New AUS-e-TUTE Resources

AUS-e-TUTE has just added new resources on the strength of conjugate acids and bases, as well as proton-transfer reactions.

The new resources will be found under the Acids and Bases Topic Heading.

http://www.ausetute.com.au

An Itchy Polypeptide

Scientists have a discovered that a small molecule, natriuretic polypeptide b (Nppb), is responsible for that itchy feeling in mice. When natriuretic polypeptide b is removed, and mice are exposed to itch-inducing substances, nothing happens! No itching! The nervous systems of mice and humans are similar, so the scientists believe that the same molecule is probably responsible for making you feel itchy.

Natriuretic polypeptide b  is a polypeptide made up of 32 amino acid residues as shown below:

 The amino acid residues in order of appearance are:

amino acid name	structure
serine
proline
lysine
methionine
valine
glutamine
glycine
cysteine
phenylalanine
arginine
aspartic acid
isoleucine
leucine
histidine

This research could be of enormous benefit to people who suffer from chronic itch conditions like eczema and psoriasis. Unfortunately, natriuretic polypeptide b is also used in other body processes in the heart and kidneys, so its removal in humans could cause major problems.

Reference:
S. K. Mishra, M. A. Hoon. The Cells and Circuitry for Itch Responses in Mice. Science, 2013; 340 (6135): 968 DOI: 10.1126/science.1233765

Further Reading:
Amino Acids 
Proteins 

Suggested Study Questions:

1.  What is meant by the term polypeptide?
2. Refer the structure of natriuretic polypeptide b. Draw up a table giving the name and the number of each amino acid present in each molecule of natriuretic polypeptide b.
3. What two functional groups are common to all amino acids?
4. On the structure of alanine shown below, label each of the functional groups:
   
   
5. What type of bond holds the amino acids together in the chain of natriuretic polypeptide b ?
6.  Using two molecules of serine, show how they are joined together to form a dipeptide.
7. What is the name given to the type of chemical reaction in which two serine molecules combine to form a dipeptide?
8. Name the type of bond shown between two cysteines on the structure of natriuretic polypeptide b shown above.
9. What is the primary structure of natriuretic polypeptide b ?
10. How would you describe the secondary structure of natriuretic polypeptide b ?   

Astatine's Ionization Energy

Astatine is the product of the radioactive decay of some heavier elements and is the rarest naturally occurring element on Earth, only a few grams of astatine is estimated be present in the whole of the Earth's crust at any one time. All of astatine's isotopes are short-lived, with astatine-210 having the longest half-life of all its isotopes, 8.1 hours. As a result, astatine was unknown until 1940, when scientists bombarded bismuth-209 with alpha particles and produced astatine.
Even today we don't know very much about astatine, but estimates about its properties have been made based on its position in the Periodic Table, right under iodine in Group 17 (halogens). The first ionization energy of astatine has been estimated to be between 849.11 and 926.29 kJ/mol (8.8 and 9.6 eV).

The ionization energy, the energy required to remove an electron from the valence shell of an atom, is one of the most important properties that influences the chemical behaviour of an element.

In May 2013 an international team of researchers announced that they had measured the first ionization energy of astatine using laser ionization spectroscopy and found it be be 9.31751 eV (899.02 kJ/mol)

Reference:
Rothe, S. et al. Measurement of the first ionization potential of astatine by laser ionization spectroscopy. Nat. Commun. 4:1835 doi: 10.1038/ncomms2819 (2013).

Further Reading:
http://www.ausetute.com.au/pertable.html

http://www.ausetute.com.au/trendgp7.html 
http://www.ausetute.com.au/trendie.html 
http://www.ausetute.com.au/isotopes.html
http://www.ausetute.com.au/nucledec.html
http://www.ausetute.com.au/halflife.html

Suggested Study Questions:

1. Use the Periodic Table to find the following:
   • astatine's chemical symbol
   • astatine's atomic number
2.  Use the Periodic Table to find the
   • The group astatine belongs to
   • the period astatine belongs to
3. How many valence electrons does an atom of astatine have? Explain your answer.
4. Describe the trend in melting points as you go down astatine's group in the periodic table, then estimate the melting point of astatine.
5. Describe what you think astatine would look like at room temperature and justify your answer on the basis of trends in the periodic table. 
6. How does astatine-207 differ from astatine-210? 
7. Astatine-211 and 2 neutrons are produced when bismuth-209 is bombarded with alpha particles.  Write a nuclear equation for this reaction.
8. Imagine working in a laboratory. You have been given 100 μg of astatine-210 at 9 am for your experiment. Assuming the half-life of astatine is 8 hours, how much astatine-210 would you have left when you leave the lab at 5 pm?
9. The half-life of astatine-219 is about 1 minute. If you had 100 μg of astatine-219 at 9 am, how much astatine-219 would you have 5 minutes later at 9:05 am ?
10. Use the information in the article above to estimate the conversion factor between electronvolts (eV) and kJ/mol. 
11. Why do we not have an accurate measure of how much astatine is found in the Earth's crust?
12. Suggest a way that scientists can estimate the amount of astatine in existence in the Earth's crust.  

AUS-e-TUTE Update

The following resources have been added to AUS-e-TUTE:

• Neutralisation Reactions (tutorial, game, test)
• Acidic, Basic, Neutral Solutions (tutorial, game, test)
• Properties of Alkanes (tutorial, game, test, exam)
• Properties of Alkanols (alcohols) (tutorial, game, test, exam)
• Properties of Alkanoic (carboxylic) acids (tutorial, game, test, exam)
• Properties of Amines (tutorial, game, test, exam)

Syllabus Study Guides have also been updated.