Generalized two-dimensional correlation spectroscopy——Theory and applications in analytical field

Since the theory of generalized two-dimensional (2-D) correlation spectroscopy was proposed, it has been keenly concerned in scientific research and its analytical method has been widely applied in various analytical fields. The mathematical process to construct generalized 2-D correlation spectroscopy and the physical meaning of 2-D correlation spectral map are described, and three examples in the fields of chemical analysis and molecular biology are provided, such as the component analysis of organic solvent, the analysis of biological molecules in the solvent with different pH values and structural analysis of protein. The theory and analytical method of generalized 2-D correlation spectroscopy are also detailedly commented.

Application of Two-Dimensional Correlation UV-Vis Spectroscopy in Chinese Liquor Moutai Discrimination

Chinese liquor Moutai is the “National alcoholic drink” in China and plays a very important role of social activities in Chinese people’s life. In pursuit of high profits, some illegal counterfeit Moutai liquors have begun to appear in the market. Therefore, it is an urgent need for new techniques to discriminate the genuine and counterfeit Moutai liquor. In this work, the conventional Ultraviolet-Visible (UV-Vis) spectroscopy and two-dimensional correlation UV-Vis spectroscopy are applied to obtain the UV-Vis characteristic of Moutai liquor and counterfeit one, respectively. The experimental results reveal that the conventional UV-Vis spectra of the genuine and counterfeit Moutai liquor are similar. However, the two-dimensional correlation UV-Vis spectra of them are different and this method would be applied to differentiate the counterfeit Moutai liquor from the genuine Moutai liquor. Compared with conventional methods, this novel method has the advantages of easy operation, simple instrumentation and direct recognition, which make it a potential tool in the fields of food safety.

Structure and Two-dimensional Correlation Infrared Spectroscopy Study of a New One-dimensional Chain Compound: (4,4’-Hbpy)_3[NaMo_8O_(26)](4,4’- bpy)_2(H_2O)_4 (bpy = Bipydine)

A novel compound, （4,4＇-Hbpy）3[NaMo8O26]（4,4＇-bpy）2（H2O）4 1 （bpy=bipydine）, was synthesized by the hydrothermal method. Single-crystal X-ray diffraction shows that compound 1 belongs to the monoclinic system, space group C2/m with a=19.1921（5）, b=18.6931（6）, c=9.3821（3） A° β=104.8020（11）°, V=3254.22（17）A°^3 C50H51Mo8N10NaO30, Mr=2062.52, Z=2, F（000）=2016, μ=1.591 mm^-1 and Dc=2.105 g/cm^3. The final R=0.0283 and wR=0.0912 for 3118 observed reflections （I〉20（I））. Compound 1 contains the β-[Mo8O26]^4-anion, sodium ion, 4,4＇-bpy and lattice crystalline water molecules. The β-[MosO26] units link the sodium ion to form a chain structure. The infinitechains of [Na（Mo8O26）]^3- blocks are surrounded by protonized 4,4＇-bpy cations, 4,4＇-bpy and lattice crystalline water molecules. The 2D-IR correlation spectroscopy study indicates that the stretching vibrations of Mo=O occur more preferentially due to the thermal effect. The TGA analysis shows that compound 1 has high thermal stability.

Evolution of Two-Dimensional Correlation Spectroscopy

A number of useful techniques associated with two-dimensional correlation spectroscopy(2DCOS)to improve its performance and utility have been developed in the last 30years.Evolution of these 2DCOS techniques,including some of the very recent developments,is reviewed with examples.Topics include merged or modified asynchronous 2Dcorrelation spectrum,two-dimensional codistribution spectroscopy(2DCDS),Pareto scaling,and null-space projection treatment of spectral dataset.

Study on the Hydrogen Bond Interaction Between Soy Protein Isolate and Glycerol Using Two-Dimensional Correlation Fourier-Transform Infrared Spectroscopy

A series of soy protein isolate(SPI)films plasticized by glycerol(Gly)were studied using attenuated total reflectance-Fourier transform infrared spectroscopy(ATR/FTIR).Perturbation-correlation movingwindow two-dimensional(PCMW2D)and two-dimensional correlation(2DCOS)analyses were applied to the amideⅠband and thus the hydrogen bond interaction between SPI and Gly was systematically investigated.When Gly concentrations were in the range 0~35%,the hydrogen bond amongβ-sheets was replaced by the one between SPI chain and Gly molecule,which caused these protein chains being changed toα-helix.However,the transformation ofβ-sheet toα-helix was saturated and both of them tend to change to random coil when Gly concentrations were in the range 35%~60%.

Generalized two-dimensional correlation near-infrared spectroscopy and principal component analysis of the structures of methanol and ethanol

Liquid state methanol and ethanol under different temperatures have been investigated by FT-NIR(Fourier transform nearinfrared) spectroscopy,generalized two-dimensional(2D) correlation spectroscopy,and PCA(principal component analysis) . First,the FT-NIR spectra were measured over a temperature range of 30-64(or 30-71) °C,and then the 2D correlation spectra were computed.Combining near-infrared spectroscopy,generalized 2D correlation spectroscopy,and references,we analyzed the molecular structures(especially the hydrogen bond) of methanol and ethanol,and performed the NIR band assignments. The PCA method was employed to verify the results of the 2D analysis.This study will be helpful to the understanding of these reagents.

Spectral Insights into Microdynamics of Thermoresponsive Polymers from the Perspective of Two-dimensional Correlation Spectroscopy

Generalized two-dimensional correlation spectroscopy （2DCOS） and its derivate technique, perturbation correlation moving window （PCMW）, have found great potential in studying a series of physico-chemical phenomena in stimuli-responsive polymeric systems. By spreading peaks along a second dimension, 2DCOS can significantly enhance spectral resolution and discern the sequence of group dynamics applicable to various external perturbation-induced spectroscopic changes, especially in infrared （IR）, near-infrared （NIR） and Raman spectroscopy. On the basis of 2DCOS synchronous power spectra changing, PCMW proves to be a powerful tool to monitor complicated spectral variations and to find transition points and ranges. This article reviews the recent work of our research group in the application of 2DCOS and PCMW in thermoresponsive polymers, mainly focused on liquid crystalline polymers and lower critical solution temperature （LCST）-type polymers. Details of group motions and chain conformational changes upon temperature perturbation can thus be elucidated at the molecular level, which contribute to the understanding of their phase transition nature.

Recent developments in two-dimensional (2D) correlation spectroscopy

Recent noteworthy developments in the field of two-dimensional（2D） correlation spectroscopy are reviewed.2D correlation spectroscopy has become a very popular tool due to its versatility and relative ease of use.The technique utilizes a spectroscopic or other analytical probe from a number of selections for a broad range of sample systems by employing different types of external perturbations to induce systematic variations in intensities of spectra.Such spectral intensity variations are then converted into2 D spectra by a form of correlation analysis for subsequent interpretation.Many different types of 2D correlation approaches have been proposed.In particular,2D hetero-correlation and multiple perturbation correlation analyses,including orthogonal sample design scheme,are discussed in this review.Additional references to other important developments in the field of 2D correlation spectroscopy,such as projection correlation and codistribution analysis,were also provided.

Two-dimensional correlation spectroscopic analysis on the interaction between humic acids and aluminum coagulant

In this study, two-dimensional correlation spectroscopy integrated with synchronous fluorescence and infrared absorption spectroscopy was employed to investigate the interaction between humic acids and aluminum coagulant at slightly acidic and neutral p H. Higher fluorescence quenching was produced for fulvic-like and humic-like fractions at p H 5. At p H 5, the humic-like fractions originating from the carboxylic acid, carboxyl and polysaccharide compounds were bound to aluminum first, followed by the fulvic-like fractions originating from the carboxyl and polysaccharide compounds. This finding also demonstrated that the activated functional groups of HA were involved in forming the Al-HA complex, which was accompanied by the removal of other groups by co-precipitation.Meanwhile, at p H 7, almost no fluorescence quenching occurred, and surface complexation was observed to occur, in which the activated functional groups were absorbed on the amorphous Al（OH）3. Two-dimensional FT-IR correlation spectroscopy indicated the sequence of HA structural change during coagulation with aluminum, with IR bands affected in the order of COOH〉 COO-〉NH deformation of amide Ⅱ〉 aliphatic hydroxyl C／OH at p H 5, and COO-〉aliphatic hydroxyl C／OH at p H 7. This study provides a promising pathway for analysis and insight into the priority of functional groups in the interaction between organic matters and metal coagulants.

Two-dimension fluorescence correlation spectroscopy to characterize the binding of organic ligands with zinc in eutrophic lake

Metal binding of organic ligands can definitely affect its environmental behavior in waters,while information on the binding heterogeneity with different organic ligands is still lacked till now.In this study,the binding of zinc with organic matters associated with cyanobacterial blooms,including dissolved organic matters（DOM） and attached organic matters（AOM）,were studied by using fluorescence quenching titration combined with two-dimensional correlation spectroscopy（2D-COS）.Metal-induced fluorescent quenching was obviously observed both for DOM and AOM,indicating the formation of metal-ligand complexes.Compared with the one-dimensional spectra,2D-COS revealed the sequences of metal-ligand interaction with the following orders：276 nm 〉 232 ran for DOM and232 nm 〉 276 nm for AOM.Furthermore,the modified Stern-Volmer model showed that the binding constant（logKM） of 276 nm in DOM was higher than that of 232 nm（4.93 vs.4.51）,while AOM was characterized with a high binding affinity for 232 nm（log KM：4.83）.The ranks of log KM values were consistent with the sequential orders derived from 2D-COS results both for the two samples.Fluorescence quenching titration combined with 2D-COS was an effective method to characterize the metal-ligand interaction.

Rapid and non-destructive decay detection of Yali pears using hyperspectral imaging coupled with 2D correlation spectroscopy

The black spot disease caused by Alternaria alternata on Yali pears is a great concern as it compromises their edible quality and commercial value.To realize rapid and non-destructive classification of this disease,hyperspectral imaging(HSI)technology was combined with two-dimensional correlation spectroscopy(2DCOS)analysis.A total of 150 pear samples at different decay grades were prepared.After obtaining the HSI images,the whole sample was demarcated as the region of interest,and the spectral information was extracted.Seven preprocessing methods were applied and compared to build the classification models.Thereafter,using the inoculation day as an external perturbation,2DCOS was used to select the feature-related wavebands for black spot disease identification,and the result was compared to those obtained using competitive adaptive reweighting sampling and the successive projections algorithm.Results demonstrated that the simplified least squares support vector model based on 2DCOS-identified feature wavebands yielded the best performance with the identification accuracy,precision,sensitivity,and specificity of 97.30%,94.60%,96.16%,and 98.21%,respectively.Therefore,2DCOS can effectively interpret the feature-related wavebands,and its combination with HSI is an effective tool to predict black spot disease on Yali pears.

二维相关振动光谱技术

从发展历史、计算方程、性质规则等方面系统地介绍了近年来发展起来的二维相关光谱技术。结合各种常见的一维振动光谱,如红外、拉曼、荧光、近红外 红外等光谱举例阐述了二维振动光谱的优势及其普适性。介绍了在广义二维相关光谱理论上最新延伸发展起来的二维样品 样品相关技术和二维杂化相关技术的基本理论,并将之与传统的二维变量 变量相关技术(广义二维相关光谱)进行了比较。

香加皮和五加皮的二维相关近红外光谱快速无损鉴别

Aim:The fast and nondestructive identification of Cortex Periplocae and Cortex Acanthopanacis by Fourier transform near infrared spectroscopy and generalized two-dimensional（2D） correlation spectroscopy were performed.Methods:Near infrared spectra of Cortex Periplocae and Cortex Acanthopanacis was used for computation of the 2D correlation spectra and comparison of the synchronous and asynchronous 2D correlation spectra.Results:Two of the analytes had similar spectral characteristics in one-dimensional near infrared while quite different in 2D correlation spectra.Cortex Periplocae and Cortex Acanthopanacis were identified visually using the 2D correlation spectra in region 5 600～4 700 cm-1and 7 200～6 600 cm-1.Conclusion:The results prove that 2D correlation spectra could enhance the resolution of near infrared spectra and increase the capacity of identification.The combination of 2D correlation spectroscopy and near infrared spectroscopy allow a new and convenient approach for evaluating the medicinal herbs.

山豆根和北豆根的二维相关近红外光谱快速鉴别

目的 结合广义二维相关光谱和近红外漫反射光谱,实现中药材山豆根和北豆根的快速鉴别.方法 检测收集山豆根和北豆根在变温（30～130℃）条件下的近红外光谱,计算二维相关光谱,比较分析同步相关光谱和异步相关光谱.结果 在一维图上,两味中药光谱非常相似,无法鉴别.利用两味中药在7 500到4 000 cm-1波段二维相关光谱特征的较大差别,并结合二维相关光谱相似度,实现了山豆根和北豆根的可视化鉴别.结论 二维相关光谱能提高近红外光谱分辨率和鉴别能力.研究结果为相关中药的快速鉴别提供了一种便捷、有力的新方法.

基于THz-TDS反射成像技术的玉米种子活力无损检测研究

应用太赫兹时域光谱反射成像技术结合广义二维相关光谱法探索玉米种子活力敏感太赫兹波段,并结合支持向量机建立快速无损判别种子活力的分析模型。实验以中地77玉米种子为例,采用人工老化方式(40℃, 100%相对湿度)将种子样本分批老化0, 1, 2, 3, 4天制备不同活力的种子样本,并按照GB/T 3543.4—1995进行种子发芽实验;同时采用Terapluse 4000太赫兹时域光谱仪及反射成像附件采集上述不同老化程度种子样本的太赫兹光谱图像。由于玉米种子的胚乳和种胚的成分差异显著,为探究种子不同组织在老化过程中与活力的相关性,本实验首先采用双高斯滤波器对THz图像中的像素点光谱消噪、峰峰值差分重构图像增强以及阈值分割等预处理无损提取玉米种子不同组织太赫兹吸光度谱。然后以老化天数为扰动量,针对上述提取的样本胚乳和种胚光谱分别作广义二维相关分析,根据实验中同步谱和异步谱中自动峰与交叉峰位置初步解析,可得到与种子活力关系密切的THz波段主要集中在75和36 cm^-1区域,同时75和36 cm^-1处的光谱信息存在强烈的协同变化且变化方向一致。种子活力与老化天数密切相关,因此根据老化天数分别建立了基于胚乳和种胚吸光度谱的五分类支持向量机模型用于种子活力定性判别,但是其判别准确率仅为59.34%和71.28%,表明该模型无法精细划分种子五个活力等级;实验进一步根据GB4401.1—2008以玉米种子发芽率85%为阈值划分活力高低等级,建立二分类种子活力判别模型,可得胚乳和种胚测试集识别准确率分别可达88.61%和91.73%,模型性能显著提升,增强了THz技术用于种子活力无损粗筛的可行性。实验结果表明:太赫兹反射成像技术以其丰富的指纹谱、低能安全以及图谱合一等特性,有望成为单粒种子活力快速无损测定领域一项崭新、有力的补充技术。

NIR assignment of isopsoralen by 2D-COS technology and model application in Yunkang Oral Liquid

Near infrared(NIR)assignment of Isopsoralen was performed using deuterated chloroform solvent and two-dimensional correlation spectroscopy(2D-COS)technology.Yunkang Oral Liquid was applied to study Isopsoralen,the characteristic bands by spectral assignment as well as the bands by interval partial least squares(iPLS)and synergy interval partial least squares(siPLS)were used to establish partial least squares(PLS)model.The coefficient of determination in calibration(R^(2)_(cal))were 0.9987,0.9970 and 0.9982.The coefficient of determination in cross validation(R^(2)_(val)) T were 0.9985,0.9921 and 0.9982.The coe±cient of determination in prediction(R^(2)_(pre)) T were 0.9987,0.9955 and 0.9988.The root mean square error of calibration(RMSEC)were 0.27,0.40 and 0.31 ppm.The root mean square error of cross validation(RMSECV)were 0.30,0.67 and 0.32 ppm.The root mean square error of prediction(RMSEP)were 0.23,0.43 and 0.22 ppm.The residual predictive deviation(RPD)were 31.00,16.58 and 32.41.It turned out that the characteristic bands by spectral assignment had the same results with the chemometrics methods in PLS model.It provided guidance for NIR spectral assignment of chemical compositions in Chinese Materia Medica(CMM).

A potential threat from biodegradable microplastics: mechanism of cadmium adsorption and desorption in the simulated gastrointestinal environment

It has been demonstrated that microplastics (MPs) can accumulate heavy metals from the environment and transfer them into organisms via the food chain. However, adsorption and desorption capacities for biodegradable MPs relative to those for conventional MPs remain poorly understood. In this study, cadmium (Cd(II)) adsorption and desorption characteristics of polylactic acid (PLA), a typical biodegradable MP, were investigated. Two conventional MPs, i.e., polypropylene (PP) and polyamide (PA) were used for comparison. The maximum Cd(II) adsorption capacities of the MPs studied in the adsorption experiments decreased in the order PA (0.96 ± 0.07 mg/g) > PLA (0.64 ± 0.04 mg/g) > PP (0.22 ± 0.03 mg/g). The Pseudo-second-order kinetic model and Freundlich isothermal model described the Cd(II) adsorption behaviors of PLA MPs well. X-ray photoelectron spectroscopy and two-dimensional Fourier transform infrared correlation spectroscopy analysis indicated that oxygen functional groups were the major and preferential binding sites of PLA MPs, which contributed to their high Cd(II) adsorption capacities. Simulated gastric and intestinal fluids both significantly enhanced the desorption capacities of the examined MPs. Notably, degradation of the PLA MPs during in vitro human digestion made the Cd(II) on the PLA MPs more bioaccessible (19% in the gastric phase and 62% in the intestinal phase) than Cd(II) on the PP and PA MPs. These results indicate the remarkable capacities of biodegradable MPs to accumulate Cd(II) and transfer it to the digestive system and show that biodegradable MPs might pose more severe threats to human health than conventional nonbiodegradable MPs.

Analysis and discrimination of ten different sponges by multi-step infrared spectroscopy

In this study,a convenient method using multi-step infrared spectroscopy,including Fourier transform infrared spectroscopy（FT-IR）,second derivative infrared spectroscopy（SD-IR） and two-dimensional correlation infrared spectroscopy（2DCOS-IR）,was employed to analyze and discriminate ten marine sponges from two classes collected from the Xisha Islands in the South China Sea.Each sponge had an exclusive macroscopic fingerprint.From the IR spectra,it was noted that the main ingredient of calcareous sponges was calcium carbonate,but that of demosponges was proteins.For sponges from the same genus or having highly similar chemical profile（IR spectral profile）,SD-IR and 2DCOS-IR were applied to successfully reveal the tiny differences.It was demonstrated that the multi-step infrared spectroscopy was a feasible and objective approach for marine sponge identification.

Superconductivity and pseudogap features of an isolated FeAs layer in KCa_(2)Fe_(4)As_(4)F_(2) unraveled by STM/STS

To reveal the intrinsic properties of the basic superconducting units,i.e.,the single layered FeSe/FeAs in iron-based superconductors or CuO_(2) planes in cuprate superconductors,is a necessary prerequisite for understanding the mechanism of high-Tc superconductivity.Up to now,an isolated FeAs layer has rarely been studied due to the difficulty in materials synthesis.Here,we report a scanning tunneling microscopy/spectroscopy(STM/STS)study on the iron-based superconductor KCa_(2)Fe_(4)As_(4)F_(2).In situ cleavage produced a single FeAs layer covered by a reconstructed K surface,which is isolated from the bulk by the underlying CaF layer and shows multi-band superconductivity with a much lower T_(c) than its bulk counterpart.In the exposed As-terminated regions with coverage of scattered K atoms,a pseudogap was observed,leading to an inhomogeneous superconductivity without long-range phase coherence in real space,which is remarkably similar to the high-T_(c) cuprate superconductors.These results provide a new perspective to understanding the origin of superconductivity in iron-based superconductors.

Enzymatic preparation of hydrophobic biomass with one-pot synthesis and the oil removal performance

Oil pollution is causing deleterious damage to aquatic ecosystems and human health.The utilization of agricultural waste such as corn stalk(CS)to produce biosorbents has been considered an ecofriendly and efficient approach for removing oil.However,most previous studies focused on the modification of the whole CS,which is inefficient due to the heterogeneity of CS.In this study,corn stalk pith(CP),which has excellent amphipathic characteristics,was selected to prepare a high-efficiency oil sorbent by grafting dodecyl gallate(DG,a long-chain alkyl)onto CP surface lignin via laccase mediation.The modified biomass(DGCP)shows high hydrophobicity(water contact angle=140.2°)and superoleophilicity(oil contact angle=0°)and exhibits a high oil sorption capacity(46.43 g/g).In addition,DGCP has good stability and reusability for adsorbing oil from the aqueous phase.Kinetic and isotherm models and two-dimensional correlation spectroscopy integrated with FTIR analyses revealed that the main sorption mechanism involves the H-bond effect,hydrophobic effect and van der Waals force.This work provides an ecofriendly method to prepare oil sorbents and new insights into the mechanisms underlying the removal of spilled oil from wastewater.