[lucas89]

Hey forum. I'm currently working in a research lab, studying heavy metal binding to protein-mineral composites. Or to narrow all that down, I'm specifically studying binding of Pb²⁺ ions to collagen fibrils. Our group has already done significant work in Lead binding to minerals.

But I've kept running into the same issues while attempting to work through the process. To induce protein fibril formation from collagen monomers, I make up a solution of NaCl/Na₂HPO₄ buffer, and "cold-start" the collagen and buffer. I then add the Pb(NO₃)₂ solution, and immediately an unwanted precipitate forms. Initially, we imagined it was a Lead hydroxide precipitate, as the collagen/buffer pH measured at around 8. However, after taking precautions to keep the pH either neutral or slightly acidic, precipitation still occurs.

We're leaning towards the idea that the precipitation may be caused by some stray PO₄^3- ions, or maybe even an unwanted Lead apatite. But I turn to you guys. You have any possible answers or solutions around this? I'd stop using phosphate buffers, but the presence of phosphate really aids in fibril formation (I've tried using CaCl₂, but examination under an Atomic Force Microscope failed to find any fibrils). So if you know any way around phosphate precipitates, do share