The age of molecular machinery
Being the basis of research behind the Nobel prize in chemistry, the area of molecular machinery is now showing a lot of promise. Biology has, for centuries, perfected the art of molecular machinery in the human body, with much of the complex tasks done by proteins a result of molecular-level machines. Now scientists are trying to synthesise this artificially in the most efficient way, and attempt to understand and mimic the process our body has been using for millennia, and catching of many within the community
The research mainly included the development of mechanically interlocked molecular architectures or molecular knots (or MIMA) such as rotaxanes and catenanes. These structures are held together by mechanical bonding. Unlike a chemical bond which focuses on the sharing or transfer of electrons, a mechanical bond involves a mechanical restraint that prevents two parts of a molecule from separating. Mechanical bonds have been shown to reduce the kinetic reactivity of the products, and this has been described as steric hindrance. However, there is no effect on the covalent bond itself leading MIMAs being further investigated in technological applications ( expand on this). The synthesis of these rotaxanes and catenanes has since been made efficient by combining supramolecular chemistry with traditional covalent synthesis.
Supramolecular chemistry, also known as “chemistry beyond the molecule”, focuses on the study of molecular recognition and high-order assemblies formed by noncovalent interactions. Supramolecular chemistry has become an interdisciplinary area of research, now playing a vital role in providing insights across biology, nanotechnology, material sciences etc. A lot of molecular structures and knots are now being recognized and explained by supramolecular chemistry, as well as creating molecular machines through non-covalent bonds.
The introduction of these have dramatically increased interest among chemists and has since changed the way they think about molecular machinery. Although they have always been thought to only exist in artificial molecules, research has since shown that they also exist in biological organisms, especially in a variety of proteins.
In 2011, a nano car - a four-wheeled benign successfully driven across a copper surface made the news. The motor has been designed to rotate in a single direction, which is extremely significant considering it is very difficult to mimic or control a molecule’s directionality since they move so randomly and constantly. The reason behind this random movement is explained by the Brownian motion, so manipulation of this principle to give the desired direction is the key to achieving successful molecular machines.
David Leigh from University old Manchester has also done some very fascinating experiments in its application within the human body. He designed a linear motor to mimic a motor protein that walks down a track, in an effort to investigate whether artificial molecular motors can function complex tasks at a nanoscale level. The reaction is dependent on the application of four external stimuli: acid, base, UV light, and visible light in the presence of iodine. Molecular motors are quite frequently used in the body, to carry the reaction away from chemical equilibrium and bring them into action once again. Gravity is negligible in the molecular world, so one foot must be locked in place so that the molecule doesn’t fly off the track when the molecule is travelling from A to B. When one foot is pinned down, the other foot will be able to step forward and lock onto the track, and vice versa. The team uses disulfide bonding on one foot through being locked in acid and hydrazone bonding on the other with basic conditions. Through changing the acid-base condition. However, to determine the direction of the motor, photochemistry comes in, isomerising a built-in stilbene unit on the track induces ring strain in the motor and entices it to move in one direction over the other.
Even though these experiments among many are going a long way in attempting to miniaturise machines in the microscopic world, there are a lot of challenges that still need to be addressed in order to bring these concepts into application in the future, many lying still in figuring out and handling the sheer complexities in these machines, and stability in their synthesis. Many scientists are still debating its use and applications within the macroscopic world, with the potential application within molecular prosthetics and transport at the molecular level. Even with decades worth of research still left in making this concept a reality, it is no doubt going to be a topic of hot research within the scientific world.
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