Raman Excitation Wavelength Research Articles

Raman excitation wavelength investigation of single red blood cells in vivo

AbstractRaman spectra are reported for oxygenated and deoxygenated haemoglobin contained within a single red blood cell in vivo using excitation wavelengths of 488, 514, 568 and 632.8 nm. The peak assigned in previous work to ν4 is observed at 1376 cm−1 in oxygenated cells and 1356 cm−1 in deoxygenated cells with the results from 488 nm excitation consistent with earlier Raman studies on isolated haem proteins. Exciting the cells with 514 nm radiation revealed two bands appearing in this region at 1372 and 1356 cm−1 in the oxygenated state, whereas in the deoxygenated state only one band at 1356 cm−1 is observed. At 632.8 nm excitation bands in the ν4 region appeared at 1367 and 1365 cm−1 in the oxygenated and deoxygenated states, respectively. Our results clearly show that the enhancement of bands in the vicinity of ν4 within single erythrocytes is influenced by the excitation wavelength. Furthermore, many other bands observed in oxygenated erythrocytes using 632.8 nm excitation were dramatically enhanced compared with the bands observed with other excitation wavelengths. Ruling out other explanations, it is hypothesized that the enhancement observed at 632.8 nm results from excitonic coupling between aligned porphyrins. The high concentration of haemoglobin in a single cell enables the porphyrins to be in close proximity to permit charge transfer between the haem moieties. The high signal‐to‐noise ratio and excellent reproducibility obtained using Raman water immersion microspectroscopy on single erythrocytes in vivo shows potential as a diagnostic tool for a variety of haemopathies. However, judicious choice of the excitation wavelength is a prerequisite especially if the technique is applied to diagnose oxidation status within erythrocytes. Copyright © 2002 John Wiley & Sons, Ltd.

Study of solvent effects on the molecular structure and the reorganization energies of 4‐nitro‐4′‐dimethylaminoazobenzene using resonance Raman intensities

AbstractResonance Raman spectroscopy was used to probe the effect of solvent polarity on the molecular structure and isomerization dynamics of 4‐nitro‐4′‐dimethylaminoazobenzene (DA). In addition, the influence of the polarity and the relaxation behavior of the solvent on the mode‐specific vibrational and solvent reorganization energies was investigated. Raman spectra were recorded in solvents with different polarity parameters, n‐hexane and benzene, using 11 excitation wavelengths in the range 450–550 nm, scanning every 10 nm using the tunable laser pulse output of an optical parametric oscillator. It was observed that the solvent polarity plays a major role in influencing the excited‐state potential energy surfaces of DA. The plot of resonance Raman intensities versus excitation wavelength (Raman excitation profiles) of the Franck–Condon‐active fundamentals of DA shows that in n‐hexane, the locally excited state is more favorable than that in benzene where the charge‐transfer state is more stable. The distortions along the N N and C–N stretching vibrations of DA in n‐hexane and benzene infer isomerization via rotation in n‐hexane and inversion in benzene. The increase in solvent and vibrational reorganization energies with increasing solvent polarity parameter suggests greater distortion in the Franck–Condon excited state following photoexcitation. Copyright © 2001 John Wiley & Sons, Ltd.

Solvation Effects on the A-Band Photodissociation of Dibromomethane: Turning a Photodissociation into a Photoisomerization

We have obtained A-band resonance Raman spectra of dibromomethane in the gas and solution phase and nanosecond time-resolved resonance Raman spectra of dibromomethane photoproducts. The A-band resonance Raman spectra suggest the short-time dynamics are similar to other dihalomethanes that are known to have direct photodissociation reactions in the gas phase. Several power dependent A-band resonance Raman bands were tentatively assigned to the C−Br stretch overtone progression of the CH2Br radical which has a strong absorption band that is coincident with the A-band resonance Raman excitation wavelength. Two-color nanosecond time-resolved resonance Raman spectra (266.0 nm pump/341.5 nm probe) were obtained and comparison of the vibrational frequencies to the results for density functional theory calculations indicate that the iso-CH2Br−Br species is mainly responsible for the transient photoproduct absorption band ∼360 nm. Our preliminary results for A-band photoexcitation of dibromomethane in conjunction ...

Irradiance inversion algorithm for estimating the absorption and backscattering coefficients of natural waters: Raman-scattering effects

We modify an algorithm for retrieving the absorption (a) and backscattering (b(b)) coefficient profiles in natural waters by inverting profiles of downwelling and upwelling irradiance so as to include the presence of Raman scattering. For a given wavelength of interest, lambda, the light field at the appropriate Raman excitation wavelength lambda(e) is first inverted to obtain the Raman source function at lambda. Starting from estimates of the inherent optical properties at lambda, the contribution to the irradiances at lambda from Raman scattering is then estimated and subtracted from the total irradiances to obtain the elastically scattered irradiances. We then inverted the elastically scattered irradiances to find new estimates of a and b(b) using our original method [Appl. Opt. 37, 3886 (1998)]. The algorithm then operates iteratively: The new estimates are used with the Raman source function to derive a new estimate of the Raman contribution, etc. Sample results are provided that demonstrate the working of the algorithm and show that the absorption and scattering coefficients can be retrieved with accuracies similar to those in the absence of Raman scattering down to depths at which the light field is significantly perturbed by it, e.g., with approximately 90% of the upwelling light field originating from Raman scattering.

Quadrupolar vibrational mode of silver clusters from plasmon-assisted Raman scattering

Absorption and low-frequency Raman-scattering experiments have been performed on thin films consisting of small silver clusters embedded in a porous alumina matrix. When the Raman excitation wavelength is close to the maximum (\ensuremath{\approx}420 nm) of the Mie band (dipolar surface plasmon resonance) the Raman spectra exhibit a strong band located around 10 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, the maximum of which depends on the cluster diameter D at the maximum of the cluster-size distribution in the sample according to the approximate law ${\ensuremath{\omega}}_{\mathrm{vib}}\ensuremath{\propto}{D}^{\ensuremath{-}1}.$ The Raman band corresponds to the excitation of the quadrupolar vibration mode of the clusters, via the plasmon-phonon interaction. Moreover, the maximum of the Raman band shifts towards lower frequencies when the excitation light is shifted to the red. This feature, as well as the rather large Mie-band width, is shown to reflect the ellipsoidal shape distribution of part of the embedded clusters.

Plasmon-phonon coupling and resonant raman scattering of silver clusters

Absorption and low-frequency Raman scattering experiments have been performed on thin films consisting of small silver clusters embedded in a porous alumina matrix. When the Raman excitation wavelength is close to the maximum (≈420 nm) of the Mie band (dipolar surface plasmon resonance) the Raman spectra exhibit a strong band located around 10 cm-1, the maximum of which depends on the mean cluster diameter 〈D〉 in the sample according to the approximate law ωvib∝〈D〉-1. The Raman band corresponds to the excitation of the quadrupolar vibration mode of the clusters. Moreover, the maximum of the Raman band shifts towards lower frequencies when the excitation light is shifted to the red. This feature, as well as the rather large Mie-band width, is thought to reflect the ellipsoidal shape distribution of part of the embedded clusters.

Surface Enhanced Raman Spectroscopic Study of Isomeric Formyl Pyridines in Silver Colloid

Surface enhanced Raman (SER) spectra of ortho, meta,and paraformyl pyridines in silver sol are compared with their normal Raman spectra in bulk and aqueous solution. Significant enhancement of Raman bands has been observed. The SER spectra suggest an almost normal orientation of the adsorbate molecular planes to the metal surface and also reveal that orthoand paraisomers exist in a hydrate form in the surface adsorbed state. The metaisomer, however, retains its original nicotinaldehyde form. On addition of the formyl pyridines (FP), the ν maxof the bands that appear on the longer wavelength side of the electronic absorption band of stable, neat silver sol show a parallel relationship with the Hammett σ (σ H) values of the isomers. Raman excitation wavelength dependence suggests that resonance to the aggregation band contributes significantly to SER spectra. The concentration dependence of the enhancement ratio shows a maximum, suggesting monolayer formation at a specific concentration for each isomer. This “first-layer effect” and also the excitation wavelength dependence of SER spectra imply a charge transfer contribution to enhancement.

Isolation of preresonance and out-of-phase dual circular polarization Raman optical activity

We report the first isolation of preresonance Raman scattering behavior in Raman optical activity (ROA) and first measurement of out-of-phase dual circular polarization (DCP II) ROA. Using a series of molecules of increasing delocalized electronic structure, we observe a correlated increase in the degree to which the DCP I and ICP u ROA backscattering spectra differ from one another. Through this comparison, ROA is shown to be a sensitive way of detecting the presence of presonance Raman scattering intensity using a single Raman excitation wavelength.

Vibrational mode-selective effects in the picosecond time-resolved resonance Raman spectrum of singlet excited trans-stilbene

Picosecond time-resolved resonance Raman spectra of singlet excited trans-stilbene have been obtained using several photolysis (pump) and Raman excitation (probe) wavelengths. Vibrational mode-selective changes in peak wavenumbers and bandwidths are dependent on the sample temperature, the pump wavelength, and the solvent. The effects are greatest for the band at ≈ 1570 cm −1, attributed to the olefinic bond stretching mode. The peak wavenumber of this band decreases and the band broadens as the temperature is raised. Excess energy of excitation results in an initial decrease of peak wavenumber and increase in width followed by an increase in peak wavenumber and decrease in width as the delay between pump and probe increases further, with a similar time dependence for peak position as for width. Fits to the sum of two exponentials give time constants in the range 1 to 5 ps for the initial and 9 to 12 ps for the later stages of the evolution. There is an similarity between the temperature and excess energy dependence, but bandwidth is more (× 2.9) sensitive than peak wavenumber to excess energy. The mode-selective changes and dynamics are interpreted with a model involving intramolecular vibrational relaxation and reorientation of the solvent cage in response to microdielectric stabilisation forces and quasi-equilibration with bulk solvent. The role of vibrationally “'hot” low-wavenumber modes is clarified.

Time-resolved resonance Raman and molecular orbital studies of the structures of the transient species involved in the photochromic reaction of 2,2′-spirobi[2H-1-benzopyran

Resonance Raman spectra of the transient species of 2,2′-spirobi[2H-1-benzopyran] in various solvents reveal that at least two isomers exist in solution, the relative abundance of which depends on the polarity and hydrogen-bond donor ability of the solvent. Vibrational assignment of the transient species based on 13C substitutions shows that the Raman bands mainly attributable to the vibrations of the open benzopyran part are enhanced by the Raman excitation wavelengths longer than 460 nm, whereas those assignable to the vibrations of the closed benzopyran part are observed only by the Raman excitation wavelengths shorter than 460 nm. Semi-empirical molecular orbital calculations show that the contribution of the ortho-quinoidal form to the resonance hybrid structure of the transient species is much larger than that of the zwitterionic form. Also, it is shown that the trans-trans-trans (TTT) configuration about the three CC partial double bonds of the transient species is most stable.

The resonance Raman spectrum of carotenoids as an intrinsic probe for membrane potential Oscillatory changes in the spectrum of neurosporene in the chromatophores of Rhodopseudomonas sphaeroides

The resonance Raman spectrum of the carotenoid neurosporene is shown to be a sensitive monitor of absorption shifts, and thus changes in membrane potential, in chromatophores of the GlC mutant of Rhodopseudomonas sphaeroides. For a Raman excitation wavelength at 472.7 nm, the intensities of the two most prominent resonance Raman features ( v 1 and v 2) respond very differently to small shifts in the absorption maxima. Thus, the ratio intensity v 1/intensity v 2 is a sensitive probe for absorption shifts. Changes in this ratio of ∼20% were observed during a valinomycin induced diffusion potential. At 5°C changes in the average intensity ratio of +6, −4 and −14% were brought about by oligomycin, FCCP and sodium deoxycholate, respectively. The changes in intensity ratio were temperature dependent and, in addition, effects due to the laser beam acting as an actinic light could be detected. Oscillatory changes were observed in absolute Raman and Rayleigh scattering intensities for chromatophores at 5°C and for intact cells under growing conditions.