title: Stacking and Branching in Self-Aggregation of Caffeine in Aqueous Solution: From the Supramolecular to Atomic Scale Clustering.
abstract: The dynamical and structural properties of caffeine solutions at the solubility limit have been investigated as a function of temperature by means of MD simulations, static and dynamic light scattering, and small angle neutron scattering experiments. A clear picture unambiguously supported by both experiment and simulation emerges: caffeine self-aggregation promotes the formation of two distinct types of clusters: linear aggregates of stacked molecules, formed by 2-14 caffeine molecules depending on the thermodynamic conditions and disordered branched aggregates with a size in the range 1000-3000 Å. While the first type of association is well-known to occur under room temperature conditions for both caffeine and other purine systems, such as nucleotides, the presence of the supramolecular aggregates has not been reported previously. MD simulations indicate that branched structures are formed by caffeine molecules in a T-shaped arrangement. An increase of the solubility limit (higher temperature but also higher concentration) broadens the distribution of cluster sizes, promoting the formation of stacked aggregates composed by a larger number of caffeine molecules. Surprisingly, the effect on the branched aggregates is rather limited. Their internal structure and size do not change considerably in the range of solubility limits investigated.
authors: Department of Food Science, Stocking Hall, Cornell University , Ithaca, New York 14853, United States.|Elettra-Sincrotrone Trieste S.C.p.A. , Strada Statale 14 Km 163.5, Area Science Park, I-34149 Trieste, Italy.
authors: Letizia
authors: L
authors: Tavagnacco
authors: Institut Laue-Langevin , 71, avenue des Martyrs, 38000 Grenoble, France.
authors: Yuri
authors: Y
authors: Gerelli
authors: Elettra-Sincrotrone Trieste S.C.p.A. , Strada Statale 14 Km 163.5, Area Science Park, I-34149 Trieste, Italy.|Department of Chemical and Pharmaceutical Sciences, University of Trieste , Via Giorgieri 1, I-34127 Trieste, Italy.
authors: Attilio
authors: A
authors: Cesàro
authors: Department of Food Science, Stocking Hall, Cornell University , Ithaca, New York 14853, United States.
authors: John W
authors: JW
authors: Brady