what governs the distribution of the solutes between the aqueous phase and the organic phase?
their relative solubilities
How can one ascertain whether a layer is the organic phase or the aqueous phase?
Add a drop of the mystery layer to 2 mL H2O.
-drop dissolves = aqueous phase.
-drop does not dissolve = organic phase
Why must extraction mixtures be vented?
Since most organic solvents are quite volatile they evaporate easily - this generates pressure inside the separatory funnel.
What three advantages are associated with the thin-layer chromatographic technique?
1. very small sample quantities are required
2. experiment is performed easily and rapidly
3. good resolution is usually obtained
What two limitations are associated with gas-liquid chromatography?
1. analysis is limited to small amounts of sample
2. samples must consist of reasonably volatile compounds
What are the six basic parts of a gas-liquid chromatograph?
1. source of high pressure pure carrier gas
2. gas flow controller
3. heated injection port
4. column and column oven
5. detector
6. recording device or data station
What three pieces of information are provided in the data table of a gas chromatogram?
1. peak retention times
2. peak areas
3. percent compositions
What must be available in order for GC analysis to permit compound identification?
authentic samples of the various components in the mixture being analyzed
What are the six items that must be determined in order to establish the sequence of a peptide (or protein)?
1. cleave all disulfide bridges and alkylate the resulting thiol groups
2. determine the constituent amino acids, both in kind and number
3. identify the N-terminal a.a.
4. identify the C-terminal a.a.
5. fragmentation through partial hydrolysis
6. identi
What conditions are employed to "completely" hydrolyze a peptide?
Digest peptide in 6M HCl at 100C for 24 hours. all amide bonds are cleaved.
An enzyme that catalyzes the hydrolysis of a peptide bond at the end of the peptide chain is called?
exopeptidase
What is the stationary phase in TLC?
a solid such as silica gel or aluminum oxide
what is the mobile phase in TLC
a liquid solvent
what types of compounds move up the TLC plate at the slowest rate?
polar compounds
what would you expect to have the shorter retention time, chemicals with higher or lower boiling point?
chemicals with relatively lower boiling point will have the shorter retention time
what mobile phase was used during our GC analysis of the butene products from units 9 and 10?
helium gas
what amino acid would have the smaller TLC Rf value?
the one with the more polar side chain would have the smaller Rf value
what is pKa
an index that expresses the acidity of weak acids
what is pI?
isoelectric point, the pH at which the amino acid has no net charge
what if pH = pI
net charge on a.a. is zero
what if pH is less than pI
then net charge on a.a. becomes more positive
what if pH is more than pI
net charge on amino acid becomes more negative