Solvents refractive index

If the scattering particles are in a dielectric solvent medium with solvent refractive index Uq, we can define the excess... 

Solvents with different polarities and refractive indexes significantly affect carotenoid optical properties. Because the refractive index is proportional to the ability of a solvent molecule to interact with the electric held of the solute, it can dramatically affect the excited state energy and hence the absorption maxima positions (Bayliss, 1950). Figure 7.2a shows three absorption spectra of the same xanthophyll, lutein, dissolved in isopropanol, pyridine, and carbon disulfide. The solvent refractive indexes in this case were 1.38, 1.42, and 1.63 for the three mentioned solvents, respectively. 

The general or universal effects in intermolecular interactions are determined by the electronic polarizability of solvent (refraction index n0) and the molecular polarity (which results from the reorientation of solvent dipoles in solution) described by dielectric constant z. These parameters describe collective effects in solvate s shell. In contrast, specific interactions are produced by one or few neighboring molecules, and are determined by the specific chemical properties of both the solute and the solvent. Specific effects can be due to hydrogen bonding, preferential solvation, acid-base chemistry, or charge transfer interactions. 

FIGURE 1. ORD spectrum of (+)-irans-9-methyl-l,4,9,10-tetrahydronaphthalene, (dots). The two lines are computational results with (dashed) or without (continuous line) correction for the solvent refractive index. Reprinted with permission from Reference 9. Copyright 1961 American Chemical Society... 

Ihrig and Smith extended their study by running a regression analysis including reaction field terms, dispersion terms and various combinations of the solvent refractive index and dielectric constant. The best least squares fit between VF F and solvent parameters was found with a linear function of the reaction field term and the dispersion term. The reaction field term was found to be approximately three times as important as the dispersion term and the coefficients of the terms were opposite in sign. 

Uses. Gauge fluid solvent refractive index liquid in microscopy... 

In these equations ns is the solvent refractive index, dn/dc the refractive index increment, c the polymer concentration in g/ml, T the temperature in K, R the gas constant, NA Avogadro s number, and n the osmotic pressure. Equation (B.8) follows from Eq. (B.7) by using the familiar virial expansion of the osmotic pressure... 

Fig. 11. (a) Far ultraviolet rotatory dispersion of ribonuclease. Corrected mean residue specific rotation vs. wavelength [to R = [aLAf/100 [3/(n2 + 2)l where a — specific rotation, M mean residue weight, and n = solvent refractive index. Bars give maximal deviation at peaks. Reproduced from Jirgensons (311). (b) Near ultraviolet rotatory dispersion of 0.48% pancreatic ribonuclease in a 1-mm cell, in (a) 0.15 M phosphate buffer at pH 62 (b) 0.15 M glycine-NaOH buffer at pH 11.5 (c) 0.1 N HC1 (d) 15% sodium dodecyl sulfate. Reproduced from Glazer and Simmons (313). (c) Far ultraviolet circular dichroic spectra of RNase-A, RNase-S, and S-protein at 25° and 3°. Reproduced from Pflumm and Beychok (313). (d) Near ultraviolet circular dichroic spectra of RNase-A as a function of pH. Reproduced from Pflumm and Beychok (313). 

In contrast, EET has been historically modelled in terms of two main schemes the Forster transfer [15], a resonant dipole-dipole interaction, and the Dexter transfer [16], based on wavefunction overlap. The effects of the environment where early recognized by Forster in its unified theory of EET, where the Coulomb interaction between donor and acceptor transition dipoles is screened by the presence of the environment (represented as a dielectric) through a screening factor l/n2, where n is the solvent refractive index. This description is clearly an approximation of the global effects induced by a polarizable environment on EET. In fact, the presence of a dielectric environment not only screens the Coulomb interactions as formulated by Forster but also affects all the electronic properties of the interacting donor and acceptor [17],... 

Here iujj is the intensity of the scattered light at an angle 9 to the incident beam 7o is that of the polarized primary beam r. the distance between the scattering molecule and the detector Ao, the wavelength of the laser beam in vacuum n 0, the solvent refractive index dn/ dc. the specific refractive index increment of the solution, M, the molar mass of the scattering particle and c. its concentration. For a dilute solution, at a given concentration, the scattered intensity can be rewritten as ... 

Furthermore, the solvent refractive index, n , required in Eq. (4) must be determined under the same wavelength and temperature conditions. 

Nonpolar solute in a nonpolar solvent. In this case, only dispersion forces contribute to the solvation of the solute. Dispersion forces, operative in any solution, invariably cause a small bathochromic shift, the magnitude of which is a function of the solvent refractive index n, the transition intensity, and the size of the solute molecule. The function (n — l)/(2n - -1) has been proposed to account for this general red shift [69, 70]. Corresponding linear correlations between this function of n and Av have been observed for aromatic compounds e.g. benzene [22], phenanthrene [71]), polyenes e.g. lycopene [23], y9-carotene [464]), and symmetrical polymethine dyes e.g. cyanines [26, 27, 292, 293]). 

Nonpolar solute in a polar solvent. In the absence of a solute dipole moment there is no significant orientation of solvent molecules around the solute molecules, and again a general red shift, depending on the solvent refractive index n, is expected. Solute quadrupole/solvent dipole interactions also have to be taken into account in this case, as shown for nonpolar aromatic solutes e.g. anthracene) [469]. 

In these equations, the subscripts P, S, and SC refer to the polymer, solvent, and side chain, respectively. I is the flrst-ionization potential, n is the solvent refractive index, Psc sc is the side-chain polarizability density, and is a geometrical factor related to the manner in which dispersion interaction varies with the spatial separation between the polymer backbone and the surrounding medium (22). 

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