Here, the calculated length of Fe-N* and N*-O* bonds was similar among all of them except that of hemin-styrene(NO) (Table , supplementary tables 4,7,10,13,15). In hemin-styrene(NO), the Fe-N* was the longest and reached 2.325 A o , while the N*=O* length was 1.157 A o , relating to weaker Fe-NO bonding than that of the others at this state. Furthermore, the ∠(Fe-N*=O*) relates to a nearly linear Fe-N=O conformation in all structures except in H-Styr(NO), which has an end-on geometry, and this angle was only 141.54 o , similar to that of hemin at M=2 (data not shown). This was accompanied with out of the porphyrin-plane movement of the Fe atom towards the • NO, with an increase in bond length between Fe and each N-atom of the pyrrole rings in all • NO-complexes except in H-Styr(NO). In the latter case, with the angular configuration of • NO molecule attached to Fe, the Fe atom moved more towards the N-plane with a decrease in bond length between Fe and the pyrrole nitrogens (Fe-N).