Hypochromic effect

Peptide-type models were synthesized by Jones et a/.44, and by Takemoto etal.45). Takemoto and co-workers46 prepared polymers of 6-methylamino-, 6-di-n-propylamino-, and 6-di-n-butylamino-9-vinylpurines. They reported that these models showed no hypochromic effect on RNA in aqueous solution. 

In this method, absorption spectra have been determined for methimazole (mercazolyl) in aqeuous acid and alkaline solutions. Aqeuous solutions of methimazole have an absorption band in the medium wave region with a max at 250 nm. In strong acid and alkaline media hypsochromic and hypochromic effects are observed (30). ... 

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. 

Complexes with less extended aromaticity such as Ru(bpy/phen)2HAT [73-76] (HAT = 1,4,5,8,9,12-hexaazatriphenylene, Fig, 2) and Ru(bpy)2PPZ [77-80] (PPZ = 4,7-phenanthrolino-[6,5-b] pyrazine. Fig. 2) exhibit also characteristics most relevant to intercalation. We can mention (1) a very slow mobility of the HAT complex along the DNA double helix [81], (2) a good protection of the complex versus reagents that remain in the bulk solution [73,79], and (3) a clear hypochromic effect on the MLCT transition in the presence of DNA [73, 75, 79,80]. 

In spite of the above advantage, the quantitation by TLC-scanner is accompanied by various difficulties. The most direct difficulty is caused by hypochromic effects in the ultraviolet spectra of copolymers, especially those containing styrene units. 

More quantitative studies have shown that, although some hypochromism effects exist, they are small. For example, Monnerie I9) examined the integrated molar extinction coefficient of atactic PS in chloroform and found only a 2 % decrease for the polymer relative to ethyl benzene. In addition, Vala and Rice 15 reported a 10% decrease in absorption for the 260 nm band of isotactic PS relative to atactic PS, which was qualitatively confirmed by Longworth18>. Similarly, Cantow 8> observed a 4% hypochromism of the 261.5 nm band of isotactic PS in dioxane relative to atactic PS. Finally, Cantow 8) observed strong hypochromism (relative to atactic PS) ranging from 19% at 262 nm to 32% at 269 nm for an alternating styrene-methyl methacrylate copolymer and for random copolymers having a low styrene content. 

PS, and of meso-2,4-diphenylpentane relative to the dl compound suggests that the hypochromic effect does not require a large number (ca. 10) of interacting rings, as proposed by Vala and Rice I5>. 

The close interaction between stacked bases in a nucleic acid has the effect of decreasing its absorption of UV light relative to that of a solution with the same concentration of free nucleotides, and the absorption is decreased further when two complementary nucleic acids strands are paired. This is called the hypochromic effect. Denaturation of a double-stranded nucleic acid produces the opposite result an increase in absorption... 

One effect of stacking is a decrease in the expected intensity of light absorption. The molar extinction coefficient of a solution of double-helical DNA or RNA is always less by up to 20-30% than that predicted from the spectra of the individual nucleosides (Fig. 5-5). This hypochromic effect is considered further in Chapter 23. 

A plot of the optical absorbance at 260 nm (the wavelength of maximum light absorption by nucleic acids) versus temperature is known as a melting curve (Fig. 5-45). The absorbance is lower, by up to 40%, for native than for denatured nucleic acids. This hypochromic effect (Chapter 23) is a result of the interaction between the closely stacked bases in the helices of the native molecules. The melting temperature Tm is taken as the midpoint of the increase in absorbance (Fig. 5-45). As the percentage of G + C increases, the nucleic acid becomes more stable toward denaturation because of the three hydrogen bonds in each GC pair. Tm increases almost linearly with increases in the G + C content. In the "standard" citrate buffer (0.15 M NaCl + 0.015 M sodium citrate, pH 7.0) Eq. 5-22 holds. The exact numerical relationship depends strongly upon the ionic composition and pH of the medium.37 72 552 553... 

Whereas proteins have their low energy absorption band at 280 nm, polynucleotides typically have maxima at 260 nm (38,500 cm ). A phenomenon of particular importance in the study of nucleic acids is the hypochromic effect. In a denatured polynucleotide the absorption is approximately the sum of that of the individual components. However, when a double helical structure is formed and the bases are stacked together, there is as much as a 34% depression in the absorbance at 260 nm. This provides the basis for optical measurement of DNA melting curves (Fig. 5-45).45,86 The physical basis for the hypochromic effect is found in dipole-dipole interactions between the closely stacked base pairs.7,86,87... 

Band group V is recorded at about 400 nm in the spectra both of 1-aryl-[64ACH(40)225] and 1,3-diaryl-substituted benzo[c]pyrylium salts (87RRC417). The batho- and hypochromic effects are discussed in detail in the case of multiple substitution in l-aryl-benzo[c]pyrylium cations. 

V. I. Krupyanko, V. M.Vagabov, L. V. Trilisenko, I. N. Schipanova, L. A. Sibel dina and I. S. Kulaev (1998). A hypochromic effect of signal attenuation in the 31P-NMR spectra of linear polyphosphates. Appl. Biochim. Microbiol. (Moscow), 34, 392-395. 

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. 

Figure 1 depicts the absorption spectrum (350-500 nm) of tilorone hydrochloride alone (continuous line with triangles) or in the presence of various amounts of calf thymus DNA. There is a characteristic change in tilorone spectrum in the presence of DNA. In the presence of calf thymus DNA the visible absorption spectrum of tilorone hydrochloride is depressed and red shifted. This hypochromic effect of DNA on the absorption of tilorone chromophore is dependent on DNA concentration. The largest hypochromic effect is observed at 2 x 10 3 M DNA-P in a 4.25 x 10 4M solution of tilorone hydrochloride. 

Hypochromic effect of native DNA on the absorption of tilorone chromophore is partially reversible by Mg2+ ions. Figure 3 depicts the absorption spectra (350— 550 nm) of tilorone hydrochloride alone, 4.25 x 10-4 (curve one), in the presence of 4 x 10" 3 M DNA-P (curve four) containing 0.01 MgC (curve two) or 0.1 M NaCl (curve three). It follows from these results that the DNA-drug interaction is... 

The base-base interaction between two polymer chains is well reflected by a hypochromic effect, which can be studied by UV spectroscopy in solution. For a series of compounds, UV measurements were done and the results discussed and compared with those of emission spectroscopy. 

The Step 2 product (2.98 mg) and 1,3-dinitrobenzene (1.80 mg) were dissolved in 10 ml of THF and then diluted 100 times. This stock solution was used for absorption spectrum measurements in a 10 mm quartz cell at ambient temperature. The intensity was 0.140 at 242 nm, which changed to 0.108 after the addition of 1,3-dinitrobenzene. By changing the 1,3-dinitrobenzene concentration from 2.5 x 10 Mand5.0x 10 M at 242 nm, the absorption intensity changed from to 0.077 and 0.059, respectively. This hypochromic effect demonstrated that the fluorene ring of the polymer and 1,3-dinitrobenzene formed a stacked complex. 

The stability of double stranded nudeic adds can be determined accurately from their melting curves. These are obtained most simply from measurement of the absorbance of the solution at 260 nm which can be monitored directly as the DNA solution is heated separation of the two strands leads to de-stacking of the nucleotide residues and a concomitant increase in the absorbance (hyperchromic effect). Analogously, formation of double stranded structures from the component single strands can be monitored by following the decrease in absorbance (hypochromic effect). 

Polymerization and copolymerization of compounds, such as 8-12 with acrylamide, m.aleic anhydride, and 1-vinylpyrrolidone have been performed. The polymeric purine derivatives are generally hygroscopic poly(9-vinyladenine) is soluble in water and gives a hypochromic effect of 13% with ribonucleic acid in aqueous solution. For a review of polycondensation of functionalized purines see ref 234. 

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