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C Sousa

Publications and source records attributed to C Sousa.

28 records · Page 2Linked to original sources
PubMed1996

Microenvironment effects on the excited state properties of psoralens: a clue to their photobiological activity.

The singlet and triplet excited state parameters (phi f, tau t and phi T) of psoralen (PSO) and derivatives 4,6,4'-trimethylangelicin (TMA) and 4,5',8-trimethylpsoralen (TMP) show an extreme sensitivity to solvation in dioxane/water mixtures. These effects are attributed to the variation of the S1-->S0 internal conversion rate constant kic, which is the nonradiative deactivation path dominating their photophysical behavior. Depending on the compound, kic is very high, (approximately 1 x 10(10) s-1) in nonpolar solvents and then decreases to a low value (3 x 10(8) s-1), with increasing solvent polarity. This work shows that dioxane/water mixtures display the same solvent-induced changes in the electronic structure of psoralens during solvation as those induced by the biological microenvironment sensed by the drug's localization. This mixture matches the photophysical parameters of psoralens observed in protic and aprotic pure solvents, in micelles, in liposomes and in human serum low-density lipoproteins (LDL). They can be used to probe the solvating ability of the interaction site in macrocyclic hosts. A particular localization site, i.e. the more (TMA and TMP) or less (PSO) lipophilic sites found when in interaction with LDL, determines the amount of the triplet reactive state of psoralens and the molecular mechanism available for photoreaction: oxic (type I and type II) or anoxic (type III) pathways.

Furocoumarins↗
PubMed1996

Solvent polarity and pH effects on the spectroscopic properties of neutral red: application to lysosomal microenvironment probing in living cells.

Neutral red is a lysosomal probe and a biological pH indicator. In aqueous solutions, the protonated (NRH) and neutral (NR) forms of monomeric neutral red exhibit distinct absorption maxima (535 and 450 nm, respectively) but have the same fluorescence with a maximum at 637 nm and a quantum yield of 0.02. The similarity of the fluorescence spectra at acidic and basic pH suggests deprotonation of cationic species in the first singlet excited state. The NR fluorescence strongly depends on the solvent polarity as shown by addition of increasing amounts of water to pure dioxane, which gradually shifts the fluorescence maximum from 540 nm in pure dioxane to 637 nm in water. The fluorescence quantum yield increases from 0.17 in dioxane to 0.3 upon addition of 7% water and then decreases, reaching 0.02 in pure water. Immediately after incubation of human skin fibroblasts with neutral red, excitation with 435 nm light produces a fluorescence whose maximum is recorded at 575 nm. This fluorescence is located in the perinuclear region and originates from large fluorescent intracytoplasmic spots, suggesting staining of the endoplasmic reticulum-Golgi complex. At longer times, this fluorescence is shifted to 606 nm, suggesting slow diffusion of the lysosomotropic dye toward the more hydrated and acidic interior of lysosomes. Addition of a lysosomotropic detergent to cells previously incubated with neutral red shifts the fluorescence to the blue. Thus, in complex biological systems, this probe cannot be a good pH indicator but is a very sensitive probe of lysosomal microenvironments.

Dioxanes↗
PubMed1995

Evora district as a new focus for canine leishmaniasis in Portugal.

On the basis of information acquired from local health authorities in Evora district of Portugal on cases of visceral leishmaniasis (VL), an epidemiology survey study was conducted. To determine the prevalence of anti-Leishmania antibodies in the local human and canine populations residing in Evora town and 14 adjacent villages, blood samples collected from 885 children and 3,614 dogs were tested in a direct agglutination test (DAT). Seropositivity for Leishmania parasite obtained by DAT in both endemic populations was further confirmed by an enzyme-linked immunosorbent assay (ELISA) and immunofluorescence test (IFAT). For identification of the responsible sandfly vector, 79 biotopes within the study areas were surveyed. In the infantile population assessed, none of the children screened showed an antibody level indicative (titer, > = 1:3200) of visceral leishmaniasis in the DAT. However, agglutinating antibody rates ranging from 0.7% to 6.9% were obtained in dogs residing in Evora and 11 adjacent villages. Concordant seropositivity of 94.04% was obtained by ELISA and IFAT in the same canine population (141) identified by DAT. Of the 159 sandflies captured, 67 were identified as Phlebotomus sergenti; 15, as P. ariasi; 58, as P. perniciosus; and 19, as Sergentomyia minuta. Unlike the results previously reported in Alto-Douro and Algarve districts of Portugal, as compared with the other three species, P. sergenti appears to be more abundant in Evora district.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Preliminary note on the distribution and ecology of Culicoides imicola in Portugal.

Data on Culicoides imicola were obtained during studies carried out during the recent outbreak of African horse sickness in Portugal. The previous most northerly published record of C. imicola in Portugal was 38 degrees 40'N (Pégöes). In the present work the geographical distribution of this species is extended to the parallel of 41 degrees 17'N. We have also confirmed the continuous presence of adult C. imicola in Southern Portugal (Alentejo and Algarve) throughout the year. In the laboratory we obtained this species from a sample of cattle faeces and from another of soil contaminated with animal excreta. In relation to host association 57.37% of C. imicola were trapped in the vicinity of pigsties. Finally, we collected 11,463 Culicoides of which 12.47% were C. imicola.

Animals↗
PubMed1993

A Rhizobium tropici DNA region carrying the amino-terminal half of a nodD gene and a nod-box-like sequence confers host-range extension.

Rhizobium tropici CIAT899 is a broad-host-range strain that, in addition to Phaseolus, nodulates other plant legumes such as Leucaena and Macroptilium. The narrow-host-range of Rhizobium leguminosarum biovars phaseoli (strain CE3) and trifolii (strain RS1051) can be extended to Leucaena esculenta and Phaseolus vulgaris plants, respectively, by the introduction of a DNA fragment 521 bp long, which carries 128 amino acids of the amino-terminal region of a nodD gene from R. tropici, as well as a putative nod-box-like sequence, divergently oriented. The 521 bp fragment, in the presence of L. esculenta or P. vulgaris root exudates, induced a R. leguminosarum bv. viciae nodA-lacZ fusion in either a CE3 or RS1051 background, respectively.

Amino Acid Sequence↗
PubMedDate not supplied

[Malignant peritoneal mesothelioma -- diagnostic and therapeutic difficulties].

Malignant Peritoneal Mesothelioma (MPM) is an uncommon tumour. Clinical presentation is indefinite and differential diagnosis with peritoneal carcinomatosis is difficult. It has a bad prognosis (survival of 6-12 months) due to the delay of the diagnosis and inefficacy of the conventional therapeutic. The authors present a case of MPM which was diagnosed over the investigation of ascitis. The laparoscopic peritoneal biopsy permitted the diagnosis. After systemic quimiotherapy, the patient is in partial remission at 42 months of follow-up.

Aged↗