Molecular Properties of Astaxanthin in Water/Ethanol Solutions from Computer Simulations

Abstract

Astaxanthin (AXT) is a reference model of xanthophyll carotenoids, which is used in medicine and food industry, and has potential applications in nanotechnology. Because of its importance, there is a great interest in understanding its molecular properties and aggregation mechanism in water and mixed solvents. In this paper, we report a novel model of AXT for molecular dynamics simulation. The model is used to estimate different properties of the molecule in pure solutions and in water/ethanol mixtures. 1The calculated diffusion coefficients of AXT in pure water and ethanol are (3.22 ± 0.01) × 10 −6 cm 2 s −1 and (2.7 ± 0.4) × 10 −6 cm 2 s −1 , respectively.Our simulations also show that the content of water plays a clear effect on the morphology of the AXT aggregation in water/ethanol mixture. In up to 75% (v/v) water concentration, loosely connected network of dimers and trimers, and two-dimensional array structures are observed. At higher water concentrations, AXT molecules form more compact three-dimensional structures that are preferentially solvated by the ethanol molecules. The ethanol preferential binding and the formation of a well connected hydrogen bonding network on these AXT clusters, suggest that such preferential solvation can play an important role in controlling the aggregate structure.

Structure of supramolecular astaxanthin aggregates revealed by molecular dynamics and electronic circular dichroism spectroscopy

“…The computed geometries are consistent with structural models proposed previously. 43 (Note that a helical longer-range arrangement was also proposed for carotenoid aggregates, 34 this however, is not possible to simulate reliably with our computational means).…”

“…A similar situation was described for AXT aggregation in mixed water-ethanol solutions. 43 AXT dimers. The computed UV-vis and ECD spectra of the dimer MD models, obtained as averages over 1000 clusters, are presented together with the experimental spectra in Fig.…”

“…Although we currently cannot model larger-scale ordering of the aggregates, molecular dynamics simulations on limited models (the AXT dimer and decamer) are used to understand formation of different supramolecular structures in different solvent mixtures, and the results are compared to experimental data. The molecular dynamics methodology has been suggested for AXT also in the past, 43 but according to our current knowledge, the dependence of the aggregation geometry and its spectral features on the solvent type has not been theoretically studied yet. Absorption and CD intensities are simulated using both time dependent density functional theory (TD-DFT) and a faster Zerner's intermediate neglect of differential overlap method (ZIndo/S).…”

A Combined Experimental and Theoretical Study on the Formation of a Cyclic Tetrameric Water Cluster and a Similar Type of Cyclic Cluster in Copper(II) Schiff Base Complexes

“…[7,8] In spite of many theoretical and experimental works on these water aggregations, researchers are still reporting new findings regarding the properties of various water clusters. [9] A number of discrete water clusters including dimersdecamers, and higher order clusters [37][38][39] have been identified by several groups. The cyclic water tetramer, as a simple two-structure model for liquid water, [40][41] is of particular interest.…”

“…Extensive experimental and theoretical research to determinate the precise structural data of various hydrogen‐bonded water aggregations has been carried out over many years The common aggregation states adopted by water clusters are classified as: discrete chains (D), discrete rings (R), infinite chains in one dimension involving no rings (C), infinite tapes in one dimension involving rings (T), infinite layers in two dimensions (L), and unclassified structures (U) ,. In spite of many theoretical and experimental works on these water aggregations, researchers are still reporting new findings regarding the properties of various water clusters …”