Synthesis of E,E-4-(6-(N-hydroxyethyl(N-ethyl)-aminostyrylquinoxalin-2-yl)vinyl)-2-dicyanomethylene-3-cyano-2,5-dihydrofurans

Abstract

Nonlinear-optical chromophores with N-hydroxyethyl-N-ethylaniline donor, tricyanofuran acceptor moieties and 3,7-divinylquinoxaline π-bridge have been synthesized. The acetyl derivatives of these chromophores exhibit an intense charge transfer band in the visible region of spectrum and a large positive and negative solvatochromism in different solvents.     

Selective reflection in the cholesteric and blue phases of a chiral-racemic mixture of CE6

Abstract

The reflection spectrum for visible light is examined for the cholesteric and blue phases of chiral CE6. Pronounced side band oscillations are observed. The Bragg wavelength for total reflection diverges towards the smectic phase with an exponent v = 0·71±0·05. Going from the cholesteric phase to BPI, the lattice parameter increases by (2)^1/2. Evidence is given for the existence of a long-lived supercooled blue phase (BPS).     

Hexamethylphosphoramide as Analytical Reagent: Simultaneous Determination of Cobalt,Iron and Nickel

Abstract

Hexamethylphosphoramide (HMPA) gives, in aqueous solutions in the presence of SCN^? ions, complexes with many metal ions, which absorb in the visible region of spectrum. The spectra have been studied in function of ligand concentration and pH for Co, Ni and Fe complexes. For the Co complex an equation was found that describes the behaviour of the absorption vs. SCN^? and HMPA concentration. Absorption follows Lambert-Beer law and can be used for analytical determinations. Analysis of solutions containing Ni and Co in various ratios of concentration has been performed and results are discussed. Co, Ni and Fe content of an alloy has been measured by this way.     

Synthesis,Characterization, and Photocatalytic Activities of BiVO4 by Carbon Adsorption Hydrothermal Method

A new idea of prepared method for BiVO₄ nano-powders hydrothermal synthesis process was developed to avert the existent shortcomings of hydrothermal method. The thermal stability, phase structure, light absorption property, and morphology of the catalyst prepared were characterized by thermogravimetric analyzer (TG), X-ray diffraction (XRD), ultraviolet visible spectrophotometer (UV/Vis), and transmission electron microscopy (TEM), respectively. Using methyl orange (MO) as the target degradation material and a 500-W dysprosium lamp as the visible light source to investigate photocatalytic performance of BiVO₄. We successfully prepared BiVO₄ powders with small particle size, less agglomeration and uniform distribution by carbon adsorption hydrothermal method, and the absorption wavelength of light was red-shifted, these all rendered the absorption capacity of visible light region enhancing with 94 % high photocatalytic degradation rate of methyl orange at 60 min. And the possible mechanism was also discussed in this study.     

Cu-grafted TiO2 photocatalysts: effect of Cu on the action spectrum of composite materials

This paper describes a simple technique for the modification of titania with copper to enhance its photocatalytic performance. In addition to the absorption of UV light resulted in band-to-band excitation of electrons, TiO₂ grafted with copper species absorbs radiation in the visible region of spectrum, and it is able to completely oxidize volatile organic pollutants both under UV and visible light. The action spectra of pristine and Cu-grafted TiO₂ photocatalysts are measured and discussed to elucidate the reasons for appearance of the activity under visible light.     

A Simple Approach Toward Solution of the Problems of Signal Instability and Interferences Observed with Spectrophotofluorometers

Abstract

Unexpected fluorescence signal changes observed by analysts are frequently due to lamp instability and interferences from other equipment near the fluorometer; The addition of a constant voltage transformer between the line and the power supply is an inexpensive and simple procedure to provide long term stability of the lamp, which leads to more reliable use of the fluorometer. Interference problems were significantly reduced by adding a filter system to the instrument.

The problem of long term stability and interferences from nearby electronic instrumentation are frequently observed by individuals using spectrophotofluorometers. Unexpected fluorescence intensity differences for samples which are believed to contain similar quantities of an analyte are an outward manifestation of these problems, which may lead to the incorrect report of the concentration of the compound of interest. We have observed such difficulties in a study of the effect of solvent composition on the luminescence of tyrosine and tryptophan (which will be reported separately) and would like to report our difficulties and the remedies to the problem, We feel that this situation is quite widespread, based on informal discussions with other individuals.

The observed fluorescence signal due to a given solution was found to vary quite drastically (up to ± 20%) as a cuvet containing an identical sample was placed in the sample chamber at various times during a day. In some cases, such drastic changes could be observed with measurements taken 15 minutes apart. The changes were not due to solute decomposition, solvent interaction with the solute, photochemical decomposition or thermal decomposition of the solute, as these changes were not reproducible, and appeared to be independent of the solute and the solvent composition.

A block of MgO was placed in the sample compartment and the fluorometer was set up for front surface emission measurement, so that the refleactance could be monitored over a period of time. The reflectance intensity therefore mirrored the lamp intensity, and any change in lamp intensity would appear as a change in the reflectance observed as a function of time. It was observed that random changes in intensity did take place, with such changes occurring over a very short time period. The reflectance intensity changes were quite random with respect to time, and individual shifts were often as much as ± 10%.

When we turned the Xe lamp off and placed a flashlight bulb powered by a 6V lantern battery in the sample chamber, the light measured by the photomultiplier did not exhibit any abrupt changes over a period of 16 hours. This confirmed that the changes in signal intensity observed with the various samples and the reflectance experiments were due to changes in the intensity of the xenon lamp. It was determined that variations in the observed reflectance could be correllated with variations in line voltage.

Our instrument is used in a large laboratory with a number of other instruments within 5 meters. We observe that noise from “external sources” was bothersome, especially on higher amplification steps of the photomultiplier amplifier. In general, the variation in signal was ± 3% full scale at the highest amplification.

We report below our solutions to the problems described above as we feel that our solutions are of interest to those using spectrophotofluorometers.     

The Determination of Bismuth By Hydride Generation and Non-Dispersive Atomic Fluorescence Detection

Abstract

A sensitive determination of bismuth by hydride generation with non-dispersive atomic fluorescence spectrometric detection is proposed. A commercially available electrodeless discharge lamp was used as the light source. Studies on interference effects from foreign elements are reported and the determination of bismuth in copper metal was considered in detail.     

PHOTOTACTIC AND PHOTOKINETIC ACTION SPECTRA OF THE DIATOM NITZSCHIA COMMUNIS

Abstract— Three different types of photomotion reactions, photokinesis, photo-topotaxis and photo-phobotaxis, have been investigated in the diatom Nitzschia communis . In photokinesis the active light appears to be absorbed by the photosynthetic pigments. Apparently, the acceleration of movement by light is due to an additional ATP supply from photosynthetic phosphorylation, as it is the case in the blue-green algae of the genus Phormidium . On the other hand, no correlations exist between photo-phobotaxis and photosynthesis, because red light does not induce photo-phobotactic responses in N. communis . The phobotactic action spectrum resembles that one of photo-topotaxis. In the visible region only violet, blue and blue-green light is active in both the reactions. However, it is not yet clear whether or not the stimuli are mediated by the same photoreceptor, mainly because of the different sensitivity of both the reactions to u.v.     

Detection of Chemical Warfare Nerve Agents via a Beckmann Fragmentation of Aldoxime

Abstract

A new (E)-pyrene-1-carbaldehyde O-tert-butyldimethylsilyl oxime 3 was synthesized for the detection of chemical warfare nerve agents, O-isopropyl methylphosphonofluoridate (GB) and O-pinacolyl methylphosphonofluoridate (GD). ¹H NMR spectrum showed that the tert-butyldimethylsilyl (TBDMS) group was deprotected using TBAF and the oximate supernucleophile was made. Upon addition of chemical warfare agents (GB and GD) (50 mol%), the reaction was completely finished within 5 min and also the color change of reaction mixture was observed under a hand-held UV lamp with the naked eye.     

Determination of Cyclodextrin-Guest Association Constants by Competition with Indicator Dyes

Abstract

The competition of some biologically interesting guests with methyl orange and phenolphthalein indicators for α- and β-cyclodextrin, respectively, has been monitored using visible spectrophotometry. A mathematical model has been developed to calculate the cyclodextrin-guest association constants using a linear plotting method.     

Thermal dimerization kinetics of 3‐(p‐bromo‐phenyl)‐pyridazinium benzoyl methylid in solutions

3‐(p‐Bromo‐phenyl)‐pyridazinium‐benzoyl methylid (BPPBM) participates in solution at 3 + 3 dipolar thermal dimerization that can be spectrally monitored by the extinction in its visible intramolecular charge transfer (ICT) band. The attenuation of ICT band intensity shows the decrease of the BPPBM concentration with the increasing of dimer concentration. The complex kinetics of light‐assisted dimerization process was studied taking into account that the thermodynamic equilibrium is reached after more than 24 h. On the basis of general order of reaction theory, we found that the dimerization reaction must be described as a multistep mechanism. The rate constants of the dimerization reactions in ethanol (k = 0.00897 s^?1) and benzene (k = 0.00774 s^?1) solutions were correlated with the BPPBM and dimer structural features established by using the HyperChem 5.02 simulation program package. A kinetic mechanism of 3 + 3 dipolar thermal dimerization for the studied ylid is proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 230–239, 2008     

721-100型可见分光光度计的故障诊断及排除

介绍721-100型分光光度计示值不稳定、光源灯不亮、电表指针大幅度偏转等几种常见故障,分析了故障产生的可能原因,并提出了可行的解决方法。     

Chemical‐Bond‐Mediated p–n Heterojunction Photocatalyst Constructed from Coordination Polymer Nanoparticles and a Conducting Copolymer: Visible‐Light Active and Highly Efficient

A visible‐light‐active p–n heterojunction photocatalyst has been synthesized by the enwrapping of poly[aniline‐co‐N‐(4‐sulfophenyl)aniline] ( PAPSA ) on a coordination polymer nanoparticle ( NCP ). Compared with the visible‐light‐inactive NCP , the new p–n heterojunction photocatalyst, PAPSA/NCP , exhibits a much higher efficiency in the reduction of Cr^VI under visible light. PAPSA performs two functions in this p–n heterojunction photocatalyst. First, as a visible‐light‐active material, it extends the photoresponse region of the photocatalyst from the ultraviolet to the visible‐light region. Secondly, as a p‐type semiconductor possessing suitable energy levels with respect to NCP , PAPSA forms a p–n heterojunction with the n‐type NCP ; the inner electric field of the p–n heterojunction accelerates the separation of electrons and holes, which enhances the photocatalytic efficiency. Furthermore, the p–n heterojunction photocatalyst exhibits outstanding stability during the photocatalytic reduction of Cr^VI.     

CARBOXYLATED ZINC-PHTHALOCYANINE, INFLUENCE OF DIMERIZATION ON THE SPECTROSCOPIC PROPERTIES. AN ABSORPTION, EMISSION, AND THERMAL LENSING STUDY

Monomer and dimer absorption and emission spectra, and dimerization constants are reported for the diamide of the zinc-tetracarboxyphthalocyanine in pure dimethylformamide (DMF) and in H₂O/DMF mixtures at room temperature. The dimerization constant increases steadily with the water content. The monomer absorption Q-band is insensitive to the solvent composition, whereas dimer spectra show great variations with the water content. Stationary emission measurements show that fluorescence originates exclusively from the monomers. The fluorescence spectrum as well as its absolute fluorescence quantum yield, measured by steady-state thermal lensing, are also insensitive to the solvent composition. The thermal lensing method is discussed for the case of two absorbing species in equilibrium.     

Determination of Ki (i = 1–3) and μj (j = 2–6) in 5CB by observing the angular dependence of Rayleigh line spectral widths

Abstract

Using Parodi's relation, all of the Leslie viscosity coefficients, except μ₁, together with the Frank elastic constants have been measured successfully by the photon correlation spectroscopy of Rayleigh scattered light. The values so determined are in good agreement with those previously determined from shear flow experiments by Chmielewski and by Skarp et al. The polar angle dependence of mode 1 spectral width is proposed as a novel method for the measurement of μ₁ and for the experimental confirmation of Parodi's relation.     

EPR Spectra and Spin Density Distribution of O,S-Dimethyl 4,4-Dithioterephthalate Radical Anions

Abstract

The preparation of O-methyl S-trideuteromethyl 4,4-dithioterephthalate and S-methyl O-trideuteromethyl 4,4-dithioterephthalate is described. The EPR spectra of the corresponding radical anions are measured. Comparison with the spectrum of O,S-dimethyl 4,4-dithioterephthalate radical anions allows the unequivocal assignment of the proton hyperfine structure (proton “hfs”) coupling constants in the above asymmetric species. Assignment of the arene proton hfs coupling constants is achieved by PM6 and density functional theory MO calculations of the spin density distribution and application of McConnell's relationship a^H _μ = ?2.4·ρ^π _μ. The spin density distribution in the asymmetric title compound is compared with those in the radical anions of dimethyl terephthalate and the corresponding symmetric sulfur analogs.     

Action spectrum and quantum yield for the photoinactivation of mnemiopsin, a bioluminescent photoprotein from the Ctenophore mnemiopsis SP.

Abstract— Ctenophores are bioluminescent marine invertebrates closely related to the coelenterates. The isolated bioluminescent systems of the ctenophores Mnemiopsis and Beroë and the hydrozoan jellyfish Aequorea are protein-luciferin complexes (photoproteins) which flash upon the addition of Ca²⁺ ions. The photoprotein mnemiopsin has an oxygen-independent quantum yield for photoinactivation of bioluminescence as high as 0.5, placing it among the most light-sensitive proteins known. We have measured the action spectrum for this photoinactivation at 107 narrow (3.4 nm) wavelength bands between 230 nm and 570 nm, covering a range of four decade units in the action. The action spectrum in the visible region is identical with the absorption spectrum of native photoprotein, implicating bound luciferin. The UV action spectrum implies that absorption by aromatic amino acid residues also leads to extremely efficient photoinactivation. Although photoinactivation is a rapid first-order reaction, destruction of the luciferin is a slower, multiple-order process. Therefore, protein-bound luciferin is not the ultimate target of the photoinactivation. Absorption of light results in the dissociation of “active oxygen” from the photoprotein. Therefore, the ctenophore photoprotein is a precharged enzyme already containing bound luciferin and oxygen.     

Preparation and Spectral Characterization of Sulphur-Containing Diarylazo Compounds

Abstract

By reaction of arylazo-substituted aryl halides with mercaptides, new arylazo-substituted arylsulfides are formed. These compounds are deeply coloured and exhibit an intense absorption band in the visible region, which can be reproduced quantitatively and interpreted satisfactorily by means of quantum chemical calculations in the framework of the PPP and LHM methods, respectively.     

Photochehical Fluorimetric Determination of Primaquine in a Flowing Solvent with Application to Blood Serum

Abstract

Primaquine in a flowing solvent is photolyzed with a 200 W Xe-Hg arc lamp and the intensely fluorescent photochemical product is measured in a fluorimeter. The effect of solvent composition and pH, irradiation time, and excitation conditions are evaluated. Primaquine in blood serum is measured by introducing a sample of blood serum into the flowing stream and performing the photochemical-fluorescence measurement. The fluorescence background of blood serum was very low allowing a detection limit of less than 0.1 μg/mL. Excellent recoveries were obtained.     

Spectral Interference in Antimony Analysis with High Temperature Furnace Atomic Absorption

Abstract

Background correction in atomic absorption spectrophotometry using a high temperature furnace has a close relation to the chemical treatment and the detection limit. Conventionally used for this correction is the D₂ lamp method, but spectral interference is inevitable in this method because the spectral bandwidth of the light from the D₂ lamp after passing through a monochromator is as wide as 0.1 to 5 nm. In the analysis of Sb in lead alloy or in steel, there is spectral interference due to high concentration of elements such as Pb, Cu or Fe, in the matrix, so accurate measurement is impossible unless these elements are removed at the pretreatment stage.

In polarized analyte Zeeman atomic absorption spectrophotometry developed by the authors, the wavelength of the measuring beam is the same as that of the reference and they are identical in spectral line profile as well as in geometrical shape. They differ only in the direction of polarization. For these reasons, we found that there is no spectral interference like that recognized in the D₂ lamp correction technique. As a result, a direct analysis was done simply by dissolving gunmetal or steel in acid without removing the matrix elements Pb, Cu or Fe.