How do I make a 6-mercapto-1-hexanol (MCH) aqueous working dilution?

Question

I am using 6-mercapto-1-hexanol (MCH) as part of the immobilization procedure for forming a self-assembled DNA monolayer on a gold surface (see the first figure of this paper for a good visual representation). Most protocols I see online and in the literature say to use 1 mM aqueous MCH. For example, this paper says "...mercaptohexanol (MCH) was co-adsorbed onto the DNA-modified gold electrodes by exposing the electrodes to a Tris buffer solution (10 mM Tris, 50 mM NaCl, pH ) 7.3) containing 1 mM MCH for 1 h", and this paper says "The slides were also exposed to a 1.0 mM aqueous solution of 6-mercapto-1-hexanol (MCH) for 1 hr".

However, I am struggling to make this working dilution. As far as I know, MCH always comes as a liquid, so I tried first making a stock 10 mM solution by mixing 1 mg of MCH liquid with 745 µL of water. The MCH appeared to be immiscible in water, however, forming distinct droplets in the water that rise to the top without mixing.

How do I make a working or stock dilution of MCH in water that isn't biphasic?

Answer 1

A very recent publication (Ref.1), stated that 6-mercapto-1-hexanol (MCH) was selected as the spacer thiol for its ability to:

1. Block nonspecific adsorption to the surface;
2. Dissolve in aqueous solution; and,
3. Avoid interference in the hybridization reaction to surface bound DNA as the six-carbon chain of MCH is the same length as the methylene group spacer in thiol-linked ssDNA.

Thus, it's pretty sure the solubility of MCH is satisfactory enough to do such extended research in literature. According to TMIC, one of manufacturers of 6-mercapto-hexan-1-ol (molar mass: $\pu{134.24 g mol-1}$), MCH is slightly soluble in water. In that website, MCH's water solubility is listed as $\pu{2.35 g L-1}$. And also, it is a very weakly acidic compound based on its $\mathrm{p}K_\mathrm{a}$, which is listed as $10.2$ (hence, it'd stay in non ionic form in both phosphate buffer and Tris buffer)). Accordingly, the concentration of its saturated solution at $\pu{20 ^\circ C}$ (assuming the solubility is given at this temperature) would be $\pu{0.0175 mol L-1}$ or $\pu{17.5 mM}$. That is above the required concentration for your stock solution.

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Reference:

1. Mingfu Chen, Thuy T. Nguyen, Nitinun Varongchayakul, Chloé Grazon, Margaret Chern, R C. Baer, Sébastien Lecommandoux, Catherine M. Klapperich, James E. Galagan, Allison M. Dennis, and Mark W. Grinstaff, "Surface Immobilized Nucleic Acid–Transcription Factor Quantum Dots for Biosensing," Advanced Healthcare Materials 2020, 9(17), 2000403 (26 pages) (DOI: https://doi.org/10.1002/adhm.202000403).