Cryptophanes are a class of
organic supramolecular compounds studied and synthesized primarily for
molecular encapsulation
In supramolecular chemistry, molecular encapsulation is the confinement of a guest molecule inside the cavity of a supramolecular host molecule (molecular capsule, molecular container or cage compounds). Examples of supramolecular host molecule ...
and recognition. One possible noteworthy application of cryptophanes is encapsulation and storage of
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
gas for potential use in
fuel cell
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...
automobiles. Cryptophanes can also serve as containers in which organic chemists can carry out
reactions that would otherwise be difficult to run under normal conditions. Due to their unique
molecular recognition
The term molecular recognition refers to the specific interaction between two or more molecules through noncovalent bonding such as hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, π-π interactions, halogen ...
properties, cryptophanes also hold great promise as a potentially new way to study the binding of organic molecules with substrates, particularly as pertaining to biological and
biochemical applications.
Discovery
Cryptophanes were discovered by
André Collet
André — sometimes transliterated as Andre — is the French and Portuguese form of the name Andrew, and is now also used in the English-speaking world. It used in France, Quebec, Canada and other French-speaking countries. It is a variation ...
and Jacqueline Gabard in 1981 when these researchers created, using template-directed synthesis, the first cryptophane, now known as cryptophane-A.
Structure
Cryptophane cages are formed by two cup-shaped
.1.1€“ortho
cyclophane units (see
cyclotriveratrylene),
connected by three bridges (denoted ''Y''). There are also choices of the peripheral substitutes ''R1'' and ''R2'' attached to the aromatic rings of the units. Most cryptophanes exhibit two
diastereomer
In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have dif ...
ic forms (''syn'' and ''anti''), distinguished by their
symmetry type. This general scheme offers a variety of choices (''Y'', ''R1'', ''R2'', and symmetry type) by which the shape, volume and chemical properties of the generally hydrophobic pocket inside the cage can be modified, making cryptophanes suitable for encapsulating many types of small molecules and even chemical reactions.
General classification
Depending on their structure, cryptophane cages are classified according to the following table.
[
]
Symmetry
The anti cryptophane isomer belongs to the D3 point group and the syn cryptophane isomer belongs to the C3h point group.[Peter Atkins, J. D. P., ''Atkins' Physical Chemistry''. Oxford: 2010.] Both molecules therefore do not exhibit a dipole moment.
References
{{Reflist
Supramolecular chemistry
Hydrogen
Cyclophanes