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J P Da Silva

Publications and source records attributed to J P Da Silva.

9 recordsLinked to original sources
PubMed2006

Pyrene-p-tert-butylcalixarenes inclusion complexes formation: a surface photochemistry study.

Diffuse reflectance and luminescence techniques were used to study the photophysics and photochemistry of pyrene within p-tert-butylcalix[n]arenes with n = 4, 6, and 8, and to study their ability to form inclusion complexes in heterogeneous media. Evidences for inclusion complex formation were found for the three hosts under study. Ground state diffuse reflectance results have shown the formation of ground state dimers of pyrene inside the cavity of calix[6]arene and calix[8]arene, with this feature much more evident for calix[6]arene. For calix[4]arene, only a monomer fits inside the cavity and the presence of pyrene microcrystals outside the cavity was detected. A luminescence lifetime distribution analysis was performed, revealing the presence of prompt emissions from the pyrene microcrystals outside the cavity in the case of calix[4]arene and from the constrained dimers inside the cavities of calix[6]arene and calix[8]arene. Transient absorption results have shown the presence of pyrene radical cation and also of trapped electrons for the three hosts under study. The formation of the phenoxyl radical of the calixarene following the laser pulsed excitation of pyrene at 355 nm is increased for calix[6]arene and calix[8]arene. This feature is particularly relevant for calix[6]arene, suggesting a very favourable situation for the hydrogen atom abstraction to occur. The analysis of the degradation products revealed the presence of hydroxypyrene as a major photodegradation product for the three hosts. Dihydro-hydroxypyrene was also formed in the case of calix[6]arene and calix[8]arene. The formation of the calixarene's phenoxyl radical and subsequent hydrogen abstraction is consistent with the formation of dihydro-dihydroxypyrene.

Journal Article↗
PubMed2006

Surface photochemistry: benzophenone as a probe for the study of silica and reversed-phase silica surfaces.

This work reports the use of benzophenone, a very well characterized probe, to study new hosts: two reversed-phase silicas. Laser-induced room temperature luminescence of argon purged solid powdered samples of benzophenone adsorbed onto the two different reversed-phase silicas, RP-18 and RP-8, revealed the existence of a low energy emission band in contrast with the benzophenone adsorbed on 60 A pore silica, where only triplet benzophenone emits. This low energy emission band was identified as the fluorescence of the ketyl radical of benzophenone, which is formed as the result of a hydrogen atom abstraction reaction of the triplet excited benzophenone from the alkyl groups of the surface of the reversed silicas. Such emission does not exist for benzophenone adsorbed onto 60 A pore silica. Room temperature phosphorescence was obtained in argon purged samples for all the surfaces under use. The decay times of the benzophenone emission vary greatly with the alkylation of the silica surface when compared with "normal" silica surface. A lifetime distributions analysis has shown that the shortest lifetimes for the benzophenone emission exist in the former case. Triplet-triplet absorption of benzophenone was detected in all cases and is the predominant absorption in the case of 60 A pore silica, while benzophenone ketyl radical formation occurs in the case of the reversed silicas. Diffuse reflectance laser flash photolysis and gas chromatography-mass spectrometry techniques provided complementary information, the former about transient species and the latter regarding the final products formed after laser irradiation, both at 266 nm or 355 nm. Product analysis and identification show that the degradation photoproducts are dependent on the excitation wavelength, the photochemistry being much more rich and complex in the 266 nm excitation case, where an alpha-cleavage reaction occurs. A detailed mechanistic analysis is proposed.

Journal Article↗
PubMed2001

Dissipation of triadimefon on the solid/gas interface.

The dissipation of triadimefon, as pure solid and in the Bayleton 5 commercial formulation, was studied under controlled and natural conditions. Volatilization and photodegradation were shown to be the main dissipation processes. The volatilization results can be described by an empirical model assuming exponential decay of the volatilization rate. The filler of the commercial formulation is determinant for the volatilization but has little effect on the photodegradation rates. The main photoproducts were identified and a reaction mechanism proposed.

Environmental Pollutants↗
PubMed1996

A consensus on the normal characteristics of corpus cavernosum EMG.

Corpus cavernosum EMG (CC-EMG) has raised much controversy since its introduction. The first workshop on CC-EMG has resulted in acceptance of a standardized technique of recording. Using this technique 110 normal potent volunteers have been examined in different centres. One year later there is an agreement among participants that an analogous recording of CC-EMG during flaccidity in normal subject results in reproducible findings. CC-EMG is characterized by highly reproducible waveforms (potentials) within the individual subject and mostly of comparable shape interindividually. Maximum peak to peak amplitude lies between 75 and > 500 microV and potentials have a mean duration of 12 s.

Adolescent↗
PubMed1994

The corpus cavernous electromyography in the erectile dysfunction diagnosis.

The single potential analysis of cavernous electric activity (CC-EMG), registration bands were studied in 144 patients with erectile dysfunction followed from November 1992 to March 1993. We attempted to correlate abnormal electromyographic records with reduction of the cavernous bodies and albuginea expansibility, as measured by cavernosometry/rigidometry. In this selected group of patients, with venous leak of different flow, the main associated causes of the erectile dysfunction were cavernous neuromyopathy (91), diabetes mellitus (20), disturbances of the arterial influx (7), endocrinological factors (4), Peyronie's disease (3). Some patients (15) presented with a penile bend. A history of alcohol and tobacco use was obtained: 38 patients smoked 15 to 60 cigarettes/day and 43 patients drank moderate to heavy. The coexistence of other pathologies, has been investigated, showed many other associated diseases. The study attempts to determine if some electromyographic standards in patients with erectile dysfunction, could, by themselves, be a formal indication to penile implant, for a PGE1 self-injection program or for use of a vacuum device. Our results suggest that at least in some cases CC-EMG studies may be clinically relevant and allow choice of optimal therapy.

Action Potentials↗
PubMed1991

[Myxoma of the right atrium].

The authors report the case of a 31 year-old male with right atrial myxoma whose clinical manifestations included: malaise, dizziness and dyspnea on great exertion. At physical examination, a tricuspid systolic and diastolic murmur of mean intensity was found. The chest radiography and the electrocardiogram signs were of right atrial and ventricular enlargement, and the diagnosis was made with the B-mode echocardiogram. The patient underwent surgical removal of the tumoral mass and diagnostic confirmation was made with the histopathologic study of the 75 x 50 x 40 mm piece. The patient obtained clinical, electrocardiographic and radiologic remission.

Adult↗
PubMed1991

[Heart-lung transplantation. Initial clinical experience].

PURPOSE: To assess this initial clinical experience with heart-lung transplantation in Brazil. METHODS: Four patients underwent heart-lung transplantation from December 1988 to March 1990, one patient with cardiomyopathy and high pulmonary resistance, two patients with primary pulmonary hypertension and another with pulmonary silicosis. The heart lung blocks were harvested from the donor using cardiopulmonary bypass and deep hypothermia. They were transplanted to the recipient by anastomosing the tracheae, right atrium or venae cavae, and the ascending aorta. RESULTS: The second patient died on the 5th postoperative day due to respiratory insufficiency with consequent brain lesions. The first and third patients had survived nine months and 42 days respectively. The 4th patients is asymptomatic eight months after the operation. The main complications were bleeding in two patients, acute pulmonary rejection in three of them and obliterans bronchiolitis in one patients. CONCLUSION: The heart lung transplantation is a challenging procedure which results are progressively improving with the development of better surgical technique and clinical concepts.

Adult↗