Regulation of the excitation energy utilization in the photosynthetic apparatus of chlorina f2 barley mutant grown under different irradiances

Acclimation of the photosynthetic apparatus of chlorophyll b-less barley mutant chlorina f2 to low light (100 micromolm(-2)s(-1); LL) and extremely high light level (1000 micromolm(-2)s(-1); HL) was examined using techniques of pigment analysis and chlorophyll a fluorescence measurements at room temperature and at 77 K. The absence of chlorophyll b in LL-grown chlorina f2 resulted in the reduction of functional antenna size of both photosystem II (by 67%) and photosystem I (by 21%). Chlorophyll fluorescence characteristics of the LL-grown mutant indicated no impairment of the utilization of absorbed light energy in photosystem II photochemistry. Thermal dissipation of excitation energy estimated as non-photochemical quenching of minimal fluorescence (SV(0)) was significantly higher as compared to the wild-type barley grown under LL. Despite impaired assembly of pigment-protein complexes, chlorina f2 was able to efficiently acclimate to HL. In comparison with chlorina f2 grown under LL, HL-grown chlorina f2 was characterized by unaffected maximal photochemical efficiency of photosystem II (F(V)/F(M), doubled content of both beta-carotene and the xanthophyll cycle pigments and considerably reduced efficiency of excitation energy transfer from carotenoids to chlorophyll a. The enormous xanthophyll cycle pool size was however associated with reduced SV(0) capacity. We suggest that the substantial part of the xanthophyll cycle pigments is not bound to the remaining pigment-protein complexes and acts as filter for excitation energy, thereby contributing to the efficient photoprotection of chlorina f2 grown under HL.     

Influence of bilayer fluctuations on the steric interactions between polymer-grafted bilayers

Abstract

We propose a mechanism, through which the low membrane bending rigidity changes the steric polymer repulsion between polymer-grafted bilayers. We calculate the energy of a polymer chain trapped between two thermally undulating surfaces. The proposed treatment is in terms of de Gennes' theory of fluctuations in liquid crystals, later developed by Helfrich for membranes. We show that the confinement energy of the polymer increases due to membrane fluctuations. Also, the repulsive forces between soft polymer-grafted bilayers can extend further from the surface than the height of the polymer layer.     

Photocatalytic Reduction of Nicotinamide Co-factor by Perylene Sensitized RhIII Complexes**

The ambitious goal of artificial photosynthesis is to develop active systems that mimic nature and use light to split water into hydrogen and oxygen. Intramolecular design concepts are particularly promising. Herein, we firstly present an intramolecular photocatalyst integrating a perylene-based light-harvesting moiety and a catalytic rhodium center ( Rh^IIIphenPer ). The excited-state dynamics were investigated by means of steady-state and time-resolved absorption and emission spectroscopy. The studies reveal that photoexcitation of Rh^IIIphenPer yields the formation of a charge-separated intermediate, namely Rh^IIphenPer ⋅ ⁺ , that results in a catalytically active species in the presence of protons.     

Synthese makrocyclischer Lactone durch Ringerweiterung. Vorläufige Mitteilung

Synthesis of Macrocyclic Lactones by Ring Enlargement Reaction Treatment of 3-(1-nitro-2-oxocyclohexyl)propanal ( 1 ) prepared by Michael addition of 2-nitrocyclohexanon and acrylaldehyde with methyltri (2-propoxy)tita-nium yielded a mixture of 2 and 3 which was converted into 6-nitro-9-decanolide ( 4 ).     

Narrow structure in the coherent population trapping resonance in rubidium

An investigation is reported of coherent resonance in the degenerate two-level system of the (Fg = 2 --> Fe = 1) transition of the 87Rb D1 line by means of a Hanle effect configuration. In a coherent population trapping experiment, a very narrow (approximately 1-kHz) resonance superimposed upon a broader resonance (approximately 100 kHz) was observed. The dependence of the width and the amplitude of the coherent resonance on the laser power density, on additional constant magnetic fields, on the laser frequency position along the fluorescence profile, and on Rb cells with different dimensions was investigated.     

Effect of substituents,solute–solute–non-polar solvent interactions and temperature on the spectral properties of bis(dithiophosphato)copper(II) complexes

Extended studies by e.p.r. and electronic spectroscopy on the effect of different non-polar solvents, temperature and disulfide concentration on the spectral properties of bis(dithiophosphato)copper(II), Cu[(RO)₂PS₂]₂, complexes [R = Me, Et and i-Pr] are reported. The molar absorptivity and e.p.r. intensity are very sensitive to the shape and size of the remote ligand substituents and increase in the order: Me < Et < i-Pr. The nature of the solvent and time after dissolution are also important regarding the magnitude of the e.p.r. intensity and molar absorptivity which, 1 h after dissolution, do not follow Beer's law. The molar absorptivities obtained at a given Cu^II(R₂–dtp)₂ concentration increase in the solvent order: n-hexane < n-heptane < CCl₄ < PhMe < PhH < CHCl₃. Twenty-four hours after dissolution the same samples exhibit: (i) linearity between absorbance and concentration of Cu^II(R₂–dtp)₂; (ii) a significant increase in molar absorptivity which is not equal for all the complexes studied and follows the same substituent and solvent orders. Beer's law is satisfied above 5 × 10^–4 M for [(RO)₂PS₂]₂Cu (R = Et, i-Pr) and above 3 × 10^–3 M for [(MeO)₂PS₂]Cu. A significant additional increase, ca. 30–40%, of molar absorptivity, is obtained by increasing the solution temperature from 20 to 50 °C. The molar absorbtivity remains unchanged during 2–3 days after reducing the temperature. Further increase of molecular absorbtivity appears after addition of the corresponding disulfide of dithiophosphate [(RO₂)PS₂–S₂P(RO)₂] to Cu^II[(RO)₂PS₂]₂. The molar absorptivity of Cu[(i-PrO)₂PS₂]₂ increases from 4.8 × 10³ cm^–1 M^–1, 1 h after dissolving the complex up to 2 × 10⁴ cm^–1 M^–1 after addition of the corresponding disulfide. The observed effects are explained on the basis of a self-redox reaction taking place in this type of sulfur containing copper(II) complexes.     

Spontaneous membrane-translocating peptides by orthogonal high-throughput screening

Combinatorial peptide chemistry and orthogonal high-throughput screening were used to select peptides that spontaneously translocate across synthetic lipid bilayer membranes without permeabilization. A conserved sequence motif was identified that contains several cationic residues in conserved positions in an otherwise hydrophobic sequence. This 9-residue motif rapidly translocates across synthetic multibilayer vesicles and into cells while carrying a large polar dye as a "cargo" moiety. The extraordinary ability of this family of peptides to spontaneously translocate across bilayers without an energy source of any kind is distinctly different from the behavior of the well-known, highly cationic cell-penetrating peptides, such as the HIV tat peptide, which do not translocate across synthetic bilayers, and enter cells mostly by active endocytosis. Peptides that translocate spontaneously across membranes have the potential to transform the field of drug design by enabling the delivery of otherwise membrane-impermeant polar drugs into cells and tissues. Here we describe the chemical tools needed to rapidly identify spontaneous membrane translocating peptides.     

A convenient synthesis of long-chain 4-substituted benzyloxycarbonyl alkanethiols for the formation of self assembled monolayers on metal substrates

New 4-substituted benzyl esters of 16-mercaptohexadecanoic acid were prepared by developing a practicable synthetic procedure and using readily available staring materials. The compounds synthesized have been characterized by NMR, MS, IR spectra and elemental analysis. The mercapto derivatives are precursors for the formation of self-assembled monolayers on metal substrates. Dedicated to Professor Dr. Manfred Hesse on the occasion of his 70 ^th birthday