Laser Techniques in the Study of Drug Photochemistry^¶

Abstract

This review describes the application of different laser time‐resolved techniques, such as time‐resolved fluorescence, phosphorescence and laser flash photolysis, to elucidate the mechanism of drug photodegradation. The assignment of transient species based on their luminescence or absorption spectra and based on their reactivity to various quenchers is illustrated. The mathematical expressions used in fitting measured transient decays over time are also discussed. Practical situations found in the literature and relevant to drug photodegradation illustrate different examples. The importance of laser power, concentration and absorbance of the ground state, as well as other parameters intrinsic to laser techniques are discussed.

Surface Photochemistry: Organic Molecules within Nanocavities of Calixarenes

“…The ability of calixarenes to form inclusion complexes, accommodating guest molecules or ions in their intramolecular cavities, greatly depends on the size and geometry of both guest molecule and host cavity [36][37][38]. In fact, experiments carried out with some polycyclic aromatic hydrocarbons possessing different dimensions and p-(diallylaminomethyl)calixarenes and p-(carboxyethyl)calixarenes showed that calix [4]arenes are too small to accept naphthalene and calix[8]arenes apparently are too small to accept coronene and decacyclene but sufficient to accommodate durene, naphtalene, anthracene, phenanthrene, fluoranthene, pyrene and perylene [37]. Typical dimensions for the hydroxylic ring (lower rim) in the calixarenes molecules measured using CPK molecular models varied from ca.…”

“…Atwood et al [41] and Shinkai et al [42] used this capacity to separate C 60 from C 70 fullerenes by the use of calix[8]arene. Several other important industrial applications of calixarenes were reported: xylene isomers separated by the use of different calix [4]arenas [35], halogenated hydrocarbons removed from water with the use of specific calixarenes [35], caesium recovery from solutions of nuclear waste materials [43] are good examples of the practical importance of these compounds.…”

“…In solution, p-tert-butylcalix [4]arene can adopt four conformations (conformers) called cone, partial cone, 1,2 alternate or 1,3 alternate. Cone conformation is the most stable in the solid state.…”

“…These conformers are interconvertible in solution but for some cases some structures are favoured. For example, p- [4]arene exists mainly as cone conformation possessing all hydroxyl groups directed to the lower rim of the macrocycle and linked by an array of hydrogen bonds. Solvents such as acetone, acetonitrile and pyridine can increase the molecular mobility by destroying these hydrogen bonds [33].…”

“…Photochemistry of organic molecules included within nanocavities has attracted considerable attention in the last two decades [1][2][3][4][5][6][7][8][9]. In order to gain more information regarding photochemical processes in heterogeneous environments (opaque or powdered samples) a considerable scientific effort was made in spectroscopic and kinetic studies of organic molecules adsorbed onto different solid substrates with relevance for the use of time-resolved methodologies, i.e., laser induced time resolved luminescence and diffuse reflectance transient absorption spectroscopies [1,3].…”