Correlated Dynamics in Ionic Liquids by Means of NMR Relaxometry: Butyltriethylammonium bis(Trifluoromethanesulfonyl)imide as an Example

1H and 19F spin-lattice relaxation experiments have been performed for butyltriethylammonium bis(trifluoromethanesulfonyl)imide in the temperature range from 258 to 298 K and the frequency range from 10 kHz to 10 MHz. The results have thoroughly been analysed in terms of a relaxation model taking into account relaxation pathways associated with 1H–1H, 19F–19F and 1H–19F dipole–dipole interactions, rendering relative translational diffusion coefficients for the pairs of ions: cation–cation, anion–anion and cation–anion, as well as the rotational correlation time of the cation. The relevance of the 1H–19F relaxation contribution to the 1H and 19F relaxation has been demonstrated. A comparison of the diffusion coefficients has revealed correlation effects in the relative cation–anion translational movement. It has also turned out that the translational movement of the anions is faster than of cations, especially at high temperatures. Moreover, the relative cation–cation diffusion coefficients have been compared with self-diffusion coefficients obtained by means of NMR (Nuclear Magnetic Resonance) gradient diffusometry. The comparison indicates correlation effects in the relative cation–cation translational dynamics—the effects become more pronounced with decreasing temperature.

Perchlorinated Triarylmethyl Radical 99% Enriched 13C at the Central Carbon as EPR Spin Probe Highly Sensitive to Molecular Tumbling

<p>Soluble stable radicals are used as spin probes and spin labels for <i>in vitro</i> and <i>in vivo</i> Electron Paramagnetic Resonance (EPR) spectroscopy and imaging applications. We report the synthesis and characterization of a perchlorinated triarylmethyl radical enriched 99% at the central carbon, <b>¹³C₁-PTMTC</b>. The anisotropy of the hyperfine splitting with the ¹³C₁ (A_x=26, A_y=25, A_z=199.5 MHz) and the g (g_x=2.0015, g_y=2.0015, g_z=2.0040) are responsible for a strong effect of the radical tumbling rate on the EPR spectrum. The rotational correlation time can be determine by spectral simulation or via the linewidth after calibration. As spin probe <b>¹³C₁-PTMTC </b>can be used to measure media microviscosity with high sensitivity. Bound to a macromolecule as spin label, <b>¹³C₁-PTMTC </b>could be used to study local mobility and molecular interactions.</p>

Perchlorinated Triarylmethyl Radical 99% Enriched 13C at the Central Carbon as EPR Spin Probe Highly Sensitive to Molecular Tumbling

<p>Soluble stable radicals are used as spin probes and spin labels for <i>in vitro</i> and <i>in vivo</i> Electron Paramagnetic Resonance (EPR) spectroscopy and imaging applications. We report the synthesis and characterization of a perchlorinated triarylmethyl radical enriched 99% at the central carbon, <b>¹³C₁-PTMTC</b>. The anisotropy of the hyperfine splitting with the ¹³C₁ (A_x=26, A_y=25, A_z=199.5 MHz) and the g (g_x=2.0015, g_y=2.0015, g_z=2.0040) are responsible for a strong effect of the radical tumbling rate on the EPR spectrum. The rotational correlation time can be determine by spectral simulation or via the linewidth after calibration. As spin probe <b>¹³C₁-PTMTC </b>can be used to measure media microviscosity with high sensitivity. Bound to a macromolecule as spin label, <b>¹³C₁-PTMTC </b>could be used to study local mobility and molecular interactions.</p>

An algebraic solution for determining overall rotational correlation times from cross-correlated relaxation rates

SummaryAn accurate rotational correlation time is critical for quantitative analysis of fast timescale NMR dynamics. As molecular weights increase, the classic derivation using transverse and longitudinal relaxation rates becomes increasingly unsuitable due to the non-trivial contribution of dipole-dipole and chemical exchange processes. Derivation using cross-correlated relaxation experiments, such as TRACT, overcome these limitations but are erroneously calculated in at approximately 50% of the citing literature. The goals of this study are to 1) investigate the potential sources of the error, 2) provide an algebraic solution, and 3) highlight that future inaccuracies can be minimized by requiring publication of sufficient raw data and computational routes for re-evaluation.

Synergetic Enhancement of Fluorescence and Magnetic Resonance Signals Assisted by Albumin Cage

<p>Bimodal fluorescence and magnetic resonance imaging (FLI/MRI) is important for early diagnosis of malignant tumors. Yet, facile and opportune strategies to synergistically enhance fluorescence intensity and magnetic resonance (MR) contrast effect have been rarely reported. Here, a facile albumin cage (AC) strategy is provided to synergistically enhance the fluorescence intensity by aggregation-induced emission (AIE) and MR contrast with prolonged rotational correlation time (<i>τ</i>_R) of Gd(III) chelates and diffusion correlation time (<i>τ</i>_D) of surrounding water molecules. The amphiphilic bimodal FLI/MRI probe of NGd, could be facilely loaded into ACs to generate supramolecular structure of NGd-albumin cages (NGd-ACs), which show excellent biocompatibility and biosafety, and exhibit superior fluorescence quantum yield and <i>r</i>₁ over NGd with 6- and 8-fold enhancement, respectively. Moreover, compared with clinical MRI contrast agent of Gd-DOTA, <i>r</i>₁ of NGd-AC shows 17-fold enhancement. As a result, NGd-ACs successfully elicit high-performance bimodal FLI/MRI <i>in vitro</i> and brighter MR signals are observed in liver and tumor after intravenous injection of NGd-ACs with a dosage of 6 μmol Gd(III)/kg body weight. This strategy is generic and feasible, and successfully realizes a “1+1>2” effect for dual-modal FLI/MRI.</p>

Synergetic Enhancement of Fluorescence and Magnetic Resonance Signals Assisted by Albumin Cage

<p>Bimodal fluorescence and magnetic resonance imaging (FLI/MRI) is important for early diagnosis of malignant tumors. Yet, facile and opportune strategies to synergistically enhance fluorescence intensity and magnetic resonance (MR) contrast effect have been rarely reported. Here, a facile albumin cage (AC) strategy is provided to synergistically enhance the fluorescence intensity by aggregation-induced emission (AIE) and MR contrast with prolonged rotational correlation time (<i>τ</i>_R) of Gd(III) chelates and diffusion correlation time (<i>τ</i>_D) of surrounding water molecules. The amphiphilic bimodal FLI/MRI probe of NGd, could be facilely loaded into ACs to generate supramolecular structure of NGd-albumin cages (NGd-ACs), which show excellent biocompatibility and biosafety, and exhibit superior fluorescence quantum yield and <i>r</i>₁ over NGd with 6- and 8-fold enhancement, respectively. Moreover, compared with clinical MRI contrast agent of Gd-DOTA, <i>r</i>₁ of NGd-AC shows 17-fold enhancement. As a result, NGd-ACs successfully elicit high-performance bimodal FLI/MRI <i>in vitro</i> and brighter MR signals are observed in liver and tumor after intravenous injection of NGd-ACs with a dosage of 6 μmol Gd(III)/kg body weight. This strategy is generic and feasible, and successfully realizes a “1+1>2” effect for dual-modal FLI/MRI.</p>

Фотофизические процессы в молекулах галогенпроизводных флуоресцеина в анионных обратных мицеллах

Studies of photophysical processes in aqueous micellar solutions of halogen derivatives of fluorescein: Eosin( E), Erythrosin (ER) and Bengal Rose (BR) by methods of dynamic light scattering, stationary and time-resolved fluorescence spectroscopy were carried out. It was found that the introduction of dye molecules into reverse AOT micelles causes an increase in their hydrodynamic radii Rh. The time-resolved fluorescence of the studied dye molecules in reverse micelles was measured. A decrease in the average time of the excited state with an increase in Rh for E, ER, and BR was found, which is associated with an increase in the mobility of water molecules and a decrease in the effect of geometric restriction of dye molecules. The degrees of anisotropy of the fluorescence r of dye molecules in reverse micelles were measured. It was shown that in micellar systems r is greater than in aqueous solutions and decreases with increasing Rh. The rotational correlation time for the studied dye molecules in micellar systems is determined, which decreases for all the studied dyes with an increase in Rh, indicating a decrease in the microviscosity of the confined aqueous medium inside the micelle. In this case , i.e., the value of the time of the rotational correlation is affected by the "heavy atom effect".

Mismatch Recognition by Saccharomyces cerevisiae Msh2-Msh6: Role of Structure and Dynamics

The mismatch repair (MMR) pathway maintains genome integrity by correcting errors such as mismatched base pairs formed during DNA replication. In MMR, Msh2–Msh6, a heterodimeric protein, targets single base mismatches and small insertion/deletion loops for repair. By incorporating the fluorescent nucleoside base analog 6-methylisoxanthopterin (6-MI) at or adjacent to a mismatch site to probe the structural and dynamic elements of the mismatch, we address how Msh2–Msh6 recognizes these mismatches for repair within the context of matched DNA. Fluorescence quantum yield and rotational correlation time measurements indicate that local base dynamics linearly correlate with Saccharomyces cerevisiae Msh2–Msh6 binding affinity where the protein exhibits a higher affinity (KD ≤ 25 nM) for mismatches that have a significant amount of dynamic motion. Energy transfer measurements measuring global DNA bending find that mismatches that are both well and poorly recognized by Msh2–Msh6 experience the same amount of protein-induced bending. Finally, base-specific dynamics coupled with protein-induced blue shifts in peak emission strongly support the crystallographic model of directional binding, in which Phe 432 of Msh6 intercalates 3′ of the mismatch. These results imply an important role for local base dynamics in the initial recognition step of MMR.

Pressure dependence of viscosity in supercooled water and a unified approach for thermodynamic and dynamic anomalies of water

The anomalous decrease of the viscosity of water with applied pressure has been known for over a century. It occurs concurrently with major structural changes: The second coordination shell around a molecule collapses onto the first shell. Viscosity is thus a macroscopic witness of the progressive breaking of the tetrahedral hydrogen bond network that makes water so peculiar. At low temperature, water at ambient pressure becomes more tetrahedral and the effect of pressure becomes stronger. However, surprisingly, no data are available for the viscosity of supercooled water under pressure, in which dramatic anomalies are expected based on interpolation between ambient pressure data for supercooled water and high pressure data for stable water. Here we report measurements with a time-of-flight viscometer down to 244K and up to 300MPa, revealing a reduction of viscosity by pressure by as much as 42%. Inspired by a previous attempt [Tanaka H (2000) J Chem Phys 112:799–809], we show that a remarkably simple extension of a two-state model [Holten V, Sengers JV, Anisimov MA (2014) J Phys Chem Ref Data 43:043101], initially developed to reproduce thermodynamic properties, is able to accurately describe dynamic properties (viscosity, self-diffusion coefficient, and rotational correlation time) as well. Our results support the idea that water is a mixture of a high density, “fragile” liquid, and a low density, “strong” liquid, the varying proportion of which explains the anomalies and fragile-to-strong crossover in water.