Investigating The Molecular Dynamics Of Caffeine In Protic And Aprotic Solvents Using ¹H NMR Relaxation Measurements

¹ Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Negeri Malang, Jl. Semarang 5, Malang, 65145, Indonesia
² Laboratory of Minerals and Advanced Materials, Faculty of Mathematics and Natural Sciences, Universitas Negeri Malang, Jl. Semarang 5, Malang, 65145, Indonesia
³ Centre of Advanced Materials and Renewable Energy, Universitas Negeri Malang, Jl. Semarang 5, Malang, 65145, Indonesia

Abstract

Coffee is renowned for its rich composition of bioactive compounds, including caffeine. While the macroscopic effects of caffeine are well documented, a comprehensive understanding of molecular dynamics at the microscopic level remains limited, particularly regarding solvent effects and spin-lattice relaxation time (T1), which are critical for quality control/authentication of coffee. This study addresses this gap by developing a Benchtop Nuclear Magnetic Resonance (NMR) spectroscopy method to investigate the molecular dynamics of caffeine by determining the spin-lattice relaxation time (T1). Our approach focuses on comparing the T1 values of pure caffeine in two distinct solvent environments, the protic heavy water (D2O) and the aprotic deuterated chloroform (CDCl3). Experimental procedures involved preparing caffeine samples in both solvents and measuring T1 values using the inversion-recovery method with relaxation delays of 3, 5.5, 11, 20, and 25 seconds. Preliminary results show that the T1 value of caffeine is influenced by both the solvent type and the relaxation delay. Specifically, the T1 values in CDCl3 were more uniform than those in D2O, suggesting substantial differences in the molecular interactions and motional dynamics of caffeine in these two environments. These findings can contribute to understanding the molecular dynamics of complex coffee, especially its caffeine behaviour.