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Biomedical subjects

T W Chan

Publications and source records attributed to T W Chan.

42 records · Page 3Linked to original sources
PubMed1977

Chemiluminescent reactions and electrophilic oxygen donating ability of 4a-hydroperoxyflavins: general synthetic method for the preparation of N5-alkyl-1,5-dihydroflavins.

The synthesis of N5-methyl- and N5-ethyl-1,5-dihydroflavin mononucleotides is reported. These compounds show no bioluminescence activity with bacterial luciferase. This feature is interpreted in terms of steric hindrance between the N5-alkyl group and a hydrogen bonding group at the active site of the luciferase. The chemiluminescence observed on reaction of N5-alkyl-1,5-dihydroflavins with oxygen and aldehydes has been shown to occur via formation of a mixed peroxide of flavin and aldehyde and to be associated with a primary deuterium isotope effect when [1-2H]aldehyde is substituted for aldehyde. The time course for light emission has been compared for aldehyde and ketone substrates. The suggestion is entertained that the peroxide bond of 4a-hydroperoxyflavin is sufficiently polarized to allow this species to act as the oxidant per se at the active site of mixed function oxidases. The second-order rate constants for reaction of hydroperoxides with thioxane and I- are compared. 4a-Hydroperoxy-3,5-dimethyllumiflavin is shown to convert thioxane to its sulfoxide 1.8 X 10(5) times faster than t-butyl hydroperoxide.

Chemical Phenomena↗
PubMedDate not supplied

Prostate and seminal vesicles after irradiation: MR appearance.

Familiarity with the morphologic changes in the prostate and seminal vesicles (SV) after pelvic irradiation is important to the correct interpretation of follow-up magnetic resonance (MR) studies. A retrospective study of 38 patients with prostatic or other pelvic tumors treated with radiation showed that 31.6% had a normal prostatic zonal pattern (peripheral zone hyperintense to central gland) on T2-weighted images, and 7.9% showed reversal of the zonal pattern; among the rest, the entire gland was diffusely isointense to fat in 42.1%, hypointense to fat in 10.5%, and hyperintense to fat in 7.9%. Sixty-three percent of the SV had a normal appearance, 21% had fewer tubules but normal signal intensity (SI), 8% had diffuse loss of SI (hypointense to fat), and 8% were hypointense to muscle. Quantitative measurements of SI of the prostate and SV demonstrated a statistically significant lower mean value for the irradiated patients relative to 10 control patients. A decrease in the size of both the prostate and SV was observed in 33% of patients with baseline studies. Use of additional treatment modalities in patients with prostatic carcinoma appeared to correlate with increased likelihood of developing abnormal changes. The authors conclude that in the irradiated patient, the prostate and SV can develop several patterns of SI abnormalities; in particular, diffuse low SI in the prostate and SV should establish radiation fibrosis as an important differential diagnosis to consider.

Adult↗