User:Monika Gasiorek/Notebook/CHEM-571 2014F/2014/09/03

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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

Phe Titration T1.png

Phe Titration T2.png

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

Arg Titration T1.png

Arg Titration T2.png

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

Glu Titration T1.png

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.

AA UVVIS 9 3 MG PR.png