An intercalation inhibitor altering the target selectivity of DNA damaging agents: Synthesis of site-specific aflatoxin B1 adducts in a p53 mutational hotspot

Aflatoxin B1 (AFB1) is a potent human carcinogen implicated in the etiology of hepatocellular carcinoma. Upon metabolic activation to the reactive epoxide, AFB1 forms DNA adducts primarily at the N7 position of guanines. To elucidate more fully the molecular mechanism of AFB1-induced mutagenesis, an intercalation inhibitor was designed to probe the effects of intercalation by AFB1 epoxide on its reaction with DNA. DNA duplexes were prepared consisting of a target strand containing multiple potentially reactive guanines and a nontarget strand containing a cis-syn thymidine-benzofuran photoproduct. Because the covalently linked benzofuran moiety physically occupies an intercalation site, we reasoned that such a site would be rendered inaccessible to AFB1 epoxide. By strategic positioning of this intercalation inhibitor in the intercalation site 5′ to a specific guanine, the adduct yield at that site was greatly diminished, indicating that intercalation by AFB1 epoxide contributes favorably to adduct formation. Using this approach it has been possible to simplify the production of site-specifically modified oligonucleotides containing AFB1 adducts in the sequence context of a p53 mutational hotspot. Moreover, we report herein isolation of site-specifically AFB1-modified oligonucleotides in sequences containing multiple guanines. Use of intercalation inhibitors will facilitate both investigation of the ability of other carcinogens to intercalate into DNA and the synthesis of specific carcinogen-DNA adducts.

Broccoli sprouts: An exceptionally rich source of inducers of enzymes that protect against chemical carcinogens

Induction of phase 2 detoxication enzymes [e.g., glutathione transferases, epoxide hydrolase, NAD(P)H: quinone reductase, and glucuronosyltransferases] is a powerful strategy for achieving protection against carcinogenesis, mutagenesis, and other forms of toxicity of electrophiles and reactive forms of oxygen. Since consumption of large quantities of fruit and vegetables is associated with a striking reduction in the risk of developing a variety of malignancies, it is of interest that a number of edible plants contain substantial quantities of compounds that regulate mammalian enzymes of xenobiotic metabolism. Thus, edible plants belonging to the family Cruciferae and genus Brassica (e.g., broccoli and cauliflower) contain substantial quantities of isothiocyanates (mostly in the form of their glucosinolate precursors) some of which (e.g., sulforaphane or 4-methylsulfinylbutyl isothiocyanate) are very potent inducers of phase 2 enzymes. Unexpectedly, 3-day-old sprouts of cultivars of certain crucifers including broccoli and cauliflower contain 10–100 times higher levels of glucoraphanin (the glucosinolate of sulforaphane) than do the corresponding mature plants. Glucosinolates and isothiocyanates can be efficiently extracted from plants, without hydrolysis of glucosinolates by myrosinase, by homogenization in a mixture of equal volumes of dimethyl sulfoxide, dimethylformamide, and acetonitrile at −50°C. Extracts of 3-day-old broccoli sprouts (containing either glucoraphanin or sulforaphane as the principal enzyme inducer) were highly effective in reducing the incidence, multiplicity, and rate of development of mammary tumors in dimethylbenz(a)anthracene-treated rats. Notably, sprouts of many broccoli cultivars contain negligible quantities of indole glucosinolates, which predominate in the mature vegetable and may give rise to degradation products (e.g., indole-3-carbinol) that can enhance tumorigenesis. Hence, small quantities of crucifer sprouts may protect against the risk of cancer as effectively as much larger quantities of mature vegetables of the same variety.

Cyp7b, a novel brain cytochrome P450, catalyzes the synthesis of neurosteroids 7α-hydroxy dehydroepiandrosterone and 7α-hydroxy pregnenolone

Steroids produced locally in brain (neurosteroids), including dehydroepiandrosterone (DHEA), influence cognition and behavior. We previously described a novel cytochrome P450, Cyp7b, strongly expressed in rat and mouse brain, particularly in hippocampus. Cyp7b is most similar to steroidogenic P450s and potentially could play a role in neurosteroid metabolism. To examine the catalytic activity of the enzyme mouse Cyp7b cDNA was introduced into a vaccinia virus vector. Extracts from cells infected with the recombinant showed NADPH-dependent conversion of DHEA (Km, 13.6 μM) and pregnenolone (Km, 4.0 μM) to slower migrating forms on thin layer chromatography. The expressed enzyme was less active against 25-hydroxycholesterol, 17β-estradiol and 5α-androstane-3β,17β-diol, with low to undetectable activity against progesterone, corticosterone, and testosterone. On gas chromatography and mass spectrometry of the Cyp7b metabolite of DHEA the retention time and fragmentation patterns were identical to those obtained with authentic 7α-hydroxy DHEA. The reaction product also comigrated on thin layer chromatography with 7α-hydroxy DHEA but not with 7β-hydroxy DHEA; when [7α-3H]pregnenolone was incubated with Cyp7b extracts the extent of release of radioactivity into the medium suggested that hydroxylation was preferentially at the 7α position. Brain extracts also efficiently liberated tritium from [7α-3H]pregnenolone and converted DHEA to a product with a chromatographic mobility indistinguishable from 7α-hydroxy DHEA. We conclude that Cyp7b is a 7α-hydroxylase participating in the synthesis, in brain, of neurosteroids 7α-hydroxy DHEA, and 7α-hydroxy pregnenolone.

Molecular recognition of angiogenesis inhibitors fumagillin and ovalicin by methionine aminopeptidase 2

Angiogenesis inhibitors are a novel class of promising therapeutic agents for treating cancer and other human diseases. Fumagillin and ovalicin compose a class of structurally related natural products that potently inhibit angiogenesis by blocking endothelial cell proliferation. A synthetic analog of fumagillin, TNP-470, is currently undergoing clinical trials for treatment of a variety of cancers. A common target for fumagillin and ovalicin recently was identified as the type 2 methionine aminopeptidase (MetAP2). These natural products bind MetAP2 covalently, inhibiting its enzymatic activity. The specificity of this binding is underscored by the lack of inhibition of the closely related type 1 enzyme, MetAP1. The molecular basis of the high affinity and specificity of these inhibitors for MetAP2 has remained undiscovered. To determine the structural elements of these inhibitors and MetAP2 that are involved in this interaction, we synthesized fumagillin analogs in which each of the potentially reactive epoxide groups was removed either individually or in combination. We found that the ring epoxide in fumagillin is involved in the covalent modification of MetAP2, whereas the side chain epoxide group is dispensable. By using a fumagillin analog tagged with fluorescein, His-231 in MetAP2 was identified as the residue that is covalently modified by fumagillin. Site-directed mutagenesis of His-231 demonstrated its importance for the catalytic activity of MetAP2 and confirmed that the same residue is covalently modified by fumagillin. These results, in agreement with a recent structural study, suggest that fumagillin and ovalicin inhibit MetAP2 by irreversible blockage of the active site.

A role for estrogen receptor β in the regulation of growth of the ventral prostate

In normal rats and mice, immunostaining with specific antibodies revealed that nuclei of most prostatic epithelial cells harbor estrogen receptor β (ERβ). In rat ventral prostate, 530- and 549-aa isoforms of the receptor were identified. These sediment in the 4S region of low-salt sucrose gradients, indicating that prostatic ERβ does not contain the same protein chaperones that are associated with ERα. Estradiol (E2) binding and ERβ immunoreactivity coincide on the gradient, with no indication of ERα. In prostates from mice in which the ERβ gene has been inactivated (BERKO), androgen receptor (AR) levels are elevated, and the tissue contains multiple hyperplastic foci. Most epithelial cells express the proliferation antigen Ki-67. In contrast, prostatic epithelium from wild-type littermates is single layered with no hyperplasia, and very few cells express Ki-67. Rat ventral prostate contains an estrogenic component, which comigrates on HPLC with the testosterone metabolite 5α-androstane-3β,17β-diol (3βAdiol). This compound, which competes with E2 for binding to ERβ and elicits an estrogenic response in the aorta but not in the pituitary, decreases the AR content in prostates of wild-type mice but does not affect the elevated levels seen in ERβ knockout (BERKO) mice. Thus ERβ, probably as a complex with 3βAdiol, is involved in regulating the AR content of the rodent prostate and in restraining epithelial growth. These findings suggest that ligands specific for ERβ may be useful in the prevention and/or clinical management of prostatic hyperplasia and neoplasia.

The synthesis, discovery, and development of a highly promising class of microtubule stabilization agents: Curative effects of desoxyepothilones B and F against human tumor xenografts in nude mice

We have evaluated two synthetic epothilone analogues lacking the 12,13-epoxide functionality, 12,13-desoxyepothilone B (dEpoB), and 12,13-desoxyepothilone F (dEpoF). The concentrations required for 50% growth inhibition (IC50) for a variety of anticancer agents were measured in CCRF-CEM/VBL1000 cells (2,048-fold resistance to vinblastine). By using dEpoB, dEpoF, aza-EpoB, and paclitaxel, the IC50 values were 0.029, 0.092, 2.99, and 5.17 μM, respectively. These values represent 4-, 33.5-, 1,423- and 3,133-fold resistance, respectively, when compared with the corresponding IC50 in the parent [nonmultiple drug-resistant (MDR)] CCRF-CEM cells. We then produced MDR human lung carcinoma A549 cells by continuous exposure of the tumor cells to sublethal concentrations of dEpoB (1.8 yr), vinblastine (1.2 yr), and paclitaxel (1.8 yr). This continued exposure led to the development of 2.1-, 4,848-, and 2,553-fold resistance to each drug, respectively. The therapeutic effect of dEpoB and paclitaxel was also compared in vivo in a mouse model by using various tumor xenografts. dEpoB is much more effective in reducing tumor sizes in all MDR tumors tested. Analysis of dEpoF, an analog possessing greater aqueous solubility than dEpoB, showed curative effects similar to dEpoB against K562, CCRF-CEM, and MX-1 xenografts. These results indicate that dEpoB and dEpoF are efficacious antitumor agents with both a broad chemotherapeutic spectrum and wide safety margins.

Cloning of a novel receptor expressed in rat prostate and ovary.

We have cloned a novel member of the nuclear receptor superfamily. The cDNA of clone 29 was isolated from a rat prostate cDNA library and it encodes a protein of 485 amino acid residues with a calculated molecular weight of 54.2 kDa. Clone 29 protein is unique in that it is highly homologous to the rat estrogen receptor (ER) protein, particularly in the DNA-binding domain (95%) and in the C-terminal ligand-binding domain (55%). Expression of clone 29 in rat tissues was investigated by in situ hybridization and prominent expression was found in prostate and ovary. In the prostate clone 29 is expressed in the epithelial cells of the secretory alveoli, whereas in the ovary the granuloma cells in primary, secondary, and mature follicles showed expression of clone 29. Saturation ligand-binding analysis of in vitro synthesized clone 29 protein revealed a single binding component for 17beta-estradiol (E2) with high affinity (Kd= 0.6 nM). In ligand-competition experiments the binding affinity decreased in the order E2 > diethylstilbestrol > estriol > estrone > 5alpha-androstane-3beta,17beta-diol >> testosterone = progesterone = corticosterone = 5alpha-androstane-3alpha,17beta-diol. In cotransfection experiments of Chinese hamster ovary cells with a clone 29 expression vector and an estrogen-regulated reporter gene, maximal stimulation (about 3-fold) of reporter gene activity was found during incubation with 10 nM of E2. Neither progesterone, testosterone, dexamethasone, thyroid hormone, all-trans-retinoic acid, nor 5alpha-androstane-3alpha,I7beta-diol could stimulate reporter gene activity, whereas estrone and 5alpha-androstane-3beta,17beta-diol did. We conclude that clone 29 cDNA encodes a novel rat ER, which we suggest be named rat ERbeta to distinguish it from the previously cloned ER (ERalpha) from rat uterus.

Leukotriene A4 hydrolase: protection from mechanism-based inactivation by mutation of tyrosine-378.

Leukotriene A4 (LTA4) hydrolase [(7E,9E,11Z,14Z)-(5S,6S)-5,6-epoxyicosa-7, 9,11,14-tetraenoate hydrolase; EC 3.3.2.6] is a bifunctional zinc metalloenzyme that catalyzes the final step in the biosynthesis of the potent chemotactic agent leukotriene B4 (LTB4). LTA4 hydrolase/aminopeptidase is suicide inactivated during catalysis via an apparently mechanism-based irreversible binding of LTA4 to the protein in a 1:1 stoichiometry. Previously, we have identified a henicosapeptide, encompassing residues Leu-365 to Lys-385 in human LTA4 hydrolase, which contains a site involved in the covalent binding of LTA4 to the native enzyme. To investigate the role of Tyr-378, a potential candidate for this binding site, we exchanged Tyr for Phe or Gln in two separate mutants. In addition, each of two adjacent and potentially reactive residues, Ser-379 and Ser-380, were exchanged for Ala. The mutated enzymes were expressed as (His)6-tagged fusion proteins in Escherichia coli, purified to apparent homogeneity, and characterized. Enzyme activity determinations and differential peptide mapping, before and after repeated exposure to LTA4, revealed that wild-type enzyme and the mutants [S379A] and [S380A]LTA4hydrolase were equally susceptible to suicide inactivation whereas the mutants in position 378 were no longer inactivated or covalently modified by LTA4. Furthermore, in [Y378F]LTA4 hydrolase, the value of kcat for epoxide hydrolysis was increased 2.5-fold over that of the wild-type enzyme. Thus, by a single-point mutation in LTA4 hydrolase, catalysis and covalent modification/inactivation have been dissociated, yielding an enzyme with increased turnover and resistance to mechanism-based inactivation.

Leukotriene A4 hydrolase: mapping of a henicosapeptide involved in mechanism-based inactivation.

Leukotriene A4 (LTA4) hydrolase [7E,9E,11Z,14Z)-(5S,6S)-5,6-epoxyicosa-7,9 ,11,14-tetraenoate hydrolase; EC 3.3.2.6] is a bifunctional zinc metalloenzyme which converts LTA4 into the chemotactic agent leukotriene B4 (LTB4). Suicide inactivation, a typical feature of LTA4 hydrolase/aminopeptidase, occurs via an irreversible, apparently mechanism-based, covalent binding of LTA4 to the protein in a 1:1 stoichiometry. Differential lysine-specific peptide mapping of unmodified and suicide-inactivated LTA4 hydrolase has been used to identify a henicosapeptide, encompassing the amino acid residues 365-385 of human LTA4 hydrolase, which is involved in the binding of LTA4, LTA4 methyl ester, and LTA4 ethyl ester to the native enzyme. A modified form of this peptide, generated by lysine-specific digestion of LTA4 hydrolase inactivated by LTA4 ethyl ester, could be isolated for complete Edman degradation. The sequence analysis revealed a gap at position 14, which shows that binding of the leukotriene epoxide had occurred via Tyr-378 in LTA4 hydrolase. Inactivation of the epoxide hydrolase and the aminopeptidase activity was accompanied by a proportionate modification of the peptide. Furthermore, both enzyme inactivation and peptide modification could be prevented by preincubation of LTA4 hydrolase with the competitive inhibitor bestatin, which demonstrates that the henicosapeptide contains functional elements of the active site(s). It may now be possible to clarify the molecular mechanisms underlying suicide inactivation and epoxide hydrolysis by site-directed mutagenesis combined with structural analysis of the lipid molecule, covalently bound to the peptide.

Identification of a plastid protein involved in vesicle fusion and/or membrane protein translocation.

Structural evidence has accumulated suggesting that fusion and/or translocation factors are involved in plastid membrane biogenesis. To test this hypothesis, we have developed an in vitro system in which the extent of fusion and/or translocation is monitored by the conversion of the xanthophyll epoxide (antheraxanthin) into the red ketocarotenoid (capsanthin). Only chromoplast membrane vesicles from red pepper fruits (Capsicum annuum) contain the required enzyme. Vesicles prepared from the mutant yellow cultivar are devoid of this enzyme and accumulate antheraxanthin. The fusion and/or translocation activity is characterized by complementation due to the synthesis of capsanthin and the parallel decrease of antheraxanthin when the two types of vesicles are incubated together in the presence of plastid stroma. We show that the extent of conversion is dependent upon an ATP-requiring protein that is sensitive to N-ethylmaleimide. Further purification and immunological analysis have revealed that the active factor, designated plastid fusion and/or translocation factor (Pftf), resides in a protein of 72 kDa. cDNA cloning revealed that mature Pftf has significant homology to yeast and animal (NSF) or bacterial (Ftsh) proteins involved in vesicle fusion or membrane protein translocation.

Biomarcatori per il monitoraggio biologico di soggetti esposti ad agenti cancerogeni per il polmone

Riassunto I biomarcatori o “marcatori biologici” svolgono un ruolo fondamentale nel monitoraggio biologico. In questo lavoro ci siamo soffermati sullo studio di biomarcatori di effetto e di esposizione a xenobiotici ambientali. Nel primo caso abbiamo valutato i micro RNA (miRNA) da utilizzare per la diagnosi precoce del tumore al polmone in matrici di facile accesso, quale il CAE e il plasma, utilizzando il miRNA-21, oncogeno, e il miRNA-486, oncosoppressore. I risultati evidenziano una loro capacità di distinguere correttamente i soggetti con tumore polmonare dai soggetti sani, ipotizzando un loro utilizzo a scopo diagnostico. Nella seconda parte del lavoro di tesi sono stati studiati i biomarcatori di esposizione a benzene per valutare gli effetti dell’esposizione a concentrazioni ambientali su bambini residenti in città e a diverso livello di urbanizzazione. Lo studio ha evidenziato una correlazione dose-effetto fra le concentrazioni di benzene e dei suoi metaboliti urinari e un danno ossidativo a livello degli acidi nucleici. Tuttavia, le concentrazioni di benzene urinario non sono influenzate dal grado di industrializzazione, a differenza dell’S-PMA e degli indicatori di stress ossidativo (8-oxodGuo e 8-oxoGuo) che sembrano risentire sia della residenza che del momento del campionamento. Infine abbiamo ricercato possibili biomarcatori di esposizione a vinilcicloesene (VCH), sottoprodotto industriale nella polimerizzazione del 1,3-butadiene, poiché non sono ancora stati proposti BEI di riferimento nonostante i bassi valori di TLV-TWA (0.1 ppm) proposti dall’ACGIH. Nella prima fase del lavoro abbiamo studiato i meccanismi di tossicità del VCH tramite modelli in vitro, testando varie linee cellulari. I risultati evidenziano come la dose reale di VCH sia di molto inferiore a quella nominale per effetto dell’evaporazione. Inoltre, nelle linee cellulari più sensibili si sono evidenziati effetti citostatici, con alterazioni del ciclo cellulare, a differenza dell’esposizione agli epossidi del VCH, il VCD e l’1,2-VCHME, che determinano lisi cellulare con IC50 di 3 ordini di grandezza inferiori a quelli del VCH. La quantificazione dei metaboliti di I fase e di II fase del VCH nelle linee cellulari epatiche ha evidenziato concentrazioni di circa 1000 volte inferiori a quelle del VCH confermando come la sua tossicità sia principalmente dovuta alla produzione degli intermedi epossidici. La trasformazione nei metaboliti di II fase conferma inoltre l’effetto detossificante del metabolismo. La trasferibilità dei risultati ottenuti in vitro su sistemi in vivo fornirà le basi per poter identificare possibili metaboliti da proporre per il monitoraggio biologico di lavoratori esposti a VCH. PAROLE CHIAVE: biomarcatori di effetto e di esposizione, tumore al polmone, miRNA, benzene, vinilcicloesene.

Estudo da seletividade de catalisadores a base de cobre e paládio em transformações de hidrocarbonetos insaturados

Compreender a correlação entre as características de um catalisador particular e seu desempenho catalítico tem sido um dos principais objetos da pesquisa em catálise heterogênea a fim de usar esse conhecimento para o desenho racional de catalisadores mais ativos, seletivos e estáveis. A seletividade é um dos fatores mais importantes a ser controlado pelo desenho de catalisadores, podendo ser alcançada de diversas maneiras, levando-se em consideração mudanças do tipo estrutural, química, eletrônica, de composição, de cinética e de energia. O trabalho descrito nessa tese de doutorado compreende a síntese e caracterização de catalisadores compostos de nanopartículas de óxido de cobre, paládio e cobre-paládio e seu estudo em reações de hidrogenação e oxidação seletivas de hidrocarbonetos insaturados. Os catalisadores foram preparados através da deposição de nanopartículas dos metais cataliticamente ativos sobre suportes magneticamente recuperáveis compostos de nanopartículas de magnetita revestidas por sílica com superfícies funcionalizada com diferentes grupos orgânicos. A natureza magnética do suporte permitiu a fácil separação do catalisador do meio reacional pela simples aproximação de um ímã na parede do reator. O catalisador pôde ser completamente separado da fase líquida, fazendo com que a utilização de outros métodos de separação como filtração e centrifugação, comumente utilizados em sistemas heterogêneos líquidos, fossem completamente dispensados. Os catalisadores foram inicialmente testados em reações de hidrogenação de alquenos e alquinos. As reações de hidrogenação foram realizadas utilizando hidrogênio molecular como agente redutor, dispensando a utilização de agentes redutores mais agressivos. Os catalisadores compostos de NPs de Pd mostram excelente atividade e capacidade de reutilização na hidrogenação de cicloexeno, podendo ser utilizados em até 15 ciclos sem perda de atividade. Nas reações de hidrogenação de alquinos, os catalisadores que contêm cobre mostraram maior seletividade para a obtenção dos produtos de semi-hidrogenação, com destaque para o catalisador composto de NPs de CuPd, que não apresenta nem traços do produto de hidrogenação completa na amostra final. Esse catalisador bimetálico alia as características do paládio (elevada atividade) e do cobre (elevada seletividade) para fornecer um catalisador ativo e seletivo para a transformação desejada. Além disso, os grupos funcionais presentes na superfície do suporte catalítico mostraram influência na atividade e seletividade para a hidrogenação de alquenos e alquinos. Os catalisadores sintetizados também foram testados na reação de oxidação de cicloexeno e mostraram seletividade para a produção do composto carbonílico α,β-insaturado, cicloex-2-en-1-ona, que é um reagente de partida de grande interesse para a síntese de diversos materiais na indústria química. As reações de oxidação foram realizadas utilizando-se apenas O2 como oxidante primário, dispensando o uso de oxidantes tóxicos como cromatos, permanganatos ou compostos halogenados, que não são recomendados do ponto de vista ambiental. Os catalisadores sintetizados puderam ser reutilizados em sucessivos ciclos de oxidação, mostrando seletividade para a formação dos produtos alílicos em todos os ciclos. Os catalisadores foram estáveis sob as condições reacionais e não apresentaram problemas de lixiviação da espécie ativa para o meio reacional, que é comum na catálise heterogênea. Um estudo cinético mostrou que, mesmo no início da reação, o catalisador tem seletividade para a ocorrência de oxidação alílica em detrimento da reação de oxidação direta que dá origem ao epóxidos correspondente, e se mostrou condizente com o mecanismo proposto na literatura para a reação de oxidação de alquenos via radicalar.

Exposição a substâncias organocloradas em São Paulo: níveis séricos em doadores de sangue e fatores associados

A utilização de pesticidas organoclorados é motivo de preocupação das entidades ligadas à área de saúde em todo o mundo. Apesar de as formas de contaminação serem bem conhecidas, não há um controle eficaz na fiscalização do seu uso no Brasil. Sabe-se que altos níveis séricos destes compostos nos organismos de seres humanos e animais acarretam sérios problemas de saúde. Tendo em vista essa realidade, foi realizado, em 2009, o Projeto Piloto do I Inquérito Nacional de Populações Expostas a Substâncias Químicas, cujo subprojeto \"doadores de sangue\" teve como objetivo mensurar as concentrações de substâncias químicas no sangue de 547 residentes da região metropolitana de São Paulo, dentre elas os pesticidas organoclorados. Este trabalho teve como objetivos avaliar as concentrações dos pesticidas hexaclorobenzeno (HCB), alfa-HCH, ?-HCH, beta-HCH, beta-HCH, heptacloro, heptacloro epóxido, dieldrin, mirex, o,p\'-DDT, p,p\'-DDT, o,p\'-DDE, p,p\'-DDE, o,p\'-DDD e p,p\'-DDD nesta população e compará-las com as encontradas em outros países e determinar fatores associados aos níveis mais elevados destas substâncias. O método analítico utilizado foi de cromatografia a gás. Os resultados deste estudo indicam que a população adulta de São Paulo não está exposta a níveis preocupantes de pesticidas organoclorados, pois dentre os compostos analisados, apenas o beta-HCH e o p,p\'-DDE tiveram um número significante de amostras acima do limite de quantificação, 10,7% e 31,2% das amostras respectivamente. Quando utilizada a metade do limite de quantificação para substituir os valores abaixo do limite de quantificação do método, o valor médio encontrado para o beta-HCH foi de 0,028 ug/dL e para o p,p\'-DDE foi de 0,045 ug/dL. Este estudo propôs dois modelos multivariados para explicar os fatores associados aos compostos beta-HCH e p,p\'-DDE no sangue dos doadores. Segundo o modelo de Regressão Logística Ordinal Multivariado, os fatores associados a níveis mais altos de beta-HCH foram ter idade entre 26 e 45 anos e ser do sexo feminino. Para o p,p\'-DDE os fatores associados a níveis mais altos foram ter idade entre 26 e 45 anos, ser do sexo feminino e ter trabalhado com pesticidas, enquanto receber renda mensal de 3 a 5 salários mínimos e consumir derivados de origem animal uma ou mais vezes por semana foram associados a níveis mais baixos de p,p\'-DDE. Segundo o modelo de Regressão Linear Múltipla, os fatores associados a níveis mais altos de beta-HCH foram o sexo feminino, ter contato prévio com pesticidas na região agrícola, ter trabalhado com pesticidas em campanhas de saúde pública, ter trabalhado em empresas de capacitores ou transformadores, ter trabalhado em indústrias de solventes clorados, ter renda mensal de 3 a 5 salários mínimos, consumo de carnes uma ou duas vezes por semana e consumo de frutos do mar uma ou duas vezes por semana, enquanto consumo frequente de cerveja e ter renda mensal de 1 a 3 salários mínimos foram associado a níveis menores de beta-HCH. Já para o p,p\'-DDE, os fatores associados a níveis mais elevados foram ser do sexo feminino, ser não branco, ter trabalhado com pesticidas e consumir água de fontes que não sejam minerais ou de rede, enquanto o consumo frequente de bebidas alcoólicas foi associado a níveis mais baixos de p,p\'-DDE

Spectroscopic, calorimetric, and catalytic evidences of hydrophobicity on Ti-MCM-41 silylated materials for olefin epoxidations

Hydrophobic Ti-MCM-41 samples prepared by post-synthesis silylation treatment demonstrate to be highly active and selective catalysts in olefins epoxidation by using organic hydroperoxides as oxidizing agents in liquid phase reaction systems. Epoxide yields show important enhancements with increased silylation degrees of the Ti-mesoporous samples. Catalytic studies are combined and correlated with spectroscopic techniques (e.g. XRD, XANES, UV-Visible, 29Si MAS-NMR) and calorimetric measurements to better understand the changes in the surface chemistry of Ti-MCM-41 samples due to the post-synthesis silylation treatment and to ascertain the role of these trimethylsilyl groups incorporated in olefin epoxidation. In such manner, the effect of the organic moieties on solids, and both water and glycol molecules contents on the catalytic activity and selectivity are analyzed in detail. Results show that the hydrophobicity level of the samples is responsible for the decrease in water adsorption and, consequently, the negligible formation of the non-desired glycol during the catalytic process. Thus, catalyst deactivation by glycol poisoning of Ti active sites is greatly diminished, this increasing catalyst stability and leading to practically quantitative production of the corresponding epoxide. The extended use of these hydrophobic Ti-MCM-41 catalysts together with organic hydroperoxides for the highly efficient and selective epoxidation of natural terpenes is also exemplified.

Organic matter based proxies from surface sediments along three transects on the Pakistan continental margin

A valid assessment of selective aerobic degradation on organic matter (OM) and its impact on OM-based proxies is vital to produce accurate environmental reconstructions. However, most studies investigating these effects suffer from inherent environmental heterogeneities. In this study, we used surface samples collected along two meter-scale transects and one longer transect in the northeastern Arabian Sea to constrain initial OM heterogeneity, in order to evaluate selective aerobic degradation on temperature, productivity and alteration indices at the sediment-water interface. All of the studied alteration indices, the higher plant alkane index, alcohol preservation index, and diol oxidation index, demonstrated that they are sensitive indicators for changes in the oxygen regime. Several export production indices, a cholesterol-based stanol/stenol index and dinoflagellate lipid- and cyst-based ratios, showed significant (more than 20%) change only over the lateral oxygen gradients. Therefore, these compounds do not exclusively reflect surface water productivity, but are significantly altered after deposition. Two of the proxies, glycerol dibiphytanyl glycerol tetraether-based TEX86 sea surface temperature indices and indices based on phytol, phytane and pristane, did not show any trends related to oxygen. Nevertheless, unrealistic sea surface temperatures were obtained after application of the TEX86, TEX86L, and TEX86H proxies. The phytol-based ratios were likely affected by the sedimentary production of pristane. Our results demonstrate the selective impact of aerobic organic matter degradation on the lipid and palynomorph composition of surface sediments along a short lateral oxygen gradient and suggest that some of the investigated proxies may be useful tracers of changing redox conditions at the sediment-water interface.