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.     

Quantitative histochemical analysis of human artery using Raman spectroscopy.

We have developed a method for using near infrared Raman spectroscopy to quantitatively analyze the histochemical composition of human artery. The main contributors to bands observed in the Raman spectra of normal and atherosclerotic aorta are the proteins collagen and elastin, cholesterol lipids, and calcium hydroxyapatite. The Raman scattering cross-sections of different bands for these components have been determined in order to understand their relative contributions to the Raman spectra of biological tissue. The Raman signal is observed to behave linearly with the concentration of the components, even in a highly scattering medium such as a powder. Using these data, we have developed a linear model that can be used to extract the quantitative contribution of an individual component to the spectrum of a mixture. The model has been applied to several mixtures of known composition of tissue constituents in order to evaluate its precision and accuracy. The calculated fit coefficients from the spectra are in agreement with the measured values within experimental uncertainties. The spectra of different types of atherosclerotic aorta have also been modeled, and we have extracted quantitative information regarding the relative concentration of biological constituents in atherosclerotic aorta.     

How many chiral centers can Raman optical activity spectroscopy distinguish in a molecule?

To study the capabilities and limitations of Raman optical activity, (-)-(M)σ-[10]helicene and (-)-(M)σ-[4]helicene serve as scaffold molecules on which new chiral centers are introduced by substitution of hydrogen atoms with other functional groups. These functional groups are deuterium atoms, fluorine atoms, and methyl groups. Multiply deuterated species are compared. Then, results of singly deuterated derivatives are compared against results obtained from singly fluorinated and methylated derivatives. The analysis required the calculation of a total of 2433 Raman optical activity spectra. The method we propose for the comparison of the various Raman optical activity spectra is based on the total intensity of squared difference spectra. This allows a qualitative comparison of pairs of Raman optical activity spectra and the extraction of the pair of most similar Raman optical activity spectra for each group of stereoisomers. Different factors were accounted for, such as the spectral resolution (modeled by line broadening) and the range of vibrational frequencies considered. In the case of σ-[4]helicene all generated stereoisomers in each group can be distinguished from one another by Raman optical activity spectroscopy. For σ-[10]helicene this holds except for the lower one of the two resolutions considered. Here, the group consisting of stereoisomers with five chiral centers contains at least one pair of derivatives whose Raman optical activity spectra cannot be distinguished from one another. This indicates that an increased molecular size has a negative effect on the number of chiral centers which can be distinguished by Raman optical activity spectroscopy. Regarding the different substituents, stereoisomers are the better distinguishable in Raman optical activity spectroscopy, the more distinct the signals of the substituent are from the rest of the spectrum.     

Standardless Analysis of Multicomponent Mixtures of Substances by Time-Resolved Vibronic Spectroscopy

A new approach to the quantitative and qualitative standardless analysis of complex substances based on experimental time-dependent vibronic luminescence spectra (in the UV and visible regions) is proposed. The approach requires no preliminary calculation of absolute intensities for molecular models. It is shown that this analysis can be carried out for both individual substances and multicomponent mixtures, including unknown substances and mixtures of unknown composition. The concentration ranges of mixture components available for the analysis are evaluated, depending on the optical properties of mixtures.     

Evaluation of protocols for reproducible electrospray in-source collisionally induced dissociation on various liquid chromatography/mass spectrometry instruments and the development of spectral libraries

Mass spectral libraries provide a tool for identifying unknown compounds using both molecular weight and fragmentation information. Mass spectrometers with electrospray ionisation (ESI) and atmospheric chemical ionisation (ApCI) sources have the capability to produce data of this type using in-source collisionally induced dissociation (CID), and in-source CID libraries can be created. Due to the variation in electrospray source design from different instrument manufacturers, the production of reproducible in-source CID spectra that can be used in libraries for all instrument types is not a trivial task. To date, the evaluation of the production of in-source CID libraries has tended to focus on similar instruments from one manufacturer. The studies have also tended to focus on specific compound classes, with a limited molecular weight range.This report describes the findings from the investigation of protocols for the creation of mass spectral libraries using ESI in-source CID on six instruments from four different manufacturers. The overall goal was to create a spectral library for the identification of unknowns. The library could then be applied across all manufacturers' electrospray instruments.Two different experimental protocols were attempted. The first used a tuning compound to establish standard ESI source conditions, with fixed fragmentation potentials. The second involved the attenuation of the [M + H](+) ion to a known degree. A diverse range of compounds (pharmaceutical, photographic, pesticides) was tested to establish the reproducibility of the spectra on the six instruments. Both protocols produced spectra on the various instruments that in many cases were very similar. In other examples, the spectra differed not only in their relative ion abundances, but also in terms of the spectral content. Important observations regarding the effect of ion source design are also reported.The degree of spectral reproducibility was calculated off-line by comparing the five most abundant ions (20% for each ion that matches) from each spectrum on each instrument. This approach was adopted, as we do not possess a software package that met our requirements for spectral comparison. Match factors (% fit) were calculated by comparing each spectrum against the spectra recorded for the same compound and then for all other compounds, on each instrument. The % fit values derived by the off-line approach gave a clear view of the spectral reproducibility from instrument to instrument and also discriminated the spectra of the various compounds from each other. The applicability of this approach was tested using a blind trial in which several compounds were presented as unknowns, their in-source CID spectra recorded and the five-ion approach used for identification.     

Raman spectra from ethylene and deuterated ethylene chemisorbed on a silica-supported nickel catalyst

The Raman spectra of ethylene and deuterated ethylene chemisorbed on silica-supported nickel have been measured in the frequency range 50–3400 cm^?1. At room temperature, a Raman spectrum is observed which corresponds to ethylene chemisorbed under dehydrogenation and it is rather similar to the spectrum of chemisorbed acetylene. For a comparison therefore, the Raman spectra of acetylene and deuterated acetylene were also measured. In addition, the vibrational spectrum of chemisorbed benzene was recorded. At temperatures T ? 200 K, ethylene is found to be associatively chemisorbed without dehydrogenation.The vibrations observed are described in the approximation of a surface molecule with covalent bonding to two or three surface nickel atoms. The symmetry seems to be slightly distorted C_2v or C_s. The vibrational spectrum is discussed with respect to a metal- surface selection rule. In order to improve the reliability of the assignments for localized vibrational modes, a normal coordinate analysis and a force constant calculation have been done for chemisorbed acetylene.     

Monitoring Phosphorylation and Dephosphorylation Reactions by Surface-Enhanced Raman Scattering (SERS) in Model Compounds

Abstract

Raman and Surface-Enhanced Raman Scattering (SERS) spectra of phosphates, polyphosphates, and various phosphate complexes have been recorded. Bands of the vibrational spectra were assigned. The comparison of SERS spectra obtained by using colloidal silver with the corresponding Raman spectrum reveals enhancement and shifts in some bands, suggesting a possible partial charge-transfer mechanism in the SERS effect. Phosphorylation and dephosphorylation reactions brought about by the reactions of cobalt (III) bis trimethylenediamine phosphate/pyrophosphate complexes with nitrophenol/nitrophenyl phosphates are described.     

Quantitative multiplex CARS spectroscopy in congested spectral regions

A novel procedure is developed to describe and reproduce experimental coherent anti-Stokes Raman scattering (CARS) data, with particular emphasis on highly congested spectral regions. The approach, exemplified here with high-quality multiplex CARS data, makes use of spontaneous Raman scattering results. It is shown that the underlying vibrational Raman response can be retrieved from the multiplex CARS spectra, so that the Raman spectrum can be reconstituted, provided an adequate signal-to-noise ratio (SNR) is present in the experimental data and sufficient a priori knowledge of the vibrational resonances involved exists. The conversion of CARS to Raman data permits a quantitative interpretation of CARS spectra. This novel approach is demonstrated for highly congested multiplex CARS spectra of adenosine mono-, di-, and triphosphate (AMP, ADP, and ATP), nicotinamide adenine dinucleotide (NAD+), and small unilamellar vesicles (SUVs) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Quantitative determination of nucleotide concentrations and composition analysis in mixtures is demonstrated.     

Quantitative NIR Raman analysis in liquid mixtures

The capability to obtain quantitative information of a simple way from Raman spectra is a subject of considerable interest. In this work, this is demonstrated for mixtures of ethanol with water and rhodamine-6G (R-6G) with methanol, which were analyzed directly in glass vessel. The Raman intensities and a simple mathematical model have been used and applied for the analysis of liquid samples. It is starting point to generate a general expression, from the experimental spectra, as the sum of the particular expression for each pure compound allow us to obtain an expression for the mixtures which can be used for determining concentrations, from the Raman spectrum, of the mixture.     

Similarity search for a 1H-NMR spectroscopic data base

A similarity-search system is described for proton-NMR spectroscopy. In order to achieve fast retrieval of reference compounds, the ¹H-NMR spectra of the data base and of the unknown are encoded in a bitsring. The individual bits of the binary signature describe different features of the spectra. Part of the coupling information is coded in such a way that effects of magnetic field strength are taken into account. The encoding thus permits a fast search for identical and structurally similar reference compounds in the data base even when the spectra were recorded at different magnetic field strengths. Because the search consists of weighted comparison of bits, each of them describing different spectral features, a choice of different kinds of searches is possible with the same signature by selecting appropriate weight vectors. Thus specific spectroscopic features can be selected for the search. Such a context-sensitive similarity-search system allows, for example, a search for compounds having similar multiplicities or similar subspectra in a given (e.g., aromatic) region of the spectrum. Furthermore, by adjusting two “software knobs” which influence the normalization of the search results, the user can choose between the two extremes of forward and reverse search, and between an identity search, similarity search or classification search. The results were tested on a small library containing 550 spectra including some mixtures and duplicates recorded under different experimental conditions at 250 and 400 MHz.     

Field desorption mass spectrometric analysis of mixtures of surfactants and inorganic salts

A field desorption mass spectrometric method is proposed for the analysis of mixtures of surfactant and inorganic salts. Different compounds in the mixture are determined with different heating currents and distinguished on the basis of the exterior character of the mass spectrum. The effectiveness of the method is demonstrated with known mixtures of surfactants and inorganic salts. Two unknown additives for electric tin plating were tested with the method.     

Rapid differentiation among bacteria that cause gastroenteritis by use of low-resolution Raman spectroscopy and PLS discriminant analysis

Use of classical microbiological methods to differentiate bacteria that cause gastroenteritis is cumbersome but usually very efficient. The high cost of reagents and the time required for such identifications, approximately four days, could have serious consequences, however, mainly when the patients are children, the elderly, or adults with low resistance. The search for new methods enabling rapid and reagentless differentiation of these microorganisms is, therefore, extremely relevant. In this work the main microorganisms responsible for gastroenteritis, Escherichia coli, Salmonella choleraesuis, and Shigella flexneri, were studied. For each microorganism sixty different dispersions were prepared in physiological solution. The Raman spectra of these dispersions were recorded using a diode laser operating in the near infrared region. Partial least-squares (PLS) discriminant analysis was used to differentiate among the bacteria by use of their respective Raman spectra. This approach enabled correct classification of 100% of the bacteria evaluated and unknown samples from the clinical environment, in less time (∼10 h), by use of a low-cost, portable Raman spectrometer, which can be easily used in intensive care units and clinical environments.     

Chiral terpenes in different phases: <Emphasis Type="Italic">R</Emphasis>-(−)-camphorquinone studied by IR–Raman–VCD spectroscopies and theoretical calculations

R-(−)-camphorquinone is a bicyclical terpenoid with many usages and application in different fields. Different experimental and theoretical works reveal that there is only one stable conformer of this chiral chemical species in agreement to the sterical restriction that the bicycle introduces. In the current work, from a complete assignment of the vibrational IR and Raman spectra, we are able to explain the VCD spectrum of the title compound. The recorded spectra of R-(−)-camphorquinone in different phases have been analyzed and compared: the first one in CCl₄ solution, the second one using Nujol and Fluorolube suspensions and the third one using thin films. Finally, to study the coupling between the two C=O stretching normal modes, a NBO analysis is performed. The present work reveals that IR, Raman and VCD, combined with quantum chemical calculations, are helpful complementary techniques to characterize chiral systems, as terpenes, in different phases.     

Raman spectroscopy as tool for the characterization of thio-polyaromatic hydrocarbons in organic minerals

Benzothiophene and dibenzothiophene have been studied by Raman microspectroscopy using a 785 nm excitation wavelength. The spectra obtained have been compared with the previously measured spectra of idrialite, a complex natural mineral composed entirely of cata-condensed polyaromatic hydrocarbons (PAHs), usually containing a thiophenic or aliphatic five-membered ring. For comparison, the Raman spectra of 2,3-benzofluorene crystals have been obtained for the first time. Some of the bands in the idrialite spectra are attributed to specific vibrational modes of thiophene or fluorene-type PAHs, especially in the region below 1000 cm(-1). These modes at 495, 705 and 750 cm(-1) along with C-H or C-H(2) stretching modes around 3000 cm(-1) can be then used to distinguish such groups of PAHs in complicated organic mineral mixtures like idrialite.     

Standardization of Raman spectra for transfer of spectral libraries across different instruments

In this paper we evaluate methods for standardization of Raman spectra that are required to improve spectral correlation computations between spectra measured on different instruments. Five commercially-available 785 nm Raman spectrometers from different vendors were included in the study. These spectrometers have diverse specifications and performance levels and range in size from laboratory-based instruments to field-deployable portable and handheld platforms. Since each Raman spectrometer has different characteristics, spectra obtained on one instrument cannot readily be compared to a library acquired on a different instrument without performing various types of spectral corrections (standardization). We outline a procedure that combines previously established Raman shift and intensity correction protocols with a resolution matching step to facilitate the comparison of a centralized master library with spectra acquired on different geographically distributed Raman spectrometers. The standardization procedure is effective in reducing the inherent instrument-to-instrument variability so that spectra from different spectrometers can be compared and reliable results obtained using library-based spectral correlation methods. The findings have important implications for the ability to transfer Raman spectral libraries between instruments.     

基于临近比较的快速拉曼光谱基线校正方法

拉曼光谱成像技术是基于拉曼散射效应所开发的一项现代检测技术,在现代生产、科学研究过程中使用非常广泛。拉曼光谱信号受荧光效应和仪器等方面的影响,往往会产生基线漂移,严重影响对信号特征的进一步提取。因此,必须对拉曼光谱信号进行基线校正。传统的基线校正方法,只针对单一光谱信号,计算量较大,在处理由大量拉曼信号组成的成像数据时,耗时较长且效果不佳。该文提出一种基于临近比较的快速基线校正方法,根据在相同背景下采集的光谱之间的相关性,实现快速基线校正,提高了拉曼成像数据的处理速度。     

Possibility of Human Gender Recognition Using Raman Spectra of Teeth

Gender determination of the human remains can be very challenging, especially in the case of incomplete ones. Herein, we report a proof-of-concept experiment where the possibility of gender recognition using Raman spectroscopy of teeth is investigated. Raman spectra were recorded from male and female molars and premolars on two distinct sites, tooth apex and anatomical neck. Recorded spectra were sorted into suitable datasets and initially analyzed with principal component analysis, which showed a distinction between spectra of male and female teeth. Then, reduced datasets with scores of the first 20 principal components were formed and two classification algorithms, support vector machine and artificial neural networks, were applied to form classification models for gender recognition. The obtained results showed that gender recognition with Raman spectra of teeth is possible but strongly depends both on the tooth type and spectrum recording site. The difference in classification accuracy between different tooth types and recording sites are discussed in terms of the molecular structure difference caused by the influence of masticatory loading or gender-dependent life events.     

FT-IR and FT-Raman spectroscopic investigation, computed vibrational frequency analysis and IR intensity and Raman activity peak resemblance analysis on 2-nitroanisole using HF and DFT (B3LYP and B3PW91) calculations

Fourier-transform Raman and infrared spectra of 2-nitroanisole are recorded (4000-100 cm(-1)) and interpreted by comparison with respective theoretical spectra calculated using HF and DFT method. The geometrical parameters with C(S) symmetry, harmonic vibrational frequencies, infrared and Raman scattering intensities are determined using HF/6-311++G (d, p), B3LYP/6-311+G (d, p), B3LYP/6-311++G (d, p) and B3PW91/6-311++G (d, p) level of theories. A detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The results of the calculations have been used to simulate IR and Raman spectra for the molecule that showed good agreement with the observed spectra. The SQM method, which implies multiple scaling of the DFT force fields has been shown superior to the uniform scaling approach. The vibrational frequencies and the infrared intensities of the C-H modes involved in back-donation and conjugation are also investigated.     

Vibrational spectrum and structure of dimethylamino-dichloroarsine

The infrared spectra of solid and gaseous dimethylaminodichloroarsine have been recorded from 4000 to 33 cm⁻¹. The Raman spectra of the liquid and solid phases have also been recorded. A comparison of the Raman spectra of the liquid and solid indicates that there is a change in conformational composition between the two phases. The isomer present at room temperature in the liquid and gas phases is assigned to the trans form. A study of the temperature dependence of the intensities of the Raman spectrum indicates that the trans form is converted to a second isomer which is believed to be the gauche isomer as the temperature is decreased. At −190°C, the Raman intensities indicate that the molecule still exists as a mixture of these two isomers. A vibrational assignment is presented and discussed in detail.     

Interpretation Automatique des Spectres de Masse de Composes Organiques. Mise au Point

Computerized methods for interpretation of mass spectra are increasing and many papers have now been published. Three different approaches can be used to identify an unknown compound. These methods are reviewed and discussed. First, the heuristic technique which tries to simulate the reasoning of the chemist and deduce the formulae. The only information needed are the mass spectra, the empirical formulae and the n.m.r. spectra. Some promising results have been obtained but the method has important restrictions. Another approach represents the mass spectra as points in a hyperspace. By developing decision surfaces it is possible to classify an unknown compound. This is called pattern recognition and the different empirical methods for recognizing patterns in mass spectral data are explained and reported. The last and simplest technique is to match an unknown spectrum against a library of standard references. When the unknown spectrum is in the library, this approach gives the best results.