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Information about AA titration curves
- # stages = # deprotonations
- low pH = fully protonated
- at midpoint [HA]=[A-] and pH = pKa *known value
- curve implies multiple point of buffer power
- pI (isoelectric point): pH when net charge = 0 (halfway between +1,0 pka values)
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Process for performing a peptide titration curves
- AA are joined by amide bonds
- Look to see if any AA have ionizable side chain (pKr)
- Assuming a 3 AA peptide.... (I, II, III)
- 1) determine the equivalent OH- portions in NaOH
- 2) plot the known values
- 0.5 Eq OH- = pKa1
- 1.5 Eq OH- = pKr
- 2.5 Eq OH- = pKa2
- 3) determine the endpoints by averaging the known pKa values for 1 Eq OH- and 2 Eq OH-
- 4) determine the initial pH by using a RICE table with the pKa converted to Ka
- 5) determine the final pH by using
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Separate the amino acids by side chain characteristics
- Nonpolar, aliphatic: glycine, alanine, proline, valine, leucine, isoleucine, methionine
- Aromatic: Phenylalanine, tyrosine, tryptophan
- Polar, uncharged: serine, threonine, cysteine, asparagine, glutamine
- Positively charged: Lysine, histidine, arginine
- Negatively charged: aspartate, glutamate
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