Binding of caffeine, theophylline, and theobromine with human serum albumin: A spectroscopic study

The interaction between three purine alkaloids (caffeine, theophylline, and theobromine) and human serum albumin (HSA) was investigated using UV/vis absorption, circular dichroism (CD), fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques. The results revealed that three alkaloids caused the fluorescence quenching of HSA by the formation of alkaloid–HSA complex. The binding site number n and apparent binding constant KA, corresponding thermodynamic parameters the free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) at different temperatures were calculated. The hydrophobic interaction plays a major role in stabilizing the complex. The distance r between donor (HSA) and acceptor (alkaloids) was obtained according to fluorescence resonance energy transfer. The effect of alkaloids on the conformation of HSA was analyzed using circular dichroism (CD), UV/vis absorption, synchronous fluorescence and three-dimensional fluorescence spectra techniques.