Separation of fluorescent 1,N6 ethenoderivatives of diadenosine polyphosphates and their enzymatic degradation products by reversed-phase high-performance liquid chromatography

Summary The retention, selectivity and elution order of fluorescent 1,N⁶-etheno derivatives of diadenosine polyphosphates and their enzymatic degradation products on octadecyl and phenyl-bonded silica columns have been studied as a function of mobile phase pH, ionic strength and organic modifier content. Good separations of the compounds of interest were achieved using mobile phases of around 0.1M potassium phosphate buffers at neutral pH containing approximately 10% methanol or 4% acetonitrile for C₁₈ columns and 5% methanol or 1.5% acetonitrile for phenyl columns. The data obtained were used to establish isocratic assays for diadenosine polyphosphate cleaving activities from chromaffin cells using Di(1,N⁶-ethenoadenosine) polyphosphates as fluorogenic substrate analogues followed by fluorescence detection.     

The Effect of cis-trans Isomerism on the Electronic-vibrational Structure of the Ground and Excited States and Reactivity of 2-(2-Furyl)- and 2-(2-Thienyl)oxazole

The fluorescent properties, structure, and electronic structure of the ground and excited singlet and triplet electronic states of the cis and trans forms of 4,5-dihydro-2-(2-furyl)oxazole, 4,4-dihydro-2-(2-thienyl)oxazole, 2-(2-furyl)oxazole (FO), and 2-(2-thienyl)oxazole (TO) have been studied. The orbital nature of the lower excited singlet and triplet states has been studied by the semiempirical INDO/S (valence approximation) and PPP/S ( approximation) methods. It was shown that for FO and TO molecules the lower triplet state is of the * type, for which delocalization of the electronic excitation on atoms is characteristic. In the singlet excitation state inversion was observed of the energy levels of the delocalized * states and n* states localized over several bonds (for the free TO and FO molecules the lower excited singlet states S₁* were assigned to * and n* types respectively). Owing to the low position of the T * and T _n* levels relative to the singlet level of * type, the rate constant for intercombination conversion is greater than the rate constant for radiative decay. Consequently an efficient population of the triplet states of the molecules occurs under conditions of electronic-vibrational excitation. The direction of reactions during synthesis was compared with the localization indices in the ground state for electrophilic, nucleophilic, and radical substitution, and also with the excitation localization numbers L for a wide selection of electronically excited states. It was concluded that the change in the structure of the azole molecule on replacing an O atom by an S atom, or on changing from a partially hydrogenated to a heteroaromatic system, was the main reason for the change of all the spectral parameters characterizing the electronic-vibrational or the spin-orbital interaction of the most reactive groups of atoms in the molecular structure.     

Generation and reactions of novel oxiranyl ‘Remote’ anions

Deprotonation of an oxiranyl β-proton takes place in a stereoselective manner providing the corresponding oxiranyl ‘remote’ anion. The anion is stabilized by chelation between the lithium and the carbonyl moiety of an ester, lactone, imide, or keto-group in the form of a five-membered cyclic intermediate. Certain ester-stabilized oxiranyl anions are stable and can be left in THF solution at −78°C for several hours. The generated anions undergo a stereoselective alkylation reaction to provide products, which could be useful intermediates in the synthesis of bioactive naturally occurring α-methylene bis-γ-butyrolactones.     

One- or two-dimensional organometallic arrays containing PdIr2(μ3-S)2 mixed-metal sulfido cluster units connected via the nicotinamide or isonicotinamide ligands on their Pd sites through hydrogen-bonding interactions

Mixed-metal sulfido cluster [(PdCl₂)(Cp*Ir)₂(μ₃-S)₂] (Cp*=η⁵-C₅Me₅) dissolved in CH₂Cl₂ reacted with two equivalent of L (L=nicotinamide, isonicotinamide, or N-methylnicotinamide) in the presence of AgBF₄ to give the cationic clusters [(PdL₂)(Cp*Ir)₂(μ₃-S)₂][BF₄]₂. The single-crystal X-ray diffraction studies of these products have disclosed that in the solid state the PdIr₂S₂ cores are self-assembled to form one-dimensional chains through the intermolecular hydrogen-bonding between the amide groups for L=nicotinamide or two-dimensional sheets via the hydrogen-bonding between the amide groups and the BF₄ anions for L=isonicotinamide, whereas no organization of the cluster cores is observed for L=N-methylnicotinamide.     

Determination of uncertainty for hardness measurement: proposal of the standard,available software

After the next revision of the ISO-standards for hardness testing (ISO 6506–6508) an estimation of the uncertainty (ISO/IEC 17025, ISO 5725) is mandatory. The two proposed approaches of part one (ISO 6506–6508) of the ISO Standards for hardness are exemplified. The calculation approach implemented in an Excel-based file, which is available via , is announced.Presented at the Metro Trade Workshop on Traceability and Measurement Uncertainty in Testing, 30–31 January 2003, Berlin, Germany     

Cholesterol modulates amiodarone-membrane interactions in model and native membranes

The effects of cholesterol, a lipid mostly found in the sarcolemmal membranes, on the interaction of amiodarone with synthetic models of dimyristoylphosphatidylcholine (DMPC) and with native models of mitochondria and brain microsomes was studied. Alterations on the structural order of lipids were assessed by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) probing the bilayer core, and of the propionic acid derivative 3-(p-(6-phenyl)-1,3,5-hexatrienyl)phenylpropionic acid (DPH-PA) probing the outer regions of the bilayer. As detected by the probes and according to classic observations, cholesterol progressively increased the molecular order in the fluid phase of DMPC. Additionally, it modulated the type and extension of amiodarone effects. For low cholesterol concentrations (≤10–15 mol%), amiodarone (50 μM) ordered DMPC bilayers and the effects were almost identical to those observed in pure DMPC. For higher cholesterol concentrations, amiodarone ordering effects decreased slightly and faded for cholesterol concentrations as high as 25 and 30 mol%, when detected by DPH-PA and DPH, respectively. Above these high cholesterol concentrations, a crossover from ordering to disordering effects of amiodarone was apparent, either in the upper region of the bilayer or the hydrophobic core. The effects of amiodarone in native membranes of mitochondria and brain microsomes, in which "native" cholesterol accounts for about 0 and 25 mol%, respectively, correlated reasonably with the results in models of synthetic lipids. There is a close relationship between cholesterol concentration and amiodarone effects, in either synthetic models or native model membranes. Therefore, it may be predicted that the lipid physicochemical properties regulated by cholesterol concentration will also modulate the effects of amiodarone in sarcolemma.     

Synthesis,Crystal Structures and Properties of Two Novel Co（Ⅱ） and Cd（Ⅱ） Complexes of N-AcetyI-L-glutamic Acid and Imidazole Ligands

Two novel complexes {[Co（A-glu）（Im）2]·0.5H2O}n （1） and [Cd（A-glu）（Im）3]n （2） （H2A-glu=N-acetyl-L-glutamic acid, Im=imidazole） have been synthesized from the reaction of H2A-glu with Co（CH3COO）2·4H2O or Cd（CH3COO）2·2H2O in the presence of Im. Both of the complexes display different coordination environment and similar one-dimensional chain structure. The magnetic susceptibility measurements for 1 show a weak antiferromagnetic interaction between two cobalt（Ⅱ） ions bridged by A-glu ligand. The complex 2 exhibits an intense fluorescent emission in solid state at room temperature.     

Novel Water Soluble Fluorescent Trimethine Indocyanines Containing N-ρ-Carboxybenzyl Group

Indocyanine dyes as fluorescent labeling reagents have been used in bioanalysis1,2. Arylsulfonate indocyanine dyes 1d and 1e developed by Waggoner A. S. et al.3,4 have excellent fluorescent properties combined with good aqueous solubility, are a new generation of fluorescent label compounds for proteins, oligonucleotides and other compounds containing hydroxyl, mercaptol or primary amine groups5. However, photostability of these dyes has been a problem. Z. G. YAO et al.6 reported that p…