Abstract
The transport and association of the dipeptide glycyl-L-phenylalanine (Gly-L-Phen) in solutions containing cyclodextrins are of prime importance given its relevance in different areas, from biochemistry to wastewater treatment. We have investigated the interaction between aqueous Gly-L-Phen and β-cyclodextrin (β-CD) by NMR, DFT calculations in parallel with UV/visible absorption, luminescence spectral measurements and diffusion experiments. Ternary mutual diffusion coefficients of aqueous {Gly-L-Phen + β-CD} solutions have been measured by using the Taylor dispersion technique. The results show that the association of Gly-L-Phen and β-CD has a significant effect on the diffusion coefficients, consistent with an association constant of about 50 to 100, assuming a 1:1 (Gly-L-Phen):(β-CD) stoichiometry. This stoichiometry has been assessed by the continuous variation (Job's plot) method and the association constant was determined by using the Hildebrand-Benesi equation modified for NMR applications. The association constant was estimated to be equal to 40. This association constant is in close agreement with that obtained by fluorescence measurements (K = 43). Additionally, from NMR, detailed structural information on the complex has been obtained. This has been complemented by DFT and TD-DFT studies.
Highlights
Glycyl-L-phenylalanine (Gly-L-Phen) is a dipeptide formed from glycine and L-phenylalanine, of relevance for different fields
We have investigated the interaction between Gly-L-Phen and β-CD using diffusiometry, NMR and fluorescence spectroscopy, and density functional theory (DFT) calculations
From Taylor diffusion technique we have found that the limiting diffusion coefficient of aqueous Gly-L-Phen is 7.66 × 10−10 m2 s−1 at 298.15 K
Summary
Glycyl-L-phenylalanine (Gly-L-Phen) is a dipeptide formed from glycine and L-phenylalanine (see Scheme 1a), of relevance for different fields. Glycyl-L-phenylalanine has been used for the synthesis of biocompatible and non-toxic metal organic frameworks (MOFs), by forming coordination polymers with metal ions (e.g., Zn (II)), with applications in the biomedical and pharmaceutical fields [1]. The ability of dipeptides to complex metal ions is used to better understand the hydrolysis processes of proteins [2] and the removal of metal ions from wastewaters [3]. As a consequence of the hydrolysis of dietary proteins, knowledge of the transmembrane transport of peptides becomes relevant [7]. Gly-L-Phen has been used, for example, as (A.C.F. Ribeiro)
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