How to memorize the formulas of thioglycosides
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How to remember the formulas of thioglycosides?
Thioglycosides – compounds that contain sulfur – are a complex of substances from the mustard plant Brassica juncea Czern., black mustard Brassica nigra (L.) Koch., and some other plants from the Brassicaceae family.
Sinigrin is a thioglycoside of mustard that, under the action of the enzyme myrosinase, decomposes into allyl thiocyanate or allyl isothiocyanate depending on external conditions.
You can easily remember the formula of sinigrin if you learn that at the beginning of the molecule it has 3 carbon atoms, which are only bonded to hydrogen, followed by a carbon from which branches extend: the upper branch: =N–O–SO3K (read in Russian – “nosok”), and the lower one: –S–C6H11O5 (Glu = glucose, meaning sinigrin is a glycoside).
In an aqueous environment at a temperature of 50–60оC, the enzyme myrosinase, which specifically cleaves sinigrin, converts it into allyl isothiocyanate, the formula of which starts with S=C=N–. This is a volatile component of mustard essential oil. It is allyl isothiocyanate that penetrates through the pores into our body when we use mustard plasters, and it is this compound that exerts antibiotic action.
When stored in the cold, myrosinase cleaves sinigrin into allyl thiocyanate (did you guess that this is an isomer of allyl isothiocyanate?), which has the same molecular formula as allyl isothiocyanate but differs from it in the position of the S=C=N– group. In allyl thiocyanate, –S–C=N completes the formula. Allyl thiocyanate is a non-volatile component and cannot easily penetrate through human skin pores.
What should we take away from all of the above? The action of mustard plasters is due to allyl isothiocyanate and some other isothiocyanates. When stored, sinigrin, which is the source of allyl isothiocyanate, decomposes into allyl thiocyanate, which does not exert the necessary antibiotic action, so it is important to consider the shelf life of mustard plasters when using them.