ABCharge

ABCharge calculates equilibrium pH and related ionic properties in complex biochemical systems using Davies' equation and iterative updates of dissociation constants, implemented as an R package.

Key Features:

• Equilibrium pH Calculation: Calculates equilibrium pH for fluids containing multiple buffers with varying dissociation constants by solving the charge-balance equation using root-finding techniques.
• Monotonicity and Charge Balance: Leverages the monotonic relationship between proton concentration and buffer systems and enforces conservation of thermodynamic dissociation constants and total buffer concentrations by updating apparent dissociation constants iteratively based on actual pH and ionic strength.
• Non-Ideal State Modeling: Models non-ideal solution behavior by applying Davies' equation to compute single-ion activity coefficients as functions of ion charge and ionic strength.
• Iterative Algorithm: Iteratively updates apparent dissociation constants from thermodynamic values to converge on equilibrium under nonideal conditions.
• Comprehensive Output: Outputs pH, activity coefficients, buffer species distributions, ionic strength, and charge-balance diagnostics for both ideal and nonideal cases.
• Default Conditions: Includes CO₂ and albumin as default components to represent common biological fluids such as blood plasma.

Scientific Applications:

• Blood gas analysis: Modeling and interpretation of equilibrium pH and buffer composition in blood gas studies.
• Metabolic buffer studies: Precise computation of buffer status and pH in metabolic experiments requiring accurate dissociation-constant handling.
• Ionic strength research: Assessment of how ionic strength and single-ion activities influence biochemical equilibrium and reaction conditions.

Methodology:

Solves charge-balance equations with root-finding algorithms, applies Davies' equation for single-ion activity coefficients, assumes fixed charges from strong ions, and iteratively updates apparent dissociation constants from thermodynamic values to determine buffer species distributions given actual pH and total buffer concentrations.