Fullerene-pyropheophorbide a complexes as sensitizer for photodynamic therapy: uptake and photo-induced cytotoxicity on Jurkat cells

The main challenge in searching for new photosensitizers is to improve their specificity for target cells to avoid toxicity towards normal cells. New modular drug delivery systems were proposed consisting of a multiplying unit with the property of carrying several drug moieties and an addressing unity with high selectivity for target cells. Following this concept, two new fullerene-bis-pyropheophorbide a derivatives were synthesized: a mono-(FP1) and a hexa-adduct (FHP1). The photophysical characterization of the compounds revealed significantly different parameters related to the number of addends at the fullerene core. In this study, the derivatives were tested with regard to their intracellular uptake and photosensitizing activity towards human leukemia T-lymphocytes (Jurkat cells) in comparison with the free sensitizer, pyropheophorbide a. The C(60)-hexa-adduct FHP1 resulted to have a significative phototoxic activity (58% dead cell, after a dose of 400 mJ/cm(2), 688 nm) while the mono-adduct FP1 had a very low phototoxicity and only at higher light doses. The photosensitizing activity of the fullerene hexa-adduct, FHP1, resulted to be lower than that of pyropheophorbide a. The lesser intracellular concentration reached by the C(60)-hexa-adduct FHP1 is probably the reason for its lower phototoxicity with respect to pyropheophorbide a.     

Microcalorimetric determination of the enthalpies of solution of oxirane in benzene,toluene, p-xylene and 2,2,4-trimethylpentane at 298.15K and 101.3k

Using a differential microcalorimeter, the enthalpies of solution, ΔH_s (298.15K, 101.3 kPa), of oxirane in benzene, toluene, p-xylene and 2,2,4-trimethylpentane are determined in the mole fraction range 0.00005<x <0.001 of the solute. ΔH_s exhibits a strong dependence on x in aromatic solvents, becoming more exothermic by 10 to 15 $\text{kJ}\text{mol}$ when x falls below 0.0005. This effect is attributed to a short-ranged structure formation of the solvent induced by the dissolved gas molecules. No dependence of ΔH_s on x is found in 2,2,4-trimethylpentane.     

Transition metal complexes of cyclic and open ozone and thiozone

Cyclic ozone (O3) has not been isolated so far, despite its computed kinetic persistence. Possibilities of "trapping" this molecule (or the valence-isoelectronic cyclic thiozone, S3) in transition metal complexes are investigated in this paper. Candidates were constructed, first using the 18-electron rule as a guide and then optimizing the structures with the DFT-B3LYP method. A variety of structures result: oxo-peroxo species, di-sigma- and pi-bonded open ozone complexes, some eta1 and eta2 cyclic ozone complexes, and a few bona fide eta3 cyclic O3 and S3 complexes. MLn fragments suitable for complex formation would need to contain very strong pi-acceptor ligands. Nitrosyl ligands were chosen to minimize an energy mismatch between the O3 donor orbitals and the MLn acceptor orbitals. On this basis, the existence of the complexes [S3W(NO)3]3+, [O3M(NO)3]3+ (M = Cr, Mo, W, Fe, Ru, Os), and [S3W(NO)2(CO)]2+ containing cyclic O3 and S3 is suggested. In another approach, facing up to the oxidizing power of O3, potential systems were built from late transition metals in high oxidation states, and also d0 early transition metal centers.     

Facile access to monodisperse ultralarge rings

A facile access to monodisperse ultralarge rings counting 126, 174, and 294 ring atoms is described. It follows a reaction sequence that is well suited for the preparation of [2]catenanes but altered just in the sequence of the two steps cyclization and carbonate formation. The carbonate acts as a covalent template that is easily formed and later cleaved. The obtained monocyclic products are constitutional isomers of the catenanes.     

Stereoselective synthesis of (1R,2S)-2-amino-1,3-diols from (R)-cyanohydrins

Vinyl substituted (1R,2S)-amino alcohols 5 were obtained by addition of vinyl magnesium bromide to the corresponding cyanohydrin O-trimethylsilyl ethers (R)-2. The O- and N-protected vinyl amino alcohols 6 were ozonized at −78°C in methanol yielding (1R,2S)-2-amino-1,3-diols7 in high enantiomeric and diastereomeric excesses. For purification, compounds 7 in some cases were acetylated to give the derivatives (1R,2S)-8. Racemic 6a was converted by oxidative ozonolysis at −78°C in methanolic NaOH solution to the corresponding methyl N-acetyl-β-hydroxy propanoate 9a. The configuration of (1R,2S)-8a was confirmed by x-ray crystallographic analysis.     

Annulated dinuclear metal-free and Zn(II) phthalocyanines: photophysical studies and quantum mechanical calculations

The results of steady-state and time-resolved absorption and fluorescence experiments as well as quantum mechanical density functional theory (DFT) calculations of metal-free and Zn(II) mononuclear and dinuclear (sharing a common benzene ring) phthalocyanines are presented. A detailed comparison between measured and calculated absorption spectra of all compounds is done, showing a good agreement between theory and experiment. The NH tautomerization for phthalocyanines with an extended pi-electron system was shown for the first time at room temperature. The photophysical properties of all possible NH tautomers of metal-free dinuclear Pc have been fully characterized. In the first tautomer, Pc(parallel), both pairs of hydrogen atoms are parallel to the connection line of two Pc units. The maximum of the lowest-energy Q absorption band, lambda abs, in Pc(parallel) is located at 832 nm, whereas the spectral position of the fluorescence maximum lies at lambdafl=837 nm. The second NH tautomer, Pc(perpendicular) (lambdaabs=853 nm, lambdafl=860 nm), presents the two pairs of hydrogen atoms perpendicularly orientated to the covalent axis, and the third one, Pc(mix) (lambdaabs=864 nm, lambdafl=872 nm), contributing in a minor extend to the absorption and fluorescence spectra of the metal-free dinuclear phthalocyanine, has one perpendicular and one parallel pair of hydrogen atoms. Obviously, only one configuration exists in the case of the Zn(II)-containing dinuclear phthalocyanine (lambdaabs=845 nm, lambdafl=852 nm).     

Intracellular uptake and phototoxicity of 3(1),3(2)-didehydrophytochlorin-fullerene hexaadducts

C(60)-fullerene derivatives are potential building blocks in modular carrier systems for selective tumor targeting. In [5:1] fullerene hexakis adducts, one position can be occupied by an addressing unit (e.g. monoclonal antibody) while the other five positions are suitable for dendrimers or spacers loaded with several drug moieties. This article reports intracellular uptake and phototoxicity of three fullerene hexakis adducts coupled with a different number of photosensitizers: a bis(3(1),3(2)-didehydrophytochlorin)-fullerene [5:1]-hexaadduct (FHP1), a fullerene [5:1]-hexaadduct with six 3(1),3(2)-didehydrophytochlorin groups (FHP6) and a fullerene [6:0]-hexaadduct that carries 12 3(1),3(2)-didehydrophytochlorin units (FHP12). The most promising complex, the hexa-3(1),3(2)-didehydrophytochlorin fullerene hexaadduct FHP6, was also compared with its fullerene-free analogous derivative P6. It was found that the extent of intracellular uptake is influenced by both nanomolecular size and asymmetry (amphiphilicity) of the fullerene complexes. The degree and mechanism of phototoxicity was found to depend on intracellular concentrations and singlet oxygen quantum yields.     

On the origin of the so-called nucleation loop during electropolymerization of conducting polymers

During the potentiodynamic preparation of conducting polymers, cyclic voltammograms of many pi-conjugated monomers and oligomers often show a marked crossing or loop effect. The so-called "nucleation loop" of the first cycle has been ascribed to the nucleation process requiring an activation energy provided by an overpotential. This paper presents cyclic voltammograms of pi-systems with trace crossing as well as loop effects that suggest that the homogeneous formation of oligomeric redoxactive follow-up products from the starting species is responsible for this occurrence. As the investigated species are typical starting components of resulting oligomers or polymers, all these findings are evidence that similar mechanisms also hold for the formation of many other classical polymers with a "nucleation loop" like polypyrrole, and that the true reason for the nucleation loop is the comproportionation reaction between an oligomeric follow-up product and the starting "monomer".     

Short and efficient synthesis of cryptophycin unit A

[reaction: see text] Two short synthetic approaches toward cryptophycin unit A comprise a catalytic asymmetric dihydroxylation as the sole source of chirality, while all further stereogenic centers are introduced under substrate control. The key step of the first route is a vinylogous Mukaiyama aldol addition, which introduces the alpha,beta-unsaturated ester moiety with defined configuration at the delta-carbon atom. Likewise, allylation with allyltributylstannane diastereoselectively gives the homoallylic alcohol that can be converted by a metathesis reaction to a unit A precursor.     

Ladders,rings and cubes as structural motifs in three new zinc(II) azide complexes: Synthesis,spectral and structural characterization

Three new zinc(II) azide complexes, namely {[Zn₂(N₃)₄(py-tetrazole)₂](py-tetrazole)}_n (1), {[Zn₂(N₃)₄(3-OHpy)] · 2H₂O}_n (2) and [Zn(N₃)₂(pym)]_n (3), where py-tetrazole = tetrazolo[1,5-a]pyridine, 3-OHpy = 3-hydroxypyridine and pym = pyrimidine, have been synthesized by the hydrothermal methods and structurally characterized. The ligand py-tetrazole was obtained through the interaction of 2-chloropyridine with the azide ion under hydrothermal condition. The structure of 1 consists of a ladder-like arrangement of 1D double chain zinc(II) azide. In the coordination chain, each zinc atom binds di-EO azide bridges connecting another zinc atom in opposite chain, and two EO bridges, one on each side, and the fifth position is occupied by a N atom of py-tetrazole ligand. The structure of 2 features 2D sheets composed of tetranuclear zinc(II) ring and octanuclear zinc(II) ring interconnected by EO azide bridges. The 2D carrying into 3D supramolecular network by the help of several hydrogen bonding interactions. The 3-OHpy molecule acts in the tautomeric keto-form as O,O-bidentate bridging ligand. Complex 3 features distorted octahedral geometry around each zinc center, N,N′-bidentate pyrimidine ligand and EE azido bridges leading to 3D network structure. The IR spectra are measured and discussed. Complex 2 only exhibits photoluminescence properties whereas the other two complexes do not luminesce at room temperature.