Photoelectrodes with titanate nanotubes sensitized by mesoporphyrin derivative from cashew nut shell

Titanate nanotubes (TiNTs) with the chemical composition Na2Ti3O7.nH2O (NaTiNT) were obtained througha hydrothermal method in highly alkaline medium. Protonated titanates nanotubes (H-TiNTs), with the compositionH2Ti3O7.nH2O, were prepared by ion exchange reaction through a suspension of Na2Ti3O7nH2Onanotubes in HCl medium, promoting the exchange of Na+ ions by H+. Both Na2Ti3O7.nH2O andH2Ti3O7.nH2O products, as well the TiO2 used as raw material for the nanotubes processing, were used asstarting material for the solar cells photoelectrodes sensitized using mesoporphyrin extracted from a precursorof cashew nut shell. Exposing the NaTiNT sample to solar radiation of 1258 W/m2, a short-circuit currentdensity (ISC) of 13 A/cm2 and an open-circuit voltage (VOC) of 370 mV were registered and, a current densityof 7.6 A/cm2 and a voltage of 256 mV for the prototype cell based on H-TiNTs. A current density of 1.1A/cm2 and an open-circuit voltage of 1.6 mV were obtained for the cell using TiO2 as electrode.Keywords: Titanate Nanotubes. Ionic exchange. Mesoporphyrin. Dye-sensitized solar cell

Studies toward the synthesis of pyrrolizidine and indolizidine alkaloids : use of (+)-retronecine and D-insoascorbic acid

Orientador: Ronaldo Aloise PilliTese (doutorado) - Universidade Estadual de Campinas, Instituto de QuimicaResumo: O trabalho desenvolvido visou a obtenção de alcalóides pirrolizidínicos e indolizidínicos utilizando a (+)-retronecina (1) e o ácido D-isoascórbico (35D) como matérias primas, respectivamente. A retronecina (1) foi isolada da espécie vegetal Senecio brasiliensis. Para a preparação da base necínica (1R,6S,7S,8R)-7- (hidroximetil)-hexaidro-1H-pirrolizina-1,6-diol (37), a retronecina (1) foi submetida à reação de epoxidação com ácido meta-cloroperbenzóico. A a-epóxi-retronecina (44), após proteção das hidroxilas com cloreto de tercbutildimetilsilila, foi submetida à abertura com níquel de Raney, e a posterior desproteção forneceu o triol 37, que foi obtido em 5 etapas e 15 % de rendimento. Os compostos (1R,2R,7R,8S)-1-(hidroximetil)-hexaidro-1H-pirrolizina-1,2,7-triol (39) e a platinecina (72) foram preparados a partir de reações de diidroxilação e hidrogenação estereosseletiva da retronecina (1) em 70 e 86 % de rendimento, respectivamente. A abordagem síntética inicial para obtenção de alcalóides indolizidínicos foi baseada na adição do 2-terc-butildimetilsililoxifurano (94) ao íon N-acilimínio derivado da lactama 90. Em função do moderado rendimento e da modesta diastereosseletividade obtida foi proposta uma segunda abordagem sintética para obtenção de indolizidinas. Os alcalóides indolizidínicos, (1R,2S,8aR)- octaidroindolizina-1,2-diol (100) (ent-epi-lentiginosina) e (1R,2S,6R,7S,8aR)- octaidroindolizina-1,2,6,7-tetrol (101) foram preparados a partir da lactona 77. Os compostos 100 e 101 foram obtidos do intermediário-chave 82, que foi preparado a partir da adição de alilamina à lactona 77, derivada do ácido isoascórbico. Em seguida a hidroxiamida 82 foi oxidada à hidroxilactama correspondente, que foi submetida à reação de acetilação fornecendo o composto 91. Reação de alilação de 91, seguido de metátese de olefinas forneceu a indolizidinona 99. Reação de hidrogenação/hidroxilação de 99, redução da lactama e desproteção do acetal levou ao diol 100 e ao tetrol 101 em rendimentos de 27 e 31 %, respectivamente, a partir da lactona 77Abstract: The aim of the present work was the synthesis of pyrrolizidine and indolizidine alkaloids using (+)-retronecine (1) and D-isoascorbic acid (35D) as starting materials, respectively. Retronecine (1) was isolated from the vegetal species Senecio brasiliensis. The synthesis of the necine base (1R,6S,7S,7aR)-7-(hydroxymethyl)-hexahydro-1H-pirrolizine-1,6-diol (37) was accomplished by the m-chloroperbenzoic acid epoxidation of retronecine (1). After hydroxyl protection with tert-butyldimethylsilyl chloride, epoxide 44 was subjected to ring opening with nickel Raney and deprotection to yield triol 37, in 5 steps and 15 % yield. Compounds (1R,7S,8R)-7-(hydroxymethyl)-hexahydro-1H-pirrolizin-1-ol (39) and platynecine (72) were prepared after stereoselective dihydroxylation and hydrogenation reactions of retronecine (1) in 70 and 86 % yield, respectively. The first approach to the synthesis of indolizidine alkaloids was based on the 2-tert-butyldimethylsilyloxyfuran addition to lactam 90-derived N-acyliminium ion. Due to moderate yield and diastereoselectivity obtained, a second synthetic approach to the synthesis of indolizidines was suggested. Indolizidine alkaloids 100 and 101 were prepared from lactone 77. Compounds 100 and 101 were obtained from key intermediate 82, which was prepared from allylamine addition to isoascorbic acid-derived lactone 77. Following that, hydroxyamide 82 was oxidized to the corresponding hydroxylactam which was subjected to acetylation, yielding compound 91. Allylation of 91 and subsequent ring closing olefin metathesisyielded indolizidinone 99. Hydrogenation/hydroxylation reaction of 99 followed by lactam reduction and deprotection of acetonide provided diol 100 and tetrol 101, in 27 and 31 % yield, respectively, from lactone 77DoutoradoQuimica OrganicaDoutor em Ciência