FT-Raman spectroscopy of biological molecules

Raman spectroscopy of biological molecules is often very difficult if not impossible due to a large fluorescence background from absorbing species, either from the molecule itself or an impurity. Photobleaching is occasionally successful in photochemically removing fluorescent impurities, but the majority of samples are not responsive to such treatment. Resonance enhancement of an absorbing species allows acquisition of Raman spectra in spite of competing fluorescence. However, the resonance Raman spectrum is characteristic of the chromophore only and little structural information is obtained from the spectrum about other parts of the molecule which are not resonantly enhanced. The newly developed technique of FT-Raman spectroscopy proves to be a solution to both of these problems for biological materials. Excitation with infrared wavelengths prevents electronic absorptions which give rise to fluorescence. In addition, the obtained spectra are completely nonresonant, allowing detection of vibrational modes of all parts of the molecule including the chromophore. We will present nonresonant, fluorescence free spectra of a range of biologically significant molecules including phospholipids and porphyrins.     

Study of normal colorectal tissue by FT-Raman spectroscopy

FT-Raman spectroscopy was employed to study normal human colorectal tissues in vitro with the aim of evaluating the spectral differences of the complex colon mucous in order to establish a characteristic Raman spectrum. The samples were collected from 39 patients, providing 144 spectra for the statistical analysis. The results enable one to estabilish three well-defined spectroscopic groups of non-altered coloretal tissues that were consistently checked by statistical (clustering) and biological (histopathology) analyses: group 1 is represented by samples with the presence of epithelial layer, connective tissue papillae, and smooth muscle tissue; group 2 comprises tissues with epithelial layer and connective tissue papillae; group 3 presented mostly fatty and slack conjunctive tissue. The study reveals the existence of an intrinsic spectral variability for each patient that must be considered when sampling tissues fragments to build a spectral database. This is the first step for future studies and applications of Raman spectroscopy to optical biopsy and diagnosis of colorectal cancer.     

Thermotropic phase behaviour of sodium oleate as studied by FT-Raman spectroscopy and X-ray diffraction

The thermotropic behaviour of sodium oleate (NaOl) has been studied in the temperature range 10–125°C by using Fourier transform-Raman spectroscopy, X-ray diffraction and differential scanning calorimetry (DSC). The temperature dependence of conformationally sensitive bands in the CH₂ stretching (2800–2900 cm⁻¹), C–C stretching (1050–1150 cm⁻¹) and CH₃ rocking region (830–900 cm⁻¹) has been used to characterize the order/disorder behaviour of alkyl chains. It is found that in phase I, NaOl exhibits the crystalline ordered lamellar structure with a repeat period of 4.51 nm. The first broad peak in the DSC trace is due to superposition of two transitions (phase I to phase II and phase II to phase III), therefore, it is not possible to determine the lamellar structure of phase II. This broad transition from phase I to phase III is associated with the melting of methyl-sided chains and increase in gauche conformers in carboxylate-sided chains. Finally, NaOl undergoes a transition from crystalline to a liquid crystalline phase IV, which is associated with the melting of the carboxylate-sided chain.     

In-situ surface-enhanced Raman scattering and FT-Raman spectroscopy of black prints

The black inkjet and laser prints were analysed with regard to application in forensic analysis of questioned documents. The purpose of this work was to study spectral properties and compare the suitability of surface-enhanced Raman scattering (SERS) with Fourier transform Raman spectra of prints. This work aimed to find optimal surface-enhanced Raman spectroscopic approach for the future analysis of documents using statistical methods. In this work, we analysed eight prints of four laser and four inkjet devices. The samples were measured using two dispersive Raman devices; (DXR Raman microscope with excitation line 532 nm, Foram 685-2 spectrometer − 685 nm) and FT-Raman device (Bruker Spectrometer MultiRAM with excitation line 1064 nm). The silver nanoparticles (AgNPs) colloid for SERS experiment were synthesised and checked by UV–vis spectroscopy and scanning electron microscopy (SEM). The remarkable differences caused by centrifugation of silver colloid were observed just in the SEM images. The main contribution of this paper is to propose the novel approach achieving sufficient SERS signal intensity of black prints using the both, laser and inkjet printers. Moreover, this method is based on just a single metal colloid, and the analysis can be performed in-situ, i.e. directly on the printed sample surface. We consider the SERS could by highly promising and universal for applications in the forensic analysis of printed documents with the combination of statistical method when conventional methods are not effective.     

Characterization of the surface properties of persimmon leaves by FT-Raman spectroscopy and wicking technique

To fit the request of developing new biomaterials using persimmon leaves as raw material, this paper reported the surface free energy and related components, e.g. the Lifshitz-van der Waals and Lewis acid-base components for persimmon leaves estimated by means of the column wicking technique. Considering this natural material might be varied of its properties with growing area, a characterization of it was initially performed by applying the FT-Raman spectroscopy. Based on the determined results, persimmon leaves have greater surface free energy, gammaS, than cellulose though it has been found rich in this component, e.g. of about 68.28%. Moreover, it was further observed that the persimmon leaves have great Lewis acid-base interactions component, gammaS(AB), contributed by the Lewis acid component, gammaS+. This suggests that the persimmon leaves are available to convert to new biomaterials expected forms.     

Monitoring of pigmented and wooden surfaces in accelerated ageing processes by FT-Raman spectroscopy and multivariate control charts

Two of the most suitable analytical techniques used in the field of cultural heritage are NIR (near-infrared) and Raman spectroscopy. FT-Raman spectroscopy coupled to multivariate control charts is applied here for the development of a new method for monitoring the conservation state of pigmented and wooden surfaces. These materials were exposed to different accelerated ageing processes in order to evaluate the effect of the applied treatments on the goods surfaces. In this work, a new approach based on the principles of statistical process control (SPC) to the monitoring of cultural heritage, has been developed: the conservation state of samples simulating works-of-art has been treated like an industrial process, monitored with multivariate control charts, owing to the complexity of the spectroscopic data collected.The Raman spectra were analysed by principal component analysis (PCA) and the relevant principal components (PCs) were used for constructing multivariate Shewhart and cumulative sum (CUSUM) control charts. These tools were successfully applied for the identification of the presence of relevant modifications occurring on the surfaces. CUSUM charts however proved to be more effective in the identification of the exact beginning of the applied treatment. In the case of wooden boards, where a sufficient number of PCs were available, simultaneous scores monitoring and residuals tracking (SMART) charts were also investigated. The exposure to a basic attack and to high temperatures produced deep changes on the wooden samples, clearly identified by the multivariate Shewhart, CUSUM and SMART charts. A change on the pigment surface was detected after exposure to an acidic solution and to the UV light, while no effect was identified on the painted surface after the exposure to natural atmospheric events.     

The state of conservation of painted surfaces in the presence of accelerated ageing processes monitored by use of FT-Raman spectroscopy and multivariate control charts

A new method has been developed for monitoring the degradation of paintings. Two inorganic pigments (ultramarine blue and red ochre) were blended with linseed oil and spread on canvas. Each canvas was subjected to simulated accelerated ageing in the presence of typical degradation agents (UV radiation and acidic solution). Periodically the painted surfaces were analysed by FT-Raman, to investigate the status of the surface. The data obtained were analysed by principal component analysis (PCA). Finally the Shewhart and cumulative sum control charts based on the relevant principal components (PC) and the so called scores monitoring and residuals tracking (SMART) charts were built. The method based on the use of PC to describe the process was found to enable identification of the presence of relevant modification occurring on the surface of the samples studied.Electronic supplementary material Supplementary material is available for this article at     

The structure of different cellulosic fibres characterized by Raman spectroscopy

Different samples of cellulosic materials were analyzed by Raman spectroscopy and wood chips from Pinus elliottii, treated with acidic and alkaline aqueous solutions, were used to evaluate diagnostic signatures of the chemical structure of the cellulosic fibres. Cotton and whiskers synthesized from cotton, ancient Egyptian linen from a mummy wrapping, and five different paper sheets used in museum handling were compared. The complementarity of the Raman spectroscopic and scanning electron microscopic data facilitated the evaluation of the crystallinity, the level of organization and chain sizes of the fibres and the identification of different oxidation products. Intensity ratios measured from pairs of key bands were used to characterize the crystallinity, chain lengths and presence of oxidative decomposition in the range of the studied samples. Finally, the Raman spectra of the ancient Egyptian linen specimen indicated a potential future application of the proposed analysis for the characterization of archaeological pieces composed of linen.     

FT-Raman Spectroscopic Investigations on the Organic Crosslinking in Hybrid Polymers Part II: Reactions of Epoxy Silanes

FT-Raman spectroscopy was used together with supplementary ¹³C-NMR measurements to analyze the reaction of the epoxy moieties of 3-glycidoxypropyltrimethoxysilane and 5,6-epoxyhexyltrimethoxysilane during sol-gel processing. Based on the results for simple epoxides reported in Riegel, Kiefer, Hofacker and Schottner (Appl. Spec. 54, 1384 (2000)) the formation of -hydroxy methyl ethers can be derived. An additional condensation of the epoxy rings yielding a mixture of oligo ethers is considered very probable from the Raman measurements. Raman and NMR assignments are proposed for 5,6-epoxyhexyltrimethoxysilane.     

稀土离子及其配合物对二棕榈酰磷脂酰乙醇胺酯双层结构的影响

随着稀土在工农业和医疗保健上的广泛应用，稀土的生物无机化学研究受到了普遍的关注．以往的研究多集中在稀土离子的宏观毒理学[1]，而研究稀土离子与生物膜的作用较少[2]．稀土的生物小分子配体的配合物与生物膜作用的研究则未见报道．本文介绍了用拉曼光谱研究稀土离子及其柠檬酸、二乙三胺五乙酸（DTPA）配合物对二栋相酸乙醇胺（DPPE）脂双层的流动性以及碳氢链的构象转变和晶格有序性排列的影响．1实验部分DPPE系Sigma公司产品。La2O3（99．9％）为跃龙化工厂产品，柠檬酸、DTPA为北京化工厂产品．L3Cl3溶液由L32O3溶于盐酸…     

Two-dimensional correlation spectroscopy and multivariate curve resolution for the study of lipid oxidation in edible oils monitored by FTIR and FT-Raman spectroscopy

Accelerate oxidative degradation of six vegetable oils was monitored using FTIR and FT-Raman spectroscopy. Two-dimensional correlation spectroscopy and multivariate curve resolution alternating least squares (MCR-ALS) were applied to the analysis of the data. The use of hetero-spectral two-dimensional correlation of FTIR and FT-Raman data allowed the use of well established band assignments to interpret less clearly assigned spectral features. With a moving window approach it was possible to obtain simplified two-dimensional correlation maps and to detect compounds evolving with different kinetic. Simultaneous analysis of the oxidation experiments of the six different oils monitored by both spectroscopic techniques was performed using MCR-ALS. Although a complete resolution of the data was not possible, the spectral changes occurring during the oxidative degradation of the oils were described with a five-component model. The two fundamentally different chemometric approaches lead to coincident results.     

Investigation of sport supplements quality by Raman spectroscopy and principal component analysis

In this work, sport supplements were investigated by Raman spectroscopy. Samples were obtained from health foods shops, gyms and sports centers covering a wide range of available supplement powders. A systematic comparison of Raman spectra of the analyzed supplements allowed identifying the supplement type through the characteristic vibrational modes of carbohydrates and proteins. The protein supplements were identified by Raman bands at 1650, 1250 and 1004 cm⁻¹, while the spectral range between 1200 and 800 cm⁻¹ was useful to identify the carbohydrate supplements. Due to the diversity in composition of sport supplements, a chemometric tool such as principal component analysis (PCA) was employed to assist in the interpretation of Raman spectra, allowing also the identification of compounds present in sport supplements. Especially, the Raman scattering of aromatic and aliphatic amino acids residues contributes to the existence of bands characteristic for the different types of proteins. This kind of information is very important for the quality control of these products, for detecting the presence of fraud or a sample composition in disagreement with the label, thus ensuring the provenance of the supplements.     

Quantitative analysis of topical gels and ointments by FT-Raman spectroscopy

A method for quantitative determination of ibuprofen (IBU), naproxen (NAP), methyl salicylate (MES) and menthol (MNT) in commercial topical gels and ointments using partial least squares (PLS) models based on FT-Raman spectra is described. The calculated relative standard errors of prediction (RSEP) were found to be in the range of 2.1–3.2% for the calibration and validation data sets. Two commercial topical gels containing 5.0% of IBU and 10% of NAP (w/w), as well as one ointment containing 15% of MES and 10% of MNT (w/w) as active pharmaceutical ingredients (APIs), were successfully quantified using the developed models with recoveries in the 99.2–101.5% range. The proposed procedure can be used as a fast, reliable and economic method for the quantification of APIs in topical gels and ointments.     

Comfortable, flexible upholstery fire barriers on base of bast, wool and thermostable fibres

The paper presents elastic barrier materials developed at the INF which play a role of filling and fire barrier material at the same time in upholstery furniture, reducing the development and spread of fire on flammable materials. The presented results of flammability and biophysical tests confirm the comfort of products.The developed barrier materials use natural fibres (wool, flax FR) characterized by good air permeability, hygroscopicity, moisture transport, elimination of electrostatic charges and have effect on climate of interiors also when blended with thermostable fibres such as Polyacrylate. These flexible structures based on blend of natural fibres and thermostable fibres with at least two barrier effects i.e. durable resistance to fire, thermal insulation, control of electrostatic phenomena.     

Characterization of PVDF membranes by vibrational spectroscopy

In order to investigate the effectiveness of vibrational spectroscopy in the characterization of polymeric membranes, several poly(vinylidene fluoride) (PVDF) membranes with different porous structures were prepared by the phase inversion process using different casting solvents. An accurate analysis of the Fourier transform Raman (FT-Raman) and the Fourier transform infrared (FTIR) spectra was performed for each sample and the scanning electron microscopy (SEM) results were noted. To highlight the specific problems related to porosity and surface roughness in the acquisition of spectra by different sampling techniques, the attenuated total reflection (ATR) and photoacoustic spectroscopy (PAS) spectra were compared with corresponding spectra obtained from dense films. A detailed analysis of these spectra highlighted their ability in determining the differences in the polymer structure between the two membrane sides. This indicates that (considering the results given by all the different techniques) thorough qualitative membrane characterization can generally be achieved. Moreover, the good quality spectra of the PVDF membrane provide information on a portion of material which depends on its structure, highlighting the usefulness of FTIR-PAS in studying porous materials which, as a rule, give low quality infrared spectra when other sampling techniques are used. However, the complex and inhomogeneous structure of these materials can make quantitative analysis more, or less, difficult.     

Binding of Co(II) and Cu(II) cations to chemically modified wool fibres: an IR investigation

Wool fibres were modified by treatment with tannic acid (TA) solution or by acylation with ethylenediaminetetraacetic (EDTA) dianhydride. The unmodified and modified fibres were subsequently treated with Cu²⁺ and Co²⁺ solutions, at alkaline pH, and analysed by Attenuated Total Reflectance, ATR/IR spectroscopy to evaluate the changes induced in the structure of the fibre by metal binding. The spectral changes were correlated to metal adsorption results obtained by Inductive Coupled Plasma-Atomic Emission Spectrometry (ICP-AES).

The IR results were discussed in relation to our previous findings on the metal binding mode of Bombyx mori and Tussah silk fibres; the changes observed in the spectra were explained by considering the different affinity of the fibres for the modifying reagent and the amount of the metal absorbed. More relevant spectral changes were observed upon Cu²⁺ complexation rather than Co²⁺ complexation, according to the metal absorption results. The most relevant changes were observed for the EDTA-modified wool sample treated with Cu²⁺, according to the higher affinity of wool for EDTA. The IR spectra were quantitatively evaluated by the intensity ratio between the Amide I and Amide II bands (I_AmideI/I_AmideII) and its trend as a function of metal absorption was reported.

The present investigation demonstrated that the interaction between fibre and metal and the subsequent fibre modification depend on the chemical nature of the fibre, the metal cation and the modifying reagent.     

A comparative study of diesel analysis by FTIR, FTNIR and FT-Raman spectroscopy using PLS and artificial neural network analysis

Diesel properties determined by ASTM reference methods as cetane index, density, viscosity, distillation temperatures at 50% (T50) and 85% (T85) recovery, and the total sulfur content (%, w/w) were modeled by FTIR-ATR, FTNIR, and FT-Raman spectroscopy using partial last square regression (PLS) and artificial neural network (ANN) spectral analysis. In the PLS models, 45 diesel samples were used in the training group and the other 45 samples were used in the validation. In the ANN analysis a modular feedforward network was used. Sixty diesel samples were used in the neural network training and other 30 samples were used in the validation. Two different ATR configurations were compared in the FTIR, a conventional (ATR1) and an immersion (ATR2) cell. The ATR1 cell presented the best results, with smaller prediction errors (root mean square error of prediction, RMSEP). The comparison of the three PLS models (FTIR-ATR1, FTNIR, and FT-Raman) shows that reasonable values of R² and RMSEP were obtained by the FTIR-ATR1 and FTNIR models in the evaluation of density, viscosity, and T50. The PLS/FT-Raman models presented reasonable results only for the T50 property. None of the techniques was able to generate suitable PLS calibration models for the determination of sulfur content. The ANN/FT-Raman models presented the best performances, with all models presenting R²-values above 85% some of them with RMSEP values significantly smaller than those obtained with FTIR-ATR and FTNIR. The ANN/FT-Raman and ANN/FTIR-ATR1 models were able to estimate the total sulfur content of diesel with 0.01% (w/w) accuracy.     

利用付立叶红外光谱与付立叶拉曼光谱初探超细羊毛粉的光谱行为

采用付立叶红外(FT-IR)和付立叶拉曼(FT-Raman)光谱仪,对美利奴原毛、机械磨碎羊毛粉、氯化或氧化预处理后经酶水解的超细羊毛粉进行分析。研究结果表明:机械磨碎羊毛粉,其化学结构与原毛相比无明显变化;氯化或氧化预处理后经酶水解的超细羊毛粉的IR谱图发生了较大的变化,羊毛大分子中胱氨酸最终氧化为磺基丙氨酸,且原胱氨酸二硫键发生了断裂,生成新的半胱氨酸磺酸盐;同时预处理时间越长,羊毛粉的平均直经越小,新产生的1 044 cm-1、1 026 cm-1吸收信号也越强。     

Solvent-dependent photoacidity state of pyranine monitored by transient mid-infrared spectroscopy.

We investigate with femtosecond mid-infrared spectroscopy the vibrational-mode characteristics of the electronic states involved in the excited-state dynamics of pyranine (HPTS) that ultimately lead to efficient proton (deuteron) transfer in H2O (D2O). We also study the methoxy derivative of pyranine (MPTS), which is similar in electronic structure but does not have the photoacidity property. We compare the observed vibrational band patterns of MPTS and HPTS after electronic excitation in the solvents: deuterated dimethylsulfoxide, deuterated methanol and H2O/D2O, from which we conclude that for MPTS and HPTS photoacids the first excited singlet state appears to have charge-transfer (CT) properties in water within our time resolution (150 fs), whereas in aprotic dimethylsulfoxide the photoacid appears to be in a non-polar electronic excited state, and in methanol (less polar and less acidic than water) the behaviour is intermediate between these two extremes. For the fingerprint vibrations we do not observe dynamics on a time scale of a few picoseconds, and with our results obtained on the O-H stretching vibration we argue that the dynamic behaviour observed in previous UV/Vis pump-probe studies is likely to be related to solvation dynamics.     

Selective surface modification of syndiotactic polystyrene films: A study by Fourier transform- and confocal-Raman spectroscopy

A helical crystalline modification of syndiotactic polystyrene (sPS), the δ-form, was employed to prepare solution-cast films selectively sulfonated on the surface. This result was achieved because of the unusual transport characteristics of the δ-form, exhibiting comparatively large diffusivity and solubility values for low-molecular weight compounds such as chloroform, which can be effectively used as a carrier solvent. The results of sulfonation of the δ-form are compared with those obtained with a trans-planar crystalline modification of sPS (β-form). The latter was found unsuitable for selective surface modification. The analysis of the sulfonated films was carried out by FT-Raman and confocal-Raman spectroscopy. The first technique was used to investigate the average composition of the samples in terms of sulfonation degree and crystalline structure. It also allowed us to construct calibration curves to be used in connection with the confocal-Raman data. The latter technique was employed to generate images with spectroscopic contrast and to quantitatively characterize the depth-profiles of the investigated films.