The Multifaceted Role of Methylaluminoxane in Metallocene-Based Olefin Polymerization Catalysis.

In single-site olefin polymerization catalysis, a large excess of cocatalyst is often required for the generation of highly active catalysts, but the reason for this is unclear. In this work, fundamental insight into the multifaceted role of cocatalyst methylaluminoxane (MAO) in the activation, deactivation, and stabilization of group 4 metallocenes in the immobilized single-site olefin polymerization catalyst was gained. Employing probe molecule FT-IR spectroscopy, it was found that weak Lewis acid sites, inherent to the silica-supported MAO cocatalyst, are the main responsible species for the genesis of active metallocenes for olefin polymerization.

100 mg acetylsalicylic acid acutely decreases red cell aggregation in women taking oral contraceptives.

Since oral contraceptives (OC) are known to impair blood fluidity and to increase the risk of venous and arterial thrombosis, while acetylsalicylic acid (ASA) decreases the thrombotic risk and modifies some rheologic parameters, we compared the hemorheologic effects of ASA on blood rheology between women treated by OC and women who never received this medication. 25 women under OC were compared to 25 matched women who had never used OC. Blood viscosity (MT90 viscometer) and RBC aggregation (Myrenne aggregometer and AFFIBIO erythroaggregometer) were measured before and 1 hr after women received per os 100 mg ASA, after an overnight fast.

Aggregability and disaggregability of erythrocytes in women suffering from ovarian cancer: evidence for an increased disaggregation threshold.

In order to further characterize the alterations of erythrocyte aggregation described in ovarian cancer, we measured it with laser backscattering in eleven women suffering from ovarian cancer (mean age: 44.7 +/- 3.6, extreme values: 28-61 yr) compared with thirteen matched control women.

Rheological properties of fetal red cells with special reference to aggregability and disaggregability analyzed by light transmission and laser backscattering techniques.

Blood viscosity factors and fetal erythrocyte aggregability were investigated with light transmission (Myrenne device) during a cross-sectional study of blood drawn in utero by cord venepunctures in 119 normal fetuses between 18 and 39 weeks gestation. There was a progressive increased blood viscosity at native hematocrit (p < 0.01) explained by a gradual increase in both hematocrit (from 33% to 40%, p < 0.

[Hemorrheological characteristics of fetal blood drawn in utero from the cord].

Extensive studies of hemorheology of cord blood (drawn just after delivery) have evidentiated a peculiar rheological pattern: less filterable red cells, reduced erythrocyte aggregation, lowered plasma viscosity. This pattern has been suggested to be important for maintaining a sufficient O2 supply to fetal tissues, by avoiding hyperviscosity despite increased RBC rigidity. However, cord blood at birth is not exactly fetal blood and we are not yet aware of studies of fetal blood drawn in utero several weeks before delivery.