The Role of Electron Transfer in the Fragmentation of Phenyl and Cyclohexyl Boronic Acids.

In this study, novel measurements of negative ion formation in neutral potassium-neutral boronic acid collisions are reported in electron transfer experiments. The fragmentation pattern of phenylboronic acid is comprehensively investigated for a wide range of collision energies, i.e., from 10 to 1000 eV in the laboratory frame, allowing some of the most relevant dissociation channels to be probed. These studies were performed in a crossed molecular beam set up using a potassium atom as an electron donor. The negative ions formed in the collision region were mass analysed with a reflectron time-of-flight mass spectrometer. In the unimolecular decomposition of the temporary negative ion, the two most relevant yields were assigned to BO- and BO2-. Moreover, the collision-induced reaction was shown to be selective, i.e., at energies below 100 eV, it mostly formed BO-, while at energies above 100 eV, it mostly formed BO2-. In order to further our knowledge on the complex internal reaction mechanisms underlying the influence of the hybridization state of the boron atom, cyclohexylboronic acid was also investigated in the same collision energy range, where the main dissociation channel yielded BO2-. The experimental results for phenyl boronic acid are supported by ab initio theoretical calculations of the lowest unoccupied molecular orbitals (LUMOs) accessed in the collision process.

Ion-Pair Formation in Neutral Potassium-Neutral Pyrimidine Collisions: Electron Transfer Experiments.

We report novel data on ion-pair formation in hyperthermal (30-800 eV) neutral potassium collisions with neutral pyrimidine (Pyr, C4H4N2) molecules. In this collision regime, negative ions formed by electron transfer from the alkali atom to the target molecule were time-of-flight mass analyzed and the fragmentation patterns and branching ratios have been obtained. The most abundant product anions have been assigned to CN- and C2H- and the electron transfer mechanisms are comprehensively discussed. Particular importance is also given to the efficient loss of integrity of the pyrimidine ring in the presence of an extra electron, which is in contrast to dissociative electron attachment experiments yielding the dehydrogenated parent anion. Theoretical calculations were performed for pyrimidine in the presence of a potassium atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process. In order to further our knowledge about the collision dynamics, potassium cation (K+) energy loss spectrum has been obtained and within this context, we also discuss the role of the accessible electronic states. A vertical electron affinity of (-5.69 ± 0.20) eV was obtained and may be assigned to a π 3 * (b 1) state that leads to CN- formation.

Evaluation of the in vitro antimicrobial activity of an ethanol extract of Brazilian classified propolis on strains of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is one of the most frequent causes of hospital acquired infections. With the increase in multiple drug resistant strains, natural products such as propolis are a stratagem for new product discovery. The aims of this study were: to determine the in vitro antimicrobial activity of an ethanol extract of propolis; to define the MIC50 and MIC90 (Minimal Inhibitory Concentration - MIC) against 210 strains of S. aureus; to characterize a crude sample of propolis and the respective ethanol extract as to the presence of predetermined chemical markers. The agar dilution method was used to define the MIC and the high performance liquid chromatography (HPLC) method was used to characterize the samples of propolis. MIC results ranged from 710 to 2,850 µg/mL. The MIC50 and MIC90 for the 210 strains as well as the individual analysis of American Type Culture Collection (ATCC) strains of Methicillin-susceptible Staphylococcus aureus (MSSA) and Methicillin-resistant Staphylococcus aureus (MRSA) were both 1,420 µg/mL. Based on the chromatographic analysis of the crude sample and ethanol extracted propolis, it was concluded that propolis was a mixture of the BRP (SP/MG) and BRP (PR) types. The results obtained confirm an antimicrobial activity in relation to the strains of the S. aureus tested.

Evaluation of the in vitro antimicrobial activity of an ethanol extract of Brazilian classified propolis on strains of Staphylococcus aureus.

Staphylococcus aureus (S. aureus) is one of the most frequent causes of hospital acquired infections. With the increase in multiple drug resistant strains, natural products such as propolis are a stratagem for new product discovery. The aims of this study were: to determine the in vitro antimicrobial activity of an ethanol extract of propolis; to define the MIC50 and MIC90 (Minimal Inhibitory Concentration - MIC) against 210 strains of S. aureus; to characterize a crude sample of propolis and the respective ethanol extract as to the presence of predetermined chemical markers. The agar dilution method was used to define the MIC and the high performance liquid chromatography (HPLC) method was used to characterize the samples of propolis. MIC results ranged from 710 to 2,850 µg/mL. The MIC50 and MIC90 for the 210 strains as well as the individual analysis of American Type Culture Collection (ATCC) strains of Methicillin-susceptible Staphylococcus aureus (MSSA) and Methicillin-resistant Staphylococcus aureus (MRSA) were both 1,420 µg/mL. Based on the chromatographic analysis of the crude sample and ethanol extracted propolis, it was concluded that propolis was a mixture of the BRP (SP/MG) and BRP (PR) types. The results obtained confirm an antimicrobial activity in relation to the strains of the S. aureus tested.