Light-Harvesting Antenna and Proton-Activated Photodynamic Effect of a Novel BODIPY−Fullerene C60 Dyad as Potential Antimicrobial Agent

A covalently linked BODIPY−fullerene C₆₀ dyad (BDP−C₆₀) was synthesized as a two-segment structure, which consists of a visible light-harvesting antenna attached to an energy or electron acceptor moiety. This structure was designed to improve the photodynamic action of fullerene C₆₀ to inactivate bacteria. The absorption spectrum of BDP−C₆₀ was found to be a superposition of the spectra of its constitutional moieties, whereas the fluorescence emission of the BODIPY unit was strongly quenched by the fullerene C₆₀. Spectroscopic, calculations, and redox studies indicate a competence between photoinduced energy and electron transfer. Protonating the dimethylaminophenyl substituent through addition of an acidic medium led to a substantial increase in the fluorescence emission, triplet excited state formation, and singlet molecular oxygen production. At physiological pH, photosensitized inactivation of Staphylococcus aureus mediated by 1 μM BDP−C₆₀ exhibited a 4.5 log decrease of cell survival (>99.997 %) after 15 min irradiation. A similar result was obtained with Escherichia coli using 30 min irradiation. Moreover, proton-activated photodynamic action of BDP−C₆₀ turned this dyad into a highly effective photosensitizer to eradicate E. coli. Therefore, BDP−C₆₀ is an interesting photosensitizing structure in which the light-harvesting antenna effect of the BODIPY unit combined with the protonation of dimethylaminophenyl group can be used to improve the photoinactivation of bacteria.     

A novel BES-gluconate-sucrose (BGS) solution for cold storage of isolated hepatocytes

We have used hepatocyte suspensions to study how hypothermic storage in a modified University of Wisconsin (mUW) solution affects liver cell metabolism and cell membrane properties. At present the UW solution is the gold standard of organ preservation. However it contains several ingredients which either are expensive or cannot easily be obtained worldwide. The aim of the present study was the development of a novel preservation solution for rat hepatocytes effective and comparable with the mUW, with enhanced buffer capacity and less expensive. In particular, we investigated the effects of the buffering agent BES, a derivate of aminosulfonic acid, on liver cells metabolism during cold storage and rewarming. In the development of this novel preservation solution we have included three key components: gluconate as impermeant anion, sucrose to give additional osmotic support and the aminosulfonic acid BES for its buffer capacity. Our results shown that BGS solution was equally effective to mUW to protect rat hepatocytes against cold preservation injury due to ischemia and reoxigenation. Also, BGS solution is a good alternative with its high buffer capacity, best indices of respiration activity and it is considerably less expensive than the mUW solution. The use of this solution for the storage of isolated hepatocytes may facilitate hepatocyte research in situations in which the more complex and expensive mUW solution is not available since the cost of one liter of BGS is about 1/3 that an equal volume of mUW solution.     

Discrete network models for the low-field Hall effect near a percolation threshold: Theory and simulations

The critical behavior of the weak-field Hall effect near a percolation threshold is studied with the help of two discrete random network models. Many finite realizations of such networks at the percolation threshold are produced and solved to yield the potentials at all sites. A new algorithm for doing that was developed that is based on the transfer matrix method. The site potentials are used to calculate the bulk effective Hall conductivity and Hall coefficient, as well as some other properties, such as the Ohmic conductivity, the size of the backbone, and the number of binodes. Scaling behavior for these quantities as power laws of the network size is determined and values of the critical exponents are found.School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, 69978, Israel     

Synthesis of the four stereoisomers of several 3-(1-aminoethyl)pyrrolidines. Important intermediates in the preparation of quinolone antibacterials

The use of S-α-methylbenzyl as a chiral auxiliary at N₁ allowed separation of diastereomeric 2-pyrrolidinones substituted with an ester, ketoester, ketone and oxime at the C₄ position. Reduction of each diastereomer of 4-[1-(hydroxyimino)ethyl]-1-(1-phenylethyl)-2-pyrrolidinone, 10s and 10r , provided a pair of epimeric amines, [ 11sr and 11ss ] and [ 11rs and 11rr ], that were separated by chromatography. The four stereoisomers of 4-(1-aminoethyl)-1-(1-phenylethyl)-2-pyrrolidinone, 11 , were elaborated into several stereochemically pure 3-(1-aminoethyl)pyrrolidines, 1 and 15-23 . These compounds are useful intermediates (C₇ side chains) for quinolone antibacterials.     

Compatibility in poly(ethylene oxide)–poly(methyl methacrylate) blends

The compatibility of poly(ethylene oxide)-poly(methyl methacrylate) (PEO-PMMA) blends were examined covering the complete composition range. Up to 20% of PEO content films were transparent and glass transition temperatures were determined by DSC and by refractive index vs. temperature measurements. Only one T_g was obtained for these samples and the relationship between T_g and composition has been evaluated. At higher PEO content crystallization took place and the films were opaque. Melting temperatuures of PEO in blends were determined by DSC. Melting point depression was observed for increasing proportion of PMMA and the binary interaction parameter has been calculated.     

Singlet molecular oxygen quenching ability of carotenoids in a reverse-micelle membrane mimetic system

The influence of the medium heterogeneity upon the bimolecular rate constants for the physical quenching, kq, and chemical quenching, kr, of singlet molecular oxygen O2(1deltag) by seven natural and three synthetic carotenoids (CAR) with different substituent patterns was studied in a reverse micelle system of sodium bis(2-ethylhexyl)sulfosuccinate, hexane and water. Because O2(1deltag) was generated inside the water pools of the reverse micelles by photosensitization of the water-soluble dye rose bengal and the CAR are mainly located in the external hexane pseudophase, the quenching process was interpreted using a pseudophase model for the partition of 02(1deltag) between the water pools and the organic pseudophases. The kq values were mainly dependent on the extent of the double-bond conjugation of the CAR, as demonstrated by a good empirical relationship between log(k(q)) and the energy E(S) of the longest wavelength transition pi-->pi* of the CAR. In contrast, the kr values were almost independent of the extent of the double-bond-conjugated system and about four orders of magnitude lower than kq. However, in all cases, CAR photobleaching was observed with the formation of various oxidation products, depending on the photosensitization time. Chromatographic and spectroscopic product analysis for the reaction products of beta-carotene with O2(1deltag) indicated the formation of the beta-carotene-5,8-endoperoxide as the primary oxidation product.     

Atomic mercury photodissociation laser in the visible

Stimulated emission on two new pulsed laser lines in atomic mercury is reported. The laser emits at 435.8 and 546.1 nm, corresponding to the transitions 7 ³S₁ → 6 ³P₁ and 7 ³S₁ → 6 ³P₀ of the neutral atomic mercury atom. Population inversion is generated by photodissociation of HgI₂ vapor with a KrF laser at 248 nm. 150mJ of KrF laser radiation were focused into the HgI₂ cell by means of a cylindrical lens in a transverse pumping configuration. With a single end mirror pulses with a peak power of 3 kW and duration of approximately 1 ns were generated. The pumping mechanism is proposed to be a sequential three-photon process.     

Photolyse des 3-Phenyl-2, 1-benzisoxazols und einiger seiner Derivate in Salzsäure bzw. Schwefelsäure

Photolysis of 3-phenyl-2,1-benzisoxazole and some derivates in hydrochloric and sulfuric acid The photolysis of 3-phenylanthranils (3-phenyl-2, 1-benzisoxazoles) in conc. hydrochloric or sulfuric acid leads to the formation of 5-substituted 2-amino-benzophenones wherein the 5-substituent is the anion of the acid employed. 5-Halo-substituted 3-phenylanthranils, however, show a differing reaction pattern in the two acids. Whereas 2-amino-3, 5-dihalo-benzophenones are obtained when photolysis is effected in conc. hydrochloric acid, irradiation in sulfuric acid causes the hydroxy group to substitute the halogen which migrates to the 4-position of the 2, 1-benzisoxazole to yield 2-amino-5-hydroxy-6-halo-benzophenones. A similar behaviour in sulfuric acid is also observed with 5, 7-dichloro-3-phenylanthranil. When the 5-position of the anthranil is blocked by a phenyl group, irradiation in conc. hydrochloric acid leads to entry of the halogen mainly in this 5-phenyl substituent, as can be expected from mesomeric structures. The reaction mechanisms for the photolytic behaviour of 3-phenylanthranils in both conc. hydrochloric and sulfuric acid is discussed.     

Monte Carlo simulation of freely jointed chains with variable bond lengths

Monte Carlo simulation of freely jointed off-lattice chains with variable bond length is usually done with local random displacements of beads and with reptation moves (displacements of a bead along a chain). In dense systems, the acceptance ratio of reptations decreases strongly with density. We discuss versions of reptation moves, which are effective in dense systems. The idea, which comes from lattice systems, is to use a pseudovacancy (walker), which has the same size as a bead of a chain. The walker is attached to a neighbor chain and then another bead of that chain is cleaved. This is equivalent to a reptation move and a nonlocal displacement of the walker and since no free volume is needed, the move can be used with advantage in dense systems. A related technique are cooperative motions, which were introduced by T. Pakula for lattice models, where several chains change their conformation concomitantly. Such cooperative loops are implemented in the Monte Carlo algorithm by creating a temporary walker by cleaving a bead from a chain, moving it with reptations and finally annihilating the walker by attaching it to the same chain it was cleaved from. These moves and the condition of detailed balance are discussed in detail. As an example, we study the integrated autocorrelation time τ_int for the radius of gyration for a two-dimensional system. For reduced densities larger than 0,4, we find that with standard reptations and local bead displacements τ_int increases strongly with density. If reptations with either a permanent or a temporary walker are used in addition to local moves, the integrated autocorrelation time changes only very little with density and very dense systems can still be simulated efficiently.     

Über Umlagerungen bei der Cyclialkylierung von Arylpentanolen zu 2,3‐Dihydro‐1H‐inden‐Derivaten, 2. Mitteilung

On Rearrangements by Cyclialkylations of Arylpentanols to 2,3‐Dihydro‐1 H ‐indene Derivatives. Part 2. An Unexpected Rearrangement by the Acid‐Catalyzed Cyclialkylation of 2,4‐Dimethyl‐2‐phenylpentan‐3‐ol under Formation of trans ‐2,3‐Dihydro‐1,1,2,3‐tetramethyl‐1 H ‐indene The acid catalyzed‐cyclialkylation of 4‐(2‐chloro‐phenyl)‐2,4‐dimethylpentan‐2‐ol ( 1 ) gave two products: 4‐chloro‐2,3‐dihydro‐1,1,3,3‐tetramethyl‐1H‐indene ( 2 ) and also trans‐4‐chloro‐2,3‐dihydro‐1,1,2,3‐tetramethyl‐1H‐indene ( 3 ). A mechanism was proposed in Part 1 (cf. Scheme 1) for this unexpected rearrangement. This mechanism would mainly be supported by the result of the cyclialkylation of 2,4‐dimethyl‐2‐phenylpentan‐3‐ol ( 4 ), which, with respect to the similarity of ion II in Scheme 1 and ion V in Scheme 2, should give only product 5 . This was indeed the experimental result of this cyclialkylation. But the result of the cyclialkylation of 1,1,1,2′,2′,2′‐hexadeuterated isomer [²H₆]‐ 4 of 4 (cf. Scheme 3) requires a different mechanism as for the cyclialkylation of 1 . Such a mechanism is proposed in Schemes 5 and 6. It gives a satisfactory explanation of the experimental results and is supported by the result of the cyclialkylation of 2,4‐dimethyl‐3‐phenylpentan‐3‐ol ( 9 ; Scheme 7). The alternative migration of a Ph or of an i‐Pr group (cf. Scheme 6) is under further investigation.