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.     

Yb3+ as an origin of the strong anti-Stokes luminescence in NIR FT-Raman spectra of some lanthanide sesquioxides

Strong anti-Stokes bands observed in FT-Raman spectra of Y2O3, Gd2O3 and Lu2O3 are explained by NIR luminescence of Yb3+ impurities present in sesquioxides after the excitation with the 1064 nm line of an Nd:YAG laser. Samples of Y2O3:Yb, Ga2O3:Yb, CeO2:Yb, Gd2O3:Yb and Lu2O3:Yb were prepared by solution combustion synthesis procedure using urea. All materials were investigated by FT-Raman and FT-NIR spectroscopy and characterized by X-ray powder diffraction.     

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.     

Critical evaluation of a handheld Raman spectrometer with near infrared (785nm) excitation for field identification of minerals

Handheld Raman spectrometers (Ahura First Defender XL, Inspector Raman DeltaNu) permit the recording of acceptable and good quality spectra of a large majority of minerals outdoors and on outcrops. Raman spectra of minerals in the current study were obtained using instruments equipped with 785 nm diode lasers. Repetitive measurements carried out under an identical instrumental setup confirmed the reliability of the tested Raman spectrometers. Raman bands are found at correct wavenumber positions within ±3 cm(-1) compared to reference values in the literature. Taking into account several limitations such as the spatial resolution and problems with metallic and black and green minerals handheld Raman spectrometers equipped with 785 nm diode lasers can be applied successfully for the detection of minerals from the majority of classes of the mineralogical system. For the detection of biomarkers and biomolecules using Raman spectroscopy, e.g. for exobiological applications, the near infrared excitation can be considered as a preferred excitation. Areas of potential applications of the actual instruments include all kind of common geoscience work outdoors. Modified Raman systems can be proposed for studies of superficial or subsurface targets for Mars or Lunar investigations.     

A new mechanism of Raman enhancement and its application

Strong electronic Raman bands corresponding to the transition between 4I9/2 and 4I11/2 manifolds of Nd3+, caused by a Raman-enhancement effect, are observed in the FT-Raman spectrum of Nd2O3. Neither resonance enhancement (RR) nor surface enhancement (SERS) accounts for the Raman enhancement observed here. We propose a new mechanism of Raman enhancement called the "feed-back" mechanism. A YAG laser excites the final state of the Raman transition (4I11/2 of Nd3+) to the 4F3/2 state and causes a significant decrease in the population of Nd3+ at the 4I11/2 state. This causes the population ratio of Nd3+ at 4I9/2 and 4I11/2 to deviate from the value required by Boltzmann's law. To restore equilibrium, Raman scattering is enhanced so that more Nd3+ ions are brought from the 4I9/2 state to the 4I11/2 state. This hypothesis gets support from the temperature-variable FT-Raman spectroscopic results. Additionally, obvious differences between the Stokes and anti-Stokes Raman spectrum of Nd3+ provide further evidence to support the feed-back mechanism. The Raman-enhancement effect confers on the electronic Raman bands a special ability to reflect the variation of coordinated structure around metal ions. The structural variations in polymer-metal ion composites and biomineralization systems have been investigated by using the electronic Raman bands.     

Non-destructive NIR-FT-Raman analyses in practice. Part II. Analyses of ''jumping'' crystals, photosensitive crystals and gems

Using an improved sampling arrangement we observed the FT Raman spectra of the different phases of a 'jumping crystal', an inositol derivative. The phase transition produced--as consequences of large changes of the unit cell constants--changes in frequency and intensity mainly of CH deformation vibrations. Photochemical reactions, usually produced with light quanta in the visible range, are not activated with the quanta from the Nd:YAG laser at 1064 nm. The Raman spectra of the 'dark' form of a dinitrobenzyl pyridine and afterwards the 'light' form, the product of its illumination in the visible range, were recorded. We could not observe changes of most bands, especially not of the NO2-vibrations; however, a new strong band appeared at 1253 cm(-1), which may be due to the expected NH-photo-isomer. Genuine gemstones and fakes can be unambiguously identified by FT Raman spectroscopy. This is especially useful for the stones whose physical properties are quite similar to those of diamonds--moissanite and zirconia. The quality of diamonds can be estimated from relative band intensities; however, this is not in complete agreement with the internationally accepted visual qualification. Synthetic diamonds produced by CVD (chemical vapor deposition) show remarkable differences from natural ones in their FT-Raman spectra.     

A comparison between PA-FTTR and FT-Raman spectroscopies in the structural analysis of annealed injected-moulded poly (ethylene terephthalate)

With the introduction of the Fourier Transform technique in Raman spectroscopy (FT-Raman) and the development of new methods in FTIR, such as FTIR with photoacoustic detection (PA-FTTR), vibrational spectroscopy has been launched into a new era of application in polymer chemistry and physics. This work provides a comparative study between PA-FTIR and FT-Raman techniques in which the potentials and limitations of these two methods are investigated by following and analyzing structural variations that take place in annealed injected-moulded poly(ethylene terephthalate) (PET). Both spectroscopic techniques appear to be suitable to detect structural changes that occur in PET submitted to different annealing temperatures. We suggest that these variations are directly related to conformational rather than crystallinity changes. The main drawbacks of PA-FTIR are the lengthy adquisition time of spectra and the photoacoustic saturation that can appear in regions with quite high optical absorption coefficient. Conversely, FT-Raman technique does not suffer from neither of these problems. However, the sensitivity to structural changes of certain infrared bands seems to be higher than that of analogous Raman bands and small structural details such as the regularity of chain folding, can only be detected in the infrared spectra.     

Fourier-transform Raman and infrared spectroscopic analysis of novel biliverdin compounds

The vibrational spectroscopy of novel biliverdin compounds were studied by Fourier-transform Raman (FT-Raman) and infrared (FT-IR) spectroscopy. The effects of type, length and position of substituents at C(8) and C(12) or C(1) and C(19) of tetrapyrroles on FT-Raman and FT-IR spectra of these compounds, are discussed. The marker bands are developed in order to distinguish between etiobiliverdin and mesobiliverdin.     

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.     

不同结构形态的NdOHCO3中Nd3+的增强电子拉曼光谱研究

利用X射线粉末衍射、场发射电子扫描显微术和透射电子显微术TEM,对不同方法制备的形态、颗粒大小不同的MdOHCO3进行钕离子的增强电子拉曼光谱和FT-IR光谱研究,发现结构形态不同的NdOHCO3由于配位环境变化,导致钕离子的电子拉曼光谱在2600～1600cm-1附近拉曼谱带的峰形、峰位和峰的数目产生显著变化.     

Enhanced Raman spectrum of lawsone on Ag surface: vibrational analyses, frequency shifts, and molecular geometry

The surface-enhanced Raman spectrum of lawsone, a well known natural dye, has been investigated. Activation with KNO(3) or Na(2)SO(4) solution was necessary to enhance the Raman signal, whereas addition of NaCl solution depletes the effects. In the enhanced Raman spectrum, the strong double-bond stretching bands are most distinctive and show large red shifts from those in the infrared and FT-Raman spectra. The observed strong double-bond stretching bands reflect lawsone coordinated perpendicular to the Ag surface. DFT computations have been carried out for the plausible configurations of lawsone coordinated to an adatom on the Ag surface. Lawsone coordinated to an Ag(+) adatom with H(+) released best reproduces the observed vibrational characteristics.     

高岭石结构缺陷的 1H MAS NMR和Raman研究

The structure default of kaolinites was characterized with ¹H MAS NMR and Raman spectra. Although the HI indexes of Suzhou and Maoming kaolinite are similar, their ¹H MAS NMR and Raman spectra are very different. ¹H MAS NMR showed that the hydroxyl proton chemical shifts of Suzhou kaolinite are in the higher field and with larger different between the inner surface hydroxyls protons and inner hydroxyls proton chemical shifts than Maoming kaolinite. Raman spectra showed that the surface hydroxyls stretching vibration bands of Suzhou kaolinite are in the high frequency region, and the half height widths of the bands are 7.0～14 cm^-1. The area ratio S_z/(S_z+S_A), where S_Z and S_A are the areas of bands 3685 cm^-1 and 3695 cm^-1 respectively, is 0.23. But the surface hydroxyls stretching vibration bands of Maoming kaolinite are in the low frequency region, and the half height widths of the bands are 8.9～15.1 cm^-1. The area ratio S_z/(S_z+S_A) is 0.77. Those data proved that Suzhou kaolinite has lower structure default than Maoming kaolinite and ¹H MAS NMR and Raman spectra are effective method for study of kaolinite structure default.     

Determination of alkaloids in capsules, milk and ethanolic extracts of poppy (Papaver somniferum L.) by ATR-FT-IR and FT-Raman spectroscopy

Fourier transform (FT) infrared spectroscopy using a diamond composite ATR crystal and NIR-FT-Raman spectroscopy techniques were applied for the simultaneous identification and quantification of the most important alkaloids in poppy capsules. Most of the characteristic Raman signals of the alkaloids can be identified in poppy milk isolated from unripe capsules. But also poppy extracts present specific bands relating clearly to the alkaloid fraction. Raman spectra obtained by excitation with a Nd:YAG laser at 1064 nm show no disturbing fluorescence effects; therefore the plant tissue can be recorded without any special preparation. The used diamond ATR technique allows to measure very small sample amounts (5-10 microL or 2-5 mg) without the necessity to perform time-consuming pre-treatments. When applying cluster analysis a reliable discrimination of "low-alkaloid" and "high-alkaloid" poppy single-plants can be easily achieved. The examples presented in this study provide clear evidence of the benefits of Raman and ATR-IR spectroscopy in efficient quality control, forensic analysis and high-throughput evaluation of poppy breeding material.     

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.     

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.     

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.     

Electron paramagnetic resonance, optical absorption and IR spectroscopic studies of the sulphate mineral apjohnite

Apjohnite, a naturally occurring Mn-bearing pseudo-alum from Terlano, Bolzano, Italy, has been characterized by EPR, optical, IR and Raman spectroscopy. The optical spectrum exhibits a number of electronic bands around 400 nm due to Mn(II) ion in apjohnite. From EPR studies, the parameters derived, g=2.0 and A=8.82 mT, confirm MnO(H(2)O)(5) distorted octahedra. The presence of iron impurity in the mineral is reflected by a broad band centered around 8400 cm(-1) in the NIR spectrum. A complex band profile appears strongly both in IR and Raman spectra with four component bands around 1100 cm(-1) due to the reduction of symmetry for sulphate ion in the mineral. A strong pair of IR bands at 1681 and 1619 cm(-1) with variable intensity is a proof for the presence of water in two states in the structure of apjohnite.     

Er~(3+)和Ce~(3+)/Ce~(4+)掺杂β-BaB_2O_4纳米棒的制备、结构与发光性质

以Ba(NO_3)_2、NaBH_4、Er_2O_3和CeO_2为原料,在十六烷基三甲基溴化铵(CTAB)表面活性剂辅助下,采用水热法制备了β-BaB_2O_4(β-BBO)纳米棒,稀土离子Er~(3+)单掺杂的β-BBO(β-BBO:Er~(3+))及Er~(3+)和Ce~(3+)/Ce~(4+)共掺杂的β-BBO(β-BBO:Er(3+)/Ce~(3+)/Ce~(4+))纳米棒.通过X射线粉末衍射(XRD)、傅里叶变换红外(FTIR)光谱、拉曼光谱、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)和光致发光(PL)光谱分别对样品的物相、结构、形貌、成分及光致发光性质进行了表征.研究结果表明:微量稀土离子掺杂并不改变β-BBO的结构,制得的纳米棒尺寸均匀,长度在200-500 nm之间,直径在10-20 nm之间;β-BBO:Er~(3+)和β-BBO:Er~(3+)/Ce~(3+)Ce~(4+)纳米棒在400nm光激发下,在可见光范围内都观察到中心波长为515和542 nm的绿光.对发光机理的初步研究表明:发光分别对应于Er~(3+)的~2H_(11/2)→~4I_(15/2),~4S_(3/2)→~4I_(15/2)跃迁,铈离子以Ce~(3+)和Ce~(4+)两种形式存在于体系中,Ce~(3+)对Er~(3+)起敏化作用,可以显著增强β-BBO:Er~(3+)/Ce~(3+)/Ce~(4+)纳米棒的发光强度,存在Ce~(3+)→Er~(3+)的能量传递过程.     

Direct qualitative and quantitative characterization of a radiosensitizer, 5-iodo-2'-deoxyuridine within biodegradable polymeric microspheres by FT-Raman spectroscopy

Non-destructive qualitative and quantitative characterization of a radiosensitizer, 5-iodo-2'-deoxyuridine (IdUrd), incorporated within injectable microspheres of a biodegradable polymer, poly(D,L-lactide-co-glycolide) (PLGA), was performed using Fourier transform (FT) Raman spectroscopy. Raman spectra of IdUrd, free and entrapped in microspheres, were recorded under fluorescence-free conditions, described and assigned. For the Raman bands of the PLGA microspheres, assignments with preferential localization of the corresponding vibrations at lactic or glycolic units were proposed. No evidence for drug-polymer interactions in microspheres was found. This allowed the FT-Raman spectra to be used for the quantification of the IdUrd content in the samples. For the microspheres with IdUrd loadings varying from 2 to 27% of the total weight, the methodology used provided good reproducibility and precision (1%). Within the sensitivity of the technique, samples exposed to sterilization doses (27 kGy) of gamma-radiation did not exhibit marked changes in the drug structure.     

FT-Raman and photoacoustic infrared spectroscopy of syncrude light gas oil distillation fractions

FT-Raman and photoacoustic (PA) infrared spectra of 12 distillation fractions derived from Syncrude light gas oil (LGO), which has a boiling range from 195 to 343 degrees C, were analyzed in detail in this study. In the fingerprint region (200-1800 cm(-1)) most of the information is obtained from the FT-Raman spectra, which display 36 bands that are assignable to various alkyl or aryl functional groups. Monocyclic, bicyclic and tricyclic aromatics in the 12 fractions were also characterized using Raman bands in this region. The corresponding section of the infrared spectra is much simpler, displaying a relatively small number of bands due to either aromatic or aliphatic CH(n) (n=1, 2 or 3) groups. The Cz.sbnd;H stretching region in both FT-Raman and PA infrared spectra of the LGO distillation fractions was curve-fitted according to procedures established in previous investigations of Syncrude samples with various boiling ranges. The PA spectra of the LGO fractions were also analyzed using an accepted integration strategy that requires no a priori assumptions with regard to the number of constituent bands or their shapes. The curve-fitting results show that the frequencies of the 11 Raman and eight infrared bands used to model the aliphatic ( approximately 2775-3000 cm(-1)) parts of the respective spectra decrease systematically as the median boiling points of the LGO fractions increase. These band positions are consistent with those determined in earlier studies of other distillation fractions. Both curve fitting and integration show that the abundance of CH(2) groups increases at the expense of CH(3) groups as the boiling points of the fractions increase within the LGO region.