An Unusual Photoreaction of 3,4-Di-O-benzyl-hypericin

 Upon irradiation of 3,4-di-O-benzyl-hypericin and proton sponge (bis-1,8-N,N-dimethylamino-naphthalene) in benzene solution, a stable radical ion pair formed which exhibited an intense absorption band around 800 nm. This was advanced by UV/Vis, NMR, and ESR spectroscopy. In presence of oxygen, irradiation of this photoproduct led to an activated oxygen species which then attacked the proton sponge.     

Fringelite D, a Model of the Protist Photosensory Pigments of the Stentorinand Blepharismin Types: The Hypericinand Fringelite D PhotosensitizedDestruction of Bilirubin

Summary.  Using the hypericin and fringelite D photosensitized destruction of bilirubin together with fluorescence spectroscopy it was found that in contrast to fringelite D hypericin behaves as an effective photodynamic agent producing mainly singlet oxygen. This makes fringelite D and concomitantly the related stentorin and blepharismin pigments better suited for the photosensory transduction chain where, as shown recently, an initial proton expulsion reaction plays the fundamental role. Thus, in organisms using these photosensory pigments the production of deleterious oxygen species becomes diminished as compared to hypericin. In addition it was found that complexation with albumin further inhibits bilirubin destruction. Received June 29, 2000. Accepted July 18, 2000     

On the Ground State Energy Hypersurface of Blepharismins and Oxyblepharismins

Summary.  AM1 calculations on blepharismins and oxyblepharismins, which are related photosensory pigments of certain protists, revealed that the accessory substituents of the natural pigments do not lead to a change of the tautomerism and conformational states of the fundamental systems. The valence tautomerism possible in principle for the blepharismins yielding a cycloheptatriene–norcaradiene system was found to reside completely on the side of the cycloheptatriene. With respect to proton tautomerism, the strong predominance of the meso-type 7,15- and 7,14-dioxo tautomers was established in both series. Whereas the conformation of the fundamental condensed aromatic ring system of the oxyblepharismins remains comparable to that of hypericin, the conformational situation of the blepharismins was found to be unique with the phenyl group in an endo-position and dihedral twisting at the unperturbed bay-site only. Received June 29, 2000. Accepted July 12, 2000     

The Keto-Enol Equilibrium of Pentane-2,4-dione Studied by ab initio Methods

Summary.  The mechanism of the keto-enol interconversion of pentane-2,4-dione (trivial name: acetylacetone, acac) was examined at the restricted Hartree-Fock (HF) level and the DFT correlation functional BLYP method using the 6-311G^** basis, both included in the program GAUSSIAN 98. Two initial enol forms are considered: the omega and sickle forms, related by a rotation of 180° around the OC*CC bond. The study is restricted to the through-space transfer of the hydroxyl proton to C(2). The two geometry-optimized enol forms are planar; the geometry optimization of the diketone forms leads to the same non-planar structure, regardless of the starting enol geometry. The transition state of the through-space omega-enol→diketone conversion has also a non-planar structure, indicating that the hydroxyl proton moves outside of the CCC plane. The BLYP-calculated energy barrier of the forward (omega-enol→diketone) conversion is 245 kJ·mol⁻¹, that of the reverse (diketone→omega-enol) conversion 222 kJ·mol⁻¹; thus, an almost symmetric barrier, which is not thermally accessible, is defined. The energy barrier for the sickle-enol→diketone conversion is considerably lower (187 kJ·mol⁻¹), to access the sickle form from the more stable omega form, a rotation is needed (energy barrier: 88 kJ·mol⁻¹). The HF-calculated barriers are 1.3–1.4 times higher than those obtained with the BLYP method. Received July 6, 2000. Accepted (revised) September 8, 2000     

Concerning the Absorption and Photochemical Properties of an ω-4-Dimethylaminobenzal Hypericin Derivative

Summary.  A hypericin derivative containing ω,ω ′-4-dimethylaminobenzal residues was shown to undergo an intramolecular [2 + 2] cycloaddition upon irradiation leading to a cyclobutane derivative whose main absorption band is hardly shifted as compared to hypericin. The corresponding ω-substituted derivative displayed a 34 nm bathochromic shift and a strongly reduced fluorescence quantum yield rendering it a nice candidate for a photodynamic therapy agent. Unfortunately, however, it produced virtually no photosensitized active oxygen species, making it thus unsuited for this purpose. Received July 11, 2001. Accepted July 18, 2001     

Phase Gratings in Photoreactive Polymers:A Way to Optically Pumped Organic Lasers

Summary.  Poly-(4-vinylbenzyl-thiocyanate) (PVBT) was investigated as a photoreactive polymer which changes its refractive index upon UV irradiation as is required for the production of phase gratings. After UV irradiation, the refractive index of PVBT films increased from n_D ²⁰ = 1.629 to n_D ²⁰ = 1.660 (Δn = +0.031). The change in the refractive index resulted mainly from the photoinduced isomerization of thiocyanate (SCN) to isothiocyanate (NCS) groups. It was possible to modify irradiated PVBT with 1-naphthylmethyl amine which lead to a further increase of the refractive index. Both the isomerization and the modification were followed with FTIR spectroscopy. This modification of the irradiated zones also yields an advantageous stabilization of phase gratings enscribed in PVBT. The investigations were carried out in the realm of novel organic distributed feedback (DFB) lasers. Received August 22, 2000. Accepted September 22, 2000     

Theoretical studies of electron and hydrogen transfer reactions between semiquinone radicals and oxygen

 To explore the interactions between ubiquinones and oxygen in living organisms, the thermodynamics of a series of electron and hydrogen transfer reactions between semiquinone radicals, as well as their corresponding protonated forms, and oxygen, singlet or triplet, were studied using the hybrid Hartree–Fock–density functional theory method Becke's three parameter hybrid method with the Lee, Yang, and Parr correlation functional. Effects of the solvent and of the isoprenyl tail on the electron and hydrogen transfer reactions were also investigated. It is found that semiquinone radicals (semiquinone anion radicals or protonated semiquinone radicals) cannot react with triplet oxygen to form the superoxide anion radical O₂ ⁻. In contrast, neutral quinones can scavenge O₂ ⁻ efficiently. In the gas phase, only protonated semiquinone radicals can react spontaneously with singlet oxygen to produce peroxyl radical (HO₂). However, both semiquinone anion radicals and protonated semiquinone radicals can react with singlet oxygen to produce harmful oxygen radicals (O₂ ^{− a l l b u l l} and HO₂, respectively) in aqueous and protein environments. The free-energy changes of the corresponding reactions obtained for different ubiquinone systems are very similar. It clearly shows that the isoprenyl tail does not influence the electron and hydrogen transfer reactions between semiquinone radicals and oxygen significantly. Results of electron affinities, vertical ionization potentials, and proton affinities also show that the isoprenyl tail has no substantial effect on the electronic properties of ubiquinones. Received: 3 July 2000 / Accepted: 6 September 2000 / Published online: 21 December 2000     

Syntheses and Crystal Structures of Polynuclear Cu(I) Complexes Containing the 1,1′-Bis-(diphenylphosphino)-ferrocene Ligand

Summary.  The reaction between [Cu(NCMe)₄][PF₆] and 1,1′-bis-(diphenylphosphino)-ferrocene (dppf) in several ratios, solvents, and conditions led to the synthesis and structural characterization of the Cu(I) complexes [Cu(dppf)(Odppf)][PF₆] (1), [(dppf)Cu(μ-dppf)Cu(dppf)][PF₆]₂ (2), and [(dppf)Cu(μ-Cl)₂Cu(dppf)] (3). Although 1 and the cation in 2 were known, the first was structurally characterized for the first time, exhibiting a significant asymmetry in the coordination sphere of Cu(I) owing to the presence of oxygen. In 2, the PF₆ ⁻ anion led to an interesting crystal packing with large open channels containing water. Finally, DFT calculations on a model of 3 showed that its HOMO exhibits, besides Fe, a significant Cu and Cl character, which is reflected in its electrochemical properties. Received July 14, 2000. Accepted July 21, 2000     

Trace Analysis by Heavy Ion Induced X-Ray Emission

 Various K-, L- and M-shell X-ray production cross sections are measured for heavy ion impact on elements in the range Z ₂ = 13 to 83. The ion species range from Z ₁ = 10 to 36, and ion energies from 1 to 16 MeV are used. Enhanced cross sections are observed when the projectile K- or L- binding energy is similar to the energy of the target K-, L- or M-shell. This effect is used to improve the analysis sensitivity for selected elements. As an example trace analysis of Fe in glass with V, Mn, Co and Ni ions is investigated. Results are compared with proton induced X-ray emission analysis on the same samples. In these samples Fe-K_α X-ray production is similar for irradiation with 3 MeV protons and 14 MeV Ni ions. However the signal to background ratio is four times higher for the irradiation with Ni ions as compared to irradiation with protons. Advantages and drawbacks of heavy ion induced X-ray emission for quantitative analysis compared to proton induced X-ray emission analysis are discussed.     

Organic-Inorganic Sol-Gel Hybrids with Ionic Properties

Summary.  A hybrid silicon precursor (ICS-PPG) obtained by reaction of 3-isocyanatopropyltriethoxy silane with poly-(propyleneglycol)-bis-(2-aminopropyl ether) was recognized as a potential host for various salts and molecular species. It has been used for electrochromic, gasochromic, photovoltaic, and fuel cell applications. This focuses on proton conducting gels (PWA/ICS-PPG, SiWA/ICS-PPG, and W-PTA/ICS-PPG) obtained after the incorporation of polyoxometalates in the ICS-PPG host. IR spectroscopic measurements are used to reveal the entrapment, the aggregation, and the interactions of W-PTA, PWA, or SiWA with the sol-gel derived network. The proton conductivity of the composites, measured using impedance spectroscopy, increases with increasing concentration of the polyoxometalates from 10⁻⁶ to 10⁻³ S/cm. Received June 23, 2000. Accepted (revised) September 18, 2000     

Solvent-Free Aminoalkylation of Phenols and Indoles Assisted by Microwave Irradiation

Summary.  Phenols and indoles were aminoalkylated in a solvent-free and environmentally friendly Mannich reaction on acidic alumina assisted by microwave irradiation in good overall yields. Received November 10, 2000. Accepted December 6, 2000     

Novel Functional Fullerene Materials: Fullerenes as Energy Acceptors

Summary.  Fullerene derivatives exhibit absorption throughout the UV/Vis region up to 750 nm. This feature is important for easy excitation. Once excited, fullerenes may become both electron and energy acceptors. The distinction between these two pathways depends strongly on the partner involved (donor) and on the conditions employed (solvent, etc.). Received June 23, 2000. Accepted July 7, 2000     

Rhodium-Catalyzed Amination of Aromatic Olefins [1]

Summary.  The oxidative amination of styrene with secondary amines in the presence of cationic rhodium catalysts yields regiospecifically the corresponding anti-Markovnikov enamines. Styrene as the hydrogen acceptor gave concomitantly ethylbenzene. In the presence of 1,5-cyclooctadiene (cod) preferential reduction to cyclooctene takes place. The addition of cod reduces the rate of the reaction, but also the amount of ethylbenzene produced. Here, for the first time the ratio of enamine: ethylbenzene is > 1, which is favourable in case of more expensive styrene derivatives. A screening of various ligands for oxidative amination reveals that hemilabile 2-(ω-phosphino-n-alkyl)-pyridines are superior ligands for this reaction compared to simple alkyl and aryl phosphines. Received May 30, 2000. Accepted July 11, 2000     

Hydrogels containing 5-Fluorouracil obtained by γ-irradiation. Synthesis, characterization and in vitro release studies

The functionalization of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) with glycidyl methacrylate (GMA) gives rise to a water-soluble copolymer PHEA-GMA (PHG) containing double bonds and ester groups in the side chain. Aqueous solutions of PHG alone or in combination with N,N′ methylenbisacrylamide (BIS) have been exposed to a γ-ray source at different irradiation doses in order to obtain polymeric networks. All samples have been prepared both as water-swellable microparticles and as gel systems. Microparticles have been characterized by FT-IR spectrophotometry and swelling measurements in aqueous media mimicking biological fluids. The effect of irradiation dose and BIS presence on rheological behavior of the gel systems had also been investigated. All prepared hydrogels are able to incorporate, during γ-irradiation, 5-Fluorouracil, (5-FU) chosen as a model drug and to release it in simulated biological fluids, as confirmed by the in vitro drug release studies at pH 1 and pH 7.4. Gels of PHG containing 5-FU, obtained in the presence or in the absence of BIS, are able to release this drug in a prolonged way, more slowly than a commercial ointment, as confirmed by in vitro studies at pH 5.5 and pH 7.4 using a Franz diffusion cell system and a synthetic membrane. Received: 12 July 2000 Revised: 10 October 2000 Accepted: 17 October 2000     

Iridium(I)-Catalyzed Asymmetric Intermolecular Hydroarylation of Norbornene with Benzamide

Summary.  Starting from the dinuclear chloro-bridged Ir(I) complexes [IrCl(PP)]₂ (PP = (R)-(6,6′-dimethylbiphenyl-2,2′-diyl)-1,1′-bis-(diphenylphosphine), (R)-(6,6′-dimethoxy-biphenyl-2,2′-diyl)-1,1′-bis-(diphenylphosphine), and (R)-1-((S)-2-(diphenylphosphino-ferrocenyl))-ethyldicyclohexylphosphine), a new class of cyclopentadienyl Ir(I) complexes containing a chiral bisphosphine ([IrCp(PP)]) was prepared and characterized. These new complexes are suited precatalysts for the direct hydroarylation of norbornene with benzamide. 2-(exo-Norbornyl)-benzamide is formed with an enantiomeric excess of up to 94% by the use of 1 mol% iridium, albeit in low yield. Received July 10, 2000. Accepted August 27, 2000     

The Role of Interfaces in Photovoltaic Devices

Summary.  Organic opto-electronic devices comprise one or more organic layers and the electrodes. The interfaces between these very different components play a crucial role to the performance of the devices. In donor–acceptor composites for photovoltaics, the electronic processes occurring at the interface will benefit from a particular interface morphology on the 10–100 nanometer level; this is demonstrated for composites of oligophenylenevinylene and C₆₀. Phase separation on such a scale may be achieved naturally in diblock copolymers. The synthesis of an OPV–C₆₀ diblock copolymer is described. Received June 23, 2000. Accepted (revised) July 18, 2000     

Corrected Structure of Aglalactone Isolated from Aglaia elaeagnoidea (Meliaceae)

Summary.  The structure of aglalactone, a dihydrobenzofuranone from Aglaia elaeagnoidea, was revised on the basis of 2D NMR data and lanthanide induced shifts (LIS). Received June 29, 2000. Accepted July 11, 2000     

Asymmetric Allylic Substitution Reactions with a Xylophos-Pd Catalyst

Summary.  The chiral diphosphine ligand xylophos (1) was tested as an auxiliary in palladium catalyzed allylic substitution reactions. Whereas its activity was found to be generally good only in the case of 1,3-diphenylprop-2-en-1-yl acetate, a fair level of asymmetric induction was achieved with sodium dimethyl malonate (83%ee) and benzylamine (66%ee) as nucleophiles. Received June 13, 2000. Accepted July 3, 2000     

The structure of benzoyldimedone from X-ray diffraction analysis

The structure of benzoyldimedone was established by X-ray diffraction analysis. The only tautomer was found. In this tautomer, the enol proton is covalently bound to the oxygen atom that is remote from the phenyl group. The role of steric and electronic factors in stabilization of the enol structure is analyzed. The geometric characteristics of the ring formed through an intramolecular hydrogen bond are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1074–1076, June, 2000.     

Synthesis of Novel 2-Aminothiophene-3-carboxylates by Variations of the Gewald Reaction

Summary.  The synthesis of the title compounds through variations of the Gewald reaction is presented. Knoevenagel condensation of methylketone derivatives with methyl cyanoacetate and subsequent treatment of the α,β-unsaturated nitriles with sulfur and amine resulted in the corresponding 2-aminothiophenes 5 or isomers 9 and 10. Reaction of methylketone derivatives bearing a leaving group at the methyl group under modified Gewald conditions selectively led to the formation of 4-substituted 2-aminothiophenes 9a and 12. The introduction of the sulfur atom occurs through nucleophilic displacement with sodium sulfide. Received July 5, 2000. Accepted (revised) August 23, 2000