Chemistry and Photochemistry of Anthocyanins and Related Compounds: A Thermodynamic and Kinetic Approach.
Anthocyanins are identified by the respective flavylium cation, which is only one species of a multistate of different molecules reversibly interconverted by external inputs such as pH, light and temperature. The flavylium cation (acidic form) is involved in an apparent acid-base reaction, where the basic species is the sum of quinoidal base, hemiketal andcis- andtrans-chalcones, their relative fraction depending on the substitution pattern of the flavylium cation. The full comprehension of this complex system requires a thermodynamic and kinetic approach. The first consists in drawing an energy level diagram where the relative positions of the different species are represented as a function of pH. On the other hand, the kinetic approach allows measuring the rates of the reactions that interconnect reversibly the multistate species. The kinetics is greatly dependent on the existence or not of a highcis-transisomerization barrier. In this work, the procedure to obtain the energy level diagram and the rates of inter-conversion in the multistate in both cases (low or high isomerization barrier) are described. Practical examples of this approach are presented to illustrate the theory, and recently reported applications based on host-guest complexes are reviewed.
LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal. nuno.basilio@fct.unl.pt.
Nuno
N
Basílio
LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal. fp@fct.unl.pt.
Fernando
F
Pina
D000465:Algorithms; D000872:Anthocyanins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D008956:Models, Chemical; D010777:Photochemistry; D013816:Thermodynamics
D000872:Anthocyanins
anthocyanins; cucurbiturils; cyclodextrins; energy level diagram; flavylium compounds; multistate chemistry