I have a mixture of DMF and water in 300 K simulated with an OPLS-AA force field. The hydrogen bonds between oxygen atoms of DMF and H atoms of water have a very short length and it's around 1.26 Å. I know that H-bonds are typically < 3.5 Å but isn't 1.26 in the range of covalent bonds?
I want to know if that's possible or if there's something wrong with my force field parameters/charges?
The RDF curve of oxygen atoms of DMF around H atoms of water (H-bonds) is shown below.
Kind regards,
Ehsan
Dear Ehsan
If you carefully study the paper on hydrogen bonds, usually three classes are distinguished: weak, moderate, and strong bonds, with energetic boundaries at about 2 and 15 kcal/mol.
The weak hydrogen bonds involve less polar X-H groups in proton donors. The weakest hydrogen bonds considered in the literature are about 0.5 kcal/mol. It has distance of upto 4.5 Armstrong.
Moderate occurs in in range of 2.0 to 3.5 Armstrong. While Strong hydrogen bonds do occur in range of 1.3 to 2.0 Armstrong. Strong hydrogen bond generally are involved in systems having high electronegative atoms.
Since you are using gromacs, which is generally based on molecular mechanics, it would be better to use quantum based techniques like DFT for better understanding of behaviour of hydrogen atoms around Oxygen atom of DMF.
Since, DMF has partial double bond character for the C-N and C-O bonds.
There is possibility that highly electronegative oxygen atom may form hydrogen strong bond with hydrogen atom of water.
Hope it will help.
regards
Tanuj
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