In situ, rapid, and temporally resolved measurements of cellulase adsorption onto lignocellulosic substrates by UV-vis spectrophotometry

This study demonstrated two in situ UV-vis spectrophotometric methods for rapid and temporally resolved measurements of cellulase adsorption onto cellulosic and lignocellulosic substrates during enzymatic hydrolysis. The cellulase protein absorption peak at 280 nm was used for quantification. The spectral interferences from light scattering by small fibers (fines) and particulates and from absorptions by lignin leached from lignocelluloses were corrected using a dual-wavelength technique. Wavelengths of 500 and 255 nm were used as secondary wavelengths for correcting spectral interferences from light scattering and absorption of leached lignin. Spectral interferences can also be eliminated by taking the second derivative of the measured spectra of enzymatic hydrolysate of cellulose or lignocelluloses. The in situ measured cellulase adsorptions in cellulose and lignocellulose suspensions by these two spectrophotometric methods showed general agreement with batch sampling assayed by the Bradford method. The in situ methods not only eliminated tedious batch sampling but also can resolve the kinetics of the initial adsorption process. The measured time-dependent cellulase adsorptions were found to follow pseudo-second-order kinetics.     

Absorption and emission spectroscopy in scattering media: modelling of fluorescence decay curves and photometric laws for systems with inhomogeneous absorber distribution

Summary The optical absorption and fluorescence of scattering samples is investigated theoretically and experimentally under the condition of steady-state and pulsed irradiation, taking into account inhomogeneous distribution of the absorbing species. Based on the Kubelka-Munk model, numerical iterative expressions for the steady-state and time-resolved light flues of excitation and emission are derived. The intensities of reflected, transmitted and forward or backward emitted radiation in layered samples with vertical concentration gradients are discussed. Modification of fluorescence spectra and decay curves due to self absorption, background absorption, secondary emission and time of flight dispersion are calculated and compared to experimental data of hydrocarbons adsorbed on polycrystalline silica gel.     

Monte Carlo simulation of near infrared autofluorescence measurements of in vivo skin

The autofluorescence properties of normal human skin in the near-infrared (NIR) spectral range were studied using Monte Carlo simulation. The light-tissue interactions including scattering, absorption and anisotropy propagation of the regenerated autofluorescence photons in the skin tissue were taken into account in the theoretical modeling. Skin was represented as a turbid seven-layered medium. To facilitate the simulation, ex vivo NIR autofluorescence spectra and images from different skin layers were measured from frozen skin vertical sections to define the intrinsic fluorescence properties. Monte Carlo simulation was then used to study how the intrinsic fluorescence spectra were distorted by the tissue reabsorption and scattering during in vivo measurements. We found that the reconstructed model skin spectra were in good agreement with the measured in vivo skin spectra from the same anatomical site as the ex vivo tissue sections, demonstrating the usefulness of this modeling. We also found that difference exists over the melanin fluorescent wavelength range (880-910 nm) between the simulated spectrum and the measured in vivo skin spectrum from a different anatomical site. This difference suggests that melanin contents may affect in vivo skin autofluorescence properties, which deserves further investigation.     

Laser excited atomic fluorescence of some transition elements in the nitrons oxide-acetylene flame

A pulsed, tunable dye laser, pumped with a nitrogen laser is used to excite the atomic fluorescence of Sc, V, Hf, Nb, Os, Zr, W, Rh and Ru. Except in the case of Rh, the nitrous oxide-acetylene flame has been used. The results obtained for Zr and W are due to scattering of the laser radiation from unvaporized particles in the flame. Since, for most elements, several fluorescence lines of comparable intensity have been observed after the primary excitation process, the usefulness of observing non-resonance fluorescence is stressed, particularly with regard to the possibility of minimizing spectral interferences. The experimental results demonstrate that the limits of detection obtained with the dye laser source are comparable or better than the best atomic absorption limits only when the same primary absorption line used for the atomic absorption measurements can be used for exciting the fluorescence.     

EDXRF方法在测量含水Fe样中Fe含量的应用

介绍了能量色散X荧光分析方法在含水Fe样品测量中的应用。用ANTG 2000型海底X荧光探测系统对含Fe为10%～60%的Fe样进行测量,建立水分对Fe元素特征Kα射线影响的校正模型。结果表明,通过该模型校正,对含饱和水情况下Fe样品的分析相对误差小于4%,具有良好的分析效果。     

中性介质中中性红与双链DNA作用的光谱

通过分子吸收、荧光发射和共振光散射测定,表征了在水溶液介质中中性红(NR)与双 螺旋DNA的作用.在pH 7.63和离子强度低于0.01的水溶液介质中,随着NR与DNA的摩尔比(R)变 化,存在有两种结合方式.第一种结合方式发生在R > 2.22,此时获得共振光散射光谱增强信 号,表明NR在DNA分子表面发生聚集,集聚特性可使用RLS测定数据进行Scatchard分析;第二种 结合方式发生在R < 2.22,此时NR内嵌到DNA分子的双链碱基对之间,具有特征波长红移和分 子吸收增色效应,发生了从DNA到NR的分子能量转移,能观察到荧光增强.     

Absorption and scattering of light by Pt, Pd, Ag, and Au nanodisks: absolute cross sections and branching ratios

Localized surface plasmons (LSPs) of metallic nanoparticles decay either radiatively or via an electron-hole pair cascade. In this work, the authors have experimentally and theoretically explored the branching ratio of the radiative and nonradiative LSP decay channels for nanodisks of Ag, Au, Pt, and Pd, with diameters D ranging from 38 to 530 nm and height h=20 nm, supported on a fused silica substrate. The branching ratio for the two plasmon decay channels was obtained by measuring the absorption and scattering cross sections as a function of photon energy. The former was obtained from measured extinction and scattering coefficients, using an integrating sphere detector combined with particle density measurements obtained from scanning electron microscopy images of the nanoparticles. Partly angle-resolved measurements of the scattered light allowed the authors to clearly identify contributions from dipolar and higher plasmonic modes to the extinction, scattering, and absorption cross sections. Based on these experiments they find that absorption dominates the total scattering cross section in all the examined cases for small metallic nanodisks (D<100 nm). For D>100 nm absorption still dominates for Pt and Pd nanodisks, while scattering dominates for Au and Ag. A theoretical approach, where the metal disks are approximated as oblate spheroids, is used to account for the trends in the measured cross sections. The field problem is solved in the electrostatic limit. The spheroid is treated as an induced dipole for which the dipolar polarizability is calculated based on spheroid geometry and the (bulk) dielectric response function of the metal the spheroid consists of and the dielectric medium surrounding it. One might expect this model to be inappropriate for disks with D>100 nm since effects due to the retardation of the incoming field across the metallic nanodisk and contributions from higher plasmonic modes are neglected. However, this model describes quite well the energy dependence of the dipolar resonance, the full width at half maximum, and the total extinction cross section for all four metallic systems, even when 100相似文献   

Morphological change during crystallization of thin amorphous solid water films on Ru(0001)

The isothermal crystallization process of thin amorphous solid water (ASW) films on Ru(0001) has been investigated in real time by simultaneously employing helium atom scattering, infrared reflection absorption spectroscopy, and isothermal temperature-programmed desorption. The measurements reveal that the crystallization mechanism consists of random nucleation events in the bulk of the ASW films, followed by homogeneous growth. Morphological changes of the solid water film during crystallization expose the water monolayer just above the substrate to the vacuum during the crystallization process.     

五氯苯酚降解的超声诱导

人为或自然因素会导致挥发性或不挥发有毒有机物存在于饮用水中,这一现象 已成为国际上共同关心的问题。从长期对健康状况来说,即使不能辨别饮用水中的 味道和气味,但只要有十亿分之几毫克的有毒有机物存在,就足以使水不能饮用。 所以,废水处理刻不容缓。同废水处理相关的实验方法中,超声作为一种处理方法 ,早有报道,因为超声化学效应主要是空化,空化是自由基,特别是羟基自由基产 生的根源,而痉基自由基是强烈而非特殊的氧化物,它能迅速同水中化合物发生反 应。作者以五氯苯酚为模拟水样,分别用低频（16 kHz）和高频[（800 ± 1） kHz]以及其组合进行超声降解研究。研究表明复频降解效果最好,最差为低频。在 Fenton类试剂存在下,与Fenton类单独降解效果相比,复频则是它的20.93倍,高 频是它的4.9倍,低频与它几乎无变化。实验表明,频率组合对有机污染物的降解 是一条有效途径,但需要更进一步的研究。     

Process analysis of biofilms by photoacoustic spectroscopy

Biofilms are aggregates of microorganisms and biopolymers which occur at aqueous interfaces. Biofilms play an important role in the degradation of pollutants in natural water systems as well as in wastewater treatment plants. In this communication, the use of photoacoustic spectroscopy (PAS) as a new biofilm monitoring technique is presented. PAS combines features of optical spectroscopy and ultrasonic tomography and allows a depth-resolved analysis of optically and acoustically inhomogeneous media. For the first time, both biofilm and bulk liquid were monitored by photoacoustic sensor heads. In this way, sorption of suspended iron(III) oxide particles on the outer and inner surfaces of the biofilm could be observed on-line and in situ. Colloids can act as carriers of pollutants and influence stability and degradation efficiency of biofilms.     

Fluorescence analysis in air pollution research

Luminescence phenomena are of value in the analysis of air pollutants. The problems arising in the use of excitation and emission spectra under various conditions are discussed. Phenomena such as solvent, pH, and photochemical effects are shown to play an important role in the fluorimetric analysis of air pollutants. Many of the fluorimetric methods used in the trace analysis of organic airborne particulates involve factors such as direct measurement of the separated pollutant on a chromatogram or pherogram, quenching phenomena, scanning, excimer formation, charge-transfer fluorescence, sensitized fluorescence, and photo-oxidation on adsorbent or in solution. In addition, fluorescence assay methods are discussed in terms of selectivity, sensitivity, speed, simplicity, accuracy, precision, interferences, and the relation between concentration and fluorescence intensity.     

Absorption and fluorescence of single molecules

Simultaneous detection of single molecules by absorption and fluorescence is demonstrated using confocal microscopy at cryogenic temperature. Dynamical processes such as blinking and spectral jumping of single emitters are observed in both detection channels. The relative magnitude of fluorescence and absorption varies between molecules. In particular, we observe molecules that do not emit detectable Stokes-shifted fluorescence but show a strong absorption signal. The fact that coherent resonant scattering underlies the absorption process is demonstrated by a correlation between small linewidth and large absorption amplitude.     

In Line Monitoring of VAc-BuA Emulsion Polymerization Reaction in a Continuous Pulsed Sieve Plate Reactor using NIR Spectroscopy

Summary: This work deals with the in line and in situ monitoring of the changes in residual monomer concentrations and polymer particle size in the process of emulsion copolymerization of vinyl acetate (VAc) and butyl acrylate (BuA) over the sections of a novel tubular reactor (pulsed sieve plate continuous reactor, PSPC) using NIR spectroscopy. Off-line measurements (gas chromatographic, gravimetric and dynamic light scattering) were used as reference for the development of the multivariate PLS calibration model. All NIR spectra were on-line collected with an IFS 28/N Bruker spectrometer using a probe (transflectance mode) immersed into the reaction medium. The calibration model and validation data were analyzed using the OPUS/QUANT software. The results indicated that there exists a good agreement between values from the NIR calibration models and the off-line reference measured experimental data. Moreover, the on-line NIR can detect efficiently the occurrence of disturbances during the polymerization reaction, a useful tool for the improving the process safety.     

Retrospective analyses of atmospheric polycyclic and nitropolycyclic aromatic hydrocarbons in an industrial area of a western site of Japan.

Thirteen polycyclic aromatic hydrocarbons (PAHs) and four nitropolycyclic aromatic hydrocarbons (NPAHs) on the surfaces of airborne particulates, which were collected at an industrial area of a western site of Japan during periods from 1976 to 1998, were retrospectively analyzed. PAHs and NPAHs were extracted from airborne particulates using hexane with ultrasonication, and then analyzed by HPLC systems with fluorescence detection and chemiluminescence detection, respectively. The total concentrations (mean +/- SD, n = 34) were 15.54 +/- 21.24 ng/m3 for PAHs and 5.85 +/- 8.16 pg/m3 for NPAHs. The concentrations of PAHs and NPAHs were found to be highest during the period between 1979 and 1982, and then reduced. The annual concentrations of PAHs and NPAHs were highly correlated with those of air pollutants from motor vehicle origin, such as carbon monoxide, suspended particulates and non-methane hydrocarbons. The results suggested that motor vehicle emissions were one of the predominant sources of atmospheric PAHs and NPAHs.     

The identification of nitrated polycyclic aromatic hydrocarbons in diesel particulate extracts and their potential formation as artifacts during particulate collection

Summary The highly complex matrix of diesel particulate extracts was analyzed for nitrated polycyclic aromatic hydrocarbons (nitro-PAH) using fused-silica capillary-column gas chromatography along with a thermionic nitrogen-phosphorus detector (TID) and high-performance liquid chromatography followed by on-line catalytic reduction of the nitro-PAH to amino-PAH and subsequent fluorescence detection. Positive isomer identification and quantitation of nitro-PAH are from retention times of authentic standards and their mass spectra. The ease of nitro-PAH formation by nitration of PAH raises the question regarding the origin of these species, whether they are produced as “native” products during the engine combustion process and/or in the exhaust, or instead, formed as the result of chemical conversion to produce artifacts during the sampling procedure. This problem is assessed examing 1-nitropyrene-concentration in particulates of three light-duty diesel engines for different sampling times. 1-Nitropyrene concentrations show only a moderate increase with sampling time under average sampling conditions. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Dendrimer-tuned formation of luminescent organic microcrystals

Microcrystals of an organic fluorescent dye, 4-n-octylamino-7-nitrobenz-2-oxa-1,3-diazole (NBD-C8), were prepared by reprecipitation in water. The crystallization kinetics was monitored by UV/vis absorption spectroscopy, and a model was proposed. The size and shape of the microcrystals were analyzed by laser light scattering, fluorescence microscopy, and scanning electron microscopy. In the presence of PAMAM dendrimers of generation 2.5, 3.5, and 4.5, the crystallization process was drastically accelerated. The crystals obtained were smaller and more regular than those formed in pure water and were not agglomerated. There are probably two levels of interaction of NBD-C8 with the dendrimers, which act as both templates and colloid stabilizers.     

Effects of polymer aggregation and quencher size on amplified fluorescence quenching of conjugated polyelectrolytes

The fluorescence of conjugated polyelectrolytes (CPEs) is efficiently quenched by low concentrations of quenchers with opposite charges. We have reported the close correlation between this amplified quenching phenomenon and CPE chain aggregation. In this paper, we further demonstrate the profound correlation between the fluorescence quenching efficiency, CPE chain aggregation, and quencher molecular size. Aggregation of a poly(phenylene ethynylene)-type CPE (PPE-CO2-) is induced by the addition of either water or Ca2+ to methanol solution, as indicated by absorption, fluorescence, dynamic light scattering, and fluorescence microscope measurements. For quencher ions with a small molecular size, such as methyl viologen (MV2+), either the loose (induced by the addition of Ca2+) or the compact (induced by the addition of water) CPE chain aggregates are beneficial to the fluorescence quenching. For quencher ions with large molecular size, such as tris(4,7-diphenyl-1,10-phenanthroline)ruthenium (Ru(dpp)32+), however, the loose chain aggregates are found to be favorable for quenching, while the quenching efficiency is lower for the compact polymer aggregates present in aqueous solution.     

One-, two-, and three-photon absorption induced fluorescence of a novel chromophore in chloroform solution

One-, two-, and three-photon absorption induced fluorescence intensities of a novel nonlinear optical chromophore have been measured by using a tunable femtosecond pulsed laser as the excitation. Four resonance peaks are observed as the excitation wavelength is tuned from 600 to 2000 nm. These peaks correspond to the one-, two- and three-photon fluorescence resonance. Except for intensity difference, the lifetime and the fluorescence spectrum are found to be the same for the one-, two-, or three-photon resonance, hence suggesting that the same excited energy level is involved in emitting the fluorescence intensity. A three-level model is developed to account for the incident excitation laser intensity dependence of the one-photon and multiphoton fluorescence intensity. The model allows the multiphoton absorption cross sections to be extracted; it can also account for the deviation observed in the linear, square, and cubic intensity dependence of the one-, two-, and three-photon fluorescence intensity, respectively. To determine the absorption cross sections, the present method does not require the fluorescence quantum efficiency data, needed in the low intensity technique.     

Formation and degradation of poly(D,L-lactide) nanoparticles and their potential application as controllable releasing devices

In the presence of surfactant, water-insoluble poly(D,L-lactide) (PLA) was dispersed into narrowly distributed nanoparticles stable in water via microphase inversion. The structure and degradation of such formed nanoparticles were investigated by a combination of static and dynamic laser light scattering. Our results revealed that the degradation rate increased with the temperature and pH so that the degradation could be regulated from minutes to days. Using anionic sodium dodecyl sulfate (SDS) as stabilizer resulted in a slower degradation than using cationic hexadecyltrimethylammonium bromide (HTAB). The phthalocyanine chromophores (PC) could be encapsulated inside these PLA nanoparticles. The degradation of individual PLA nanoparticles led to a controllable releasing of PC. The absorption and fluorescence studies revealed a correlation between the degradation and the releasing of PC. Our results showed that a higher PC/PLA ratio could lead to a faster degradation.     

Hyper-Rayleigh scattering measurements of nonlinear optical chromophores at 1907 nm

Hyper-Rayleigh scattering measurements are performed on nonlinear optical chromophores using an excitation wavelength of 1907 nm. This wavelength is the longest that has yet been reported for the hyper-Rayleigh scattering experiment and allows measurements of the first hyperpolarizability of chromophores that are free of contributions from two-photon absorption induced fluorescence and reduces one and two photon resonance enhancement to a minimum. Using the 1907 nm setup we demonstrate good agreement between our results and those obtained with the electric field induced second harmonic generation (EFISHG) technique previously performed at this wavelength.