Vibrational spectroscopic study of brazilin and brazilein,the main constituents of brazilwood from Brazil

In this work, the vibrational spectra (FT-Raman and infrared spectra) of brazilin, the major component of brazilwood Caesalpinia echinata (from Bahia, Brazil), and brazilein, the oxidised pigment, are investigated. The FT-Raman spectra of the compounds show different patterns in the carbonyl stretching region, where brazilein presents a Raman feature at 1697 cm⁻¹ that is tentatively assigned to a coupled vibrational mode described by CO and aromatic CC stretching. Infrared measurements are used to support this assignment. The spectral region between 1700 and 1500 cm⁻¹ is also proposed as a fingerprint for brazilin and brazilein. Comparisons with some quinones and polyalcohols as parent molecules and other deep red resin pigments such as “dragon’s blood” are undertaken to assist the vibrational assignment. As a test of the spectroscopic protocol for the identification of these pigments in natural brazilwoods, an 80-year-old archival specimen of Caesalpinia echinata was analysed non-destructively and the feature of brazilein shown from the Raman spectrum.     

Combined FT–Raman spectroscopic and mass spectrometric study of ancient Egyptian sarcophagal fragments

The application of combined Raman spectroscopic and GC–MS analytical techniques for the characterisation of organic varnish residues from Egyptian Dynastic funerary sarcophagal and cartonnage fragments from the Graeco-Roman period, ca. 2200 BP, is described. The nondestructive use of Raman spectroscopy was initially employed to derive information about the specific location of organic material on the specimens, which were then targeted in specific areas using minimal sampling for GC–MS analysis. In the case of the sarcophagal fragment, a degraded yellow-brown surface treatment was identified as a Pistacia spp. resin; this provides additional evidence for the use of this resin, which has previously been identified in Canaanite transport amphorae, varnishes and “incense” bowls in an Egyptian Late Bronze Age archaeological context. The cartonnage fragment also contained an organic coating for which the Raman spectrum indicated a degradation that was too severe to facilitate identification, but the GC–MS data revealed that it was composed of a complex mixture of fatty acid residues. The combined use of GC–MS and Raman spectroscopy for the characterisation of organic materials in an archaeological context is advocated for minimisation of sampling and restriction to specifically identified targets for museum archival specimens.     

Analytical discrimination between sources of ginseng using Raman spectroscopy

Ginseng is a widely used medicinal product that grows mainly in Korea, China and America. American ginseng is classified as an endangered species, and so the import and export of this type of ginseng is illegal in certain countries. Due to this restriction it is becoming increasingly important to be able to distinguish between different types of ginseng. FT-Raman spectroscopy has the ability to discriminate between ginseng specimens according to the country of origin and the effects of processing on the ginseng material. The ginsenoside content of ginseng differs in both conformation and concentration depending on the source of the ginseng, which means that ginseng grown in different countries should express unique spectral features. The presence or absence of these features, therefore, could indicate the geographical origin of the sample. Several spectral features were identified for a range of ginsengs, such as a peak at 980 cm(-1) that was only found in Chinese ginseng, and the different wavenumber positions of characteristic ginseng bands near 1600 cm(-1). This indicates that Raman spectroscopy can be used to pinpoint the origin of an unknown ginseng sample and that it would provide a rapid nondestructive analytical technique for formally discriminating between restricted and permitted imports.     

Ancient biodeterioration: an FT–Raman spectroscopic study of mammoth and elephant ivory

Raman spectra of mammoth ivory specimens have been recorded using near-infrared excitation, and comparisons made with modern Asian and African elephant ivories. Whereas the most ancient mammoth ivory (60–65 ky) showed no evidence for an organic collagen component, more recent samples of mammoth ivory indicated that some preservation had occurred, although with biodeterioration of the protein structure exhibited by the amide I and III bands in the 1200–1700 cm⁻¹ region of the Raman spectrum. The consequent difficulties encountered when applying chemometrics methods to ancient ivory analysis (which are successful for modern specimens) are noted. In the most ancient mammoth ivory specimens, which are extensively fragmented, evidence of mineralization is seen, with the production of gypsum, calcite and limonite; Raman microscopic analysis of crystalline material inside the fissures of the mammoth ivory shows the presence of gypsum as well as cyanobacterial colonisation. The application of Raman spectroscopy to the nondestructive analysis of archaeological materials in order to gain information of relevance to their preservation or restoration is highlighted.     

Raman spectroscopic identification of usnic acid in hydrothermal minerals as a potential Martian analogue

Raman spectroscopy using 785 nm excitation was tested as a nondestructive method for determining the presence of the potential biomarker, usnic acid, in experimentally prepared mineral matrices. Investigated samples consisting of usnic acid mixed with powdered hydrothermal minerals, gypsum and calcite were studied. Various concentrations of usnic acid in the mineral matrix were studied to determine the detection limits of this biomarker. Usnic acid was mixed with gypsum (respectively, calcite) and covered by a UV-transparent crystal of gypsum (CaSO(4) x 2 H(2)O), thereby creating artificial inclusions similar to those which could be present in Martian minerals. A Raman usnic acid signal at the concentration level as low as 1 g kg(-1) was obtained in the powdered mineral matrix and 5 g kg(-1) when analyzed through the monocrystal. The number of registered usnic acid key Raman bands was dependent on the particular mineral matrix. If a similar concentration of usnic acid could persist in Martian samples, then Raman spectroscopy will be able to identify it. Obtained results will aid both in situ Raman analyses on Mars and on Earth.     

Raman spectroscopic analyses of preserved historical specimens of human hair attributed to Robert Stephenson and Sir Isaac Newton

The Raman spectra of two historical specimens of human hair attributed to the engineer Robert Stephenson and scientist Sir Isaac Newton, preserved in private collections are reported. Comparisons are made with the Raman spectra of modern hair specimens and with hair from archaeological excavations. The hair spectra collected with a laser excitation of 785 nm are of a better quality than those collected using 1064 nm. The historical hair specimens are remarkably well-defined spectroscopically in terms of the amide I vibrational mode and the [small nu](SS), ascribed to a predominantly gauche-gauche-gauche CSSC conformation. The contrast with degraded hair specimens recovered from archaeological excavations is striking. The presence of a weak feature near 2590 cm(-1) in the hair samples attributed to a [small nu](SH) vibration could be indicative of a reduction process operative on the CSSC cystine keratotic linkages and a possible origin of this is bacterial biodegradation identified histologically. This study demonstrates the molecular information available from non-destructive Raman spectroscopic analysis from single hair shafts or small bundles of fibres which complements information available from histological and destructive analytical techniques for rare biological specimens subjected to conservation or curation procedures in museums or private collections.     

Analysis of human tear fluid by Raman spectroscopy

Tear fluid is a complex aqueous solution containing proteins, metabolites, electrolytes and lipids. This study uses Raman spectroscopy to analyse the composition of human tear fluid from three healthy volunteers. Two different methods are used to obtain Raman spectra from the 3 μL tear samples: (i) solution-phase Raman spectroscopy, and (ii) drop coating deposition Raman spectroscopy (DCDRS). Tear samples were either basal fluid, or yawn reflex secreted fluid. Calibration of the solution technique with standard protein solutions (5-15 mg mL⁻¹) showed that this method could predict the protein concentration (cross-validation) with an error of less than 1 mg mL⁻¹. The Raman signals from the tear fluid were very weak but signals due to protein and urea were clearly observable in all samples. The drop coating deposition technique was shown to produce very high signal-to-noise spectra for relatively short acquisition times, and small sample volumes. Raman point mapping combined with principal components analysis showed that the protein, urea, bicarbonate and lipid could all be detected in the tear samples and that the distribution of these components was inhomogeneous. Their position within the drying pattern was shown to depend on their relative solubilities. The results of this study suggest that solution Raman measurements may be calibrated to give the total tear protein concentration and DCDRS could be used to give a fingerprint of the tear protein (and lipid) composition.     

激光波长对拉曼光谱检测地质成分的影响

随着激光技术的不断发展,以激光为光源的拉曼光谱检测技术由于其快速、无损、无接触探测等优势,已成为地质样品成分鉴别的一种重要途径。由于激光波长是样品拉曼效应的重要决定因素之一,进一步明确其在地质样品成分检测中的影响,能够为开展行星矿物成分研究提供重要参考依据。本工作基于自主建立的532nm/785nm双色光源激光拉曼光谱探测系统,开展了不同激光波长对地质样品成分拉曼光谱的影响研究,获得了包括硝酸根、碳酸根、磷酸根、硅酸根等分子基团以及硫化物、氧化物等多种地质样品主要成分的拉曼特征光谱。通过对比表明,532nm激发光具有更高的光子能量,能够检测更多的样品成分,但荧光效应较强,785nm激发光存在拉曼信号强度较低问题,但是具有很好的荧光抑制效果,可根据实际样品种类进行最佳激发光波长的选择。     

基于多阶导数拉曼光谱组合技术的矿物油模式分类

为了实现对法庭科学领域重质矿物油物证的快速、准确、无损的鉴定,该文基于光谱分析技术提出了一种多阶导数光谱数据组合分析的方法。收集了80种不同型号、不同厂家的重质矿物油样本,利用傅里叶变换拉曼光谱分析法采集样本的原始光谱数据和导数光谱数据,并通过结合化学计量学构建分类模型。在构建的主成分分析(PCA)结合径向基函数神经网络(RBF)分类模型中,对单独的原始光谱、一阶导数谱和二阶导数谱数据的训练集准确率分别为80.0%、86.7%和86.2%,测试集准确率分别为73.3%、80.0%和72.7%;对组合后的原始光谱+一阶导数谱、原始光谱+二阶导数谱和一阶导数谱+二阶导数谱数据的分类中,训练集准确率分别为97.0%、96.7%和100%,测试集准确率分别为85.7%、90.0%和100%。结果表明,对组合后的导数光谱与原始光谱构建分类模型,准确率更高。其中,基于一阶导数谱+二阶导数谱数据构建的PCA结合RBF分类模型的结果最为理想,准确率达100%。而K最近邻算法模型由于受到样本不均匀的影响,整体分类准确率均较低。利用组合的导数光谱与原始光谱数据构建分类模型能够实现对重质矿物油样本的快速、准确、无损鉴别,可为光谱组合技术在法庭科学及其他分析测试领域的应用提供一定的借鉴和参考。     

Towards a nondestructive chemical characterization of biofilm matrix by Raman microscopy

In this study, the applicability of Raman microscopy (RM) for nondestructive chemical analysis of biofilm matrix, including microbial constituents and extracellular polymeric substances (EPS), has been assessed. The examination of a wide range of reference samples such as biofilm-specific polysaccharides, proteins, microorganisms, and encapsulated bacteria revealed characteristic frequency regions and specific marker bands for different biofilm constituents. Based on received data, the assignment of Raman bands in spectra of multispecies biofilms was performed. The study of different multispecies biofilms showed that RM can correlate various structural appearances within the biofilm to variations in their chemical composition and provide chemical information about a complex biofilm matrix. The results of RM analysis of biofilms are in good agreement with data obtained by confocal laser scanning microscopy (CLSM). Thus, RM is a promising tool for a label-free chemical characterization of different biofilm constituents. Moreover, the combination of RM with CLSM analysis for the study of biofilms grown under different environmental conditions can provide new insights into the complex structure/function correlations in biofilms.     

In-situ detection of drugs-of-abuse on clothing using confocal Raman microscopy

This study describes the application of confocal Raman microscopy to the detection and identification of drugs-of-abuse in situ on undyed natural synthetic fibres, and coloured textile specimens. Raman spectra were obtained from drug particles trapped between the fibres of the specimens. Pure samples of cocaine hydrochloride and N-methyl-3,4-methylenedioxy-amphetamine HCl (MDMA-HCl) were used in this study. Raman spectra were collected from drug particles of an average size in the range 5-15 μm. Despite the presence of spectral bands arising from the natural and synthetic polymer and dyed textiles, the drugs could be identified by their characteristic Raman bands. If necessary, interfering bands could be successfully removed by spectral subtraction. Furthermore, Raman spectra were recorded from drug particles trapped between the fibres of highly fluorescent specimens. Interference from the fibres, including background fluorescence, was overcome by careful focusing of the confocal beam and the resulting spectra allow ready differentiation from interference from the fibres substrate bands. Spectra of several drugs-of-abuse on dyed and undyed clothing substrates were readily obtained within 3 min with little or no sample preparation and with no alteration of the evidential material.     

Discrimination of herbal medicines by molecular spectroscopy and chemical pattern recognition

The molecular spectroscopy (including near infrared diffuse reflection spectroscopy, Raman spectroscopy and infrared spectroscopy) with OPUS/Ident software was applied to clustering ginsengs according to species and processing methods. The results demonstrate that molecular spectroscopic analysis could provide a rapid, nondestructive and reliable method for identification of Chinese traditional medicine. It's found that the result of Raman spectroscopic analysis was the best one among these three methods. Comparing with traditional methods, which are laborious and time consuming, the molecular spectroscopic analysis is more effective.     

Raman spectroscopic signature of blood and its potential application to forensic body fluid identification

Near-infrared (NIR) Raman spectroscopy was used to measure spectra of dried human blood samples from multiple donors. Two major questions addressed in this paper involve the influence of sample heterogeneity and potential Raman spectral variations that could arise between different donors of blood. Advanced statistical analysis of spectra obtained from multiple spots on dry samples showed that dry blood is chemically heterogeneous, and its Raman spectra could be presented very well as a linear combination of a fluorescent background and two Raman spectroscopic components that are dominated by hemoglobin and fibrin, respectively. Each sample Raman spectrum contains the same major peaks, but the relative contribution of the hemoglobin and fibrin components varies with the donor. Therefore, no single spectrum could adequately represent an experimental Raman spectrum of dry blood in a quantitative way, but rather the combination of hemoglobin and fibrin spectral components could be considered to be a spectroscopic signature for blood. This proof-of-concept approach shows the potential for Raman spectroscopy to be used in forensic analysis to identify an unknown substance such as blood.     

基于非接触式拉曼光谱分析人血与犬血的PCA-LDA鉴别方法

将拉曼光谱分析法与数理统计方法有机结合,构建人血与犬血种属判别模型,实现了不同种属血液样本的高效无损鉴别.采用拉曼光谱的无损测试模式对血液样本进行测试,考察了抗凝管管材、聚焦位置及曝光时间等对血液样本拉曼光谱的影响,在激发波长为632.8 nm,光谱扫描范围为200~1800 cm-1,功率衰减率50%,曝光时间5 s及累加次数为2次的优化条件下,获得了无损检测条件下的血液样本拉曼光谱图.针对血液样本组分复杂、拉曼光谱信号基底背景高等问题,提出了基于小波变换去噪,进行分段多项式基线校正的预处理方法,有效解决了血液样本拉曼光谱谱图的高噪音和基线漂移问题.实验选择30例正常人血和33例比格犬血为样本训练集,5例正常人血和5例比格犬血为测试集,基于主成分分析法(PCA)联合线性判别法(LDA)模型,训练集分类正确率达到95.23%,盲测集分类正确率达90.00%.这种基于非接触式血液样本拉曼光谱和PCA-LDA判断模型的测试方法在进出口检验检疫等涉及血液无损鉴别的领域具有广泛的应用价值和前景.     

Raman spectroscopy based analysis of milk using random forest classification

The development of a classification system based on the Raman spectra of milk samples is proposed in present study. Such development could be useful for nutritionists in suggesting healthy food to infants for their proper growth. Previously, molecular structures in milk samples have been exploited by Raman spectroscopy. In the current study, Raman spectral data of milk samples of different species is utilized for multi-class classification using a dimensionality reduction technique in combination with random forest (RF) classifier. Quantitative and experimental analysis is based on locally collected milk samples of different species including cow, buffalo, goat and human. This classification is based on the variations (different concentrations of the components present in milk such as proteins, milk fats, lactose etc.) in the intensities of Raman peaks of milk samples. Principal component analysis (PCA) is used as a dimensionality reduction technique in combination with RF to highlight the variations which can differentiate the Raman spectra of milk samples from different species. The proposed technique has demonstrated sufficient potential to be used for differentiation between milk samples of different species as the average accuracy of about 93.7%, precision of about 94%, specificity of about 97% and sensitivity of about 93% has been achieved.     

Studying disorder in graphite-based systems by Raman spectroscopy

Raman spectroscopy has historically played an important role in the structural characterization of graphitic materials, in particular providing valuable information about defects, stacking of the graphene layers and the finite sizes of the crystallites parallel and perpendicular to the hexagonal axis. Here we review the defect-induced Raman spectra of graphitic materials from both experimental and theoretical standpoints and we present recent Raman results on nanographites and graphenes. The disorder-induced D and D' Raman features, as well as the G'-band (the overtone of the D-band which is always observed in defect-free samples), are discussed in terms of the double-resonance (DR) Raman process, involving phonons within the interior of the 1st Brillouin zone of graphite and defects. In this review, experimental results for the D, D' and G' bands obtained with different laser lines, and in samples with different crystallite sizes and different types of defects are presented and discussed. We also present recent advances that made possible the development of Raman scattering as a tool for very accurate structural analysis of nano-graphite, with the establishment of an empirical formula for the in- and out-of-plane crystalline size and even fancier Raman-based information, such as for the atomic structure at graphite edges, and the identification of single versus multi-graphene layers. Once established, this knowledge provides a powerful machinery to understand newer forms of sp(2) carbon materials, such as the recently developed pitch-based graphitic foams. Results for the calculated Raman intensity of the disorder-induced D-band in graphitic materials as a function of both the excitation laser energy (E(laser)) and the in-plane size (L(a)) of nano-graphites are presented and compared with experimental results. The status of this research area is assessed, and opportunities for future work are identified.     

Aldose reductase inhibitory, anti-cataract and antioxidant potential of selected medicinal plants from the Marathwada region, India

The water, ethanol and chloroform extracts of selected plants such as Adhatoda vasica (L.) (Acanthaceae), Caesalpinia bonduc (L.), Cassia fistula (L.) (Caesalpiniaceae) and Biophytum sensitivum (L.) (Oxalidaceae) were evaluated for rat lens aldose reductase inhibitory (RLAR) potential, anti-cataract and antioxidant activities. All the samples inhibited the aldose reductase considerably and exhibited anti-cataract activity, while C. fistula (IC(50), 0.154 mg mL(-1)) showed significant RLAR inhibitory activity as compared to the other tested samples, and was further found to be more effective in maintaining sugar-induced lens opacity in the rat lens model. The antioxidant potential of plant extracts was determined using DPPH (2,2-diphenyl-1-picryl hydrazine), hydroxyl (OH), nitric oxide (NO) and hydrogen peroxide (H(2)O(2)) scavenging activities, along with determination of reducing power, ferrous ion chelating ability and inhibition of polyphenol oxidase (PPO). The extracts of the tested plant showed significant free radical scavenging activities and inhibited the activity of enzyme PPO, a model oxidising enzyme. The plant samples were found to possess considerable amounts of vitamin C, total polyphenols and flavonoids.     

Determination of the carbonyl groups in native lignin utilizing Fourier transform Raman spectroscopy

A near-infrared Fourier transform Raman (NIR-FTR) spectroscopic technique was utilized to determine the chemical structure of lignin in a woody matrix. In the NIR-FTR spectra of coniferaldehyde and coniferyl alcohol, the Raman bands for the carbonyl group and the alpha, beta unsaturated bond were detected at 1620 and 1660 cm(-1), respectively. These peaks were also found in the NIR-FTR spectra of chemically synthesized lignins, isolated lignin from conifer wood, and conifer wood meal. Upon the reduction of carbonyl groups in the lignin samples and wood meal, the band at 1620 cm(-1) disappeared; on the other hand, the band at 1660 cm(-1) remained unchanged. However, upon the oxidation of reduced lignin at the benzyl hydroxyl group using dicyanodichrolobenzoquinone, the band at 1620 cm(-1) clearly appeared, strongly suggesting that the band at 1620 cm(-1) can be assigned as a carbonyl marker band. The hydrogenation reaction optimized for the reduction of the unsaturated bond in lignin caused the disappearance of the band at 1660 cm(-1), indicating that the band at 1660 cm(-1) is an alpha, beta unsaturated bond marker band. The change in carbonyl content during the wood decay process was also shown to be monitored using the Raman intensity of the carbonyl marker band. It was indicated that the NIR-FTR spectroscopic techniques were suitable analytical method for a rapid and nondestructive analysis of wood samples.     

The isolation and structure elucidation of new cassane diterpene-acids from Caesalpinia crista L. (Fabaceae), and review on the nomenclature of some Caesalpinia species

New cassane diterpene-acids, neocaesalpins H and I, were isolated from the leaves of Caesalpinia crista (Fabaceae), and their structures were deduced on the basis of the spectroscopic and chemical basis. These compounds were characterized as having an alpha,beta-butenolide hemiacetal ring that is rare in nature. The lacking of 5-hydroxy group also distinguished neocaesalpins H and I from cassane diterpenes (caesalpins) occurring in other Caesalpinia species from the phytochemical viewpoint. The nomenclature of three Caesalpinia species was also reviewed, and it was found that some species belonging to the genus Caesalpinia are improperly named and should be changed to valid names.