«Kinetic Investigations of Thiolate Protected Gold Nanoparticles: Protein Interactions, Electron Transfer, and Precursor Formation By Brian N. Turner ...»
The solution was allowed to warm to RT. 0.80 g of tetramethylthiuram disulfide was dissolved in 10 mL of freshly distilled dichloromethane and purged with Ar. The Grignard solution was, again, cooled in an ice bath, and the thiuram solution was added cautiously. The solution was filtered, evaporated, and eluted on a silica gel column with DCM/hexanes. 1H NMR 7.78 ppm, d, 2H, J = 8.44 Hz (aromatic close to iodine); 7.19 ppm, d, 2H, J = 8.44 Hz (aromatic close to thiuram); 3.57 ppm, s, 3H, thiuram methyl a);
3.50 ppm, s, 3H, (thiuram methyl b).
Synthesis of p-tetramethylthiurylphenylethynylbenzene (PEPSTMT) via Sonogashira Cross-Coupling of IPhSTMT
0.47 g IPhSTMT from the previous synthesis (1.55 mmol), 121 mg Pd(PPh3)4 (10 mol%), and 29 mg CuI (10 mol %) were dissolved in freshly distilled Hunig’s base (9mL) and THF (4mL), and purged with argon. 186 µL of phenylacetylene was syringed in, and the reaction was stirred for 24 hours at 100 °C. The product was extracted in ether, washed 3x with water, dried over MgSO4, filtered, and evaporated. The product was further purified on a silica gel column with DCM/hexanes. 1H NMR: 7.73 ppm, m, 4H; 7.49 ppm, m, 5H (aromatic); 3.56 ppm, s, 3H (first thiuram methyl); 3.35 ppm, s, 3H (second thiuram methyl). Reaction worked extremely well, but was irreproducible in later trials. This was attributed this to humidity, as every repeat was performed in the summer, and a Schlenk line was not utilized (only argon balloons).
Deprotection of PEPSTMT to p-mercaptophenylethynylbenzene (PEPSH) The product above was deprotected by NaOH (24 mg), Zn (3 mg), H2O 1.8 mL, THF (3 mL) and stirring for 3 hours, followed by quenching and acidifying with HCl. A greenish, semi-crystallin solid was obtained and recrystallized once from iso-octane. 1H NMR 7.71 ppm, m, 2H; 7.59 ppm, m, 2H; 7.51 ppm, m, 3H; 7.07 ppm, m, 2H (aromatic); 2.34 ppm, bs, 1H (thiol). Thiuram-like byproduct present, 3.62 ppm, bs, 6H (in thiuram it is at 3.60 ppm).
I would like to thank Bryan Ringstrand for his constant and willing help in various aspects of the organic syntheses: devising reaction pathways, preparing solvents, using catalysts, purification, and setting up reactions under inert atmosphere. I would also like to thank Dr. Piotr Kaszynski for recommending the triisopropylsilanethiol as a protected thiolating reagent. I would also like to acknowledge some assistance from Joe Keene during his rotation in the lab.
PURIFICATION AND CHARACTERIZATION DATA FOR SYNTHETIC PEPTIDES
USED IN THIS STUDY OR OTHERWISE DESIGNED AND PURIFIEDTable 14: Characterization data for peptides synthesized by this author. The sequences are labeled as the single letter amino acid abbreviations, the identity of the termini (unlabeled termini indicates that both termini were left as the free amine or carboxylic acid, CONH2 is an amidated C terminus, and Ac is an acetylated N terminus), and (PEG) 6 indicates a hexaethyleneglycol spacer. Retention times are from reverse phase, preparatory scale HPLC and represent the time (rounded to the nearest minute) at which collection of the highest absorbing fraction was began. Calculated m/z values represent the value calculated for the most abundant isotope for reflectron mode, or the average mass for linear mode. The most prevalent ions in the MALDI spectrum of the highest absorbing fraction were recorded. [M + H] and [M + Na] were assumed to be indicative of a successful synthesis, while [M + O] is indicative of an oxidized methionine residue (not generally considered to effect peptide-antibody binding). Mode indicates reflectron (R) or linear (L) time of flight for the MALDI characterization.
The Vanderbilt Summer Academy is a collaborative effort within Vanderbilt that invites gifted high school underclassmen to campus in order to learn about nanoscale science and engineering. Every year, the research group of David Cliffel participates and teaches kids about gold nanoparticles through a brief lecture followed by a hands-on experience.
For that section, an article from J.Chem. Ed from Mirkin and coworkers, entitled “Color my Nanoworld” is used, in which the students make citrate stabilized gold nanoparticles and study their properties colorimetrically. In order to enhance this experience, I designed an addendum to the experience where the students study hexanethiol protected
gold nanoparticles from a Brust synthesis. The addendum is as follows:
Brian Turner 6-23-10 Monolayer Protected Cluster Supplement for “Color my Nanoworld” Vanderbilt Summer Academy Chemicals required
4. NaBH4: For a 30 mM solution, dissolve _____g of NaBH4 in _____mL of water. This solution should be prepared immediately before use. It is possible that this solution loses its potency, and requires a new preparation part way through the lab.
Procedure for the Preparation of 3nm Gold Hexanethiol Monolayer Protected Clusters (MPCs)
2. Option A: Cap and shake the vial vigorously to temporarily mix the layers together. Option B: Use a dropper to mix the layers over and over. Either method should be done until you have 1 red layer and 1 colorless layer (not faintly yellow).
3. Use a pipet to remove the clear aqueous layer (which should be dilute hydrobromic acid). The remaining layer should be toluene with 1mM tris(tetraoctylammonium) gold(III).
4. To the red organic layer, add ____ µL of C6SH (3:1 molar excess).
Subsequent reduction of gold(III) to gold(I) may be observed by a color change from red to colorless.
5. Immediately upon fading of the red color, CAUTIOUSLY add 1 dropper full of NaBH4 solution (in the hood). Continuously mix with the dropper.
Capping and shaking is an option, but should be done carefully while holding the lid on very tightly, and easing the lid off after reduction. This should render a black solution.
1. It should be noted that these particles are more stable than the citrate particles because they are protected by covalently bonded layer of hexanethiolate molecules.
2. Throughout the course of all of the experiments, the children have observed a variety of colors.
3. This is a good time to tell the kids about how scientists can use light to gain details about molecules and particles such as their size.
The numbers are left blank so that the teaching assistants customize to suit the class.
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