Why don't small crystals dissolve

From: Enrico Stura
Date: 8 February 2012 11:49


Theresa,

A little off from the original question.

You should have started a new thread.

The answer to your question is very simple.  Small crystals will dissolve when the degree of saturation
of the solution becomes too low to support their relatively high surface to volume ratio.
The larger crystals will still continue to grow because of their higher surface/volume ratio but will do so slowly.
I have achieved the dissolving of small crystals in favour of large ones only once with 10 µl drops.
While it is difficult to achieve this with spontaneously nucleated crystals, with seeding thing are very different.
This phenomenon is an every day observation if you use streak seeding on drops that have been
equilibrated for different amount of time against different concentrations of precipitant and you can
also add an additional variable by using different ratios of protein to precipitant in the drop.
The goal is to seed at a low degree of superstauration. The small seeds will be visible along the streak
immediately after seeding. When you look later on you will see only the bigger crystals.
Streak seeding is great if you want to play this game.

Enrico.


On Wed, 08 Feb 2012 12:08:23 +0100, Theresa H. Hsu  wrote:

A little off from the original question. Why don't small crystals dissolve to make a bigger crystal, especially when the small ones grow on top of each other? Can the clustered 3D crystals (I think it is called macroscopic twin) be used for full data collection?

Again, thank you.

Theresa

--
Enrico A. Stura 

----------
From: David Schuller


Sometimes they do. Key phrase: Ostwald ripening.

http://xray.bmc.uu.se/terese/crystallization/tutorials/tutorial6.html

--
=======================================================================
All Things Serve the Beam
=======================================================================
                              David J. Schuller

----------
From: Pius Padayatti


Hi Enricho,
The scenario of streak seeding follows Ostwald ripening but will
this happen in other situations as follows

But in a special case where you have some crystals that appear as large
rods which dissolved when taken out of the incubator (or) during the
observation( these were antibody-complex crystals which were grown in
bicelles(DMPC:CHAPSO
and detergent mixtures and cholestrol, conditions citric acid pH 4.5,
with 2.4 M ammonium sulfate).
The crystals re-apparered in a day over noght incuabtion as heavy
showers of needles with heavy precipitate around.

Very hard to reproduce the conditions.
Still trying to work around these conditions.

Would like to know your thoughts if this is against the laws small
crystals to large crystals (energetically
favoured) conditions.

Also any suggestions welcome for improvements.

Pius

--
Pius S Padayatti,PhD,

----------
From: Enrico Stura


Pius,

The situation you describe is an off-equilibrium situation. You have applied  a perturbation
and that may not be reversible!

Enrico.