Molecule of the Day: Caffeine

Caffeine (C8H10N4O2) is a white solid that is sparingly soluble in water. It is a naturally occurring alkaloid and is the most commonly consumed drug worldwide. It is consumed for its ability to promote wakefulness and reduce lethargy.

It does so by acting as an antagonist to adenosine receptors in the central nervous system. Since the binding of adenosine to the receptors leads to drowsiness, this inhibition temporarily promotes alertness. Furthermore, it promotes the release of neurotransmitters such as acetylcholine, resulting in its stimulant effects.

Caffeine can be found in many different beverages:

Caffeine is usually extracted from coffee beans using supercritical carbon dioxide. While carbon dioxide normally sublimes and deposits under normal pressures, bypassing the liquid phase, under high pressures, it can exist as a supercritical liquid. Liquid carbon dioxide is a good solvent for caffeine extraction, as it is non-polar and leaves the aroma chemicals intact.

While caffeine is readily available from decaffeination processes, it can still be synthesised from dimethylurea and malonic acid:

In nature, it is biosynthesised from xanthosine instead:

Caffeine consumption results in a mild form of drug dependence; furthermore, upon regular consumption, tolerance can be built up, resulting in the need for an increasing amount of caffeine to produce the same effects. In small doses, caffeine reduces cardiovascular problems, but it increases its probability in larger doses (over 5 cups of coffee).

Originally posted by such-vodka

Molecule of the Day: Methylphenidate

Methylphenidate (C14H19NO2), also known as Ritalin, is a white powder that is slightly soluble in water. It is commonly used to treat ADD, ADHD, and narcolepsy.

Methylphenidate inhibits dopamine and norepinephrine transporter proteins, thus preventing dopamine and norepinephrine in the synaptic cleft from being reuptaken into the presynaptic knob. The resultant higher concentration of these substances in the synapse causes the receptors on the postsynaptic knob to be stimulated at a greater frequency, thus achieving greater synaptic transmission. This produces a psychostimulant effect, allowing it to be used in the treatment of ADHD.

In small amounts, methylphenidate has also been shown to enhance memory and control, caused by the activation of dopamine and adrenergic receptors. However, in large doses, it can have the opposite effect.

It has few side effects, which include loss of appetite, nausea, and insomnia. However, like many strong dopamine reuptake inhibitors, it can result in dependence, and is often seen as a gateway drug. 

Methylphenidate is industrially synthesised through a multi-step pathway from 2-bromopyridine and benzyl cyanide.

Requested by @zenbra

Molecule of the Day: Luminol

Luminol, of CSI fame, is a white-to-yellow solid that is insoluble in water that has the formula C8H7N3O2. It exhibits chemiluminescence when it reacts with an oxidising agent in the presence of a catalyst, a useful property that is utilised in forensics for detecting traces of blood.

It is synthesised by reacting 3-nitrophthalic acid with hydrazine to form 3-nitrophthalhydrazide, which is then reduced by sodium dithionite to form luminol.

In the presence of a base, luminol is deprotonated and isomerises to form the O-dianion, which then reacts with the oxidising agent in the presence of a catalyst (atmospheric oxygen and iron in the blood in the case of forensics) to produce an excited dianion. When the anion falls back to its ground state, light energy is released, which is observed in the form of a blue glow.

However, blood isn’t the only substance that can catalyse the reaction; other contaminants present, such as copper, bleach, and horseradish sauce, can produce false positives.

Regardless, it remains a useful tool in forensics, and who doesn’t love a lovely eerie blue glow?

Originally posted by rudescience


Molecule of the Day: Nalidixic acid

Nalidixic acid (C12H12N2O3) is a cream-coloured powder that is insoluble in water. Discovered in the 1960s, it has since been used as an antibiotic due to its ability to kill bacteria. 

It does so by inhibiting topoisomerase and DNA gyrase, which help to relieve overwinding strain during DNA replication. Since DNA, which is normally coiled in a double helix, is unzipped by helicase when it is replicated, the DNA to the sides of the replication bubble experience overwinding strain, much like how 2 ropes twisted together are difficult to separate by pulling them apart in opposite directions, since they become more and more tightly twisted together as they are separated. Consequently, the DNA becomes supercoiled.

Since DNA gyrase relieves this strain by cleaving, rewinding, and rejoining the 2 DNA strands, and topoisomerase separates the 2 interlocking circular bacterial DNA, their inhibition results in strain on the DNA molecule during replication and prevents separation of DNA into the daughter cells during binary fission. This either inhibits replication in low doses or produces double-strand breaks in the DNA at high doses. Consequently, nalidixic acid is bacteriostatic at low doses and bactericidal at high doses.

Nalidixic acid can be synthesised from 2-amino-6-methylpyridine and diethyl ethoxymethylenemalonate: