The properties of the electron Tariquidar spin, such as T2 relaxation times in the ns-range and spectral widths that can range from 30 MHz to thousands of MHz, make pulsed methods in EPR technically more demanding than in NMR. Therefore, pulsed methods are a much more recent development in EPR than in NMR. The present introduction starts by identifying the parameters defining the resonance of an EPR or an NMR line. These parameters already contain information about the molecular and electronic structure of the center associated with the spin, e.g., the photosynthetic cofactor containing an unpaired electron or nuclei with a magnetic moment. Next are spin interactions, followed by a few examples which illustrate

these points. Conceptually simple examples were chosen, since they allow the discussion of the learn more phenomena without going into the detail that is at the heart of the research presented in the following sections. Fundamental magnetic resonance parameters Electron and nuclear spin in the magnetic field Electron and nuclear spins are aligned in an external magnetic field. For the electron with a spin quantum number S = 1/2 and for the nuclei with a nuclear quantum number I = 1/2, two energy check details levels result. The energy difference between the two levels is given by the resonance condition (Eq. 1). $$ \textEPR:\Updelta

E = h\nu = g_\texte \beta_\texte B_0 \quad \textNMR:\Updelta E = h\nu = (1 – \sigma )g_\textn \beta_\textn B_0 $$ (1)Here, ν is the frequency, B 0 is the static magnetic field at which the resonance occurs, g e and g n are the electron and nuclear g-factors, respectively, βe and βn are the Bohr and the nuclear magnetons, respectively, and σ is the chemical shielding. Figure 1 shows the energy levels as a function of the magnetic field. Transitions between these energy levels

can be induced by electromagnetic radiation resulting in an EPR or NMR resonance line. The resonance frequencies in EPR are in the microwave range, typically from 9 to several 100 GHz at magnetic fields from 0.3 to 12 T, and in NMR from several hundred to 900 MHz at magnetic fields from a few T to around 20 T. To define 17-DMAG (Alvespimycin) HCl the resonance position of such a line, two parameters are needed: the magnetic field B 0 and the frequency of the electromagnetic radiation ν. In EPR, the position of the line is defined by g, the g-factor. In NMR, the chemical shielding σ plays that role. To define the resonance of nuclei independent of the measurement field, the chemical shift δ is introduced. $$ \delta = 10^6 \frac(\nu – \nu_\textref )\nu_\textref = \frac(\sigma_\textref – \sigma )1 – \sigma_\textref \approx 10^6 (\sigma_\textref – \sigma ) $$ (2)The chemical shift parameter δ is dimensionless and is given in ppm, parts per million (Hore 1995). Fig.