Our group has determined the structure of PW2 in DPC, SDS micelles and PC:PE vesicles by high-resolution nuclear magnetic resonance (NMR). The comparison between these three structures of PW2 showed similarities mainly in the motif WWR, that has the same orientation in the three systems. Experimental data suggested that the WWR is the region responsible for anchoring the peptide to the interface. In this work we will describe the NMR studies of spin-labeled PW2 to better understand its structural properties and to verify if it exhibits structural tendency in solution. The paramagnetic probe used in this work was 4-amino-2,2,6,6-tetramethypiperidine-1-oxyl-4-carboxylic acid (TOAC) an amino acid containing a nitroxide.  The results obtained in this work showed that the probe incorporation did not change the PW2 structure, since no important differences were observed in the TOCSY spectrum. We also did not observe PW2 aggregation, as all measured parameters were independent on concentration. The peptide conformation can be evaluated by measuring relaxation parameters. The paramagnetic effect is dependent on the distance between the spin-label and the studied hydrogen. We used the TOAC effect in the R1 and R2 values to calculate the distances between the N-terminal and amide hydrogen. The relaxation parameters data showed that PW2 is not extended in solution. The distances were compatible to a curvature around WWR, similar to the results in SDS and DPC. This structural tendency of the peptide in solution resulted probably from fluctuation among structure families. Recent data showed that in many systems the active conformation is selected by the target from families of existing structures. This can be the case for PW2, where the interface selects one of the existing structures. This feature can decrease the entropy penalty for binding. All these data can help to understand the PW2 properties in solution and can give more information for the development of new drugs against coccidiosis.