A review of history, properties, classification, applications and challenges of natural and synthetic dyes.

Natural dyes have been used for centuries for coloring textiles, food, and other materials. Synthetic dyes are particularly popular due to their ease of use, wide range of available colors, and fastness. However, their usage comes with significant environmental and health challenges. In recent years, there has been a renewed interest in natural dyes due to their eco-friendliness, ready availability, affordability, non-toxicity, and sustainability. Hence, natural dyes are fast gaining popularity as better alternatives to synthetic dyes. Nature is blessed with a rich diversity of plant species with varying colors and properties which can be harnessed in textile, printing, cosmetics, and food industries. This paper presents a comprehensive review on natural and synthetic dyes with particular focus on their history, properties, classification, extraction methods, applications, and health challenges. Although many plants have been suggested as potential sources of natural dyes, there is insufficient information on their exploration and application. Additionally, chemical analyses of these dyes have not been extensively done. Overall, the results of studies conducted so far identified a number of promising taxa for further investigation as plant-based dyes with many indigenous plants as potential sources of natural dyes.

Cheminformatics Bioprospection of Broad Spectrum Plant Secondary Metabolites Targeting the Spike Proteins of Omicron Variant and Wild-Type SARS-CoV-2.

The spike protein (SP) of SARS-CoV-2 (SC-2) is susceptible to high mutation and has contributed to the multiple waves of COVID-19 being experienced. Hence, targeting the SP remains a logical approach in the development of potent therapeutics against SARS-CoV-2. Here, a computational technique was adopted to identify broad-spectrum plant secondary metabolites with indigenous relevance in the management of respiratory infections against the SPs of the SC-2 wild- type (SC-2WT) and omicron variants. Following 100 ns molecular dynamic (MD) simulation and binding free energy calculation of the top five compounds identified through molecular docking, maysin (SC-2WT (-34.85 kcal/mol), omicron (-38.88 kcal/mol)) and geraniin (SC-2WT (-36.90 kcal/mol) omicron (-31.28 kcal/mol)) had better broad-spectrum activities for the investigated SPs than zafirlukast (SC-2WT (-33.73 kcal/mol) omicron (-22.38 kcal/mol)). Furthermore, 6-hydroxycyanidin-3-rutinoside (-42.97 kcal/mol) and kaempferol-7-glucoside (-37.11 kcal/mol) had the best affinity for the SPs of omicron and SC-2WT, respectively. Interestingly, except for Kaempferol-7-glucoside against omicron SP, all the top-ranked compounds were thermodynamically stable with the SP of both variants, and this observation was linked to the number, nature, and bond length in the resulting complexes in each case. Also, except for geraniin, all the top-ranked compounds had lower toxicity profiles compared to zafirlukast and this could be attributed to their phenolic moieties. Nevertheless, the in vitro and in vivo confirmation of the activities observed in this study is recommended, especially for maysin and geraniin with the best broad-spectrum activity, towards development of COVID-19 drug candidates.