Cartalax dissolves readily in bacteriostatic water, and that is the standard solvent for it in research. It is a very small, strongly acidic peptide with a net negative charge at the pH of bacteriostatic water, so it needs no acid, no organic solvent and no special technique beyond adding the water slowly and swirling.
Why Cartalax dissolves so easily
The sequence Ala-Glu-Asp explains it. None of its three residues is hydrophobic: alanine is the smallest side chain after glycine, and glutamic acid and aspartic acid both carry carboxyl groups that ionise in water. PubChem’s computed XLogP for Cartalax is minus 4.9, a strongly hydrophilic value (PubChem CID 87815447). No chemical supplier data sheet with a measured water figure was available to us, so no number is given here.
Charge does the rest. Counting the ionisable groups gives three acidic groups (Glu2, Asp3 and the C-terminal carboxyl) against one basic group, the N-terminal amine. From that count we calculate a net charge of about minus 2 at pH 7 and an isoelectric point near pH 2.9. These are our calculations from standard pKa values, not a measured figure. A peptide is least soluble at its isoelectric point, where its charges cancel and molecules stop repelling each other. Bacteriostatic water sits well above pH 2.9, so dissolved Cartalax molecules carry a like negative charge and repel one another.
Bacteriostatic water first
Bacteriostatic water is sterile water with 0.9% benzyl alcohol, which allows a refrigerated vial to be accessed more than once. For Cartalax it is the solvent of choice: the peptide dissolves fully in it, and the preservative supports repeated access over the 8 to 12 week fridge window described on how long Cartalax lasts. Sterile water works for a vial that will be accessed once. The difference is explained in bacteriostatic water explained.
Why not acetic acid?
Laboratories sometimes add a little dilute acetic acid to coax hydrophobic or basic peptides into solution, because lowering the pH gives them a positive charge. Cartalax is neither, and acid works against it twice over: it would push the solution toward the calculated isoelectric point near pH 2.9, the one range where this peptide is least soluble, and in model aspartate peptides acidic conditions favoured hydrolysis of the backbone next to the aspartate (Oliyai and Borchardt, Pharmaceutical Research, 1993). Plain bacteriostatic water avoids both.
Saline and sodium chloride
Cartalax is expected to dissolve in 0.9% sodium chloride. Salt ions screen the charges on a peptide, which can reduce solubility for peptides that rely on charge repulsion near their isoelectric point. At the pH of saline Cartalax is far from that point and is hydrophilic to begin with, so this is not a practical concern at research concentrations. This is general peptide chemistry rather than a Cartalax measurement, and we have no figure for Cartalax in saline. For a multi-access vial, bacteriostatic water remains the choice because of its preservative.
Concentrations that dissolve cleanly
A 20 mg vial is commonly mixed with 2 mL of bacteriostatic water, giving 10 mg/mL; 1 mL gives 20 mg/mL, 4 mL gives 5 mg/mL and 5 mL gives 4 mg/mL. These are the figures our Cartalax reconstitution page uses for its tables. All of them should dissolve to a clear, colourless solution with gentle swirling.
A larger water volume does not change the amount of peptide; it spreads it more thinly. Whatever volume is chosen, write the concentration on the vial.
Cloudiness and gelling: what causes them
Because Cartalax dissolves so readily, persistent haze is uncommon and usually points to technique or storage rather than the peptide:
- Water jetted onto the cake. A strong stream can trap air and create foam, which looks cloudy. Running the water down the inside wall of the vial avoids it.
- Shaking. Vigorous agitation creates air and liquid interfaces where peptides can unfold and clump. Swirling or rolling is enough for this peptide.
- Cold water onto cold powder. Both at fridge temperature slows dissolving. Letting the vial and the water reach room temperature first helps.
- Haze appearing later in storage. This suggests the vial was kept too warm, frozen and thawed, or contaminated, and the solution is discarded.
Brief cloudiness that clears within 10 to 15 minutes of mixing is normal and usually trapped air. The general causes are covered in why peptides gel or go cloudy, and the mixing method step by step is in how to reconstitute peptides with bacteriostatic water.
Related Cartalax pages
How the dissolved peptide behaves over time is on the Cartalax stability page, and bench technique is on the Cartalax handling page.
All products supplied by Vistara Labs are intended for laboratory research use only. They are not drugs, are not approved for human or veterinary use, and are not intended to diagnose, treat, cure or prevent any condition. Nothing on this page constitutes medical advice or guidance for use in humans.
