Ultraviolet spectral shifts

X0 is the value of the property in the gas phase. (In practice, X and X0 are often the logarithm of the property in question.) The parameters a and p are measures of a solvent s ability to donate and accept hydrogen bonds, respectively, and tt is an index of its polarity/polarizability. They were initially assigned on the basis of ultraviolet spectral shifts of certain dyes in a variety of solvents, and hence were labeled solvatochromic parameters.186"188... 

Pi-complexing is most commonly used to rationalize effects observed in aromatic solvents. The most frequent evidence cited is magnetic anisotropy effects on chemical shifts in the solute molecule. As was the case for hydrogen bonding no quantitative correlations with substantive parameters such as ultraviolet spectral shifts have been attempted. 

Dispersion interactions have been shown in the absence of other effects to be responsible for gas-to-liquid changes of chemical shifts 1>2). The dispersion contribution to the electric field effect on infrared and ultraviolet spectral transitions has been shown to be proportional to McRae term 10 n)... 

The extinction features at energies where water is transparent are rapidly squelched in the ultraviolet as the onset of electronic transitions greatly increases bulk absorption. In the infrared, however, vibrational absorption bands in water are carried over into similar bands in extinction (dominated by absorption if a A) by a water droplet. Unlike MgO there are no appreciable spectral shifts in going from the bulk to particulate states. The reason for this lies in the strength of bulk absorption and will be discussed more thoroughly in Chapter 12. 

The carbonyl stretching frequencies of a number of heteroannular ferro-cenecarboxylic acids have been measured (41). The spectral shifts vary in the direction expected from the electronic effects of the substituent groups, and parallel the effects of these substituents on the acid constants. Little and Clark have also demonstrated resonance interaction of the ferrocenyl group in ferro-cenylazobenzenes by measuring shifts in the absorption maxima in the visible and ultraviolet spectra (49). 

Tissue also contains some endogenous species that exhibit fluorescence, such as aromatic amino acids present in proteins (phenylalanine, tyrosine, and tryptophan), pyridine nucleotide enzyme cofactors (e.g., oxidized nicotinamide adenine dinucleotide, NADH pyridoxal phosphate flavin adenine dinucleotide, FAD), and cross-links between the collagen and the elastin in extracellular matrix.100 These typically possess excitation maxima in the ultraviolet, short natural lifetimes, and low quantum yields (see Table 10.1 for examples), but their characteristics strongly depend on whether they are bound to proteins. Excitation of these molecules would elicit background emission that would contaminate the emission due to implanted sensors, resulting in baseline offsets or even major spectral shifts in extreme cases therefore, it is necessary to carefully select fluorophores for implants. It is also noteworthy that the lifetimes are fairly short, such that use of longer lifetime emitters in sensors would allow lifetime-resolved measurements to extract sensor emission from overriding tissue fluorescence. 

If this interaction is not possible, the shift does not occur.37 The ultraviolet spectra have been studied in connection with the structure of aliphatic 3 and cyclic enamines,1, 28,37, 43 cis-trans isomerism about their double bond,27 and the structures of enamines with additional functional groups.17, 20, 31,32 Ultraviolet spectral data have been used also as a general method to determine the structure of alkaloids and in the study of some reaction mechanisms. 

Ultraviolet and visible spectral shifts (Hiskey and Downey, 1954 Mulley and Metcalf, 1956 Riegelman et al., 1958 Riegelman, 1960 ... 

Kamlet and Taft recast Eq. [18] in the form of Eq. [19] with a set of empirical parameters designed to model the various terms. This so-called solvatochromic parameter set (ti, 82, ai, pi) was derived from ultraviolet (UV) spectral shifts of solutes in solvents. The subscript 2 refers to solute parameters solvent parameters may have different values. 

The Russian workers claim that substituents on the azido group which increase the asymmetry, presumably by changing the equivalence of the bonding, shift the bands in question to higher frequency. They also suggest that this asymmetric stretching band for aromatic sulphonyl azides can be correlated by a Hammett Opp relationship where p has a small value. (They find the ultraviolet spectral parameters responding in similar fashion.)... 

Table X shows a comparison between the ultraviolet spectral maxima obtained in this study and the literature values. The standard and collected GLC spectra are qualitatively the same. The characteristic shift to lower wavelength by an organophosphate oxon is evident. The shift to a lower wavelength when a phosphate ester replaces the H atom of the hydrolysis product is noted also (Diazinon).

Individual MO pair correlations, can be related to the localized ones, directly using Eq. (149), This may provide a semi-empirical method by which, from localized correlations which are easily estimated, MO pair correlations are obtained. Such a method may help ultraviolet spectral assignments based on simple MO theory by giving estimates of shifts due to correlation, w-tt transitions would be particularly interesting to consider. 

The fluorescence, ultraviolet and visible spectra of the series were reported in Russian [78] spectral shifts are related directly to LCAO MO calculations. Following the correlations between carcinogenicity and theoretical molecular electronic transition energies made by Mason [79—81], Birks [82], and Steele, Cusachs and McGlynn [83, 84] and in part experimentally confirmed by Sung and Lazar [85], the Russian results emphasise the importance of electronic transitions in the carcinogenic involvement of the series.]... 

In tabulating thermodynamic and spectroscopic basicity scales, 1 1 complexation constants, Gibbs energies, enthalpies, entropies and ultraviolet (UV) and infrared (IR) spectral shifts are therefore given in 1 mol (identical with dm mol ), kJ mol , J K mol and cm , respectively. Logarithms of equilibrium constants (log K) are to base 10 and without units since the calculated quantity is log (K/l 1 mol ). 

Hahde complexes of Cu with nitrogen base ligands are known to exhibit another form of reversible spectral change known as fluorescence thermochromism. The example of Cu4l4(Py)4 from Table 1 is typical and shows red shifting ia the visible emission spectmm while the sample is both cooled and irradiated with a 364 nm ultraviolet source (7). 

With imines, salts formation is accompanied by characteristic spectral changes (153) (a) a bathochromic shift in the ultraviolet region by as much as 50 m/i, according to compound type and to properties of any auxochrome present, and (b) a high frequency shift of the... 

---