Contrasting hydration dynamics in DME and DMSO aqueous solutions: A combined optical pump-probe and GHz-THz dielectric relaxation investigation

Mahanta, Debasish Das; Islam, Sk Imadul; Choudhury, Samiran; Das, Dipak K.; Mitra, Rajib Kumar; Barman, Anjan

doi:10.1016/j.molliq.2019.111194

Cited by 13 publications

(9 citation statements)

References 77 publications

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“…In studies using binary solvent mixtures, synergistic effects are sometimes encountered such that a certain effect is more pronounced in the mixture than in the neat solvents. For instance, this has been observed for the ring-closure of a merocyanine or for excited-state lifetimes and quenching in various systems. − Saini and Das − have studied curcumin in toluene/methanol mixtures and observed that the nonradiative rates associated with an intramolecular hydrogen bond in curcumin are modulated by the presence of protic cosolvents. In our study, TPF in its red I form is also stabilized by an intramolecular hydrogen bond that is not present in the yellow I isomer.…”

Section: Resultsmentioning

confidence: 98%

Sensitivity of Isomerization Kinetics of 1,3,5-Triphenylformazan on Cosolvents Added to Toluene

2021

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Formazan molecules exhibit photochromism because isomerization processes following excitation may occur in both the azo group and the hydrazone group; thus, each formazan may be present in various forms with different colors. The ratio of these forms depends on the illumination conditions and the environment of the formazan with a most incisive sensibility of the thermal anti-syn relaxation of the CN toward slight traces of impurities in toluene solutions, as reported most prominently for 1,3,5-triphenylformazan. Here, we study the latter compound with transient absorption spectroscopy to investigate the role of these traces by adding small amounts of both protic and aprotic cosolvents. Whereas the activation barrier decreases if the binary solvent mixture has a higher polarity, the role of hydrogen bonding can have a reverse impact on the thermal isomerization rate. Both the addition of an aprotic cosolvent and the addition of a protic cosolvent can slow the reaction due to their hydrogen-bond accepting and hydrogen-bond donating properties, respectively. In the case of methanol as a cosolvent, this effect outweighed that of the polarity increase for small concentrations, which was not observed for the fluorinated alcohol hexafluoroisopropanol. The results are explained in the context of a competition between solute−cosolvent and cosolvent−cosolvent hydrogen bonding.

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Section: Resultsmentioning

confidence: 98%

Sensitivity of Isomerization Kinetics of 1,3,5-Triphenylformazan on Cosolvents Added to Toluene

2021

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“…Das Mahanta et al have investigated the change in the collective hydration dynamics in presence of DMSO at different concentrations using THz-TDS. We found that α(ν) of the mixed solvents shows a non-linear change with X DMSO [111]. This change has been correlated with the water-DMSO structural heterogeneity in the mixed solvents.…”

Section: Alcohols and Other Solventsmentioning

confidence: 64%

Probing Biological Water Using Terahertz Absorption Spectroscopy

Mitra¹,

Palit²

2022

Terahertz Technology

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Hydrogen bonding properties of water molecules, which are confined in microcavities of biological interfaces, are significantly different from those of bulk water and drive most of the complex biological processes. While NMR, X-ray and UV–vis-IR spectroscopic techniques have been found inadequate for describing the dynamics of the thick (20–40 Å) sheath of hydration layer around biomolecules, recently developed THz spectroscopy has emerged as a powerful technique to directly probe the collective dynamics of hydrogen bonds in the hydration layer, which control all important functions of the biomolecules in life. Both laser and accelerator-based THz sources are intense enough to penetrate up to about 100 μm thick water samples, which makes THz transmission and/or dielectric relaxation measurements possible in aqueous solutions. These measurements provide valuable information about the rattling and rotational motions of hydrated ions, making, breaking and rearrangement of hydrogen bonds in hydration layer as well as hydrophilic and hydrophobic interactions between biomolecule and water. THz spectroscopy has also been successfully applied to study the effect of modulation of the physical conditions, like temperature, pH, concentration of proteins and chemical additives, on the structure and dynamics of hydration layer. THz spectroscopy has also been applied to study the processes of denaturation, unfolding and aggregation of biomolecules.

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“…On the other hand, recording the emission in a variable environment also allows to obtain information on the latter. These versatile properties could be further manipulated by employing solvent mixtures with perturbed hydrogen-bond dynamics, [68][69][70][71][72][73][74] applying high pressures [26,[75][76][77] or spatially encapsulating the compound. The latter approach was demonstrated for other photoacids confined in small solvent droplets, [16] as e. g. also possible in (reverse) micelles, [24,[78][79][80][81][82][83][84][85][86] or small container molecules, [87][88][89] which further alters the ESPT characteristics.…”

Section: Discussionmentioning

confidence: 99%

Excited‐State Proton Transfer Dynamics of a Super‐Photoacid in Acetone‐Water Mixtures

et al. 2022

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Super‐photoacids, that is, photoacids with a negative pKnormala value in the electronically excited state, can trigger an excited‐state proton transfer (ESPT) to the solvent. For the neutral pyranine‐derived super‐photoacid studied here, even indications for ESPT in acetoneous solution are reported. The characteristics of ESPT in this environment, that is, which intermediates exist and what the impact of cosolvents is, remain unsettled though. In this work, we study ESPT in acetone‐water mixtures by steady‐state and time‐resolved fluorescence spectroscopy. Various effects are observed: First, the addition of water supports the formation of a hydrogen‐bonded ground‐state complex comprising one water molecule and the photoacid, whose excitation triggers the formation of a hydrogen‐bonded ion pair on a sub‐ns time scale. Second, water has an overall accelerating effect on the fluorescence dynamics of the involved emitting species, whose contributions are disentangled in a global analysis scheme, enabling the identification of emission from the free photoacid, a photoacid‐water complex, a hydrogen‐bonded ion pair, and the deprotonated photoacid. At least two water molecules are necessary for ESPT in the environment. Third, additional acidification thwarts an efficient ground‐state complex formation of the photoacid and water. However, upon excitation, complexation may occur on a timescale faster than the photoacid's excited‐state lifetime, so that emission from a nascent complex emerges.

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Contrasting hydration dynamics in DME and DMSO aqueous solutions: A combined optical pump-probe and GHz-THz dielectric relaxation investigation

Cited by 13 publications

References 77 publications

Sensitivity of Isomerization Kinetics of 1,3,5-Triphenylformazan on Cosolvents Added to Toluene

Sensitivity of Isomerization Kinetics of 1,3,5-Triphenylformazan on Cosolvents Added to Toluene

Probing Biological Water Using Terahertz Absorption Spectroscopy

Excited‐State Proton Transfer Dynamics of a Super‐Photoacid in Acetone‐Water Mixtures

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