Comparative Photophysical Study of Disulfonated Aluminum Phthalocyanine in Unilamellar Vesicles and Leukemic K562 Cells

Abstract— The photophysical properties of cis -disulfonated aluminum phthalocyanine (AlPcS₂) in unilamellar vesicles (liposomes) of DL-a-dipalmitoyl-phosphatidylcholine have been measured. Both the fluorescence and triplet quantum yields decreased with increasing sensitizer concentration. The time-resolved fluorescence decays, analyzed by both the sum of exponentials and decay time distribution analyses, are compared with those reported for AlPcS₂ in leukemic K562 cells. Information on the pho-todynamic transport and localization mechanism has been obtained by drawing correlations between the two systems, indicating active transport of the phthalocyanine into tumor cells involving lysosomal accumulation.     

DEUSS: a perdeuterated poly(oxyethylene)-based resin for improving HRMAS NMR studies of solid-supported molecules

A novel resin called DEUSS (perdeuterated poly(oxyethylene)-based solid support) has been prepared by anionic polymerization of deuterated [D4]ethylene oxide, followed by cross-linking with deuterated epichlorohydrin. DEUSS can be suspended in a wide range of solvents including organic and aqueous solutions, in which it displays a high swelling capacity. As measured by proton HRMAS of the swollen polymer, the signal intensity of the oxyethylene protons is reduced by a factor of 110 relative to the corresponding nondeuterated poly(oxyethylene)poly(oxypropylene) (POEPOP) resin, thus facilitating detailed HRMAS NMR studies of covalently linked molecules. This 1H NMR invisible matrix was used for the solid-phase synthesis of peptides, oligoureas, and a series of amides as well as their characterization by HRMAS NMR spectroscopy. On-bead NMR spectra of high quality and with resolution comparable to that of liquid samples were obtained and readily interpreted. The complete absence of the parasite resin signals will be of great advantage, for example, for the optimization of multistep solid-phase stereoselective reactions, and for the conformational study of resin-bound molecules in a large variety of solvents.     

Solvating,manipulating, damaging,and repairing DNA in a computer

This work highlights four different topics in modeling of DNA: (i) the importance of water and ions together with the structure and function of DNA; the hydration structure around the ions appears to be the determining factor in the ion coordination to DNA, as demonstrated in the results of our MD simulations; (ii) how MD simulations can be used to simulate single molecule manipulation experiments as a complement to reveal the structural dynamics of the studied biomolecules; (iii) how damaged DNA can be studied in computer simulations; and (iv) how repair of damaged DNA can be studied theoretically. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Element neighbourhoods in twofold triple systems

The method of differences is used to establish that every 2-regular multigraph onv– 10,2 (mod 3) points occurs as the neighbourhood graph of an element in a twofold triple system of orderv, with two exceptions: C₂C₃and C₃C₃.Dedicated to Professor Hanfried Lenz on the occasion of his seventieth birthday     

Unramified forcing preserving the law of double negation

Shoenfield's unramified version of Cohen's forcing is defined in two stages: one which does not preserve double negation and the other which modifies the former so as to preserve double negation. Here we express the unramified forcing, which preserves double negation, in a single stage. Surprisingly enough, the corresponding definition of forcing for equality acquires a rather simple form. In [2] forcing ∥- is expressed in terms of strong forcing \( \Vdash * \) viap∥-Q iffp \( \Vdash * \) ¬ ¬Q for every formulaQ ofZF set theory and every elementp of a partially ordered set (P, ≦). In its turn,p \( \Vdash * \) Q is defined by the following five clauses: (1) $$p \Vdash * a \in biff(\exists c)(\exists q \geqq p)((c,q) \in b \wedge p \Vdash * a = c)$$ (2) $$\begin{gathered} p \Vdash * a \ne biff(\exists c)(\exists q \geqq p)(((c,q) \in a \wedge p \Vdash * c \notin b) \hfill \\ ((c,q) \in b \wedge p \Vdash * c \notin a)) \hfill \\ \end{gathered} $$ (3) $$p \Vdash * \neg Qiff(\forall q)(q \leqq p \to \neg (q \Vdash * Q))$$ (4) $$p \Vdash * (Q \vee S)iff(p \Vdash * Q) \vee (p \Vdash * S)$$ (5) $$p \Vdash * (\exists x)Q(x)iff(\exists b)(p \Vdash * Q(b))$$ .     

Solution conformation of a nitrobenzoxadiazole derivative of the polyene antibiotic nystatin: a FRET study

Nystatin is a polyene antibiotic frequently applied in the treatment of topical fungal infections. In this work, a 7-nitrobenz-2-oxa-1,3-diazole (NBD) hexanoyl amide derivative of nystatin was synthesized and its detailed photophysical characterization is presented. The average conformation of the labelled antibiotic in tetrahydrofuran, ethanol and methanol was determined by intramolecular (tetraene to NBD) fluorescence resonance energy transfer measurements. At variance with the literature [Can. J. Chem. 63 (1985) 77-85], it was concluded that there is no need to invoke a solvent-dependent conformational equilibrium between extended and closed conformers of the antibiotic, because the mean tetraene-to-NBD separating distance was found to remain constant (approximately 18 A) in all the solvents studied. In addition, the large solvent dependence of the fluorescence anisotropy observed for the non-derivatized nystatin, was rationalized on the basis of the prolate ellipsoidal geometry of the molecule. It was concluded that the rod shaped and amphipathic antibiotic remains monomeric in different solvents within the concentration range studied (2-20 microM).     

Characterization of the Fe(III)‐binding Site in Sepia Eumelanin by Resonance Raman Confocal Microspectroscopy¶

The resonance Raman spectrum of Sepia eumelanin is discussed by analogy to model compounds containing catechol (CAT)‐like structural units. These data are then compared with the analogous data on Fe(III)‐enriched Sepia eumelanin. In contrast to the natural eumelanin, the Fe(III)‐enriched samples exhibit absorption features in the visible and near‐IR spectral regions, which are attributed to ligand‐to‐metal charge‐transfer (LMCT) bands. Resonance Raman spectra collected by exciting these LMCT bands reveal bands at 580 and 1470 cm^?1; the intensity of these features increases wioth increasing Fe(III) content. The 580 and 1470 cm^?1 bands are assigned to Fe‐OR stretching and ring deformation modes, respectively. These data further substantiate that the Fe(III)‐ melanin‐binding site in melanin is composed of CAT‐like structural units.