Fluorescence spectroscopy matrix isolation

Techniques other than UV-visible spectroscopy have been used in matrix-isolation studies of Ag see, for example, some early ESR studies by Kasai and McLeod 56). The fluorescence spectra of Ag atoms isolated in noble-gas matrices have been recorded (76,147), and found to show large Stokes shifts when optically excited via a Si j — atomic transition which is threefold split in the matrix by spin-orbit and vibronic interactions. The large Stokes shifts may be explained in terms of an excited state silver atom-matrix cage complex in this... 

The technique of matrix isolation has been shown to produce highly characteristic spectra of individual components of complex samples combination of MI spectroscopy with separation techniques promises to increase further the analytical capabilities of the technique. While our research to date has emphasized FTIR and molecular fluorescence spectrometry, MI as a sampling procedure is not limited to these two forms of spectrometry. For example, some interesting preliminary analytical results by MI Raman spectrometry recently have been described (32). It should also be stressed that the cryogenic procedures required for the vast majority of MI spectral studies are neither difficult nor unduly expensive except in very special cases, closed-cycle cryostats requiring no cryogenic liquids (and no prior experience in low-temperature techniques) are entirely satisfactory for MI... 

In the past decade a number of physical techniques have been used to evaluate the unique barrier properties of mammalian skin [1]. This chapter deals with the use of another physical technique, fluorescence spectroscopy, to study the barrier properties of the human stratum corneum (SC), specifically with respect to the transport of ions and water. The SC is the outermost layer of the human epidermis and consists of keratinized epithelial cells (comeo-cytes), physically isolated from one another by extracellular lipids arranged in multiple lamellae [2]. Due to a high diffusive resistance, this extracellular SC lipid matrix is believed to form the major barrier to the transport of ions and water through the human skin [3-5]. The objective of the fluorescence studies described here is to understand how such extraordinary barrier properties are achieved. First the phenomenon of fluorescence is described, followed by an evaluation of the use of anthroyloxy fatty acid fluorescent probes to study the physical properties of solvents and phospholipid membranes. Finally, the technique is applied to the SC to study its diffusional barrier to iodide ions and water. 

The approach to low-temperature spectroscopy that we have chosen to pursue is termed matrix isolation (MI). In MI, the sample is vaporized and then mixed with a large excess of a diluent gas (18,19,20), The gaseous mixture then is deposited on a window at low temperature for spectroscopic examination. The purpose of mixing the sample with the solvent (matrix gas) in the vapor phase is to secure an essentially random distribution of solute molecules, such that each analyte molecule has only matrix gas molecules as nearest neighbors. If this objective is achieved, and if the dilution is sufficiently great that the average distance between any two solute molecules is sufficiently large, then the fluorescence of any one analyte in a complex sample should be essentially unperturbed by the... 

Diatomic cations, neutral molecules, and anions represent the type of inorganic species which has been most extensively studied by resonance Raman spectroscopy. Iodine in the gaseous, dissolved, and matrix-isolated states has been the subject of particularly detailed studies, and it is this molecule for which the greatest number of members (25) of a resonance Raman progression has so far been observed (66). The relation between resonance Raman and resonance fluorescence spectra has been discussed in Section 2, but it is worth illustrating the general principles involved by reference to the work on iodine. 

Vibrational frequencies for example result from the appUcation of infrared, laser-induced fluorescence, Raman, and Raman resonance spectroscopy. Spectroscopy in the visible and near-UV regions yields information on electronic transitions. Electron spin resonance spectroscopy is used in determining the geometric and electronic structure. These methods were applied to study the gaseous species trapped at low temperatures in a solid inert rare gas matrix (matrix isolation technique) as well as in the free state. 

The applicability of these methods is, however, often restricted due to the available concentration of the DOM and due to the disturbing inorganic matrix effects. On the other hand, to avoid denaturating, it is attractive to avoid isolation and to use whereever possible the original aqueous samples. This applies mainly to UV-vis, fluorescence-, and FT-IR spectroscopy (Kalbitz et al., 2000). 

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