A composition for encapsulation and controlled release comprises a water-insoluble matrix comprising a host molecule that is non-covalently crosslinked by multi-valent cations, that is non-polymeric, that has more than one carboxy functional group, that has at least partial aromatic or heteroaromatic character, and that comprises at least one pterin or 5-substituted pterin moiety. The composition can further comprise a guest molecule (for example, a drug) that can be encapsulated within the matrix and subsequently released.