From: Richard Henchman <henchman@manchester.ac.uk>
Date: Thu, Dec 2, 2010 at 11:36 PM
Subject: IUPAC Hydrogen Bond Definition
To: "arunan@ipc.iisc.ernet.in" <arunan@ipc.iisc.ernet.in>
 
 
Dear Prof. Arunan,
 
I read with great interest your efforts to update the IUPAC definition of
the hydrogen bond. This is a question my group has been considering a great
deal in regards to the total number of hydrogen bonds in liquid water. This
quantity relates to the entropy of water. We came up with a hydrogen-bond
definition that avoids arbitrary parameters and accurately resolves
transition states of hydrogen-bond switching:
 
"A hydrogen is defined as donating to its nearest noncovalently bonded
oxygen as long as this oxygen-hydrogen (OH) distance is the shortest OH
distance between the two water molecules involved"
 
The other notable points are: hydrogen bonds are defined in a relative
sense; correlation between potential hydrogen bonds is taken into account.
The application of this definition is described in our recent publication,
attached to this email. We explain how the more general form with multiple
types of donor and acceptor could be defined in terms of the most
attractive electrostatic force instead of nearest distance. This would
appear to be largely consistent with the IUPAC definition that you are
proposing.
 
Best wishes,
 
Richard Henchman