User:Melissa Novy/Notebook/CHEM-571/2012/11/28

Objectives

• Analyze AuADA solutions made on 2012/11/27 with UV-vis and AA spectroscopy.
  • Please refer to Keyun Wang's entry for observations on and photographs of the solutions.
• Resuspend AuADA fibers in solutions made on 2012/11/27 with Tris buffer.

UV-Vis Analysis of AuADA Solutions

• The spectra of AuADA solutions were collected over 200 nm to 800 nm.
• Exactly 3 mL of AuADA solution was pipetted into a quartz cuvette and then placed in the UV-vis spectrophotometer.

• A peak at around 520 nm was visible in the spectra of the following mole ratio Au:ADA solutions: 60 through 130. This peak is likely due to the presence of GNPs in these solutions.
• Purple fibers were observed in all of the solutions. The liquid in each test tube was transparent purple.
• Whereas undialyzed ADA did not form GNPs, these solutions using dialyzed ADA appeared to form GNPs. It is possible that either the decrease in concentration of buffer salts between undialyzed and dialyzed ADA or the use of plastic test tubes to contain the Au and dialyzed ADA solutions contributed to the formation of GNP-ADA fibers.

• The absorbance of 60 AuADA was the highest and the absorbance decreased as the mole ratio of the solutions increased. Overlooking any experimental error, which is discussed below, this indicates that 60 AuADA created the most GNPs in solution and that this mole ratio was the best at forming the maximum number of GNPs out of the solutions tested.
• One source of experimental error is resuspension of AuADA fibers that contain GNPs. If they were resuspended, the GNPs in these fibers would be released into solution and contribute to the absorbance at 520 nm.

Analysis of AuADA AAS Data

• Please refer to Keyun Wang's entry for the concentration of Au in AuADA solutions obtained from AAS, and the calibration curve used to calibrate the AAS with standard solutions of HAuCl₄ in 1 N HCl.
• There were no deviations from the standard protocol for analyzing solutions with AAS.

• The lowest percent change in Au ppm was observed in the 80 AuADA solution. It can be assumed that this mole ratio is the best at forming the most GNPs relative to the amount of Au initially added. As all solutions formed purple fibers and the supernatant was transparent purple in color, it can be assumed that GNPs were formed in all solutions. However, in the solutions 90 through 150 AuADA, it can be inferred from the AAS and percent change [Au] data that the GNPs were entrapped in ADA fibers.

Resuspension of AuADA Fibers

• Tris buffer was made on 2012/09/04.
• Please refer to Keyun Wang's entry for volumes and concentrations of Tris buffer added to the AuADA fibers. Six solutions of mole ratio Au:ADA from 60 to 110 were chosen arbitrarily.
  • Note that the mole ratios of Au to ADA were irrelevant for these experiments, because the goal was to determine the effect of buffer pH and concentration on resuspending an arbitrary amount of AuADA fibers.
  • Within seconds after the addition of Tris buffer, all AuADA solutions became transparent purple in color and the fibers disappeared.
    • Please refer to Keyun Wang's entry for a table of approximate time taken to resuspend the fibers after adding Tris buffer.
• According to the data, it took a shorter amount of time to resuspend AuADA fibers in pH 10 Tris buffer. This corresponds to protein theory, as any variance from a protein's optimal pH will denature or unfold it. The optimal pH of ADA is between 6 and 7. A pH of 10 has the greatest difference between the protein's optimal pH and therefore may have caused ADA to unfold more quickly.