  Citation: Çoruh, O.; Gündüz, G.; Çolak, Ü.; Mavi¸ s, B. pH-Dependent Coloring of Combination Effect Pigments with Anthocyanins from Brassica oleracea var. capitata F. rubra. Colorants 2022, 1, 149–164. https:// doi.org/10.3390/colorants1020010 Academic Editor: Ugo Caruso Received: 21 February 2022 Accepted: 30 March 2022 Published: 1 April 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article pH-Dependent Coloring of Combination Effect Pigments with Anthocyanins from Brassica oleracea var. capitata F. rubra Orkun Çoruh 1,2 , Güngör Gündüz 3 , Üner Çolak 4,5 and Bora Mavi¸ s 6, * 1 Institute of Science and Technology Austria, 3400 Klosterneueburg, Austria; mehmetorkun.coruh@ist.ac.at 2 Nanotechnology and Nanomedicine Division, Hacettepe University, Beytepe, Ankara 06800, Turkey 3 Chemical Engineering Department, Middle East Technical University, Ankara 06531, Turkey; ggunduz@metu.edu.tr 4 Energy Institute, Istanbul Technical University, Maslak, ˙ Istanbul 34469, Turkey; unercolak@itu.edu.tr 5 Nuclear Engineering Department, Hacettepe University, Beytepe, Ankara 06800, Turkey 6 Mechanical Engineering Department, Hacettepe University, Beytepe, Ankara 06800, Turkey * Correspondence: bmavis@hacettepe.edu.tr; Tel.: +90-312-297-6210 Abstract: Mica-titania pearlescent pigments (MTs) were previously coated with organic molecules to obtain combination pigments (CPs) for achieving certain improvements or functionalities. Antho- cyanins (ACNs) are molecules that can be extracted from natural resources and exhibit color changes via pH modifications of the enclosing medium. The purpose of the study was to produce a new series of CPs by depositing ACNs on MTs at different pH values, to observe the changes in color, and to associate these changes to thermogravimetrically determined deposition efficiencies in light of spectral differences. The extraction and deposition methods were based on aqueous chemistry and were straightforward. The ACN deposition generally increased with increasing pH and correlated with the consistency between the charges of the MT surfaces and the dominant ACN species at a specific pH value. The fluorescence of the CPs was inversely correlated with the deposition quantities invoking the possibility of a quenching effect. Keywords: mica; titania; pearlescent; anthocyanin; deposition; fluorescence 1. Introduction The trend towards sustainability in engineered systems necessitates the development and improvement of reproducible, cheap, and harmless resources as a major design element, leading to the consideration of natural pigments as functional materials, dye or dye compo- nents, and building blocks for many applications [1]. The anthocyanin (ACN) molecules of plants, functioning in protection against light stress and oxidative stress in addition to serving as allurers to seed dispersers [2], have a high potential as colorants and functional molecules with their complex chemistry, bearing control over stability and color diversity. Being glucosides of polyhydroxy and polymethoxy derivatives of 2-phenylbenzoprylium or flavylium salts, ACNs are responsive to alterations in the pH of the surrounding medium [3]. The coupling of two aromatic rings by an oxygenated heterocycle not only provides the pH responsiveness but also enriches the capabilities of the entity by providing anchoring points for sugars, which further promote the molecule by the potential attachment of aliphatic or aromatic acids, enabling proton transfer, hydration, and tautomeric reactions as well as metal complexation and copigmentation reactions, making ACNs highly tractable molecu- lar tools for various potential applications [4,5], particularly as sensitizing components of photocatalytic, photovoltaic, or electrochemical sensor systems [6–9]. However, the limited stability of these molecules and their structural/physicochemical versatility contingent upon pH governed equilibrium dynamics [10] unambiguously elaborates the applications, obliging structured investigations of ACN behavior on surfaces. Colorants 2022, 1, 149–164. https://doi.org/10.3390/colorants1020010 https://www.mdpi.com/journal/colorants