In a small container, dissolve 2 g of table sugar (sucrose) in 10 mL of distille
ID: 515769 • Letter: I
Question
In a small container, dissolve 2 g of table sugar (sucrose) in 10 mL of distilled water to make a - 1 M solution. Into each of four glass vials or clear, colorless plastic cups, place 3 mL of the gold nanoparticle solution you prepared in Part A. Add 3 mL distilled water to each vial. With a dropper, add 5-10 drops, one at a time, of the salt solution form part B, step to one of the vials. Record your observations. (Refer to an unused solution for comparison). What is happening to the nanoparticles in solution? With a dropper, add 5-10 drops, one at a time, of the sugar solution form part B, step 2 to one of the vials containing fresh nanoparticle solution. Record your observations. (Refer to an unused solution for comparison) Choose another substance to add to a third vial. One suggestion is a household liquid such as vinegar. Check with your instructor about your choice. Before adding the substance, predict whether or not a color change will occur. Based on the fact that the citrate anions cover the surface of each nanoparticle, explain what keeps the nanoparticles from sticking together (aggregating) in the original solution. Why does adding the salt solution produce a different result from adding the sugar solution? How could the effect in part B be used to detect the binding of bimolecules, such as DNA or antibodies, that stick to one another or to other molecules? How could these molecules be used to cause aggregation of the nanoparticles? Information from the World Wide Web (accessed February 2004) National nanotechnology initiative: for students K-12. http://www.nano.gov/html/edu/eduk12.html Left A micrograph of 13 nm-diameter Au nanoparticles. Right: An illustration an Au nanoparticle surface. Each nanoparticle is mode of many (more than 500,000) Au atoms. Citrate anions cover the nanoparticle surface.Explanation / Answer
1. The citric acid solution after ionization forms the di-citrate anions are adsorbed on the Au surface by coordinating with carboxylate groups.
The coordinated citrate interacts with other adsorbed species through hydrogen bonds between the terminal carboxylic acid groups. The H-bonded H2Citrate anions produce citrate chains, which interact with each other through Vanderwall force attraction between proximal CH2 moieties, leading to the formation of a self-assembled layer of citrate molecules adsorbed on AuNP. Because of these forces Citrate, groups covered on the surface of the Au Nanoparticles.
2. The AuNP suffers from surface charge repulsions when they consider individual interaction for aggregation. but whenever the addition of the salt solution (which ionizes to form ions) to the AuNP they replace the energy barrier produced between the two AuNP to interact with each other and to form aggregation which results in producing some color to the solution. whereas by adding a sugar solution in which the sugar molecules are individual and they do not ionize to form ions as like salts. so there was such kind of changes occur to AuNP by adding the sugar solution.