@article {46334, title = {Arresting an unusual amide tautomer using divalent cations}, journal = {Journal of Physical Chemistry B}, volume = {123}, year = {2019}, month = {OCT}, pages = {8419-8424}, type = {Article}, abstract = {

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.

}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.9b08463}, author = {Kashid, Somnath M. and Singh, Reman K. and Kwon, Hyejin and Kim, Yung Sam and Mukherjee, Arnab and Bagchi, Sayan} } @article {47453, title = {Reply to {\textquotedblleft}comment on {\textquoteleft}arresting an unusual amide tautomer using divalent cations{\textquoteright}{\textquotedblright}}, journal = {Journal of Physical Chemistry B}, volume = {125}, year = {2020}, month = {DEC}, pages = {479{\textendash}483}, type = {Article}, abstract = {

In our publication, we assigned the blue-shifted shoulder of\ N-methylacetamide (NMA) in the infrared (IR) spectrum (\~{}1645 cm{\textendash}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{\textendash}1\ in the presence of 1 M DCl, which shows a 17 cm{\textendash}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.

}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.0c06005}, author = {Kashid, Somnath M. and Singh, Reman K. and Kwon, Hyejin and Seol, Jin Gyu and Kim, Yung Sam and Mukherjee, Arnab and Bagchi, Sayan} }