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
   
   
   
   

Sweeter Natural Gas

Natural gas extracted from the coal beds and methane-rich geologic features must first be purged of hydrogen sulfide before it can be used as fuel in a process called "sweetening".

Thermal Swing Regeneration, a common industry process used for sweetening natural gas, uses chemical sponges called sorbents to remove toxic and flammable gases, such as rotten-egg smelling hydrogen sulfide from natural gas. The gas must first be treated with a solution of chemical sorbents that are dissolved in water. That solution must then be heated up and boiled to remove the hydrogen sulfide, in order to prepare the sorbent for future use. Once the hydrogen sulfide is boiled off, the sorbent is then cooled and ready for use again. The repeated heating and cooling requires a lot of energy and markedly reduces the efficiency of the process.

A new process called Antisolvent Swing Regeneration takes advantage of hydrogen sulfide's ability to dissolve better in some liquids than others at room temperatures. In this process, the hydrogen sulfide "swings" between different liquids during the processing at nearly room temperature, resulting in its removal, in just a few steps, from liquids that can be reused again and again.

First hydrogen sulfide is dissolved in a substance known as a DMEA which is a recyclable binding organic liquid, a substance that can hold onto hydrogen sulfide without the addition of water. DMEA forms a salt with hydrogen sulfide. The salty DMEA is then mixed with hexane (or hexadecane and a small amount of heat) which returns most of the hydrogen sulfide back to the gaseous state which is then bubbled out of the mixture. Separating the hexane from the DMEA allows these substances to be re-used.

Scientists estimate that the Antisolvent Swing Regeneration method could reduce the amount of energy needed to complete the sweetening process by at least 10%.

Reference
Phillip K. Koech, James E. Rainbolt, Mark D. Bearden, Feng Zheng, David J. Heldebrant. Chemically selective gas sweetening without thermal-swing regeneration. Energy & Environmental Science, 2011; DOI: 10.1039/c0ee00839g

Further Reading:
Writing Ionic Formulae
Naming Straight Chain Alkanes
Intermolecular Forces

Study Questions:

1. Write the chemical formula for each of the following:
   
   • methane
   • hydrogen sulfide
   • hexane
2. In a sample of each of the following pure substances, what type of forces would you expect to attract molecules to each other?
   
   • methane
   • hydrogen sulfide
   • hexane
3. Describe what would happen if each of these pure substances was mixed with water.
4. Describe what would happen if each of these substances were mixed with a petroleum-based oil.
5. Use the description of the Thermal Swing Regeneration process to draw a flow chart for this method of sweetening natural gas.
   
6. Use the description of the Antisolvent Swing Regeneration process to draw a flow chart for this method of sweetening natural gas.