Solid-state NMR characterization of pyrene-cuticular matter interactions

One- and two-dimensional nuclear magnetic resonance (NMR) experiments were performed on Agave americana cutan and tomato cutin to examine the interactions between a hydrophobic pollutant, pyrene, and cuticular material. Variable-temperature NMR experiments show that cutan, an acid- and base-resistant cuticular biopolymer, undergoes the characteristic melting behavior of "polyethylene-like" crystallites, while the tomato cutin does not. The melting point of A. americana cutan was found to be approximately 360 K, which is consistent with the thickness of the polyethylene crystallites of 30-40 methylene units. Sorption models predict that the sorption behavior of hydrophobic pollutants should depend on the phase of the cuticular material. 13C NMR experiments on labeled pyrene were performed. The 13C T1 of pyrene decreases significantly from that of crystalline pyrene upon sorption to both tomato fruit cutin and A. americana cutan, indicating that the pyrene is mobile upon sorption. Magic angle spinning experiments at low spinning frequencies (2-4 kHz) provided the chemical shift anisotropy (CSA) parameters delta, the anisotropy, and eta, the asymmetry parameter, for crystalline and sorbed pyrene. For crystalline pyrene, two types of crystallographically distinctive pyrenes were observed. The first had delta = -97.4+/-0.5 ppm and eta = 0.934+/-0.006, while the second had delta = -98.1+/-0.5 ppm and eta = 0.823+/-0.008. After sorption to cutan, these CSA parameters were found to be delta = -78.9+/-5.3 ppm and eta < 0.70 independent of the length of time since completion of the sorption procedure. In tomato cutin, the CSA parameters were found to be dependent upon the time since completion of the sorption procedure. One and one-half months after sorption, delta was found to have a value of -30.4 ppm < delta < 0.0 ppm and eta was undeterminable, while after 22 months these values become delta = -80.0 +/-3.3 ppm and eta< 0.42. These changes in the CSA parameters demonstrate that upon sorption of pyrene to cutan, the pyrene undergoes anisotropic motion, while in cutin pyrene initially can tumble isotropically, but after 22 months this motion also becomes anisotropic. 2D heteronuclear correlation experiments indicate that pyrene is in close proximity to aliphatic cuticular materials after sorption. This work is directly relevant toward understanding the physical and chemical mechanisms of pollutant sorption to soil organic matter and, thus, help develop improved sorption models and pollution remediation techniques.     

超细涂料轧染染色工艺研究

在超细涂料液中加入阳离子改性剂，对纯棉织物进行轧染染色。探讨了改性剂、粘合剂浓度对超细涂料染色的影响。试验表明，与传统的焙烘方式相比，添加改性剂的超细涂料采用汽蒸固色，能提高织物的染色深度和鲜艳度，降低粘合剂用量；较佳的汽蒸条件为102℃×10min；染中深色时，改性剂和粘合剂的最佳用量分别为30g/L和15g/L。     

纳米科学创造崭新食品系统

<正> 美国食品科技学会第四届国际食品纳米科学会议展示纳米科学、工程、及工业之进步和应用纳米科学具有利于食品工业的潜力,其范围它包括从稳定和传送食物中生物活性物质到创造新抗菌食品包装质材。这些是列在去年食品科技年会上的议程里之主题,百余位食品科学专家参与讨论。     

Characterizing the interactions between trace metals and dissolved organic matter using excitation-emission matrix and parallel factor analysis

Natural dissolved organic matter (DOM) is composed of a variety of organic compounds, which can interact with metals in aquatic environments. The interactions between DOM and two metals of environmental concern (Cu(II) and Hg(II)) were studied using fluorescence quenching titrations combined with excitation-emission matrix (EEM) spectra and parallel factor analysis (PARAFAC). This allowed characterizing the specific interactions between eight fluorescent components in DOM and two metals. Triplicate titration experiments showed good reproducibility when assessing the interactions between humic-like components with Cu(ll). Our data show clear differences in metal-DOM interaction for samples of different DOM composition and between two different metals. The results demonstrate that the combination of fluorescence quenching titrations with EEM-PARAFAC was reproducible and sensitive to determine the binding properties of humic-like components with trace metals. The enhancement in fluorescence intensity after its initial decrease for the protein-like components with addition of Cu(II) was observed at mangrove-dominated sites, suggesting changes in the molecular environments of protein-like components due to increased Cu(II) interaction. The application of EEM-PARAFAC in fluorescence quenching studies is a useful tool to evaluate intermolecular DOM and DOM-trace metals interactions.     

纳米级食品保鲜膜的研究进展

纳米技术的迅速发展为食品保鲜领域提供了一种新方法,近年来纳米级食品保鲜膜成为国内外科研人员研究热点。本文介绍纳米级聚烯烃基膜和纳米级可食性膜的最新研究进展,并对纳米级食品保鲜膜的前景进行展望。     

Quantification of solute-solute interactions using negligible-depletion solid-phase microextraction: measuring the affinity of estradiol to bulk organic matter

The interaction of trace organic contaminants with bulk organic matter has implications for the transport and behavior of organic trace contaminants within the aquatic environment as well as water and wastewater treatment processes. Partition coefficients (K(OM)) of the steroidal trace organic contaminant estradiol were quantified for environmentally relevant concentrations of bulk organic matter (12.5 mg C/L) using a full mass balance form of solid-phase microextraction (SPME). The results indicated that the method is successful and can be used at environmental concentrations. Estradiol had the greatest affinity for bulk organic matter that contained phenolic and benzoic acid ester groups, namely tannic acid, compared to organics containing predominately carboxylic functional groups. The solution chemistry (pH) was found to influence the interaction, as estradiol had a lower affinity for negatively charged and hydrophilic bulk organic matter. The partition coefficients determined using SPMEwere consistentwith partition coefficients derived using solubility enhancement and fluorescence quenching measurements, confirming that SPME is a powerful technique to quantify the affinity of estradiol for low concentrations of bulk organic matter and trace contaminants. Further, this novel method can be applied to a range of trace contaminants.     

Evaluation of fluorescence quenching for assessing the importance of interactions between nonpolar organic pollutants and dissolved organic matter

The assumptions behind the fluorescence quenching (FQ) method were thoroughly evaluated to assess its potential for quickly and accurately assessing the importance of hydrophobic organic contaminant-macromolecular organic carbon interactions in aquatic systems. Perylene was used as the probe molecule to avoid problems encountered with other fluorescent probes. Results from a wide range of wetland samples suggest that static quenching dominates, that other quenchers do not interfere with analyses, and that full quenching on sorption does not occur for all samples. The latter result indicates that the quantum yield of the sorbed probe must be accounted for in quantifying the magnitude of Kmoc values by FQ. Observed Kmoc values compared favorably with those measured by the solubility enhancement method. Overall, our results suggest that FQ can be used as a quick and reliable screening tool as long as precautions are taken to ensure the validity of the results.     

Recent advances in the analysis of dairy product quality using methods based on the interactions of light with matter

As demonstrated by physicists in the past centuries, light interacting with matter contains information that may reveal the concentration or/and the structure of components of the investigated matter. The use of spectroscopy (absorption in the visible, infrared, fluorescence, Raman, etc.) in food science has increased tremendously in the last couple of decades as it has been demonstrated that the detection and content of a number of food constituents, as well measurement of food properties, may be achieved by measuring the radiations that is either absorbed or emitted at different wavelengths by the product. These developments have been made possible, thanks to multivariate chemometric methods that are appropriate and useful for the evaluation of fluorescence or infrared spectra exhibiting slight differences such as the ones recorded on dairy products, allowing the development of prediction models. Recently, imaging technology such as confocal laser scanning microscopy or hyperspectral imaging coupled to image analysis techniques has successfully been used to study highly heterogeneous products such as cheese. Indeed, image analysis techniques such as mathematical morphology or image texture analysis make it possible to quantify structures in the images and to show the influence of different manufacturing processes on the protein network microstructure of cheeses. The aim of this article is to summarise those aspects of spectroscopy and imaging methods that may have value for solving problems in dairy science and technology.     

Fate of prions in soil: interactions of RecPrP with organic matter of soil aggregates as revealed by LTA-PAS

The contribution of soil organic matter (OM) to the adsorption of a recombinant prion protein (RecPrP) was studied in microcosm systems (soil aggregates from two different soils) before and after OM removal by low temperature ashing (LTA). The LTA technique allows a controlled removal of OM layer by layer, like a peeling of an onion skin, with minimal disturbance of the mineral matrix. Soil aggregates were selected as a representative model of the "in situ" conditions. Adsorption from batch vs percolation experiments were compared, and the aggregates were characterized by photoacustic Fourier-transform IR spectroscopy (PAS-FTIR). High affinity (H-type) adsorption isotherms were found with complete removal of RecPrP from solution for protein/soil ratios up to 1:62.5. OM removal from aggregates decreased the adsorbed RecPrP in amounts corresponding to 330-1000 microg mg(-1) of soil organic carbon (OC) indicating that native OM has specific adsorption capacity comparable and/or superior to the mineral matrix. The coupled LTA-PAS-FTIR approach demonstrated that, albeit OM composition was homogeneous throughout the aggregates, its presence in the most external surfaces of the aggregates affects the diffusion dynamics of RecPrP within the aggregates during percolation.     

MIL系列铁基金属-有机骨架在表面增强拉曼光谱中的应用

近年来研究者们将铁基金属有机骨架与等离激元纳米粒子(plasmonic- nanostructures/nanoparticles,NPs)联合应用于表面增强拉曼光谱(Surface-enhanced Raman spectroscopy,SERS)检测中,实现了特定成分检测和检测后产物的无害化处理。本文介绍了MIL系列Fe-MOFs在SERS中应用的最新进展,讨论了在Fe-MOFs表面修饰锚定NPs、在Fe-MOFs内部嵌入NPs以及在NPs周围自行组装Fe-MOFs的制备方法。其次,介绍了当前Fe-MOFs材料在SERS检测领域中的研究进展,以及基于Fe-MOFs的SERS技术的相关应用。最后,讨论了目前NPs@Fe-MOFs复合SERS基底亟待解决的问题,并对未来的应用领域和发展前景进行了展望。     

Investigating the molecular interactions of oxytetracycline in clay and organic matter: insights on factors affecting its mobility in soil

The interactions of oxytetracycline with model clay adsorbents were investigated as a function of suspension pH. The clay adsorbents used were native montmorillonite (SWy-2), Na-montmorillonite (Na-SWy-2), and hexadecyl trimethylammonium-montmorillonite (HDTMA-montmorillonite). The adsorption of oxytetracycline to the clay could be described by Freundlich-type adsorption isotherms. It was observed that the adsorption of oxytetracycline in the native and sodium forms of montmorillonite decreases with increasing pH in the order pH 1.5 > 5.0 > 8.7 > 11.0. This trend is consistent with cationic exchange interactions that are dominant at lower pH values when oxytetracycline has a net positive charge. On the other hand, hydrophobic interactions when oxytetracycline is zwitterionic (at pH 5.0) are predominant over other mechanisms, as evident from the FT-IR spectrum of the HDTMA-montmorillonite and humic acid-montmorillonite adsorbed with oxytetracycline. The presence of a large amount of dissolved organic matter (DOM) was also found to decrease the sorption of oxytetracycline to clay, suggesting that DOM may increase its mobility in the natural environment. Several mechanisms of interaction of oxytetracycline in clay are proposed based on the adsorption isotherms and the results from X-ray diffraction (XRD) and Fourier transform-infrared (FT-IR) analyses.