Pokročilá NMR spektroskopie

Measurement of samples with low concentration

The sensitivity is the most limiting factor in NMR measurement and in some cases you cannot obtain reasonable spectra using self-service measurement on 400 MHz spectrometers due to low concentration of the sample. Therefore, we offer NMR measurement using helium-cooled 5 mm cryoprobes that boost sensitivity up to 4 times over a conventional room temperature probe. This equipment is available on Bruker Avance III 500 MHz and Bruker Avance III 600 MHz spectrometers. The ultimate sensitivity can be achieved by 1.7 mm micro-cryoprobe, which is available for the 600 MHz system.

NOE-based experiments

NMR can help in solving 3D structure of your compound and determining e.g. relative configuration, cis/trans isomerism, rotamers etc. We offer measurement and interpretation of NOE-based spectra such as proton 1D-NOESY, 1D-ROESY, 2D-NOESY and 2D-ROESY spectra. In the case of fluorinated compounds, we provide measurement and interpretation of heteronuclear NOE such as H,F-HOESY spectra.

Variable temperature NMR

The chemical exchange is common phenomenon in NMR and provides an evidence of conformational change, tautomerism, hydrogen bonding etc. Sometimes it causes severe line broadening that prevent the observation of some signals. In such cases, we offer NMR measurement at various temperatures ranging from −140 to +140 °C. Such measurements can be done on Bruker Avance II 500 MHz. Measurements at elevated temperature (up to +140 °C) can be also performed on JEOL ECZR 500 MHz spectrometer. Temperature range for both cryoprobe systems Bruker Avance III 500 MHz and Bruker Avance III 600 MHz is from 0 to +120 °C.

Other nuclei

Self-service NMR enables measurement of ¹H, ¹³C, ¹⁹F, ³¹P and ¹¹B nuclei. This list can be extended to other NMR active nuclei such as ²H, ¹⁵N, ²⁹Si, ⁷⁷Se, ¹¹⁹Sn, ¹²⁵Te and ¹⁹⁵Pt. The list is not complete - other nuclei can be measured on demand.

Less common experiments

We offer acquiring of less common NMR experiments that are not available in self-service NMR regime. Such experiments include for example ¹⁹F selective decoupling; ¹H & ¹⁹F double decoupling techniques such as ¹³C{¹H,¹⁹F}; fluorine-carbon correlation such as C,F-HMQC and C,F-HMBC; proton-nitrogen correlation such as H,N-HSQC and H,N-HMBC; spin system mapping such as H,H-TOCSY; or diffusion-related experiments such as DOSY. This list is not complete - other experiments could be performed on demand.

Monitoring of reaction kinetics

We offer monitoring of reaction kinetics by observing one or more sensitive nuclei such as ¹H, ¹⁹F or ³¹P. The measurement can be also performed at various temperatures.

In-situ optical irradiation

NMR with in situ irradiation is a unique method combining NMR spectroscopy and continuous irradiation by UV/vis light. This setup is suitable for monitoring photochemical processes and provides both structural and kinetic information. Light is guided via an optical fiber directly to the NMR tube inside NMR spectrometer and the irradiation wavelengths can be switched outside the spectrometer, no need to manipulate with the sample. Currently we have lamps with wavelengths of 365, 405, 470, 505 and 660 nm. This setup has several advantages:

1. NMR spectra can be recorded in real time during irradiation at variable temperatures,
2. metastable forms can be characterized: long-lasting NMR experiments (e.g. ¹³C, 2D) can be recorded during continuous generation of the metastable forms, and
3. the light intensity can be tuned in order to accelerate/slow down the reaction.

Contact: Eliška Procházková (prochazkova@uochb.cas.cz)

Paramagnetic NMR

Are you sure, that your sample is inside the tube, but no signal has been acquired? Maybe your material is paramagnetic. In this case special setup and pulses sequences are required to obtain meaningful result. Contrary to the common opinion, NMR of paramagnetic species is possible and revealing - both in paramagnetic solids and solutions as well. The techniques are especially suited for metal complexes where EPR fails due to short electronic relaxation.

Contact: Jan Blahut (jan.blahut@uochb.cas.cz)

Solid-state NMR

Solid materials are typically studied in the form of powder. The sample (1–20 mg, dependent on conditions and requirements) is packed into zirconium-oxide rotor and measured under magic-angle-spinning (MAS) conditions. State-of-the-art hardware is available within JEOL 600-MHz spectrometer including a probe for ultra-fast MAS and a probe with extended temperature range (from –100 to +200˚C). In addition to routine ¹³C CP-MAS experiments, we can measure spectra of many exotic NMR active nuclei and also directly detected ¹H and ¹⁹F spectra with high resolution due to fast MAS (up to 70kHz). H–C, H–P, H–N and similar correlation spectra can measured, as well as relaxation and recoupling experiments (REDOR, RESPDOR, TEDOR, etc.).

Contact: Jan Blahut (jan.blahut@uochb.cas.cz), Martin Dračínský (dracinsky@uochb.cas.cz)