01853nas a2200157   4500008004100000022001400041245008200055210006900137260007100206300001400277490000600291520125500297100001801552700001801570856010701588       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<p>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.</p>1 aHaldar, Tapas1 aBagchi, Sayan  uhttp://library.ncl.res.in/content/electrostatic-interactions-are-key-co-n-pi-shifts-experimental-proof02237nas a2200181   4500008004100000022001400041245012800055210006900183260000900252300001400261490000800275520156400283100002301847700001801870700001901888700001801907856013001925       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<p>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.</p>
1 aChatterjee, Srijan1 aHaldar, Tapas1 aGhosh, Deborin1 aBagchi, Sayan  uhttp://library.ncl.res.in/content/electrostatic-manifestation-micro-heterogeneous-solvation-structures-deep-eutectic-solvents