Science Buddies: "Ask an Expert"

I wanted to look at the chiral properties of sucralose -- the artificial sweetener used in Splenda.

I made a polarimeter and it seems to work well.
First I tested chirality of sucrose, glucose and fructose. I was able to detect large amounts of chirality.
I also varied the color of the light source and was able to see difference in the measurements that I made.

But I wanted to test chirality of sucralose. I tried using pure sucralose, not Splenda.
I was wondering if the results would be similar to sucrose because I think the molecule structure is similar.
I tested first with a 5% solution and then with a 10% solution (with water as solvent), but I saw very little, if any, optical activity.
I have seen that people say that sucralose is chiral.
I saw a web page that says that sucralose has 9 chiral centers -- I don't exactly know what that means.
What could explain that I don't see optical activity? Maybe the chiral centers somehow cancel each other out?
Do I need to make a higher concentration solution?

Hi,

Sucralose is trichlorosucrose. Three of the --OH groups on sucrose were replaced with --Cl so the molecule cannot be metabolized, allthough it is sweeter than sucrose.

Sucrose has 9 chiral centers and so does sucralose. These are the carbon atoms where there are 4 different groups attached: http://www.chem.sc.edu/faculty/shimizu/ ... 5a.ii.html

Since sucrose has no double bonds, all the C atoms except the three --CH2Cl are chiral centers.

I checked the optical rotation of sucrose and here is that information from wiki (https://en.wikipedia.org/wiki/Sucrose)

"The purity of sucrose is measured by polarimetry, through the rotation of plane-polarized light by a solution of sugar. The specific rotation at 20 °C using yellow "sodium-D" light (589 nm) is +66.47°."

The optical rotation of sucralose is similar to that od sucrose (http://pubchem.ncbi.nlm.nih.gov/compoun ... Solubility)

Specific optical rotation: +68.3 deg at 25 deC/D (c = 1.1. in ethanol)
O'Neil, M.J. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Whitehouse Station, NJ: Merck and Co., Inc., 2006., p. 1523

Sorry. I hit Submit before I finished.

I just wanted to ask you where you purchased the sucralose and if the company gave you a data sheet. If the compound contains equal amounts of D and L enantiomers, called a racemic mixture, the optical rotations will cancel out. I am thinking that your compound may be a racemate.

Did you test some commercial Splenda in your polarimeter? That might be worth doing to see if there's a difference.

You can try increasing the sucralose concentration. I noticed that the sucralose in the link that I sent you was dissolved in ethanol. I don't think that would change the rotation, but I'm not an expert in polarimetry.

Post back and let us know what you find out. I'd like to know if Splenda shows rotation similar to sucrose.

Sybee