01365nas a2200205 4500008004100000022001400041245006300055210006300118260000800181300001400189490000800203520073300211100002400944700002100968700001700989700001901006700002101025700001801046856009501064 2019 eng d a1520-610600aArresting an unusual amide tautomer using divalent cations0 aArresting an unusual amide tautomer using divalent cations cOCT a8419-84240 v1233 a

Ion-specific effects on peptides and proteins are key to biomolecular structure and stability. The subtle roles of the cations are far less understood, compared to the pronounced effects of the anions on proteins. Most importantly, divalent cations such as Ca2+ and Mg2+ are crucial to several biological functions. Herein, we demonstrate that an amide-iminolate equilibrium is triggered by the binding of the divalent cations to the amide oxygen in aqueous solution. The excellent agreement between the experimental and theoretical results confirms the arrest of an unusual amide tautomer by the divalent cations, which is a rarely known phenomenon that might open up an array of applications in chemistry and biology.

1 aKashid, Somnath, M.1 aSingh, Reman, K.1 aKwon, Hyejin1 aKim, Yung, Sam1 aMukherjee, Arnab1 aBagchi, Sayan uhttps://library.ncl.res.in/content/arresting-unusual-amide-tautomer-using-divalent-cations06213nas a2200217 4500008004100000022001400041245009500055210006900150260000800219300001400227490000800241520546200249100002405711700002105735700001705756700001905773700001905792700002105811700001805832856014505850 2020 eng d a1520-610600aReply to “comment on ‘arresting an unusual amide tautomer using divalent cations’”0 aReply to comment on arresting an unusual amide tautomer using di cDEC a479–4830 v1253 a

In our publication, we assigned the blue-shifted shoulder of N-methylacetamide (NMA) in the infrared (IR) spectrum (∼1645 cm–1) to an iminolate tautomer stabilized in the presence of divalent metal cations (e.g., 5 M Ca2+).(1) Cremer and co-workers comment that this shoulder arises from the dehydration of the amide oxygen upon interaction with the metal cations.(2,3) Their assignment is based on three interesting experimental observations: (1) the IR spectrum of 15N-isotope-labeled NMA does not show any considerable red-shift compared to that of NMA; (2) a new peak appears for NMA at 1680 cm–1 in the presence of 1 M DCl, which shows a 17 cm–1 red-shift for 15N-labeled NMA; and (3) the IR spectrum of acetone C═O stretch also demonstrates a blue-shifted shoulder in the presence of a high concentration of CaCl2.

1 aKashid, Somnath, M.1 aSingh, Reman, K.1 aKwon, Hyejin1 aSeol, Jin, Gyu1 aKim, Yung, Sam1 aMukherjee, Arnab1 aBagchi, Sayan uhttps://library.ncl.res.in/content/reply-%E2%80%9Ccomment-%E2%80%98arresting-unusual-amide-tautomer-using-divalent-cations%E2%80%99%E2%80%9D