The PH Effects On The Binding,Partition And Diffusion Properties Of Chemicals Into Hair And Related Models

The permeation and absorption of various chemicals in human hair is highly relevant to a wide range of applications including the formulation design of hair care products,development of water pollution control and remediation,and risk assessment of environmental or consumer exposure.The pH of the surrounding media is a key factor affecting the permeation and absorption of chemical in hair.Change in pH will cause changes in the physicochemical properties of both hair and chemical,which will significantly affect the absorption rate and amount of chemical by hair.Development of mathematical models that explore the theoretical correlation between hair permeability and the properties of hair,chemical and media,which could help better explain the mechanisms of hair permeation kinetics and pH effects,is of great scientific significance and practical application value.In this study,based on a comprehensive consideration of the effects of physicochemical properties of hair,chemical and solvent on hair permeation and absorption,the mechanism of the influence of pH on the binding,partition and diffusion properties of various neutral,cationic and anionic chemicals into hair was thoroughly explored.The new quantitative structure property relationship(QSPR)models have been proposed for the partition coefficient and effective diffusion coefficient of chemicals in hair.On this basis,this study also developed a numerical model for predicting permeation of chemicals into hair based on the Fick’s law.Through combining experimental research and theoretical analysis,this study enabled better insights into the mechanisms of hair permeation kinetics,and provided methodological support and a theoretical basis for the formulation design of hair care products,optimization of wastewater treatment process and environmental exposure assessment strategies.The main innovation achievements and conclusions were obtained as follows.1.The effects of pH on the binding properties of hair keratin and cationic chemicals(theophylline,nortriptyline,and amitriptyline)were studied using fluorescence quenching,ultrafiltration,and microscale thermophoresis(MST).The single binding site model can be used to describe the binding interactions of hair keratin and these three chemicals in a ratio of 1:1.The fitted thermodynamic parameters suggested that cationic chemical binding to hair keratin is driven by both hydrophobic and electrostatic interactions.Hydrophobic interaction dominates for the binding of the three cationic chemicals with keratin.Electrostatic interaction can be interpreted as the pH effect of the binding process.The binding of keratin with theophylline can be described by the Langmuir isotherm model,indicating that the interaction is monolayer binding.The results of the three test methods are in good agreement.Considering that the fluorescence quenching method has the characteristics of high sensitivity,wide application range,simple operation,easy access to the binding thermodynamic parameters and so on,it is preferred as a research method to study hair keratin binding properties.2.The hair-water partition of various chemical not only depends on the hydrophobicity of the chemical but also the electrostatic interaction with hair.Changing pH does not affect the hair-water partition of neutral chemicals but has a significant impact on hair-water partition of ionized chemicals.Based on the new physicochemical insight of the pH effects on hair-water partition,a new QSPR model has been proposed(R2 = 0.91,RMSE = 0.23,N= 99),taking into account of both the hydrophobic interaction and electrostatic interaction of chemical with hair fiber.3.The diffusion of chemical into hair not only depends on the molecular size of the chemical but also the electrostatic interaction with hair.Changing pH does not affect the hair diffusion of neutral chemicals,but has a significant impact on hair diffusion of ionized chemicals.The diffusion rate of chemicals in hair increased due to electrostatic attraction but decreased due to electrostatic repulsion.Based on the new physicochemical insight of the pH effect on hair diffusion,a new QSPR model has been proposed(R2 =0.92,RMSE = 0.24,N = 58).The new QSPR model is based on the Nernst-Planck equation,taken into account of both the molecular size and electrostatic interaction.4.By combining with the QSPR models of hair partition coefficient and effective diffusion coefficient,a numerical model for predicting permeation of chemicals into hair has been proposed based on the Fick’s law and conservation of mass theory.The model was numerically solved using MATLAB,and a simulation software for the permeation process of chemical into hair(MHPC)was developed.The software enters the physicochemical parameters of hair,chemical and solution through human-machine dialogues to achieve the prediction of partition coefficient,effective diffusion coefficient,dynamic changes of concentration distribution and absorption amount in hair.