端基含己氧基偶氮苯基元的一代光致变色液晶碳硅烷树状物的光响应行为研究

研究了端基含己氧基偶氮苯基元新的一代碳硅烷光致变色液晶树状物G1及其偶氮基元化合物M3在各种溶液中的反顺光异构化反应速率常数、光回复异构化反应速率常数、热回复异构化反应速率常数、量子产率、活化能和异构转换率.G1和M3的光致变色速率常数为0.1s^-1,比对应的光致变色液晶聚硅氧烷的光响应速度快10⁷倍.     

Characteristic and spectroscopic properties of the Schiff-base model compounds

Two series of conjugated aromatic imines (Schiff-base model compounds) with different central groups and various side-group substitutions have been synthesized and characterized by elemental analysis, differential scanning calorimetry (DSC) technique, hydrogen nuclear magnetic resonance (¹H NMR), Fourier transform infrared (FTIR) and ultra-violet and visible light (UV–vis) spectroscopy measurements. The UV–vis absorption of solutions of these compounds in dimethylacetamid (DMA), chloroform and methanol was investigated in the optical range from 240 to 450 nm, where two distinct absorption bands: at 250–280 and 315–360 nm with the different level of absorption have been observed. The influence of compound molecular structure and polarity of solvent on the absorption spectra and the possible optical transitions have been discussed. Structure of diamines in the azomethine models fundamentally affected their spectroscopic properties and conjugation of π-electrons.     

ULTRAVIOLET ACTION SPECTRUM FOR FLUOROGEN PRODUCTION IN THE OCULAR LENS

Abstract— …Previous work has demonstrated that fluorescent material (360nm excitation, 440nm emission), whose concentration normally increases with age in human lenses, can be generated artificially by exposing cultured human or animal lenses to UV radiation. In the present paper we report measurements of the rate of production of this fluorescent material in rat lenses in vitro as a function of UV irradiation wavelength. A plot of the observed rate of fluorogen production normalized to constant photon flux vs irradiation wavelength shows little action at 360 or 320nm, increases sharply at 300nm, remains relatively constant in the range 300–280nm, and then exhibits a further gradual rise from 270–250nm. The results on rat lenses are compared with results reported elsewhere for tryptophan in aqueous solution. The action spectrum for photochemical destruction of tryptophan in solution closely parallels that for fluorogen production in rat lenses. This result and other evidence suggest that photochemical destruction of tryptophan might be the initial event in UV-induced fluorogen production in the ocular lens.     

Improvement of glass ionomer restoration by adding ZnO nanoparticles prepared by laser in (Vitro study)

The technique of pulsed laser ablation in liquid media was successfully used to prepare zinc oxide ZnO nanoparticles NPs to enhance glass ionomer GI restorative. The synthesized ZnO NPs were confirmed using UV–Visible spectroscopy, XRD, and TEM. The absorption spectra revealed that the absorbance intensity of the prepared ZnO NPs increased as the number of laser pulses increased, with an absorbance peak at 230 nm due to quantum confinement. The crystalline nature of NPs with hexagonal structure is revealed by XRD analysis. The TEM images demonstrated the nanorod shape with a length of about 3.33 nm and there were spherical nanoparticles ranging from 5 nm to 30 nm. ZnO NPs with and without GI were tested for antibacterial activity against Streptococcus mutans bacteria, which shows slight improvement after adding ZnO NPs to glass ionomer as a result of containing effective ingredients in its composition. The agar well diffusion method results revealed that ZnO with GI had a higher antibacterial activity compared with pure ZnO NPs. Finally, the compressive strength test illustrated significant enhancement of up to 50% associated with the ZnO NP's concentration increase.     

Latitudinal Gradient of UV Attenuation Along the Highly Transparent Red Sea Basin

The tropical and subtropical oceans experience intense incident ultraviolet radiation (280–400 nm) while their water columns are thought to be highly transparent. This combination represents a high potential for harmful effects on organisms, yet only few reports on the UV penetration properties of oligotrophic tropical waters exist. Here, we present the pattern of UV attenuation over a wide latitudinal range of the oligotrophic Red Sea. We recorded spectroradiometer profiles of PAR and UV, together with chlorophyll‐a (Chl‐a) and light absorption by chromophoric dissolved organic matter (CDOM) to determine the contribution of phytoplankton and CDOM toward UV attenuation. Transparency to UV exhibited a distinct latitudinal gradient, with the lowest and highest diffuse attenuation coefficients at 313 nm (K_d (313)) of 0.130 m^?1 and 0.357 m^?1 observed at the northern coast off Duba, and in the south close to the Farasan islands, respectively. Phytoplankton and CDOM both modulated UV attenuation, but CDOM was found to be the key driver despite the lack of riverine inputs. We confirm that ultraviolet radiation can reach deeper into the Red Sea than previously described, which means its potential to act as a stressor and selective driver for Red Sea organisms may have been underestimated to date.     

Influence of temperature on the thermo-oxidative degradation of polyamide 6 films

The thermo-oxidative degradation of polyamide 6 (PA6) was studied at relative high temperatures (between 120 and 170 °C) using oxygen uptake and hydroperoxide determination methods, chemiluminescence, FT-IR and UV-VIS spectroscopy as well as solution viscosity and tensile property measurements.The relation between the results of the different analytical techniques and influence of temperature on these relations was determined. Arrhenius plots of the degradation determined with the different methods are linear; however the activation energies determined from these plots depend on the analytical method used. For oxygen uptake measurements and changes in UV absorbance (at 280 nm) and solution viscosity an activation energy of about 120 kJ/mol was calculated, for the increase in carbonyl index of about 80 kJ/mol and for the decrease in elongation at break of about 150 kJ/mol.The changes in oxygen uptake UV absorbance and solution viscosity are probably due to the same chemical process. The lower activation energy from changes in the carbonyl index is attributed to the formation of gaseous products, which play a larger role at higher temperatures. The higher activation energy from the elongation at break measurements was ascribed to the contribution of physical changes that play the largest role at the highest temperatures.     

Solid water at room temperature?

Previously, we have shown that water adjacent to many hydrophilic substances excludes colloidal and molecular solutes. It was labelled “exclusion zone” (EZ) or “fourth phase” water. A salient feature is its characteristic light absorbance at or near 270 nm. In this study, EZ water formed against three chemically distinct surfaces, Nafion, ghee, and Whatman-5 filter paper was extracted, characterized by UV–Visible absorbance spectroscopy, and solidified either by lyophilizing or evaporation in an oven. The resulting highly stable solid was dissolved in water and confirmed as EZ water by its characteristic absorbance at 270–280 nm. We used mass spectroscopy to verify the absence of ionizable contaminants that could reproduce the characteristic “signature EZ” spectra in the three liquid preparations, or in the solids formed from desiccated EZ water that had been reconstituted in deionized water. Hence, a solid form of EZ water may, indeed, exist at room temperature.     

Polymer-based triphenyl tetrazolium chloride films for ultraviolet radiation monitoring

Ultraviolet (UV) radiation monitoring films were prepared from solutions of polymers (polyvinyl, alcohol, PVA, or polyvinyl butyral, PVB), containing triphenyl tetrazolium chloride dye (TTC). These films have a pronounced response to the main UV radiation spectral regions [UV-A (400–320 nm), UV-B (320–280 nm), and UV-C (280–180 nm)] showing different sensitivities. PVA/TTC film has its maximum sensitivity in the UV-A region, while PVB/TTC film has its maximum sensitivity in the UV-C region. Both films have almost the same sensitivity in the UV-B region. The radiation-induced colour change is analysed spectrophotometrically at the maximum of the visible absorption band peaking at 492 nm wavelength. The measurement uncertainty of estimating ultraviolet radiation energy incident per unit area on the films is found to be about 3.5% (1 σ). The study of the effect of radiance exposure, incident wavelength, and storage conditions have been carried out to characterise the use of these films for actinometric monitoring artificial ultraviolet radiation sources which are used for medical and industrial applications.     

UV-absorption and radiation effects in different glasses doped with iron and tin in the ppm range

Intrinsic and extrinsic ultraviolet absorption and radiation-induced effects were investigated in different glass types, fluorides, phosphates and borosilicates. High-purity glass samples were prepared and their intrinsic absorption was measured in the vacuum ultraviolet region. The influence of doped iron and tin species in the ppm range on the ultraviolet absorption and radiation-induced effects were studied. The maximum of the dominating Fe³⁺ charge transfer band has the lowest energy (4.8 eV) and intensity in the fluoride glass and the highest energy (5.6 eV) and intensity in the borosilicate glass samples. The charge-transfer band for Fe²⁺ has much lower intensity and higher energy (∼5.7 eV) than those for Fe³⁺ in all glasses investigated. Photo-oxidation of Fe²⁺ to (Fe²⁺)⁺ hole centres and glass-matrix-related electron centres by UV irradiation increases the UV absorption drastically in all glasses. The kinetics was measured and simulated depending on the glass matrix. In fluoride and phosphate glasses, Fe³⁺ complexes are very stable against UV irradiation and do not participate in UV-radiation-induced processes. Only in silicate glasses, Fe³⁺ is able to form a (Fe³⁺)^– electron centre defect which decreases the charge transfer absorption of Fe³⁺ near 220 nm, but increase the absorption of hole centre defects, with a maximum at 280 nm. So, the defect generation in the ultraviolet region increases drastically with increasing Fe content in the range 10–200 ppm. Three or four electronic s → p transitions for Sn²⁺ were detected by optical absorption and luminescence spectroscopy shifted to longer wavelength in the range fluoride → phosphate → silicate glass samples. Sn⁴⁺ absorption bands were found at shorter wavelength in the vacuum ultraviolet region in all cases investigated. Sn²⁺ ions are photo-oxidised under UV radiation very fast, which leads to an decrease of absorption near 200 nm and to an increase near 250 nm. Both Sn²⁺ and Sn⁴⁺ are involved in the radiation-induced processes. In contrast to phosphate and silicate glasses, tin-doped fluoride glasses are very resistant against UV lamp but not against UV laser irradiation. The mechanisms are very complicated, with maximums and minimums in the defect formation curves.     

Impact of Fe3+ on UV absorption of K2Al2B2O7 crystals

K₂Al₂B₂O₇ (KABO) is a new nonlinear optical crystal capable of laser harmonic generation in the UV range. However, abnormal UV absorption prevents its application in effectively generating UV light with wavelength shorter than 300 nm. The transmittance spectra of the grown crystals show distinct absorption bands at 216 nm and 264 nm. It is observed that the UV absorption is strongly correlated with iron impurity at a parts per million (ppm) level. Furthermore, electron paramagnetic resonance (EPR) spectra of the absorbing crystals show a strong signal at g = 2.00 position corresponding to a Fe³⁺ center. A new crystal growth method which reduces the iron content has been proposed and results show that the new KABO crystal is free from the Fe³⁺ UV absorptions.     

Synthesis of CeO<Subscript>2</Subscript> or α–Mn<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles via sol–gel process and their optical properties

Nanocrystalline cubic fluorite/bixbyite CeO₂ or α–Mn₂O₃ has been successfully synthesized by using methanol as a solvent via sol–gel method calcined at 400 °C. The obtained products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV–vis absorption and Photoluminescence (PL) spectroscopy. TEM reveals that the as-synthesized ultra-fine samples consist of elliptical/spherical and sheet-like morphology of crystalline particles of 8/30 nm, which are weakly aggregated. Optical absorbance spectra reveal that the absorption of ceria in the UV region originates from the charge- transfer transition between the O²⁻ (2p) and Ce⁴⁺ (4f) orbit in CeO₂. However, α–Mn₂O₃ nanostructures with nearly pure band gap emission should be of importance for their applications as UV emitters.     

A highly fluorescent water-soluble boronic acid reporter for saccharide sensing that shows ratiometric UV changes and significant fluorescence changes

One water-soluble naphthalene-based fluorescent boronic acid, 6-(dimethylamino)-naphthalene-2-boronic acid (6-DMANBA, 1), has been synthesized. 6-DMANBA shows significant ratiometric UV absorbance changes upon addition of a sugar. For example, addition of 50 mM fructose shifted the UV absorption wavelengths of 6-DMANBA from 306 and 251 to 280 and 244 nm, respectively. In addition, 6-DMANBA is highly fluorescent with a quantum yield of 89% in the absence of a sugar and shows significant fluorescence intensity changes with the addition of a saccharide in aqueous phosphate buffer at physiological pH. For example, with the addition of 50 mM fructose, 6-DMANBA shows an 80% fluorescent intensity decrease at 432 nm. All these spectroscopic properties make compound 1 unique and useful.     

Substitution in barbituric acids

Aromatic and aliphatic aldehydes readily condense with thiobarbituric acid to form 5-arylidenethiobarbituric acids or 5-arylidenebis(thiobarbituric acid)s. A longer time is required for condensation with ketones. The UV spectra of the arylidene derivatives have two absorption bands, with maxima at 240–275 and 280–405 nm, while the spectra of the alkylidene derivatives only one absorption band, with a maximum at 280–295 nm.For part I, see [1].     

Ultraviolet radiation and the snow alga Chlamydomonas nivalis (Bauer) Wille

Aplanospores of Chlamydomonas nivalis are frequently found in high-altitude, persistent snowfields where they are photosynthetically active despite cold temperatures and high levels of visible and ultraviolet (UV) radiation. The goals of this work were to characterize the UV environment of the cells in the snow and to investigate the existence and localization of screening compounds that might prevent UV damage. UV irradiance decreased precipitously in snow, with UV radiation of wavelengths 280-315 nm and UV radiation of wavelengths 315-400 nm dropping to 50% of incident levels in the top 1 and 2 cm, respectively. Isolated cell walls exhibited UV absorbance, possibly by sporopollenin, but this absorbance was weak in images of broken or plasmolyzed cells observed through a UV microscope. The cells also contained UV-absorbing cytoplasmic compounds, with the extrachloroplastic carotenoid astaxanthin providing most of the screening. Additional screening compound(s) soluble in aqueous methanol with an absorption maximum at 335 nm played a minor role. Thus, cells are protected against potentially high levels of UV radiation by the snow itself when they live several centimeters beneath the surface, and they rely on cellular screening compounds, chiefly astaxanthin, when located near the surface where UV fluxes are high.     

Transient absorption induced by a picosecond electron pulse in the fused silica windows of an optical cell

The transient absorption induced by picosecond pulse radiolysis in the windows of a fused silica optical cell is investigated with pump probe techniques in the UV and the visible range. After excitation with an electron pulse of 7 MeV and an effective duration of around 10 ps the absorbance changes during relaxation are recorded up to nanoseconds with a supercontinuum and a single wavelength probe at 263 nm. The complex spectral signatures and kinetics of the empty cell are set into relation with the transient absorption of water radiolysis. Special care is taken to assure equal irradiation conditions for the comparative measurements over the large spectral range. The results reveal clearly that the transient absorption induced in the fused silica cell is not negligible. The transient signals due to the cell should be considered in picosecond pulse radiolysis of solutions in order to avoid important errors on the time dependent yield of transient species, particularly of those absorbing in the UV.     

π‐Plasmon absorbance films of carboxylic functionalized CNTs coupled with renewable PGP platforms

π‐Plasmon absorbance films of carboxylic functionalized multiwall carbon nanotubes (CNTs) coupled with renewable and recycled polycaprolactone grafted pectin (PGP) platforms as successful alternative for ordinary nondegradable platforms were investigated. Characterization of the synthesized carboxylic functionalized CNTs was performed using ¹H NMR and attenuated total reflectance Fourier transform infrared for structural identification, thermogravimetric analysis and derivative thermogravimetric analysis for thermal stability, and X‐ray powder diffraction for crystal structure, whereas the characterization of prepared PGP was done by means of attenuated total reflectance Fourier transform infrared for chemical structure, differential scanning calorimetry for melting endotherms of polycaprolactone and high crystalline structure of PGP, and thermogravimetric analysis and derivative thermogravimetric analysis for thermal stability of PGP. Fabrication of water‐dispersed carboxylic functionalized CNTs coupled with PGP films was performed by casting technique in the presence of Ca²⁺ as cross‐linker. The thin films were tested for π‐plasmon absorbance using UV‐Vis spectrometry. Different fractions of carboxylic functionalized CNTs and PGP films demonstrated π‐plasmon absorbance broad peaks at λ_max = 232 nm, which corresponded to 5.36 eV. The fabrication of novel films from renewable recycled PGP platform and advanced carboxylic functionalized CNTs properties will be the key features for many of next forthcoming technologies. The PGP considered as environment‐friendly and easily degradable platforms will be a successful alternative for conventional nondegradable electronic platforms, and water‐dispersed carboxylic functionalized CNTs with advanced properties will be finding accelerating executive applications.     

Physicochemical parameter influences and their optimization on the biosynthesis of MnO2 nanoparticles using Vernonia amygdalina leaf extract

The manganese dioxide nanoparticles (MnO₂ NPs) were synthesized using Vernonia amygdalina leaf extract which was used as a reducing, capping, and stabilizing agents due to the presence of bioactive phytochemical compounds. Twenty five runs were designed to investigate the effect of V. amygdalina leaf extract ratio (A), initial potassium permanganate (KMnO₄) concentration (B), pH (C), and reaction time (D) on the biosynthesized MnO₂ NPs using 4-factor, 4-level D-Optimal Response Surface Quadratic Design Model approach. The relationship between physicochemical variables and absorption responses were established using transform second degree polynomial quadratic model. The effects of each absorption responses were analyzed by ANOVA principle using quadratic equations. A very low p-values (<0.0001), non-significant Lack of Fit F-values, and reasonable regression coefficient values (coefficient R² = 0.9790, adjusted R² = 0.9496, and predicted R² = 0.8452) suggested that there is an effective correlation between experimental results and predicted values. Numerical and graphical optimized results demonstrated that the optimized conditions for the predicted absorbance at 320 nm (1.095) were suggested at 43.72%, 1.81 mM, 6.02, and 103.42 min for V. amygdalina leaf extract ratio, initial KMnO₄ concentration, pH, and reaction time, respectively. Under these optimal conditions, the average absorbance from four experimental run was recorded to be 0.9678. This result was very closest to the predicted values. The average size elucidated by X-ray diffraction (XRD) analysis was found in the range between 20 nm and 22 nm. The stretching/or and vibrational, surface topography, thermal, and surface roughness as well as its porosity distributions were investigated by UV–Vis spectroscopy, Fourier transforms infrared (FTIR), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and Gwyddion software analysis.     

Experimental Study of a Closed System in the Chlorine Dioxide-Iodine-Malonic Acid-Sulfuric Acid Oscillation Reaction by UV-vis Spectrophotometric Method

The appearance of oscillations depends critically on the pH for the closed system ClO₂-I₂-malonic acid in the absence of sulfuric acid, and was investigated by determining the absorbance of I₃⁻ with reaction time at 280 nm. The pH should be 3.2–3.8. The initial concentrations of malonic acid, chlorine dioxide, iodine and sulfuric acid have great influence on the oscillation at 280 or 350 nm. The oscillation occurs as long as the reactants are mixed at 280 nm. However, at 350 nm the oscillation is preceded by a pre-oscillatory or induction period. The amplitude is small at the beginning stage but then increases with the reaction time. Finally, the oscillation ceases suddenly. The amplitude and the number of oscillations are associated with the initial reactant’s concentration. The higher is the initial concentration of malonic acid, iodine or sulfuric acid, the bigger is the amplitude. Also, the number of oscillations becomes small. An opposite influence exists for chlorine dioxide. The oscillation curve is more regular and smooth at 350 nm than that at 280 nm. The oscillation becomes more obvious by adding starch at 581 nm for I₃⁻–starch complex (SI₃⁻) than that observed without adding starch at 280 nm. The curve’s shape at 581 nm is very different from that at 280 or 350 nm. The equation for the triiodide ion reaction rate changing with reaction time and the effect of initial concentrations on the oscillation stage were obtained. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.     

A europium(II) complex with bis-pyridino-18-crown-6

A new Eu(II) complex, bis(perchlorato)(bis-pyridino-18-crown)europium(II), has been obtained in the crystalline form by electrolytic reduction. The metal ion is 10-coordinated and its surrounding consists of four macrocycle O atoms, two N ones and four O atoms from perchlorate anions. The compound shows a very broad absorption band, starting gently from 600 nm towards the UV region, and two weak luminescence bands with maxima at 430 and 500 nm. The performed density functional theory (DFT) calculations have shown that the absorption results from mixed f–d, f–s and charge transfer transitions. The possible mechanism of luminescence is also discussed.     

EFFECT OF CHRONIC UV EXPOSURE ON EPIDERMAL FORWARD SCATTERING-ABSORPTION INSK–1 HAIRLESS MOUSE SKIN

Abstract— Clinical and histological precancerous responses to UV irradiation are complicated dynamic functions of total dose, dose fractionation, fluence rate, and spectral distribution. This may be due, in large part, to the ability of UV to decrease epidermal-stratum corneum transmission by stimulation of hyperplasia. This work provides quantitative measurement of dose- and wavelength-dependent optical changes inSK–1 hairless mouse epidermis-stratum corneum occurring under irradiation with “monochromatic” UV wavebands, at 280, 290, 300, 307, and 313 nm. Mice were irradiated 5 days per week with a filtered Xenon-Hg high-intensity grating monochromator, starting with 0.9 minimal erythemal dose (MED), followed by incremental increases in the radiation dose by 20% of the original dose every tenth irradiation day, for2–8 consecutive weeks. Subsequent irradiations (for longer experiments) were followed by 30% incremental increases after the 8th week every 10th irradiation day until cessation of radiation at the end of 14 weeks. Irradiated and control full-thickness epidermis/ stratum corneum were examined histologically and by forward-scattering absorption spectroscopy. Chronic irradiation of hairless mice resulted in significant hyperplasia which was optically manifested by a general increase in forward-scattering absorbance. At moderate local doses (7.2 MED), the absorbance increase per MED was approximately the same for all excitation wavelengths, whereas at large total doses (? 100 MED) the optical increase per delivered MED progressively decreased in the order 313> 307> 300? 290> 280 nm. The increase in skin thickening, expressed as observed increase in absorption at 320 nm, correlated well with histological and clinical data. We propose that optical changes induced by UV-induced thickening can account in large part, if not entirely, for dynamic changes in action spectra for (pre) cancerous processes under chronic irradiation conditions.