User:Mary Mendoza/Notebook/CHEM 571 Experimental Biological Chemistry I/2012/09/04

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UV-Vis Spectroscopy of Aug. 29 Au/BSA solutions

  • In reference to the entry of Wednesday, August 29 (a week ago), the Au and BSA solutions were made using a metal spatula. Due to its hygroscopic nature, HAuCl4 reacted with the metal spatula.
  • The Au/BSA solutions of Aug. 29 were still examined using UV-Vis. The values for each mole ratio were plotted by its intensity vs. time using MS Excel.
  • Micropipets were used to transfer the Au/BSA solution from their test tube to the cuvette.
  • One single cuvette was used for all UV-Vis scans to avoid fluctuations in the UV-Vis scan readings.
  • During the UV-Vis scans, some of the fibers were stuck in the micropipet tips. These fibers were discarded. Hence, some of the volume of the Au/BSA solution were lost. The lost is negligible though.


Image:AuBSAaug29edited.png

  • UV-visible scans of different Au/BSA mole ratios (batch August 29) incubated at 85 degrees Celsius for 4 h.


Image:CloseupofAuBSA29.png

  • A closer view of the peaks of the UV-Visible scan of Au/BSA mole ratios from above.

Preparation of Au and BSA solutions

  • The metal spatulas used for preparation of stock solutions were wrapped with parafilm. This was done to inhibit HAuCl4 from reacting with the metal.
  • BSA solution was prepared by dissolving .0254 g of white crystalline powder of BSA in .025 L of water.
  • Molarity of BSA was obtained from the following calculation:

0.254 g of BSA × (1 mol of BSA ÷ 66430 g of BSA) = 3.82 × 10-7

3.82 × 10-7 ÷ .025 L of water = 1.53 × 10-5 mM/L

  • Initially, 0.0924 g of HAuCl4 was weighed. The substance, due to its hygroscopic nature, reacted with the weighing paper, leaving behind residues. The weight of the paper and residue amounted to 0.0285 g and was subtracted from the original weight of the substance.
  • HAuCl4 stock solution was prepared by dissolving 0.0639 g of the orange, granular solid of HAuCl4 in .025 L of water.
  • Molarity of HAuCl4 was obtained from the following calculation:

0.0639 g of HAuCl4 × (1 mol ÷ 339.79 g) of HAuCl4 = 0.0001880 mol of HAuCl4

0.0001880 mol of HAuCl4 ÷ 0.025 L of water = 7522 μM of HAuCl4

Preparation of Tris Buffers

  • Two tris buffers, pH 8 and 10, were made to test the effect of pH on the formation of AuNPs.
  • Both buffers were prepared to have a .1 M concentration. The tris buffer has a formula weight of 121.14 g. By adjusting the decimal point, it was verified that only 1.21 g is needed to be dissolved in 100 mL of water and obtain a .1 M concentration.
  • 1.213 g of white crystalline powder of tris buffer was dissolved into 85 mL of water. A pH probe was inserted in the tris buffer solution while stirring.
  • HCl was gradually added to the tris buffer with the pH probe until the desired pH was reached. 9 mL of HCl was added to the .1 M tris buffer to maintain pH 8.
  • For the preparation of pH 10, 1.2125 g of white crystalline powder of tris buffer was also dissolved in 85 mL of water. A pH probe was inserted in the tris buffer solution while stirring. HCl was gradually added until the pH meter indicates pH 10.
  • 2 mL of HCl was added to tris buffer pH 10.
  • After acquiring the desired the pH levels, water was used to fill up the solution to a total volume of 100 mL.
  • The tris buffers were refrigerated for storage.


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