Polyquat Stability in Reef Tank

[jda]

Does anybody have any idea how long polyquat, or other QACs, would stay stable in saltwater after dosing them? Hours, days, weeks?

Also, do they seem likely to be bound to GAC or get skimmed out thus diminishing their effectiveness over time?

Thanks in advance.

 

[Dan_P]

Does anybody have any idea how long polyquat, or other QACs, would stay stable in saltwater after dosing them? Hours, days, weeks?

Also, do they seem likely to be bound to GAC or get skimmed out thus diminishing their effectiveness over time?

Thanks in advance.

Possibly biodegradable. Being surface active, they may be skimmed out. No opinion about adsorption by GAC. Generally very stable compounds.

 

[Randy Holmes-Farley Verified Community Expert]

I do not know the half life in a reef tank, but I think the time would be short because it will bind to any negatively charged surface, including organism tissues and maybe even rocks and sand.

 

[Dan_P]

I do not know the half life in a reef tank, but I think the time would be short because it will bind to any negatively charged surface, including organism tissues and maybe even rocks and sand.

I wondered about binding to negatively charged surfaces in a sea of negative charges, or flipping it around, the availability of negatively charged surfaces in a sea of calcium and magnesium. I punted.

 

[Randy Holmes-Farley Verified Community Expert]

I wondered about binding to negatively charged surfaces in a sea of negative charges, or flipping it around, the availability of negatively charged surfaces in a sea of calcium and magnesium. I punted.

Salts do reduce, but do not prevent polyvalent negatively charged materials from binding to polyvalent positively charged materials.

The effect is well known, and is driven partly/mostly by entropy.

Take a linear polyquat with, say, 10 associated negative charges. While those negative charges would be constantly changing in seawater, those that are most closely associated with the positive charges at any instant in time are suffering greatly reduced entropy (i.e., inhibited freedom of movement) compared to free negative charges in the solution.

If you then bring that complex up to a negatively charged surface, there are multiple interactions where the negative charged surface replaces one of the negative charge ions associated with the polyquat. Likewise, some of the the positively charged ions associated with the negatively charged surface are displaced.

The net effect is that a bunch of ions are released from the polyquat (increasing entropy), and a bunch are released from the surface (increasing entropy), and one polyquat molecule becomes attached to the surface (decreasing entropy). Overall, that gives an increase in entropy that drives the interaction.

Here's a really detailed analysis of those minor aspects of the interactions between polystyrene sulfonate (a polyanion) and polydiallyldimethylammoniun chloride (a polycation) in salt solution that are not entropic, but they note that the primary effect is entropy.

https://pubs.acs.org/doi/10.1021/jacs.5b11878

"Over the range 0.1–2 M NaCl, the driving force for complex formation between PSS and PDADMAC is between 90% and 100% entropic."

FWIW, if all the ions in seawater were sodium chloride, it would be about 0.6 M.

 

[jda]

...so if I am reading this right, they will quickly attach to any negatively charged surface where they will stay stable until they are absorbed (life like coral or algae) or later break down after some time (sand or rock)? Maybe safe to assume that with the plethora of negatively charged things to bind with, this will happen long before effective filtration can get into the mix? Where is my Reef Biology forum? Thanks for the replies.

 

[Randy Holmes-Farley Verified Community Expert]

...so if I am reading this right, they will quickly attach to any negatively charged surface where they will stay stable until they are absorbed (life like coral or algae) or later break down after some time (sand or rock)? Maybe safe to assume that with the plethora of negatively charged things to bind with, this will happen long before effective filtration can get into the mix? Where is my Reef Biology forum? Thanks for the replies.

That is my expectation, but I cannot show data or claim with certainty.

FWIW, most tissue surfaces (e.g., cells) are negatively charged.

 

[jda]

Thank you. Not only is that plenty more than we had, it aligns with anecdotal usage of products with known polyquat, like API AlgaeFix, where the use of carbon, skimming or other filtration seems to matter not.

 

[Dan_P]

Salts do reduce, but do not prevent polyvalent negatively charged materials from binding to polyvalent positively charged materials.

The effect is well known, and is driven partly/mostly by entropy.

Take a linear polyquat with, say, 10 associated negative charges. While those negative charges would be constantly changing in seawater, those that are most closely associated with the positive charges at any instant in time are suffering greatly reduced entropy (i.e., inhibited freedom of movement) compared to free negative charges in the solution.

If you then bring that complex up to a negatively charged surface, there are multiple interactions where the negative charged surface replaces one of the negative charge ions associated with the polyquat. Likewise, some of the the positively charged ions associated with the negatively charged surface are displaced.

The net effect is that a bunch of ions are released from the polyquat (increasing entropy), and a bunch are released from the surface (increasing entropy), and one polyquat molecule becomes attached to the surface (decreasing entropy). Overall, that gives an increase in entropy that drives the interaction.

Here's a really detailed analysis of those minor aspects of the interactions between polystyrene sulfonate (a polyanion) and polydiallyldimethylammoniun chloride (a polycation) in salt solution that are not entropic, but they note that the primary effect is entropy.

https://pubs.acs.org/doi/10.1021/jacs.5b11878

"Over the range 0.1–2 M NaCl, the driving force for complex formation between PSS and PDADMAC is between 90% and 100% entropic."

FWIW, if all the ions in seawater were sodium chloride, it would be about 0.6 M.

Thanks for the explanation and article. Crystal clear now. Article is understandable, though a second reading is called for.

 

[taricha]

Is there a striaghtforward chemical explanation for differentiation between algae and bacterial cells? That is, why would a polyquat like algaefix would still be disruptive to algae cells in saltwater when it barely bothers bacterial cells in saltwater?

(saltwater bacterial cultures are not slowed by anything at or several times above recommended dose of algaefix - but obviously, algae is strongly effected.)

 

[Dan_P]

Is there a striaghtforward chemical explanation for differentiation between algae and bacterial cells? That is, why would a polyquat like algaefix would still be disruptive to algae cells in saltwater when it barely bothers bacterial cells in saltwater?

(saltwater bacterial cultures are not slowed by anything at or several times above recommended dose of algaefix - but obviously, algae is strongly effected.)

I bet the answer is “no”