Adsorption of dicarboxylic acids onto nano‐structured silver surfaces – surface‐enhanced Raman scattering studies of pH‐dependent adsorption geometries

Understanding and shaping adsorption orientations of molecular compounds on nano‐structured metallic surfaces is an important issue across many areas of contemporary research including the design of nano‐structured surfaces and catalytic processes. Here, we used surface‐enhanced Raman spectroscopy to study these orientations on nano‐structured silver surfaces using dicarboxylic acids (maleic acid and fumaric acid) as model substances. Results revealed a clear pH dependence of the observed adsorption geometries of dicarboxylic acids correlating well with the dissociation states of the two acidic groups. Our data demonstrate the potential of the technique and contribute to an improved understanding of adsorption orientations of molecules at the interface between nano‐structured metal surfaces and a liquid phase. Copyright © 2012 John Wiley & Sons, Ltd.     

红外光谱结合二维相关分析研究堆肥过程腐殖酸演化规律

堆肥材料中腐殖酸的组成和结构直接影响堆肥产品品质和腐熟度。为研究堆肥腐殖酸的组成和形成过程,进行了生活垃圾堆肥并提取了不同堆肥阶段样品中的胡敏酸和富里酸,采用红外光谱和二维相关分析,探讨了堆肥过程胡敏酸、富里酸的组成、结构及随时间演化规律。红外光谱结果显示,堆肥胡敏酸组成复杂,在2 917～2 924,2 844～2 852,2 549,1 662,1 566,1 454,1 398,1 351,990～1 063,839,711 cm-1均出现了吸收峰;相对于胡敏酸,堆肥富里酸结构简单,仅在1 725,1 637,990 cm-1出现了吸收峰。上述吸收峰的出现表明堆肥胡敏酸和富里酸均含有木质素来源的苯环和糖类结构,但胡敏酸还含有丰富的脂族和蛋白类结构,这些在富里酸中含量较低;堆肥过程糖类、脂类、蛋白类及木质素结构均发生了降解,但是在胡敏酸和富里酸中它们的降解优先顺序不同。二维相关光谱分析结果表明,胡敏酸中降解先后顺序为脂肪类—蛋白类—多糖类和木质素,而富里酸中为蛋白质—多糖和脂肪类,降解过程均生成了羧酸、酮类和酯类结构,其中羧酸类物质一部分在堆肥中形成了碳酸盐。研究结果表明,红外光谱结合二维相关分析不仅可以获得堆肥腐殖酸官能团组成,还可以揭示堆肥过程这些官能团降解顺序,确定堆肥腐殖酸合成机制和动力学过程。     

Fabrication and Optimization of Poly(vinyl alcohol)/Zirconium Acetate Electrospun Nanofibers Using Taguchi Experimental Design

This paper presents an investigation regarding poly(vinyl alcohol)/zirconium acetate (organic–inorganic) (PVA/Zrace) nanofibers prepared by electrospinning which could be used as a precursor for fabricating ceramic metal oxide nanofibers. The effect of some processing variables, including polymer solution concentration, tip to collector distance and applied voltage of electrospinning, and the amount of Zrace and their interactions, on the diameter of the nanofibers were studied. Taguchi experimental design and a statistical analysis (ANOVA) were employed and the relationship between experimental conditions and yield levels determined. It was concluded that to obtain a narrow diameter distribution as well as maximum fiber fineness, a polymer concentration of 10 wt%, tip to collector distance of 18 cm and applied voltage of 20 kV variables were the optimum. Furthermore, it was also concluded that the ratio of Zrace (6 g) to PVA solution (10% wt) played an important role for achieving the minimum fiber diameter. Under these optimum conditions, the diameters of the electrospun composite fibers ranged from 86 nm to 381 nm with a diameter average of 193 nm. The experiments were done with Qualitek-4 software with “smaller is better” as the quality characteristics. The optimized conditions showed an improvement in the fibers diameter distribution and the average fibers diameter showed good resemblance with the result predicted using the Taguchi method and the Qualitek-4 software. The ANOVA results showed that all factors had significant effects on the fibers diameter and distribution, but the effect of PVA concentration and zirconium acetate were more significant than the other factors.     

Microwave-assisted digestion with a single reaction chamber for mineral fertilizer analysis by inductively coupled plasma optical emission spectrometry

A systematic approach is proposed to evaluate microwave-assisted digestion in a single reaction chamber for the simultaneous determination of elements in the mineral fertilizer and raw material by inductively coupled plasma optical emission spectrometry. A reference material was digested using 12 acid mixtures containing nitric, hydrochloric, orthophosphoric, hydrofluoric or boric acid. Principal components analysis was applied for data treatment. Three digestion procedures based on diluted acids exhibited the most accurate results, with relative errors for reference values ranging from ?15% to +?9%. Limits of quantification were in the range of 0.2?mg cadmium kg^?1 up to 1000?mg aluminum kg^?1.     

Relaxation dynamics and fragility during liquid–glass transitions of poly(propylene glycol)s

The acoustic and thermal properties of the liquid–glass transitions of propylene glycol and its oligomers, poly (propylene glycol)s, were studied by temperature modulated DSC and Brillouin scattering. The fragility indices were determined from Angell plots using the observed modulation frequency dependence of the complex heat capacity. The variation in the glass transition temperatures is discussed on the basis of the free volume theory. The relaxation time of the structural relaxation obeys the Vogel–Fulcher law, and its high frequency end is in good agreement with the result of the dielectric measurement in the literature. The correlation between the observed thermal expansion coefficients and the glass transition temperature is discussed based on the free volume theory. The sound velocity and attenuation were accurately determined as a function of the temperature by Brillouin scattering by combination with the refractive index measurement. The relaxation dynamics were discussed by considering the relaxation from segmental motions. All of these physical properties were discussed based on the third-order anharmonicity and the Grüneisen parameter.     

Preparation and characterization of poly(lactic acid)/poly(methyl methacrylate) blend tablets for application in quantitative analysis by micro Raman spectroscopy

Poly(lactic acid) (PLA) is a biodegradable polymer that has a variety of applications, one of which is as biomaterial in surgery or as functional layers on implants, due to its compatibility with living tissue. This paper reports the possibilities of quantification of poly(lactic acid) (PLA) in a polymer matrix such as poly(methyl methacrylate) (PMMA) by micro Raman spectroscopy (MRS). Blends of amorphous poly(DL‐lactic acid) with poly(methyl methacrylate) were prepared by the procedure of dissolution/precipitation. Thermal properties of the blends such as the glass transition temperature (Tg) were characterized by differential scanning calorimetry (DSC). The PLA/PMMA blends exhibited only a single glass transition region, indicating that this system is miscible. The PLA/PMMA system obeys the Gordon–Taylor equation (Tg versus PLA content). Various concentration ratios of PLA blends were prepared to use as a basis for quantitative analysis by MRS. Intensities of the characteristic bands at 813 cm⁻¹ (νCOC of PMMA) and 873 cm⁻¹ (νC―COO of PLA) were used for the calculation. The calibration graph showed a good linear correlation with an R² value of 0.9985. On the basis of the calibration curve obtained, the determined content of several PLA/PMMA blends was in good agreement when compared with nominal contents. The limit of detection (LOD) and quantification (LOQ) were calculated by the calibration data set as signal‐to‐noise method. The relative standard deviation of this method was lower than 10% and the accuracy better than 4%. This study demonstrated that Raman spectroscopy provides an alternative non destructive method for quantitative analysis of PLA in a PMMA matrix. Copyright © 2015 John Wiley & Sons, Ltd.     

Theoretical study of14N pure quadrupole resonance in amino acids

The theoretical hybridization model of Vega is adapted to the tetrahedral environment around the nitrogen nucleus in eleven amino acids to estimate the orbital occupation numbers using the experimental values of the quadrupole coupling constant and asymmetry parameter of¹⁴N quadrupole resonance and the results are discussed.     

高压结晶PET/PC共混体系中大尺寸聚合物伸直链晶体的形态观察

 大尺寸聚合物伸直链晶体在低维体系物理学的研究中具有不可替代的重要作用。但以往高压合成的聚合物伸直链晶体,尺寸较小且合成时间过长,使其作用至今未能显现。加入10%（质量分数）聚碳酸酯（PC）于聚对苯二甲酸乙二醇酯（PET）中,在研究PET/PC共混体系高压结晶行为的过程中快速合成了大量生长厚度超过100 μm 的聚合物伸直链晶体,并采用扫描电子显微镜对其进行了深入研究。研究表明,高压结晶PET/PC共混体系中存在不同类型的大尺寸伸直链晶体：完善的伸直链晶体、沿平行或垂直于C轴方向发生断裂的伸直链晶体、内聚能密度较大而发生内聚破裂的伸直链晶体、不同断裂方式下呈不同形态的楔形状伸直链晶体以及弯曲的伸直链晶体。同时对不同形态伸直链晶体的形成机理作了阐述。     

几种N-取代马来酰胺酸辅酶模型的核磁共振研究

我们对8种N-取代马来酰胺酸辅酶模型与不同类型的亲核试剂反应后生成的产物进行了¹H、¹³C NMR的研究, 测得¹H、¹³C谱化学位移,研 究探讨其规律性, 并测试了IR谱和元素分析.     

15N/14N Analysis of Amino Acids with GC-C-IRMS - Methodical Investigations and Ecotoxicological Applications

Abstract

In order to perform the ¹⁵N/¹⁴N analysis of amino acids using a gas chromatograph and isotope ratio mass spectrometer linked up via a combustion interface (GC-C-IRMS), the amino acids must be derivatized. Tert-butyldimethylsilylation is examined using various techniques (direct conversion to nitrogen gas, ConFlo-IRMS [1], GC-C-IRMS [2]) and subsequently applied to isotopic characterization of amino acids from wheat protein hydrolyzate obtained from plants exposed to ozone. The method provides a reliable tool for studying ecotoxicological effects on plants at a molecular level in addition to the investigation of the natural variations of different N fractions.