Analysis of close proximity quenching of phosphorescent metalloporphyrin labels in oligonucleotide structures

Polymeric structure of a coproporphyrin I ruthenium(II) complex: a powder diffraction study

Porphyrin complexes of ruthenium are widely used as models for the heme protein system, for modelling naturally occurring iron-porphyrin systems and as catalysts in epoxidation reactions. The structural diversity of ruthenium complexes offers an opportunity to use them in the design of multifunctional supramolecular assemblies. Coproporphyrins and metallocoproporphyrins are used as sensors in bioassay and the potential use of derivatives as multiparametric sensors for oxygen and H⁺ is one of the main factors driving a growing interest in the synthesis of new porphyrin derivatives. In the coproporphyrin I Ru^II complex catena-poly[[carbonylruthenium(II)]-μ-2,7,12,17-tetrakis[2-(ethoxycarbonyl)ethyl]-3,8,13,18-tetramethylporphyrinato-κ⁵N,N',N'',N''':O], [Ru(C₄₄H₅₂N₄O₈)(CO)]_n, the Ru^II centre is coordinated by four N atoms in the basal plane, and by axial C (carbonyl ligand) and O (ethoxycarbonylethyl arm from a neighbouring complex) atoms. The complex adopts a distorted octahedral geometry. Self-assembly of the molecules during crystallization from a methylene chloride-ethanol (1:10 v/v) solution at room temperature gives one-dimensional polymeric chains.

Phototoxic effects of pyropheophorbide-a from chlorophyll-a on cervical cancer cells

Photodynamic therapy (PDT) is a promising modality in both the curative and palliative treatment against a variety of experimental and naturally occurring human cancers. At present, chlorophyll a derivatives are extensively used for the synthesis of photosensitizers (PSs) for PDT of tumors. In the present study, chlorophyll-a was extracted from the blue-green algae Spirulina platensis by refluxing with acetone. The extract was further acid treated to obtain methylpheophorbide-a (MPa), which was then refluxed in collidine and methylpyropheophorbide-a (Mppa) was obtained. After that, Mppa was converted to pyropheophorbide-a (Ppa) by treatment with 50% sulfuric acid. Finally, phototoxicity and dark toxicity of purified Ppa in two different cell lines, TC-1 and CaSki, were examined by MTT assay. The results suggest that Ppa is more toxic to TC-1 cell line than CaSki cell line. In vivo, the photosensitizing efficiency of Ppa was also higher than those of unloaded PS. These results indicate the potential of Ppa in PDT.

Phosphorescent sensing of carbon dioxide based on secondary inner-filter quenching

A study of different strategies to prepare phosphorescence-based sensors for gaseous CO(2) determination has been performed. It includes the characterization of different configurations tested, a discussion of the results obtained and possibilities for the future. The optical sensor for gaseous CO(2) is based on changes in the phosphorescence intensity of the platinum octaethylporphyrin (PtOEP) complex trapped both on oxygen-insensitive poly(vinylidene chloride-co-vinyl chloride) (PVCD) membranes and PVCD microparticles, due to the displacement of the alpha-naphtholphthalein acid-base equilibrium with CO(2) concentration. A secondary inner-filter mechanism was tested for the sensor and a full range linearized calibration was obtained by plotting (I(100)-I(0))/(I-I(0)) versus the inverse of the CO(2) concentration, where I(0) and I(100) are the detected luminescence intensities from a membrane exposed to 100% nitrogen and 100% CO(2), respectively, and I at a defined CO(2) concentration. The different configurations tested included the use of membranes containing luminophore and pH-sensitive dye placed on two opposite sides of a transparent support to prevent the observed degradation of the PtOEP complex in the presence of the tetraoctylammonium hydroxide (TOAOH) phase transfer agent, which produced better results regarding stability and sensitivity. The CO(2) gas sensor based on PtOEP homogeneous membranes presented better properties in terms of response time and sensitivity than that based on PtOEP microparticles. With a detection limit of 0.02%, the response time (10-90% maximum signal) is 9 s and the recovery time (90-10%) is 115 s. The lifetime of the membranes for CO(2) sensing preserved in a 94% RH atmosphere and dark conditions is longer than at least 4 months.