Dithiaporphyrin derivatives as photosensitizers in membranes and cells

We synthesized a series of analogues of 5,20-diphenyl-10,15-bis(4-carboxylatomethoxy)phenyl-21,23-dithiaporphyrin (I) as potential photosensitizers for photodynamic therapy (PDT). The photosensitizers differ in the length of the side chains that bind the carboxyl to the phenol at positions 10 and 15 of the thiaporphyrin. The spectroscopic, photophysical, and biophysical properties of these photosensitizers are reported. The structural changes have almost no effect on the excitation/emission spectra with respect to I's spectra or on singlet oxygen generation in MeOH. All of the photosensitizers have a very high, close to 1.00, singlet oxygen quantum yield in MeOH. On the contrary, singlet oxygen generation in liposomes was considerably affected by the structural change in the photosensitizers. The photosensitizers possessing short side chains (one and three carbons) showed high quantum yields of around 0.7, whereas the photosensitizers possessing longer side chains showed smaller quantum yield, down to 0.14 for compound X (possessing side-chain length of 10 carbons), all at 1 microM. Moreover a self-quenching process of singlet oxygen was observed, and the quantum yield decreased as the photosensitizer's concentration increased. We measured the binding constant of I to liposomes and found Kb = 23.3 +/- 1.6 (mg/mL)-1. All the other photosensitizers with longer side chains exhibited very slow binding to liposomes, which prevented us from assessing their Kb's. We carried out fluorescence resonance energy transfer (FRET) measurements to determine the relative depth in which each photosensitizer is intercalated in the liposome bilayer. We found that the longer the side chain the deeper the photosensitizer core is embedded in the bilayer. This finding suggests that the photosensitizers are bound to the bilayer with their acid ends close to the aqueous medium interface and their core inside the bilayer. We performed PDT with the dithiaporphyrins on U937 cells and R3230AC cells. We found that the dark toxicity of the photosensitizers with the longer side chain (X, VI, V) is significantly higher than the dark toxicity of sensitizers with shorter side chains (I, III, IV). Phototoxicity measurements showed the opposite direction; the photosensitizers with shorter side chains were found to be more phototoxic than those with longer side chains. These differences are attributed to the relationship between diffusion and endocytosis in each photosensitizer, which determines the location of the photosensitizer in the cell and hence its phototoxicity.     

Effect of the immobilisation of DNA aptamers on the detection of thrombin by means of surface plasmon resonance

We report a multichannel surface plasmon resonance (SPR) sensor for detection of thrombin via DNA aptamers immobilized on the SPR sensor surface. A detailed investigation of the effect of the immobilisation method on the interaction between thrombin and DNA aptamers is presented. Three basic approaches to the immobilisation of aptamers on the surface of the SPR sensor are examined: (i) immobilisation based on chemisorption of aptamers modified with SH groups, (ii) immobilisation of biotin-tagged aptamers via previously immobilized avidin, neutravidin or streptavidin molecular linkers, and (iii) immobilisation employing dendrimers as a support layer for subsequent immobilisation of aptamers. A level of nonspecific binding of thrombin to immobilized human serum albumin (HSA) for each of the immobilisation methods is determined. Immobilisation of aptamers by means of the streptavidin–biotin system yields the best results both in terms of sensor specificity and sensitivity.     

Noncovalent triblock copolymers based on a coiled-coil peptide motif

The formation of a noncovalent triblock copolymer based on a coiled-coil peptide motif is demonstrated in solution. A specific peptide pair (E and K) able to assemble into heterocoiled coils was chosen as the middle block of the polymer and conjugated to poly(ethylene glycol) (PEG) and polystyrene (PS) as the outer blocks. Mixing equimolar amounts of the polymer-peptide block copolymers PS-E and K-PEG resulted in the formation of coiled-coil complexes between the peptides and subsequently in the formation of the amphiphilic triblock copolymer PS-E/K-PEG. Aqueous self-assembly of the separate peptides (E and K), the block copolymers (PS-E and K-PEG), and equimolar mixtures thereof was studied by circular dichroism, dynamic light scattering, and cryogenic transmission electron microscopy. It was found that the noncovalent PS-E/K-PEG copolymer assembled into rodlike micelles, while in all other cases, spherical micelles were observed. Temperature-dependent studies revealed the reversible nature of the coiled-coil complex and the influence of this on the morphology of the aggregate. A possible mechanism for these transitions based on the interfacial free energy and the free energy of the hydrophobic blocks is discussed. The self-assembly of the polymer-peptide conjugates is compared to that of polystyrene-b-poly(ethylene glycol), emphasizing the importance of the coiled-coil peptide block in determining micellar structure and dynamic behavior.     

RGDS‐ and SIKVAVS‐Modified Superporous Poly(2‐hydroxyethyl methacrylate) Scaffolds for Tissue Engineering Applications

Three‐dimensional hydrogel supports for mesenchymal and neural stem cells (NSCs) are promising materials for tissue engineering applications such as spinal cord repair. This study involves the preparation and characterization of superporous scaffolds based on a copolymer of 2‐hydroxyethyl and 2‐aminoethyl methacrylate (HEMA and AEMA) crosslinked with ethylene dimethacrylate. Ammonium oxalate is chosen as a suitable porogen because it consists of needle‐like crystals, allowing their parallel arrangement in the polymerization mold. The amino group of AEMA is used to immobilize RGDS and SIKVAVS peptide sequences with an N‐γ‐maleimidobutyryloxy succinimide ester linker. The amount of the peptide on the scaffold is determined using ¹²⁵I radiolabeled SIKVAVS. Both RGDS‐ and SIKVAVS‐modified poly(2‐hydroxyethyl methacrylate) scaffolds serve as supports for culturing human mesenchymal stem cells (MSCs) and human fetal NSCs. The RGDS sequence is found to be better for MSC and NSC proliferation and growth than SIKVAVS.

     

Voltametric,Amperometric, and Chronopotentiometric Determination of Submicromolar Concentrations of Carboxin

New procedures for the determination of pesticide carboxin were developed using differential pulse voltammetry, HPLC with amperometric detection and chronopotentiometry at carbon paste electrode and reticulated vitreous carbon electrode, respectively. Developed procedures based on electrochemical oxidation of carboxin were successfully applied on the determination of carboxin in the model samples of drinking and river water. Limits of detection in samples of river water were in 10^?7 mol L^?1 concentration range for all procedures and electrodes used. All developed procedures proved to be sensitive, accurate and, due to the resistance of the electrode to the passivation, also simple to handle.     

Second generation of primaquine ureas and bis-ureas as potential antimycobacterial agents

Molecular Diversity - Here, we describe design and synthesis of twelve novel compounds bearing primaquine motif and hydroxy- or halogenamine linked by an urea or bis-urea spacer. Preparation of...     

A Reduced SNARE Model for Membrane Fusion

Let's get together : A minimal model system was developed to mimic the SNARE‐protein‐mediated fusion of biological membranes (see picture). Fusion between two populations of liposomes is controlled by a pair of complementary lipidated oligopeptides that form noncovalent coiled‐coil complexes and thereby force the membranes into close proximity to promote fusion. The model system displays the key characteristics of in vivo fusion events.

     

Existence of solutions to a phase transition model with microscopic movements

We prove the existence of weak solutions for a 3D phase change model introduced by Michel Frémond in (Non‐smooth Thermomechanics. Springer: Berlin, 2002) showing, via a priori estimates, the weak sequential stability property in the sense already used by the first author in (Comput. Math. Appl. 2007; 53 :461–490). The result follows by passing to the limit in an approximate problem obtained adding a superlinear part (in terms of the gradient of the temperature) in the heat flux law. We first prove well posedness for this last problem and then—using proper a priori estimates—we pass to the limit showing that the total energy is conserved during the evolution process and proving the non‐negativity of the entropy production rate in a suitable sense. Finally, these weak solutions turn out to be the classical solution to the original Frémond's model provided all quantities in question are smooth enough. Copyright © 2008 John Wiley & Sons, Ltd.     

Annual variation in photo acclimation and photoprotection of the photobiont in the foliose lichen Xanthoria parietina

Seasonal variation in maximal photochemical quantum yield (F(V)/F(M)) of photosystem II (PS II), light adapted quantum yield (Phi(II)) of PS II, non-photochemical quenching (NPQ), contents of chlorophylls, and xanthophyll cycle pigments (VAZ) was studied in Xanthoria parietina repeatedly sampled in one location in S Norway during one year. The seasonal course in the susceptibility to photoinhibition was evaluated as high light-induced changes (1,800 micromol photons m(-2) s(-1) for 24h) in F(V)/F(M), Phi(II), and NPQ, measured as the ability to recover after 2 and 20 h at low light in control thalli with a natural cortical parietin screen, and in thalli from which parietin had been removed prior to high light exposures. F(V)/F(M), Phi(II), chlorophyll content, and the conversion state of VAZ (DEPS) reached minimum in spring. At the same time, yearly maxima of VAZ content and NPQ were recorded. Thereafter, F(V)/F(M), Phi(II), and chlorophyll content increased gradually, reaching maximum values in late autumn. DEPS peaked already in summer. Similarly, VAZ and NPQ decreased from early summer until winter. All data show that the X. parietina photobiont acclimates to seasonal changes in solar radiation, consistent with the lichen's preference for well-lit habitats. However, a comparison with a study of seasonal acclimation in the X. parietina mycobiont shows that in order to understand the seasonal photobiont acclimation, one has to consider the seasonal variation in internal screening caused by the fungal regulation of the PAR-absorbing parietin. A joint effort of both bionts seems to be required to avoid serious photoinhibition.