Bimodal Fluorescence/Magnetic Resonance Molecular Probes with Extended Spin Lifetimes.

Bimodal molecular probes combining nuclear magnetic resonance (NMR) and fluorescence have been widely studied in basic science, as well as clinical research. The investigation of spin phenomena holds promise to broaden the scope of available probes allowing deeper insights into physiological processes. Herein, a class of molecules with a bimodal character with respect to fluorescence and nuclear spin singlet states is introduced.

Spontaneous Enhancement of Magnetic Resonance Signals Using a RASER.

Nuclear magnetic resonance is usually drastically limited by its intrinsically low sensitivity: Only a few spins contribute to the overall signal. To overcome this limitation, hyperpolarization methods were developed that increase signals several times beyond the normal/thermally polarized signals. The ideal case would be a universal approach that can signal enhance the complete sample of interest in solution to increase detection sensitivity.

Gradient selected pure shift EASY-ROESY techniques facilitate the quantitative measurement of H,H-distance restraints in congested spectral regions.

For elucidating molecular structure and dynamics in solution, NMR experiments such as NOESY, ROESY and EXSY have been used excessively over the past decades, to provide interatomic distance restraints or rates for chemical exchange. The extraction of such information, however, is often prohibited by signal overlap in these spectra. To reduce this problem, pure shift methods for improving the spectral resolution have become popular.

Hyperpolarization of N-pyridinium and N-aniline derivatives by using parahydrogen: new opportunities to store nuclear spin polarization in aqueous media.

Hyperpolarization techniques hold the promise to improve the sensitivity of magnetic resonance imaging (MRI) contrast agents by over 10 000-fold. Among these techniques, para-hydrogen induced polarization (PHIP) allows for generating contrast agents within seconds. Typical hyperpolarized contrast agents are traceable for 2-3 minutes only, thus prolonging tracking-times holds great importance for the development of new ways to diagnose and monitor diseases.

Hyperpolarization of Amino Acids in Water Utilizing Parahydrogen on a Rhodium Nanocatalyst.

NMR offers many possibilities in chemical analysis, structural investigations, and medical diagnostics. Although it is broadly used, one of NMR spectroscopies main drawbacks is low sensitivity. Hyperpolarization techniques enhance NMR signals by more than four orders of magnitude allowing the design of new contrast agents.

perfectBASH: Band-selective homonuclear decoupling in peptides and peptidomimetics.

Band selective techniques offer the highest sensitivity of all pure shift approaches and thus are the best choice for decoupling well-separated H-frequency regions, such as the amide- or the α-proton region of α-peptides. They are inept to fully decouple the amide- and the α-proton region simultaneously, though. Herein, we present a new homonuclear decoupling technique, which extends the capabilities of band selective decoupling using the perfect echo principle.

A pure shift experiment with increased sensitivity and superior performance for strongly coupled systems.

Motivated by the persisting need for enhanced resolution in solution state NMR spectra, pure shift techniques such as Zangger-Sterk decoupling have recently attracted widespread interest. These techniques for homonuclear decoupling offer enhanced resolution in one- and multidimensional proton detected experiments by simplifying multiplet structures. In this work, a modification to the popular Zangger-Sterk technique PEPSIE (Perfect Echo Pure Shift Improved Experiment) is presented, which decouples pairs of spins even if they share the same volume element.

Uncovering Key Structural Features of an Enantioselective Peptide-Catalyzed Acylation Utilizing Advanced NMR Techniques.

We report on a detailed NMR spectroscopic study of the catalyst-substrate interaction of a highly enantioselective oligopeptide catalyst that is used for the kinetic resolution of trans-cycloalkane-1,2-diols via monoacylation. The extraordinary selectivity has been rationalized by molecular dynamics as well as density functional theory (DFT) computations. Herein we describe the conformational analysis of the organocatalyst studied by a combination of nuclear Overhauser effect (NOE) and residual dipolar coupling (RDC)-based methods that resulted in an ensemble of four final conformers.

Distinction of trans-cis photoisomers with comparable optical properties in multiple-state photochromic systems - examining a molecule with three azobenzenes via in situ irradiation NMR spectroscopy.

Photochromic compounds like azobenzenes are widely used for the production of stimuli responsive materials. To analyse cascaded azobenzene switching inside a benzene-tricarboxamide (BTA) with three azobenzene moieties in a site-specific fashion, we used in situ irradiation NMR spectroscopy. Four photoisomers can be distinguished by their chemical shifts.

Extraction of distance restraints from pure shift NOE experiments.

NMR techniques incorporating pure shift methods to improve signal resolution have recently attracted much attention, owing to their potential use in studies of increasingly complex molecular systems. Extraction of frequencies from these simplified spectra enables easier structure determination, but only a few of the methods presented provide structural parameters derived from signal integral measurements. In particular, for quantification of the nuclear Overhauser effect (NOE) it is highly desirable to utilize pure shift techniques where signal overlap normally prevents accurate signal integration, to enable measurement of a larger number of interatomic distances.

CLIP-COSY: A Clean In-Phase Experiment for the Rapid Acquisition of COSY-type Correlations.

The COSY experiment is an essential homonuclear 2D NMR experiment for the assignment of resonances. Its multiplet line shape, however, is often overly complicated, potentially leads to signal intensity losses, and is responsible for long minimum overall acquisition times. Herein, we present CLIP-COSY, a COSY-type experiment yielding clean in-phase peaks.

Accurate determination of one-bond heteronuclear coupling constants with "pure shift" broadband proton-decoupled CLIP/CLAP-HSQC experiments.

We report broadband proton-decoupled CLIP/CLAP-HSQC experiments for the accurate determination of one-bond heteronuclear couplings and, by extension, for the reliable measurement of small residual dipolar coupling constants. The combination of an isotope-selective BIRD((d)) filter module with a non-selective (1)H inversion pulse is employed to refocus proton-proton coupling evolution prior to the acquisition of brief chunks of free induction decay that are subsequently assembled to reconstruct the fully-decoupled signal evolution. As a result, the cross-peaks obtained are split only by the heteronuclear one-bond coupling along the F2 dimension, allowing coupling constants to be extracted by measuring simple frequency differences between singlet maxima.

The influence of electronic modifications on rotational barriers of bis-NHC-complexes as observed by dynamic NMR spectroscopy.

There has been much debate about the σ-donor and π-acceptor properties of N-heterocyclic carbenes (NHCs). While a lot of synthetic modifications have been performed with the goal of optimizing properties of the catalyst to tune reactivity in various transformations (e.g.