Biomedical subjects

T K With

Publications and source records attributed to T K With.

At least 37 records · Page 2Linked to original sources

PubMed1977

Molar absorption coefficients of porphyrin esters in chloroform determined by copper titration.

Chromatographically pure porphyrin esters free from metalloporphyrins were titrated with Cu2+ to determine the molar amount of porphyrin present. The end point of the titration was defined by a t.l.c. method detecting traces of metal-free porphyrin ester in admxture to its copper complex. From spectrometric measurement at the Soret maximum and the molar amounts found by the titration, epsilonM was calculated for proto-, copro-, penta-, hexa- and hepta-carboxylic and uro-porphyrin permethyl esters. The values for uroporphyrin showed perfect agreement with those of previous workers, whereas those for coproporphyrin were about 5% lower and those for protoporphyrin more than 20% lower. The implications of the findings are discussed. Determinations of epsilonM of some higher esters (ethyl to pentyl) and some partial methyl esters with one carboxyl group free are also presented.

Chloroform↗

PubMed1977

Determination of mass spectrometric sensitivity of different metalloporphyrin esters relative to porphyrin ester.

Quantitative determination of metalloporphyrin contamination in preparations of biologically important porphyrins was achieved mass spectrometrically by application of the integrated ion current technique. For this purpose, the relative molecular ion sensitivities of the contaminating metal complexes were determined from the ratios of the integrated molecular ion currents of a series of calibration samples containing a porphyrin ester and one of its metal complexes in known molar ratio. Complexes formed with divalent ions of Cu, Zn, Fe, Co and Ni of copro- as well as uro-porphyrin permethylester were all found to have the same molecular ion sensitivities as their metal-free porphyrin ester. The relative metalloporphyrin ester content in a sample of porphyrin ester was thus obtained directly as the integrated ion current ratios of the normalized molecular ions. The preparation of calibration samples, including complex formation and the mass spectrometric methodology, is described and discussed.

Chemical Phenomena↗

PubMed1977

Porphyrins in erythrocytes and blood plasma: preliminary studies with qualitative thin-layer chromatography.

1. A simple chromatographic method for the study of porphyrins in erythrocytes and blood plasma, requiring little technician time, is described. The findings in adults and neonates are presented as well as those from severely ill patients. 2. The regular occurrence of uro-, copro- and proto-porphyrin in erythrocytes is deomonstrable as well as sporadic occurrence of tri-, penta-, hexa- and hepta-carboxylic porphyrin. The method gives, however, irregular values for protoporphyrin, which seems to occur in a more labile form in some subjects than in others; this is especially the case in erythropoietic protoporphyria. 3. In blood plasma, uroporphyrin occurs regularly, and coproporphyrin less regularly. Protoporphyrin and penta- to hepta-carboxylic porphyrin are found only occasionally.

Adult↗

PubMed1976

Metalloporphyrin contaminations in purified porphyrin preparations as demonstrated by mass spectrometry.

Mass spectrometric studies were performed on selected specimens from my collection of over 700 crystalline porphyrin esters prepared over 20 years as well as on similar preparations from other laboratories. Mass spectrometry was performed by J Moller (Department of Chemistry, Odense University) and Elfinn Larsen (Department of Chemistry, The Experimental Division, Risoe, of the Danish Atomic Energy Commission). Nearly all typical crystalline porphyrins contained Cu- and Ni- and minor amounts of Zn- and Fe2-porphyrins, most often above one molar per cent, sometimes 5--10% and occasionally more, up to 35%. There was no close correlation between the metal content and the melting point. A method is proposed for preparation of metal-free ester preparations: Dissolution of either free or esterified porphyrin in conc. H2SO4; mixing of the solution with 19 volumes of methanol; after at least 12 hours adding of 2 vol. CHCl3 and 2 vol. H2O, and washing the CHCl3, phase with 1/2 vol. distilled water until washwater becomes neutral (8--10 times). Preparations made in this way showed below 0.5% metalloporphyrin contamination. The method does not work with protoporphyrin, which is oxidized by conc. H2SO4. The acid extraction leaves some porphyrin partially esterified, which can be removed by preparative TLC. A TLC-method for detection of metalloporphyrin in porphyrin esters is described.

Coproporphyrins↗

PubMed1975

Decarboxylation of uroporphyrin by heating at atmospheric pressure.

Free uroporphyrin is decarboxylated by heating in the air to 150--200 degrees C. Complete decarboxylation occurs after heating to 200 degrees C for 5 min, with a yield of 66--75%. Heptacarboxylic porphyrin can be prepared with a yield of 40% by heating uroporphyrin to 150 degrees C for 60 min, and hexacarboxylic porphyrin with a yield of about 20% by heating to 150 degrees C for 2h.

Atmospheric Pressure↗

PubMed1975