Chemical affinity and dispersibility of boron nitride nanotubes.

Boron nitride nanotubes (BNNTs) are electrically insulating nanoparticles that display highly competitive elastic modulus and thermal conductivity. Long presented as potential fillers for nanocomposite applications, their poor dispersibility in most commodity polymers has, however, limited their spread. In this work, the chemical affinity of purified BNNTs, measured in terms of Hansen solubility parameters (HSP), were obtained through sedimentation tests in a wide set of organic solvents, taking into account relative sedimentation time. The parameters obtained were {δ d; δ p; δ h} = {16.8; 10.7; 14.7} ± {0.3; 0.9; 0.3} MPa1/2, with a Hildebrand parameter, δ t = 24.7 MPa1/2 and a sphere radius of 5.4 MPa1/2. The solubility parameters were determined considering complete dispersion of the purified nanomaterial, as well as the viscosity and density of the host solvent. These factors, combined with the high purity of the BNNTs, are crucial to minimize the uncertainty of the HSP characterization. Such refined values provide necessary insights both to optimize the solvent casting of unmodified BNNTs, and to orient the surface modification efforts that would be needed to integrate these nanomaterials into a wider range of host matrices.

Analysis of the Saccharomyces cerevisiae exosome architecture and of the RNA binding activity of Rrp40p.

The exosome is a complex of eleven subunits in yeast, involved in RNA processing and degradation. Despite the extensive in vivo functional studies of the exosome, little information is yet available on the structure of the complex and on the RNase and RNA binding activities of the individual subunits. The current model for the exosome structure predicts the formation of a heterohexameric RNase PH ring, bound on one side by RNA binding subunits, and on the opposite side by hydrolytic RNase subunits. Here, we report protein-protein interactions within the exosome, confirming the predictions of constituents of the RNase PH ring, and show some possible interaction interfaces between the other subunits. We also show evidence that Rrp40p can bind RNA in vitro, as predicted by sequence analysis.

Randomized trial of direct coronary angioplasty versus intravenous streptokinase in acute myocardial infarction.

OBJECTIVES: The objective of this study was to obtain preliminary data on the relative clinical utility of direct coronary angioplasty compared with that of intravenous thrombolytic therapy for patients with acute myocardial infarction. BACKGROUND: The relative merits of intravenous thrombolytic therapy and direct coronary angioplasty as treatment for acute myocardial infarction are incompletely understood, and randomized trials of these treatments have been extremely limited. METHODS: One hundred patients with ST segment elevation presenting to a single high volume interventional center within 6 h of the onset of chest pain were randomized to receive either streptokinase (1.2 million U intravenously over 1 h) or immediate catheterization and direct coronary angioplasty. Patients were excluded for age > or = 75 years, prior bypass surgery, Q wave infarction in the region of ischemia or excessive risk of bleeding. All patients were then treated with aspirin (325 mg orally/day) and heparin (1,000 U intravenously/h) for 48 h until catheterization was performed to determine the primary study end point, namely, infarct-related artery patency at 48 h. Secondary end points were in-hospital death, left ventricular ejection fraction at 48 h and time to treatment. RESULTS: There was no difference in the baseline characteristics of the two treatment groups. Overall patient age was 56 +/- 10 years, 83% of patients were male, 11% had prior infarction, 40% had anterior infarction and 97% were in Killip class I or II. Although time to treatment was delayed in the angioplasty group (238 +/- 112 vs. 179 +/- 98 min, p = 0.005), there was no difference in 48-h infarct-related artery patency or left ventricular ejection fraction (patency 74% vs. 80%; ejection fraction 59 +/- 13% vs. 57 +/- 13%; angioplasty vs. streptokinase, p = NS for both). There were no major bleeding events, and the mortality rate with angioplasty (6%) and streptokinase (2%) did not differ (p = NS). CONCLUSIONS: These results suggest that intravenous thrombolytic therapy might be preferred over coronary angioplasty for most patients because of the often shorter time to treatment.

[Early and late results of myocardial revascularization after coronary thrombolysis with intravenous streptokinase in the treatment of acute myocardial infarction]. / Resultados imediatos e tardios da revascularização cirúrgica do miocárdio pós-trombólise coronariana com estreptoquinase intravenosa no tratamento do infarto agudo do miocárdio.

PURPOSE: To study the early and late results of patients treated initially intravenous streptokinase and then with coronary artery bypass surgery. METHODS: One hundred and twenty one patients with acute myocardial infarction less than 6 hours duration were treated initially with intravenous streptokinase, and 1-38 days after (median 8.80 days) coronary artery bypass was undertaken. Ninety six patients were operated with extracorporeal circulation and 25 without it. RESULTS: Overall operative mortality was 3.30% (4/121). Reoperations due to bleeding was necessary in 3.30% (4/121). Late mortality was 5.40% with survival probability of 94.60% after 36 months and 92.30% after 70 months. Late morbidity events in terms of angina and cardiac insufficiency demonstrated that 7 patients had angina, 4 cardiac insufficiency and two angina and cardiac insufficiency; probability to be free from these events was 88.20% after 46 months and 66.40% after 70 months. CONCLUSION: Coronary artery bypass surgery after intravenous streptokinase can be undertaken with security and excellent early and late results.

[Thrombolysis in acute myocardial infarction. Streptokinase or r-TPA?]. / Trombólise no infarto agudo do miocárdio. Estreptoquinase ou r-TPA?

PURPOSE: To compare the results of intravenous thrombolytic therapy with streptokinase (SK), with those of the recombinant human tissue-type plasminogen activator (r-TPA), in acute myocardial infarction (AMI). MATERIAL AND METHODS: One hundred patients with AMI of less than 6 hours duration were randomized in two groups: 50 patients were allocated to 1.200.000 IU of SK (Group SK) and 50 patients received 100 mg of r-TPA over 180 minutes. The two groups were similar respecting age, sex, location and previous infarction. The angiographic study was performed 48 h after the thrombolytic therapy. RESULTS: In the angiographic study, 85% of the Group SK vs 66% of Group r-TPA had patient infarct-related vessel (p = 0.025). Reocclusion was 6.6% in Group SK vs 19% in Group r-TPA and hospital mortality was similar in the two groups. CONCLUSION: In the late angiographic evaluation (48 h), the frequency of coronary patency was found to be higher after intravenous SK than after intravenous r-TPA.

[Coronary angioplasty in elderly patients. A therapeutic option]. / Angioplastia coronariana em pacientes idosos. Uma opçáo terapêutica.

Of 304 consecutive percutaneous transluminal coronary angioplasties (PTCA) performed between March 86 and March 88, 61 patients were 65 years or older. The indications for PTCA were: stable angina, unstable angina and acute myocardial infarction with suitable anatomy. In elderly patients, the female sex, and the calcific deposits, were more frequent than in the younger group (p less than 0.0001). Primary success was achieved in 82%, vs 88% in patients younger than 65 years; complications and mortality were also statistically irrelevant between the two groups. Late clinical follow-up ranging from 3 to 36 months (mean 10) showed that symptomatic improvement was achieved in 86% of elderly patients in whom PTCA was successful (vs 80% in the younger group). These data support the safety and clinical effectiveness of PTCA in elderly symptomatic patients with suitable anatomy.

Surgical myocardial revascularization without using extracorporeal circulation in patients with acute myocardial infact treated previously with intravenous streptokinase

The utilization of thrombolytic agents during the first hours of acute myocardial infarct has been accepted as one of the main methods to limit infarct extension. However, persistence of residual stenosis requires a complementary revascularization method. Twenty-five patients with a diagnosis of acute myocardial infarct were successfully treated within six hours from onset of symptioms with intravenous streptokinase, followed 1 to 21 days (mean of 8 days) afterwards by surgical revascularization of the myocardium without extracorporeal circulation. The mean age of the group was 53.8 years and the mean ejection fraction 60 per cent; 10 patients were uniarterial, 14 biarterial and 1 triarterial; in 15 patients the infarct was located at the anterior wall and in 10 at the posterior wall. Eight patients received one bypass and 17, two. Our nosocomial mortality was 0 per cent and in none was there a need for reoperation due to bleeding. Surgical revascularization of the myocardium withou using extracorporeal circulation is thus a method that can be used in some patients with acute myocardial infarct with excellent results regarding morbidity and nosocomial mortality