Complexation of common metal cations by cyanins: Binding affinity and molecular structure

Abstract

The ability of diverse metal cations to form complexes with cyanin has been investigated by means of Density Functional Theory (DFT) and the Quantum Theory of Atoms in Molecules (QTAIM). The strongest preference is shown by trivalent metals which exceed that of Mg(II), indicating that ion replacement processes are suitable detoxification mechanisms for plants. Molecular structure analysis indicates that the larger the metal affinity of Cy− the longer the C2‐C1’ bond length and smaller ρb value. This is understood as upon metal complexation the Cy− ligand molecular structure is more compatible with a dienolate‐like structure rather than the 4′‐keto‐quinoidal‐like structure. The weight of the former increases as stronger the binding. QTAIM charges indicate that the stronger the binding energy the larger the charge transfer from Cy− to the metal, reducing its positive charge below the values indicated by the corresponding Lewis structure.

First Characterization of the Formation of Anthocyanin–Ge and Anthocyanin–B Complexes through UV–Vis Spectroscopy and Density Functional Theory Quantum Chemical Calculations

“…In order to reduce the computational cost, cyanidin-3-O-glucose is modeled replacing the glucose group attached to O3 by a methyl one as its effect in Cy–metal binding or in color change due to complexation can be assumed to be negligible. ,, …”

“…In order to reduce the computational cost, cyanidin-3-O-glucose is modeled replacing the glucose group attached to O3 by a methyl one as its effect in Cy−metal binding or in color change due to complexation can be assumed to be negligible. 20,25,26 All cyanidin-3-O-methyl forms and their metalloid complexes with Ge/B were optimized with the B3LYP density functional as implemented in Gaussian 09. 39 The 6-31++g(d,p) basis set was employed for all atoms including the metalloid atom.…”

“… 19 In addition, theoretical calculations have become ubiquitous and have given support for previous hypotheses. 20 Theoretical chemistry offers the possibility of gaining further knowledge at a molecular level of the ACN–Me n + complexation process. Also, molecular absorption simulations, 21 on ACN–Me n + model complexes, would help in rationalizing experimental measures with the aim of getting a deeper understanding of this interesting research topic.…”

“…Changes to the conjugation of the chromophore system of ACNs is, in turn, accompanied by chromatic changes that can be detected by UV–vis spectroscopy, which can be considered to be one of the most informative analytical tools to detect ACN–Me n + complexes . In addition, theoretical calculations have become ubiquitous and have given support for previous hypotheses . Theoretical chemistry offers the possibility of gaining further knowledge at a molecular level of the ACN–Me n + complexation process.…”

An Update in Computational Methods for Environmental Monitoring: Theoretical Evaluation of the Molecular and Electronic Structures of Natural Pigment–Metal Complexes

“…In developing a metal detector from natural pigments, the excitation energy can be used to predict whether there is a change in colour and how the colour changes [71,81]. However, before studying the excitation energy of a molecule, studying the interactions that occur through analysing bond energy, total energy, affinity, and ground-state energy calculations is also important to do as a preliminary study to find out whether the bond will be formed between natural pigments and metals because, to produce colour changes, natural pigments must be able to bind to metal [17,82]. Apart from that, various other calculations such as the stability of the complexes, optical properties, and the geometry of the complexes formed can also be very helpful in the development of metal detectors from natural pigments [64,75,83].…”