The Chemistry Behind the Gifts for the King of Kings

This time, it is less than a week until Christmas and it is quite appropriate if this time we are digging one of the stories around Christmas, which is the adoration of the magi. The magi, sometimes they are called the wise men or kings, travelled from far east to Bethlehem following the Star of Bethlehem to pay homage to the Infant Jesus. They also brought three gifts to be given to the King of kings: gold, frankincense, and myrrh. This story and the gifts they brought are immortalised in several Christmas carols, one of them is "We Three Kings" by John Henry Hopkins.
We Three Kings arr. Martin Neary and sung by King's College Choir at 2012 Festival of Nine Lessons and Carols. For lyrics, click here.

This time, for Christmas special, we'll see the chemical significance of those gifts for the Infant Jesus.

The golden story of gold

The golden funeral mask of Tutankhamun (wikipedia) 
Gold has been interacting with humans since the dawn of civilisation and it has been synonymous with wealth. It is likely that gold is the first elemental metal known to man. According to Inca people, gold is the tears of the Sun God Inti while the Ancient Egypt believed gold is the skin and the flesh of the Sun God Ra. The connection between gold and the god of the Sun by ancient people is due to one of its unique properties which is its golden colour; caesium could also be considered to have a golden hue. The golden colour of gold can be explained but we need to dig down into its electrons. 
Gold in periodic table (webelements.com)
To understand the electrons of gold, we need to know the position of gold in the periodic table. Gold with the symbol Au, from aurum, lies in group 11, or known as coinage metals, with copper (Cu), silver (Ag), and roentgenium (Rg) and in period 6, the second lowest row in of the periodic table, with the neighbouring elements of platinum (Pt) and mercury (Hg). This position means gold has quite high number of protons in the nucleus which means its electrons move at a speed close to the speed of light. Then, considering the Einstein's theory of general relativity, the moving electrons are heavier than the electrons at rest due to relativistic effect. Hence, the contraction of the size of atomic orbitals happens. For gold, its two highest energy atomic orbitals corresponds to blue light. Therefore, electrons in gold absorb blue and violet light, reflecting red and orange wavelengths and appearing gold-coloured.
Emission spectrum of gold (http://chemistry.bd.psu.edu/jircitano/Au.gif)


Frankincense and myrrh

Frankincense and myrrh (shutterstock)
Similar to gold, frankincense and myrrh have been intertwined with humanity trough time, from the frankincense pellets found in the ancient tomb of Tutankhamun to myrrh-infused brandy was used to preserve a 19th century British war hero Vice Admiral Horatio Nelson. The substance musky plumes of smoke are most often associated with embalming, perfumes, and religious rituals including in the ancient temples of Jerussalem and modern Roman Catholic liturgies.

Frankincense and myrrh are gum resins from trees; frankincense are collected from trees in the Boswellia genus, and myrrh are collected from the trees in the Commiphora trees. Both plants commonly grow on the Arabian peninsula. To access the aromatic resins, the farmers slice gashes into the trees at harvest time and collect the milky resins that come out from their bark. Once to expose to air and sun, myrrh dires and hardens to reddish-brown pea-sized chuncks, whereas frankincense dries to pale yellow-tear-shaped droplets.

The biochemistry of the plants and also the chemical entities of myrrh and frankincense are affected by the geography and the climate where the plants grow. Therefore, it is impossible to know an exact chemical composition of myrrh or frankincense. Howeveer, both resins do contain sugar chains, proteins, and steroids, and are mostly a blend of terpenes, a diverse family of hydrocarbons made frpm five-carbon building blocks.

For example, frankincense contains a significant percentage of triterpenoids such as boswellic acids, but this compound does not contribute to the smell because it is too heavy to be volatile compounds. Instead, a range of different compounds are present in the smoke: octyl acetate, octanol and various terpenoid compounds and recently researchers have identified that olibanic acid as the key chemical which are responsible for its distinctive aroma, despite only being present in trace amounts. Meanwhile, myrrh's aroma comes mostly from furanosesquiterpenes such as furanoeudesma-1,3-diene.

Besides their aroma, humans have been investigating both resins for centuries but in just recent years researchers have been able to investigate their bioactivity. For example, a study led by researchers at from the USA suggested that frankincense extract provides relief to arthritic knees patients. Such extracts have been used for centuries in traditional medicine but the new study was funded by a company that makes frankincense extract, and the claims have not been evaluated by the Food and Drug Administration.

Another study in Italy showed myrrh could have analgesic effects in mice. The team suggested that furanoeudesma-1,3-diene and another terpene are responsible for these effects by affecting opioid receptors which influence pain perception. 

A study conducted at the Hebrew University of Jerussalem found evidence that a compound in frankincense resin exhibits depression- and anxiety-dampening effects in mice. Besides that, the team demonstrated that the compound, a diterpenoid called incensole acetate, activates an ion channel involved in warmth perception in the skin.

Although, no results have been showed in humans it is possible that incensole acetate intensify the euphoric feeling produced during religious.

Finally, I wish you all a happy Christmas!

References
The articles
  1. C. Drahl, What's That Stuff, 2008, 86, 38. https://pubs.acs.org/cen/whatstuff/86/8651sci2.html
  2. Compound Interest: The chemistry of Gold, Frankinsence, and Myrrh, 2014, http://www.compoundchem.com/2014/12/23/gold-frankincense-myrrh/
  3. Compound Interest: The Aroma of Frankinsence, 2016, http://www.compoundchem.com/2016advent/2016advent17/
Research Journals
  1. J. R. Riley, A.D. Smith, D.R. Reynolds, A.S. Edwards, J.L. Osborne, I.H. Williams, N.L. Carreck, and G. M. Poppy, Nature, 1996, 379, 29.
  2. K. Sengupta, K.V. Alluri, A. R. Satish, S. Mishra, T. Golakoti, K.V.S. Sarma, D. Dey, and S. P. Raychaudhuri, Arthritis Res. Ther., 2008, 10, R85.
  3. A. Moussaieff, N. Rimmerman, T. Bregman, A. Straiker, C.C. Felder, S. Shoham, Y. Kashman, S.M. Huang, H. Lee, E. Shohami, and K. Mackie, FASEB J., 2008, 22, 3024-3034.

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