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Quenched-flow data for propene polymerization with rac-Me2Si(2-Me-4-Ph-1-indenyl)2ZrCl2/MAO support a picture where removal of MAO qualitatively changes the kinetic profile from a mainly enthalpic to a mainly entropic barrier. DFT studies suggest that a not previously recognized singly-bridged end-on coordination mode of Me6Al2 to catalytically active centers may be kinetically relevant as a resting state. In contrast, the more traditional doubly-bridged complex of Me3Al is proposed to be more relevant to chain transfer to cocatalyst. [ABSTRACT FROM AUTHOR]

Despite decades of thorough mechanistic investigations, it is still hard to predict the activity of a novel olefin polymerisation catalyst, even when the precursor is a well-defined molecular entity. In the present study, we highlight the crucial importance of activation entropy on the polymerisation rate and how weak interactions of the catalytic species with electron donating species in the reaction pool can ultimately lower the activation free energy. [ABSTRACT FROM AUTHOR]

Introduction: Patients with heart failure frequently develop renal failure, which increases the mortality rate among patients undergoing cardiac transplantation.Purpose: To determine whether preoperative renal function influenced postoperative mortality in cardiac transplantation recipients.Materials and methods: The measurements of plasma urea, plasma creatinine, and 24-hour creatinine clearance in patients who underwent cardiac transplantation were correlated with mortality at 30, 90, and 365 days after the procedure, using Student t test for continuous variables and the chi-square test for categorical variables.Results: All variables correlated with mortality, particularly plasma creatinine at 30, 90, and 365 days (P = .029, .003, and .0029, respectively).Conclusion: Preoperative renal failure is a mortality indicator in cardiac transplantation recipients. [Copyright &y& Elsevier]

Klebsiella pneumoniae carbapenemase ( KPC)-producing K. pneumoniae is spreading globally and represents a challenge in infection control and treatment. Solid organ transplant ( SOT) recipients are especially at risk for infection by multidrug-resistant bacteria, and little is known about infection with KPC-producing organisms in this setting. The aim of this study was to describe the clinical and microbiologic aspects of KPC-producing K. pneumoniae infections in SOT recipients. A KPC-2-producing K. pneumoniae outbreak was identified in a public teaching tertiary care hospital in São Paulo, Brazil, in June 2009. During the outbreak, cases of KPC-2-producing K. pneumoniae infection in SOT recipients occurred between July 2009 and February 2010; these cases were retrospectively reviewed. Overall, 12 episodes of infection with KPC-producing K. pneumoniae occurred in 2 heart, 4 liver, and 6 kidney transplant recipients with incidence rates of 16.7%, 12.9%, and 26.3% in heart, liver, and kidney transplantation, respectively. Infection occurred at a median time of 20 days after transplantation. Primary infection sites were as follows: 4 urinary tract infections, 4 bloodstream infections, 2 pneumonias, and 2 surgical site infections. All patients except one had received antibiotics in the last 30 days, mostly piperacillin-tazobactam or glycopeptides. All strains exhibited susceptibility to amikacin and gentamicin. Patients were treated with tigecycline plus polymyxin B (3 cases), polymyxin B plus carbapenem (3 cases), polymyxin B alone (3 cases), or tigecycline plus imipenem (1 case). In 2 cases, patients received only carbapenem, and death occurred before the final culture result. The overall 30-day mortality rate was 42%. In this series of KPC-producing K. pneumoniae infection in SOT recipients, the infection occurrence was high during an institutional outbreak and was potentially life threatening. [ABSTRACT FROM AUTHOR]