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PYRROLE DERIVATIVES. 299
answered; still there does not seem to be any doubt that there exists
an isophonopyrrolcarboxylic acid, which can be obtained from the blood
as from the bile pigments. From the mixture of acid cleavage products
obtained by the reduction of haemin with hydriodic acid, and glacial acetic
acid Piloty and Dormann 1
have obtained as well characterized prod-
ucts, phonopyrrolcarboxylic acid and isophonopyrrolcarboxylic acid and
also xarithopyrrolcarboxylic acid, C10H15NO2 and they consider the
existence of this acid as positively proved. The melting-point of the
crystalline acid was 108°, the picrate 143°, and the oxime 208°. The
corresponding values for isophonopyrrolcarboxylic acid was 122°, 146°
and 210° respectively. An isomeric xanthopyrrolcarboxylic acid, called
D-phonopyrrolcarboxylic acid, seems also to occur.
It is extremely difficult to correlate the somewhat contradictory
statements of the various authors in this subject and to draw quite
positive conclusions from these statements. It is nevertheless positive
that from the haemopyrrol mixture the three pyrrols, cryptopyrrol,
isohaemopyrrol and phyllopyrrol can be obtained and also that there
are two haemopyrrolcarboxylic acids (phonopyrrol- and isophonopyrrol-
carboxylic acids), of which one possibly is related to the crypto-
pyrrol and the other to the isohaemopyrrol. On account of the uncer-
tainty of the experimental foundation it is difficult to enter into a
discussion of the variously proposed hypothetical constitutional formulae
for the derivatives of the blood pigments. The same is true for the
disputed question as to the form of binding of the iron in haematin and
in hsemin. It is generally admitted that the iron here is trivalent. The
views are different in regard to the valence of the iron in haemoglobin,
namely, Maxchot considers that haemoglobin is a ferric combination
while Kuster 2
on the contrary considers it a ferrous combination.
Haematoporphyrin gives with hydrochloric acid a compound which
crystallizes in long brownish-red needles. If the solution in hydrochloric
acid is nearly neutralized with caustic soda and then treated with sodium
acetate, the pigment separates out as amorphous, brown flakes not
readily soluble in amyl alcohol, ether, or chloroform, but readily soluble
in ethyl alcohol, alkalies, and dilute mineral acids. The compound
with sodium crystallizes as small tufts of brown crystals and several
other salts of haematoporphyrin are known such as the methyl and ethyl
esters. The acid alcoholic solutions have a beautiful purple color,
which become violet-blue on the addition of large quantities of acid.
The alkaline solution has a beautiful red color, especially when too much
alkali is not present.
1
Piloty and Dormann, Ber. d. d. chem. Gesellsch., 46.
2
Manchot, Zeitschr. f. physiol. Chem., 70; Kuster, ibid., 71.
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