Narrow Results

The synthesis and characterization of novel phthalocyanines containing o-carborane groups are described. These new tetrasubstituted phthalocyanines are of interest for the use in cancer therapy. The activities of the carboranyl substituted phthalocyanines were evaluated by the photooxidation of (S)-(−)-citronellol to give a high oxygen consumption comparable to the photosensitizers tetrasulfophthalocyanine zinc complexes.

The importance of singlet oxygen mechanism in photooxidation of phthalocyanine chromophore has been studied for promising singlet oxygen sensitizers: metal-free tetra-tert-butyl phthalocyanine and its Zn, Mg or Al complexes. It has been found that involvement of singlet oxygen in phthalocyanine photodegradation is dependent on the presence and character of the central metal atom, being the most prominent for the metal-free compound and almost negligible for the Al complex. The interaction of dioxygen with metal centers results in a sharp increase of phthalocyanine photooxidation rate.

The synthesis of three novel unsymmetrical free base, zinc(II) phthalocyanine derivatives obtained from 3,6-di-(thiophen-3-yl)phthalonitrile and 3,6-didecylphthalonitrile are described. The synthesis of novel 3,6-substituted phthalonitriles bearing heteroaromatic derivatives were achieved through Suzuki-coupling reaction by treatment of 3,6-di(trifluoromethanesulfonyloxy)phthalonitriles and heteroaromatic boronic acids. Two of the newly synthesized complexes showed a high efficiency against a model biological substrate, such as N-acetyl-L-tryptophanamide NATA, and shows a high singlet oxygen quantum yield.

μ-(dihydroxo)dipalladium(II) complex with N²¹, N²²-etheno bridged tetraphenylporphyrin ligand was employed in the catalytic photooxidation of phenol derivative in aerated homogeneous solution with visible light irradiation. The Pd complex promoted the degradation of p-tert-butylphenol as well as Cu phthalocyanine under basic conditions and it worked as a photosensitizer even in neutral conditions in contrast with Cu phthalocyanine. Some phenol derivatives afforded corresponding quinones selectively in this photooxidation. The present Pd complex coordinated by the bidentate porphyrin ligand showed higher photosensitizing ability than tetraphenylporphyrin free-base and ordinary tetradentate tetraphenylporphyrin palladium(II) complex for photooxidation of 2,6-di-tert-butylphenol. This bidentate Pd complex showed higher light durability even under the conditions where photodegradation of porphyrin free-base and tetradentate Pd porphyrin were observed by extensive irradiation.

The photodegradation of a series of water-soluble Zn(II) and Al(III) phthalocyanines has been studied in aerobic aqueous solutions. The photobleaching quantum yields of zinc phthalocyanine derivatives range from 2.2 × 10^-4 for octacarboxy- to 1.5 × 10^-5 for ZnPc, bearing 16 positively charged groups on periphery. Their aluminum counterparts are more photostable and photobleach with quantum yields in the narrow range (0.75 ÷ 2 × 10^-6). The pH dependences of the photobleaching quantum yields for aluminum phthalocyanines show enhanced photodegradation for molecules with deprotonated axial H₂O ligand. Some aspects of the mechanism of dyes photodegradation were studied and discussed. It was found that contribution to photooxidation of type II pathways depends upon a particular dye structure. Thus, no contribution of singlet oxygen to the photooxidation of cationic phthalocyanines has been found, even though singlet oxygen is involved in the photodegradation of negatively charged phthalocyanines.

A variety of aromatic and aliphatic aldehydes were oxidized to the corresponding carboxylic acids in the presence of platinum porphyrin, sunlight and air in acetonitrile solvent under mild conditions. Nitrobenzaldehydes were found to be very efficient ¹O₂ scavengers that quench the formation of acids from any aldehyde in the presence of free-base porphyrin sensitizers. However, nitrobenzaldehydes were converted to the corresponding acids in the presence of platinum porphyrins. The platinum porphyrins are very good and efficient catalysts for a wide range of applications in the aerobic conversion of aldehydes to acids.

Metallophthalocyanines form a very important class of commercial dyes and have achieved significant success in a variety of applications, in which their photostability is of fundamental importance. On this ground, considerable data on phthalocyanine photobleaching were published over recent years. We do not intend to give exhaustive compilation of the photobleaching quantum yields, which are known for wide circle of phthalocyanines in different solvents. This review begins by discussing pertinent background information about processes following phthalocyanine excitation. Then using selected examples of the recent literature, including authors' works, we survey a variety of photobleaching effects from the fundamental origins to specific for phthalocyanine chromophore. Finally, the mechanisms of phthalocyanine oxidative photobleaching are discussed.

Although tungsten porphyrins are known as mimicking models in biology, only a few papers about its chemical properties have been reported, the rarity of studies being attributed to the difficulties encountered in their synthesis due to their low stability. In this paper 5,10,15,20-tetra-p-phenyl-porphyrin tungsten(VI) chlorine (TPPWCl₄) was studied, this metallo-porphyrin characterized by different analytical techniques: UV-vis, FTIR, ESR, mass spectrometry, including photophysical determination of its singlet oxygen quantum yield, too. Its photodegradation reaction with the mechanism and species involved into this destruction reaction processes is discussed, too. Also, in order to maintain its photostability, TPPWCl₄ has been incorporated into solid substrates, such as ZnO and TiO₂, and these composites were subsequently tested in the photooxidation reaction of isoamylenes (2-methyl-2-butene and 2-methyl-1-butene mixture).

A series of chiral A₄, A₂B₂, and AB₃ porphyrins bearing proline moieties at the meso-phenyl group has been synthesized. Photostability studies revealed that the number of L-proline units and their position on meso-phenyl rings strongly influence the decomposition rate of the catalyst. 5,10,15-Tris(mesityl)-20-(3-prolinanilidylphenyl)-21,23H-porphyrin is the most stable while porphyrin bearing four 3-prolinanilidylphenyl substituents completely decomposes in CHCl₃ within 3 h. Singlet oxygen quantum yields of the conjugates were determined by measuring the peak areas of the NIR emission of ¹O₂ (1280 nm) generated by these compounds and compared to that generated by the reference standard TPP. Selected porphyrins were tested as catalysts in the photooxidation of carbonyl compounds at the α-position.

Copper(I) complexes coordinated with a N²¹,N²²-etheno bridged porphyrin ligand were synthesized as a unique coordination structure. The copper porphyrin complexes promoted photooxidations of a phenol derivative in organic solution under aerobic condition with visible photoirradiation. The complexes could be immobilized on silica gel as a support and the obtained copper porphyrin composites showed high ability as photocatalysts for heterogeneous photooxidation of a phenol derivative in aqueous solution. The composites could be easily recovered and re-used after the reaction. The structural study found that the active species contributing to the photooxidation reaction was the di(μ-hydroxo)dicopper(II) complex of N²¹,N²²-etheno bridged porphyrin generated by oxidation of corresponding copper(I) complex in the reaction system under homogeneous and heterogeneous condition.

The photosynthetic characteristics of four transgenic rice lines overexpressing maize phosphoenolpyruvate carboxylase (PEPC; line PC), pyruvate, orthophosphate dikinase (PPDK; line PK), PEPC + PPDK (line CK), and NADP-malic enzyme (NADP-ME; line ME) were investigated using outdoor-grown plants. Relative to untransformed wild-type (WT) rice, PC transgenic rice exhibited high PEPC activity (a 25-fold increase) and enhanced activity of carbonic anhydrase (more than a twofold increase). The PC transgenic plants also showed a higher CO₂ uptake rate and carboxylation efficiency, and slightly reduced CO₂ compensation point. Furthermore, PC transgenic rice produced 22% more grains than WT plants. Labeling with ¹⁴CO₂ for 20 s showed more ¹⁴C distributed to C₄ primary photosynthate aspartate and feeding with exogenous C₄ primary products such as oxaloacetate (OAA), malate (MA), or phosphoenolpyruvate (PEP) showed an increment of photosynthetic rate in PC transgenic rice, suggesting that a limited C₄ cycle exists in leaves of transgenic rice.

Introduction of the maize PEPC gene could activate or induce activities of the key enzymes scavenging active oxygen, such as superoxide dismutase (SOD) and peroxidase (POD).

The line JAAS45 manifested higher photosynthetic rates and photochemical efficiency of PS II (F_v/F_m). The value of δ¹³C in PC transgenic rice was similar to that in untransformed rice, demonstrating that transgenic rice is still a C₃ plant.

How can we redesign C₄ rice from the limited C₄ features of photosynthesis reached currently? In future work, introduction of the PEPC gene from a CAM plant into C₄-enzyme transgenic rice could carry out higher photosynthesis day and night. Simultaneously, the enhancement of endogenous ATP in PK transgenic rice through genetic engineering would increase its operation of the C₄ cycle. Most importantly, recent advanced techniques such as laser capture microdissection enable us to study the mechanisms of cellular differentiation, for example, of bundle sheath cells. From the above suggestions, these techniques might shed light on a new green revolution in rice breeding.