Narrow Results

The synthesis and X-ray diffraction-based characterization of a texaphyrin-type non-aromatic expanded porphyrin, 13,18,22,27-tetraethyl-14,17,23,26-tetramethyl-20-p-nitrophenyl-3,10,28,29,30,31-hexaazahexacyclo[23.2.1.0^4,9.1^12,15.1^16,19.1^21,24]untriaconta-2, 4, 5, 7, 10,12,14,16,18,-20,22,24(30),25,27-tetradecaene (1), is reported. This Schiff base macrocycle was prepared in good yield via the 1:1 HCl-catalyzed condensation of a tetrapyrrole dialdehyde precursor, (di(5-formyl-4,4'-diethyl-3,3'-dimethyl-2,2'-bipyrrole)-p-nitrophenylmethine), with 1,2-phenylenediamine. Compound 1 was assigned as being a 26 π-electron non-aromatic benzannulene on the basis of both proton NMR and single-crystal X-ray diffraction analyses. The latter studies, in particular, revealed a non-planar macrocyclic structure co-crystallized with a molecule of water. By varying either the diamine used in the cyclization step and/or the substituent in the meso-position of the tetrapyrrolic precursor, a range of other systems analogous to 1 could be obtained. The resulting systems were found to present good stability both in the solid state and in solution.

Porphine is the parent compound of a family of biologically and chemically relevant compounds called porphyrins. The potential of these compounds is enormous and it would be advantageous to use the porphine (porphyrin) unit as a building block for the synthesis of diverse porphyrin complexes with a wide range of applications. However, despite first being synthesized over 70 years ago, porphine has not been utilized to its full extent due to low yield syntheses and poor solubility. Recent advances have now overcome many of these problems. The purpose of this review is to illustrate the advances made in porphine chemistry to illustrate the inherent potential of this simple compound.

Free base porphyrin in chloroform solution irradiated with focused laser beam, in an open Z-scan set-up, changed color from purple to green, which was associated with protonation of the porphyrin with protonic species from photodegradation of the solvent. Protonation is demonstrated as a simple means to improve the optical limiting performance of free base porphyrin nonlinear optical (NLO) materials.

Six monophenyltripyridylporphyrin derivatives were synthesized and characterized by spectroscopy in order to demonstrate their potential usefulness as photosensitizers for anticancer therapy purposes. Compounds 1 and 3–5 are amphiphilic, thus they may be suitable for transfer inside cells. Photochemical parameters such as fluorescence yield and singlet oxygen yield were determined. The former parameter does not exceed 10% which makes them unsuitable for photodynamic diagnosis (PDD). However, singlet oxygen yields are high and sufficient for these compounds to be considered as potential photodynamic therapy (PDT) photosensitizers.

Several families of herbicides, especially diphenyl ether (DPE) and pyrimidinedione, target the plant tetrapyrrole biosynthesis pathways and in particular one key enzyme, protoporphyrinogen IX oxidase (PPO). When plants are treated with DPE or pyrimidinedione, an accumulation of protoporphyrin IX, the first photosensitizer of this pathway, is observed in cytosol where it becomes very deleterious under light. Indeed these herbicides trigger plant death in two distinct ways: (i) inhibition of chlorophylls and heme syntheses and (ii) a huge accumulation of protoporphyrin IX in cytosol. Recently, a strategy based on plant transgenesis that induces deregulation of the tetrapyrrole pathway by up- or down-regulation of genes encoding enzymes, such as glutamyl-$t$RNA reductase, porphobilinogen deaminase and PPO, has been developed. Against all expectations, only transgenic crops overexpressing PPO showed resistance to DPE and pyrimidinedione. This herbicide resistance of transgenic crops leads to the hypothesis that the overall consumption of herbicides will be reduced as previously reported for glyphosate-resistant transgenic crops. In this review, after a rapid presentation of plant tetrapyrrole biosynthesis, we show how only PPO enzyme can be the target of DPE and how transgenic crops can be further resistant not only to herbicide but also to abiotic stress such as drought or chilling. Keeping in mind that this approach is mostly prohibited in Europe, we attempt to discuss it to interest the scientific community, from plant physiologists to chemists, who work on the interface of photosensitizer optimization and agriculture.

Several families of herbicides, especially diphenyl ether (DPE) and pyrimidinedione, target the plant tetrapyrrole biosynthesis pathways and in particular one key enzyme, protoporphyrinogen IX oxidase (PPO). When plants are treated with DPE or pyrimidinedione, an accumulation of protoporphyrin IX, the first photosensitizer of this pathway, is observed in cytosol where it becomes very deleterious under light. Indeed these herbicides trigger plant death in two distinct ways: (i) inhibition of chlorophylls and heme syntheses and (ii) a huge accumulation of protoporphyrin IX in cytosol. Recently, a strategy based on plant transgenesis that induces deregulation of the tetrapyrrole pathway by up- or down-regulation of genes encoding enzymes, such as glutamyl-tRNA reductase, porphobilinogen deaminase and PPO, has been developed. Against all expectations, only transgenic crops overexpressing PPO showed resistance to DPE and pyrimidinedione. This herbicide resistance of transgenic crops leads to the hypothesis that the overall consumption of herbicides will be reduced as previously reported for glyphosate-resistant transgenic crops. In this review, after a rapid presentation of plant tetrapyrrole biosynthesis, we show how only PPO enzyme can be the target of DPE and how transgenic crops can be further resistant not only to herbicide but also to abiotic stress such as drought or chilling. Keeping in mind that this approach is mostly prohibited in Europe, we attempt to discuss it to interest the scientific community, from plant physiologists to chemists, who work on the interface of photosensitizer optimization and agriculture.