ethanol-methanol - (Mar/23/2006 )

A very basic question:

The chemical difference between ethanol+methanol is one extra carbon. How does that affect the properties when we use either of the 2 for nucleic acid isolation? Which of the 2 is more efficient and why?
Thank you for ur time:)

EtOH is more efficient because of the extra C. propanol (especially isopropanol) is even more efficient.

But what is it that this extra C does?

This is by no means the truth but it's my educated guess.

It may have something to do with increase polarity of the -OH group on the alcohol as you increase the chain length.

The alcohols cause DNA precipitation by effectively removing the hydration sphere around the DNA. They lower the effective water content which causes the DNA to precipitate. They probably do this by forming hydrogen bonds between the water and the alcohol hydroxy group.

In the hydroxy group the polarity is produced by the electronegative oxygen atom. It retains a small negative charge whilst the hydrogen is slightly positive. In methanol, there is a methyl group attached to the hydroxy group. Alkyl groups are electron-donating and the longer they are, in general, the more electron density the donate to wards the hydroxy group.

Simplistically, the additional electron density strengthens the slight negative charge (and reenforces the lone pairs) on the oxygen atom. This increases its ability to form H-bonds. So the longer the alcohol chain, the better the precipitation. This explains why isopropanol works better than 1-propanol. The oxygen is symmetrical about the carbons and so receives the greatest electron density.

I happen to use n-butanol in my precipitations. Works extremely well, though it is toxic and smells of vomit!

Let me know if I'm way off.

i think your explanation really makes sense.. Maybe i should refresh my chemistry!! Thank you so much for the help.