Fluorescent Molecular Recognition and Sensing System of Bis-Dansyl Modified γ-Cyclodextrins

Flexible hosts, 6A,6B-; 6A,6C-; 6A,6D-; and 6A,6E-bis dansylglycine-modified -cyclodextrins (-1, -2, -3, and -4, respectively) have been synthesized as a sensing molecule for organic guests including terpenoids and bile acids. These host compounds show a pure monomer fluorescence whose intensity is decreased or enhanced upon addition of guest species. The value I/I₀, where I and I₀ are fluorescence intensities in the presence and absence of a guest and I is I₀- I, was used as a parameter of sensitivity. These hosts exhibit highly sensitive and selective molecular recognition ability, particularly, for lithochoic acid, chenodeoxycholic acid, and ursodeoxycholic acid. The behaviors of the appended moieties of these hosts when host–guest complexation occurs are studied by induced circular dichroism (ICD) spectra and fluorescence spectral change on accommodation of a guest. The ICD pattern of these hosts alone or on accommodation of a guest is very similar, indicating that the behavior of the appended moieties are very similar. The guest-induced variations in the fluorescence or ICD intensity suggest that the appended moieties act as a hydrophobic cap that enables the cyclodextrin to form 1 : 1 host–guest complexes.     

三芳基咪唑类化合物的合成及其双光子吸收性能研究

双光子吸收是指物质分子或原子在强激光激发下同时吸收两个光子,从基态跃迁到两倍光子能量激发态的过程。目前,双光子吸收材料已广泛地应用到双光子激发显微[1]、频率上转换激射[2-3]、光学限幅、三维光信息存储[4]以及光生物学等领域。但在已报道的双光子诱导上转换荧光的有机     

γ-Fe2O3纳米粉的低热固相制备及其电磁损耗特性(英)

The Fe(OH)₃ precursor was prepared by solid -state reaction with Fe(NO₃)₃·9H₂O, NaOH and dispersed poly-ethylene glycol at low heating temperature(25 ℃). Synthesis of iron oxide (γ-Fe₂O₃) nanoparticle was achieved by thermal decomposition of Fe(OH)₃·xH₂O precursor. The nanoparticle was characterized by TG-DTA, X-ray diffra-ction, TEM etc. The results showed that the nanoparticle was composed of γ-Fe₂O₃ and was a better absorber for electromagnetic wave within the low frequency band.     

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.     

Solid-state polyamidation of hexamethylenediammonium adipate. II. The influence of acid catalysts

Loss of diamine and distinct transition phenomena from the solid to the melt state restrain solid-state polymerization (SSP) of nylon salts from industrial application. To depress these phenomena temperatures well below the melting point of the starting material are employed, resulting however in low reaction rates. The need to use catalysts arises and accordingly in this study hexamethylenediammonium adipate (HMA) particles were polymerized containing a strictly controlled amount of uniformly distributed catalyst. The catalysts included boric, sulphuric, and phosphoric acids with boric acid being the most effective in accelerating the reaction while eliminating the tendency to agglomeration. In general, catalyst concentration up to a critical value plays a considerable role in the overall behavior. Furthermore, in agreement with non catalytic processes, the reaction temperature remains an influential parameter. © 1994 John Wiley & Sons, Inc.     

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.     

Photogeneration of Silver Particles in PVA Fibers and Films

Fibers and films prepared from blends of poly(vinyl alcohol) and poly(acrylic acid) were found to be suitable matrices for the solid-state photoreduction of silver ions in the presence of air. Fast generation of nanometer-sized silver crystallites was observed when fibers of polymer blends crosslinked with dimethyl sulfoxide were irradiated with 350nm light. Optical determinations of the formation kinetics were carried out using thin films of noncrosslinked as well as lightly and heavily crosslinked polymer blends. Small Ag clusters were detected initially, which were stable in the dark but transformed into larger metal particles upon further illumination. Both formation processes occurred only under high light intensity illumination and the kinetic data were inconsistent with monophotonic mechanisms.