas por difusão em meio aquoso. Foi observada uma dependência significativa da constante de velocidade de desativação do estado singleto excitado com a temperatura, onde o aumento da temperatura proporciona um decréscimo da constante de velocidade sugerindo a existência de um complexo [FMN...PLP] no estado fundamental o qual foi confirmado por espectroscopia de fluorescência resolvida no tempo. O PLP mostrou-se reativo frente ao estado tripleto excitado da FMN com constante de velocidade de 3kq = 3,0 108 L mol-1 s-1 em meio de tampão fosfato pH 6,4 ou em meio de óxido de deutério a 25 °C. Não foi observada diferença significativa entre as constantes de desativação do estado tripleto excitado em meio aquoso e de óxido de deutério o que corrobora com um processo direto de transferência de elétrons do PLP para a 3FMN* ao invés de um processo de transferência de átomo de hidrogênio. As vitaminas (biotina e niacina) mostraram-se não reativas frente aos estados singleto e tripleto excitados da vitamina B2 o que pode ser atribuído aos altos potenciais de oxidação, Eo > 2 V vs. NHE, observados para estas vitaminas em meio aquoso. A voltametria cíclica do PLP apresentou um processo anódico e irreversível (E= 1,07 V vs. NHE), controlada cineticamente por transferência de elétrons heterogênea do PLP para o eletrodo. O rendimento quântico de fotodegradação do PLP em meio aquoso e aerado é 2,5 vezes superior ao encontrado para a reação em meio anaeróbico, o que sugere a participação do íon superóxido no processo global de degradação do PLP. O ácido fólico demonstrou-se igualmente reativo frente ao estado tripleto excitado das flavinas (3kq= 4,8 108 L·mol-1 s-1 e Φ = 0,26 (meio aerado) e Φ = 0,32 (meio anaeróbico)) e a sua complexação pela β-LG (Φ = 0,032 (meio aerado) e Φ = 0,055 (meio anaeróbico)) uma eficiente abordagem na proteção desta vitamina frente a fotodegradação sensibilizada por flavinas. / Among several factors responsible for the chemical instability of vitamins in food, exposure to light radiation is decisive, especially in supplemented or fortified food with vitamin B2. This study investigated the photosensitized degradation of B-vitamins (folic acid, pyridoxal, biotin and niacin) by flavins. The pyridoxal-5\'-phosphate (PLP) reacted with singlet and triplet excited states of flavins with rate constant for quenching of 1kq = 1,03 1011 L mol-1 s-1 for the singlet state, this value is higher than expected value of bimolecular reactions controlled by diffusion in an aqueous solvent. A significant dependence was observed for the rate constant for deactivation of singlet excited state with temperature, the increase of the temperature leads to a decrease of the rate constant suggesting the existence of a complex [FMN...PLP] in ground state confirmed by time resolved fluorescence spectroscopy. PLP reacted with FMN triplet excited state with rate constant 3kq = 2,96 108 L mol-1 s-1 in phosphate buffer pH 6,4 or deuterium oxide at 25 °C. There was no significant difference between the rate constant of deactivation of the triplet-excited of FMN in aqueous solution or deuterium oxide which confirms a direct process of electron transfer to PLP for 3FMN* rather than a process of transfer of hydrogen atom. Biotin and niacin unreacted with singlet and triplet excited states of vitamin B2 which can be attributed to high oxidation potentials, Eo > 2 V vs. NHE, observed for this vitamins in aqueous solution. The cyclic voltammetry of PLP had an irreversible anodic oxidation process (E = 1.07 V vs. NHE) kinetically controlled by heterogeneous electron transfer from PLP to the electrode. The quantum yield of photodegradation of PLP in aerobic condition is 2.5 times higher than that found for the reaction in anaerobic condition, which suggests the of participation of superoxide ion in the PLP global degradation process. Folic acid demonstrated reactive with triplet excited state of flavins (3kq= 4,8 108 L·mol-1 s-1 and Φ = 0,26 (aerobic condition) and Φ = 0,32 (anaerobic condition)) and the complexation with β-LG (Φ = 0,032 (aerobic condition) and Φ = 0,055 anaerobic condition)) an efficient approach in protecting the vitamin against photodegradation sensitized by flavins.
26

Flavin-containing monooxygenase, tissue specific regulation in rabbit

Lee, Min-young 25 September 1991 (has links)
Graduation date: 1992
27

Redox and functional characterization of a surface loop spanning residues 536 to 541 in the flavin mononucleotide-binding domain of flavocytochrome P450BM-3 from Bacillus megaterium

Chen, Huai-Chun, January 2009 (has links)
Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 143-152).
28

Aspectos da reatividade de vitaminas do complexo B frente ao estado tripleto excitado de flavinas / Aspects of the reactivity of B vitamins towards flavins triplet excited state

Leandro de Oliveira Rodrigues Arrivetti 14 September 2012 (has links)
Dentre os diversos fatores responsáveis pela instabilidade química das vitaminas nos alimentos, a exposição à radiação luminosa é determinante, principalmente em alimentos contendo vitamina B2. O presente trabalho investigou a degradação fotossensibilizada das vitaminas do complexo B (ácido fólico, piridoxal, biotina e niacina) por flavinas. O piridoxal-5\'-fosfato (PLP) mostrou-se reativo frente aos estados singleto e tripleto excitado das flavinas com constante de desativação de 1,03 1011 L mol-1 s-1 para o estado singleto, valor este superior ao valor esperado para reações bimoleculares controladas por difusão em meio aquoso. Foi observada uma dependência significativa da constante de velocidade de desativação do estado singleto excitado com a temperatura, onde o aumento da temperatura proporciona um decréscimo da constante de velocidade sugerindo a existência de um complexo [FMN...PLP] no estado fundamental o qual foi confirmado por espectroscopia de fluorescência resolvida no tempo. O PLP mostrou-se reativo frente ao estado tripleto excitado da FMN com constante de velocidade de 3kq = 3,0 108 L mol-1 s-1 em meio de tampão fosfato pH 6,4 ou em meio de óxido de deutério a 25 °C. Não foi observada diferença significativa entre as constantes de desativação do estado tripleto excitado em meio aquoso e de óxido de deutério o que corrobora com um processo direto de transferência de elétrons do PLP para a 3FMN* ao invés de um processo de transferência de átomo de hidrogênio. As vitaminas (biotina e niacina) mostraram-se não reativas frente aos estados singleto e tripleto excitados da vitamina B2 o que pode ser atribuído aos altos potenciais de oxidação, Eo > 2 V vs. NHE, observados para estas vitaminas em meio aquoso. A voltametria cíclica do PLP apresentou um processo anódico e irreversível (E= 1,07 V vs. NHE), controlada cineticamente por transferência de elétrons heterogênea do PLP para o eletrodo. O rendimento quântico de fotodegradação do PLP em meio aquoso e aerado é 2,5 vezes superior ao encontrado para a reação em meio anaeróbico, o que sugere a participação do íon superóxido no processo global de degradação do PLP. O ácido fólico demonstrou-se igualmente reativo frente ao estado tripleto excitado das flavinas (3kq= 4,8 108 L·mol-1 s-1 e Φ = 0,26 (meio aerado) e Φ = 0,32 (meio anaeróbico)) e a sua complexação pela β-LG (Φ = 0,032 (meio aerado) e Φ = 0,055 (meio anaeróbico)) uma eficiente abordagem na proteção desta vitamina frente a fotodegradação sensibilizada por flavinas. / Among several factors responsible for the chemical instability of vitamins in food, exposure to light radiation is decisive, especially in supplemented or fortified food with vitamin B2. This study investigated the photosensitized degradation of B-vitamins (folic acid, pyridoxal, biotin and niacin) by flavins. The pyridoxal-5\'-phosphate (PLP) reacted with singlet and triplet excited states of flavins with rate constant for quenching of 1kq = 1,03 1011 L mol-1 s-1 for the singlet state, this value is higher than expected value of bimolecular reactions controlled by diffusion in an aqueous solvent. A significant dependence was observed for the rate constant for deactivation of singlet excited state with temperature, the increase of the temperature leads to a decrease of the rate constant suggesting the existence of a complex [FMN...PLP] in ground state confirmed by time resolved fluorescence spectroscopy. PLP reacted with FMN triplet excited state with rate constant 3kq = 2,96 108 L mol-1 s-1 in phosphate buffer pH 6,4 or deuterium oxide at 25 °C. There was no significant difference between the rate constant of deactivation of the triplet-excited of FMN in aqueous solution or deuterium oxide which confirms a direct process of electron transfer to PLP for 3FMN* rather than a process of transfer of hydrogen atom. Biotin and niacin unreacted with singlet and triplet excited states of vitamin B2 which can be attributed to high oxidation potentials, Eo > 2 V vs. NHE, observed for this vitamins in aqueous solution. The cyclic voltammetry of PLP had an irreversible anodic oxidation process (E = 1.07 V vs. NHE) kinetically controlled by heterogeneous electron transfer from PLP to the electrode. The quantum yield of photodegradation of PLP in aerobic condition is 2.5 times higher than that found for the reaction in anaerobic condition, which suggests the of participation of superoxide ion in the PLP global degradation process. Folic acid demonstrated reactive with triplet excited state of flavins (3kq= 4,8 108 L·mol-1 s-1 and Φ = 0,26 (aerobic condition) and Φ = 0,32 (anaerobic condition)) and the complexation with β-LG (Φ = 0,032 (aerobic condition) and Φ = 0,055 anaerobic condition)) an efficient approach in protecting the vitamin against photodegradation sensitized by flavins.
29

Proton-Coupled Electron Transfer for Long-Lived Charge Separation and Photocatalytic Water Splitting

Kucheryavy, Pavel Vladimirovich 12 November 2010 (has links)
No description available.
30

Flavins and Their Analogues as Natural and Artificial Catalysts

Sichula, Vincent A. 02 March 2011 (has links)
No description available.

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