ARTICLE FROM AN INTERESTING SITE
CALLED ANCIENT ORIGIN
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| PHARAONIC GOLD RING |
The periodic table of chemical
elements turns 150 this year. The anniversary is a chance
to shine a light on particular elements some of which seem ubiquitous but which
ordinary people beyond the world of chemistry probably don’t know much about.
One of these is gold, which was
the subject of my postgraduate degrees in chemistry, and which I have been studying for almost 30 years. In chemistry, gold can be considered a
late starter when compared to most other metals. It was always considered to be
chemically “inert” but in recent decades it has flourished and a variety of
interesting applications have emerged.
A long, curious history
Gold takes its name from the Latin
word aurum (“yellow”). It’s an element with a long but rather mysterious
history. For instance, it’s one of 12 confirmed elements on the periodic table
whose discoverer is unknown . The
others are carbon, sulfur, copper, silver, iron, tin, antimony, mercury, lead,
zinc and bismuth.
Though we’re not sure who
discovered it, there’s evidence to suggest it was known to the ancient
Egyptians as far back as 3000 BC .
Historically, its primary use was for jewellery; this is still the case today, it’s also used in mint coins.
Gold is also found in ancient and modern art: it’s used to prepare ruby or
purple pigment, or as gold leaf.
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| Egyptian golden lion sculpture (Dieter Hawlan / Adobe Stock) |
South Africa was once the top gold-producing country by far: it mined over 1,000 tonnes in
1970 alone. Its annual output has steadily fallen since then – the top three
gold producing countries in
2017 were China, Australia and
Russia, with a combined output of almost 1000 tonnes. South Africa has dropped
to 8th position, even surpassed by Peru and Indonesia.
But gold’s uses and its chemical
properties extend into many other areas beyond jewels and minted coins. From
pharmaceutical research to nanotechnology, this ancient element is being used
to drive new technologies that are pushing the world into the future.
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| Ancient Egyptian jewelry bracelets and necklaces of gold (EdNurg / Adobe Stock) |
Why and how it’s useful
Of the 118 confirmed elements in
the periodic table, nine are naturally occurring elements with radioactive isotopes that are used in so-called
nuclear medicine. Gold is not radioactive but is nevertheless very useful in
medicine in the form of gold-containing drugs.
There are two classes of gold drugs used to treat rheumatoid arthritis. One is
injectable gold thiolates – molecules with a sulfur atom at one end, and a
chemical chain of virtually any description attached to them – found in drugs
such as Myocrisin, Solganol and Allocrysin. The other is an oral complex
called Auranofin.
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| GOLD SHOES OF KING TUTANKHAMON (1332 BC) |
Gold is also increasingly being
used in nanotechnology. A
nanomaterial is generally considered a material where any of its three
dimensions is 100 nanometres (nm) or less. Nanotechnology is useful because it
is not restricted to a particular material – any material could in principle be
made into a nanomaterial – but rather a particular property: the property of
size.
For example, gold in its bulk form
has a distinct yellow colour. But as it is broken up into very small pieces it
starts to change colour, through a range of red and purple, depending on the
relative size of the gold nanoparticles. Such nanoparticles could be used in a
variety of applications, for example in the biomedical or optical-electronic fields.
Another exciting advancement for
gold in nanotechnology was the discovery in 1983 that a clean gold surface
dipped into a solution containing a thiolate could form self-assembled monolayers . These
monolayers modify the surface of gold in very innovative ways. Research into
surface modification is important because the surface of anything can show very
different properties than the bulk (that is, the inside) of the same material.
More to come
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| Pharaonic Gold dentistry |
Gold nanoparticles have also
proven to be an effective catalyst. A catalyst is a material that increases the
rate of a chemical reaction and so reduces the amount of energy required
without itself undergoing any permanent chemical change. This is important
because catalysis lies at the heart of many manufactured goods
we use today. For example, a catalyst turns propylene into propylene
oxide, which is the first step in making antifreeze.
Two discoveries in the 1980s made
scientists look at gold catalysis differently. Masatake Haruta, in Osaka,
Japan, made mixed oxides containing gold – and discovered the material was remarkably active to catalyse
the oxidation of toxic carbon monoxide into carbon dioxide. Today, this
catalyst is found in vehicle exhausts.
At the same time Graham Hutchings , who was working in
industry in Johannesburg, South Africa,
discovered a gold catalyst
that would work best for acetylene hydrochlorination. This process is
central to PVC plastic, which is used in virtually all plumbing production.
Until then, the industrial catalyst for this process was using environmentally
unfriendly mercuric chloride material.
3D illustration of gold
nanoparticles (Kateryna_Kon / Adobe Stock)
Many applications
In my opinion, gold has many more
uses that haven’t yet been discovered. There is much more to come in the world
of gold research .
There will, in the next few years,
be new developments in how the element is used in, amongst others, medicine,
nanotechnology and catalysis. It will also find new applications in
relativistic quantum chemistry (combining relativistic mechanics with quantum
chemistry), surface science (the physics and chemistry of surfaces and how they
interact), luminescence and
photophysics – and more.
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| Ancient Peruvian mask made of gold (Carlos Santa Maria / Adobe Stock) |
The article ‘ From medicine to
nanotechnology: How gold quietly shapes our world ’ by Werner van Zyl was first
published on The Conversation and has been republished under a Creative Commons
license.
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This article is the property of "Ancient Origin"
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