Abundant Chemistry of Life: Nitrogen and our Chemical History

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Earth observation image of the Moon taken during STS-100 Image Courtesy of NASA

Earth observation image of the Moon taken during STS-100
Image courtesy of NASA

Molecular nitrogen (N2), the most abundant constituent in our atmosphere, figures strongly in Earth’s biochemical cycles. If you were to look for nitrogenous compounds on the moon, Mars, or Venus, however, you would not readily find nitrogen-containing compounds. Ammonia and molecular nitrogen do not appear prominently in any organic or geochemical cycle. That, in a few words, may be a ‘telling point for non-existence of life’ beyond Earth.

Because of nitrogen’s relative abundance, one may assume it played a major role in the evolution of life upon Earth. So as with carbon and hydrogen, nitrogen is an element that is important to our life in the habitable zone.

Chemical Elements Come From Stars

The birth of the chemical elements lies in the stars; and especially with the first stars formed in the Universe. Based on science’s calculations, the first stars were primarily hydrogen/helium supergiants whose lifespans were rarely more than one billion years.

At the end of their lifespans, these supergiants probably underwent hyper supernovae. The reasons for the hyper supernovae plays into the question of size; larger size stars burn through their fuel much more readily than smaller stars like the Sun. Thus, these supergiants were perhaps tens of thousands of times the size of the Sun. It was during the throes of hyper-novae, the supergiants created other elements. In this process, termed nucleosynthesis, we come to see the energetics of element creation; an energetics that rivals the Big Bang.

Our Solar System’s Chemical History

Although the Solar System appeared on the scene 10 billion years after the Big Bang, a chemical history of our Solar System might be summed with the following sentence.

Our specialness, our uniqueness and our place is due to the quantum mechanical laws governing CHNOPS molecules (Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus and Sulfur) in a watery mixture.

In other words, the natural laws of the Universe dictate how life would follow from hot energetic mix of particles at Universe’s birth to habitable zone temperatures of which we are familiar.

The element nitrogen, in bio-molecules, is a part of the ‘water-loving neighborhood of elements’ (Oxygen, Nitrogen, and Hydrogen) that help to determine much of the reaction chemistry and machinery (the most energetically stable form of molecule) of biomolecules.

Hydrogen bonding, in a nutshell, was how Watson and Crick (utilizing the X-ray data of Dr. Rosalind Franklin) deduced the structure of DNA (to be the double helix). That stable form of DNA interconnects the molecule in profound ways that have further repercussions for life upon Earth.

Nitrogen-hydrogen Bonding

Nitrogen-hydrogen bonding plays other roles in the molecular machinery of life. If one finds Earthly life present, water is nearby along with the previously mentioned elements of hydrogen, oxygen, and nitrogen. Nitrogen and its role in the hydrogen bond prevails in the chemistry of hemoglobin and other proteins as well. In most cases of nitrogen-hydrogen bonds, one will find ‘stability,’ a geometric type of stabilization one does not find in cases where nitrogen or hydrogen might be replaced with another element.

The periodic table of the element may include more elements in the future. Photo by 2012RC

The periodic table of the elements – what does it tell you about our universe? Image by 2012RC

A specific case study is when one looks upon the periodic table of the elements; directly below nitrogen is phosphorus and below phosphorus is arsenic. Within the cross-disciplines of physical science, lies a fundamental notion utilizing Occam’s razor. (Occam’s razor states that the simplest explanation for anything is most likely correct.)

A geologist utilizes the simplest explanation of a concept that would rationalize his data and hypothesis: substituting phosphorus or arsenic into his work seems logically consistent.

An analytical chemist, on the other hand, could not readily make that generalization based upon Occam’s razor. The context of each decision is the periodic table, but the results from experimentation are inconsistent.

We see hydrogen bonding readily with nitrogen but it is weak to non-existent with the phosphorus and arsenic analogs. Thus we find no ‘stabilization due to the hydrogen bond’ and no ‘life-compelling reason’ for phosphorus to bond with nitrogen.

Most Abundant Elements of Life: CHNOPS

What is ‘CHNOPS’? This acronym comes from the chemical abbreviations of carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S), the most abundant elements of life.

From the stars to Earth, chemistry joins life to the Universe.

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