September 3, 2014
Hydrophobic Amino Acid Titration: Phenylalanine
A solution of phenylalanine was titrated with 0.1575 M NaOH titrant in order to produce a characteristic titration curve for phenylalanine.
- 0.5199 g of solid phenylalanine was dissolved in 20 mL of 21 mM HCl and 20 mL of H20 [Trial 1]
- 0.5200 g of solid phenylalanine was dissolved in 20 mL of 21 mM HCl and 20 mL of H20 [Trial 2]
- the amount of solvent was doubled because Phe is very hydrophobic and was resisting solvation
A pH probe was calibrated and used to track the change in pH as additional amounts of 0.1575 M NaOH were added over time.
- two trials were done, with respective data presented below
- trial 1 following a basic schematic of 5 mL increments, followed by a more thorough 2nd trial guided by the data demonstrated in trial 1
- a pH curve was constructed from the data points in each trial
| Trial
|
NaOH added (mL)
|
pH
|
| 1
|
0.00
|
3.027
|
| 1
|
5.00
|
8.494
|
| 1
|
10.00
|
9.147
|
| 1
|
15.00
|
9.618
|
| 1
|
20.00
|
10.267
|
| Trial
|
NaOH added (mL)
|
pH
|
| 2
|
0.00
|
3.016
|
| 2
|
0.50
|
3.127
|
| 2
|
1.00
|
3.259
|
| 2
|
1.50
|
3.458
|
| 2
|
2.00
|
3.798
|
| 2
|
2.50
|
5.648
|
| 2
|
3.00
|
7.666
|
| 2
|
3.50
|
8.035
|
| 2
|
4.00
|
8.212
|
| 2
|
4.50
|
8.349
|
| 2
|
5.00
|
8.468
|
| 2
|
10.00
|
9.125
|
| 2
|
15.00
|
9.584
|
| 2
|
20.00
|
10.272
|
Positively Charged Amino Acid Titration: Arginine
A solution of arginine was titrated with 0.1575 M NaOH titrant in order to produce a characteristic titration curve for arginine.
- 0.5435 g of solid chlorinated arginine was dissolved in 10 mL of 21 mM HCl and 10 mL of H20 [Trial 1]
- 0.5485 g of solid non-chlorinated arginine was dissolved in 10 mL of 21 mM HCl, 10 mL of H20, and 3 mL of 1 M HCl [Trial 2]
NOTE:Trial 2 was run twice as the source of the solid amino acid sample changed from a chlorinated to not chlorinated one, thus changing the necessary concentrations of acid needed to observe sufficient results. 1 mL of 1 M HCl was added to the second solution of non-chlorinated arginine.
A pH probe was calibrated and used to track the change in pH as additional amounts of 0.1575 M NaOH were added over time.
- two trials were done, with respective data presented below
- trial 1 following a basic schematic of 5 mL increments, followed by a more thorough 2nd trial
- a pH curve was constructed from the data points in each trial
| Trial
|
NaOH added (mL)
|
pH
|
| 1
|
0.00
|
3.149
|
| 1
|
5.00
|
8.343
|
| 1
|
10.00
|
8.951
|
| 1
|
15.00
|
10.058
|
| 1
|
20.00
|
11.935
|
| Trial
|
NaOH added (mL)
|
pH
|
| 2
|
0.00
|
1.397
|
| 2
|
0.50
|
1.490
|
| 2
|
1.00
|
1.529
|
| 2
|
1.50
|
1.549
|
| 2
|
2.00
|
1.588
|
| 2
|
2.50
|
1.615
|
| 2
|
3.00
|
1.641
|
| 2
|
4.00
|
1.704
|
| 2
|
5.00
|
1.791
|
| 2
|
6.00
|
1.853
|
| 2
|
7.00
|
1.941
|
| 2
|
8.00
|
2.018
|
| 2
|
9.00
|
2.108
|
| 2
|
10.00
|
2.192
|
| 2
|
11.00
|
2.291
|
| 2
|
13.00
|
2.512
|
| 2
|
15.00
|
2.801
|
| 2
|
17.00
|
3.584
|
| 2
|
17.50
|
5.974
|
| 2
|
18.00
|
7.686
|
| 2
|
19.00
|
8.281
|
| 2
|
19.50
|
8.423
|
| 2
|
20.00
|
8.520
|
| 2
|
25.00
|
9.236
|
Negatively Charged Amino Acid Titration: Glutamic Acid
A solution of glutamic acid was titrated with 0.1575 M NaOH titrant in order to produce a characteristic titration curve for glutamic acid.
- 0.4650 g of solid glutamic acid was dissolved in 20 mL of 21 mM HCl and 20 mL of H20 [Trial 1]
- the amount of solvent was doubled because Glu was resisting solvation; flask was heated and mixed with a magnetic stir bar
A pH probe was calibrated and used to track the change in pH as additional amounts of 0.1575 M NaOH were added over time.
- only one trial was completed in the time allotted, with respective data presented below
- a pH curve was constructed from the data
| Trial
|
NaOH added (mL)
|
pH
|
| 1
|
0.00
|
2.448
|
| 1
|
5.00
|
3.185
|
| 1
|
10.00
|
3.800
|
| 1
|
15.00
|
4.298
|
| 1
|
20.00
|
4.960
|
| 1
|
25.00
|
8.876
|
Preparation of Amino Acid Stock Solutions for UV/VIS and Fluorescence Spectra
5 100 mL stock solutions were prepared, each with a 200 μM concentration of amino acid
- 0.00222 g of valine was added to a 100 mL volumetric flask of H20
- 0.00335 g of phenylalanine was added to a 100 mL volumetric flask of H20
- 0.00381 g of arginine was added to a 100 mL volumetric flask of H20
- 0.00316 g of glutamic acid was added to a 100 mL volumetric flask of H20
- 0.00273 g of threonine was added to a 100 mL volumetric flask of H20
Approximately 2 mL of each stock was transferred into a cuvette and a UV/VIS spectra was obtained for characterization purposes.
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