H2S Helps Hearts

NO and H₂S are two important gases that regulate heart function in humans.

H₂S is a colourless, poisonous, flammable gas with the characteristic foul odour of rotten eggs at concentrations up to 100 parts per million. It is produced in swamps and sewers from the bacterial breakdown of organic matter in the absence of oxygen. It also occurs in volcanic gases, natural gas, and is produced naturally in the human body as a signalling molecule.

NO which also occurs naturally in the body, is highly reactive, having a biological lifetime of a few seconds, yet diffuses freely across membranes. People who live at high altitudes have higher levels of NO which helps them live with the lower oxygen concentration.

Scientists at the Peninsula Medical School at the University of Exeter and the National University of Singapore have analyzed the complex 'cross talk' between H₂S and NO and found that the interaction may offer potential strategies in the management of heart failure. The two gases were found to interact together to form a thiol-sensitive compound (probably HNO) which produces muscular contraction and muscular relaxation effects in the heart. This crosstalk suggests that there is the potential to produce a molecule that may be of benefit to the heart and which could be the basis of a new drug therapy based on elements that occur naturally in the body.

Reference
Qian-Chen Yong, Jia Ling Cheong, Fei Hua, Lih-Wen Deng, Yok Moi Khoo, How-Sung Lee, Alexis Perry, Mark Wood, Matthew Whiteman, Jin-Song Bian. Regulation of Heart Function by Endogenous Gaseous Mediators—Crosstalk Between Nitric Oxide and Hydrogen Sulfide. Antioxidants & Redox Signaling, 2011; 14 (11): 2081 DOI: 10.1089/ars.2010.3572

Further Reading
Naming Ionic Compounds
Molecular Mass (Formula Weight)
Percentage Composition
Concentration (ppm)
Lewis Structures
Shapes of Molecules
Molecule Polarity
Intermolecular Forces

Study Questions:

1. Name each of the following compounds:
   
   • H₂S
   • NO
   • HNO
2. Calculate the molecular mass (formula weight) for each of the following:
   
   • H₂S
   • NO
   • HNO
3. Calculate the percentage composition of each of the following:
   • H₂S
   • NO
   • HNO
4. H₂S can be detected by its odour at concentrations of 100ppm. Convert this to a concentration in
   
   • mg/L
   • μg/mL
   • % by mass (% by weight)
   • mol/L (M)
5. Draw a Lewis Structure (electron dot diagram) for each of the following molecules
   
   • H₂S
   • NO
   • HNO
6. Describe the shape of each of the following molecules:
   • H₂S
   • NO
   • HNO
7. Label each of the following molecules as polar or non-polar and explain why:
   • H₂S
   • NO
   • HNO
8. Which of the following molecules is most likely to have the highest boiling point, and explain why:
   • H₂S
   • NO
   • HNO
   
   
   
   

New Nitrogen Oxide Compound

Chemists already know about a number of compounds composed of nitrogen and oxygen:

• Nitric oxide is a colourless gas which is produced during the combustion of fossil fuels. It has a melting point of -163.6^oC, a boiling point of -150.8^oC, and rapidly oxidizes in air to form nitrogen dioxide. Its solubility in water is 7.4ml/100ml.
  
• Nitrogen dioxide is a reddish-brown toxic gas. Its melting point is -11.2^oC and its boiling point is 21.1^oC. It reacts with water to produce nitric acid.
• Nitrous oxide is a colourless gas commonly referred to as laughing gas. It is a greenhouse gas and also causes ozone depletion. Its melting point is -90.86^oC and its boiling point is -88.48^oC. Its solubility in water is 0.15g/100ml.
• Dinitrogen trioxide is a deep blue liquid at low temperatures. It has a melting point of -100.1^oC, a boiling point of 3^oC , and is very soluble in water.
• Dinitrogen tetroxide is a colourless liquid which is a powerful oxidizing agent and highly toxic. Its melting point is -11.2^oC, its boiling point is 21.1^oC, and it reacts with water to produce both nitrous aid and nitric acid.
• Dinitrogen pentoxide exists as colourless crystals. It is unstable and potentially dangerous oxidizer. It has a melting point of 30^oC and it sublimes at 47^oC. Dinitrogen pentoxide reacts with water to produce nitric acid.
  

Chemists at the Royal Institute of Technology in Sweden have discovered a new molecule in this nitrogen oxide group. The new molecule, composed only of nitrogen and oxygen, is called trinitramid. Trinitramid has the chemical formula N(NO₂)₃ and is shaped like a propeller.

Reference
Martin Rahm, Sergey V. Dvinskikh, István Furó, Tore Brinck. Experimental Detection of Trinitramide, N(NO₂)₃. Angewandte Chemie International Edition, 2011; (forthcoming)

Further Reading
Molecular Mass
Percentage Composition
Definitions of a Mole
Mass-Mole Calculations
Lewis Structures
Intermolecular Forces

Study Questions

1. Give the chemical formula for each of the following molecules:
   • nitric oxide
   • nitrogen dioxide
   • nitrous oxide
   • dinitrogen trioxide
   • dinitrogen pentoxide
2. Calculate the molecular mass (formula weight) of each of the molecules above.
3. Calculate the percentage composition of each of the molecules above.
4. Draw a Lewis Structure (electron dot diagram) for each of the molecules above.
5. Use the information in the article above, as well as your calculations, tabulate the melting points, boiling points and solubility of each molecule.
6. Graph melting points and boiling points against molecular mass.
   
7. Can you identify any trends in the melting points, boiling points, or solubilities of these molecules? Explain any trends you identify.
8. So far, scientists have only produced enough trinitramid to detect it. What do you predict its melting point, boiling point and solubility in water to be? Explain your answer.