Herein, we report on the initial step of the design process of new hair dyes with the desired properties. The first step is dedicated to the development of the largest, publicly available database of hair dye substances (containing temporary and semipermanent hair dyes as well as permanent hair dye precursors) used in commercial hair dye formulations. The database was utilized to perform a cheminformatics study assessing the computed physicochemical properties of the different hair dye substances, especially within each cluster of structurally similar dyes. The various substances could be differentiated based on their average molecular weight, hydrophobicity, topological polar surface area, and number of hydrogen bond acceptors, with some overlap also observed. In particular, we found that dyes such as C.I. Basic Orange 1 and 2 were clustered among the precursors, suggesting that their diffusion behavior is similar to that of permanent hair dye precursors. We anticipate taking advantage of this interesting knowledge in the second design phase of our investigation. As a step in that direction, we used QSAR models and noted that 65% of the substances were predicted to be mutagenic (22 with confidence thresholds >90%), whereas 79% were predicted to be skin sensitizers (37 with confidence thresholds >90%). We discuss the relevance of these preliminary calculations in view of literature-extracted experimental data.
We report on part 2 of the cheminformatics-assisted
development
of sustainable hair dyes with enhanced technical and toxicological
properties. In this study, an initial similarity search analysis was
performed using two reference probes (C.I. Basic Orange 1 and Orange
2) as structural templates for the identification of potential analogs
among the Max Weaver Dye Library (MWDL). The analysis revealed an
interesting subset of 158 MWDL compounds that were close analogs of
the classical aminoazobenzene dyes. A more detailed similarity search
analysis of this subset ultimately led to the selection of four dyes
for further in silico quantum calculations and experimental
dye uptake (color depth on hair) studies. Results from quantum calculations
indicated that the ESP surface properties of these dyes were consistent
with nonionic interactions between dye and keratin. Among the four
dye analogs, 2-amino-6-methyl-5-(phenyldiazenyl)pyrimidin-4-ol and
2-amino-4-chloro-1,6-dimethyl-5-(phenyldiazenyl)-pyrimidin-1-ium methyl
sulfate achieved the best dye uptake on hair (∑K/S 227.31 and 149.26). The results of this study
show that cheminformatics-based tools can be used to both build and
screen dye databases containing potential alternatives to colorants
believed to pose environmental concerns, providing a more sustainable
(green) approach to hair dye design, by reducing the number of compounds
requiring synthesis and analysis before suitable replacements are
identified.
The technology for generating high quality keratin films has recently advanced and led to their implementation in a variety of applications. As an initial step toward investigating the films as a screening tool for predicting the efficacy of potential hair dyes, CI Acid Orange 7 was applied to a set of opaque and translucent films. Overlaid time‐of‐flight secondary ion mass spectrometry images arising from protein and dye fragments revealed that dye uniformly penetrated both film types. Results also showed that the relative concentration of dye in each film complemented outcomes from ultraviolet‐visible analysis and revealed that the translucent film contained a higher dye concentration. Scanning electron microscopy analysis of film morphology suggested that the observed difference was due to the higher porosity of the opaque film, which facilitated dye desorption during the rinsing step. Consequently, the translucent film was judged to be a better substrate for screening potential new hair dyes.
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