Betaines

Betaines are found in plants, animals and microorganisms. Rich sources of betaines in the human diet are seafood, spinach and wheat germ or bran. Research is beginning to indicate that betaines are important nutrients for the prevention of chronic disease. Researchers are also interested in incorporating betaines into polymer brushes used for antifouling and lubrication.

Betaines are compounds with a positively charged functional group linked to a negatively charged functional group with an alkyl chain in between. The alkyl chain is often referred to as an alkyl chain spacer.  The general structure of an N-alkyl betaine is shown below:

The first betaine discovered was found in sugar beets in the nineteenth century. This betaine is (trimethylammonio)acetate, also known as trimethylglycine, and its skeletal structure is shown below:

Another example of a betaine is 2-(trimethylammonio)octadecanoate (also known as hexadecylbetaine) with the skeletal structure shown below:

2-(Trimethylammonio)tetradecanoate, or dodecylbutaine or laurylbutaine, is also a butaine and its skeletal structure is shown below:

Betaines are strongly attracted to water molecules because of these two charged functional groups.
The solubility of betaines in water is dependent on the length of the carbon chain, as well as on temperature and pH. 
In acidic solution, betaines acquire a net positive charge and act like a cationic surfactant. In anionic solutions, betaines acquire a net negative charge and act like an anionic surfactant.

Betaines can also be used in polymer brushes which are polymers bound to a surface. Polymer brushes can be used for antifouling and lubrication because the hydration of the ionic groups reduces the ability of other materials to adhere to the surface. 

Researchers at Kyushu University recently investigated a series of alkly chain spacers of different lengths bound to a silicon surface. They found that the polymer brushes swelled in humid air and water. It is believed that this is due to electrostatic repulsion between charged groups, and not dependent on the length of the alkyl chain.
In deionised water, net positive cations and net negative anions are repelled because of the  electrostatic force which causes the chain dimension to expand, whereas they shrink under high ionic strength by a charge screening effect of the bound ions.

Reference:
https://www.sciencedaily.com/releases/2017/08/170821094302.htm

Further Reading
Introduction to Functional Groups
2-Dimensional Structural Formula
Condensed Structural Formula
Molecular Formula
Amino Acids
Surfactants ( as found in synthetic detergents)
Intermolecular Forces and Solubility

Suggested Study Questions

1. Locate and identify each functional group on the skeletal structural formula of
• general formula N-alkyl betaine 
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
2. Draw a 2-dimensional structural formula for each of the following molecules:
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
3. Write the condensed structural formula for each of the following molecules:
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
4. Write the molecular formula for each of the following molecules:
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
5. Compare the structure of betaines to that of 2-amino acids. Can N-alkyl betaines be classified as alpha amino acids (2-amino acids) ? Justify your answer.
6. Write chemical equations to describe what happens to an N-alkyl betaine in:
• acidic aqueous solution
• basic aqueous solution
7. Compare the structure of N-alkyl betaines to the surfactants found in synthetic detergents. In what ways are surfactant molecules 
• similar to N-alkyl betaines
• different from N-alkyl betaines
8. Explain how N-alkyl betaines act like 
• a cationic surfactant in acidic aqueous solution
• an anionic surfactant in basic aqueous solution
9. Consider the structure of (trimethylammonio)acetate and 2-(trimethylammonio)octadecanoate. Which molecule do you expect to be more soluble in water? Justify your answer.
10. Consider the structure of (trimethylammonio)acetate and 2-(trimethylammonio)octadecanoate. Which molecule do you expect to be more soluble in paraffin oil? Justify your answer.

Nanoparticles to Remove Coral Bleaching Oxybenzone

Sunblocks contain a number of different compounds including oxybenzone which acts as a UV filter. The skeletal structural formula of oxybenzone is shown below:

Oxybenzone is soluble in water.
Before you go snorkeling in the Great Barrier Reef to be amazed by the beautiful corals, fascinating fish and other exciting wonders, you smother yourself in sunblock. When you step into the water, the oxybenzone starts to dissolve. Unfortunately, oxybenzone contributes to coral bleaching, the killing off of the tiny, colourful zooxanthellae marine algae that live inside corals. The result is that the coral loses its colour and appears white, as if it has been bleached.

Researchers have found a way to soak up the oxybenzone from the seawater using magnetite nanoparticles.

Magnetite, Fe₃O₄ , is a mineral made up of iron(II) and iron(III) oxides and is one of the main iron ores, that is, magnetite is mined in order to produce iron. Magnetite is ferromagnetic, that is, it is attracted to a magnet. It is the most magnetic naturally occurring mineral on Earth. If you could get the oxybenzone in the seawater to attach to magnetite nanoparticles then you could pull the oxybenzone out of the water using a magnet.

First, the researchers coated the magnetite nanoparticles with sodium oleate. The skeletal structural formula of sodium oleate is shown below:

Next, they oxidised the oleate coating to increase the number of hydroxyl (OH) functional groups:

Since oxybenzone can interact with other molecules via hydrogen bonds, magnetite nanoparticles  covered in a coating rich with hydroxyl functional groups increases the interactions between oxybenzone and the nanoparticles. Once the oxybenzone has hydrogen bonded to the nanoparticle coating, a magnet can be used to extract the particles from water.

Does it work?
One brave researcher applied sunblock, stepped into the ocean, waited 10 minutes, then collected a sample of the surrounding seawater. Back at the lab, chromatography was used to determine the concentration of oxybenzone in the water, 1.3 ppm. This is a disturbing result since it is known that the concentration needed to bleach coral is measured in parts per billion.
Next, the researchers prepared seawater samples. Some had no magnetite nanoparticles added, others had the nanoparticles added. Then they added 30 ppm oxybenzone to  all the samples. The concentration of oxybenzone in the samples with no nanoparticles did not change in an hour. In the samples that contained the nanoparticles, 95% of the  oxybenzone  was removed within the hour.

Reference
American Chemical Society. "Sopping up sunblock from oceans to save coral reefs." ScienceDaily. ScienceDaily, 21 August 2017.

Further Reading
Solutions Concepts
Water as a Solvent
Transition Metals (magnetism)
Fatty Acids
Carboxylic Acids
Nanoparticles and Nanotechnology
Parts per Million (ppm)
Chromatography
Experimental Design
Variables
2-Dimensional Structural Formula
Skeletal Structural Formula
Molecular Formula

Suggested Study Questions

1. For a molecule of oxybenzone:
• draw the 2-dimensional structural formula
• give the molecular formula
2. On the 2-dimensional structural formula of oxybenzone identify and name each functional group present.
3. Use diagrams to explain why oxybenzone is soluble in water.
4. Draw the 2-dimensional structural formula for oleic acid.
5. On your structural formula of oleic acid, identify and name the functional group(s).
6. Suggest a method by which you could change oleic acid into sodium oleate in the laboratory.
7. Suggest a method by which you could oxidise sodium oleate in the laboratory.
8. Explain the term "nanoparticle".
9. Why do you think the researchers chose nanoparticles of magnetite rather than bulk magnetite for this research?
10. Consider the description of the experiment used to determine the effectiveness of the magnetite nanoparticles in removing oxybenzone from seawater:
• What was the hypothesis being tested?
• What was the aim of the experiment?
• What variables need to be considered in this experiment?
• What is the independent variable in the experiment?
• What is the dependent variable in the experiment?
• Which variables are constant variables in the experiment?
• Why did the experimenters add nanoparticles to some samples but not to others?
• Write out a suitable method for this experiment.

Acenes

Acenes are molecules in which benzene rings, shown below, are fused together.

 

Researchers are very keen on making acenes because of their interesting properties.

Naphthalene, produced from the distillation of coal tar in the nineteenth century and traditionally used in mothballs, is a molecule in which 2 benzene rings are fused:

 

 Anthracene, a component of coal tar that is used to make dyes, has 3 fused benzene rings:

Tetracene (or naphthacene), is a semiconductor used to make organic light-emitting diodes (OLEDs) and organic field-transmitters (OFETs), has 4 fused benzene rings:

Pentacene is a semiconductor relevant to the building of photoelectronic devices. It oxidises when exposed to UV and visible light. It has 5 fused benzene rings:

The longer the acene molecule is, the less stable it is so the longer acenes are so unstable they do not occur in nature. Indeed, nonacene, in which 9 benzene rings are fused together was only detected recently, in 2010. Yet researchers are still interested in developing longer acenes because of their unique electronic properties.

In 2017, researchers from the Institute for Materials Science and Center for Advancing Electronics at Technische Universität of Dresden (TUD) and the research center CiQUS (University of Santiago de Compostela) were able to make the elusive decacene in which 10 benzene rings are fused together.
Individual decacene molecules were visualised by high-resolution Scanning Tunneling Microscopy (STM):

The decacene molecule is so reactive that it had to be prepared on a gold surface under a high vacuum in order to stabilise it.

Reference

Technische Universität Dresden. "Researchers obtain decacene, the largest acene synthesized ever." ScienceDaily. ScienceDaily, 14 August 2017. .

Further Reading

Benzene: Structure and Properties

Introduction to IUPAC Nomenclature of Organic Compounds

Empirical Formula

Molecular Formula

2-Dimensional Structural Formula

Condensed Structural Formula

Skeletal Structural Formula

Suggested Study Questions:

1. Draw the 2-dimensional structural formula for each of the following molecules:
• benzene
• naphthalene
• anthracene
• tetracene
• pentacene
2. Draw the condensed structural formula for each of the following molecules:
• benzene
• naphthalene
• anthracene
• tetracene
• pentacene
3. Give the molecular formula for each of the following molecules:
• benzene
• naphthalene
• anthracene
• tetracene
• pentacene
4. Give the empirical formula for each of the following molecules:
• benzene
• naphthalene
• anthracene
• tetracene
• pentacene
5. Name the following molecules found in the acene series:
• 6 benzene rings fused together
• 7 benzene rings fused together
• 8 benzene rings fused together
• 9 benzene rings fused together
6. Consider the structure of the molecules in the acene series. Explain why Chemists use the term "fused" rather than "bonded" or "linked" to refer to how the benzene rings are joined together to make the acene molecules.
7. Place the molecules in the acene series from benzene to decacene in order of increasing reactivity.
8. What feature of the molecules in the acene series makes them useful semiconductors?
9. Explain why the reactivity of the molecules in the acene series increases as the number of benzene rings fused together increases.
10. Explain why decacene had to be prepared under a high vacuum.

Law of Conservation of Energy

We use the Law of Conservation of Energy all the time.
Every time I plug the kettle in to boil some water (for a nice hot cup of tea), electrical energy is converted into thermal energy. As I sit and watch steam rising up from my mug of tea I realise that thermal energy is being transformed into kinetic energy. The sugar I added to my tea might get converted (eventually) into the mechanical energy required to walk from my chair to the kitchen, or it might get stored (eventually) as chemical potential energy in my body (probably as fat).
How important is the Law of Energy Conservation (otherwise known as the First Law of Thermodynamics) in Chemistry?
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