Determination of the Rotational Diffusion Tensor of Porphycene by ¹³C and ¹H Spin Relaxation Methods

The longitudinal 13C and 1H relaxation rates were determined in porphycene in CD2Cl2 solution. These data, augmented by 13C{1H} NOE enhancements were numerically analyzed to evaluate the rotational diffusion tensor of the molecule and the vibrational correction for the one-bond 13C–1H dipolar couplings. The 13C and 1H relaxation data seem to be consistent with each other, and the emerging picture of the rotational dynamics of porphycene compares well with the results that can be found in the literature

Carbon-13 NMR Relaxation Study of 1,8-Bis(dimethylamino)naphthalene in Isotropic Solution

Carbon-13 nuclear spin relaxation in 1,8-bis(dimethylamino)naphthalene (DMAN) was investigated in a dimethylformamide-d7 solution. In addition, the chemical shielding tensors were measured in the crystalline powder. Detailed analysis of 13C longitudinal relaxation in this molecule yielded its rotational diffusion tensor. Comparison to the protonated form of DMAN, DMANH+, leads to conclusions concerning interaction of the latter with its counterion

NMR Relaxation Study of the Protonated Form of 1,8-Bis(dimethylamino)naphthalene in Isotropic Solution: Anisotropic Motion outside of Extreme Narrowing and Ultrafast Proton Transfer

The protonated form of 1,8-bis(dimethylamino)naphthalene (DMANH+) consists of a rigid, aromatic framework, substituted by two amino groups that are connected by a strong, symmetric (on the NMR time-scale) hydrogen bond bridge. The reorientational motion of the molecule in dimethylformamide-d7 solution was characterized by T1 and NOE measurements for aromatic 13C nuclei. Treating the reorientation of DMANH+ as anisotropic rotational diffusion of a rigid body, the diffusion tensor was determined with good accuracy. Measurements and interpretation of 15N T1 and NOE indicate that the proton transfer between potential minima in the hydrogen bond bridge is faster than the molecular reorientation

Frozen Rotation of the Ammonium Group Observed for the First Time in Liquid-Phase NMR Spectra

Hindered rotation of the −NH₃⁺ group in a sterically crowded molecular environment was frozen on the NMR time scale. These effects were observed for solutions of 1,2,3,4-tetrabromotriptycyl-9-ammonium tetrafluoroborate in tetrahydrofuran with and without excess of HBF₄. In the absence of acid, the hindered rotation is accompanied by a number of other effects originating in part from practically nonremovable traces of water in the solvent. Because of these additional effects, an effective rate constant of the hindered rotation could be evaluated at only one temperature for the neutral solution of the salt. For one of the acidified samples, which was prepared with special precautions against moisture, these complications are practically nonexistent at low and intermediate temperatures. For the latter sample, the Arrhenius parameters of the hindered rotation could be determined from the rotation rates evaluated in the range 194–226 K

Quasistatic Disorder of NH···N Bonds and Elastic-Properties Relationship in 2‑Phenylimidazole Crystals

The molecular aggregation in 2-phenylimidazole is analogous to that observed in the new class of NH···N bonded ferroelectrics and relaxors. Disordered H-atoms in NH···N hydrogen-bonded chains in the average crystal structure of 2-phenylimidazole persist to 100 K, but the relaxation time of this process is very long even above 340 K. Above 200 K, a gradual increase of the electric permittivity along chains testifies to the activation of dipolar fluctuations, associated with proton transfers in the quasistatic disordered chains. However, the chemical shifts of nitrogen atoms (equivalent according to the average crystal symmetry) remain clearly distinguished as protonated and unprotonated in ¹⁵N NMR spectra up to 340 K at least. The 2-phenylimidazole crystal exhibits an unusual negative-linear thermal expansion (NTE) in the entire 140–340 K range, induced by subtle rotations of the NH···N bonded molecules. The NTE direction is the softest in the hydrostatically compressed crystal, which violates the inverse relationship rule of compression and thermal expansion. The crystal compression is monotonic, but clearly nonlinear, which is connected with the pressure enforced adjustments in the molecular packing between 0.1 MPa and 0.4 GPa, when small voids between molecules are eliminated

Carbon-13 NMR Relaxation Study of the Internal Dynamics in Cyclodextrins in Isotropic Solution

13C nuclear spin relaxation processes in seven cyclodextrins (from six-membered α to twelve-membered η) were investigated in 2H2O solution at multiple magnetic fields. Detailed analysis of 13C longitudinal relaxation in laboratory and rotating frames and 13C{1H} nuclear Overhauser enhancement in these molecules yielded their rotational diffusion tensors and a semiquantitative picture of their internal dynamics

Size-Dependent Interaction of Amyloid β Oligomers with Brain Total Lipid Extract BilayerFibrillation Versus Membrane Destruction

Amyloid β, Aβ(1–42), is a component of senile plaques present in the brain of Alzheimer’s disease patients and one of the main suspects responsible for pathological consequences of the disease. Herein, we directly visualize the Aβ activity toward a brain-like model membrane and demonstrate that this activity strongly depends on the Aβ oligomer size. PeakForce quantitative nanomechanical mapping mode of atomic force microscopy imaging revealed that the interaction of large-size (LS) Aβ oligomers, corresponding to high-molecular-weight Aβ oligomers, with the brain total lipid extract (BTLE) membrane resulted in accelerated Aβ fibrillogenesis on the membrane surface. Importantly, the fibrillogenesis did not affect integrity of the membrane. In contrast, small-size (SS) Aβ oligomers, corresponding to low-molecular-weight Aβ oligomers, created pores and then disintegrated the BTLE membrane. Both forms of the Aβ oligomers changed nanomechanical properties of the membrane by decreasing its Young’s modulus by ∼45%. Our results demonstrated that both forms of Aβ oligomers induce the neurotoxic effect on the brain cells but their action toward the membrane differs significantly

Size-Dependent Interaction of Amyloid β Oligomers with Brain Total Lipid Extract BilayerFibrillation Versus Membrane Destruction

Amyloid β, Aβ(1–42), is a component of senile plaques present in the brain of Alzheimer’s disease patients and one of the main suspects responsible for pathological consequences of the disease. Herein, we directly visualize the Aβ activity toward a brain-like model membrane and demonstrate that this activity strongly depends on the Aβ oligomer size. PeakForce quantitative nanomechanical mapping mode of atomic force microscopy imaging revealed that the interaction of large-size (LS) Aβ oligomers, corresponding to high-molecular-weight Aβ oligomers, with the brain total lipid extract (BTLE) membrane resulted in accelerated Aβ fibrillogenesis on the membrane surface. Importantly, the fibrillogenesis did not affect integrity of the membrane. In contrast, small-size (SS) Aβ oligomers, corresponding to low-molecular-weight Aβ oligomers, created pores and then disintegrated the BTLE membrane. Both forms of the Aβ oligomers changed nanomechanical properties of the membrane by decreasing its Young’s modulus by ∼45%. Our results demonstrated that both forms of Aβ oligomers induce the neurotoxic effect on the brain cells but their action toward the membrane differs significantly

Mechanochemical vs Wet Approach for Directing CO₂ Capture toward Various Carbonate and Bicarbonate Networks

The distinct research areas related to CO2 capture and mechanochemistry are both highly attractive in the context of green chemistry. However, merger of these two areas, i.e., mechanochemical CO2 capture, is still in an early stage of development. Here, the application of biguanidine as an active species for CO2 capture is investigated using both solution-based and liquid-assisted mechanochemical approaches, which lead to a variety of biguanidinium carbonate and bicarbonate hydrogen-bonded networks. We demonstrate that in solution, the formation of the carbonate vs bicarbonate networks can be directed by the organic solvent, while, remarkably, in the liquid-assisted mechanochemical synthesis employing the same solvents as additives, the selectivity in network formation is inversed. In general, our findings support the view of mechanochemistry not only as a sustainable alternative but rather as a complementary strategy to solution-based synthesis