Hyperchromic effect

Increasing the number of conjugated double bonds leads to a marked bathochromic shift and to a hyperchromic effect, as predicted by Woodward s and Fieser s rules8. 

Shifts in absorption spectra due to the effect of substitution or a change in environment (e.g. solvent) will be discussed in Chapter 3, together with the effects on emission spectra. Note that a shift to longer wavelengths is called a bathochromic shift (informally referred to as a red-shift). A shift to shorter wavelengths is called a hypsochromic shift (informally referred to as a blue-shift). An increase in the molar absorption coefficient is called the hyperchromic effect, whereas the opposite is the hypochromic effect. 

The compound was dissolved in solvents that has various polarity. The optimum conditions for concentration were investigated with respect to maximum absorption. Increasing concentration as 10 , 10, 10 M was lost spectral fine stracture when there was hyperchromic effect in absorption spectra. Optimal conditions were chosen as 1.5 x 10 M, since this gives the highest absorbance value. The solutions of the compounds were prepared daily in 10 M of MeOH, CHCI, THF, DMF and DMSO. 

Denaturation can be detected by the increase in absorbance of a DNA solution at a wavelength of 260 nm. This increase is known as the hyperchromic effect. 

Nucleic Acid Structure Explain why the absorption of UVlight by double-stranded DNA increases (hyperchromic effect) when the DNA is denatured. 

Calculate the ratio A2mT]/A2(M2 ) for each of the three tubes. Why are the three ratios not the same Explain the experimental observation in terms of the molecular structure of DNA. What was the percentage increase in the overall hyperchromic effect Give a qualitative answer regarding the purity of the DNA sample you used. 

Chenabine (99), C37H40N207, along with its 7 -0-demethyl analog, jhelu-mine (100, Section II,C,49), was isolated from Berberis lycium Royle (Ber-beridaceae). Chenabine shows [ajjy5 +40° (c 0.18, MeOH), IR 1680 cm 1 (aromatic aldehyde), NMR (CDC13) 8 3.25 (7 -OMe), 5.23 (s, H-8), MS m/e 624 (M+, 0.2%), 397 (base), and 227 (4, both from cleavage at a). The UV spectrum shows a bathochromic shift as well as a hyperchromic effect with base, typical of a p-hydroxybenzaldehyde. 

Thalictrum minus L. var. microphyllum (Ranunculaceae) was the source of the amorphous base (+)-uskudaramine (358), C39H44N208, [a] 5 +84° (c 0.15, MeOH). The structure proof of uskudaramine was simplified by comparison of its properties with those of the isomeric (+)-istanbulamine (173, Section II,C,47), isolated from the same source. Notably, the NMR spectrum of 358 lacks the H-8 (8 6.84) singlet of 173, and its UV spectrum shows not only a bathochromic base shift but also a hyperchromic effect, characteristic of a 3- or 9-hydroxyaporphine. 

Double-helical DNA in solution can undergo strand separation or dena-turation as a consequence of extremes of pH, heat, or exposure to chemicals such as urea or amides. Decrease in viscosity, increase in absorbance at 260 nm (hyperchromic effect), decrease in buoyant density, or negative optical rotation indicates denaturation of DNA. The denaturation process disrupts only noncovalent interactions between the two strands of DNA. Since G-C base pairs are held together by three hydrogen bonds in contrast to two for an A-T base pair, A-T rich DNA is easily denatured compared to G-C rich DNA (Figure 6.3). Electron microscopy can detect these A-T-rich regions in a DNA molecule since they form bubblelike structures. Hence the temperature of melting (Tm) of DNA increases in a linear fashion with... 

While denaturation can be detected readily through changes in viscosity, a much more convenient way to detect it is by ultraviolet (uv) absorption measurement. The difference in the uv absorption spectra of the native (double-helical) and denatured (single-stranded) forms of DNA is shown in Fig. 7-7. At the wavelength of maximum absorption (260 nm), absorption by single-stranded DNA is approximately 40 percent higher than by double-stranded DNA. This is referred to as the hyperchromic effect and results from the unstacking of the base pairs in the helix. 

This increase in the absorption spectrum following denaturation (destruction of secondary structure) is termed the hyperchromic effect (Fig. V-9). Conversely, the decrease in the absorption spectrum on renaturation of these types of nucleic acids (restoration of secondary structure) is termed the hypochromic effect. These effects are observed in Experiment 19. 

This experiment will also provide you with experience in characterizing DNA samples by determining their ultraviolet absorption spectra and observing their thermal denaturation by means of the hyperchromic effect. These topics were discussed in the introduction to Section V. 

Most naturally occurring RNA molecules are singled-, not double-stranded duplexes, yet RNA also shows a hyperchromic effect on melting. Explain. 

Chemistry of multilayered cyclophanes has been reviewed and their physical and chemical properties have also been extensively discussed [52]. The UV spectra are known to show large bathochromic shifts with sizeable hyperchromic effects and become structureless as the number of layers increases. These features are more apparent for up to four-layered cyclophanes. This was explained primarily by the transannular n-n interaction/delocalization, while the effect of deformation of the benzene rings was thought to be rather negligible [53]. Despite the UV spectral study, only a limited amount of effort has been devoted so far to the study of the chiroptical properties of layered cyclophanes. 

Ionization of phenolic hydroxyl groups in lignin with alkali causes a batho-chromic shift and a hyperchromic effect in the absorption spectrum. An alkaline ionization difference spectrum is obtained by subtracting the spectrum of the solute in a neutral solution from the corresponding spectrum measured in an alkaline medium. The difference spectrum may be measured directly with a spectrophotometer according to the following procedure ... 

Auxochrome An atom or group which, when added to or introduced into a chro-mophore, causes a bathochromic shift and/or a hyperchromic effect in a given band of the chromophore, usually in that of lowest frequency. This term is obsolete. 

Hyperchromic effect Increase in the intensity of a spectral band due to substituents or interactions with the molecular environment. 

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