Carbon Capture and Storage

CCS, or sequestration, stores the carbon dioxide produced from power stations that would otherwise have been released into the air. It is then stored in underground porous rocks and old oil and gas fields.

At the moment, power stations burn methane from natural gas as fuel.

CH₄(g) + 2O₂(g) ——-> CO₂(g) + 2H₂O(l)

In Scotland, they are developing decarbonised fuels to reduce carbon dioxide emission. 

CH₄(g) + 2H₂O(g) ——-> CO₂(g) + 4H₂(g)

The hydrogen produced is used in generating electricity and the carbon dioxide stored away. This way, more energy is produced without having to produce as much CO_2.

 Storage as carbonates

CO₂ can also be stored as carbonates by reacting them with metal oxides. The carbonates would be stable and happens naturally.

CaO(s) + CO₂(g) ———> CaCO₃(s)

However, it takes a lot of energy to speed up this slow natural process so more research has to be carried out in order to make this technique more efficient.

Secondary Structure of Proteins (Beta sheets)

Beta sheets

• Also known as the beta pleated sheet due to the pleated appearance of the protein structure from a side view.
• No strict rules to how they are formed because the hydrogen bonds can be formed between distant amide hydrogen and carbonyl oxygen.
• They are two or more strands distant from each other in the primary structure that form hydrogen bonds with each other side by side. 
• There are two types of beta sheet structures; parallel and anti-parallel. Parallel beta sheets have strands that run in the same direction as each other and anti-parallel beta sheets have strands that run in opposite direction to each other. The hydrogen bonding in anti-parallel beta sheets are usually more linear.
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• The N-H and C=O groups on the outer edge of the beta sheet structure are not hydrogen bonded to other strands of the primary sequence.
• If the R-groups along the outer edge of the beta sheets are polar, it can interact with solvents such as water. If they are non-polar, they can interact with hydrophobic structures such as lipids. 
• They can also pack closely against side chains of nearby alpha helix structures.
• Almost all of the polar amide groups are hydrogen bonded to each other in the beta sheet structure.
• Parallel sheets are almost always buried in the inside of the structure of a protein and anti-parallel sheets are mostly exposed to solvent due to the amino acids that make up that part of the structure. Therefore, anti-parallel sheets are seen as being more stable structures than parallel sheets.
• Parallel sheets usually have other structures, such as helices, separating them from other parallel sheets.
• They have a right handed twist to the beta strands due to the steric factors of the L-amino acid configuration.
• Isoleucine and valine are often found in these beta sheets because they are hydrophobic. 
• Beta strands can be amphipathic because of the alternating side chains of amino acids next to each other. These amphipathic strands are found on the surface of proteins.
• A large anti-parallel beta sheet can also form a barrel structures (such as retinol binding protein). The last strand of the beta sheet is hydrogen bonded to the first strand so it forms a closed barrel shape.
• The exterior of the structure is usually surrounded by solvent as it is hydrophilic and the interior is where the hydrophobic residues are found so non-polar species can be found here (e.g retinol).

Secondary Structure of Proteins (Alpha helices)

The only bonds in the secondary structure of a protein are regular repeated hydrogen bonds from the peptide bonds of the amide groups and carbonyl groups. You can also classify protein families by their secondary structures.

Helices 

• This is the most common secondary structure of proteins. 
• The carbonyl oxygen atom act as a hydrogen bond acceptor and the hydrogen attached to the nitrogen atom of the amide group act as the hydrogen bond donor. 
• The carbonyl oxygen atom (n) bonds to the hydrogen of the amide group four residues along (n+4) by hydrogen bonding. 
• Can be formed when the R-groups in the primary structure is not 'bulky'.
• If proline is present, the hydrogen bond formation would stop because the amine group is bonded to the R-group in proline. This is why proline is known as the 'helix breaker'.
• The first amine group and the last carbonyl group of the helix are not involved in the hydrogen bonding of the secondary structure.
• The helix forms a cylinder shape, with the hydrogen bonds forming the walls of the cylinder and the R-groups pointing outwards. 
• The properties of the R-groups that make up the primary structure dictates the interactions the helix has with other parts of the protein chain and with other molecules. It also means that the helix can be amphipathic (e.g. one side of the helix is hydrophobic and the other side is hydrophilic).
• They can be right-handed (going clockwise) or left-handed (anti-clockwise) but left-handed helices are very rare. 
• The helices can be any length because they have no limit. 
• Other variations of the alpha helix exist but are also very rare.