# Protein Self-Assembly States Modulate Lithium Carbonate Biomineralization: From Ion Chelation to Nucleation Sites

## TL;DR

This study shows how proteins can both inhibit and accelerate the formation of lithium carbonate crystals depending on salt concentration.

## Contribution

The first investigation of protein-Li2CO3 interactions revealing dual effects on nucleation and crystal growth.

## Key findings

- At low supersaturation, proteins inhibited Li2CO3 nucleation by 20–40% through chelation.
- At high supersaturation, proteins accelerated nucleation by 10–40%.
- Protein aggregation states modulate Li2CO3 crystallization dynamics and crystal size distribution.

## Abstract

Understanding protein–salt interactions is important
for
controlling crystallization, including biomineralization, biopharmaceutical
purification, biocatalytic enzymes, and environmental biointerfaces.
This study for the first time investigated interactions between three
proteins (lysozyme, red fluorescence protein, and bovine hemoglobin)
and Li2CO3 (formation from the reaction of LiCl
with Na2CO3) under different protein and salt
concentrations. For the crystallization of Li2CO3, at low supersaturation (S), the proteins inhibited
Li2CO3 nucleation by 20–40% through chelation.
At high S, the proteins accelerated nucleation by
10–40%. The dual effects of the protein on Li2CO3 biomineralization have been discussed. With the increase S of Li2CO3, the dispersion state
of proteins in solution undergoes a transition from dimers to oligomers
and finally to aggregates. In all ranges of S, the
protein reduced the agglomeration of Li2CO3 crystals.
In lysozyme crystallization, increasing the Li2CO3 concentration yielded a larger number of smaller crystals. At equal
concentration of lysozyme, twice more of LiCl and Na2CO3 in the solution led to more than 5 times the crystal number
and 5 times smaller average crystal size. The interactions among protein
molecules, salt ions in solution, and Li2CO3 crystals have been discussed. Dynamic light scattering measurements
and the fluorescence microscopy image suggest that the dual effect
of proteins on Li2CO3 crystallization at different
supersaturation levels is associated with protein molecular aggregation
under varying salt concentrations, resulting in both thermodynamic
and kinetic influences on the crystallization process.