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The nanoviscosity experienced by molecules in solution may be determined through measurement of the molecular rotational correlation time, τc, for example, by fluorescence and NMR spectroscopy. With this work, we apply PAC spectroscopy to determine the rate of rotational diffusion, λ=1/τc, of a de novo designed protein, TRIL12AL16C, in solutions with viscosities, ξ, from 1.7 to 88 mPa⋅s. TRIL12AL16C was selected as molecular probe because it exhibits minimal effects due to intramolecular dynamics and static line broadening, allowing for exclusive elucidation of molecular rotational diffusion. Diffusion rates determined by PAC data agree well with literature data from fluorescence and NMR spectroscopy, and scales linearly with 1/ξ in agreement with the Stokes–Einstein–Debye model. PAC experiments require only trace amounts (∼1011) of probe nuclei and can be conducted over a broad range of sample temperatures and pressures. Moreover, most materials are relatively transparent to γ‐rays. Thus, PAC spectroscopy could find applications under circumstances where conventional techniques cannot be applied, spanning from the physics of liquids to in‐vivo biochemistry. [ABSTRACT FROM AUTHOR]

Molecules in solution experience rotational diffusion. For large biomolecules such as proteins, the rotational correlation times, τc, are often on the nanosecond time scale. PAC isotopes exhibit lifetimes of the intermediate nuclear level on the time scale of nanoseconds, and the hyperfine interactions measured by PAC spectroscopy are therefore sensitive to dynamics on this time scale. With this work we have compiled experimentally determined rotational correlation times, τcexp, reported in the literature in the slow reorientation limit, and compared to calculated rotational correlations times, τccalc, using the simple Stoke-Einstein-Debye approximation. In a number of cases τcexp agrees with the calculated value within the experimental error, including proteins which are expected to be rigid. In several cases, however, τcexp is smaller than the theoretical value, presumably due to local dynamics at the PAC probe site. In support of this interpretation, τcexp < τccalc is observed for many enzymes, which are expected to display dynamics at the PAC probe site due to water coordination to the active site metal. [ABSTRACT FROM AUTHOR]

The nanoviscosity experienced by molecules in solution may be determined through measurement of the molecular rotational correlation time, τ c , for example, by fluorescence and NMR spectroscopy. With this work, we apply PAC spectroscopy to determine the rate of rotational diffusion, λ=1/τ c , of a de novo designed protein, TRIL12AL16C, in solutions with viscosities, ξ, from 1.7 to 88 mPa⋅s. TRIL12AL16C was selected as molecular probe because it exhibits minimal effects due to intramolecular dynamics and static line broadening, allowing for exclusive elucidation of molecular rotational diffusion. Diffusion rates determined by PAC data agree well with literature data from fluorescence and NMR spectroscopy, and scales linearly with 1/ξ in agreement with the Stokes-Einstein-Debye model. PAC experiments require only trace amounts (∼10 11 ) of probe nuclei and can be conducted over a broad range of sample temperatures and pressures. Moreover, most materials are relatively transparent to γ-rays. Thus, PAC spectroscopy could find applications under circumstances where conventional techniques cannot be applied, spanning from the physics of liquids to in-vivo biochemistry., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Accurate nuclear quadrupole moment values are essential as benchmarks for nuclear structure models and for the interpretation of experimentally determined nuclear quadrupole interactions in terms of electronic and molecular structure. Here, we present a novel route to such data by combining perturbed γ-γ angular correlation measurements on free small linear molecules, realized for the first time within this work, with state-of-the-art ab initio electronic structure calculations of the electric field gradient at the probe site. This approach, also feasible for a series of other cases, is applied to Hg and Cd halides, resulting in Q(^{199}Hg,5/2^{-})=+0.674(17)  b and Q(^{111}Cd,5/2^{+})=+0.664(7)  b.