K. De Clerck

The potential of anthocyanins from blueberries as a natural dye for cotton: A combined experimental and theoretical study

K.T. Phan, E. Van den Broeck, V. Van Speybroeck, K. De Clerck, K. Raes, S. De Meester
Dyes and Pigments
176, 108180
2020
A1

Abstract 

Natural dyes might be more environmentally sustainable compared to their synthetic counterparts, however in general their performance is worse. Therefore, typically metallic mordants are applied to improve the natural dye's affinity towards substrates, but this is not a suitable technique in a ‘green story’. In this paper, we test the potential of using anthocyanins from blueberry waste for dyeing cotton with biomordants, which are selected to tailor the intermolecular interactions such as hydrogen bonds, ionic bonds and π-π interactions with the dye molecule. In the experimental part, parameters during extraction and dyeing were optimized (e.g. temperature, pH, dyeing time and concentration). The effect of the (bio)mordants was monitored by Fourier transform infrared spectroscopy, spectrophotometric measurements and standard ISO wash and light tests. It was shown that stannous chloride stands out as metallic mordant, while no biomordants show sufficient intermolecular interactions to replace this metal salt. The experimental study has been corroborated with a series of molecular modeling calculations to obtain more insight into the intermolecular interactions between dye and (bio)mordants. To this end, both static Density Functional Theory based calculations as semi-empirical and force field based molecular dynamics calculations have been performed. The results indeed confirm that, in general, too small interaction energies for the biomordants of interest with the dye molecules are found, in correspondence with experimental findings. Overall, by performing systematic experiments in combination with the interpretation of the molecular models, this study yields valuable insights into the development of green routes towards use of anthocyanins as a natural dye for cellulose-based materials.

Open Access version available at UGent repository

Acidity constant (pKa) calculation of large solvated dye molecules: evaluation of two advanced molecular dynamics methods

T. De Meyer, B. Ensing, S.M.J. Rogge, K. De Clerck, E.J. Meijer, V. Van Speybroeck
ChemPhysChem
17 (21), 3447–3459
2016
A1

Abstract 

pH-sensitive dyes are increasingly applied onto polymer substrates for the creation of novel sensor materials. Recently, these dye molecules have been modified to form a covalent bond with the polymer host. This can have a large influence on the pH-sensitive properties, in particular on the acidity constant (pKa). Obtaining molecular control over the factors that influence the pK$_a$ value is mandatory for future intelligent design of sensor materials. Herein, we show that advanced molecular dynamics (MD) methods have reached the level where pKa values of large solvated dye molecules can be predicted with high accuracy. Two MD methods are used in this work: steered or restrained MD and the insertion/deletion scheme. Both are first calibrated on a set of phenol derivatives and afterwards applied to the dye molecule Bromothymol Blue. Excellent agreement with experimental values is obtained, which opens perspectives for using these methods for designing dye molecules.

Open Access version available at UGent repository

Halochromic properties of sulfonphthaleine dyes in a textile environment: the influence of substituents

T. De Meyer, I. Steyaert, K. Hemelsoet, R. Hoogenboom, V. Van Speybroeck, K. De Clerck
Dyes and Pigments
124 (2016), 249-257
2016
A1

Abstract 

The application of pH-sensitive dye molecules onto textile materials is a promising method for the development of sensor materials. Ten commonly used pH-indicators, namely sulfonphthaleine dyes, are applied onto polyamide 6 using two distinct methods: conventional dyeing of fabrics and dye-doping of nanofibres. The influence of the substituents of each dye on their interaction with polyamide, as well as the difference between both application methods is investigated. For the conventionally dyed fabrics, halogen substituents are needed to result in a pH-sensitive fabric. This can be traced back to halogen bonding and is supported by theoretical simulations. Dye-doped nanofibrous non-wovens show significant dye leaching, which can be understood based on the very acidic electrospinning solution. The use of a complexing agent improves the leaching properties, especially for dyes containing four bromine substituents. These findings indicate the importance of halogen substituents on sulfonphthaleines for further research in the development of pH-sensitive sensors.

Open Access version available at UGent repository

Exploring the Vibrational Fingerprint of the Electronic Excitation Energy via Molecular Dynamics

A. Van Yperen-De Deyne, T. De Meyer, E. Pauwels, A. Ghysels, K. De Clerck, M. Waroquier, V. Van Speybroeck, K. Hemelsoet
Journal of Chemical Physics
140 (2014), 134105
2014
A1

Abstract 

A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed.

Substituent effects on absorption spectra of pH-indicators: An experimental and computational study of sulfonphthaleine dyes

T. De Meyer, K. Hemelsoet, V. Van Speybroeck, K. De Clerck
Dyes and Pigments
102, 241-250
2014
A1

Abstract 

Sulfonphthaleine dyes are an important class of pH indicators, finding applications in novel (textile) sensors. In this paper, we present a combined experimental and theoretical study to elucidate the halochromic behaviour of a large set of sulfonphthaleine compounds. Starting from an experimental analysis consisting of UV/Vis spectroscopy, the pH region and the absorption wavelengths related to the colour shift are obtained and pKa values are derived. The effect of the substituents on the pH region can be traced back to their electron donating/withdrawing properties. Time-Dependent Density Functional Theory (TD-DFT) is able to adequately produce the trend in experimental wavelengths. Proton affinities are used to assess the effect of substituents on the pH region. The combination of theory and experiment is able to give a better understanding of the pH sensitivity; the methodology in this work will be useful in future dye design and is applicable to other dye classes as well.

Open Access version available at UGent repository

Polycaprolactone and polycaprolactone/chitosan nanofibres functionalised with the pH-sensitive dye Nitrazine Yellow

L. Van der Schueren, T. De Meyer, I. Steyaert, O. Ceylan, K. Hemelsoet, V. Van Speybroeck, K. De Clerck
Carbohydrate Polymers
91 (1), 284-293
2013
A1

Abstract 

Nanofibres functionalised with pH-sensitive dyes could greatly contribute to the development of stimuli-responsive materials. However, the application of biocompatible polymers is vital to allow for their use in (bio)medical applications. Therefore, this paper focuses on the development and characterisation of pH-sensitive polycaprolactone (PCL) nanofibrous structures and PCL/chitosan nanofibrous blends with 20% chitosan. Electrospinning with added Nitrazine Yellow molecules proved to be an excellent method resulting in pH-responsive non-wovens. Unlike the slow and broad response of PCL nanofibres (time lag of more than 3 h), the use of blends with chitosan led to an increased sensitivity and significantly reduced response time (time lag of 5 min). These important effects are attributed to the increased hydrophilic nature of the nanofibres containing chitosan. Computational calculations indicated stronger interactions, mainly based on electrostatic interactions, of the dye with chitosan (ΔG of -132.3 kJ/mol) compared to the long-range interactions with PCL (ΔG of -35.6 kJ/mol), thus underpinning our experimental observations. In conclusion, because of the unique characteristics of chitosan, the use of PCL/chitosan blends in pH-sensitive biocompatible nanofibrous sensors is crucial.

Open Access version available at UGent repository

The influence of a polyamide matrix on the halochromic behaviour of the pH-sensitive azo dye Nitrazine Yellow

L. Van der Schueren, K. Hemelsoet, V. Van Speybroeck, K. De Clerck
Dyes and Pigments
94 (3), 443-451
2012
A1

Abstract 

It is of great interest to introduce pH-sensitive dyes into fibrous materials since this may result in flexible sensor systems. However, to date, the effect of a textile matrix on the halochromic properties of dyes is still unknown which severely limits their further development. Therefore, this paper focuses on an in-depth study of the halochromism of the azo pH-indicator dye Nitrazine Yellow in solution and incorporated in polyamide textile matrices with different structures. Based on both experimental spectroscopic data and computational calculations, an azo hydrazone tautomerism was found to be responsible for the halochromism of Nitrazine Yellow in solution. The hydrazone tautomer was most stable in neutral pH while the deprotonated dye molecule was believed to be an azo tautomer, resulting in a bathochromic shift with increasing pH. This tautomerism was, moreover, also present in the polyamide matrices. However, the equilibrium was clearly affected by the polymeric environment resulting in a shift and broadening of the dynamic pH-range. The polyamide type and textile structure influenced the halochromic response due to different interactions and accessibility of the dye. In conclusion, the halochromism of Nitrazine Yellow is present in all studied systems and is always based on an azo hydrazone tautomerism but the polyamide matrix causes distinct alterations in the tautomeric equilibrium.

Investigating the Halochromic Properties of Azo Dyes in an Aqueous Environment by Using a Combined Experimental and Theoretical Approach

T. De Meyer, K. Hemelsoet, L. Van der Schueren, E. Pauwels, K. De Clerck, V. Van Speybroeck
Chemistry - A European Journal
18 (26), 8120-8129
2012
A1

Abstract 

The halochromism in solution of a prototypical example of an azo dye, ethyl orange, was investigated by using a combined theoretical and experimental approach. Experimental UV/Vis and Raman spectroscopy pointed towards a structural change of the azo dye with changing pH value (in the range pH 5–3). The pH-sensitive behavior was modeled through a series of ab initio computations on the neutral and various singly and doubly protonated structures. For this purpose, contemporary DFT functionals (B3LYP, CAM-B3LYP, and M06) were used in combination with implicit modeling of the water solvent environment. Static calculations were successful in assigning the most-probable protonation site. However, to fully understand the origin of the main absorption peaks, a molecular dynamics simulation study in a water molecular environment was used in combination with time-dependent DFT (TD-DFT) calculations to deduce average UV/Vis spectra that take into account the flexibility of the dye and the explicit interactions with the surrounding water molecules. This procedure allowed us to achieve a remarkable agreement between the theoretical and experimental UV/Vis spectrum and enabled us to fully unravel the pH-sensitive behavior of ethyl orange in aqueous environment.

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