Nuclear magnetic resonance (NMR) has established itself over the last decades as a valuable spectroscopic tool. It is capable of probing the microscopic environment in chemical and biological systems and is a non invasive imaging tool commonly used in the field of medicine and known as MRI. However, the main drawback of NMR and MRI is their inherently low signal to noise ratio (SNR) compared to other type of spectroscopies and imaging techniques. The reason for this is the small energy difference between the nuclear spin states when placed in a magnetic field. This energy difference depends on the magnetic moment of the nuclear spins and on the strength of the external magnetic field. Even with the strongest field currently available (23.5 Tesla), the magnetic energy levels populations, which depend on the temperature according to Boltzmann law, are almost equal at room temperature. This results in only minute population difference, called polarization, measured in parts per million (ppm).
Solid State NMR has the unique advantage in exploring the inherent anisotropic interactions that are normally averaged out in the liquid state. These interactions, carrying useful information about the structure in terms of their tensor properties are also a source of line broadening, and result in low resolution spectra that are hard to interpret. This effect is especially pronounced in systems of coupled protons, making high resolution proton solid state NMR challenging and interesting task.
The phases of the pulses are given by , where i is the pulse number varying between 1 ≤ i ≤ n and here n = 5.
The parameters that need to be optimized when setting up the experiment are – tp (the individual pulse's length), ν1 (the RF amplitude), w (the window's length) and the RF offset.
Optimization should be done on a model compound, such as glycine. It's best to work with a sample confinde to the center of the rotor by the spacers.
Dynamic 2H MAS NMR of amino acids in an aqueous environment at the inner surface of meso porous materials
In this project our interest is to study the mobility and interaction of amino acids and small peptides, in aqueous solution, in the vicinity of silica surfaces. We mostly study materials with high surface areas, such as SBA-15 and MCM-41, for gaining better signal-to-noise ratios.