Deep Ultraviolet Excitation Research Articles

Protein secondary structure from deep‐UV resonance Raman spectroscopy

AbstractRaman spectra of proteins that are obtained with deep ultraviolet excitation contain resonance‐enhanced amide bands of the polypeptide backbone, as well as aromatic side chain bands. The amide bands are sensitive to conformation, and can be used to estimate the backbone secondary structure. UV Raman spectra are reported at 206.5 and 197 nm, for a set of 12 proteins with varied secondary structure content, and are used to establish quantitative signatures of secondary structure via least‐squares fitting. Amide band enhancement is greater at 197 nm, where basis spectra are established for β‐turn, as well as α‐helix, β‐sheet and unordered structures; the lower signal strength at 206.5 nm does not provide a reliable spectrum for the first of these. Application of these basis spectra is illustrated for the melting of apo‐myoglobin. The amide band positions and cross sections are discussed. Copyright © 2006 John Wiley & Sons, Ltd.

A new single grating spectrograph for ultraviolet Raman scattering studies

AbstractA state‐of‐the‐art single grating spectrograph for Raman scattering studies within the deep ultraviolet (DUV) region of the electromagnetic spectrum is discussed. It is based on a high throughput DUV version of a single‐stage monochromator originally designed for use in the visible spectral region. Its key components are two identical, newly designed calcium fluoride camera lenses each consisting of five different individual optical elements. The first of these lenses collimates the Raman scattered DUV radiation entering the spectrometer through its entrance slit. The second lens focuses the collimated beam of dispersed Raman scattered DUV radiation emerging from a high‐resolution reflection grating onto a charge coupled device (CCD) detector with enhanced DUV sensitivity. A novel high transmission edge filter is used as a blocking device for a sufficient rejection of the Rayleigh line generating a relatively sharp transmittance cutoff at a Stokes Raman wavenumber shift of about ∼450 cm−1 employing 257 nm DUV excitation. Overall, this new spectrograph enables rapid collection of Stokes DUV Raman scattered photons at f/2 wide apertures with sufficiently large signal‐to‐noise ratios (SNRs) in relatively short acquisition times and with an effective spectral resolution of approximately ∼6 cm−1. Backscattered Raman spectra of the following chemicals are presented as typical results illustrating the excellent performance characteristics of this new DUV spectrograph for a variety of experimental conditions within different scattering scenarios and for a relatively wide range of commonly used sample preparation techniques: neat cyclohexane, laboratory air, polycrystalline D‐glucose, single crystal L‐alanine and a dilute aqueous solution of 2′‐deoxyadenosine. Copyright © 2005 John Wiley & Sons, Ltd.

Tunable kHz Deep Ultraviolet (193–210 nm) Laser for Raman Applications

The performance characteristics of a kilohertz solid-state laser source for ultraviolet Raman spectroscopy are described. Deep ultraviolet (UV) excitation in the 193-210 nm region is provided by mixing of the fundamental and third harmonics of a Ti-sapphire laser, which is pumped by the second harmonic of a Q-Switched Nd-YLF laser. The combination of tunability, narrow linewidth, high average power, good stability, and kilohertz repetition rate makes this laser suitable for deep UV resonance Raman applications. The short pulse duration (approximately 20 ns) permits nanosecond time resolution in pump-probe applications. The low peak power and high data rate provide artifact-free spectra with a high signal-to-noise ratio. UV Raman cross-section and Raman excitation profiles are reported for gaseous O2 (relative to N), aqueous ClO4-, tyrosine, phenylalanine, tryptophan, histidine, and hemoglobin excited between 193 nm and 210 nm to illustrate laser performance.

Deep-ultraviolet Raman spectroscopy study of the effect of aging on human cortical bone

The age-related deterioration in bone quality and consequent increase in fracture incidence is an obvious health concern that is becoming increasingly significant as the population ages. Raman spectroscopy with deep-ultraviolet excitation (244 nm) is used to measure vibrational spectra from human cortical bone obtained from donors over a wide age range (34-99 years). The UV Raman technique avoids the fluorescence background usually found with visible and near-infrared excitation and, due to resonance Raman effects, is particularly sensitive to the organic component of bone. Spectral changes in the amide I band at 1640 cm(-1) are found to correlate with both donor age and with previously reported fracture toughness data obtained from the same specimens. These results are discussed in the context of possible changes in collagen cross-linking chemistry as a function of age, and are deemed important to further our understanding of the changes in the organic component of the bone matrix with aging.

UV Raman Spectroscopy of Single-Walled Carbon Nanotubes

Deep UV Raman spectroscopy is emerging as a useful tool for the characterization of carbon materials that has many advantages over visible Raman spectroscopy. However, because of resonance enhancement and other effects, UV Raman spectra are often different from visible Raman spectra. UV Raman spectra have not been reported for even some of the most widely known carbon materials. We report Raman spectra of single-walled carbon nanotubes (SWNTs) collected with deep ultraviolet (4.8 eV) laser excitation. There are significant differences between the deep UV and the visible Raman spectrum of SWNTs for the graphitic “G” modes and “disorder-induced” “D” modes, which are common to a wide range of forms of carbon. Furthermore, only semiconducting tubes are observed in the UV Raman spectrum, which is not consistent with an expected resonance enhancement of the scattering from metallic tubes at 4.8 eV.

Determination of the isoflavone formononetin in red clover (Trifolium pratense L.) by micellar electrokinetic chromatography combined with deep‐UV laser‐induced wavelength‐resolved fluorescence detection

Micellar electrokinetic chromatography (MEKC) was combined with a special mode of laser-induced fluorescence (LIF) detection for the determination of isoflavonoids and more especially formononetin in red clover. In this LIF mode, deep-ultraviolet (UV) excitation is performed and fluorescence spectra are recorded on-line. The native-fluorescent isoflavonoids were excited at 275 nm by a modified large-frame argon-ion laser and on-line recording of fluorescence emission spectra was performed by an intensified diode-array detector mounted on a spectrograph. The potential of this approach for target analysis is demonstrated by the identification and quantification of formononetin in a clover extract at a concentration of 3×10−5 M or 17 μg formononetin per gram red clover. Sample clean-up was performed by off-line solid-phase extraction. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 347–352, 1999

Determination of the isoflavone formononetin in red clover (Trifolium pratense L.) by micellar electrokinetic chromatography combined with deep-UV laser-induced wavelength-resolved fluorescence detection

Micellar electrokinetic chromatography (MEKC) was combined with a special mode of laser-induced fluorescence (LIF) detection for the determination of isoflavonoids and more especially formononetin in red clover. In this LIF mode, deep-ultraviolet (UV) excitation is performed and fluorescence spectra are recorded on-line. The native-fluorescent isoflavonoids were excited at 275 nm by a modified large-frame argon-ion laser and on-line recording of fluorescence emission spectra was performed by an intensified diode-array detector mounted on a spectrograph. The potential of this approach for target analysis is demonstrated by the identification and quantification of formononetin in a clover extract at a concentration of 3×10−5 M or 17 μg formononetin per gram red clover. Sample clean-up was performed by off-line solid-phase extraction. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 347–352, 1999