Porphyrin–quinone compounds as synthetic models of the reaction centre in photosynthesis

Abstract

Working in the weak-field approximation, we study the scattering of quantum fields from a gravitational source. For definiteness, we consider the electromagnetic radiation field as well as a massive scalar field, both propagating in a slightly curved spacetime and employ the first-order Born approximation to deduce the scattering cross-sections of the process. We find that the (unpolarized) cross-section for the electromagnetic field coincides (at the tree level) with the classical value, predicted by general relativity; also our results fairly agree with those obtained by other authors in some previous works. On the other hand, our analysis of the massive scalar field leads to results which are quite different when compared with those presented, e.g., in the papers by Golowich et al (1990 Am. J. Phys. 58 688) and by Uno et al (1996 Phys. Lett . A 223 137). Actually, we find that the quantum behavior deviates from its classical counterpart, showing an enhancement in the cross-section as the massive field approaches the non-relativistic regime. We critically discuss and compare our results and those of the above references, attempting to give a possible physical justification of such a puzzling issue in terms of quantum non-locality.

Synthesis of Zn-, Mn-, and Fe-Containing Mono- and Heterometallated Ethanediyl-Bridged Porphyrin Dimers

“…The origin of the more efficient fluorescence quenching of Mn dimers 1 and 3 compared to that of Fe dimers 2 and 4 may be a result of the differences in solvation modes and ratio of anti/non-anti conformational population due to the flexibility of the covalent ethanediyl bridge, since the DG values are essentially the same for both metal complexes [1k]. An appearance of weaker emission of the monometallated dimers 3 and 4 in comparison with that of the bimetallic dimers 1 and 2 is possibly due to the same reason, because this effect is in contrast to the general tendency of enhanced electron-transfer efficiency and, consequently, fluorescence quenching for [ Zn(porphyrinato)]-containing donor-acceptor systems due to the larger À DG values [23].…”

“…The products were recrystallized from CH 2 Cl 2 / MeOH and dried in vacuo: 55 mg (46%) of 2 and 30 mg (25%) of 14. 23 ,kN 24 }i-ron(1 ) Chloride (4). As described for 3, 2 (12.3 mg, 0.01 mmol) in CHCl 3 (30 ml) was treated with 2m HCl (50 ml).…”

Probing Ground‐state Hole Transfer Between Equivalent, Electrochemically Inaccessible States in Multiporphyrin Arrays Using Time‐resolved Optical Spectroscopy

“…The filtrate was concentrated ($2 mL) under reduced pressure. The resulting dipyrromethane-dicarbinol 3-diol was diluted with CH 2 Cl 2 (total volume of 100 mL), and treated with dipyrromethane 4 (264 mg, 1.00 mmol) and Yb(OTf) 3 (198 mg, 0.320 mmol) at room temperature for 15 min. A sample of DDQ (681 mg, 3.00 mmol) was added in one portion, and the resulting mixture was stirred for 1 h. Triethylamine (0.8 mL) was added.…”

“…Key to functionality in such systems is the production of a long-lived charge-separated state that allows the associated chemical potential to be captured. Inspired by the general design of natural photosynthetic reaction centers, a widely used approach has been to slow wasteful charge recombination by using sequential steps to increase hole-electron spatial separation within multicomponent architectures, including tetrapyrrole-based triads and larger arrays (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). For example, in a generic triad of covalently linked redox-active pigments denoted ABC, photoexcitation of B and subsequent excited-state electron transfer to C is followed by a hole shift to A in the sequence AB*C fi AB + C ) fi A + BC ) .…”

A Comparative Study of Catalytic Activity of Fe, Mn and Cu Porphyrins Immobilized on Mesoporous MCM-41 in Oxidation of Sulfides

“…[4][5][6][7][8] Metalloporphyrins have been investigated extensively for biomimetic oxidation of organic compounds as models of cytochrome P450s due to their innate properties, and also because of existence in many natural and fundamental products. [9][10][11][12] These metallo-complexes are able to catalyze selective oxidation processes with a variety of oxygen donors. [13][14][15] Unfortunately, metalloporphyrins as homogeneous catalysts encountered with some drawbacks, i.e, they may easily be destroyed during the reaction and has little stability toward oxidative degradation and they cannot be easily recovered after the reaction.…”