How the change of the ligand from L = porphine, P 2À , to L = P 4 -substituted porphine, P(P) 4 2À , affects the electronic properties and the M–L binding energies for the first-row transition metals M = Sc–Zn: Comparative study Aleksey E. Kuznetsov ⇑ Departamento de Química, Universidade Federal de São Carlos, Rodovia Washington Luiz, Km 235, Caixa Postal 676, CEP 13565-905 São Carlos, SP, Brazil article info Article history: Received 10 November 2015 In final form 18 February 2016 Available online 27 February 2016 Keywords: P 4 -substituted transition-metal-porphyrins Density functional theory Electronic properties NBO analysis Binding energies abstract We performed comparative DFT study, including Natural Bond Orbitals (NBO) analysis, of the binding energies between all the first-row transition metals M n+ (M = Sc–Zn) and two ligands of the similar type: porphine, P 2À , and its completely P-substituted counterpart, P(P) 4 2À . The main findings are as follows: (i) complete substitution of all the pyrrole nitrogens with P-atoms does not affect the ground spin state of metalloporphyrins; (ii) generally, for the MP(P) 4 compounds the calculated HOMO/LUMO gaps and opti- cal gaps are smaller than for their MP counterparts; (iii) the trends in the change of the binding energies between M n+ and P(P) 4 2À /P 2À are very similar for both ligands. The complete substitution of the pyrrole nitrogens by the P-atoms decreases the M n+ -ligand binding energies; all the MP(P) 4 compounds studied are stable according to the calculated E bind values and therefore can be potentially synthesized. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Metalloporphyrins have been of great interest because of being cofactors in numerous enzymes [1–4] and due to their various technological applications [5–12]. The porphyrins biological functions include: (i) O 2 transport (hemoglobins) and storage (myoglobins); (ii) xenobiotic detoxification (cytochrome P450s); (iii) oxidative metabolism (cytochrome c oxidase); (iv) gas sensing (soluble guanylate cyclases); (v) input/regulation of the circadian clock (nuclear hormone receptor, Reverb a, mPER2); (vi) microRNA processing (DGCR8); (vii) antibactericides/microbicides (myeloperoxidase); (viii) thyroid hormone synthesis (thyroperoxi- dase); (ix) collection and transport of light energy (antennae complexes); (x) conversion of solar energy to chemical energy (photosynthetic reaction centers); (xi) electron transfer (cyto- chromes); (xii) oxidative phosphorylation; (xiii) NO scavenging, and a large number of other enzymatic reactions (peroxidases, catalases, cytochromes P450, methylreductases, methyltrans- ferases, etc.) [1–4]. Technological applications of porphyrins and their derivatives include: catalysis [1,2,5–7], molecular photonic devices [6,8], medicine [1,2,6], artificial photosynthesis [9–11], sensitizers for dye-sensitized solar cells [12], and sensor devices [6,13]. In Nature, aerobic oxidation processes are carried out in a highly selective manner by mono- or dioxygenases under mild conditions [5,7]. Cytochrome P450, a well-known type of monooxygenase, pos- sesses an Fe-porphyrin core and can catalyze a wide variety of oxidation reactions: epoxidation, hydroxylation, dealkylation, dehydrogenation, and oxidation of amines, sulfides, alcohols and aldehydes [5,7]. This fact stimulated extensive studies of metallo- porphyrins, with a core structure closely resembling that of the iron porphyrin core of cytochrome P450, as effective catalysts for oxidation reactions [1,2,5,7]. Also, the rich and extensive absorp- tions (i.e., p–p / transitions) in porphyrins, which are essentially ‘the pigments of life’ [9], hold strong promise for an efficient use of the solar spectrum. Over the recent decades, porphyrins have attracted ever growing attention as light harvesting building blocks in the construction of molecular architectures [9–12]. The structural and electronic properties along with the binding ability of porphyrins can be easily and broadly tuned by replacing one or several pyrrole nitrogens with other elements [14–16]. Until recently, the effects of the pyrrole nitrogen replacement in porphyrins with phosphorus were investigated for just a few por- phyrins and their derivatives [17–29]. Thus, the study by Delaere and Nguyen [17] performed using the density functional theory (DFT) on the P-containing porphyrins with one or two pyrrole http://dx.doi.org/10.1016/j.chemphys.2016.02.010 0301-0104/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Tel.: +55 1633518062. E-mail address: aleksey73kuznets@gmail.com Chemical Physics 469-470 (2016) 38–48 Contents lists available at ScienceDirect Chemical Physics journal homepage: www.elsevier.com/locate/chemphys