Specific optical dispersion

The specific optical dispersion (ASTM D-1807) serves as an indication of aromatic content. The difference in refractive index of the oil as measured at two wavelengths is determined, divided by the relative density (all measurements are at the same temperature) and multiplied by 100 values above 97 are stated to bear a direct relationship to the aromatic content of the oil. 

however, there is reason to be particularly interested in the aromatic content, it is preferable to assess this by one of the more direct methods. 

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ASTM D1807 Test Methods for Refractive Index and Specific Optical Dispersion of Electrical Insulating Liquids... 

With heating from 5 to 45°C, thermal changes in conformation in the major /3-casein are observed by spectral methods (Garnier 1966). From measurements of the optical density at 286 nm and of the specific optical rotation at 436 nm, a rapidly reversible endothermic transition (AH 30 kcal/mole) with a half-transition temperature of 23-24°C is observed. The optical rotatory dispersion data suggest a decrease in the poly-L-proline II structure (12 to 5%) and a slight increase in a-helix (11 to 16%) with increasing temperature. This transition probably occurs prior to association, since it is rapid, and the carboxyacyl derivative of the monomer, which does not polymerize with increasing temperature, also demonstrates the optical rotatory disperson thermal transition. 

ABA absorbs ultraviolet with maxima at 240 nm (e 2.1 x 104, a shoulder peak), 260 nm (e 2.6 x 104), and 320 nm (e 50) in an acidic methanol solution.590 Irradiation with UV with a wavelength shorter than 305 nm isomerizes the 2-(Z)-double bond to (E) to give an equilibrium mixture of ABA and its 2-( )-isomer with a ratio of 1 1, and also causes decomposition of ABA to unidentified compounds by the excitation of the 7t-7t transition of the side chain and the enone groups. ABA has a strong optical activity, and its specific optical rotation is +430° in an acidic methanol solution.591 In the optical rotatory dispersion (ORD)591 and the circular dichroism (CD) spectra,558 ABA shows a positive Cotton effect from 300 to 200 nm. Phaseic acid and dihydrophaseic acid and its epimer, which did not have the enone group, show a small specific optical rotation with a minus value and also a negative plain curve in the ORD. 

The transition can perhaps most conveniently be followed polarimet-rically. Figure 1 shows the change in specific optical rotation of a 3% PBG solution (solvent, 70 volume % DCA-30 volume % DCE) as the temperature is varied through the transition range. From optical rotatory dispersion measurements one may obtain the Moffitt parameter, bQ, and from this it has been shown that for PBG the high temperature form (with positive [o ]d) corresponds to the helical conformation of the polypeptide (12). 

In 1958 we had reported that in contrast to most globular proteins, the specific optical rotation, [a], the hydrodynamic properties, and, most of all, the enzymic activity of pepsin remain unaltered if the protein is dissolved in concentrated urea solution or in guanidine hydrochloride, or if the solution is heated to 60°C. However, if the temperature is raised to 70°C., the rotatory dispersion constant, Xc, increases from 216 to 236 m/z (15, 18). Although hydrogen bonds of the type C = O. . . H — N and those involving the phenolic hydroxyls of tyrosine and the carboxylate ions of the acidic amino acid residues—i.e.,... 

Figure 3. Dependence of specific optical rotation and rotatory dispersion constant...

Combinations of several pigments are necessary in order to achieve an accurate final shade or a specific optical property. Also, pigment concentrates such as granules composed of colorant and processing polymers are preferred in order to avoid dust in polymer processing. They assure an optimum dispersion and are easier to measure. 

The focus of this chapter is photon spectroscopy, using ultraviolet, visible, and infrared radiation. Because these techniques use a common set of optical devices for dispersing and focusing the radiation, they often are identified as optical spectroscopies. For convenience we will usually use the simpler term spectroscopy in place of photon spectroscopy or optical spectroscopy however, it should be understood that we are considering only a limited part of a much broader area of analytical methods. Before we examine specific spectroscopic methods, however, we first review the properties of electromagnetic radiation. 

Papermaking additives can be categorized either as process additives or as functional additives. Process additives are materials that improve the operation of the paper machine, such as retention and drainage aids, biocides, dispersants, and defoamers they are primarily added at the wet end of the paper machine. Functional additives are materials that enhance or alter specific properties of the paper product, such as fillers (qv), sizing agents, dyes, optical brighteners, and wet- and dry-strength additives they may be added internally or to the surface of the sheet. 

Some of the most memorable scenes in a motion picture are the creation of special effects technicians. One standard tool in the entertainment industry to create ambience, simulate specific designs such as volcanoes or swamps, or accentuate optical effects is fog production. (In the theatrical sense, the terms fog and smoke are used interchangeably for mist consisting entirely of liquid droplets. In the chemical sense, fog refers to a liquid phase dispersed in a gas, while smoke contains solid particulate matter dispersed in a gas.) There are a variety of approaches to creating artificial fog or smoke. 

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