02097nas a2200229 4500008004100000022001400041245015800055210006900213260000800282300001400290490000800304520125600312100002301568700001901591700001801610700001601628700002301644700002701667700002401694700001801718856013101736 2019 eng d a1520-610600aHydrocarbon chain-length dependence of solvation dynamics in alcohol-based deep eutectic solvents: a two-dimensional infrared spectroscopic investigation0 aHydrocarbon chainlength dependence of solvation dynamics in alco cNOV a9355-93630 v1233 a

Deep eutectic solvents (DESs) have gained popularity in recent years as an environmentally benign, inexpensive alternative to organic solvents for diverse applications in chemistry and biology. Among them, alcohol-based DESs serve as useful media in various applications due to their significantly low viscosity as compared to other DESs. Despite their importance as media, little is known how their solvation dynamics change as a function of the hydrocarbon chain length of the alcohol constituent. In order to obtain insights into the chain-length dependence of the solvation dynamics, we have performed two-dimensional infrared spectroscopy on three alcohol-based DESs by systematically varying the hydrocarbon chain length. The results reveal that the solvent dynamics slows down monotonically with an increase in the chain length. This increase in the dynamic timescales also shows a strong correlation with the concomitant increase in the viscosity of DESs. In addition, we have performed molecular dynamics simulations to compare with the experimental results, thereby testing the capacity of simulations to determine the amplitudes and timescales of the structural fluctuations on fast timescales under thermal equilibrium conditions.

1 aChatterjee, Srijan1 aGhosh, Deborin1 aHaldar, Tapas1 aDeb, Pranab1 aSakpal, Sushil, S.1 aDeshmukh, Samadhan, H.1 aKashid, Somnath, M.1 aBagchi, Sayan uhttps://library.ncl.res.in/content/hydrocarbon-chain-length-dependence-solvation-dynamics-alcohol-based-deep-eutectic-solvents01987nas a2200193 4500008004100000022001400041245008500055210006900140260000800209300001400217490000800231520133800239100002301577700001901600700002201619700001901641700001801660856011501678 2021 eng d a1520-610600aCurious case of aqueous warfarin: structural isomers or distinct excited states?0 aCurious case of aqueous warfarin structural isomers or distinct  cMAR a2871-28780 v1253 a

Warfarin is a potent anti-coagulant drug and is on the World Health Organization's List of Essential Medicines. Additionally, it displays fluorescence enhancement upon binding to human serum albumin, making warfarin a prototype fluorescent probe in biology. Despite its biological significance, the current structural assignment of warfarin in aqueous solution is based on indirect evidence in organic solvents. Warfarin is known to exist in different isomeric forms-open-chain, hemiketal, and anionic forms-based on the solvent and pH. Moreover, warfarin displays a dual absorption feature in several solvents, which has been employed to study the ring-chain isomerism between its open-chain and hemiketal isomers. In this study, our pH-dependent experiments on warfarin and structurally constrained warfarin derivatives in aqueous solution demonstrate that the structural assignment of warfarin solely on the basis of its absorption spectrum is erroneous. Using a combination of steady-state and time-resolved spectroscopic experiments, along with quantum chemical calculations, we assign the observed dual absorption to two distinct pi ->pi* transitions in the 4-hydroxycoumarin moiety of warfarin. Furthermore, we unambiguously identify the isomeric form of warfarin that binds to human serum albumin in aqueous buffer.

1 aSakpal, Sushil, S.1 aGhosh, Deborin1 aManae, Meghna, A.1 aHazra, Anirban1 aBagchi, Sayan uhttps://library.ncl.res.in/content/curious-case-aqueous-warfarin-structural-isomers-or-distinct-excited-states03975nas a2200205 4500008004100000022001400041245008600055210007400141260000800215300001400223490000700237520326500244100002803509700002303537700002303560700002103583700001803604700002303622856012403645 2021 eng d a1523-706000aEvidence of an nN(amide) → π*Ar interaction in N-Alkyl-N,N′-diacylhydrazines0 aEvidence of an nNamide → πAr interaction in NAlkylNN′diacylhydra cMAY a7003-70070 v233 a

1,2-Dibenzoyl-1-tert-butylhydrazine (RH-5849) and related N-alkyl-N,N′-diacylhydrazines are environmentally benign insect growth regulators. Herein, we show that an unusual nN(amide) → π*Ar interaction mediated by a hydrazide amide nitrogen atom plays a crucial role in stabilizing their biologically active trans–cis (t–c) rotameric conformations. We provide NMR and IR spectroscopic evidence for the presence of these interactions, which is also supported by X-ray crystallographic and computational studies.

1 aDeka, Jugal, Kishore Ra1 aSahariah, Biswajit1 aSakpal, Sushil, S.1 aBar, Arun, Kumar1 aBagchi, Sayan1 aSarma, Bani, Kanta uhttps://library.ncl.res.in/content/evidence-nnamide-%E2%86%92-%CF%80ar-interaction-n-alkyl-nn%E2%80%B2-diacylhydrazines01406nas a2200217 4500008004100000022001400041245010200055210006900157260000900226300001400235490000700249520064500256100002000901700002300921700002300944700002800967700002100995700001801016700002301034856013101057 2021 eng d a1523-706000aStabilization of Azapeptides by N-amide center dot center dot center dot H-N-amide Hydrogen Bonds0 aStabilization of Azapeptides by Namide center dot center dot cen cJUL  a4949-49540 v233 aAn unusual N-amide center dot center dot center dot H-Namide hydrogen bond (HB) was previously proposed to stabilize the azapeptide beta-turns. Herein we provide experimental evidence for the N-amide center dot center dot center dot H-Namide HB and show that this HB endows a stabilization of 1-3 kcal.mol(-1) and enforces the trans-cis-trans (t-c-t) and cis-cis-trans (c-c-t) amide bond conformations in azapeptides and N-methyl-azapeptides, respectively. Our results indicate that these N-amide center dot center dot center dot H-Namide HBs can have stabilizing contributions even in short azapeptides that cannot fold to form beta-turns.1 aBaruah, Kalpita1 aSahariah, Biswajit1 aSakpal, Sushil, S.1 aDeka, Jugal, Kishore Ra1 aBar, Arun, Kumar1 aBagchi, Sayan1 aSarma, Bani, Kanta uhttps://library.ncl.res.in/content/stabilization-azapeptides-n-amide-center-dot-center-dot-center-dot-h-n-amide-hydrogen-bonds01633nas a2200193 4500008004100000022001400041245011200055210006900167260000800236300001400244490000700258520093500265100002301200700002701223700002301250700001901273700001801292856012901310 2021 eng d a1948-718500aTransition of a deep eutectic solution to aqueous solution: a dynamical perspective of the dissolved solute0 aTransition of a deep eutectic solution to aqueous solution a dyn cSEP a8784-87890 v123 aDisruption of the deep eutectic solvent (DES) nanostructure around the dissolved solute upon addition of water is investigated by polarization-selective two-dimensional infrared spectroscopy and molecular dynamics simulations. The heterogeneous DES nanostructure around the solute is partially retained up to 41 wt % of added water, although water molecules are gradually incorporated in the solute's solvation shell even at lower hydration levels. Beyond 41 wt %, the solute is observed to be preferentially solvated by water. This composition denotes the upper hydration limit of the deep eutectic solvent above which the solute senses an aqueous solvation environment. Interestingly, our results indicate that the transition from a deep eutectic solvation environment to an aqueous one around the dissolved solute can happen at a hydration level lower than that reported for the ``water in DES'' to ``DES in water'' transition.1 aSakpal, Sushil, S.1 aDeshmukh, Samadhan, H.1 aChatterjee, Srijan1 aGhosh, Deborin1 aBagchi, Sayan uhttps://library.ncl.res.in/content/transition-deep-eutectic-solution-aqueous-solution-dynamical-perspective-dissolved-solute02349nas 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