Chemistry of Mighty Putty

Oh no… my shelf just broke! What should I do??

I should use mighty putty! Take a look below…

 

What is it?

Mighty Putty is a simple and useful chemical reaction that can be done by anyone! There’s no degree in chemical engineering required!  But how? How is it that everyone has the ability to complete a complex epoxy reaction in the palm of their hand? That’s where the chemistry comes in.

 

Where did it come from?

In the 1930s, a German firm called I.G. Farben Industries began researching epoxy reactions purely out of academic curiosity. They gained more fame as viable products in the 1950s after being introduced to North America by Jim Peters B.Sc., the founder of the company Industrial Formulators. His revolutionary experiments using Epoxy Reactions eventually lead the front for industrial applications of epoxide chemistry around the world.

The first U.S. scientist to work with this branch of science was  Dr. S.O. Greenlee, who discovered Epoxy Reactions soon after Peters. Over time, U.S. companies continued developing epoxy reactions until they were finally released to the public.

Today, a well-known example is advertised on TV as Mighty Putty. Mighty Putty’s quick spread throughout the U.S. has only added to the interest in this chemical reaction.

Yet even today, new experiments with Epoxy Reactions are still being performed. Anything could happen in the next few years.

 

How does it work?

To induce the reaction, the two parts of the Mighty Putty must be mixed together, and a multi-step reaction process begins.  Around the outside is the epoxy resin and on the inside lies the curing agent, or hardener. Pay close attention to these two terms throughout the following explanation.

 

The epoxy resin is composed of Bisphenol A (BPA) and epichlorohydrin (ECH). In part one of this two-part reaction, two epoxy groups are formed on the ends of the Bisphenol A compound as it begins mixing with the ECH. This produces a thick, glue-like product that can be molded and shaped to the user’s preferences. This is consistent with the malleable consistency of Mighty Putty as the user molds it into the desired shape.

 Reaction between Bisphenol A and epichlorohydrin, for more info click on the picture!

 

The second step involves setting or “curing” the reaction to make it strong. The hardening component in Mighty Putty, also known as the “curing agent” of an epoxy reaction, can only react with the initial reaction’s final product. The curing agent is composed of polyamines which are very similar to ammonia in structure, and are strongly alkaline.

Structure of polyamines. Note the three amine groups, as they become important in the later reaction.

 

The amine groups in the hardener react with the epoxy groups that were formed earlier in the first reaction to form a “cured” resin. This reaction is exothermic, and slowly cools to form an impressively strong substance.

The total cure time required for this reaction depends on the rate determining step.  In this case, the initial endothermic elementary step of the reaction between Bisphenol A and epichlorohydrin will determine the speed at which it goes to completion. Thus having a greater mass of epoxy resin – as seen around the outside of the Mighty Putty – can increase the speed of the reaction. This is also why the reaction is known to accelerate, as the heat from the second step begins to aid in the reaction of the initial step. By this same logic, the reaction slows down as the hardening agents overwhelm the mixture and the substance cools.

 

So why is it SO strong?

The strength of Mighty putty can also be explained through its chemistry. Epoxy resins are also known to be thermosetting materials. Thermosetting plastics can be cured and “set” to hold a particular form – the reaction for which was just explained. These reactions also form tightly linked cross-polymer structures.

This diagram shows the difference between polymer chains and cross-linked polymer chains.  The structure is much more connective and stable.

 

These structures explain the immense strength of the product, because bonds can be formed not just between and within molecules, but also across the polymer chains – which explains the name. In addition, strong polar bonds between the putty and its applied surface keep it locked in tight.

 

What else can Epoxy Reactions do?

Although Mighty Putty is a great example of epoxy reactions, that’s certainly not the only way they are can be applied. Epoxy reactions can also occur as a foam, liquid, and adhesive backing.

When used as a foam or liquid, cooling time is key.  These reactions can be more sensitive to surrounding environments and temperatures. The sharp scent of ammonia can also be dangerous to work with which is why this is mostly seen with professionals.  However, the end result is still a rather rigid yet lightweight material that can bond two surfaces together.

Otherwise, Epoxy Reactions are simply used as putty adhesives or some variation thereof. When used as an adhesive it can fix almost anything. Examples include creating a mug handle, fixing leaking pipes, and most importantly fixing that broken shelf!

 

Ready to buy it yet? 

         So maybe not everyone has a “broken shelf” to go fix, but the immensely useful applications that result from a simple chemical reaction are clear. And how can Mighty Putty have the strength to pull an entire truck?!  It’s all in the chemistry of epoxy reactions.  Just another way to show how the little things in life can end up being the most important.

 

Stay tuned for the next Chemistry of Infomercials blog post… coming soon!

More Sonochemistry!

As discussed in the previous blog post, the most practical use for sonochemistry in the lab is for reactions involving liquids and solids, because of the acoustic cavitation process.  Again, acoustic cavitation refers to the ultrasound-induced implosive collapse of a gas bubble in a liquid, and it occurs when the alternating regions of high pressure and low pressure in the sound wave cause the bubble to becomes too large for the intermolecular forces to hold it together, as pictured below.

Acoustic cavitation occurs both when a homogeneous liquid solution is exposed to ultrasound and when a heterogeneous solution with solids is exposed to ultrasound. However, the specific effects of this process are significantly different for each of the two phases, so acoustic cavitation in homogeneous liquid solutions must be distinguished from acoustic cavitation in heterogeneous solutions with liquid-solid interfaces.

For acoustic cavitation in homogeneous liquid solutions, the bubble collapse produces extremely large amounts of energy by converting sound energy to kinetic energy of the liquid molecules, and then to heat energy.  The site of the bubble collapse becomes a localized high energy spot in the solution, having temperatures of about 5200 K and pressures of hundreds of atmospheres, according to experiments done by Dr. Kenneth S. Suslick, a chemistry professor at the University of Illinois.  These extreme conditions inside the cavities induce many effects in the rest of the system, one notable effect being chemical reactions.  The heat energy in the cavities can be used to overcome the activation energy barrier, and the unequal distribution of pressure as a result of the high pressure cavities spontaneously mixes the solution, which of course, causes the reaction to occur at a faster rate.  Therefore, sonochemical reactions involving homogeneous liquid solutions occur in the same way as traditional reactions (reactions that are induced simply by directly adding heat) just at faster rates.  Another effect that the localized high energy cavities can have on homogeneous liquid solutions, under certain conditions, is sonoluminescence.  Sonoluminescencerefers to the ultrasound-induced emission of light from imploding bubbles.  The exact mechanism of sonoluminescence is uncertain, but it occurs when various atoms present in the cavity become ionized because of the extremely high temperatures, and then recombine with the removed electrons and release photons.  Here is an image of sonoluminescence reproduced in a lab.


For acoustic cavitation in heterogeneous solutions with a liquid-solid interface, the bubbles still collapse and create local high energy spots, but one major difference is that the collapses occur in irregular shapes, as opposed to the spherical shapes of the collapses in homogeneous liquid solutions.  The cavities occur in irregular shapes because of the uneven distribution of solid particles around the bubble, which of course restricts the bubbles’ spacial arrangements.  It is partly because of these irregularly shaped cavities that sonoluminescence does not generally occur in heterogeneous solutions with a liquid-solid interface; sonoluminescence is a process that only occurs in homogeneous liquid solutions.  Another major difference is that the extreme conditions of the local high energy cavities have different effects on liquid-solid interfaces than they do on just liquid interfaces.  In liquid interfaces, the extreme conditions really only result in the liquids mixing with each other, but in liquid-solid interfaces, the extreme conditions can generate jets of high speed liquid, as shown in the image below.

 

These jets of high – speed liquid can reach speeds of up to 100 m/s can accelerate the solid particles in the solution, if they come into contact with them, which often results in high velocity collisions between solid particles (see video above starting at 2:05).  These collisions can cause significant damage to the solid particles, including changing the surface morphology and composition.  There are also high-pressure shock waves associated with the high-speed jets, that can have pressures as large as 10^4 atm.  These shockwaves themselves can also cause deformation of the solid particles.  These effects on the solids are significant for the chemical system as a whole, because they can drastically change the mechanisms of the chemical reactions that occur, or even cause completely different reactions to occur, reactions that would never happen if only heat was added to the system.

Crème de la Crème: Chemistry Behind Ice Cream and Whipped Cream

I scream; you scream; we all scream for ice cream! This very familiar rhyme is nostalgic for many, who instantly remember a much happier time in their lives. The sounds of children chasing an ice cream truck that constantly exudes kid-friendly tunes. To many, ice cream is a sweet treat savored on a hot summer’s day. Whipped cream, on the other hand, is a delectable addition at any time of the year. It could be sprayed on strawberries or atop a freshly baked pie. What you may not know, are all of the minute factors that make these forms of cream such an attraction.

 

Fat agglomeration examples

Fat destabilization, also known as fat agglomeration, is something that is necessary to create milkfat structures such as ice cream and whipped cream. Fat agglomeration is a general term referring to the different ways that fat globules destabilize and stabilize when undergoing different chemical reactions. This includes things such as flocculation and partial coalescence, both integral processes in the creation of cream substances. Flocculation is an irreversible clustering of fat globules, or particles. The way that these fat globules cluster can be explained by partial coalescence. This dictates that fat globules are combined and held together by fat crystals and liquid fat found in cream. Now that we have identified the fat globules found in cream, we can look deeper into how ice cream and whipped cream is actually formed.

Partially coalesced fat globules

When ice cream is made after the process of churning, the liquid ice cream is churned as it freezes until it’s as thick as softly whipped cream. While it is being churned, air is added so the ice cream has a greater volume. This is called emulsion, which will be further explored later. The main difference between ice cream and whipped cream is that ice cream is usually made from homogenized milk. Homogenized milk prevents creaming because it decreases the size of globules as well as even them out. Other ingredients are then added to ice cream to create its texture, such as salt. Milk does not freeze at 32°F like water, so salt is poured on the ice and the temperature reaches 0°F (-18°C) and it has a briny texture instead of having solid ice.

Think back to when you made ice cream in class using two plastic bags. There would be a larger bag that is full of ice and salt, and a smaller bag that contained the milk, sugar and vanilla. Then you put the smaller bag inside the bag of ice and shake. The liquid in the smaller bag begins to freeze if there is no salt added to the ice. Since salt is added to the ice, the ice will melt faster, preventing the bag containing the milk and sugar, from freezing, instead making a slushy texture. When it comes to churning ice cream, the whipping action causes the fat emulsion to break down partially and flocculate. The air bubbles that are being beaten are stabilized by partially coalesced fat. Without emulsifiers, the fat globules would resist the coalescing because of proteins being absorbed to the globule preventing air bubbles from stabilizing and the texture would not be smooth.

Fat structure in ice cream and creation of fat 3D network

Similarly to ice cream, whipped cream is formed due to a phenomenon called an emulsion. This is when air is suspended in a fatty liquid, the fat molecules being integral in stabilizing the solution. Since cream is 35-40% fat, when emulsified, it becomes whipped cream, or when the temperature is low enough, ice cream. But, this is not all there is to emulsion. In fact, the dictionary definition of emulsion is being able to combine two liquids that usually do not mix together due to effects of polarity. Fats, being a lipid, are non-polar. The non-polar hydrocarbon chains that make up fatty acids are hydrophobic, meaning they do not want to bond with water. Unlike fats, water is a polar molecule, having a partially positive and partially negative end. For an emulsion to occur, an emulsifier must be added to the solution of water and fat to make them bond together. The emulsifier for ice cream is different than that of whipped cream, simply because there’s different ingredients to create desired taste and these ingredients include different proteins. But once we have fat globules and an emulsifier, the whipping begins.

 

Whipping cream allows air bubbles to be integrated into the fat globules and then the cream partially coalesces. As mentioned previously, this is an irreversible clustering of fat globules held together by both fat crystals and liquid fat. The cream only becomes what we know as whipped cream due to emulsifiers such as lactose and other proteins that are trapped in the spaces between fat and air. A distinct protein found in milk is casein, which is dispersed in the form of micelles. Here is a quick video on the structure of micelles.

Though the specific structure of micelles is not fully understood, it is known to have a hydrophobic and a hydrophilic end. Because of the way micelles form, with the hydrophilic ends on the outside and the hydrophobic ends on the inside, the fat globules can now bond with each other and water, which end up being trapped between the fat globules and air alongside lactose and proteins.

Fat globule with and without emulsifier

Whether its ice cream or whipped cream, chemistry does a lot of work to be able to create these dairy delicacies. Each bite, filled with fat globules, air bubbles, casein micelles, lactose, salt, sugar, and many other different proteins and lipids that you probably have never heard of. Its not easy for cream to foam or freeze to satisfy your sweet tooth. So, the next time you taste a scoop of ice cream or top off your dessert with a dollop of whipped cream, thank fat agglomeration for the beauty of which is a product of pure chemistry and biological compounds.

The Science of Scented Markers

Children love to color. Getting your first set of markers is almost like a rite of passage. It used to be “cool” just to get have even the plain 8 crayola colors, but now that there are so many types of markers out there, who needs the originals? Continuing with our recent theme if marker-based posts, we are here to talk about the oh so popular Mr. Sketch Markers! So how does the scent of banana, apple, and licorice get into the ink of a marker? It can all be attributed to what chemistry refers to as esters. 4.22

Where did the idea start?

Esters have been around forever. Seriously, forever. Naturally occurring esters can be found in almost every fruit in the world. In fact, perfumes and other fragrance-containing items were used throughout history by royalty before anyone even knew the actual chemistry behind them.

In the early 1800s, scientists finally began to question where the mysterious scent came from, and how they could make it last longer. The first ester was believed to have been synthesized in a laboratory in the 1800s, but information surrounding the event is vague and the name and date of the scientist to do so has been lost.

Later, German chemist Leopold Gmelin was credited with coining the term “esters” in his published paper in 1848. From this point on, esters were more commonly known and produced in laboratory settings for commercial value.

With the aid of technological advances throughout the next century, scientists can currently produce almost every scent known to man using the synthesization reaction use of esters.

 

How are they made?

Esters are the result of a combination of an alcohol and a carboxylic acid. The science here is mostly classified as organic chemistry because it puts a large focus on functional groups. Functional groups are groups of atoms bonded together in a specific pattern that reveal specific chemical properties. The structure of an ester functional group is shown below. Note the distinct central Oxygen atom, an easy way to categorize the molecule as an ester.

The formation of an ester is a result of a multi step chemical reaction as shown below. For example purposes, the reaction shows an arbitrarily chosen acid and alcohol combination. However, in reality, different combinations of these two requirements will yield different ester scents and characteristics.

As mentioned before, the chemical reaction to form an ester is a result of the combination of an alcohol and carboxylic acid. The conditions for ester formation are very specific. It requires a catalyst of concentrated sulfuric acid and the addition of heat. This means the reaction is endothermic and has a positive change in free energy, or in other words, it has a catalyst and requires an activation energy.

This reaction is also known to be sped along by using LeChatelier’s Principle. By adding excess alcohol or acetate in the formation can aid in pushing the reaction to produce more ester. In addition, a common technique used by manufacturers is to evaporate the water, also forcing the reaction to the right.

By adding the ester solution to the natural dye of the marker, Mr. Sketch is essentially creating a scented ink. So when we draw on paper and smell the result, what we’re really recognizing is the presence of esters.

 

Where else do we find esters?

Esters have tons of uses that benefit everyone from the prankster to the king. Have you ever smelt a stink bomb? That is an ester. Have you ever smelt perfume? That, too, is made from esters. The wide variety of ester combinations allow for a plethora of smells, both good and bad.

But lets focus on the good. Every scented perfume, shampoo, and creme makes use of esters to produce the smell that we the consumers find so appealing. Lab workers labor tirelessly to mix and combine different ester scents to create newer, better smells every day.

Another, unexpected, use of esters is actually in the production of polymers. Liquid esters of low volatility often serve as softening agents for some resins and plastics. Plexiglass, a solid transparent plastic, is composed of Polymethyl methacrylate, Terylene, Fortrel, and Dacron contain polythylene terephthalate as a film or fiber.

 

What now?

          As you can there are many wonderful uses for esters in the world around us. As complicated as esters are, there are hundreds of things in your house right now that are made using this process. From cleaners and perfumes, to candy and markers, esters are all around us making our lives smell differently, for better… or worse! Good thing we have Mr. Sketch Markers brighten the day and “make the stench go away”!

How It’s Made: the Drug Discovery Edition

Medicine, drugs, remedies–whatever you call them, they are a necessary part of 21st century society, and each and every one of them has been discovered or synthesized through a series of reaction. Previously, we have talked about specific drugs, specific structures, and what they did individually, and now, we’re going to tell you why it all works.

Many of the drugs that you take on a daily basis are not naturally occurring, and so they have to be synthesized in a lab through a series of reactions.Many of these reactions include the creation of chemical structures through the combination of molecules at certain places. But I can hear you asking, “Why does it bond together?” Here’s why…

Organic Chemistry and Thermodynamics and Kinetics

This image shows the structures of diamond and graphite.In chemistry, molecules bond with each other if the conditions are thermodynamically favorable, or in other words, if the change in Gibb’s free energy is negative and the reaction is therefore spontaneous. When talking about synthesis for reaction that are spontaneous, it is also extremely important in pharmacology to consider the kinetics of the reaction. There may be a way to create a life-saving drug through one, spontaneous reaction, however if the reaction is kinetically extremely slow, there will never be enough to create a viable amount of the drug. Thus, in drug synthesis, it is important to consider variables that will increase the rate of reaction such as temperature, pressure, and using catalysts. To help visualize this, think of diamonds: the reaction of the crystal turning into graphite is spontaneous, because graphite is a more stable state, but it happens so slowly that you never notice it happening to your own jewelry. So, when creating a drug, developing a reaction is not all that there is to think about.

However, that step is also very important, especially when thinking about how much energy is needed to create the compound, whether or not it would form properly, and if the reverse reaction would be spontaneous if the forward reaction is not. In addition, when considering the reaction itself, it is necessary to consider the chemical structure of the compounds, and how they would bond together. For this, it is necessary to consider their organic chemistry of the compounds, and how they would bond to create the lowest possible energy state for the highest stability. Thus can be done by considering resonance structure, orbitals, bonds, and electron configurations. This is significant because the molecules will form the most stable compound with the lowest potential energy, which in some cases may not be the intended structure.

This shows the reaction for the synthesis of the Quinoline Ring, indicating the structure with the lowest potential energy and thus the most stability.

Intermolecular Forces and Kinetics

When talking about drugs, it is imperative to consider the human body, or whatever body the drug is going into, and the molecules that are in that body. The first main thing to consider is the intermolecular forces between the molecules in the drug and the the molecules in the body. As there will always be London Dispersion forces, and those are dependent on size, it is not as significant as Hydrogen bonding and Dipole-Dipole forces. These forces may impact how the  drugs spread throughout the body, especially with certain enzymes and proteins. Kinetics within the body is also extremely important, because aspects such as the rate of reaction with a certain molecule or organism is important to how concentrated the drug will be, the dosage, and how fast it This is a graph for the half life of a compound, showing the relative time and amount of substance.is intended to work. Also, with kinetics, the half-life of drugs is very important to the parameters of the drug, because depending on the drug, it could be able to stay in the body for weeks or longer because of a very long half life, or have been processed by the body within a matter of hours. One example where this is important is with antiretroviral medications given to patients with HIV. These medications must be taken very often because they have very short half lives and are digested by the body at a very high rate, so in response researchers are trying to develop a drug with a much longer half life so that the drug can be taken much less often and will become a sustainable solution.

Electrochemistry

Electrochemistry is very important in the development of drugs, both for synthesis and for gathering information on different parameters and properties. Some specific examples where electrochemistry is used in research is the investigation of reactive oxygen species, the biooxidative and bioreductive activation of pro-drugs, and DNA alkylation. As for the synthesis, electrochemistry is a widely known and widely used method to create certain physiologically active compounds.

The StruggleThese statistics show the increasing costs of creating new drugs.

The struggle in the synthesis of new drugs is forming an initial reaction that would actually occur. This takes place even before the laboratory, by chemists who research different molecules and how they can be broken and form new bonds with other molecules. In many cases, certain molecules with key structures such
as those mentioned before (beta-lactam ring and quinoline ring) must first have certain bonds broken in order to bond with another molecule at another place. The second task is to find a reaction such that the formation or breaking of bonds at certain places is thermodynamically viable so that the reaction will occur. The next part of this is done in a lab, to test the reaction, to measure its kinetic properties, and to see if the creating of the therapeutic molecule is capable of commercial viability. From there, there are countless reactions that were not planned for which may cause fatal reactions in animal models which make the drug unsuitable for human consumption.

According to recent statistics, only 1 out of 5,000 drugs which are initially created in a preclinical setting are approved by the Food and Drug Administration to come onto the market, making the cost of creating new drugs astronomically high. Not only does this hinder the drug companies, but also the people who buy these expensive medicines. That, is the pharmacological struggle.

The Future of Medicine: Drug Designing

Using C-F Bonds to Slow Drug Metabolism and Increase Potency

 There is a lot of chemistry that can be discussed about established medicine currently on the market. However, one of the most interesting topics to look into is how new drugs are being developed. With the advanced technology we have today and the vast knowledge of both chemistry and biology that we possess, there is a lot that is done to manipulate chemicals to get the best drugs we can for the purposes we need them for. This is the exciting field of drug synthesis.

Illustration of the various components of a good medicine: the best possible activity, solubility, bioavailability, half-life, and metabolic profile

Of course, there is so much that can be delved into just for this one topic. There are so many factors that make a drug a “medicine.”  The characteristics of a particular molecule are important, and even necessary, to how it functions. Now, what the pharmaceutical industry is trying to figure out how to make these drugs in the most efficient way possible, create more of them with new techniques, and to find those which are most effective in the human body.

Redox Chemistry and Hydrogen Bonding

One of the most studied and crucial characteristics of a drug to know about is how it is metabolized in the body. Most basically, drug metabolismdescribes how a drug is processed and excreted from the body. The metabolism of a certain drug effects how long it will stay in the body, which in turn affects how long effective concentrations of the drug will be able to perform their functions. Of course, therefore, drug metabolism is of interest to many people, particularly to pharmaceutical companies creating new medicines. Luckily, drug metabolism  is largely affected by the chemical interactions of the the drug molecules, which is something that we can control by manipulating chemical structure. Two things in particular, the oxidation of the drugs as well as hydrogen bonding are often taken into consideration.

Here is a quick overview of redox reactions to go over:

Here is a quick overview of hydrogen bonding.

The Carbon-Fluorine Bond

Let us regress for a second, and establish a basis for what we shall talk about. Naturally there are no carbon-fluorine bonds in the human body. Why? They simply do not occur in nature and hence do not show up in the human body. (Usually in nature there are carbon-hydrogen bonds instead.) Yet, strangely enough, looking at the chemical structures of many drugs, many of them do contain carbon-fluorine bonds. This helps the body more effectively process the drugs, since the body does not know how to digest these molecules and they remain in the body longer. This is because of the particular nature of the bonds, namely that it is polar. The fluorine atom is more electronegative than carbon atoms, and therefore pulls electrons towards itself. The fluorine side of the bond is therefore pseudo-negative whereas the carbon side is pseudo-positive. In a drug molecule, polarity hence also pulls the electrons aways from the rest of the molecule. Recall that redox reactions involve the transfer of electrons. An electron poor molecule therefore will not oxidize easily.

Some examples of the incorporation of C-F bonds can be seen below. Cipro is an antibiotic drug, Paxil is an antidepressant drug, and Sitagliptin is an anti-diabetic drug.

 blog 5.JPG

Benefits of Being Harder to Oxidize – Solubility

blog5d.JPG

The above picture shows a Cyp enzyme bound to the  anticoagulant drug warfarin.

Drugs are metabolized through a redox reactions with two enzymes in the liver, P450 and Cyp. An enzyme is a natural protein that catalyzes chemical reactions in the body. To briefly go over the kinetics, this means means that it is present as a reactant in the first elementary step of a chemical reaction, but also present as a product in the last elementary step. How an enzyme works is heavily tied to kinetics. The two enzymes mentioned work by oxidizing small molecules, which of course includes all drugs. This oxidation make the molecules more polar as the electron distribution in the molecule changes. In every redox reaction there is an oxidizing agent that gains electrons and a reducing agent that loses electrons. In the case of the chemical reactions taking place in the liver, the liver enzymes take electrons away from all the molecules that pass through the system. Often, these extra electrons are transferred and used in many other reactions throughout the body.

 The redox reaction makes the drug molecules more water-soluble which leads to the drug’s secretion from the body. They are more soluble because they are then polar. Recall that water is also a polar molecule. Two polar molecules are often very soluble in one another due to their attraction to each other. Because of this timeless saying, “like dissolves like” the drug is able to dissolve much more easily in the body and spread through the body. Again, the goal going towards the future is to create drugs whose dissolution is more thermodynamically favorable due to a more negative deltaH3, and thus will occur at a faster rate and with more consistent results. Additionally, because it makes the dissolving of the drug spontaneous, with a negative change in Gibb’s free energy. (Overall the change is enthalpy would be negative and change in entropy would be positive, resulting in negative change in free energy.)

A drug that is easily oxidized will be cleared from the body more quickly than one that is difficult to oxidize. Recall that C-F bonds make a molecule electron-poor. Since the drug molecules are the reducing agent in the redox reaction (they are oxidized and hence give electrons,) they are therefore not as reactive with liver enzymes with a C-F bond as they would be if they had a C-H bond instead. Overall, thus, C-F bonds make drug molecules more metabolically stable.

blog 5b.JPGFluorine as a Hydrogen Bond Acceptor

There are more reasons that medicinal chemists replace C-H bonds in drug molecules with C-F bonds. This is because the fluorine atoms, which, as mentioned before, are very electronegative, can be hydrogen-bond acceptors. In other words, hydrogen atoms can be attracted to them. To understand why this is important, it is important to understand how drugs work. Many drugs work by binding to and inhibiting the activity of a target enzyme. How tightly a drug binds to a specific binding pocket of an enzyme determines how potent, specific, and effective a drug is. The more tightly it can bind, the better drug it is. Fluorine increased the potential hydrogen bonding interactions interactions between the drug and its target. In other words, it increases the intermolecular forces

blog 5c.JPG

It has been proven that C-F bonds increase the potency of a drug. One specific example is the drug Januvia, shown below. This is a drug that is used to treat Type II Diabetes. It is composed of six C-F bonds, three of which are in an aromatic ring. While the drug was being developed, the researchers found that even just one fluorine in the aromatic ring increased the potency of the drug three-fold. Three fluorines increased potency 25-fold.

The Future of Drugs (We Hope!)

 The goal for the future is to be able to create drugs more easily and effectively. That would mean being able to make reactions go forward, and find ways to incorporate certain bonds in the structure that would metabolize better in vivo. In addition, creating new reactions, both with the help of redox reactions and with many different synthesis applications such as electrochemistry and the organic chemistry of electron movement is very important for the creating of new drugs. Finding ways to do this that work effectively and efficiently, or in other words are thermodynamically favorable and thus spontaneous, is also a necessary step of the future. Being able to test drugs in a non-animal environment, yet still being able to predict its effects on the body is also a substantial step that needs to be taken, so fewer ineffective drugs will have to go through clinical trials unnecessarily. Overall, the chemists who work in the pharmaceutical industry have a far way to go, and a bright future to go into.

 

They’re Rare from Earth and Metals

The name “Rare Earth Metals” has a special ring to it, branding the set of 17 elements on the periodic table as exclusive and elusive.  However, as we will soon see, this is misleading, and does not show the whole picture.  Much like helium, the rare earth metals are actually quite plentiful in the Earth’s crust.  For instance, cerium is the 25th most abundant element in the earth’s crust. But what exactly are the rare earth elements (REE)? REE are the elements in the lanthanides series as well as Yttrium and Scandium that share unique magnetic, phosphorescent and catalytic properties that make them so essential to our modern technologies. However, currently the major supplier of rare earth metals to the rest of the world is China and they have been restricting their trade.  Since rare earth metals are used in a myriad of applications ranging from hybrid cars to portable electronics, there is a desperate demand for them that is not being filled.

Rare Earth Metals are produced through several different processes usually involving high temperatures and a series of reactions. In the case of Lanthanum which will be the focus of this post, a derivation of what is called the Ames process is used to purify and create the REE. Lanthanum is generally found in its most stable state:, La2O3 and can be readily found in the earth’s crust at around 32 parts per million (ppm). The shortage, as mentioned before, arises because most of the deposits are not economically viable for extraction. This rare metal oxide then has to be reduced to a pure solid so that it can be used for its various purposes. There are even variations of the Ames process for Lanthanum, but an example will be provided and explained as well as a video with a slightly different reaction.

One reaction is the one below:

La2O3 + 6HF → 2 LaF3 + 3H2O

LaCl3 + 3Li → La + 3LiCl

In the first step of this reaction Lanthanum is fluoridated to become LaF3. However in the second reaction Lanthanum is reduced from an oxidation state of +3 to 0, while Lithium is oxidized from 0 to +1. This reaction does a disservice in understanding just how complicated the process is, which takes many steps, and manipulations of temperature. A very similar Ames process and the steps necessary are further explained in the second half of below video.

 

One important application of rare earth metals is in hybrid cars.  Lanthanum is used to make nickel-metal hydride batteries which are used in most hybrid vehicles.  A battery for a Toyota Prius required 10 to 15 kg of Lanthanum; a significant amount of Lanthanum is clearly needed for hybrid cars to expand in use.  The electrochemistry of nickel-metal hydride batteries is as follows.  The battery contains a positive electrode of nickel oxyhydroxide (NiOOH) and a negative electrode of a hydrogen-absorbing alloy.  The discharge reaction on the negative electrode is as follows:

OH− + MH is in equilibrium with H2O + M + e−

As you can see the M, which stands for an intermetallic compound that will be discussed shortly, is being oxidized into MH.  The reaction on the positive electrode is as follows:

NiO(OH) + H2O + e−is in equilibrium with Ni(OH)2 + OH−

In this half-reaction, the Ni is reduced from an oxidation state of +3 to one of +2.  The overall discharge reaction is as follows:

Ni(OH)2 + M is in equilibrium with NiO(OH) + MH

During the overall discharge, the hydrogen ion moves from the negative electrode to the positive electrode which is the principle behind the reaction.  The M in the negative electrode reaction is usually a compound written as AB5 in which A is a mixture of rare earth metals, including lanthanum and B is a mixture of nickel and cobalt, among other metals.  This compound of rare earth metals is of vital importance in forming the metal hydride compound necessary for the reaction to take place.

Now that we exploited the useful properties of rare earth metals, there’s no turning back; rare earth metals are too widely used to be abandoned.  Although they are non-renewable resources, they are relatively abundant in our earth.  Another country needs to step up to take the near monopoly away from China.  This is an unnecessary shortage, and certainty a solvable one.