Visible spectroscopy tris

UV-visible spectroscopy was one of the earliest techniques to be applied to try and resolve the question over the identity of the carriers in polypyrrole and was employed ex situ on the free-standing as-grown film. Two important experimental approaches were employed ... 

EXPERIMENT 5.2 VISIBLE SPECTROSCOPY OF TRIS(BIDENTATE CHELATE)COBALT(III) 117... 

UV/visible spectroscopy was used in order to obtain more information about the relative binding constants Kt = JCpeptide/ indicator of the Cp Rh complex 16 for various peptides [59]. The results are summarized in Table 1. For peptides containing either His or Met at - or adjacent to - the AT-terminus, the nearly complete replacement of the indicator upon addition of the peptide was observed (Ki > 740) (entries 1-6). It was suggested that for those peptides, a simultaneous coordination of the amino and the respective side-chain occurs. Such a mode of coordination is less hkely for tri- or longer peptides with His/Met residues in the middle or at the C-terminus and consequently lower relative binding constants were observed (entries 7-10). 

A hydrocarbon-soluble trifunctional initiator was synthesized by reacting three moles of scc-butyllithium (s-BuLi) with one mole of l,3/5-tris(l-phenylethenyl)benzene (tri-DPE) (Scheme 2). It was formd that the initiator was efficient for the polymerization of styrene only in the presence of THE in a ratio of [THE]/[s-BuLi] =20. The polymerization reaction was monitored by UV-visible spectroscopy. Extreme precision over the stoichiometry of the reaction between s-BuLi and tri-DPE is needed and a minimum arm molecular weight around 6 x 10 is required for a successful initiation and synthesis. 

UV-visible spectroscopy UV-visible absorbance microspectrophotometry and microspectrofluorime-try are used as nondestructive methods for analyzing inks directly on paper. They measure, respectively, the absorption and emission spectrum of inks and allow the discrimination of similarly colored inks. Therefore, they are a convenient way to render the comparison of ink colors more objectively than the naked eye. 

Such unusual phenomena as reabsorption lines of molecular oxygen and water require a confirmation by an additional independent technique. The best way is to try to detect the corresponding absorption lines by UV-visible spectroscopy. The problem is that sedimentary apatite samples are in the form of non-transparent powder, which is not suitable for optical spectroscopy. The photoacoustic spectroscopy (PAS), which allows measurement of absorption spectra of powdered opaque samples, has been chosen for this purpose (Gaft et al. 1998). PAS works as follows ... 

The adsorption of transition metal complexes by minerals is often followed by reactions which change the coordination environment around the metal ion. Thus in the adsorption of hexaamminechromium(III) and tris(ethylenediamine) chromium(III) by chlorite, illite and kaolinite, XPS showed that hydrolysis reactions occurred, leading to the formation of aqua complexes (67). In a similar manner, dehydration of hexaaraminecobalt(III) and chloropentaamminecobalt(III) adsorbed on montmorillonite led to the formation of cobalt(II) hydroxide and ammonium ions (68), the reaction being conveniently followed by the IR absorbance of the ammonium ions. Demetallation of complexes can also occur, as in the case of dehydration of tin tetra(4-pyridyl) porphyrin adsorbed on Na hectorite (69). The reaction, which was observed using UV-visible and luminescence spectroscopy, was reversible indicating that the Sn(IV) cation and porphyrin anion remained close to one another after destruction of the complex. 

Another technique is vacancy spectroscopy. In this application, an eluent is used that absorbs uv or visible radiation. When the sample passes through the detector, less radiation is absorbed because of the vacancy. For example, the benzene ring in a mixture of 4 mM salicylic acid - (Tris) is measured at 254 nm. Alternately, the eluent for cations can be Ce and the decrease in the yellow color monitored in the visible region. 

There are two broad approaches to solving the problem of the absorption of light by the solvent when trying to collect vibrational spectra (1) Use Raman spectroscopy, which has the advantage of employing radiation in the visible region, which is not absorbed by the solvents commonly employed in electrochemical studies. This is outside the scope of this... 

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