Subject ultraviolet absorption

Section A,7, Applications of infrared and ultraviolet absorption spectra to organic chemistry, should provide a brief introduction to the subject. 

Gaudette and Coatney [115] reported that primaquine phosphate was unstable when subjected to dry heat of 100 °C in the presence of sodium chloride for 24 h, when boiled in water for 24 h and when heated for 24 h at 100 or 200 °C in melted hydrogenated vegetable oil. These findings exclude the use of primaquine phosphate as a salt additive in cooking. Primaquine phosphate was isolated from the test preparations at alkaline pH by extraction into ethylene chloride, after which primaquine phosphate was returned to an aqueous phase by shaking with 0.1 N sulfuric acid the concentration of primaquine phosphate was then determined spectrophotometrically. The ultraviolet absorption curve of primaquine phosphate has maxima at 224, 266, 282, and 300 nm, and minima at 216, 250, 276, and 310 nm. A solution containing 10 yl/mL has an optical density of 0.375 at 282 nm optical densities were proportional to concentrations. 

In one study of the effects of additives,9 it was found that on electrochemical oxidation of rubrene, emission was seen in dimethylforma-mide, but not in acetonitrile. When water, n-butylamine, triethylamine, or dimethylformamide was added to the rubrene solution in acetonitrile, emission could be detected on simply generating the rubrene cation.9 This seems to imply that this emission involves some donor or donor function present in all but the uncontaminated acetonitrile system. The solvent is not the only source of impurity. Rubrene, which has been most extensively employed for these emission studies, is usually found in an impure condition. Because of its relative insolubility and its tendency to undergo reaction when subjected to certain purification procedures, and because the impurities are electroinactive and have relatively weak ultraviolet absorptions, their presence has apparently been overlooked, They became evident, however, when quantitative spectroscopic work was attempted.70 It was found, for example, that the molar extinction coefficient of rubrene in benzene at 528 mjj. rose from 11,344 in an apparently pure commercial sample to 11,980 (> 5% increase) after repeated further recrystallizations. In addition, weak absorption bands at 287 and 367 m, previously present in rubrene spectra, disappeared. 

The use of ultraviolet absorption spectra in the study of protein structure was reviewed by Beaven and Holiday in Volume 7 of the Advances, ten years ago. There has been a vast outpouring of articles on the subject since. The use of ultraviolet spectra for the exploration of protein structure has ramified in many directions, and it is becoming an increasingly powerful tool for the study of the finer details of protein structure. In the final review of this volume D. B. Wetlaufer surveys the field as it stands today. 

Most of the work reported on irradiation is concerned with changes in physical properties (such as color formation or ultraviolet absorption), and little emphasis has been placed on isolation and identification of products. An earlier review in this Series on this subject mentioned the diflSculties encountered, and gave information concerning the technical possibilities. ... 

During the exposure period, the Seal Beach area was subjected to fog and haze because of its location near the ocean. The estimated days of effective sunlight at each sampling date are shown in Table I along with the actual exposure time. The concentration data were calculated from the ultraviolet absorption spectra of samples taken at the indicated times, and the final point was confirmed by bioassay. 

The triarylmethyl cations are particularly stable because of the conjugation with the aryl groups, which delocalizes the positive charge. Because of their stability and ease of generation, the triarylmethyl cations have been the subject of studies aimed at determining the effect of substituents on carbocation stability. Many of these studies used the characteristic ultraviolet absorption spectra of the cations to determine their concentration. In acidic solution, equilibrium is established between triarylcarbinols and the corresponding carbocation. 

D. A. Ramsay and co-workers has provided many constants for one of the excited singlet states CAJ of glyoxal, and the rotational structure within many of the vibrational levels of this state can be described with exceedingly high precision. Benzene, the subject of the present discussion, is another example where a fairly detailed description of numerous stationary aspects of both the ground and upper electronic states are now available. As a result of Callomon, Dunn, and Mills beautiful analysis of rotational band contours in the ultraviolet absorption spectrum, much is known about even the Coriolis constants for vibronic levels in the excited singlet state. Numerous other examples could be cited in which the geometries and many upper state constants in polyatomics are well known. 

Similar results were obtained with urinary albumin, the cystine content of which was found to vary with that of the plasma albumin of individual nephrotic subjects, although the decrease in cystine content of urinary albumin was distinctly less marked. Alving and Mirsky emphasized the importance of working with sufficiently purified fractions in studies on nephrotic albumin, citing Hewitt (141,1 ), who was unable to differentiate urinary albumin from normal serum albumin by specific rotations, refractive indices, or ultraviolet absorption spectra in highly purified preparations, and Widdowson (377), who also found no distinct differences on the basis of racemization curves, osmotic pressures, and specific refractions. 

In many instances, visible fluorescence methods are less subject to interference by other polymer additives present in the extractant than are ultraviolet methods. Thus, Uvitex OB has an intense ultraviolet absorption at a wavelength high enough (378 nm) to be outside the region where many interfering substances in the extractant would be excited to fluoresce. Therefore, in some instances visible fluorimetry offers a method of determining an extractant constituent without interference from other constituents when this would not be possible by ultraviolet spectroscopy. 

To visualize whether or not wood can be delignified by laccase III, ultraviolet photomicrographs (280nm) were taken before and after treatment of 0.5 mjLt cross-sections of red pine with laccase III (Figure 11). After enzyme treatment areas having an absorbance less than 0.2 in the secondary wall, and an absorbance less than 0.4 in the middle lamella, appeared. Each part of the secondary wall, middle lamella, and cell junction was subjected to ultraviolet microscopy, and absorption curves in the 240-300nm region were determined. The absorption curves of three samples after treatment... 

That the hydrated electron is a separate chemical entity has been demonstrated by the technique of pulse radi l sis This consists of subjecting a sample of pure water to a very short pulse of accelerated electrons. The energetic electrons have the same effect upon water as a beam of y-ray photons. Shortly after the pulse of electrons has interacted with the water, a short flash of radiation (ultraviolet and visible radiation from a discharge tube) is passed through the irradiated water sample at an angle of 90° to the direction of the pulse to detect the absorption spectra... 

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