Raman spectroscopy interference enhanced

By tuning the laser source to the absorption maximum of the chromophore, the Raman spectrum obtained is the enhanced spectrum of that chromophore with little interference from the dense vibration modes of the protein or the water itself. For a quantitative discussion of resonance Raman spectroscopy (14) and its application to biological systems (15), the reader is referred to other papers. 

The use of resonance Raman spectroscopy for the study of transient species, including free radicals, has been reviewed be Hester (1978). Provided only that excitation may be achieved within an intense absorption band specific to the intermediate species, selective resonance enhancement permits the detection and characterization of such species at concentrations in the lO" - 10 molar range without serious interference from spectra of other dissolved species such as excess reactant and product molecules. 

Holt, R.E. and Cotton, T.M. (1987) Free flavin interference in surface enhanced resonance Raman-spectroscopy of glucose oxidase. Journal of the American Chemical Society, 109,1841-1845. 

As has been mentioned Raman spectroscopy is very well suited for spectroelectrochemical studies of conjugated polymers. The spectra can be obtained for polymers deposited on practically any electrode suitable for electrochemical investigations. Due to strong resonant enhancement of the bands originating from the polymer, the signals from the solvent are nonexistent or negligible and practically do not interfere. 

Raman spectroscopy has shown great potential in forensic science because it is nondestructive, it has a high selectivity, and the analyses are fast. Methods to minimize interference and enhance the Raman signal caused this renewed interest. 

Despite the extensive studies of the anodic layers on Pt with various ultraviolet-visible optical methods, they have not provided a clear indication of the electronic or structural properties of the layers. Rather these optical methods have been more than just another form of readout to complement the electrochemical measurements of charge and current response of the layer to potential and time. Vibrational spectroscopic data from infrared and Raman measurements would be more helpful in establishing the nature of the layers but it is difficult to use these techniques to study metal-electrolyte and similar interfaces because of solvent interference and sensitivity problems. A noteworthy exception is the quite successful in situ use of Raman spectroscopy to study the electrochemically formed oxide layers on silver by Kotz and Yeager. In the instance of silver electrodes, there is a large surface enhanced Raman effect and the signal-to-noise ratio is not a problem. Unfortunately this is not the situation with other metal surfaces such as Pt. Even so, with improved instrumentation there is hope that in situ Raman studies of the anodic layers on Pt will become practical. 

IR and Raman spectroscopy are common tools to study organic compounds like. The methods are rapid, non-destructive and with no need for sample preparation [78]. There is a considerable number of experimental studies using IR spectroscopy to characterise PBI-type polymers doped with phosphoric acid [7-9, 60, 61, 74, 79, 80]. The number of Raman studies is still limited, despite the fact that the intensity of vibration modes from polymer skeleton are enhanced compared to N-H and O-H vibration modes, i.e. there are less interferences due to the presence of water. 

Resonance Raman spectroscopy (RRS) leads to increased selectivity in Raman spectral measurements. The Raman spectrum of individual components in a complex mixture can be selectively enhanced by a judicious choice of laser wavelength. Only the Raman bands of the chromophore which is in resonance at the wavelength of excitation are significantly enhanced. Raman bands of non-absorbing species are not enhanced and do not interfere with those of the chromophore. Clearly, resonance Raman is a very sensitive analytical tool capable of providing detailed molecular vibrational information. 

Though normal Raman spectroscopy is a very selective technique for chemical analysis, there are some serious experimental disadvantages related to the sensitivity, large fluorescence interference, and lack of time resolution of the technique. These weaknesses have been addressed in the creation of new Raman-based techniques. The weak Raman signals due to inherently small Raman scattering efficiencies has been addressed by resonance Raman, surface-enhanced Raman and SPP-Raman techniques. Fourier transform-Raman spectroscopy and con-focal Raman microscopy address the disadvantage of... 

A major advantage of Raman spectroscopy for the analysis of biomolecules stems from the fact that water has a weak Raman spectrum. Spectra can be recorded for aqueous solutes at 10 -10 M with little interference from the solvent. For a chromophore under the RR condition the accessible concentration range becomes 10 " -10 M. Moreover, the intensity enhancement associated with the RR effect confers the important advantage of selectivity, allowing one to observe selectively the vibrational spectrum of a chromophore that is just one component of an extremely complex biological system. Because many biomolecules have chromophores with an ultraviolet (UV) resonance condition, one may also selectively excite a chromophore by irradiating these molecule with UV light. This technique is known as Ultraviolet Resonance Raman Spectroscopy (UVRRS). In recent years, Raman difference spectroscopy (RDS) has been developed in... 

Valuable spectroscopic studies on the dithiolene chelated to Mo in various enzymes have been enhanced by the knowledge of the structure from X-ray diffraction. Plagued by interference of prosthetic groups—heme, flavin, iron-sulfur clusters—the majority of information has been gleaned from the DMSO reductase system. The spectroscopic tools of X-ray absorption spectroscopy (XAS), electronic ultraviolet/visible (UV/vis) spectroscopy, resonance Raman (RR), MCD, and various electron paramagnetic resonance techniques [EPR, electron spin echo envelope modulation (ESEEM), and electron nuclear double resonance (ENDOR)] have been particularly effective probes of the metal site. Of these, only MCD and RR have detected features attributable to the dithiolene unit. Selected results from a variety of studies are presented below, chosen because their focus is the Mo-dithiolene unit and organized according to method rather than to enzyme or type of active site. 

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