Effect of external electric field on the tautomeric equilibrium and structure of 2‐carbamido‐1,3‐indandione

Abstract

Abstract2‐Carbamido‐1,3‐indandione (CAID) is a new reliable fluorescent biomarker and it exists in two tautomeric forms: 2‐(hydroxyl‐aminomethylidene)‐indan‐1,3‐dione (A) and 2‐carboamide‐1‐hydroxy‐3‐oxo‐indan (B). The structures of the tautomers and the transition state for intramolecular proton transfer are located at MP2/6‐31+G(d) level for each magnitude and for opposite directions of the applied electric field. According to our SCS‐MP2/6‐31+G(d) field‐free calculations tautomer A prevails (59.3%) while variation of the electric field strength along the direction from the indandione moiety to the carbamido fragment (+x‐direction) leads to stabilization of tautomer B. The two tautomeric forms become isoenergetic at 2.571 V/Å when the applied electric field is parallel to the direction from amino to the hydroxyl group (−y‐direction) in CAID, and at 3.085 V/Å tautomer B (51.9%) is slightly favored. Apparently, an external electric field has a strong influence on the tautomeric equilibrium in the CAID molecule.