I was reading an article on how medicines degrade over time and how that could be a problem on a trip to Mars.
Which got me thinking. Surely the obvious solution is to store them at low temperatures. After all, space is COLD.
Which raises another questtion - can low temperatures ever degrade chemical compositions?
Lower temperature cannot degrade medicines faster in space since this goes against chemical kinetics and Arrhenius law; however low temperature can induce other undesirable changes in the solid state such as phase changes or glass transition and their corresponding solubility in the body. The major issue is time (shelf-life) and unfriendly UV and other forms of radiation that can fry humans and medicines on Mars despite being an extremely cold planet.
can low temperatures ever degrade chemical compositions?
Some proteins, such as insulin, can become denatured by freezing.
According to Childrens Hospital of Philadelphia
The protein in frozen insulin denatures and won’t work in the same way.
Yes, cold temperatures can degrade medicines. For example, let's say there is a medicine in which active ingredients must be homogeneously dissolved in water. At lower temperatures, the solvation power of the water decreases, which can lead to a non-homogeneous mixture. In this non-homogeneous mixture, the active ingredients can form clumps, degrading the medicine.
Similarly, crystallization can occur, which also degrades the quality of the medicine. There are many factors that can lead to the degradation of medicine at lower temperatures.
Some of the drugs have to be accessible on board the spacecraft. Perhaps there are cold modules where an additional supply can be stored but the formulation would have to be modified in some cases. You might ask how supplies might be safely transported outside passenger modules in the space exploration SE site.
The article refers to "terrestrial shelf-life data" with compounds stored under conventional conditions on Earth (perhaps refrigerated but often room temperature), not at near absolute zero. The effect of radiation is not the main question, it is formulation stability (for instance phase separation) and retaining the activity of the API which by degrading loses potency and generates unwanted compounds.
Like most engineering problems many issues are considered during formulation including cost, route and ease of administration, dose, potency, and stability. Like a $100 hammer (or is it 1 million these days?), the preparations might be reformulated to behave better under longer periods and more extreme conditions. Degradation decreases at lower temperatures for kinetic reasons (if not thermodynamic) but storing stuff at very low T might alter phase stability. It might be reasonable to take along ingredients that must be combined upon arrival to Mars or as needed along the way:
However, for inherently unstable drugs, preventive measures can include altering the dosage form in a number of ways. For liquid dosage forms, the hydrolysis of drugs is dependent on the presence of water, and thus storage of dry powders followed by reconstitution in water before dispensing minimizes hydrolysis. Similarly, if a drug is known to be susceptible to hydrolysis at room temperature, its storage in a cool place is advised, and patients can be counseled on this practice. Additionally, pharmacists should provide the correct labeling on the packaging.
Note also that this is not a pleasure cruise. Humans intending to undertake interplanetary travel are probably less risk averse than the average person. At minimum it is important to remain functional on board the spacecraft. Although mission failure due to an unstable formulation would be undesirable, some increased extent of API degradation under the duration of the journey might be acceptable, provided degradation compounds have limited side effects. Bureaucratic hurdles would have to be overcome (somebody would have to sign off on allowing violation of FDA standards).
Most of chemicals (especially organic compounds) degrade at low temperatures. Just slower than at higher temperatures. So the question is not if, but how fast. As the rule of thumb there is the van't Hoff's rule the rate of chemical reactions increases typically 2-4 times by increasing temperature by $\pu{10 ^{\circ}C}$. For organic compounds would would count rather with 2 times.
Also, one thing is temperature of space background radiation 2.7 K, other thing is kinetic energy of interplanetary molecules ( with density of molecules $\approx \pu{5 cm-3}$ we cannot talk about their temperature), and yet another things is the effective temperature of space capsule surface, periodically exposed to Solar radiation. The capsule would have to rotate to simulate gravity and stabilize capsule orientation.
As cosmic radiation is very penetrating, it is not easy to shield it.
Yes, even simple binary compounds do. It is called eutectoid reaction if it can be reversed by simply raising the temperature again.
Notice that this is not applicable to the decomposition of drugs since most of them are molecular, and molecules do not form by raising the temperature.
Here is an example of binary phase diagram with an eutectoid: http://www-g.eng.cam.ac.uk/mmg/teaching/typd/addenda/eutectoidreaction1.html
Kaolin, used for stomach upsets and diarrhoea, is a clay which turns into crystals in low temperature and stays that way (making it useless as a medicine). You're not even allowed to put it in the fridge, and supposed to be careful if you leave it in the car in cold weather. Probably an unusual example.
