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A Simple Low-temperature Cryostat for Resonance Raman Studies of Frozen Protein Solutions
Volume 37, Number 3 (June 1983) Page 297-298
Czernuszewicz, Roman S.; Johnson, Michael K.
A frequent problem encountered in resonance Raman studies of aqueous protein solutions is that of protein denaturation due to localized heating by the laser beam. The problem has been circumvented, with varying degrees of success, by using spinning cells, flowing solutions through capillary tubes (both 90° scattering geometry), or by backscattering from cooled, spinning NMR tubes (135° scattering geometry). In our experience the latter technique is most successful. However, it has limitations when used to investigate the low-frequency region (0 to 500 cm−1), because broad nonresonant Raman scattering from the glass or quartz NMR tubes produces an ill-defined envelope of bands between 300 and 500 cm−1. These bands often dominate resonance Raman spectra in this region, obscuring weak sample bands (e.g., see Fig. 2). These difficulties have led us to design a simple cryostat that can be used to obtain resonance Raman spectra via 135° backscattering directly from the surface of a frozen protein solution (Fig. 1.)