Organic compounds, with natural fluorescence

Fluorescence spectroscopy is characterized by a greater selectivity when compared with other spectro-photometric techniques because there is an excitation and an emission spectra, with maxima usually quite characteristic of a particular compound. It is also selective because of the limited number of organic compounds that fluoresce. It has greater sensitivity than spectrophotometric methods in solution 10 9-10 12 M can usually be measured while on a thin-layer chromatogram some naturally fluorescent compounds may be detected instrumentally in sub-nanogram amounts. 

As mentioned above, weak UV irradiation (325-427 nm) is frequently used for excitation. When far-UV radiation is used, however, increased fluorometric response and more information on structural properties of dissolved organic compounds can be obtained, since organic molecules found in natural waters have a greater absorbance at shorter wavelengths. Stabel (personal communication) attempted to differentiate between probable sources of DOM in lakes using fluorescence spectra of DOM from various inland waters, such as softwater, hardwater, and saline systems. With exci-... 

Polyamides can, as a rule, be brightened with those products suitable fi protein fibres. They have, however, an affinity for insoluble dispersions ( organic compounds and, because of their hydrophobic nature, it is on derivatives of this type that can be applied to polyesters. Water-insolub fluorescent brightening agents, in the form of dispersions, are based, one example, on compounds derived from (12) which are favoured becau of their comparatively good light-fastness ... 

This work was initiated by the problem of investigating the photophysical properties of complex protein molecules and performing the diagnostics of such molecules in water environment. At the present time, fluorescence spectroscopy (fluorimetry) is widely used to study complex organic compounds (COC) (Lakowicz, 1999). Together with spectrophotometry these methods form the basis for fast and nondestructive diagnostics of COC in the natural environment, i.e. they present the diagnostic methods in vivo and in situ. However, the conventional (linear) fluorescence spectroscopy methods can not provide complete information on fluorescent objects under study because of insufficient selectivity (fluorescence bands of most COC are broad and structureless at room temperature). 

SoHELLENBEBO [144] uses a variation of the well-known fluorescence test with morin sensitivity is relatively low (limit of detection 2 jjig). Saeoeb and Tuppy s [95] fluorescence test seems to us to be rather uncertain in the absence of cellulose. Naturally, all procedu which depend on destruction of the organic compounds yielding brown or black products (Bgt. Nos. 46, 241) can be used here, in contrast to PC. 

This article will deal with the nature of organic molecular fluorescence, its dependence upon molecular structure, reactivity and interactions with the environment and its utility in the trace analysis of organic compounds. 

In some instances, the ability of an organic compound to form complexes with metals results in enhanced fluorescence. This is the case for a number of colorimetric indicator compounds used to indicate the presence of some metals and cations in water samples (Skoog and West, 1982). Havones are one of the natural product classes that exhibit enhanced fluorescence when complexed by metals, and this reaction has been used to detect the presence of both flavanols and metals alike (Wolfbeis, 1985). A common example is the compound morin, which is nonfluorescent in the uncomplexed state but fluoresces in the presence of AP+ and other metals (Brown et al., 1990). The reaction of morin with Al has been used to study the speciation of AP+ in natural waters as well as in the study of the effects of Al on plant materials (Eticha et al., 2005). In a final example, the fluorescence of salicylic acid is enhanced in the presence of As " and sodium dodecyl sulfate (Karim et al., 2006), whereas interactions with Fe " result in fluorescence quenching (Cha and Park, 1998). 

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