Ultrafast structure and dynamics in ionic liquids: 2D-IR spectroscopy probes the molecular origin of viscosity

The viscosity of imidazolium ionic liquids increases dramatically when the strongest hydrogen bonding location is methylated. In this work, ultrafast two-dimensional vibrational spectroscopy of dilute thiocyanate ion ([SCN] -) in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4C1im][NTf2]) and 1-butyl-2,3- dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([C4C 1C12im][NTf2]) shows that the structural reorganization occurs on a 26 ± 3 ps time scale and on a 47 ± 15 ps time scale, respectively. The results suggest that the breakup of local ion-cages is the fundamental event that activates molecular diffusion and determines the viscosity of the fluids. © 2014 American Chemical Society

Complex transitions between dihydrate and anhydrate forms of ectoine - unexpected behavior of a highly hygroscopic compatible solute in the solid state

The crystalline dihydrate of the compatible solute ectoine undergoes a loss of water at ambient conditions and transforms into a highly hygroscopic anhydrate form. This unexpected transition is studied combining single-crystal and powder X-ray, single crystal neutron diffraction measurements and quantum mechanical calculations. Overall, our study provides a rationale for the important uptake and loss of water by ectoine in the solid state

Interstitial cells of Cajal mediate mechanosensitive responses in the stomach

Changes in motor activity are a basic response to filling of smooth muscle organs. Responses to gastric filling, for example, are thought to be regulated by neural reflexes. Here, we demonstrate a previously uncharacterized aspect of stretch-dependent responses in visceral smooth muscles that is mediated by mechanosensitive interstitial cells of Cajal. Length ramps were applied to the murine antral muscles while recording intracellular electrical activity and isometric force. Stretching muscles by an average of 27 ± 1% of resting length resulted in 5 mN of force. Increasing length caused membrane depolarization and increased slow-wave frequency. The responses were dependent on the rate of stretch. Stretch-dependent responses were not inhibited by neuronal antagonists or nifedipine. Increases in slow-wave frequency, but not membrane depolarization, were inhibited by reducing external Ca(2+) (100 μM) and by Ni(2+) (250 μM). Responses to stretch were inhibited by indomethacin (1 μM) and were absent in cyclooxygenase II-deficient mice, suggesting that cyclooxygenase II-derived eicosanoids may mediate these responses. Dual microelectrode impalements of muscle cells within the corpus and antrum showed that stretch-induced changes in slow-wave frequency uncoupled proximal-to-distal propagation of slow waves. This uncoupling could interfere with gastric peristalsis and impede gastric emptying. Stretch of antral muscles of W/W(V) mice, which lack intramuscular interstitial cells of Cajal, did not affect membrane depolarization or slow-wave frequency. These data demonstrate a previously uncharacterized nonneural stretch reflex in gastric muscles and provide physiological evidence demonstrating a mechanosensitive role for interstitial cells of Cajal in smooth muscle tissues

Using a Combined Theoretical and Experimental Approach to Understand the Structure and Dynamics of Imidazolium-Based Ionic Liquids/Water Mixtures. 1. MD Simulations

The structural and dynamic properties of 1-butyl-3-methylimidazolium bromide ([C4mim]Br)/water mixtures with different molar ratios have been investigated using classical molecular dynamics (MD) simulations, and the reliability of the results has been assessed by comparison with extended X-ray absorption fine structure experimental data. The analysis of the MD trajectories has highlighted the presence of a complex network of interactions among cations, anions, and water molecules, even if water molecules have been found to interact preferentially with the Br- anion. The existence of solvent-shared ion pairs has been detected in all of the investigated mixtures with one or more water molecules acting as a bridge between the cation and the anion, also when water is present in great excess ([C4mim]Br/water ratio of 1:200). The dynamic behavior of the systems has been characterized starting from the MD trajectories. Water molecules have been found to quicken the dynamics of the IL cations and anions, and acceleration involves all of the investigated motions. © 2013 American Chemical Society