02487nas a2200181 4500008004100000022001400041245009500055210006900150260007100219300001600290490000800306520178100314100002402095700002102119700001802140700001902158856012802177 2015 eng d a1520-610600aCosolvent effects on solute-solvent hydrogen-bond dynamics: ultrafast 2D IR investigations0 aCosolvent effects on solutesolvent hydrogenbond dynamics ultrafa a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcDEC a15334-153430 v1193 a

Cosolvents strongly influence the solute-solvent interactions of biomolecules in aqueous environments and have profound effects on the stability and activity of several proteins and enzymes. Experimental studies have previously reported on the hydrogen-bond dynamics of water molecules in the presence of a cosolvent, but understanding the effects from a solute's perspective could provide greater insight into protein stability. Because carbonyl groups are abundant in biomolecules, the current study used 2D IR spectroscopy and molecular dynamics simulations to compare the hydrogen-bond dynamics of the solute's carbonyl group in aqueous solution, with and without the presence of DMSO as a cosolvent. 2D IR spectroscopy was used to quantitatively estimate the time scales of the hydrogen-bond dynamics of the carbonyl group in neat water and 1:1 DMSO/water solution. The 2D IR results show spectral signatures of a chemical exchange process: The presence of the cosolvent was found to lower the hydrogen-bond exchange rate by a factor of 5. The measured exchange rates were 7.50 X 10(11) and 1.48 X 10(11) s(-1) in neat water and 1:1 DMSO/water, respectively. Molecular dynamics simulations predict a significantly shorter carbonyl hydrogen-bond lifetime in neat water than in 1:1 DMSO/water and provide molecular insights into the exchange mechanism. The binding of the cosolvent to the solute was found to be accompanied by the release of hydrogen-bonded water molecules to the bulk. The widely different hydrogen-bond lifetimes and exchange rates with and without DMSO indicate a significant change in the ultrafast hydrogen-bond dynamics in the presence of a cosolvent, which, in turn, might play an important role in the stability and activity of biomolecules.

1 aKashid, Somnath, M.1 aJin, Geun, Young1 aBagchi, Sayan1 aKim, Yung, Sam uhttps://library.ncl.res.in/content/cosolvent-effects-solute-solvent-hydrogen-bond-dynamics-ultrafast-2d-ir-investigations-001961nas a2200181 4500008004100000245013300041210006900174260000800243300001400251490000600265520127600271100002401547700002101571700002301592700001901615700001801634856012701652 2017 eng d00aTwo-dimensional infrared spectroscopy reveals cosolvent-composition-dependent crossover in intermolecular hydrogen bond dynamics0 aTwodimensional infrared spectroscopy reveals cosolventcompositio cAPR a1604-16090 v83 aCosolvents have versatile composition-dependent applications in chemistry and biology. The simultaneous presence of hydrophobic and hydrophilic groups in dimethyl sulfoxide (DMSO), an industrially important amphiphilic cosolvent, when combined with the unique properties of water, plays key roles in the diverse fields of pharmacology, cryoprotection, and cell biology. Moreover, molecules dissolved in aqueous DMSO exhibit an anomalous concentration-dependent nonmonotonic behavior in stability and activity near a critical DMSO mole fraction of 0.15. An experimental identification of the origin of this anomaly can lead to newer chemical and biological applications. We report a direct spectroscopic observation of the anomalous behavior using ultrafast twodimensional infrared spectroscopy experiments. Our results demonstrate the cosolventconcentration-dependent nonmonotonicity arises from nonidentical mechanisms in ultrafast hydrogen-bond-exchange dynamics of water above and below the critical cosolvent concentration. Comparison of experimental and theoretical results provides a molecular-level mechanistic understanding: a distinct difference in the stabilization of the solute through dynamic solute solvent interactions is the key to the anomalous behavior.1 aKashid, Somnath, M.1 aJin, Geun, Young1 aChakrabarty, Suman1 aKim, Yung, Sam1 aBagchi, Sayan uhttps://library.ncl.res.in/content/two-dimensional-infrared-spectroscopy-reveals-cosolvent-composition-dependent-crossover01542nas a2200217 4500008004100000245012100041210006900162260000800231300001400239490000600253520079700259100001601056700002101072700002301093700001601116700001701132700001501149700001801164700001901182856012301201 2018 eng d00aInterconverting hydrogen-bonding and weak n -> pi* interactions in aqueous solution: A direct spectroscopic evidence0 aInterconverting hydrogenbonding and weak n pi interactions in aq cSEP a5425-54290 v93 a

Molecular structure and function depend on myriad noncovalent interactions. However, the weak and transient nature of noncovalent interactions in solution makes them challenging to study. Information on weak interactions is typically derived from theory and indirect structural data. Solvent fluctuations, not revealed by structure analysis, further complicate the study of these interactions. Using 2D infrared spectroscopy, we show that the strong hydrogen bond and the weak n -> pi* interaction coexist and interconvert in aqueous solution. We found that the kinetics of these interconverting interactions becomes faster with increasing water content. This experimental observation provides a new perspective on the existence of weak noncovalent interactions in aqueous solution.

1 aDeb, Pranab1 aJin, Geun, Young1 aSingh, Santosh, K.1 aMoon, Juran1 aKwon, Hyejin1 aDas, Aloke1 aBagchi, Sayan1 aKim, Yung, Sam uhttps://library.ncl.res.in/content/interconverting-hydrogen-bonding-and-weak-n-pi-interactions-aqueous-solution-direct01365nas 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%9D02349nas a2200217 4500008004100000022001400041245008500055210006900140260000800209300001200217490000800229520163400237100001901871700002301890700002301913700002701936700001701963700001901980700001801999856011402017 2022 eng d a1520-610600aAssociation-dissociation dynamics of ionic electrolytes in low dielectric medium0 aAssociationdissociation dynamics of ionic electrolytes in low di cJAN a239-2480 v1263 a

Ionic electrolytes are known to form various complexes which exist in dynamic equilibrium in a low dielectric medium. However, structural characterization of these complexes has always posed a great challenge to the scientific community. An additional challenge is the estimation of the dynamic association-dissociation time scales (lifetime of the complexes), which are key to the fundamental understanding of ion transport. In this work, we have used a combination of infrared absorption spectroscopy, two-dimensional infrared spectroscopy, molecular dynamics simulations, and density functional theory calculations to characterize the various ion complexes formed by the thiocyanate-based ionic electrolytes as a function of different cations in a low dielectric medium. Our results demonstrate that thiocyanate is an excellent vibrational reporter of the heterogeneous ion complexes undergoing association-dissociation dynamics. We find that the ionic electrolytes exist as contact ion pairs, dimers, and clusters in a low dielectric medium. The relative ratios of the various ion complexes are sensitive to the cations. In addition to the interactions between the thiocyanate anion and the countercation, the solute-solvent interactions drive the dynamic equilibrium. We have estimated the association-dissociation dynamics time scales from two-dimensional infrared spectroscopy. The exchange time scale involving the cluster is faster than that between a dimer and an ion pair. Moreover, we find that the dynamic equilibrium between the cluster and another ion complex is correlated to the solvent fluctuations.

1 aGhosh, Deborin1 aSakpal, Sushil, S.1 aChatterjee, Srijan1 aDeshmukh, Samadhan, H.1 aKwon, Hyejin1 aKim, Yung, Sam1 aBagchi, Sayan uhttps://library.ncl.res.in/content/association-dissociation-dynamics-ionic-electrolytes-low-dielectric-medium