Tryptophan

Tryptophan is an essential amino acid used by the human body. It is abreviated W or Trp and has an IUPAC name of (2S)-2-amino-3-(1H-indol-3-yl)propanoic acid. There are two sterioisomers of tryptophan, the L and D sterioisomers, but only the L is found in the human body system, the D is only found in naturally produced peptides. Its structure is represented below.

Tryptophan has a amine group, a caboxylic acid and a indole functional group. The pKa values for each functional group are as follows:

carboxyl - 2.39

Amino - 9.39

indole - 16.2

isoelectric point - pH- 5.89

The indole ring, located on the beta carbon, is the most significant, have the capability to hyrdrogen bond donate and thus the nitrogen is often in contact with solution. Tryptophan is used as a precurser for the neurotransmiter serotonin and the vitamin niacin. The group of peptides known as cystine peptides contain tryptophan.

Electrophilic Aromatic Substitution Journal

This weeks blog assignment was to locate a peer reviewed journal article containing an electrophilic aromatic substitution reaction. It was difficult to find an article outside of the CU database, but I was able to have some luck. The article that I chose contained not just one, but many simple EAS reactions. The article, Average Local Ionization Energies on the Molecular Surface of Aromatic Systems As Guides to Chemical Reactivity, published by Per Sjoberg, compares the reactivites of various electrophiles on benzene, to form many derivatives.The results were compared in a table showing the relationship between each compound and the various energies released during the formation of each compound.The relative reactivity with an electrophile is determined in this experiment by the strenght of the l(r) value. The lower ethe l(r) value, the more reactive the substance will be with the electrophile.

 The article analyzes benzene derivatives such as toluene, aneline, benzoic acid, and 1-florobenzene and determines the relative reactivity of the electrophile in each compound (CH3, NH2, F. COH...) The tendencies of each electrophile are analyzed and recorded. I found this article particularly interesting, it was simple to understand at an undergraduate level, yet still was able to provide new, valuable information. Posted is a link to the article.

http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?issn=1480-3291&volume=68&issue=8&startPage=1440

Source:

SjobergLast, Per. "Average Local Ionization energies on the molecular surface of aromatic systems as guides to chemical reactivity." Can J. Chem. 68. (1990): 1440-44. Print