The performance of the B3LYP density functional theory
calculations has been studied for the epoxidation
reactions of ethylene, propene, and cis- and
trans-2-butene with peroxyformic acid and of ethylene
with
dioxirane and dimethyldioxirane. The transition structures for the
epoxidation of ethylene and propene with
peroxyformic acid and of ethylene with dioxirane and dimethyldioxirane
calculated at the B3LYP level as
well as at the QCISD and CCSD levels are symmetrical with nearly
identical C−O bond distances, whereas
the MP2 calculations favor unsymmetrical transition structures.
The geometrical parameters of the transition
structures calculated using the B3LYP functional are close to those
found at the QCISD and CCSD levels.
While the activation barriers for the epoxidation reactions
calculated at the B3LYP/6-31G* and B3LYP/6-31+G* levels are very close to the MP4SDTQ/6-31G*//MP2/6-31G* and
MP2/6-31G*//MP2/6-31G* values,
these activation energies are systematically lower (up to 5−6
kcal/mol) than the barrier heights calculated at
such higher correlated levels as the
QCISD(T)/6-31G*//QCISD/6-31G*,
CCSD(T)/6-31G*//CCSD/6-31G*,
and BD(T)/6-31G*//QCISD/6-31G*. The calculations on the
epoxidation reactions of ethylene and propene
with peroxyformic acid using the BH&HLYP functional also lead to
symmetrical transition structures, but
the calculated barriers are overestimated when compared with the
QCISD(T) results. The activation barriers
calculated for these epoxidation reactions at the
QCISD(T)/6-31G*//B3LYP/6-31G* level are very close to
those computed at the QCISD(T)/6-31G*//QCISD/6-31G*
level.
The hitherto unknown 3-nitrobenzothiazolo-and 3-nitrobenzoxazolo[3,2-a] quinolinium salts were synthesized via the photochemically induced cyclization of the corresponding 2-(2-chloro-5-nitrostyryl)benzothiazole and 2-(2chloro-5-nitrostyry1)benzoxazole. Results on their cytotoxic and antitumor activity are presented.The benzo[c]phenanthridine alkaloids fagaronine ( la)2and nitidine (lb)3 represent a class of compounds isolated from the Rutaceae family that show potent antitumor activity against L1210 and P-388 murine leukemias.Coralyne (2) ,* a berbenium alkaloid structurally related to the benzo[c]phenantridines, exhibits antitumor activity against both tumor screens. Studies on the mechanism of action of fagaronine and nitidine indicate that both alkaloids inhibit DNA synthesis probably by interacting with A-T base pairs.5 Derivatives of these compounds have been synthesized in order to study the structureactivity relationships and showed that the positively charged nitrogen atom is necessary for their reported antitumor activity.6-10 +University of Puerto Rico, Rio Piedras Campus.
Consumption of Arrabidaea bilabiata fresh leaves produces a paraplegic syndrome in cattle. For isolation of the active principle, isopropanol and methanol extracts were prepared from the aerial parts of the plant; these were administered to Sprague-Dawley rats at doses of 0.5, 1, and 2 mg/kg, orally, to determine the presence of substances affecting spontaneous motor activity. The isopropanol extract produced significant increases of long-pause and short-pause movements (112 and 54%, respectively). The methanol extract tended to increase motor activity, but the effect did not reach statistical significance. Chemical and spectroscopic analysis of the isopropanol extract showed allantoin was the major constituent. It was administered to rats, at doses of 1.2, 12, and 120 mg/kg. A complex dose-response curve was observed, but at the highest dose, there was a 52% increase in the number of long-pause movements. It was inferred that allantoin and the constituents of the alcholic extracts might not be responsible for the paraplegic synndrome in cattle. The alteration of cattle motor activity could be caused by other non-alcoholic constituents. Additionally, extracts were assayed for in vitro activity against Escherichia coli , Klebsiella pneumonae , Pseudomonas aeruginosa , Staphylococcus aureus , Bacillus sp. and Candida albicans . All microbial strains were found to be resistant to the extracts with the exception of C. albicans , suggesting a possible antifungal activity.
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