Preprocessing Strategies for Sparse Infrared Spectroscopy: A Case Study on Cartilage Diagnostics

The aim of the study was to optimize preprocessing of sparse infrared spectral data. The sparse data were obtained by reducing broadband Fourier transform infrared attenuated total reflectance spectra of bovine and human cartilage, as well as of simulated spectral data, comprising several thousand spectral variables into datasets comprising only seven spectral variables. Different preprocessing approaches were compared, including simple baseline correction and normalization procedures, and model-based preprocessing, such as multiplicative signal correction (MSC). The optimal preprocessing was selected based on the quality of classification models established by partial least squares discriminant analysis for discriminating healthy and damaged cartilage samples. The best results for the sparse data were obtained by preprocessing using a baseline offset correction at 1800 cm⁻¹, followed by peak normalization at 850 cm⁻¹ and preprocessing by MSC.     

The Use of Constituent Spectra and Weighting in Extended Multiplicative Signal Correction in Infrared Spectroscopy

Extended multiplicative signal correction (EMSC) is a widely used preprocessing technique in infrared spectroscopy. EMSC is a model-based method favored for its flexibility and versatility. The model can be extended by adding constituent spectra to explicitly model-known analytes or interferents. This paper addresses the use of constituent spectra and demonstrates common pitfalls. It clarifies the difference between analyte and interferent spectra, and the importance of orthogonality between model spectra. Different normalization approaches are discussed, and the importance of weighting in the EMSC is demonstrated. The paper illustrates how constituent analyte spectra can be estimated, and how they can be used to extract additional information from spectral features. It is shown that the EMSC parameters can be used in both regression tasks and segmentation tasks.     

段式正交信号校正方法及在小麦近红外光谱数据分析中的应用

针对光谱数据峰宽、局部效应显著、含有噪音、变量个数多及彼此间常存在严重的复共线性等问题,改进和设计一种光谱数据局部校正方法:基于窗口平滑的段式正交信号校正方法,并将之结合偏最小二乘回归,以实现光谱数据的预处理及定量分析。通过NIPALS算法初始化将滤去的正交成分,以近邻分段方式进行逐个波长点的正交信号校正。而后将去噪后的光谱矩阵作为新的自变量阵,通过偏最小二乘回归构建其与性质参变量间的校正模型。通过小麦近红外漫反射光谱数据的应用实验结果表明,本方法正交成分估计稳定,去噪明显,模型的预报性能优于其它方法,PLS成分数减少,模型更加简洁。     

背景吸收强度可调控与扣除干扰组分影响的红外光谱测量方法

多组分混合物的红外光谱由于特征谱带的重叠或部分重叠而给谱峰的归属辨认带来极大的困难。本研究通过扫描两个背景样品(纯KBr压片(1)和KBr+C18TCNQ压片(2))实时合成一系列背景单光束谱。每个背景单光束谱既含有背景样品1的贡献也含有背景样品2的贡献。干扰组分C18TCNQ在系列背景谱中的吸收强度随扫描次数变化而改变。当待测混合物和背景样品中干扰组分的吸收强度相等时,就可以完全扣除干扰组分的影响。本测量方法用于硬脂酸与C18TCNQ混合物中扣除硬脂酸(或者C18TCNQ)的干扰,得到令人满意的结果。合成背景样品中干扰组分的含量在测量时成为与扫描次数有关的变量,为扣除干扰组分的影响提供了直接便利的红外光谱测量方法。     

Monitoring of water quality in South Paris district by clustering and SIMCA classification

With the aim of obtaining a monitoring tool to assess the quality of water, a multivariate statistical procedure based on cluster analysis (CA) coupled with soft independent modelling class analogy (SIMCA) algorithm, providing an effective classification method, is proposed. The experimental data set, carried out throughout the year 2004, was composed of analytical parameters from 68 water sources in a vast southwest area of Paris. Nine variables carrying the most useful information were selected and investigated (nitrate, sulphate, chloride, turbidity, conductivity, hardness, alkalinity, coliforms and Escherichia coli). Principal component analysis provided considerable data reduction, gathering in the first two principal components the majority of information representing about 92.2% of the total variance. CA grouped samples belonging to different sites, distinctly correlating them with chemical variables, and a classification model was built by SIMCA. This model was optimised and validated and then applied to a new data matrix, consisting of the parameters measured during the year 2005 from the same objects, providing a fast and accurate classification of all the samples. The most of the examined sources appeared unchanged during the 2-year period, but five sources resulted distributed in different classes, due to statistical significant changes of some characteristic analytical parameters.     

偏最小二乘法结合傅里叶变换红外漫反射光谱快速测定煤质

发热量、挥发分和灰分等是衡量煤质的质量指标。通常,烟煤的发热量、挥发分和灰分是按行业标准方法[1]分别进行测定的,操作过程繁琐,速度慢,且费用高。随着化学计量学多元校正方法的发展与广泛应用,董庆年采用最小二乘法结合红外光谱成功测定了灰分[2];而应用偏最小二乘法[3](P     

煤焦油的拉曼光谱表征和组分识别

用355 nm激光作为激发光源检测了煤焦油常温拉曼光谱;应用两种量子化学计算程序(Gaussian-DFT和ADF)模拟了占总量1%以上的15种煤焦油组分的拉曼光谱,模拟结果与实验光谱能较好匹配,并对振动模式进行了归属分析。研究表明,煤焦油组分主要由共轭六元环构成,其拉曼光谱特征谱带主要在1 660、1 420和1 265 cm^-1附近,当共轭六元环成链式结构时,1 420 cm^-1谱带特征明显;五元环嵌入共轭六元环链式结构会导致其拉曼光谱在1 265和1 660 cm^-1谱带相对强度增大;五元环、杂原子基团和甲基侧链依附在共轭六元环上,则对组分的拉曼光谱影响不显著。     

有指导的正交投影技术结合斜率/截距校正法实现小试水分近红外定量模型向中试传递

针对小试制剂过程建立的近红外定量模型难以直接应用于中试或大生产过程中的问题,该文以小试和中试条件下多批次药用糊精流化床制粒过程为载体,在线采集其近红外光谱数据并测定水分含量,建立小试过程水分近红外定量模型,提出并应用有指导的正交投影技术结合斜率/截距校正的模型传递方法跨尺度预测中试样本,使中试两个测试集A和B的水分相对预测误差分别由51.04%和26.64%降至4.90%和3.99%,显著提高了模型预测的准确度。将该结果与无指导的正交投影技术结合斜率/截距校正法以及模型更新相比较,该方法能更加有效地去除待测样本光谱中的干扰信息,适用范围广,为小试建立的模型放大应用到中试甚至大生产过程提供了新方案。     

利用红外光谱和拉曼光谱研究离子液体结构与相互作用的进展

热力学实验、理论计算以及计算机模拟是离子液体微观结构与相互作用研究中常用的三种手段,但是目前采用这些手段对离子液体结构的认识尚处于初步探索阶段,还没有完全找到离子液体性质随结构变化的规律,尚未完全能够对离子液体进行"设计",这也使得对离子液体的进一步开发和应用受到极大的限制.近年来,谱学方法成为研究溶液结构的重要手段.其中,红外光谱(IR)和拉曼光谱(Raman)等谱学手段在离子液体的结构与相互作用研究中发挥着越来越重要的作用.本文着重概述了红外光谱和拉曼光谱在纯离子液体及离子液体混合溶液结构与相互作用方面的研究进展、挑战以及发展方向.     

Infrared study of aging of edible oils by oxidative spectroscopic index and MCR-ALS chemometric method

One of the most suitable analytical techniques used for edible oil quality control is Fourier transform mid infrared spectroscopy (FT-MIR). FT-MIR spectroscopy was used to continuously characterize the aging of various edible oils thanks to a specific aging cell. There were differences in the spectra of fresh and aged oils from different vegetable sources, which provide the basis of a method to classify them according to the oxidative spectroscopic index value. The use of chemometric treatment such as multivariate curve resolution-alternative least square (MCR-ALS) made it possible to extract the spectra of main formed and degraded species. The concentration profiles gave interesting information about the ability of the various oils to support the oxidative treatment and showed that all oils present the same aging process. Both methods led to concordant results in terms of induction times determined by the oxidative spectroscopic index and the appearance of oxidation products revealed by MCR-ALS.     

Quality control of the powder pharmaceutical samples of sulfaguanidine by using NIR reflectance spectrometry and temperature-constrained cascade correlation networks

Temperature-constrained cascade correlation networks (TCCCNs) were applied to the identification of the powder pharmaceutical samples of sulfaguanidine based on near infrared (NIR) diffuse reflectance spectra and their first derivative spectra. This work focused on the comparison of performances of the uni-output TCCCN (Uni-TCCCN) and multi-output (Multi-TCCCN) by near infrared diffuse reflectance spectra and their first derivative spectra of sulfaguanidine. The TCCCN models were verified with independent prediction samples by using the “cross-validation” method. The networks were used to discriminate qualified, un-qualified and counterfeit sulfaguanidines pharmaceutical powders. The results showed that single outputs network generally worked better than the multiple outputs networks, and the first derivative spectra were more suitable for the identification comparing with original diffuse reflectance spectra. With proper network parameters the pharmaceutical powders can be classified at rate of 100% in this work. Also, the effects of parameters and related problems were discussed.     

X射线荧光光谱在Fe、Mn化学态分析中的应用

采用普通X射线荧光光谱仪,在多种不同条件下测量了Fe、Mn及其多种化合物的Kβ和L系谱线,用PeakF it谱处理软件,分解重叠谱峰获得各个单一的谱峰参数(谱锋位置、峰高和半高宽等),对各个谱峰产生的原因进行了讨论,结果表明,对Mn及其化合物K系谱线而言,采用L iF(200)分析晶体与二级衍射提高了仪器的分辩率,能更好的用于进行曲Mn及其化合物的价态的定性分析;对Fe及其化合物而言,采用L系谱峰测量的效果优于采用Kβ谱峰测试。以上研究有助于拓宽普通X射线荧光光谱仪的应用领域,且对定性分析Fe、Mn及其化合物的价态有实际意义。     

Physicochemical Characterization of the Loganic Acid–IR,Raman, UV-Vis and Luminescence Spectra Analyzed in Terms of Quantum Chemical DFT Approach

The molecular structure and vibrational spectra of loganic acid (LA) were calculated using B3LYP density functional theory, the 6–311G(2d,2p) basis set, and the GAUSSIAN 03W program. The solid-phase FTIR and FT-Raman spectra of LA were recorded in the 100–4000 cm⁻¹ range. The assignment of the observed bands to the respective normal modes was proposed on the basis of the PED approach. The stability of the LA molecule was considered using NBO analysis. The electron absorption and luminescence spectra were measured and discussed in terms of the calculated singlet, triplet, HOMO, and LUMO electron energies. The Stokes shift derived from the optical spectra was 20,915 cm⁻¹.     

Infrared and Raman spectra,DFT investigation of the tautomerism,conformational equilibrium,structure and vibrational assignment of 1-(2-benzothiazolyl)-3-methyl pyrazol-5-one

The low energy conformations of the three tautomers, imine-enol, enamine-keto and imine-keto forms of the title compound have been determined at the B3LYP/6-31 + G(d) level of theory using the relaxed PES scan method and their geometries have been refined at B3LYP/6-311 + G(d,p) and PBE0/6-311 + G(d,p) levels. The results show that the title compound exists in the imine-enol tautomeric form, in contrast to the enamine-keto form which exists in the solid crystalline state, followed by enamine-keto and imine-keto forms with extremely low abundances. The geometry parameters of all tautomeric forms calculated at PBE0/6-311 + G(d,p) and B3LYP/6-311 + G(d,p) levels have been compared with those from the experimental X-ray diffraction. The vibrational (FT-IR and Raman) spectroscopic studies of the most stable tautomer, enamine-keto form have been carried out. The assignment of the fundamental bands observed in the IR and Raman spectra have been facilitated by the SQM force field procedure. The frequencies from SQM procedure have a very good fit to the experimental ones. The total root-mean-square error is only ca. 11 cm⁻¹.     

Efficient evaluation of sampling quality of molecular dynamics simulations by clustering of dihedral torsion angles and Sammon mapping

A direct conformational clustering and mapping approach for peptide conformations based on backbone dihedral angles has been developed and applied to compare conformational sampling of Met-enkephalin using two molecular dynamics (MD) methods. Efficient clustering in dihedrals has been achieved by evaluating all combinations resulting from independent clustering of each dihedral angle distribution, thus resolving all conformational substates. In contrast, Cartesian clustering was unable to accurately distinguish between all substates. Projection of clusters on dihedral principal component (PCA) subspaces did not result in efficient separation of highly populated clusters. However, representation in a nonlinear metric by Sammon mapping was able to separate well the 48 highest populated clusters in just two dimensions. In addition, this approach also allowed us to visualize the transition frequencies between clusters efficiently. Significantly, higher transition frequencies between more distinct conformational substates were found for a recently developed biasing-potential replica exchange MD simulation method allowing faster sampling of possible substates compared to conventional MD simulations. Although the number of theoretically possible clusters grows exponentially with peptide length, in practice, the number of clusters is only limited by the sampling size (typically much smaller), and therefore the method is well suited also for large systems. The approach could be useful to rapidly and accurately evaluate conformational sampling during MD simulations, to compare different sampling strategies and eventually to detect kinetic bottlenecks in folding pathways.     

Structure Elucidation of a Melam–Melem Adduct by a Combined Approach of Synchrotron X-ray Diffraction and DFT Calculations

Melam-melem (1:1), an adduct compound that can be obtained from dicyandiamide in autoclave reactions at 450 °C and elevated ammonia pressure, had previously been described based on mass spectrometry and NMR spectroscopy, but only incompletely characterized. The crystal structure of this compound has now been elucidated by means of synchrotron microfocus diffraction and subsequent quantum-chemical structure optimization applying DFT methods. The structure was refined in triclinic space group P based on X-ray data. Cell parameters of a=4.56(2), b=19.34(8), c=21.58(11) Å, α=73.34(11)°, β=89.1(2)°, and γ=88.4(2)° were experimentally obtained. The resulting cell volumes agree with the DFT optimized value to within 7 %. Molecular units in the structure form stacks that are interconnected by a vast array of hydrogen bridge interactions. Remarkably large melam dihedral angles of 48.4° were found that allow melam to interact with melem molecules from different stack layers, thus forming a 3D network. π-stacking interactions appear to play no major role in this structure.     

New insights into the use of hydroxypropyl cellulose for drug solubility enhancement: An analytical study of sub-molecular interactions with fenofibrate in solid state and aqueous solutions

Hydroxypropyl cellulose (HPC) is a solubility enhancer used for poorly soluble drugs, nano-suspensions and amorphous solid dispersions (ASD). However, the underlying mechanism remains unclear. ASDs of a poorly soluble drug, fenofibrate (FEN), were analyzed using liquid nuclear magnetic resonance (NMR) and solid state NMR (ss-NMR). Liquid NMR revealed interactions between the pyranose ring of the HPC molecule and the diphenylketone from FEN. The water accessibility of the CH₃ groups in HPC and FEN is very low, they form a hydrophobic zone in aqueous solution that may sustain the drug nucleation. Moreover, ss-NMR measurements confirmed very low drug crystallinity for HPC-FEN ASDs. Cross-polarization and direct polarization ¹³C spectra, ¹³C-CPMAS and ¹³C-PARIS, distinguished the most rigid and flexible portions in concordance with the ss-NMR proton T₁ and T_1r relaxation results. Although HPC side chains (hydroxypropoxy) are the most flexible portions, their flexibility is moderate and high rigidity is the predominant. The ss-NMR proton relaxation indicates a rather homogeneous distribution of the components (HPC and FEN) in the solid mixtures. The versatile NMR methodology proposed can be used to study other polymer-drug systems and it may contribute to understand relevant functional aspects such as the rate of drug-delivery and their stability.     

Pt电极上CO的同位素取代吸附机理研究

本文依据偶极耦合理论和相干势近似方法,合理选择粗糙电极上吸附分子的频率分布函数、一氧化碳(CO)吸附层的结构参数以及偶极耦合作用常数,对13CO/12CO同位素取代过程记录的红外光谱进行了拟合.研究发现,只有在拟合过程中引入低频CO分子优先取代,就可成功地模拟整个同位素取代过程的红外光谱随表面吸附的13CO/12CO组分的变化,并由此提出了吸附驱动的脱附机理,COad的脱附不是热激发脱附,而是吸附到表面的CO分子为其邻近位置COad的脱附提供能量.伸缩振动频率较低的COad处于台阶或缺陷位等较开阔的位置(尽管其吸附能较高),周围有较大的空间,利于来自溶液的CO分子的吸附,因此在台阶或缺陷位优先发生同位素的取代.