Hydrophobicity and colorimetry

  • Thread starter Andy13
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In summary, the instructor is asking you to think about the structure of the chromophore and the solvent in which it is embedded.
  • #1
Andy13
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Homework Statement



Given four compounds that are variations on amines (compound one has -OH funcitonal groups, compound 2 has a carboxy group, etc.). I am also given a bright yellow compound, which will ultimately be covalently linked to each of the four compounds via amide bond (it is a ringed aromatic compound with a carboxy group and a nitrate group). I am supposed to contrive an experimental approach using a colorimetric readout to order the compounds' hydrophobicity from most to least.

Obviously, I am including only an overview without posting the actual compounds. I'm hoping I can just bounce around ideas.


The Attempt at a Solution



I was initially thinking that more hydrophilic compounds would be impeded from bonding with the colored compound by a shell of water molecules forming H-bonds. Then, a colorimeter could be used to measure relative strength of color. More color would mean that the compound bonded more fully to the colored compound, because it was less impeded by water and hence more hydrophobic. Then I could order them that way.

My TA told me (somewhat cryptically) that parts of my idea were right but parts were missing. She then said to think about other products of amide linkage. The only other product I can think of is just NH3. Can someone tell me what's right and shove me in the right direction?

Note: If I don't respond to your well-meaning comment, it's because it came after this problem set is due and I no longer really care. Unfortunately I've left physics forum as a sort of last resort. However, help would be appreciated!
 
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  • #2
Andy13 said:
The only other product I can think of is just NH3.

Is this really what you mean?
 
  • #3
You are reacting four amine compounds with an aromatic carboxylate to produce an amide. The other product of that reaction is going to be water. The answer was more than cryptic, it was misleading. Maybe she meant to look at the other functional groups left over once the amine functionality was reacted away.

You should think about the structure of the chromophore itself. Is the chromophore a charged or ionized species? What is the solvent? In more polar solvents like water, more hydrophobic molecules will tend to self associate rather than associate strongly with the solvent. What type of association will modulate either the color or the intensity of color?
 

What is hydrophobicity?

Hydrophobicity refers to the tendency of a substance to repel or be unreactive to water molecules. This is due to the nonpolar nature of the substance, which does not interact well with the polar water molecules.

How does hydrophobicity affect colorimetry?

Hydrophobic substances can interfere with colorimetry measurements, as they can cause particles to clump together and affect the absorption or reflection of light. This can result in inaccurate measurements and affect the reliability of colorimetric data.

What is colorimetry?

Colorimetry is a scientific technique that measures the intensity of color in a substance. It involves the use of a colorimeter or spectrophotometer to measure the absorbance or transmittance of light by a sample, which can then be used to determine the concentration of a substance or the presence of a particular chemical.

How does colorimetry work?

Colorimetry works by passing a specific wavelength of light through a sample and measuring the amount of light that is absorbed or transmitted. This information is then used to calculate the concentration of a substance in the sample, based on the Beer-Lambert law, which states that the amount of light absorbed is directly proportional to the concentration of the substance in the sample.

What are some applications of hydrophobicity and colorimetry?

Hydrophobicity and colorimetry have various applications in the scientific field, including environmental monitoring, medical diagnostics, and biochemical analysis. They can also be used in industries such as food and beverage, pharmaceuticals, and cosmetics for quality control and product development.

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