@Article{JAmChemSoc_128_6347, author = {G. Maheut and A. Castaings and J. P{\'e}caut and L.M. {Lawson Daku} and G. Pescitelli and L. {Di Bari} and J.-C. Marchon}, title = {{Chiroptical and Computational Studies of a Bridled Chiroporphyrin and of Its Nickel(II), Copper(II), and Zinc(II) Complexes}}, journal= {J. Am. Chem. Soc.}, ISSN = {0002-7863}, volume= {128}, number= {19}, pages = {6347-6356}, url = {http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/2006/128/i19/abs/ja054926o.html}, eprint= {http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref00864.pdf}, doi= {10.1021/ja054926o}, abstract = {{Circular dichroism (CD) spectra and density functional theory (DFT) calculations are reported for a series of conformationally bistable chiroporphyrins with 8-methylene bridles MBCP-8, which can display either an $\alpha\alpha\alpha\alpha$ or an {\em $\alpha\beta\alpha\beta$} orientation of their meso substituents. From DFT geometry optimizations, the most stable form of ZnBCP-8 is found to be the $\alpha\alpha\alpha\alpha$ conformer. By passing to NiBCP-8, there is a strong stabilization of the {\em $\alpha\beta\alpha\beta$} conformation with respect to the $\alpha\alpha\alpha\alpha$ conformation, consistent with the X-ray structures of $\alpha\alpha\alpha\alpha$-ZnBCP-8 and {\em $\alpha\beta\alpha\beta$}-NiBCP-8. A correlation between the sign of the CD signal in the Soret region and the conformation of the BCP-8 compounds is reported: the $\alpha\alpha\alpha\alpha$ conformers H$_2$BCP-8 and ZnBCP-8 show a positive CD signal, whereas the {\em $\alpha\beta\alpha\beta$} conformers NiBCP-8 and CuBCP-8 exhibit a negative signal. The possible contributions to the rotational strengths of {\em $\alpha\beta\alpha\beta$}-NiBCP-8 and $\alpha\alpha\alpha\alpha$-ZnBCP-8, calculated on the basis of their crystal structures, have been analyzed. The CD signals are found to result from a combination of both the inherent chirality of the porphyrin and of extrinsic contributions due to the chiral bridles. These results may have a broad significance for understanding the chiroptical properties of chiral porphyrins and hemoproteins and for monitoring stimuli-responsive, conformationally bistable chiroporphyrin compounds.}}, year = {2006} }