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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Problem of the Week Archive => Topic started by: Borek on April 15, 2013, 12:01:48 PM

Title: Problem of the week - 15/04/2013
Post by: Borek on April 15, 2013, 12:01:48 PM
Naturally occurring aminoacid A enzymatically decomposes to biologically active compound B. During the reaction side chain of the aminoacid doesn't change. When 31.0 mg (0.2 mmol) of the aminoacid was burnt, products contained 52.8 mg of CO2 and 16.2 mg H2O and no traces of sulfur were detected. During analysis the substance B 1 mmol (111 mg) sample produced 33.6 mL of dry nitrogen, 220 mg of CO2 and 81 mg of H2O. Identify A and B and explain what is the enzymatic reaction.
Title: Re: Problem of the week - 15/04/2013
Post by: delta609 on April 21, 2013, 12:40:12 PM
L-Histidine (A) decompsoing into Histamine (B).  I believe this reaction explains the inflammatory response we receive in our mucas membranes during allergy season. 
Title: Re: Problem of the week - 15/04/2013
Post by: Sunil Simha on April 22, 2013, 08:37:52 AM
A is Histidine because it is the  sole amino-acid which contains no sulfur and 6 carbon and 9 hydrogen atoms.
B is C5H9N3. It appears as though the enzymatic process is de-carboxylation of Histidine to form histamine.
Title: Re: Problem of the week - 15/04/2013
Post by: Borek on April 22, 2013, 06:22:12 PM
Yes, these were both the right answers (although only the second one mentioned it is decarboxylation).
Title: Re: Problem of the week - 15/04/2013
Post by: Big-Daddy on April 24, 2013, 01:45:50 PM
How did you work out the moles of N2 gas produced by the reaction, given the volume is 33.6 cm3? Don't we need the molar volume or mass?
Title: Re: Problem of the week - 15/04/2013
Post by: Borek on April 24, 2013, 02:01:41 PM
Quote from: Big-Daddy on April 24, 2013, 01:45:50 PM
How did you work out the moles of N2 gas produced by the reaction, given the volume is 33.6 cm3? Don't we need the molar volume or mass?

If no other information is given you should assume STP.
Title: Re: Problem of the week - 15/04/2013
Post by: Big-Daddy on April 24, 2013, 02:05:03 PM
Quote from: Borek on April 24, 2013, 02:01:41 PM
Quote from: Big-Daddy on April 24, 2013, 01:45:50 PM
How did you work out the moles of N2 gas produced by the reaction, given the volume is 33.6 cm3? Don't we need the molar volume or mass?

If no other information is given you should assume STP.

If Vm=24 dm3mol-1 then I got the answers as above, except with the moles of N in the formula for B being 2.8. I wasn't too sure I could round this up to 3, so I thought I might have made a mistake.

Anyway thanks, good practice for combustion analysis.