Spectroscopy UV absorptions

Burdett, R.A., L.W. Taylor and L.C. Jones Jr (1955), Determination of aromatic hydrocarbons in lubricating oil fractions by far UV absorption spectroscopy , p. 30. In Molecular Spectroscopy Report Conf. Institute of Petroleum, London. 

An initial solution was prepared by dissolving metallic niobium powder in 40% hydrofluoric acid. The dissolution was performed at elevated temperature with the addition of a small amount of nitric acid, HN03, to accelerate the process. The completeness of niobium oxidation was verified by UV absorption spectroscopy [21]. The prepared solution was evaporated to obtain a small amount of precipitate, which was separated from the solution by filtration. A saturated solution, containing Nb - 7.01 mol/1, HF - 42.63 mol/1, and corresponding to a molar ratio F Nb = 6.08, was prepared by the above method. The density of the solution at ambient temperature was p = 2.0 g/cc. Concentrations needed for the measurements were obtained by diluting the saturated solution with water or hydrofluoric acid. 

Molecules which contain a chiral cobalt as well as an asymmetric nitrogen exist in four possible optical isomeric forms. These are represented for Co(sar)(hbg) +, hbg = NH2C( = NH)NHC(=NH)NH2 in Fig. 7.12. All four optically-active isomers have been isolated and characterized by cd, nmr and vis/uv absorption spectroscopy. The kinetics of... 

Calandra P, Goffredi M, Liveri VT (1999) Study of the growth of ZnS nanoparticles in water/AOT/n-heptane microemulsions by UV-absorption spectroscopy. Colloids Surf A 160 9-13... 

MS. This section will rather briefly concentrate on some of the more recent applications of UV absorption spectroscopy in the flavonoid field. It will mainly cover online UV absorption spectroscopy in chromatography (Section 2.5.1). Because of the current importance of UV Vis in the study of anthocyanins, some more UV Vis spectral details have been included related to this pigment group (Section 2.5.2). Section 2.5.3 indicates the recent use of this technique in studies of flavonoids interacting with other compounds. 

Following a two photon excitation of hydrated hydroxyl ions (FhO/NaOH = 55) with femtosecond UV pulses (/.purnp = 310 nm, Eexdtation = 2x4 eV), short-time electron transfer trajectories have been investigated by near-IR and UV absorption spectroscopies at room temperature. The energy of the pump beam is 1011 W cm 2. 

Peroxy radicals are intermediates in the atmospheric oxidation of air pollutants and in oxidation reactions at moderate temperatures. They are rapidly formed from free radicals by addition of 02. Free radicals in the atmosphere are quantitatively converted to R02 with a half-time of about 1 fis. The peroxy radicals are then removed by reaction with other trace species. The dominant pathways are reactions with NO and NOz. Only a few peroxy radicals have been detected with a mass spectrometer, and extensive research on these reactions has been done by UV absorption spectroscopy with the well-known and conveniently accessed band in the 200- to 300-nm region. Nevertheless, FPTRMS has been used for some peroxy radical kinetics investigations. These have usually made use of the mass spectrometer to observe more than one species, and have given information on product channels. The FPTRMS work has been exclusively on atmospheric reactions of chlorofluoromethanes and replacements for the chlorofluoromethanes. 

The self-recombination reactions of HOj, CF3CFHO, and CF3O) have been studied using pulse radiolysis/time-resolved UV absorption spectroscopy.215 The addition of the cumylperoxy radical to a range of alkyl-substituted biphenyls has been studied and the rate constants compared with reactions with related monosubstituted benzenes.216... 

In practice, UV absorption spectroscopy (in the region from 200 to 380 nm) is for the most part yields information only about the conjugated system present in the molecule. However, when taken in conjunction with the wealth of detail provided by infrared (IR) and nuclear magnetic resonance (NMR) bands may lead to successful structural elucidations. The principal characteristics of an UV absorption band are its position (2max) and intensity (emax or log emax). 

TDPI was prepared by reacting 2-chloro-1,3,2-dioxaphosphorin-ane 2-oxide (I, X=C1) with m(N,N-dimethylamino) phenol followed by methyl iodide to produce pale yellow crystals. 1p and H nmr spectroscopy, tic and C,H,P,N analyses verified the structure and homogeneity of TDPI. UV-absorption spectroscopy indicates that free phenol (TMPH), if present, is less than 0.2%. 

In mechanistic studies, aprotic solvents are preferred because electrochemical intermediates (particularly anion radicals) often have sufficient stability to enable their identification by spectroscopic techniques such as ESR or UV absorption spectroscopy. Follow-up chemical reactions frequently proceed slowly enough to allow rate measurements. 

Similarly, using UV absorption spectroscopy Gracia and Prello [148] studied the influence of membrane chemical composition and drug structure on the localization of benzodiazepines at the lipid-water interface. Their results revealed that the benzodiazepines can be incorporated as an integral part of the bilayer and are not located only at the core, as reported from fluorescence polarization experiments [149]. 

Previous studies on the reactions of CH employed either the vacuum ultra-violet photodissociation (2) or the electron beam dissociation (3) of CH4 to generate the radical. The formation and decay of the CH was monitored by UV absorption spectroscopy on the C — X transition at 314 nm. The results of the former study (2), which relied partly on final product analysis, are considerably smaller (by a factor of 10 to 40) than the values of Bosnali and Perner (3) and our present data for the reactions with H2, N2 and CH4. The agreement between ours and those of Bosnali and Perner, although significantly better, is only fair and lies within a factor of 2 to 5. Further work is certainly needed in order to reconcile these two sets of data. 

If h > 0, then helical assemblies do not form. There is an isodesmic polymerization from monomers to "disordered" supramolecular polymers that takes place around X l. The theory of Section 1 applies and the equivalent equilibrium constant obeys K = exp [. jy. Its value can be probed by means of radiation scattering, fluorescence decay, and UV absorption spectroscopy (Brunsveld et al., 2001 Jonkheijm et al., 2006). 

There are various kinds of spectroscopy visible and ultraviolet (UV) absorption spectroscopy, Raman and infrared spectroscopy, nuclear magnetic resonance spectroscopy, and electron-spin resonance (ESR) spectroscopy. A brief description of the principles of these techniques and their application to the study of ions in solution follows (see also Section 2.11). 

Atoms, neutral molecules, and ions (simple and assoeiated) ean exist in several possible electronic states this is the basis of visible and UV absorption spectroscopy. Transitions between these energy states occur by the absorption of discrete energy quanta A which are related to the frequency v of the light absorbed by the well-known relation... 

The method of visible and UV absorption spectroscopy is at its best when the absorption spectra of the free ions and the associated ions are quite different and known. When the associated ions cannot be chemically isolated and their spectra studied, the type of absorption by the associated ions has to be attributed to electronic transitions known from other well-studied systems. For example, there can be an electron transfer to the ion from its immediate environment (charge-transfer spectra), i.e., from the entities associated with the ion or transitions between new electronic levels produced in the ion under the influence of the electrostatic field of the species associated with the ion (crystal-field splitting). Thus, there is an influence of the environment on the absorption characteristics of a species, and this influence reduces the clarity with which spectra are characteristic of species rather than of their environment. Herein lies what may be considered a disadvantage of visible and UV absorption spectroscopy. 

Visible and UV absorption spectroscopy are based on studying that part of the incident light transmitted (after absorption) through an electrolytic solution in the same direction as the original beam. However, a certain amount of light is scattered in other directions. 

Also, as a word of caution, it should be noted that nucleic acids precipitated by PEG can contain macromolecular impurities originating from the PEG these impurities are not detectable by the usual methods (e.g., electrophoresis or UV absorption spectroscopy) and they cannot be readily removed even by CsCl gradient centrifugation. 

UV absorption spectroscopy is usually not sensitive enough to monitor ions direetly in the jet. Even if the original ion pair is somehow dissociated in to two separate ions having a eharacteristie absorption, their detection by high-resolution absorption speetroscopy is often impraetieal. The nascent product ions are formed in a large number of quantum states, and the small population of a single state eannot be detected with reasonable signal-to-noise ratio. 

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