Triclosan

Triclosan is an organic compound used as an antibacterial and antifungal agent in some products. The structure of triclosan is given below

Triclosan has the systematic IUPAC name of 5-chloro-2-(2,4-dichlorophenoxy)phenol.
Since its development in the 1960s, it has been used as a hospital scrub. Its use spread beyond our hospitals and into our homes where it can be found as an additive in toothpaste, soaps and detergents.
In 2007, University of Michigan School of Public Health undertook a study which found that consumer-grade antibacterial soaps containing Triclosan are just as effective as plain soap for removing bacteria from your hands.
University of Cambridge researchers may have found a new use for Triclosan; as an anti-malarial agent.
Malaria kills more than 500,000 people every year. Unfortunately, malaria parasites are becoming more resistant to the drugs we have been using to treat malaria.. It appears that Triclosan inhibits an enzyme in the malaria parasite and works even in drug-resistant parasites! It is hoped a new anti-malarial drug based on Triclosan can be developed in the future.

Reference:
Elizabeth Bilsland, Liisa van Vliet, Kevin Williams, Jack Feltham, Marta P. Carrasco, Wesley L. Fotoran, Eliana F. G. Cubillos, Gerhard Wunderlich, Morten Grøtli, Florian Hollfelder, Victoria Jackson, Ross D. King, Stephen G. Oliver. Plasmodium dihydrofolate reductase is a second enzyme target for the antimalarial action of triclosan. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-19549-x

Further Reading:
IUPAC Nomenclature (organic): http://www.ausetute.com.au/namctut1.html
Introduction to functional groups: http://www.ausetute.com.au/fungroup.html
Benzene: http://www.ausetute.com.au/benzene.html
Molecular Formula: http://www.ausetute.com.au/molecularformula.html
2-dimensional structural formula: http://www.ausetute.com.au/structural2D.html
Condensed structural formula: http://www.ausetute.com.au/condensedsf.html
Skeletal structural formula: http://www.ausetute.com.au/skeletal.html 
Pure substances and mixtures: http://www.ausetute.com.au/puresubs.html
Solutions concepts: http://www.ausetute.com.au/solutions.html
Percentage composition: http://www.ausetute.com.au/percentc.html
Mass-mole calculations:  http://www.ausetute.com.au/massmole.html
Concentration (molarity): http://www.ausetute.com.au/concsols.html
Parts per million (ppm): http://www.ausetute.com.au/partspm.html
weight/weight (mass/mass) concentration: http://www.ausetute.com.au/weightpc.html

Suggested Study Questions:

1.  Use the skeletal structural formula for Triclosan to draw a 2-dimensional structural formula.
2. On your structural formula, identify each halogen.
3. On your structural formula, identify a hydroxyl functional group
4.  On your structural formula, identify an ether link
5. On your structural formula, identify a benzene ring
6. Give the molecular formula for Triclosan
7.  An antibacterial handwash contains 0.5% by mass Triclosan. For 250 g of this handwash, calculate:
   • mass in grams of Triclosan present
   • moles of Triclosan present
8. Calculate the concentration of Triclosan in the same 250 g of handwash in units of:
   • mol L^-1
   • g/100g
   • parts per million (ppm)
9. Is toothpaste a pure substance or a mixture? Explain your answer.
10. Is Triclosan a pure substance or a mixture? Explain your answer.

 

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.

Structure of Benzene

AUS-e-TUTE has just uploaded new resources for the Benzene topic.
You will find the new Structure of Benzene tutorial, game and test under the Aromatic Compound heading when you log-in to the Test Centre.
Relevant syllabus study guides have also been updated to include these new links.
The key concepts can be found in the "free-to-view" tutorial at
http://www.ausetute.com.au/benzene.html
There is a clickable link on that benzene page which will take AUS-e-TUTE members straight to the complete new tutorial.

Pthalate in Plastics

Researchers in the USA have found a link between premature births and the exposure of  pregnant women to a group of organic (carbon based) chemicals known as phthalates.

Phthalates have been used for more than 50 years as plasticizers, substances which are added to plastics to increase their flexibility, transparency, durability and longevity. For example, adding phthalates to polyvinyl chloride (PVC) makes the PVC soft and flexible, ideal for flexible plastic tubing. You will find phthalates in many products you come into contact with every day, from vinyl upholstery and floor tiles, to plastic food containers and wrappers, to personal care products like perfumes, moisturizer, and liquid soap.

Phthalates have the general structural formula shown below:

R and R' represent alkyl groups.
If R and R' are both CH₃ (methyl) groups, the molecule is known as dimethyl phthalate (abbreviated as DMP).
If R and R' are both C₂H₅ (ethyl) groups, the molecule is known as diethyl phthalate (abbreviated DEP).
When R and R' are very small alkyl groups, like methyl or ethyl groups, the phthalates are colourless, odourless liquids at room temperature and pressure.
The phthalates are added to molten plastic, allowing the phthalates to mix with with the polymer. The polar C=O groups in the phthalate molecules interact with partial positive charges on atoms in the polymer chain, for example, the C^δ+ of the C-Cl covalent bond in a polyvinyl chloride polymer.
When the plastic is cooled, the interactions between the phthalate and the polymer chains remain, and the alkyl groups of the phthalate screen the polymer chains from interacting with each other so that the polymer chains can slide over each other. This results in a more flexible plastic.


Reference:
http://www.abc.net.au/news/2013-11-19/common-plastics-chemical-linked-to-pre-term-births/5101828

Further reading:
Esters and Esterification
Bond Polarity
Intermolecular Forces


Suggested Study Questions:

1. Draw the structural formula for
   • dimethyl phthalate
   • diethyl phthalate
2. Give the molecular formula for
   • dimethyl phthalate
   • diethyl phthalate
3. On the structural formula for dimethyl phthalate, circle a benzene ring.
4. On the structural formala for diethyl phthalate, circle an ester functional group.
5. Dimethyl phthalate can be prepared in an esterification reaction using phthalic acid and methanol. Draw the most likely structural formula for phthalic acid. 
6. In chemistry, what is meant by a polar bond?
7. On the structural formula of diethyl phthalate,  show the partial charges of the atoms in the polar areas of the molecule.
8. Draw a diagram to show the interaction between dimethyl phthalate and a section of the polyvinyl chloride polymer.

Smell of Danger

Harvard Medical School scientists have discovered a single compound, found in high concentrations in the urine of carnivores, that lets rodents like rats and mice sense carnivores in general from a safe distance.
Mice have about 1200 kinds of odour receptors and 14 kinds of TAARs (Trace Amine-Associated Receptors), in comparison, humans have about 350 odour receptors and 5 TAARs because humans rely much more on sight than on smell.
Working with commercially available predator and prey urine, used by gardeners to keep pests out of their crops and by hunters to mask their own scent or as lures for prey, the scientists discovered that one of the 14 mice TAARs, TAAR4, detected the odour of several carnivores.
The compound that activates TAAR4 is 2-phenylethylamine, a product of protein metabolism.
Elevated levels of 2-phenylethylamine are found in many species of carnivores, but not found in non-carnivores (including rabbits and deer). In a series of behavior tests, rats and mice showed a clear, innate avoidance to the smell of 2-phenylethylamine.
The structural formula of 2-phenylethylamine is shown here.
2-phenylethylamine is an amine, consisting of a benzene ring and an aminoethyl group. It is a colourless liquid at room temperature, is strongly basic, and has a fishy odour to
humans, but has the smell of danger to mice and rats..


Reference
D. M. Ferrero, J. K. Lemon, D. Fluegge, S. L. Pashkovski, W. J. Korzan, S. R. Datta, M. Spehr, M. Fendt, S. D. Liberles. Detection and avoidance of a carnivore odor by prey. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1103317108

Further Reading
Amines
Functional Groups
Structural Isomers
Percentage Composition

Study Questions

1. Write the molecular formula for 2-phenylethylamine.
2. Draw a structural formula for a possible structural isomer of 2-phenylethylamine.
3. Calculate the percentage composition of 2-phenylethylamine.
4. Circle the functional group in the structural formula of 2-phenylethylamine.
5. Circle the benzene ring in the structural formula of 2-phenylethylamine.
6. Is 2-phenylethylamine a primary, secondary, or tertiary amine? Explain your answer.
7. 2-phenylethylamine is soluble in water and ethanol (ethyl alcohol). Explain why 2-phenylethylamine dissolves in water and ethanol.
8. Ethylamine, CH₃CH₂NH₂, has a boiling point of 17^oC and K_b=4.7 x 10^-4. Predict the boiling point and base dissociation constant for 2-phenylethylamine giving reasons for your answer.
   
9. Write a balanced chemical equation for the reaction between 2-phenylethylamine and hydrochloric acid.
10. Trimethylamine, a compound related to 2-phenylethylamine, activates TAAR5 receptors in humans.
    • Draw the structural formula for trimethylamine.
    • Give the molecular formula for trimethylamine.
    • Discuss the similarities between trimethylamine and 2-phenylethylamine.
    
    

PBDEs

Polybrominated diphenyl ethers, PBDEs, have been used as flame retardants in many common household products such as blankets, couches, food wrappers, as well as in motor vehicles and airplanes.
A diphenyl ether molecule has the following structure:

One of the polybrominated diphenyl ether compounds is 2,2',4,4',5-pentabromodiphenyl ether and it has following structure
There are 209 possible substances which are included in the family of polybrominated diphenyl ethers (PBDEs) and these are called congeners. Congeners include dibromodiphenyl ethers, tribromodiphenyl ethers, tetrabromodiphenyl ethers, pentabromodiphenyl ethers, hexabromodiphenyl ethers, heptabromodiphenyl ethers, octabromodiphenyl ethers, nonabromodiphenyl ethers and decabromodiphenyl ethers.

PBDEs with 1-5 bromine atoms per molecule are considered to be more dangerous than PBDEs with more bromine atoms per molecules because they are more efficient at accumulating in living things. In humans they effect hormone levels in the thyroid which can lead to alterations in behaviour. Studies have shown that children in developed countries have higher levels of blood PBDEs than adults, ranging from 24 to 114 parts per billion.

Most PBDEs have either been banned or are in the process of being phased out, eg,:

• Penta and octa PBDEs are no longer manufactured in the USA because of the health risks while the European Union banned their use in 2004.
• Deca PBDE has commonly been used in the electronics industry but has now been banned in Europe.

There is, however, growing concern that PBDEs may have a long environmental life.

Reference
Crystal Y. Usenko, Eleanor M. Robinson, Sascha Usenko, Bryan W. Brooks, Erica D. Bruce. PBDE developmental effects on embryonic zebrafish. Environmental Toxicology and Chemistry, 2011; DOI: 10.1002/etc.570

Further Reading
Nomenclature
Haloalkanes
Structural Isomers
Functional Groups
Percentage Composition
Parts per Million Concentration

Study Questions

1. For the diphenyl ether molecule:
   • identify the ether functional group
   • give the molecular formula
   • calculate the molecular mass (formula weight)
   • calculate the percentage composition
2. For the 2,2',4,4',5-pentabromodiphenyl ether molecule:
   • identify the ether functional group
   • give the molecular formula
   • calculate the molecular mass (formula weight)
   • calculate the percentage composition
3. How many bromine atoms would be found in a molecule of each of the following:
   
   • dibromodiphenyl ether
   • tribromodiphenyl ether
   • tetrabromodiphenyl ether
   • pentabromodiphenyl ether
   • hexabromodiphenyl ether
   • heptabromodiphenyl ether
   • octabromodiphenyl ether
   • nonabromodiphenyl ether
   • decabromodiphenyl ether
4. Draw one structural isomer of each of the molecules above.
5. Name each of the molecules you have drawn in question 4 above.
6. Give the molecular formula for the molecules you have drawn that have been considered to be the least dangerous.
7. The blood of a child is found to have 70ppb PBDE. Convert this to:
   • ppm
   • mg/g
   • g/L
8. Assuming the child above has 4.7L of blood in his/her body, calculate the mass of PBDE present.
9. In the USA, the EPA set a "safe" limit of 7 micrograms per kilogram of body weight for PBDE. If the child above has a mass of 18kg, is the amount of PBDE in his/her blood considered safe? Explain your answer.
   
   
   
   

Cardanol

Chemists at The City College of New York have designed a molecule which has both water-adhering and water-repelling ends, from cardanol (the structure on the right), a naturally available material found in cashew nutshell liquid.

When mixed with water, the designer molecules formed a self-assembled structure called a micelle with a water-adhering exterior and water-repelling interior.

At 50^oC the micelles take on a 3-dimensional structure known as a vesicle that is about 200 times larger and more viscous. The molecules stick together enough to be draw out into a thin strand, just like glue.

Cooling the material allows the molecules to revert to their original micellar structure.

Heating causes the micelles to re-arrange themselves into an interlocking bi-layer which undergoes curvature. The structure is stabilized in part by the hydrogen bonding.

Reference
Vijai S. Balachandran, Swapnil R. Jadhav, Padmanava Pradhan, Sacha De Carlo, George John. Adhesive Vesicles through Adaptive Response of a Biobased Surfactant. Angewandte Chemie International Edition, 2010; DOI: 10.1002/anie.201005439

Further Reading
Detergents
Soaps and Saponification
Functional Groups
Percentage Composition
Intermolecular Forces
Intramolecular Forces

Study Questions

1. Identify the functional groups present in a molecule of cardanol.
2. Give the molecular formula for cardanol.
3. Calculate the percentage of carbon, hydrogen and oxygen present in a mole of cardanol.
4. On the molecular structure of cardanol, identify the water-adhering area and the water-repelling area.
5. What is the name given to a molecule that adheres to water?
6. What name is given to a molecule the repels water?
7. Draw a diagram to show how cardanol molecules could form a micelle.
8. Given the description of the behaviour of the designer molecule in the article above, in what ways do you think it differs from the structure of cardanol?
   

Organic Chemicals in Smoker's Breath

The Chemistry Department of the University of Girona (UdG) has been investigating the chemicals present in the breath of smokers. They analysed some volatile organic compounds such as benzene, 2,5-dimethylfurane, toluene, o-xylene and p-xylene, which could be used as bio-indicators of the condition of a smoker, and have shown that only 2,5-dimethylfuran provides effective results for breath samples. 2,5-dimethylfuran can also be present in the breath of passive smokers if they have had direct contact with tobacco smoke over a prolonged period.

Benzene is only useful as a bio-indicator when tobacco consumption is relatively high and when testing takes place 1-2 hours after a smoking a cigarette.

Toluene and xylene levels are only significant for those who smoke a lot and when little time has passed since smoking the last cigarette.

Reference:
Monica Alonso, Mar Castellanos, Juan M. Sanchez. Evaluation of potential breath biomarkers for active smoking: assessment of smoking habits. Analytical and Bioanalytical Chemistry, 2010; 396 (8): 2987 DOI: 10.1007/s00216-010-3524-z