Are N-methyl groups of Tetramethylurea (TMU) Hydrophobic? A composition and temperature-dependent fluorescence spectroscopic investigation of TMU/water binary mixtures

Indra, Sandipa; Biswas, Ranjit

doi:10.1007/s12039-016-1072-6

Cited by 9 publications

(11 citation statements)

References 74 publications

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“…At 5 wt % trehalose concentration, the intensity of the peaks of the O(T)–O(T) RDF is ∼3 times greater than that at 20 wt % trehalose concentration. This suggests, like in dilute aqueous solutions of tetramethyl urea, , aggregation among trehalose molecules at low concentrations in glycerol. Upon increasing the trehalose concentration to 20 wt %, the intensity of the O(T)–O(T) RDF decreases.…”

Section: Results and Discussionmentioning

confidence: 91%

How Heterogeneous Are Trehalose/Glycerol Cryoprotectant Mixtures? A Combined Time-Resolved Fluorescence and Computer Simulation Investigation

Indra

Biswas

2016

J. Phys. Chem. B

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Heterogeneity and molecular motions in representative cryoprotectant mixtures made of trehalose and glycerol are investigated in the temperature range 298 ≤ T (K) ≤ 353, via time-resolved fluorescence Stokes shift and anisotropy measurements, and molecular dynamics simulations of four-point density-time correlations and H-bond relaxations. Mixtures containing 5 and 20 wt % of trehalose along with neat glycerol are studied. Viscosity coefficients for these systems lie in the range 0.30 < η (P) < 23. Measured solute (Coumarin 153) rotation and solvation times reveal a substantial departure from the hydrodynamic viscosity dependence, suggesting the strong microheterogeneous nature of these systems. Fluorescence anisotropy decays are highly nonexponential, reflecting a non-Markovian character of the medium friction. A complete missing of the Stokes shift dynamics in these systems at 298 K but partial detection of it at other higher temperatures (shift magnitude being ∼400-600 cm) indicates rigid solute environments. An amorphous solid-like feature emerges in the simulated radial distribution functions at these temperatures. Analyses of mean squared displacements reveal rattling-in-a-cage motion, non-Gaussian displacement distributions, and strong dynamic heterogeneity features. Simulated dynamic structure factors and four-point correlations hint, respectively, at very long α-relaxation and correlated time scales at 298 K. This explains the long solute rotation times (∼80-200 ns) measured at 298 K. Stretched exponential decay of the simulated H-bond relaxations with long time scales further highlights the strong temporal heterogeneity and slow dynamics inherent to these systems. In summary, this work provides the first insight into the molecular motions and interspecies interaction in a representative cryoprotectant mixture, and stimulates further study to investigate the interconnection between cryoprotection and dynamic heterogeneity.

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Section: Results and Discussionmentioning

confidence: 91%

How Heterogeneous Are Trehalose/Glycerol Cryoprotectant Mixtures? A Combined Time-Resolved Fluorescence and Computer Simulation Investigation

Indra

Biswas

2016

J. Phys. Chem. B

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“…A clear change in the slope of coordination number vs. X TBA curve for O TBA -O TBA at X TBA = 0.2 is indicative of different nature of structural evolution below and above this mole-fraction. Similar structural analyses would be useful to understand the recently reported aggregation behaviour in aqueous solutions of protein denaturant, 66 oxyalcohol, 67 and cycloether. 68 It would also be interesting to study the solvent polarization modes and solvation shell structure of ionic species when dissolved in such mixtures.…”

Section: Discussionmentioning

confidence: 89%

Three-dimensional Morphology and X-ray Scattering Structure of Aqueous tert-Butanol Mixtures: A Molecular Dynamics Study

Kaur

Kashyap

2017

J Chem Sci

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It is well established that water-alcohol mixtures exhibit anomalous properties at very low as well as at very high alcohol concentrations. Almost all the studies in this regard intend to link these anomalies to the microscopic structural changes as water (or alcohol) concentration increases in the mixture. However, it is important to note that the nature of these structural changes could be different at the water-and TBA-rich concentrations. In this article, our goal is to address such structural change overs, if really present, in the mixtures of water and tert-butanol (TBA) by using simulated X-ray scattering structure function, S(q), real space radial and spatial distribution functions and heterogeneity order parameter. By using a judicial partitioning scheme, we show that structural characteristic of pure water is qualitatively retained for X TBA < 0.1. The simulated S(q) peaks at around q=2 and q=2.8 Å −1 , which correspond to water oxygen correlations, begin to fade away only after X TBA ≥ 0.1. This is a clear indication of microscopic structural transition at X TBA ≈ 0.1. Beyond X TBA = 0.1, the TBA structural features begin to take over to that of water. The peak at q=1.3 Å −1 which primarily corresponds to nonpolar-nonpolar correlations in pure TBA begin to rise at X TBA ≈ 0.1. However, the pre-peak at around q=0.75 Å −1 , which is due to polar-polar and nonpolar-polar correlations in pure TBA, seems to appear at lower q value only at the equi-molar concentration of the mixture. From the solvent cage surrounding the TBA molecules, we observe that while the aggregation of TBA alkyl groups, due to hydrophobic interaction, is maximum at 10% TBA, the intervening hydrogen bonding interactions between water and TBA molecules tend to lower the hydrophobic interactions between the alkyl groups of alcohol with increasing concentration of TBA. In addition to this, we also observe dimers and small clusters of water molecules in the TBA-rich regime. The computed heterogeneity order parameters for the individual components of the mixture reveal enhanced non-uniform distribution of the TBA molecules near X TBA ≈ 0.1 to 0.3. These results are also supported by the radial distribution functions and nearest neighbour coordination numbers of water and TBA oxygen atoms around TBA oxygen.

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“…This “passing through a minimum” for absorption spectral shifts occurs at a very low concentration of the amphiphile and is specific to amphiphilic hydrophobicity. This is shown in Table 1 , wherein x cosolvent min represents this concentration in mole fraction for a variety of amphiphiles that include 2-butoxyethanol (2-BE), 35 TBA, 34 , 36 − 38 tetrahydrofuran (THF), 39 1,4-dioxane (dioxane), 39 tetramethylurea (TMU), 40 and ethanol. 34 The composition-dependent spectral shift in these systems is reproduced in the upper panel of Figure 1 from earlier literature.…”

Section: Introductionmentioning

confidence: 99%

“… 34 The composition-dependent spectral shift in these systems is reproduced in the upper panel of Figure 1 from earlier literature. 34 − 40 The reason for this red shift in absorption spectra in the upper panel is that the local environment gets stiffened at low mole fractions during the accommodation of amphiphiles in the three-dimensional hydrogen-bond network of water. This is felt by the fluorescence solute as an “increase” in the local density that causes a red shift.…”

Section: Introductionmentioning

confidence: 99%

Dynamical Anomaly of Aqueous Amphiphilic Solutions: Connection to Solution H-Bond Fluctuation Dynamics?

Baksi

Biswas

2022

ACS Omega

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We have investigated the possible connection between “dynamical anomaly” observed in time-resolved fluorescence measurements of reactive and nonreactive solute-centered relaxation dynamics in aqueous binary mixtures of different amphiphiles and the solution intra- and interspecies H-bond fluctuation dynamics. Earlier studies have connected the anomalous thermodynamic properties of binary mixtures at very low amphiphile concentrations to the structural distortion of water. This is termed as “structural anomaly.” Interestingly, the abrupt changes in the composition-dependent average rates of solute relaxation dynamics occur at amphiphile mole fractions approximately twice as large as those where structural anomalies appear. We have investigated this anomalous solution dynamical aspect by considering (water + tertiary butanol) as a model system and performed molecular dynamics simulations at several tertiary butanol (TBA) concentrations covering the extremely dilute to the moderately concentrated regimes. The “dynamical anomaly” has been followed via monitoring the composition dependence of the intra- and interspecies H-bond fluctuations and reorientational relaxations of TBA and water molecules. Solution structural aspects have been followed via examining the tetrahedral order parameter, radial and spatial distribution functions, numbers of H bonds per water and TBA molecules, and the respective populations participating in H-bond formation. Our simulations reveal abrupt changes in the H-bond fluctuations and reorientational dynamics and tetrahedral order parameter at amphiphile concentrations differing approximately by a factor of 2 and corroborates well with the steady-state and the time-resolved spectroscopic measurements. This work therefore explains, following a uniform and cogent manner, both the experimentally observed structural and dynamical anomalies in microscopic terms.

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Are N-methyl groups of Tetramethylurea (TMU) Hydrophobic? A composition and temperature-dependent fluorescence spectroscopic investigation of TMU/water binary mixtures

Cited by 9 publications

References 74 publications

How Heterogeneous Are Trehalose/Glycerol Cryoprotectant Mixtures? A Combined Time-Resolved Fluorescence and Computer Simulation Investigation

How Heterogeneous Are Trehalose/Glycerol Cryoprotectant Mixtures? A Combined Time-Resolved Fluorescence and Computer Simulation Investigation

Three-dimensional Morphology and X-ray Scattering Structure of Aqueous tert-Butanol Mixtures: A Molecular Dynamics Study

Dynamical Anomaly of Aqueous Amphiphilic Solutions: Connection to Solution H-Bond Fluctuation Dynamics?

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