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At least 757 records · Page 42Linked to original sources
PubMed1980

The synthesis and properties of 4,5-dioxovaleric acid, a possible intermediate in the biosynthesis of 5-aminolaevulinic acid, and its in vivo formation in Scenedesmus obliquus.

The formation of 5-aminolaevulinic acid for chlorophyll biosynthesis in the pigment mutant C-2A' of the unicellular green alga Scenedesmus obliquus occurs via two pathways: the first and major pathway uses glycine and succinyl-CoA as precursors and the second, the C-5 pathway, uses the intact five C-atom skeleton of either glutamate or 2-oxoglutarate. The intermediates in this latter pathway of 5-aminolaevulinic acid biosynthesis are still a matter of controversy and discussion but, in this paper, we have demonstrated in this Scenedesmus mutant that 4,5-dioxovaleric acid occurs in the cells when illuminated in the presence of laevulinic acid and the amount of 4,5-dioxovaleric acid formed is dependent on the period of illumination. In a preliminary experiment we have shown, under similar conditions, that labelled 4,5-dioxovaleric acid can be obtained from both DL-[1-(14)C]glutamate and [2-(14)C]glycine. This suggests that 4,5-dioxovaleric acid is formed enzymically from the intact five C-atom skeleton of glutamate but may also arise from the deamination of ALA formed by the condensation of succinyl-CoA and glycine by the 5-aminolaevulinic acid synthase pathway. To obtain positive identification the naturally occurring, and also the labelled, 4,5-dioxovaleric acid were isolated as the more stable benzoquinoxaline derivative by condensation with 2,3-diaminonaphthalene and identified by comparison with the benzoquinoxaline derivative of an authentic sample of 4,5-dioxovaleric acid prepared by the hydrogenation of the ozonide of benzylidene laevulinic acid. The structures of the authentic sample of 4,5-dioxovaleric acid and its benzoquinoxaline derivative were confirmed by NMR and mass spectroscopy and both were further characterized by TLC and by infrared, ultraviolet and fluorescence spectroscopy.

Aminolevulinic Acid↗
PubMed1989

The determination of chlorpromazine, related impurities and degradation products in pharmaceutical dosage forms.

The literature relating to the determination of chlorpromazine, related impurities and degradation products in pharmaceutical preparations is reviewed. Related impurities and degradation products are defined and official methods of analysis are described. Analytical methods including gravimetric, titrimetric ultraviolet-visible spectrophotometric, chromatographic and electrochemical techniques are discussed.

Chlorpromazine↗
PubMed2004

Effects of fiber-optic probe design and probe-to-target distance on diffuse reflectance measurements of turbid media: an experimental and computational study at 337 nm.

Fiber-optic probes are widely used in optical spectroscopy of biological tissues and other turbid media. Only limited information exists, however, on the ways in which the illumination-collection geometry and the overall probe design influence the interrogation of media. We have investigated both experimentally and computationally the effect of probe-to-target distance (PTD) on the diffuse reflectance collected from an isotropically (Lambertian) scattering target and an agar-based tissue phantom. Studies were conducted with three probes characterized by either common (single-fiber) or separate (two bifurcated multifiber probes) illumination and collection channels. This study demonstrates that PTD, probe design, and tissue scattering anisotropy influence the extent of the transport of light into the medium, the light-collection efficiency, and the sampling volume of collected light. The findings can be applied toward optimization of fiber-optic probe designs for quantitative optical spectroscopy of turbid media including biological tissues.

Computer Simulation↗