The reaction of protonated methionine with the lowest electronically excited state of molecular oxygen O(2)(a(1)Δ(g)) was studied in a guided ion beam apparatus, including the measurement of reaction cross sections over a center-of-mass collision energy (E(col)) range of 0.1-2.0 eV. A series of electronic structure and RRKM calculations were used to examine the properties of various complexes and transition states that might be important along the reaction coordinate. Only one product channel is observed, corresponding to generation of hydrogen peroxide via transfer of two hydrogen atoms (H2T) from protonated methionine to singlet oxygen. At low collision energies, the reaction approaches the collision limit and may be mediated by intermediate complexes. The reaction shows strong inhibition by collision energy, and becomes negligible at E(col) > 1.25 eV. A large set of quasi-classical direct dynamics trajectory simulations were calculated at the B3LYP/6-21G level of theory. Trajectories reproduced experimental results and provided insight into the mechanistic origin of the H2T reaction, how the reaction probability varies with impact parameter, and the suppressing effect of collision energy. Analysis of the trajectories shows that at E(col) = 1.0 eV the reaction is mediated by a precursor and/or hydroperoxide complex, and is sharply orientation-dependent. Only 20% of collisions have favorable reactant orientations at the collision point, and of those, less than half form precursor and hydroperoxide complexes which eventually lead to reaction. The narrow range of reactive collision orientations, together with physical quenching of (1)O(2) via intersystem crossing between singlet and triplet electronic states, may account for the low reaction efficiency observed at high E(col).
T he primary purpose of intraoperative pathologist consultation (IC) is to guide immediate surgical management;1 ICs can provide surgeons with important information that may be used to modify or even terminate a surgical procedure. Frozen sections performed during ICs can also be used Background: Correlation of intraoperative frozen section diagnosis with final diagnosis can be an important component of an institution's quality assurance process. Methods:We performed a quality assurance review of 1207 frozen section diagnoses from 812 surgical cases performed in the Hamilton Regional Laboratory Medicine Programme during a 6-month period in 2007. We reviewed the frozen section and permanent slides from all potentially discordant cases using a multiheaded microscope to arrive at a consensus pertaining to the type and reason for error. We reviewed the clinical record to determine whether there had been a potential adverse impact on immediate clinical management.Results: Frozen sections were most commonly requested for head and neck, nervous system and female genital tract specimens. Twenty-eight frozen sections (3%) were deferred. We identified 24 discordant diagnoses involving 3% of cases and 2% of specimens. The organ systems showing the greatest frequency of discordance relative to the total number from that system were the nervous system, head and neck, and the lungs. Of the errors identified, most occurred owing to diagnostic misinterpretation, followed by problems related to tissue sampling. There was a potential adverse impact on immediate clinical management in 14 cases.
Context: Preeclampsia is regarded as a risk factor in pregnancy and it leads to placental insufficiency. This, in turn causes both maternal and fetal morbidity and mortality. The present study intends to compare the morphological changes of placenta in preeclampsia with that of normal placenta. Study design: A descriptive type of study. Place and period of study: Department of Anatomy, Dhaka Medical College, Dhaka, from August 2005 to June 2006. Materials: 60 human placentae, 30 were from normal pregnant women as control and 30 from pregnancies complicated by preeclampsia were taken for this study. Method: Samples were grouped as Group A and Group B on the basis of presence or absence of preeclampsia. All samples were studied morphologically. Result: Different shapes of placenta were found with some having accessory lobes in both groups. There was significant reduction (p< 0.001) in diameter and volume of placenta in Group B. The thickness of placenta was reduced in Group B but the difference did not reach a significant level. The number of cotyledon was significantly reduced in Group B (p<0.05). Conclusion: In this study, it was found that the preeclamptic placentae underwent definite morphological changes. These changes seemed to be the result of insufficiency of placenta in preeclampsia. However, further histological and morphometric placental study in a larger sample has to be conducted to come up with a conclusive decision. Key Words: Placenta, Preeclampsia, Morphology. doi: 10.3329/bja.v7i1.3026 Bangladesh Journal of Anatomy January 2009, Vol. 7 No. 1 pp. 49-54
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