Anti-Stokes Yb3+ emission--valuable structure information in spectra of rare earth compounds measured with FT-Raman spectrometers

Raman spectroscopy is a powerful and simple method which proved to be very useful in studies of solids. The most widely used Raman spectrometers are FT-Raman instruments with YAG:Nd(3+) laser as an excitation source. However, in the case of samples containing rare earth elements, the quality of FT-Raman spectra is often low due to strong fluorescence effects. We show that, in such cases, anti-Stokes part of the Raman spectra often contains strong, well resolved bands identified as multiphonon-assisted emission bands of Yb(3+) present as an impurity. We show on several examples that analysis of these bands may provide useful structure information, similar to that obtained by "Eu structure probe" method in optical spectroscopy. The Yb(3+) emission can be also measured using standard luminescence detection systems. However, the application of FT-Raman system allows one to obtain good quality spectra in a much cheaper, easier and faster way (in times as short as a few seconds). Moreover, high-sensitivity of FT-Raman spectrometers allows to detect even very small amounts of Yb(3+) impurity.     

Monitoring of enzyme catalysed reactions by Fourier transform Raman spectrometry

Esterification of mandelic acid catalysed by Candida antarctica lipase B was studied by Fourier transform (FT) Raman spectrometry in non-aqueous medium. It was found that there is a strict correlation between the intensity of the Raman scattering and the activity of the enzyme. FT-Raman spectrometry seems to be a fast and reliable method for selecting the appropriate enzyme and for determining the optimal enzyme water content. In addition, valuable information can be obtained from the spectra regarding the mechanism of enzyme–substrate bonding.     

Assessment of hand-held Raman instrumentation for in situ screening for potentially counterfeit artesunate antimalarial tablets by FT-Raman spectroscopy and direct ionization mass spectrometry

Pharmaceutical counterfeiting has become a significant public health problem worldwide and new, rapid, user-friendly, reliable and inexpensive methods for drug quality screening are needed. This work illustrates the chemical characterization of genuine and fake artesunate antimalarial tablets by portable Raman spectroscopy and validation by FT-Raman spectroscopy and ambient mass spectrometry. The applicability of a compact and robust portable Raman spectrometer (TruScan™) for the in situ chemical identification of counterfeit tablets is reported.     

On-line FT-Raman and dispersive Raman spectra database of artists’ materials (e-VISART database)

Raman spectroscopy has been widely applied in the analysis of different types of artwork. This technique is sensitive, reliable, non-destructive and can be used in situ. However, there are few references in the literature regarding specific Raman spectra libraries for the field of artwork analysis. In this paper, the development of two on-line databases with Fourier transform Raman (FT-Raman; 1064 nm) and dispersive Raman (785 nm) spectra of materials used in fine art is presented; both are implemented in the e-vibrational spectroscopic databases of artists materials database (e-VISART). The database provides not only spectra, but also information about each pigment. It must be highlighted that for each pigment or material several spectra are available from different dealers. Some of the FT-Raman spectra available in the e-VISART database have not been published until now. Some examples in which the e-VISART database has been successfully used are presented.     

Step-scan near-infrared Fourier-transform Raman spectroscopy with 100 picosecond laser pulses

Time-resolved Fourier-transform Raman scattering with picosecond excitation is reported for the first time. The resonance Raman spectrum of 9,10-diphenylanthracene in its excited single state was obtained by Raman excitation at 1064 nm with 100 ps pulses, following photoexcitation at 355 nm. The implementation and characterization of time-resolved FT-Raman spectroscopy with a step-scan interferometer is discussed. FT-Raman spectra generated with continuous and mode-locked beams in the continuous-scan mode of the interferometer are compared with step-scan FT-Raman spectra generated with 2 kHz pulses.     

Library of FT-Raman spectra of pigments, minerals, pigment media and varnishes, and supplement to existing library of Raman spectra of pigments with visible excitation.

Sixty pigments, minerals and media have been analysed by Fourier-transform Raman (FT-Raman) microscopy in order to assemble a database of reference FT-Raman spectra for scientists working at the Arts-Science interface. An earlier library of Raman spectra compiled using visible excitation has been extended by the addition of 22 further reference spectra obtained with 780.0, 647.1, 632.8 and/or 514.5 nm excitation. The relative merits of 1064 nm and visible excitation are discussed.     

FT-Raman spectrometry determination of Malathion in pesticide formulations

A fast and environmentally friendly method has been developed for Fourier transform-Raman (FT-Raman) spectrometry determination of Malathion in pesticide emulsifiable concentrate formulations. The method is based on the measurement of intensity peak height values at 1737 cm⁻¹ Raman shift corrected using a baseline defined at 1900 cm⁻¹. Samples were diluted with CHCl₃ and the FT-Raman spectra collected in back-scattering mode over 3.3 min at a nominal resolution of 4 cm⁻¹ accumulating 50 scans per spectra and using a laser power of 1250 mW. The developed procedure provided a limit of detection of 1.8% w/w in the original sample. Results found by FT-Raman spectrometry were statistically comparable with those obtained by flow injection Fourier transform infrared spectrometry, FIA-FTIR, and gas chromatography (GC) and were in good agreement with those reported by the manufacturer. The FT-Raman developed procedure reduces drastically the chlorinated solvent waste generation and avoids the contact of the operator with toxic products, being a fast alternative to the CIPAC recommended GC procedure.     

Fourier transform Raman microspectroscopy

Summary This paper shows some preliminary results taken with a commercially available Raman microscope which is based on the Fourier Transform Raman technique using near infrared laser sources. The micro apparatus is described and measurement examples are given. A comparison between spectra taken with the microscope and a conventional macro sample device which is usually utilized in FT-Raman spectroscopy is carried out. Furthermore the differences of FT-Raman and FT-IR microanalysis are studied on the basis of practical results received from spectral data. Limitations due to the physical properties of infrared and Raman microspectroscopy are discussed.The data partly contained in this paper were first presented at the 12th Int. Raman conference, August 1990, Columbia, S.C.Dedicated to the 60th birthday of Professor Bernhard Schrader     

Raman spectra of inorganic ions

This paper contains the Raman spectra of 79 inorganic salts and sulphur which may be used as an aid in qualitative inorganic analyses. These were obtained some years ago by conventional Raman spectroscopy. No such collection exists and the order of the reference spectra is identical to those in a collection of IR spectra. A table of characteristic frequencies for 17 polyatomic ions is given. These data have increased relevance following the emergence of FT-Raman as a rapid and efficient modern technique.     

Fluorescence rejection in Raman spectra of Syncrude Sweet Blend distillation fractions

Four techniques for the reduction or elimination of fluorescence from Raman spectra of Syncrude process samples were examined in this study. These methods are based on the retrieval of Raman bands from differential, or derivative spectra. Differential data were generated by subtracting similar spectra of a given sample obtained in three ways: (a) shifted detection utilizing an array detector and two successive spectrometer settings; (b) shifted excitation (dispersive Raman) where the two spectra are recorded using neighbouring laser lines and ordinary photon counting; (c) shifted excitation (FT-Raman) in which the laser frequency is changed in software before acquisition of the second spectrum. In addition to these differential techniques, derivative spectra were acquired directly with a dispersive Raman system by modulating the wavelength during scanning. These fluorescence rejection methods were applied to two groups of Syncrude Sweet Blend distillation fractions. For light gas oils (boiling range, 195-343 degrees C) the ratio of monocyclic and bicyclic aromatic species was determined and bands due to aliphatic CH(n) groups were characterized. Heavy gas oils (343-524 degrees C) yielded bands that allowed quantitation of monocyclic, bicyclic and total aromatic groups. Bands due to aliphatics were also identified for the heavy gas oils. These results constitute a significant advance compared to the information obtainable using conventional dispersive and FT-Raman spectroscopy for the analysis of hydrocarbon distillation fractions.     

Experimental aspects of Fourier transform Raman spectroscopy

Using a commercial Fourier transform infrared spectrometer and the 1.064m line of a CW NdYAG laser, we have measured the Raman spectra of a wide variety of materials. The Raman scattered light, Stokes shifted toward the mid-infrared, is collected, using a 90° lens geometry, and focused through the emission port of the spectrometer. After passing through the Michelson interferometer, the light is detected by a thermoelectrically-cooled high-sensitivity germanium detector. The Fourier transform of the resulting interferogram gives the Raman spectrum. This new technique allows spectra to be obtained of samples which were previously completely masked by competing fluorescence. In addition, FT-Raman also allows moieties, such as hydrocarbon chains, which are not present in resonance enhanced spectra, to be investigated. We will discuss our approach toward FT-Raman, which is compatible with traditional Raman spectroscopy, present representative spectra of liquids and solids, and draw some comparisons and contrasts between dispersive and FT measurements.     

Electronic modulation of dithienothiophene (DTT) as pi-center of D-pi-D chromophores on optical and redox properties: analysis by UV-Vis-NIR and Raman spectroscopies combined with electrochemistry and quantum chemical DFT calculations

In this paper, we study three symmetrical D-pi-D chromophores containing dithieno[3,2-b:2',3'-d]thiophene (DTT) as the pi-center and various donor end moieties, by means of UV-vis-NIR and FT-Raman spectroscopy and in situ spectroelectrochemistry. The compounds display dual redox properties: all exhibited two oxidations and single stable reduction peaks contrarily to the one or two oxidations and none reduction which could be anticipated in view of their chemical structures. We analyze the possible electronic modulation by the pi-conjugated DTT relay in the redox process and electronic coupling between the two electron donor (D) units attached through conjugation to opposite sides of the pi-linker. To this end, the UV-vis-NIR and FT-Raman spectra of the neutral compounds and of the charged species generated upon in situ p- or n-doping have been recorded and interpreted with the help of Density Functional Theory (DFT) calculations. The analysis of the peculiar Raman features of these pi-conjugated chromophores is guided by the formalism of the Effective Conjugation Coordinate (ECC) theory. This research shows that the Raman spectroscopic characterization of this type of D-pi-D structures is a powerful tool to derive information about their pi-conjugational properties in the pristine and doped states.     

青蒿素的Raman光谱研究

本文对固态青蒿素的FT-Raman光谱和普通Raman光谱以及低浓度(1×10^-^5mol/L)青蒿素水溶液的表面增强Raman散射(SERS)光谱进行了检测, 着重观察了1756cm^-^1六元内酯环振动谱带, 发现其在FT-Raman和普通Raman光谱中表现为强振动, 而在SERS光谱中此振动谱带消失, 说明分子内酯环发生了破裂。根据1756cm^-^1谱带的变化以及724cm^-^1过氧基团振动频率的位移, 对青蒿素在银表面上的吸附取向进行了研究。还研究了青蒿素与氯高铁血红素的作用情况, 发现两者作用后, 明显改变了青蒿素在银表面上的吸附。     

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.     

High-pressure vibrational study of the catalyst candidate cis-dimercaptobis(triphenylphosphine)platinum(II), cis-[(Ph3P)2Pt(SH)2

Infrared and FT-Raman spectra of cis-dimercaptobis(triphenylphosphine)platinum(II), cis-[(PPh3)2Pt(SH)2], have been measured at high external pressures up to 55 kbar with the aid of a diamond-anvil cell (DAC). The wavenumber (v) versus pressure (P) plots from the Raman data indicate the occurrence of a pressure-induced phase transition at around 15 kbar. The metal-ligand stretching mode, v(Pt-S), and the C-H stretching mode of the phenyl rings, v(C-H), are highly sensitive to the application of pressure (dv/dP approximately 1.0 cm(-1) kbar(-1)). The IR results are generally consistent with the Raman data. The pressure-induced phase transition is most probably attributable to the reorientation of the phenyl rings in the complex; similar results have been obtained for other phenyl derivatives.     

Non-destructive Raman analyses--polyacetylenes in plants

Ferdinand Bohlmann has described the isolation, the identification and the structure elucidation of acetylene compounds in many plants, and confirmed it by its synthesis. We have recorded the Raman spectra of most of these plants non-destructively by FT-Raman spectroscopy using radiation at 1064 nm. We could not observe any interfering fluorescence. We found acetylene compounds in some plants, even distinct compounds with different concentration in various parts of it. The distribution of the different compounds over the plant can be observed and their changes during the ontogenesis can be followed by a FT-Raman mapping technique. Of special help is a library of Raman and IR spectra and the structure of the compounds, synthesized by Bohlmann. Thus, the Raman technique allows analyses in a very short time replacing the usual time-consuming separation procedures and avoiding artefacts during clean-up procedures.     

Applications of Fourier transform Raman spectroscopy in inorganic chemistry—a considered view

A sudy of a wide variety of coloured main group metal, transition metal coordination and transition metal organometallic complexes using Fourier transform Raman (FT-Raman) spectroscopy has demonstrated a high success rate (ca 50%) with good quality spectra obtained in short periods of time. It is suggested that FT-Raman spectroscopy should now be regarded as a routine spectroscopic tool for use in inorganic as well as organic research and teaching laboratories.     

Vibrational spectra of 1-methyluracilate complex with silver(I) and theoretical studies of the 1-MeU anion

The FT-Raman and FT-infrared spectra of (1-methyluracilato)silver, [Ag(C(5)H(5)N(2)O(2))] in the solid state have been studied. The complex is a polymer in which one silver ion is linearly bonded to two 1-MeU ligands through the deprotonated N(3) sites and another silver ion is tetrahedrally coordinated to the four 1-MeU ligands through the O2 and O4 carbonyl oxygen atoms. The harmonic vibrational frequencies, infrared intensities and Raman scattering activities of the N(3)-deprotonated 1-methyluracilate anion have been calculated using density functional (B3LYP) and ab initio (HF and MP2) methods with the 6-31G(d,p) and 6-31++G(df,pd) basis sets. The calculated potential energy distribution (PED) for the 1-MeU anion has proved to be of great help in assigning the spectra of the title complex. It can be concluded that the two strong Raman bands at 1263 and 796 cm(-1) are diagnostic for the N3-deprotonation of the 1-methyluracilate ring and complexation with silver ion. The linear N-Ag-N stretching vibrations are assigned to the bands at 448 and 362 cm(-1) (IR) and 453, 362 cm(-1) (Raman). The Ag-O stretching vibrations are assigned to the bands in the range of 280-250 cm(-1).     

Fourier transform infrared and Raman spectral investigations of 5-aminoindole

Fourier transform infrared (FT-IR) and Raman (FT-Raman) spectra of 5-aminoindole has been recorded and analysed. The FT-IR spectrum of the compound was recorded in a BrukerIFS 66 V spectrometer in the range 4000-400 cm(-1) and the FT-Raman spectrum was also recorded in the same instrument in the region 3500-100 cm(-1). Observed frequencies for normal modes are compared with those calculated form normal co-ordinate analysis. The shift in the frequencies of the fundamental modes with the substituent amino group and the mixing of different normal modes are discussed with the help of potential energy distribution (PED) calculated through normal co-ordinate analysis.     

FT-Raman, FTIR and surface-enhanced Raman spectroscopy of the antiviral and antiparkinsonian drug amantadine

FT-Raman, FTIR and surface-enhanced Raman spectroscopy (SERS) are applied to the vibrational characterization of the antiviral and antiparkinsonian drug amantadine. SERS spectroscopy is employed for the first time for characterizing the interfacial behavior of this molecule and to study its interaction with colloidal silver. The comparison of SERS spectrum with the Raman spectra of amantadine in solid state and in aqueous solution reveals remarkable changes attributed to the interaction of the drug with the metal through the unprotonated amino group and the formation of a self-assembled amantadine layer on the metal surface. A tentative assignment of the obtained vibrational spectra is carried out on the basis of the vibrational spectra of the structurally related molecules adamantane and tert-buthylamine and the ab initio calculations accomplished for amantadine.