User:Klare Lazor/Notebook/Chem-496-001/2011/08/31

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Objective

The purpose of this experiment is to determine the ideal pH for the synthesis of Au nanoparticles. For this experiment, Au nanoparticles will be created by reducing HAuCl4 with bovine serum albumen (BSA) in an aqueous solution with a pH of 7.55, as well as with a temperature range between 74-82 degrees Celsius.

Description

Protocol: Materials needed included Chloroauric Acid (HAuCl4), bovine serum albumen (BSA), and zein protein. BSA(0.0015-0.015mM) and HAuCl4(0.25-10mM) were used to create 10mL aqueous mixtures. Each mixture was transferred to a screw-capped glass bottle. The mixtures were kept in a water thermostat bath a 40, 60, or 80±1˚C for 6 hours. The solutions changed from colorless to pink-purple and finally purple. The samples were then removed from the bath and left to cool overnight. Next, they were purified with distilled water two times in order to remove any excess BSA, using a centrifuge at 10,000-14,000rpm for five minutes. The samples were placed in different temperature baths to observe how temperature affects the synthesis of the gold nanoparticles. In addition, in order to determine the absorbance caused by surface plasmo resonance, UV-visible spectra were taken of each sample using an UV Spectrophotometer with a wavelength range of 200-900nm. Time dependent scans were also taken to collect data on the growth kinetics of AU nanoparticles. Other data was collected using a pH meter, SEM, TEM, X-ray diffraction and AFM. Last, zein protein film formation was carried out using the BSA conjugated nanoparticles. A clear solution of zein (10%w/v) in aqueous ethanol (90%v/v) along with glycerol (30% on zein weight basis) was prepared. Then, the BSA conjugated nanoparticles (10%v/v) was added into this solution. Five grams of this solution was placed in a petri dish and swirled to coat the dish. It was placed in an 40˚C oven for 24 hours to eventually lead to protein film formation. A texture analyzer was then used in order to determine the mechanical properties of the films containing different samples of BSA conjugated Au nanoparticles. (“Protein Films of Bovine Serum Albumen Conjugated Gold Nanoparticles: A Synthetic Route from Bioconjugated Nanoparticles to Biodegrable Protein Films” by Mandeep Singh Bakshi, Harpreet Kaur, Poonam Khullar, Tarlok Singh Banipa, Gurinder Kaur, and Narpinder Singh).

Procedure: In a screw-capped glass bottle, 10mL of BSA(1.5mM) and HAuCl4(0.25mM) were added to 10mL of TRIS that was titrated to a pH of 7.55. The TRIS was already titrated by instructor. A UV-visible spectra was taken of the solution with a wavelength of 200-800nm, as well as of the buffer for a standard. The solution was then placed in a 74-82˚C water thermostat bath for 30 minute intervals. After each interval, a UV-visible spectra was taken of the solution to determine the absorbance caused by the surface plasmo resonance.

Data

Calculations

  • BSA: 1.5E-6M x 66.76g/mol = 0.10014g/L, so 0.100164g/L x 1L/1000mL x 10mL = 0.0010014 grams of BSA
  • HAuCl4: 0.00025M x 339.7g/mol= 0.084945 g/L, so 0.084945g/L x1L/1000mLx 10mL= 0.00084945 grams of HAuCl4
  • Buffer: 50mM pH 7.55 Tris (prepared by instructor) 10mL

Data Charts


Image:Aug31chart1.png

Image:Aug31new.png

Notes

Actual Amounts Used

  • BSA= 0.0013 grams
  • HAuCl4= 0.0007 grams
  • Used a little distilled water to rinse each into 10ml of Buffer

Observations

  • There was no color change in the solution. Remained clear throughout the experiment.

Conclusion

  • From the data, it was concluded that the HAuCl4 was not reduced entirely to Au nanoparticles. Colloidal Au nanoparticles usually show absorbance due to surface plasmon resonance at 520-550nm (protocol). This was not seen in image 3 of our data. However, in image 2, you can see a slight bump between 243-312nm. This slight bump can be representing HAuCl4 ions that have not be completely reduced. BSA is known to have a weak reducing behavior. Without the correct reaction conditions, it is unable to convert HAuCl4 completely into Au nanoparticles (protocol). Furthermore, plotting the intensity of the 550nm peak versus the reaction time, as seen in image 1, is related to the number density of Au nanoparticles (protocol).
  • For this experiment, it was assumed that the ideal temperature for the synthesis of Au nanoparticles was above 70 degrees Celsius. This assumption was based off of the protocol, "Protein Films of Bovine Serum Albumen Conjugated Gold Nanoparticles". Therefore, since few nanoparticles were produced, the pH of the aqueous solution was not correct for the synthesis of Au nanoparticles. According to the protocol, acidic pH is generated by the dissociation of HAuCl4 to release H+ ions, which allows interactions between R-NH3+ groups and AuCl4- ions. Thus, high temperature and low pH increase reduction of HAuCl4. In addition, the protocol also states that a lower pH than isoelectric point, pH=4.7, is primarily responsible for the denaturation of BSA, which allows the HAuCl4 to reduce. The aqueous solution for this lab with a pH of 7.55 was not ideal for the synthesis of Au nanoparticles. Apparently, BSA can not unfold in the pH range 5-7. However, once the pH falls below the isoelectric point, more reducing amino acids are released from BSA and participate in the reduction of HAuCl4 better (protocol).




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