01512nas a2200157 4500008004100000022001400041245012700055210006900182260007100251300001400322490000600336520084200342100002401184700001801208856012801226 2014 eng d a1948-718500aExperimental determination of the electrostatic nature of carbonyl hydrogen-bonding interactions using IR-NMR correlations0 aExperimental determination of the electrostatic nature of carbon a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcAUG a3211-32150 v53 a

Hydrogen-bonding plays a fundamental role in the structure, function, and dynamics of various chemical and biological systems. Understanding the physical nature of interactions and the role of electrostatics in hydrogen-bonding has been the focus of several theoretical and computational research. We present an experimental approach involving IR-C-13 NMR correlations to determine the electrostatic nature of carbonyl hydrogen-bonding interactions. This report provides a direct experimental evidence of the classical nature of hydrogen-bonding interaction in carbonyls, independent of any theoretical approximation. These results have important implications in chemistry and biology and can be applied to probe the reaction mechanisms involving carbonyl activation/stabilization by hydrogen bonds using spectroscopic techniques.

1 aKashid, Somnath, M.1 aBagchi, Sayan uhttps://library.ncl.res.in/content/experimental-determination-electrostatic-nature-carbonyl-hydrogen-bonding-interactions-001854nas a2200157 4500008004100000022001400041245008200055210006900137260007100206300001400277490000600291520125500297100001801552700001801570856010801588 2016 eng d a1948-718500aElectrostatic interactions are key to C=O n-pi* shifts: an experimental proof0 aElectrostatic interactions are key to CO npi shifts an experimen a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcJUN a2270-22750 v73 a

Carbonyl n-pi* transitions are known to undergo blue shift in polar and hydrogen-bonding solvents. Using semiempirical expressions, previous studies hypothesized several factors like change in dipole moment and hydrogen-bond strength upon excitation to cause the blue shift. Theoretically, ground-state electrostatics has been predicted to be the key to the observed shifts, however, an experimental proof has been lacking. Our experimental results demonstrate a consistent linear correlation between IR (ground-state phenomenon) and n-pi* frequency shifts (involves both ground and excited electronic-states) of carbonyls in hydrogen-bonded and non-hydrogen-bonded environments. The carbonyl hydrogen-bonding status is experimentally verified from deviation in n-pi*/fluorescence correlation. The IR/n-pi* correlation validates the key role of electrostatic stabilization of the ground state toward n-pi* shifts and demonstrates the electrostatic nature of carbonyl hydrogen bonds. n-pi* shifts show linear sensitivity to calculated electrostatic fields on carbonyls. Our results portray the potential for n-pi* absorption to estimate local polarity in biomolecules and to probe chemical reactions involving carbonyl activation/stabilization.

1 aHaldar, Tapas1 aBagchi, Sayan uhttps://library.ncl.res.in/content/electrostatic-interactions-are-key-co-n-pi-shifts-experimental-proof02238nas a2200181 4500008004100000022001400041245012800055210006900183260000900252300001400261490000800275520156400283100002301847700001801870700001901888700001801907856013101925 2020 eng d a1520-610600aElectrostatic manifestation of micro-heterogeneous solvation structures in deep-eutectic solvents: a spectroscopic approach0 aElectrostatic manifestation of microheterogeneous solvation stru cMAY  a3709-37150 v1243 a

Deep eutectic solvents have emerged as inexpensive green alternatives to conventional solvents for diverse applications in chemistry and biology. Despite their importance as useful media in various applications, little is known about the microscopic solvation structures of deep eutectic solvents around solutes. Herein, we show that the electrostatic field, which can be estimated both from infrared experiments and theory, can act as a unified concept to report on the microscopic heterogeneous solvation of deep eutectic solvents. Using a fluorophore containing the carbonyl moiety as the solute and the electrostatic field as a descriptor of the solvation structure of the deep eutectic solvents, we report the residue-specific distribution, orientation, and hydrogen bonding in deep eutectic solvents constituting of choline chloride and alcohols of varying chain-lengths. We observe that an increase in alcohol chain-length not only affects the alcohol's propensity to form hydrogen bond to the solute but also alters the spatial arrangement of choline cations around the solute, thereby leading to a microheterogeneity in the solvation structure. Moreover, to extend our electrostatic field based strategy to other deep eutectic solvents, we report an emission spectroscopy based method. We show that this method can be applied, in general, to all deep eutectic solvents, irrespective of their constituents. Overall, this work integrates experiments with molecular dynamics simulations to provide insights into the heterogeneous DES solvation.

1 aChatterjee, Srijan1 aHaldar, Tapas1 aGhosh, Deborin1 aBagchi, Sayan uhttps://library.ncl.res.in/content/electrostatic-manifestation-micro-heterogeneous-solvation-structures-deep-eutectic-solvents03975nas 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-diacylhydrazines