PHOTOTRANSFORMATION OF AGGREGATED FORMS OF PROTOCHLOROPHYLLIDE IN ISOLATED ETIOPLAST INNER MEMBRANES

Abstract— Irradiation of an etioplast inner membrane fraction caused the transformation of two photoactive spectroscopically different protochlorophyllide forms into two chlorophyllide forms. A weak light flash, 6% of a saturating flash, preferentially caused the formation of a short wavelength chlorophyllide form absorbing at 672 nm and emitting at 676 nm. A saturating flash resulted in the formation of the 684 nm absorbing form of chlorophyllide with an emission maximum at 698 nm.
The circular dichroism (CD) signals of the newly formed chlorophyllide forms indicated that they are pigment aggregates of different sizes. These aggregates are probably connected to protochlorophyllide reductase and NADPH or NADP. In the absence of NADPH a decomposition of the pigment aggregates took place as revealed by a decrease in the CD-signal. A model is suggested which describes the structural changes of the pigment-protein aggregates after irradiation.     

Synthesis and Complexation of 1,2-Bis[(monoaza[15]crown-5)-N-yl]glyoxime. Crystal Structure of (1,2-Bis[(monoaza[15]crown-5)-N-yl]glyoximato)palladium(II)

A new vicinal dioxime ligand with two crown-ether groups, 1,2-bis[(monoaza[15]crown-5)-N-Yl]-glyoxime(LH₂), has been prepared from cyanogen di-N-oxide and monoaza[15]crown-5. Ni(II), Pd(II), and Pt(IV) complexes of LH₂ with or without alkali-metal ions bound to macrocyclic groups have been isolated. The high affinity of [Pd(LH)₂] and [Ni(LH)₂] for the K⁺ ion is observed in solvent extraction experiments. A single-crystal X-ray structure confirms the postulated geometry of [Pd(LH)₂]- The Pd-atom of the centro-symmetric molecule has square-planar PdN₄ coordination where Pd–N distances range from 1.978(3) to 1.970(3) Å. The N–Pd–N intraligand angle is 79.9(1)^°.     

Preparation and characterization for mineral elements and total dietary fiber and testing for stability of β-carotene of an ARC/CL carrot powder multipurpose candidate reference material

As part of the analytical assurance system of the FAO European Cooperative Research Network on Trace Elements programme an ARC/CL-coded carrot flakes powder (CFP) candidate reference material (RM) has been prepared from a lot of commercial carrot flakes. The candidate RM has been homogenized using a Robot Coupe blender fitted with titanium blades, carefully homogenized in large teflon/polypropylene containers, bottled in 1000 numbered polyethylene containers (20 g samples) and tested for homogeneity. Interlaboratory comparison studies for 9 essential elements, cadmium and total dietary fiber (TDF) based on the AOAC-method resulted in the characterization of the contents of those compounds in the above material. After exclusion of outliers, mean values from at least nine different laboratories based altogether on three independent analytical principles have been used to calculate the recommended concentration ranges for mineral elements. Testing of homogeneity and stability for β-carotene over a period of one year has been additionally carried out. The mean water content in the material amounted to 4.97% and remained stable over a one-year period. Homogeneity of the RM was within 3.0% for almost all included mineral elements as tested for a sample size of 0.5 g. The 95% confidence limits for the mean values of the established recommended concentrations of mineral elements in the present ARC/CL Carrot Powder candidate RM fell within 5% for all the other elements and TDF except for Fe (6.3%) and B (5.7%). The stability of β-carotene in the present candidate RM stored in darkness over a one-year period at room temperature was within 6.3%.     

Metal complexes of macrocyclic ligands. Part XXIV. Binuclear complexes with tetraazamacrocycle-N,N′,N″,N‴-tetraacetic acids

The three ligands H₄dota, H₄teta, and H₄heta give binuclear complexes with Cu²⁺ and Ni²⁺, the spectral properties of which have been studied. The structures of Cu₂(dota)·5H₂O and Cu₂(teta)·6H₂O have been established by X-ray diffraction analysis.     

C2-Symmetrical Pyrrolidine Derivatives Chiral Auxiliaries in Radical Chemistry

Fumaramides 3b and 3c bearing the C₂-symmetrical pyrrolidine moieties (2R,5R)-2,5-bis(methoxymethyl)pyrrolidine ( 2b ) or 1,3:4,6-di-O-benzylidene-2,5-dideoxy-2,5-imino-L -idit ( 2c ), respectively, as a chiral auxiliary lead to high diastereoselectivities in radical reactions (‘tin method’;Scheme 1). Removal of the chiral auxiliaries affords the corresponding alkylated fumaric acids Scheme 2. Single-crystal X-ray structures of 3b and 3c support arguments that lead to the model of 1,4-stereoinduction.     

Time-resolved fluorescence measurements using microlens array and area imaging devices

Time-resolved fluorescence (TRF) assay formats are frequently used technologies in high-throughput screening. In this article, we have characterised the novel Plate::Vision(2) 96-microlens array reader (Carl Zeiss Jena GmbH, Germany) and compared it to the novel LEADseeker Generation IV multimodality imaging system (LEADseeker Gen IV; Amersham Biosciences UK Ltd., UK) for applications in the TRF mode. In europium measurements using the TRF mode, the Plate::Vision displayed a limit of detection for europium of approximately 3 pM, which was comparable to two established TRF readers, the Discovery and the Victor V (both PerkinElmer Life Sciences Inc., USA). The LEADseeker's limit of detection only extended down to europium concentrations of approximately 10 pM in these experiments. For TRF resonance energy transfer (TR-FRET) experiments, a europium-biotin (Eu-biotin) conjugate was titrated with a streptavidin-allophycocyanin (SA-APC) conjugate. The Plate::Vision produced Z' values larger than 0.5 for the acceptor fluorophor emission with concentrations of Eu-biotin as low as 3 nM combined with 175 pM SA-APC. To achieve Z' values of at least 0.5 with the LEADseeker, concentrations of 10 nM Eu-biotin combined with SA-APC of at least 0.8 nM were required. In a drug screening application using TR-FRET, the energy transfer from a europium-labelled protein X (Eu-protein X) to a complex of biotinylated peptide Y with SA-APC was measured. Using the Plate::Vision, a Z' factor larger than 0.5 for the acceptor fluorophor emission was only obtained for a Eu-protein X concentration of at least 10 nM in combination with biotinylated peptide Y/SA-APC at saturating concentrations. Both the Plate::Vision and the LEADseeker show good quality results for applications in the TRF mode and enable an increased throughput based on their shortened measurement time in comparison to classic photomultiplier tube-based readers.     

Metal Complexes with Macrocyclic Ligands. Part XLI. Nickel(II) and copper(II) complexes with mono-N-functionalized dithiadiazamacrocycles

Three N₂S₂ macrocycles ( 3, 10, 12 ) carrying an amino group as a pendant arm have been synthesized and their complexation properties towards Ni²⁺ and Cu²⁺ studied. The crystal structures of the Cu²⁺ complexes with 10-methyl-1,4-dithia-7,10-diazacyclododecane-7-ethanamine ( 3 ) and 11-methyl-1,4-dithia-8,11-diazacyclotetradecane-8-ethanamine ( 10 ) show that, in both cases, the Cu²⁺ is pentacoordinated by the four donor atoms of the macrocycle and the amino group of the side chain. In aqueous solution, however, two forms of the complexes with stoichiometries [MLH] and [ML] (M = Cu²⁺ or Ni²⁺) have been observed. In [MLH], the amino group is protonated and does not bind to the metal ion, whereas in [ML] the amino group is bound, and a pentacoordinated geometry results. The pK_a values for the equilibrium [ML] + H⁺?[MLH]⁺ decrease in the order 12 > 10 > 3 , indicating that the 2-aminoethyl side chain binds better to the Cu²⁺ than the 3-aminopropyl side chain. Cyclic voltammetry for the Cu²⁺/Cu⁺ pair shows that the 2-aminoethyl pendant arm stabilizes the Cu²⁺ oxidation state, when the metal ion is in the 14-membered ring ( 10 ), whereas it stabilizes Cu⁺ for the 12-membered macrocycle ( 3 ).     

Structure and “oxidation behavior” of W24O70, a new member of the {103} CS series of tungsten oxides

Reduced tungsten trioxide crystals WO_3?x, formed by vapor transport from a preparation with bulk composition WO_?2.90, have been studied by X-ray diffraction and electron microscopy. A single-crystal X-ray investigation showed the existence of the ordered {103} CS-structure W₂₄O₇₀, a new member of the homologous series W_nO_3n?2. Electron diffraction patterns of crystal fragments, with a few exceptions, showed the presence of the W₂₄O₇₀ phase (composition WO_2.917). Lattice images, however, indicated a fairly ordered {103} CS-phase, W₂₄O₇₀, intergrown with slabs of WO₃ giving gross compositions of the examined crystals in the range WO_2.93WO_2.96. The wide WO₃ slabs were probably formed by an oxidation process during the preparation.     

Potential energy curves of diatomic molecular ions from high-resolution photoelectron spectra. II. The first six electronic states of Xe2 +

The pulsed-field-ionization zero-kinetic-energy photoelectron spectrum of Xe(2) has been measured between 90 000 and 109 000 cm(-1) following single-photon excitation from the ground neutral state. Transitions to five of the six low-lying electronic states of Xe(2) (+) could be observed. Whereas extensive vibrational progressions were observed for the X0(g) (+)-->I(1/2u), I(3/2g), and II(1/2u) photoelectron transitions, only the lowest vibrational levels of the I(3/2u) and II(1/2g) states could be detected. Unambiguous assignments of the vibrational quantum numbers were derived from the analysis of the isotopic shifts of the vibrational bands and of the intensity distribution and from the modeling of the potential energy curves. Analytical potential energy curves of spectroscopic accuracy (i.e., approximately 1 meV) were determined for all six low-lying electronic states using a global model, which includes the first (charge-induced dipole, proportional to 1/R(4)) member of the long-range interaction series and treats the spin-orbit interaction explicitly. The assumption of an R-independent spin-orbit coupling constant was tested and found to be an excellent approximation.     

Localized changes in the structural stability of myoglobin upon adsorption onto silica particles,as studied with hydrogen/deuterium exchange mass spectrometry

A new method is presented for monitoring the conformational stability of various parts of a protein that is physically adsorbed onto nanometer-sized silica particles. The method employs hydrogen/deuterium (H/D) exchange of amide hydrogens, a process that is extremely sensitive to structural features of proteins. The resulting mass increase is analyzed with Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Higher structural specificity is obtained by enzymatically cleaving the adsorbed proteins prior to mass spectrometric analysis. The mass increases of four peptic fragments of myoglobin are followed as a function of the H/D exchange time. The four peptic fragments cover 90% of the myoglobin structure. Two of the peptic fragments, located in the middle of the myoglobin sequence and close to the heme group, do not show any adsorption-induced changes in their structural stability, whereas the more stable C- and N-terminal fragments are destabilized. Interestingly, for the N-terminal fragment, comprising residues 1-29, two distinct and equally large conformational populations are observed. One of these populations has a stability similar to that in solution (-23 kJ/mol), whereas the other population is highly destabilized upon adsorption (-11 kJ/mol).