Selective resonant energy transfer from all trans β-carotene to dimeric chlorophyll a in vitro

From analysis of the excitation spectrum of the 625 and 688 nm fluorescence of dimeric chlorophyll a (Chl a). and the 668 nm fluorescence of the monomer in the presence or absence of all-trans β-carotene it is concluded that resonant energy transfer occurs between β-carotene and dimeric Chl a. This transfer could involve the 2¹A⁻_g electronic state of all-trans β-carotene which is resonant with the second set of pseudo-exciton states of the dimer.     

Structure investigations on assembled astaxanthin molecules

The carotenoid r,r-astaxanthin (3R,3′R-dihydroxy-4,4′-diketo-β-carotene) forms different types of aggregates in acetone–water mixtures. H-type aggregates were found in mixtures with a high part of water (e.g. 1:9 acetone–water mixture) whereas two different types of J-aggregates were identified in mixtures with a lower part of water (3:7 acetone–water mixture). These aggregates were characterized by recording UV/vis-absorption spectra, CD-spectra and fluorescence emissions. The sizes of the molecular assemblies were determined by dynamic light scattering experiments. The hydrodynamic diameter of the assemblies amounts 40 nm in 1:9 acetone–water mixtures and exceeds up to 1 μm in 3:7 acetone–water mixtures. Scanning tunneling microscopy monitored astaxanthin aggregates on graphite surfaces. The structure of the H-aggregate was obtained by molecular modeling calculations. The structure was confirmed by calculating the electronic absorption spectrum and the CD-spectrum where the molecular modeling structure was used as input.     

Photo-luminescence of Risø B3 and PVB films for application in radiation dosimetry

Risø B3 film dosimeters (23 μm) prepared from poly(vinyl butyral) (PVB) incorporating pararosaniline cyanide, as the radiation-sensitive element and PVB films (25 μm) prepared from PVB without any additives are investigated for γ-radiation measurement using spectrofluorimetry based on their emission properties. The unirradiated Risø B3 film when excited at 554 nm shows an emission band at 602 nm while PVB film shows an emission band at 305 nm when excited at 235 nm wavelength. The fluorescence intensity of both emission bands decreases with the increase of absorbed dose due to the damage caused by ionizing radiation. The useful dose range of Risø B3 film extends up to 120 kGy while that of PVB film extends up to 60 kGy. The response of Risø B3 film increases with the increase of relative humidity during irradiation while that of PVB has less effect in the humidity range of 20–70%. The percent uncertainty associated with the measurement of the dose response was found to be ±3% (1σ) for both films. Risø B3 and PVB films show good post-irradiation stability in dark and indirect daylight where the deviation in the response overall a 2-month storage period was found to be ±5% for Risø B3 and ±2% for PVB.     

在TiO2上CO的光催化氧化

最近在“氧化的”TiO₂(即表面无氧空位和Ti³⁺)上进行的CO光催化氧化研究发现:室温下,以黑光灯(峰值λ=365nm)光照时,“氧化的”TiO₂无CO催化氧化的活性,但以杀菌灯(峰值λ=253.7nm)光照时,则对CO产生显著的催化活性.参照CO在过渡金属表面的催化氧化机理,对本现象进行了解释:黑光灯照时,O₂在TiO₂表面只生成O_2(a)^-,而O_2(a)^-不能使CO氧化,只有以杀菌灯照时,TiO₂表面产生O_(a)^-,CO氧化反应才能发生.     

Hydroxypropyl-β-cyclodextrin effect on the fluorescence of auxin and skatole and on the simultaneous determination of binary mixtures of indole compounds in urine by first derivative spectrofluorimetry

The effect of hydroxypropyl-β-cyclodextrin (HPβCD, β-cyclodextrin (βCD) derivative) was determined on the fluorescence emission spectra of skatole (3-methylindole, MI) and auxin (indole 3-acetic acid, IA). The experiments were conducted at excitation wavelength (λ_ex) = 280 nm, in aqueous solutions at different pH values, with and without HPβCD as receptor. The enhanced fluorescence in the presence of the receptor showed a 1:1 host–guest interaction and the values of the association constants K_A were between 100 and 200 mol⁻¹ L. The effects of methanol and propanol with and without receptor were also studied. The limit of detection (L_D) for the HPβCD enhanced fluorimetric method at pH = 7.00 were 0.279 and 0.765 ng mL⁻¹ for MI and IA, respectively. For the determination of indole compounds with closely overlapping spectral bands a zero-crossing first derivative spectrofluorimetric method with or without HPβCD is described. Binary mixtures of MI or IA with melatonin (N-acetyl-5-methoxytryptamine, M) or 5-methoxytryptamine (5-methoxy-3-(2-aminoethyl)indole, 5M) were analysed in the presence of HPβCD. In the absence of receptor, binary mixtures of MI with IA and M with 5M were determined. The matrix effect was evaluated in urine samples by the method of standard addition. Good apparent recoveries were found for each indolic compound by the direct method (98–105% with R.S.D. 0.5–5%) and for mixtures of them by the first derivative method (90–105% with R.S.D. 1–5%) indicating the applicability of them with the advantage of their simplicity, low cost in materials, no time consuming and no requirement of the use of a sophisticate calibration program.     

Spectroscopic studies into the influence of UV radiation on elastin in the presence of collagen

An investigation into the influence of UV irradiation on elastin hydrolysates in the presence of collagen was carried out using UV-Vis spectroscopy and spectrofluorometry. It was found that the absorbance of elastin hydrolysates in solution increased during irradiation more than the absorbance of the elastin/collagen blend. The fluorescence of elastin hydrolysates was observed at 305nm and at 380nm after excitation at 270nm. For the elastin/collagen mixture in solution, fluorescence spectrum shows only one maximum at 305nm. UV irradiation caused fluorescence fading at 305nm. For irradiated elastin the fluorescence at 305nm decreased faster than for the irradiated elastin/collagen mixture. The maximum of the fluorescence peak was shifted for elastin by 4nm, whereas for the elastin/collagen blends the shift was only 1-2nm. All the obtained results point out the ability of mixing elastin and collagen, and suggest that the elastin/collagen mixture in solution is less sensitive to UV irradiation than elastin hydrolysates alone.     

Ultrasensitive assays of trans- and cis-β-carotenes in vegetable oils by high-performance liquid chromatography–thermal lens detection

The fact that β-carotene might be the protective factor against various cancers, suggests the need for a rapid reliable assay for this potential marker. We have proposed the method for selective, precise and simple profiling of carotenoids as well as for simultaneous ultrasensitive assaying of trans-β-carotene (TBC) and cis-β-carotene(s) (CBC) in five vegetable oils. The oil samples diluted 20 or 100 times were directly injected and analysed by means of the isocratic non-aqueous reversed-phase high-performance liquid chromatography (HPLC) combined with ultrasensitive thermal lens detection (TLS).

Elution of TBC was followed by CBC; both were identified and determined in olive, safflower, sesame, wheat germ and linseed oil by standard addition method. The presence of lutein/zeaxanthin, some xanthophyll and/or early eluting carotene may be also presumed in the aforementioned oils. The examined oils showed different and characteristic carotenoid/carotene profiles and characteristic TBC-to-CBC ratios. Both analytes were selectively detected in the presence of palmitic, oleic, linoleic, linolenic and stearic acid, β-sitosterol and --tocopherol. This extends applicability of the method to other vegetable oils as well.

Favourable analytical performances (high sensitivity, low limits of detection (LODs) and wide linearity span) enabled the direct analyses of highly diluted oils. This resulted in several major benefits of the proposed method, among which (i) reduced risk of stationary phase deterioration, (ii) avoiding the risk of carotenoids transformations and (iii) substantial labour and time savings. The TBC and CBC in diluted vegetable oils were reliably measured at ultratrace level (1–26 ng ml⁻¹) with the S/N ratio ranging from 4 to 140 and precisely determined (imprecision 0.4–8.3%). The concentrations of TBC+CBC estimated in the original oils were as follows: 90.5+51.2 ng ml⁻¹ in sesame oil, 146.0+164 ng ml⁻¹in safflower oil, 464.6+206.1 ng ml⁻¹in linseed oil, 453.7+143.3 ng ml⁻¹ in olive oil and 2.31+2.63 μg ml⁻¹ in wheat germ oil. The characteristic and variable portion of TBC within total β-carotene may serve as a reliable indicator of both, quality and authenticity of the vegetable oil. The HPLC–TLS assay proposed may therefore be successfully applied in nutritional, agricultural and epidemiological studies.     

Investigation of the photocatalytic degradation of organochlorine pesticides on a nano-TiO2 coated film

The photocatalytic degradation of organochlorine pesticides including -, β-, γ-, δ-hexachlorobenzene (BHC), dicofol and cypermethrin were carried out on a nano-TiO₂ coated films under UV irradiation in the air. The photocatalytic conditions, including the amount of TiO₂, irradiation time and the intensity of light were optimized. The pesticides were most effectively degraded under the condition of 2.24 mg/cm² on TiO₂ film and a 400 W UV irradiation of high-pressure mercury lamp with a wavelength of 365 nm. A typical organochlorine pesticide, 20 μg -BHC, was dipped onto the TiO₂ film surface and degraded completely within 20 min. In addition, the photocatalytic degradation pathways on the nano-TiO₂ coated film were discussed.     

Indirect fluorescent determination of selected nitro-aromatic and pharmaceutical compounds via UV-photolysis of 2-phenylbenzimidazole-5-sulfonate

An indirect fluorescence (FL) detection method via the reactivity of UV-photolyzed 2-phenylbenzimidazole-5-sulfonate (PBSA) has been developed for non-fluorescent aromatic compounds. At high pH with UV photolysis, PBSA in the excited state is known to be quenched by reaction with oxygen species and analyte compounds that are reactive toward these oxygen species produced during photolysis can lessen the loss of PBSA FL. After off-line photolysis of PBSA in the presence of various nitro-aromatic test compounds, the increase in PBSA FL is clearly evident. A flow injection (FI) instrument using a PBSA mobile phase propelled through a Teflon coil wrapped around a Hg lamp is optimized and modified for use for liquid chromatography (LC). For the on-line FI determination of the non-fluorescent nitro-aromatic compounds such as 4-nitroaniline, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, and -nitronaphthalene, a positive linear response for PBSA FL from about 0.5 to 15 μM and detection limits generally between 0.2 and 1 μM (4–20 pmol) are found. Linear responses and detection limits of selected pharmaceutical compounds such as the antibacterial nitrofurantoin, antihistamines chlorpheniramine and brompheniramine, and other compounds were similar. In general, detection limits using UV detection at about 214 nm were not as good in the 1–2 μM range but linearity extended up to 100 μM. The amino acid phenylalanine and small peptides containing this aromatic amino acid were also determined using this method. Application of this detection method for the liquid chromatography determination of 4-nitroaniline, 2-nitrophenol, nitrofurantoin, and salicylate is shown.     

Ultraviolet laser-induced fluorescence detection strategies in capillary electrophoresis: determination of naphthalene sulphonates in river water

Various UV-laser-induced fluorescence detection strategies for capillary electrophoresis (CE) are compared, i.e. two UV-laser systems (a pulsed laser providing up to 25 mW of tunable emission, applied at 280, 290 and 325 nm, and a continuous wave (cw) laser providing up to 100 mW of 257 nm emission) and different methods to collect the fluorescence emission signal and to reduce the background. Attention is focused on the determination of amino- and hydroxy-substituted naphthalene sulphonates (NS) in river water; these analytes exhibit native fluorescence upon UV excitation. Optimum results were obtained by applying only a minor portion of the available (average) laser powers, viz. 0.7 mW at 280 nm for the pulsed laser, and 5 mW for the cw laser. For emission collection, the most favourable results were obtained with a mirror-based microscope objective, which facilitates efficient spatial filtering and does not produce impurity fluorescence upon UV-laser irradiation. For standard solutions, the cw laser gave around 20-fold better detection limits (10⁻⁹–10⁻¹⁰ M) than the pulsed laser. For river water, excitation of interferences (presumably humic acids, which exhibit native fluorescence) could be much better suppressed if the pulsed laser was used with selective excitation at 280 nm. Therefore, for real-sample analysis the latter combination is to be preferred. The set-up was used for the identification and quantification (at the 1–35 μg l⁻¹ level) of NS in a river Elbe sample.     

Excited species in the FBX dosimeter system

In the FBX dosimeter solution, the excitation of xylenol orange (XO) produces maximum emission at 550–575 nm both at room and liquid nitrogen temperatures (about 85%) having a lifetime of 0.20–0.36 ns. In addition, at room temperature there is an emission at 350 nm for the excitation at 260 nm (about 15%) having a longer lifetime of 3.71–4.01 ns. Benzoic acid (BA) has excitation at 284–295 nm and emission at 320–365 nm having a lifetime of 1.38 ns. In an aqueous solution containing 5×10⁻³ mol dm⁻³ BA, 2×10⁻⁴ mol dm⁻³ XO and 0.04 mol dm⁻³ H₂SO₄ there is no XO emission at 550 nm due to UV absorption at 260 nm by BA. In this solution, 2 emissions are observed near 350–360 nm, having lifetimes of 1.25 ns (89%) and 2.86 ns (11%). The wavelengths for the emission of XO and absorption of ferric-XO complex are nearly the same. Excited XO produces oxidation of ferrous ions and BA increases the chain length.     

Photoprotection of Mammalian Acid-Soluble Collagen by Cuttlefish Sepia Melanin In Vitro

Several important clinical conditions can result in close association between the pigment melanin and dermal collagen. Because melanin and its precursors can be chemically reactive in ground and excited states, it is important to know whether the resulting melanin-collagen interaction results in photoprotection or photoaggression. Acidic and neutral air-saturated collagen suspensions (0.033%) were irradiated with0–2.6 times 104 J/m2 UVC or with0–83 times 104 J/m2 solar-simulating UV radiation (SSR). Photochemical destruction of a photolabile collagen fluorophore (δ_em 360 nm) and collagen chain degradation were monitored as functions of irradiation time in the presence and absence of added (0–100μg) sepia eumelanin. Melanin retarded collagen photodamage but did not qualitatively alter the fluorescence fading kinetics. Both H202 and 02 can be produced by UV irradiation of eumelanin. Added H202 and K02 destroyed collagen fluorescence and caused 50% chain degradation at ca10–20-fold molar excess. Previous studies have demonstrated that eumelanins efficiently scavenge 02 . We demonstrated that eumelanin also efficiently scavenges H202 as evidenced by its ability to (a) compete with scopoletin for peroxide uptake and (b) directly take up H202 through a dialysis bag. The latter observation suggests that peroxide scavenging could occur in vivo by melanin sequestered in melanophages. Thus, neither UV-generated 02 nor H202 are likely to be present in concentrations high enough to cause measurable collagen damage. Absorption and/or scattering of excitation radiation away from the target chromophore appears to be the primary photoprotection mechanism, although scavenging of active 02 intermediates may play an important, if subtle role.     

Measurement of binary diffusion coefficient from impulse response curve having extremely low absorbance intensity under supercritical condition by noise elimination technique

A noise elimination technique was applied to the determination of binary diffusion coefficients D₁₂ from the response curves having extremely low absorbance intensities in impulse response methods under supercritical conditions of carbon dioxide. The effectiveness of this technique was experimentally examined for the analyses of response curves through both the curve-fitting and the moment methods in two cases: the chromatographic impulse response method for phenol and β-carotene with a polymer-coated capillary column, and the Taylor dispersion method for acetone with an uncoated capillary column. Unreliable D₁₂ values were obtained from the moment method of the response curves at lower absorbance intensities, even treated with noise elimination. The curve-fitting method with the noise elimination treatment was quite effective for determining the D₁₂ values accurately, and was valid at the lowest absorbance intensities, on the order of 10⁻⁴ absorbance unit of UV-Vis multi-detector, corresponding to the smallest quantity of the solute, i.e. 6×10⁻⁵, 6×10⁻⁶, and 5×10⁻² μ mol for phenol, β-carotene, and acetone, respectively, under conditions studied. Infinite dilution regions for binary diffusion coefficients were obtained by injecting various amounts: the binary diffusion coefficients showed constant values at concentrations less than 0.6, 0.004, and 0.08 mol m⁻³ for phenol, β-carotene, and acetone, respectively, in supercritical carbon dioxide at 313.2 K and 16–18 MPa.     

Determination of mercury in microwave-digested soil by laser-excited atomic fluorescence spectrometry with electrothermal atomization

A sample digestion procedure was developed which employs microwave heating of soil and sediment in concentrated nitric acid in a high-pressure closed vessel. Complete dissolution of mercury into the sample solution occurs within 5 min at 59 W/vessel without loss of analyte through overpressurization. Laser-excited atomic fluorescence spectrometry with electrothermal atomization (LEAFS-ETA) was used as the detection method. The scheme uses a two-step excitation, with λ₁ = 253.7 nm and λ₂ = 435.8 nm. Direct line fluorescence was measured at 546.2 nm. The absolute instrumental limit of detection was 14 fg; 1.4 pg/ml with a 10 μl sample injection. The recoveries of mercury in two spiked samples were 94 and 98%. The SRM 8406 (Mercury in River Sediment) was digested and analyzed for mercury, and the results (58.4 ± 1.8 ng/g) agreed well with the reference value of 60 ng/g. The results obtained by LEAFS-ETA with microwave sample digestion are in good agreement with those found by cold vapor atomic absorption spectrometry with EPA Series Method 245.5 sample digestion, which is one of the most commonly used methods for the determination of mercury in soil.     

Photochemical stability of poly(vinyl alcohol) in the presence of collagen

The photochemical stability of poly(vinyl alcohol) (PVA) in the presence of 1%, 3% and 5% of collagen has been studied by Fourier Transform Infrared (FTIR) Spectroscopy, UV-vis spectroscopy, and Differential Scanning Calorimetry (DSC). PVA samples containing 1%, 3% and 5% of collagen were irradiated with UV light wavelength λ = 254 nm in air.The results have shown that PVA in the presence of 1%, 3% and 5% of collagen is less stable under UV radiation than pure PVA. A small amount of collagen in PVA enhances photooxidation in the PVA. The amount of crystallinity in PVA containing 1%, 3% and 5% of collagen decreases faster with UV irradiation time than that for pure PVA films.     

光还原法制备不同形貌银纳米粒子及其形成机理

光还原法制备不同形貌银纳米粒子及其形成机理;光还原;纳米银;形成机理     

Monitoring the structural alterations induced in β-lactoglobulin during ultrafiltration: learning from chemical and thermal denaturation phenomena

This work aims to identify of non-reversible structural changes induced in β-lactoglobulin by permeation through porous ultrafiltration membranes. The evaluation of these structural changes is performed using a fluorescence methodology, which combines the use of three different, complementary, fluorescence techniques: steady-state fluorescence, picosecond time-resolved fluorescence and steady-state fluorescence anisotropy. The identification of the nature of the structural changes induced upon permeation is possible through comparison of the fluorescence responses obtained for β-lactoglobulin solutions collected after permeation (permeates and retentates) with those induced by chemical (addition of Guanidine hydrochloride, GndHCl) and thermal denaturation of β-lactoglobulin.

The fluorescence approach used allowed to identify irreversible losses of structural integrity of β-lactoglobulin in the permeates, while β-lactoglobulin retentates seemed to be unaffected by the ultrafiltration process.

The mechanisms that regulate the structural alterations of β-lactoglobulin and the magnitude of these alterations depend on the protein to membrane pore size ratio, λ, being more substantial at higher λ (severe pore constriction). Under these conditions (permeation with a 10 kDa membrane) the structural changes induced in the proteins are dictated by the high shear stress at the membrane pore walls. The increase of the membrane cut-off (30 kDa membrane) induces a decrease in the magnitude of the shear stress and the effect of protein–membrane chemical interactions becomes noticeable.     

Structural transformations of isotactic polypropylene induced by heating and UV light

Samples of commercial-grade isotactic polypropylene, both neat and nucleated with a specific β-nucleating agent (N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide), were exposed to annealing and UV irradiation. Structural parameters were assessed by X-ray diffraction. Tensile mechanical characteristics were derived from stress–strain curves. The specific nucleation caused more than 70% of the crystalline phase to occur in the trigonal β-modification. The content of the β-phase introduced by the specific nucleation distinctly decreased after a certain induction period, different for annealing at 140 °C and UV exposure. At the same time, the size of the -crystallites increased while the size of the β-crystallites remained virtually unchanged. These results indicate the β →  recrystallization. On the other hand, the strain-at-break values continuously and monotonically decreased with increasing exposure time reflecting defect formation, both at the surface and in the bulk of the specimens. The differences between the effects of thermal ageing and UV degradation are discussed.     

Cyclodextrin-enhanced fluorescence and photochemically-induced fluorescence determination of five aromatic pesticides in water

The effect of β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) aqueous solutions upon the fluorescence and photochemically-induced fluorescence (PIF) properties of five pesticides, including coumatetralyl, pirimiphos-methyl, chlorpyriphos, deltamethrin and fenvalerate was investigated. A 1:1 stoichiometry was found for the β-CD and HP-β-CD complexes formed with all compounds. Binding constant values, ranging between about 90 and 830 M⁻¹ were calculated using the iterative nonlinear least-squares regression approach. Cyclodextrin-enhanced fluorescence and PIF methods were developed for the determination of these pesticides with linear dynamic ranges over two orders of magnitude, and limits of detection (LOD) between 0.2 and 54 ng ml⁻¹ according to the compound. Application to the analysis of tap water and river water samples yielded satisfactory recoveries (88–116%). The method seems to be suitable for environmental water analysis.     

Detection of traces of oxidized and reduced sulfur compounds in small samples by combination of different high-performance liquid chromatography methods

Depending on the sulfur species, picomoles of different inorganic sulfur compounds can be detected and separated by HPLC in one arrangement in a sample volume less than 50 μl. The combination of fluorescence labelling of reduced inorganic sulfur compounds such as sulfide (S²⁻), sulfite(SO₃²⁻ and thiosulfate (S₂O₃²⁻) with monobromobimane followed by an extraction of elemental sulfur (S°) by chloroform treatment enables the detection of all mentioned sulfur compounds as well as sulfate (remaining aqueous phase) in the same sample. While the derivatized sulfur compounds could be detected by their fluorescence emission at 480 nm, elemental sulfur is identified by its UV absorption at 263 nm. Sulfate in the remaining aqueous phase is detected by HPLC with indirect UV detection at 254 nm. Detection ranges for the different sulfur compounds examined are as follows: sulfide (5 μM to 1.5 mM), sulfite (5 μM to 1.0 mM), thiosulfate (1 μM to 1.5 mM), elemental sulfur (2 μM to 32 mM) and sulfate (5 μM to >1 mM).