Page 321 - Pharmacognosy 2 PG303

Pharmacognosy-2 (PG303) Level 2 Clinical Pharmacy-Pharm D

of ammonium hydroxide; a rose-red color is produced in the ammoniacal layer
with Curaçao, and Socotrine but not with Zanzibar and Cape Aloes.
3- Test for barbaloin (bromine water test): To 1 ml of the filtrate, add 1 ml of
bromine T.S.; a copious pale yellow precipitate is formed.
4- Nitric acid test: Mix 2.5 ml of the filtrate with 1 ml of nitric acid, a yellow-
brown color, passing rapidly to vivid green is produced with Cape Aloes, a deep
brownish-red color with Curaçao Aloes, and a yellowish-brown color with
Socotrine and Zanzibar Aloes.
5- Test for isobarbaloin (Cupraloin test, Klungs reaction): Dilute 2 ml of the
filtrate to 10 ml with water, add a drop of copper sulphate T.S., warm, and add
about 0.5 ml of sodium chloride T.S., and then about 1 ml of alcohol 90 %; a
deep wine-red color is produced with Curaçao Aloes and an evanescent pale
wine-red color with Cape Aloes. The test is negative with Socotrine and
Zanzibar Aloes.
6- Histed’s test: Transfer 5 drops of a solution of Aloes (1/100) to a porcelain dish
and add 1 ml of sulphuric acid, followed by a drop of fuming nitric acid; no green
color is produced (c.f. Natal Aloes).

Note
Natal Aloe is a substitute of the official aloes. It is obtained from Aloe
cadelabrum. It contains nataloin, homonataloin and resin. It can be characterized
from the official aloes by Histed’s test.

Constituents
The principal constituent of all the foregoing varieties of Aloes is the pale
yellow crystalline anthraquinone glycoside, barbaloin (aloin, C-glycoside).

In Curaçao Aloes the barbaloin is accompanied by isobarbaloin, a crystalline
isomer of barbaloin. Socotrine and Zanzibar Aloes contain no isobarbaloin, and
Cape Aloes traces only. The crystalline aloin is accompanied by an amorphous aloin
(β-barbaloin) which is isomeric with barbaloin. β-barbaloin is particularly abundant
in Cape Aloes. Other constituents of Aloes are resin and aloe-emodin (hydrolytic
decomposition product of barbaloin).

Uses
All the varieties of Aloes have a powerful purgative action., all of them acting
with remarkable slowness. Aloes is one of the most valuable purgatives in certain
forms of constipation, as it improves the digestion and does not lose in activity by
repetition.

The fresh mucilagenous gel of Aloe vera leaves has been used for years in the
treatment of burns, abrasions, and other skin irritations. Recently, the gel has been
advocated for its moisturising and emolient effects.

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