近红外光谱用于低温水结构的分析

采用近红外光谱分析并结合拉曼光谱和分子动力学模拟研究了二甲基亚砜(DMSO)-水混合物中水在低温时的结构,对DMSO降低水冰点的机理进行了讨论.通过对不同DMSO含量混合物的近红外和拉曼光谱分析,发现了DMSO与水相互作用的光谱信息,表明DMSO与水在混合物中主要以摩尔比1∶2和2∶1的氢键结构(DW2和D2W)的形式存在,结构形式主要取决于DMSO和水在混合物中的比例.通过对水和30%(摩尔分数)DMSO-水混合物的温控近红外光谱分析,发现DW2结构抑制四面体水结构的形成是混合物冰点降低的主要原因.采用分子动力学模拟对DMSO-水混合物体系进行的模拟进一步证明了结论的可靠性.     

温控近红外光谱用于葡萄糖的高灵敏检测

温控近红外光谱在混合体系定量分析以及分子间相互作用分析中已得到应用.本工作利用互因子分析方法(MFA)探索了温控近红外光谱技术测定血清样品中低浓度葡萄糖含量的可行性.测量了不同温度下葡萄糖含量分别为1.0～15.0 mmol/L和0.0～1.0 mmol/L的两组血清溶液的近红外光谱,并利用MFA进行了定量计算.结果表明,利用该方法可以实现样品中微量葡萄糖的准确定量,MFA提取的标准信号(SS)的相对强度和葡萄糖浓度之间的线性相关系数R分别为0.9923和0.9895,预测均方根误差(RMSEP)分别为0.35和0.07 mmol/L.     

近红外光谱分析中的化学计量学算法研究新进展

近红外光谱是一种绿色、快捷的分析技术,在科学研究、工业生产以及日常检测中得到广泛应用。化学计量学算法的应用在近红外光谱技术的发展过程中发挥了重要作用。化学计量学方法通过寻找测量变量之间的相关性,构建数学模型,量化样本间的差异性,并发现事物变化的内在规律,实现较合理准确的未知预测。这也是"大数据"战略的重要环节和主旨所在。该文针对近红外光谱吸收信号较弱、谱峰重叠严重,以及光谱测量过程中易受背景、噪声、无信息变量和外界环境因素干扰等,导致借助化学计量学方法建立的光谱与研究目标的定性定量分析模型变差问题,总结了近年来在近红外光谱领域所提出的一些化学计量学新方法,包括光谱预处理、变量选择、多元校正和模型转移,从不同角度阐述了这些方法在消除近红外光谱模型的干扰因素,提高模型的可靠性、预测准确性和适用性等方面的作用。     

近红外光谱用于低共熔溶剂中水结构的分析

采用近红外光谱技术研究了含水量(摩尔分数)在5%～95%范围内水结构对低共熔溶剂(DESs)的氢键网络结构的影响.通过分析氯化胆碱与尿素混合后不同时间的近红外光谱,发现了尿素—NH基团与氯化胆碱Cl^-相互作用的光谱信息,表明DESs熔点降低的原因主要是NH···Cl^-氢键的形成.通过分析不同含水量的DESs-水混合物的近红外光谱,发现了水分子之间以及水分子与尿素中—NH和C=O基团相互作用的光谱信息,表明水在DESs中主要以3种结构存在:类大体积水、与尿素C=O键合的水以及—NH分子间的桥连水.类大体积水破坏DESs中NH···Cl^-,使体系的稳定性降低,而尿素—NH分子间的桥连水和与C=O键合的水使体系的稳定性增加.DESs中3种水结构的相对比例与含水量有关,含水量在40%～80%既能有效降低体系的黏度,又能维持DESs的性质.     

近红外光谱结合新型模型传递方法用于糖料的在线质量监控

当采用近红外光谱技术对糖香料的生产过程进行在线质量监控时,糖香料的温度变化严重影响近红外光谱校正模型的预测性能,使其对糖浆样本中主要成分预测结果的平均均方根误差从2.4%增大到29.2%。本研究将近红外光谱技术与载荷空间标准化新型模型传递方法相结合,有效消除了温度变化对近红外光谱校正模型定量分析结果的影响,使其对糖浆样本中主要成分预测结果的平均均方根误差维持在3.8%的水平,实现了利用近红外光谱技术对糖香料的质量进行快速准确的监测和控制。本研究的研究结果为糖料的配制和使用提供了技术保障。     

直链烷烃近红外光谱的温度效应与应用研究

近红外光谱的温度效应已得到关注,在结构分析和定量分析方面得到了尝试.以直链烷烃为例,对烷烃有机体系近红外光谱的温度效应进行了研究.采集了20~60℃范围内五种直链烷烃(正己烷到正癸烷)及其混合物的近红外光谱并进行了对比分析,仅发现某些谱峰的强度随温度发生微小变化.采用交替三线性分解算法对光谱数据进行了解析,考察了光谱的特征以及随温度和结构的变化.结果表明,链端C₂H₅和链中CH₂基团的光谱受温度的影响不同,但其光谱信号的强度与温度之间都具有良好的线性关系,可根据光谱预测体系的温度;两种基团的光谱信号强度与烷烃分子的碳数或两种基团在分子中相对含量都具有良好的线性关系,可用于直链烷烃混合物组成的估算.     

近红外光谱在无机微量成分分析中的应用

由于近红外光谱的独特优势, 在实际复杂样品分析中发挥了重要作用. 但由于近红外光谱的信号相对较弱, 无机离子在近红外光谱中一般没有响应, 因此难以用于微量成分特别是无机微量组分的测定. 总结了近红外光谱技术在环境、土壤、植物及生物样品分析中的应用, 说明了近红外光谱用于无机微量成分分析的原理. 由于近红外光谱技术一般通过多元校正方法进行定性定量分析, 利用组分间的相互作用或组分含量之间的相关性可以实现微量组分或无光谱响应组分的定量分析. 还总结了富集技术在近红外光谱分析中的应用, 利用富集技术可实现稀溶液中金属离子含量的快速测定, 并可以改善分析的灵敏度和检测限.     

大豆蛋白的中红外和近红外光谱研究*

大豆蛋白在各领域的应用已得到广泛的关注,因此大豆蛋白及其改性材料在结构性能方面的研究显得越来越重要。中红外光谱(mid-infrared spectroscopy,MIR)和近红外光谱(near-infrared spectroscopy,NIR)正是对蛋白质进行定性定量分析的有力手段。中红外光谱可以有效地分析大豆蛋白在溶液和薄膜中的二级结构以及大豆衍生材料内蛋白质的结构变化情况。近红外光谱则在蛋白质定量分析方面有着独特的优势。本文介绍了运用这两种光谱技术进行研究的一些工作,这些实例表明了中红外和近红外光谱在大豆蛋白研究领域的重要应用价值。     

基于近红外光谱技术的内燃机油鉴别研究

针对常规近红外光谱技术测试内燃机油时光谱信号响应低,对大分子基团分辨率不高,以及光谱信息与其结构组成之间存在非线性关系等难点,提出了一种基于电压为外扰方式的内燃机油二维近红外光谱测试技术,介绍了近红外光谱具有分形的特征.运用小波变换将近红外光谱分解至不同分辨尺度,然后计算各尺度分量的分形维数(盒维数),用近红外光谱的小波基分形参量替代近红外光谱的采样值.计算结果表明,在不同小波基和不同分解尺度下,内燃机油近红外光谱具有不同的盒维数,得到了近红外光谱在分形意义下的特征信息.以美孚、埃索和壳牌3种内燃机油品种鉴别分类问题为实例,比较研究了近红外光谱采样值与小波基分形参量,K近邻法的交互验证计算结果表明,小波基分形参量的分类效果优于近红外光谱采样值.采用近红外光谱技术测试内燃机油的结构组成信息是可行的.     

近红外光谱在蛋白质和含酰胺基团聚合物研究中的应用*

近红外光谱(near-infrared spectroscopy,NIR)是一种常用的无损表征手段,但谱带强度弱、交叠情况严重等缺点局限了它的应用范围。本文介绍了几种常见的改善近红外光谱技术不足的方法,如二阶导数法、二维相关光谱法和化学计量法等,并举例阐述了近红外光谱在蛋白质和含酰胺基团聚合物的结构和含量等方面的应用。这些方法对近红外光谱的定性定量分析起了很好的辅助作用,有效地拓宽了近红外光谱技术的应用领域。     

Chemometrics: An Excavator in Temperature-Dependent Near-Infrared Spectroscopy

Temperature-dependent near-infrared (NIR) spectroscopy has been developed and taken as a powerful technique for analyzing the structure of water and the interactions in aqueous systems. Due to the overlapping of the peaks in NIR spectra, it is difficult to obtain the spectral features showing the structures and interactions. Chemometrics, therefore, is adopted to improve the spectral resolution and extract spectral information from the temperature-dependent NIR spectra for structural and quantitative analysis. In this review, works on chemometric studies for analyzing temperature-dependent NIR spectra were summarized. The temperature-induced spectral features of water structures can be extracted from the spectra with the help of chemometrics. Using the spectral variation of water with the temperature, the structural changes of small molecules, proteins, thermo-responsive polymers, and their interactions with water in aqueous solutions can be demonstrated. Furthermore, quantitative models between the spectra and the temperature or concentration can be established using the spectral variations of water and applied to determine the compositions in aqueous mixtures.     

Tautomerization equilibria in aqueous micellar solutions: a spectrophotometric and factor-analytical study

The keto-enol equilibria of benzoylacetone (BZA) as a model for 1,3-dicarbonyl compounds are studied in aqueous acid and cationic micellar solution. Evolving factor analysis (EFA), multivariate curve resolution-alternating least-squares (MCR-ALS), and rank annihilation factor analysis (RAFA) are used for complete resolving of measured spectrophotometric data. The acidity constants of the enolic, KaE, and ketonic, KaK, forms of BZA and also the tautomerization constant, Kt, and its related thermodynamic parameters have been determined by using EFA and MCR-ALS methods and spectral variation of BZA solutions in various pHs and temperatures. The concentration and spectral profiles of all species were calculated without any assumption about chemical models. The spectral variation of BZA solutions as a function of cationic micelle concentration sufficiently beyond its critical micelle concentration is analyzed according to the partition model for distribution between water and micellar pseudo-phase and RAFA. The outputs of using RAFA on measured rank deficient data are the spectrum of enolic form in the micellar pseudo-phase, free from contribution of the enolic form in the aqueous phase, the partition coefficient of enolic form, KdE, between the micelle and water phases, and the tautomerization constant in the micellar pseudo-phase, Ktm.     

Sorption of Nickel Ions from Aqueous Solutions by Ion Exchangers

Sorption of Ni²⁺ions from aqueous solutions by ion exchangers differed in their chemical nature and structure was studied. Based on the endothermic curves of ice melting obtained by a differential scanning calorimetry, the amounts of freezing and non-freezing water present in free volumes (pores) of the studied ion exchangers were calculated. Comparison of results obtained from the kinetic curves of nickel ion sorption with data on differential scanning calorimetry indicates a role of structural factor in the sorption of nickel ions. It was found that, depending on the total amount of freezing and non-freezing water, the KU-2-8 sulfonated cationite is the most preferable ion exchanger for the sorption of nickel ions from aqueous solutions. Therefore, sorbent efficiency in this case is determined by its structure rather than by chemical nature.     

Aqueous solvation of amphiphilic solutes: concentration and temperature dependent study of the ultrafast polarisability relaxation dynamics

An understanding of the influence of hydrophilic and hydrophobic interactions on the dynamics of solvating water molecules is important in a diverse range of phenomena. The polarisability anisotropy relaxation dynamics of aqueous solutions of the amphiphiles TBA (t-butyl alcohol) and TMAO (trimethylamine N-oxide) have been measured as a function of concentration and temperature. TMAO is shown to have a greater effect on the picosecond relaxation dynamics of water than TBA. This result is consistent with hydrophilic interactions being mainly responsible for the slowing down the polarisability relaxation in aqueous solutions. The room temperature Raman spectral densities of the two solutions are remarkably similar to that of bulk water, an effect which is tentatively ascribed to the formation of nanoscale structure in the solutions, allowing the formation of bulk-like water pools. The temperature dependent spectral density of TMAO remains similar to that of bulk water at all temperatures, while that for TBA shows a marked decrease in the amplitude of the response usually ascribed to a water-water stretch with increasing temperature. This is discussed in terms of the temperature dependent structure of TBA aggregates in solution.     

A comparative study on the aggregate formation of two oxazine dyes in aqueous and aqueous urea solutions

The visible absorption spectra of two oxazine dyes, brilliant cresyl blue and nile blue, in aqueous and aqueous urea solutions (0.01-1 M) were studied as a function of the dye concentration. Due to structural similarity of the investigated dyes, their spectral features were compared. The dimerization behavior of the dyes in water with or without urea was analyzed in terms of monomer-dimer equilibrium. The nature and structure of the interacting pairs for these dyes were discussed using the exciton theory. The dimerization constant values of the dyes in aqueous and aqueous urea solutions were calculated. For both the dyes in aqueous urea solutions, a reduction in dimer formation was observed. The excitonic parameters were compared with those of oxazine-1, which is structurally similar to the investigated dyes.     

Thermal degradation of polyaniline films prepared in solutions of strong and weak acids and in water - FTIR and Raman spectroscopic studies

Polyaniline (PANI) films were prepared in situ on silicon windows during the oxidation of aniline with ammonium peroxydisulfate in aqueous solutions of strong (0.1 M sulfuric) or weak (0.4 M acetic) acid or without any acid. In solutions of sulfuric acid, a granular PANI is produced, in solutions of weak acids or without any acid, PANI nanotubes are obtained. The thermal stability and structural variation of the corresponding films produced on silicon windows during treatment at 80 °C for three months were studied by FTIR and Raman spectroscopies. The morphology of the films is preserved during the degradation but the molecular structure changes. The results indicate that the spectral changes correspond to deprotonation, oxidation and chemical crosslinking reactions. The films of PANI salts loose their protonating acid. PANI bases are more stable than the salt forms during thermal ageing. The films obtained in water or in the presence of acetic acid are more stable than those prepared in solutions of sulfuric acid. The protonated structure is more prone to crosslinking reactions than deprotonated one. The molecular structure corresponding to the nanotubular morphology, which contains the crosslinked phenazine- and oxazine-like groups, is more stable than the molecular structure of the granular morphology.     

The Hydrophobic Effects: Our Current Understanding

Hydrophobic interactions are involved in and believed to be the fundamental driving force of many chemical and biological phenomena in aqueous environments. This review focuses on our current understanding on hydrophobic effects. As a solute is embedded into water, the interface appears between solute and water, which mainly affects the structure of interfacial water (the topmost water layer at the solute/water interface). From our recent structural studies on water and air-water interface, hydration free energy is derived and utilized to investigate the origin of hydrophobic interactions. It is found that hydration free energy depends on the size of solute. With increasing the solute size, it is reasonably divided into initial and hydrophobic solvation processes, and various dissolved behaviors of the solutes are expected in different solvation processes, such as dispersed and accumulated distributions in solutions. Regarding the origin of hydrophobic effects, it is ascribed to the structural competition between the hydrogen bondings of interfacial and bulk water. This can be applied to understand the characteristics of hydrophobic interactions, such as the dependence of hydrophobic interactions on solute size (or concentrations), the directional natures of hydrophobic interactions, and temperature effects on hydrophobic interactions.     

A kinematic approach to ionic transport in aqueous electrolyte solutions and structural theory of hydration of alkali metal ions

While considering the self-diffusion processes in aqueous electrolyte solutions, transport of ions, not only by jumps of single ions, but also by jumps of their solvation shells, are to be taken into account. Samoilov estimated the relative number of the two kinds of ionic jumps from experimental data on diffusion assuming an approximately uniform value for the α factor. In the present paper entirely different theory of the α factor based on the structural hydration model of one of the authors (S.V.T.) for alkali metal ions is given and its ion-wise values are calculated at different temperatures. The theory not only dispenses with the approximate fixation of α but also throws light on the structure of water, formation of clusters and their population variation with temperature.     

The structure of water in polymer systems as revealed by Raman spectroscopy

A review on the structure of water in aqueous polymer systems as revealed by Raman spectroscopy is presented. Various interpretations and analysis procedures for Raman bands of liquid water which have been proposed are introduced. The structure and hydrogen-bonding properties of water which exist in aqueous polymer solutions and gels are described. Effects of chemical properties of polymer chains and size of water domains surrounded by polymer chains on the structure of water are discussed.     

1,2-丙二醇水溶液玻璃化转变与结构松弛

为了考察水含量对1, 2-丙二醇水溶液玻璃化转变和结构松弛参数的影响, 用差示扫描量热法(DSC), 测量了5种高浓度1, 2-丙二醇水溶液(60%、70%、80%、90%、100%, w)玻璃化转变区域的表观比热容. 用5种降温速率(1、2、5、10、20 K·min-1)和10 K·min-1的升温速率获得玻璃化转变的相关参数. 玻璃化转变温度分析结果表明, 虽然水含量增加能从总体上降低体系的玻璃化转变温度, 但与纯羟基类多元醇相比, 水对1, 2-丙二醇的增塑作用并不显著. 结构松弛活化能计算结果表明, 体系水含量的增加能明显降低结构松弛活化能. 脆度分析结果表明, 随着体系水含量增加, 动力学脆度逐渐降低, 但热力学脆度是先升高后降低, 在80%左右达到最大值. 结构松弛协同重排域计算结果表明, 当浓度由60%增加至100%时, 玻璃化转变特征长度由2.79 nm增加至3.57 nm.