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Biomedical subjects

David M Lewis

Publications and source records attributed to David M Lewis.

11 recordsLinked to original sources
PubMed2006

Use of fourier transform infrared spectroscopy to follow the heterocumulene aided thermal dehydration of phthalic and naphthalic acids.

Fourier transform infrared (FT-IR) spectroscopy has been successfully employed to follow the formation of phthalic anhydride and 1,8-naphthalic anhydride on heating their corresponding acids. The effects of three heterocumulenes, cyanamide, dicyandiamide, and sodium cyanate, on the temperature of formation of the anhydrides were also investigated using this method. It was found that the carbodiimides cyanamide and dicyandiamide dramatically lowered the temperature at which thermal dehydration of the acid led to anhydride formation. It was noted that cyanamide had a stronger catalytic effect than dicyandiamide, presumably due to the electron-withdrawing effect of the amidine group. Sodium cyanate was also found to promote the thermal dehydration of the acids to form the corresponding anhydrides. Under more severe conditions, phthalic acid anhydride formed is seen to react further, leading to the formation of phthalimide. The discrepancy between the products obtained with cyanamide and sodium cyanate leads to the conclusion that, unlike earlier claims, imide formation is not due to the reaction of the anhydride with the urea formed but with sodium cyanate itself. However, only the phthalic anhydride five-membered ring system is sufficiently reactive towards the CNO- nucleophile to form the imide; the six-membered 1,8-naphthalic anhydride system does not react in this way.

Journal Article↗
PubMed2005

Micellar electrokinetic capillary chromatography analysis of phthalic acid isomers.

A capillary electrophoretic method for the analysis and separation of ortho- and para-phthalic acid isomers was developed. The best separation was achieved using micellar electrokinetic capillary chromatography (MECC) performed in a 110 mM borate buffer pH 8.3 also containing 40 mM sodium dodecyl sulfate (SDS) and 20% methanol. The effect of the addition of methanol, acetonitrile, and beta-cyclodextrin on the separation of the isomers was investigated. The buffer system developed was shown to provide a dependable method of analysis from which the concentration of each analyte could be reliably determined.

Chromatography, Liquid↗
PubMed2003

Caliber-persistent labial artery.

Caliber-persistent labial artery presents as a soft tissue elevation of labial mucosa that can be bluish or normal in color, disappears when stretched, and pulsates on gentle palpation. Often the artery can be visualized through the stretched mucosa. Such lesions occur in an elderly population (average age = 58 years), are equally distributed between males and females, and are twice as common in the upper lip than in the lower (Figs. 4 & 5). The occurrence of multiple lesions has been reported, along with increased incidence of other vascular lesions. The [figure: see text] lesions are usually asymptomatic with a few being associated with surface ulceration. When the lesion is clinically mistaken for a mucocele, fibroma [figure: see text] or other vascular lesion and biopsied, brisk bleeding is encountered.

Arteries↗
PubMed2003

Oral pathology.

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Adult↗