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

Stochastic Modeling of Flexible Biomolecules Applied to NMR Relaxation. I. Internal Dynamics of Cyclodextrins: γ‑Cyclodextrin as a Case Study

In this work, we address the description of the dynamics of cyclodextrins in relation with nuclear magnetic resonance (NMR) relaxation data collected for hydroxymethyl groups. We define an integrated computational approach based on the definition and parametrization of a stochastic equation able to describe the relevant degrees of freedom affecting the NMR observables. The computational protocol merges molecular dynamics simulations and hydrodynamics approaches for the evaluation of most of the molecular parameters entering the stochastic description of the system. We apply the method to the interpretation of the 13C NMR relaxation of the −CH2OH group of cyclodextrins. We use γ-cyclodextrin as a case study. Results are in agreement with quantitative and qualitative analyses performed in the past with simpler models and molecular dynamics simulations. The element of novelty in our approach is in the treatment of the coupling of the relevant internal (glucopyranose ring twisting/tilting and hydroxymethyl group jumps) and global (molecular tumbling) degrees of freedom

Dynamics of Chloromethanes in Cryptophane-E Inclusion Complexes: A ²H Solid-State NMR and X-ray Diffraction Study

In this paper, we present a variable temperature 2H solid-state NMR investigation of cryptophane-E:chloroform and cryptophane-E:dichloromethane inclusion complexes. The 2H line shapes and nuclear spin relaxation rates were analyzed in terms of the distribution of C−D bond orientations and the time scale of the guest dynamics. It was found that encaged chloroform produces broad 2H spectra, and that its reorientation is relatively slow with a correlation time of ∼0.17 μs at 292 K. In contrast, the 2H line shapes of encaged dichloromethane are narrow and the motion of this guest molecule is fast with a correlation time of ∼1.4 ps at 283 K. The 2H NMR data were complemented by an X-ray diffraction study of the cryptophane-E:dichloromethane structure, which was utilized in the analysis of the NMR parameters

Inclusion of Chloromethane Guests Affects Conformation and Internal Dynamics of Cryptophane-D Host

Cryptophane-D is composed of two nonequivalent cyclotribenzylene caps bound together by three OCH₂CH₂O bridges in a syn arrangement. Host–guest complexes with chloroform and dichloromethane were investigated in solution by NMR spectroscopy. Variable temperature NMR ¹H and ¹³C spectra showed effects of chemical exchange between the free and bound guest and of conformational exchange for the host, strongly and specifically affected by guest binding. We found in particular that the carbon-13 chemical shifts for the linkers connecting the two cyclotribenzylene units are very informative. The NMR results were supported by DFT calculations. The guest exchange was also studied quantitatively, either by EXSY measurements (for chloroform as guest) or by line-shape analysis (for dichloromethane as guest). In the case of chloroform guest, we also investigated cross-relaxation between the guest and host protons, as well as carbon-13 longitudinal relaxation and heteronuclear NOE at three different fields. The results were interpreted in terms of orientation and dynamics of the guest inside the host cavity. Putting together various types of evidence resulted in remarkably detailed insight into the process of molecular recognition of the two guests by cryptophane-D host

Stochastic Modeling of Flexible Biomolecules Applied to NMR Relaxation. 2. Interpretation of Complex Dynamics in Linear Oligosaccharides

A computational stochastic approach is applied to the description of flexible molecules. By combining (i) molecular dynamics simulations, (ii) hydrodynamics approaches, and (iii) a multidimensional diffusive description for internal and global dynamics, it is possible to build an efficient integrated approach to the interpretation of relaxation processes in flexible systems. In particular, the model is applied to the interpretation of nuclear magnetic relaxation measurements of linear oligosaccharides, namely a mannose-containing trisaccharide and the pentasaccharide LNF-1. Experimental data are reproduced with sufficient accuracy without free model parameters