Experiment 4: Titration Curve of Amino Acids
page 31 – 42
Simple amino acid Acidic amino acid Basic amino acid
7
OH- equivalents
In this experiment we will determine the titration curve for an amino acid and use this curve to estimate the pKa values of the ionizable groups of the amino acid and the amino acid\u2019s pI.
A titration curve of an amino acid is a plot of the pH of a weak acid against the degree of neutralization of the acid by standard (strong) base. Consider the ionization of a weak organic acid such as acetic acid by NaOH.
As more of the strong base (titrant) is added to the aqueous solution, more of the weak acid is converted to its conjugate base. During this process, a buffer system forms and the pH of the system will follow the Henderson-Hasselbalch relationship. The titration curve of the neutralization of acetic acid by NaOH will look like this:
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When a weak monoprotic acid is titrated by a base, a buffer system is formed. The pH of this system follows the Henderson-Hasselbalch equation:
This curve empirically defines several characteristics (the precise number of each characteristic depends on the nature of the acid being titrated): 1) the number of ionizing groups, 2) the pKa of the ionizing group(s), 3) the buffer region(s).
Based on the number of plateaus on a titration curve, one can determine the number of dissociable protons in a molecule. The one plateau observed when acetic acid is titrated indicates that it is a monoprotic acid (i.e., has only one dissociable H ). Many organic acids are polyprotic (have > one dissociable H ).
The protein building blocks, amino acids, are polyprotic and have the general structure
The majority of the standard amino acids are diprotic molecules since they have two dissociable protons: one on the alpha amino group and other on the alpha carboxy group. There is no dissociable proton in the R group. This type of amino acid is called a \u201csimple amino acid\u201d. A simple amino acid is electrically neutral under physiological conditions. NOTE: Under this definition it is possible to have a simple amino acid which is triprotic. Which of the 20 common
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or standard amino acids are simple<\/p>\n","protected":false},"excerpt":{"rendered":"
Experiment 4: Titration Curve of Amino Acids page 31 – 42 Simple amino acid Acidic amino acid Basic amino acid 7 OH- equivalents In this experiment we will determine the titration curve for an amino acid and use this curve to estimate the pKa values of the ionizable groups of the amino acid and the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[10],"class_list":["post-51874","post","type-post","status-publish","format-standard","hentry","category-research-paper-writing","tag-writing"],"_links":{"self":[{"href":"https:\/\/papersspot.com\/blog\/wp-json\/wp\/v2\/posts\/51874","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/papersspot.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/papersspot.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/papersspot.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/papersspot.com\/blog\/wp-json\/wp\/v2\/comments?post=51874"}],"version-history":[{"count":0,"href":"https:\/\/papersspot.com\/blog\/wp-json\/wp\/v2\/posts\/51874\/revisions"}],"wp:attachment":[{"href":"https:\/\/papersspot.com\/blog\/wp-json\/wp\/v2\/media?parent=51874"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/papersspot.com\/blog\/wp-json\/wp\/v2\/categories?post=51874"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/papersspot.com\/blog\/wp-json\/wp\/v2\/tags?post=51874"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}