Chiroptical and Computational Studies of a Bridled Chiroporphyrin and of Its Nickel(II), Copper(II), and Zinc(II) Complexes

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 alphaalphaalphaalpha or an alphabetaalphabeta orientation of their meso substituents. From DFT geometry optimizations, the most stable form of ZnBCP-8 is found to be the alphaalphaalphaalpha conformer. By passing to NiBCP-8, there is a strong stabilization of the alphabetaalphabeta conformation with respect to the alphaalphaalphaalpha conformation, consistent with the X-ray structures of alphaalphaalphaalpha-ZnBCP-8 and alphabetaalphabeta-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 alphaalphaalphaalpha conformers H2BCP-8 and ZnBCP-8 show a positive CD signal, whereas the alphabetaalphabeta conformers NiBCP-8 and CuBCP-8 exhibit a negative signal. The possible contributions to the rotational strengths of alphabetaalphabeta-NiBCP-8 and alphaalphaalphaalpha-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.

Optically Active Oxo(phthalocyaninato)vanadium(IV) with Geometric Asymmetry: Synthesis and Correlation between the Circular Dichroism Sign and Conformation

“…[18] TDDFT combines computational efficiency with often quite reliable accuracy, and has been applied successfully to optically active porphyrinoid systems. [19] We have also studied in detail the effect of the relative orientation of the peripheral substituents on the Q-band CD of the present system .…”

“…[27] The geometry optimization of VOPc with four methoxy groups (VOPc Me -a) was performed at the UB3LYP/6-31G* level, [19] using C 4 symmetry restriction. Sixty excitation energies, oscillator strengths, and rotatory strengths for the optimized structure were calculated by TDDFT.…”

Thermostability Improvement of a Streptomyces Xylanase by Introducing Proline and Glutamic Acid Residues

“…Currently, xylanase has been attracting much attention due to its wide biotechnological applications in the food, animal feed, pulp and paper, and textile industries and in the deconstruction of lignocellulose for biofuel production (2)(3)(4)(5)(6). On the basis of the catalytic domains, xylanases are mainly classified into glycoside hydrolase (GH) families 5,8,10,11,30, and 43 (7); GH10 and GH11 xylanases are the best studied.…”

A New Route towards Redox Bistability through the Inspection of Manganese–Porphyrin Complexes

“…[20][21][22][23][24][25] With this goal in mind, porphyrin derivatives have appeared as candidates of choice since they simultaneously display non-innocent electronic structures and flexibility. [26,27] However, manganese-porphyrins have received little attention from the theoretical point of view. [28][29][30][31][32][33] Clearly, the presence of several unpaired electrons makes those systems particularly attractive experimentally and theoretically.…”