UV hypochromicity

Fig. 15. Time dependence of UV hypochromicity (squares) compared to circular dichroism (CD) increase in ellipticity (circles) occurring when mixing dioleylphosphatidyl (DOP)-adenosine and DOP-uridine (taken from [33])...

Table 4. Maximum apparent UV hypochromicities(%) in the mixing curves of anionic polynucleotides (or their analogs) and catonic mononucleotide analogs. ...

Spectroscopic techniques are generally used to detect associations between bases (NMR, IR, UV). These studies have shown that Ade and Lira derivatives, on one hand, and Gua and Cyt derivatives, on the other, interact much more strongly with each other than with themselves or other bases to form hydrogen bonded heterodimers. Since in non-polar solvents the amino protons of the bases do not exchange, they can be studied by NMR techniques. Large downfield shifts of these protons or the displacement of the amino or N-H stretch frequencies have been observed. Similarly, the small UV hypochromism caused by the association between the bases (Fig. 6.17) has been interpreted as evidence for the 1 1 association between complementary bases in a planar fashion. In contrast, no other associations except those between A and U or G and C (or I and C) have been observed. 

The method of preparation of this complex is simple enough and consists of mixing of fullerene solution in toluene with solution of PVP in chloroform with the following evaporation of organic solvents and dissolution of the residue in water. It was shown that the complex formation caused the bathochromic and hypochromic shifts of the fullerene absorption bands in UV-VIS spectra (Yamakoshi et al., 1994). 

In order to prepare the complexes with low association of fullerene molecules it is necessary to start with diluted solutions of C60 (in toluene) and PVP (in CHCy, but the goal can be achieved only at relatively low content of fullerene in the complex. Thus, the degree of association of C60 molecules depends also on the molecular mass of PVP, and low associated complexes can be obtained only with PVP 10,000 and fullerene low concentration. It must be mentioned however that such complexes are relatively unstable - during their storage for about several months the association of fullerene molecules changes what can be seen from the shift of the band in UV-VIS spectra between 330 and 340 ran (bathochromic and hypochromic shifts). 

The heparin and poly-L-glutamate titrations show a markedly different behavior than do the DNA titrations. As polyanion is added, the fluorescence of the an-thrylpolyamine solution decreases until a well-defined minimum is reached. A new emission at 510 nm, which we assign to the anthracene excimer of 14, increases and decreases coincidently with the titrated fluorescence minimum. Likewise, the UV spectrum of 10 fiM 14 with added heparin shows hypochromism that occurs and disappears coincidently with the fluorescence minimum and a 2-nm red shift. We have proposed template-directed excimer formation as the physical basis for these observations. In the absence of heparin, fluorescence of the unassociated probe is observed. As heparin is added, the fluorescence decreases as a result of heparin-directed interaction between probe molecules. Additional heparin permits the fluorophore population to diffuse over the length of the poly anion, thus avoiding excimer formation and yielding a net CHEF. 

Dimethyl-1,2,4-oxadiazole has no UV absorption above 200 nm. For 3-phenyl-1,2,4-oxa-diazole = 238 nm (a = 14000), for the 5-phenyl isomer = 250 nm (a = 16100), and for 3,5-diphenyl-1,2,4-oxadiazole 2maj = 245 nm (a = 37200) (ether) have been reported <64HCA942>. 3-Ethyl-5-phenyl-1,2,4-oxadiazole has 2n,ax(CHCl3 or 2-propanol) = 284 nm, while for the fluorescence maxfCHCh) = 310 nm has been observed <77JOCi555>. Hypochromism with increase in con-... 

In summary, the UV absorbance spectrum of atactic PS in both poor and good solvents was found to be substantially unchanged from that of ethyl benzene or isopropylbenzene. The hypochromism at 261 nm of isotactic PS relative to atactic... 

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... 

Melting and helix formation of nucleic acids are often detected by the absorbance of ultraviolet light. This process can be understood in the following way The stacked bases shield each other from light. As a result, the absorbance of UV light whose wavelength is 260 nanometers (the Amo) of a double-helical DNA is less than that of the same DNA, whose strands are separated (the random coil). This effect is called the hypochromicity (less-color) of the double-helical DNA. 

A few of these UV resonance Raman studies have reported excitation profiles of oligonucleotides [158, 177], These studies show that the hypochromism in the resonance Raman intensities can be as large as 65% for bands enhanced by the ca. 260 nm absorption band for poly(dG-dC) and that the hypochromism can vary substantially between vibrational modes [177], In the duplex oligonucleotide poly(rA)-poly(rU) [158], similar hypochromism is seen. Although theUV resonance Raman excitation profiles of oligonucleotides have been measured, no excited-state structural dynamics have been extracted from them. 

Thus far, only one report of the UV resonance Raman excitation profiles of nucleic acids has appeared in the literature. The excitation profiles of calf thymus DNA [177] shows the same hypochromism as that observed in both single-stranded and duplex oligonucleotides. Also as expected, the excitation profiles are quite complex. Although an excitation profile is obtained for every vibrational mode, numerous bases are contributing to the Raman intensity observed in every vibration, each in its own microenvironment. Thus, the resonance Raman intensities currently are not useful for elucidating the excited-state structural dynamics of nucleic acids. 

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 existence of base stacking interaction for poly-VUr was also suggested from UV spectra25). At pH 12, the value of hypochromicity for poly-VUr was 29 to 51 % as compared to 1-ethyluradl. For poly-U solution, the value is only a few percent at room temperature while at lower temperature, about 30% of hypochromicity is observed which is attributed to the formation of a stacked helical polynucleotide structure. It seems therefore likely that the high value of hypochromicity observed for poly-VUr solution may be due to base stacking interactions. 

The UV spectra of C-aminotriazoles are not affected by change from neutral to acid solvents (67JCS(B)64i). The considerable hyperchromic effects combined with hypochromic or bathochromic shifts shown by 3-amino-5-(3-pyridyl)-l,2,4-triazole in aqueous solutions containing varying concentrations of hydrochloric acid are due to the pyridine moiety (54JCS4508). 

Recently, the tranquilizer action of phenothiazine derivatives has been connected with the flexibility of their molecules. They form complexes with charge transition. These complexes have been obtained as a result of the interactions between phenothiazine derivatives, dextrans, and pectins. IR spectroscopy. X-ray diffraction, UV spectroscopy, and Dreiding models (a 3-D research model) have been applied. " Hypochromic effects (changes in the band s intensity) in UV spectra have been observed. The degree of complex binding correlates with the concentrations of dextrans. 

The application of UV spectrophotometers to the analysis of styrene containing copolymers has been extensively reported in the literature. However, hypochromic effects and band shifts which result in deviations from Beer s Law have limited the use of UV detectors as mass or composition detectors in size exclusion chromatography applications. Deviations from Beer s Law for low conversion styrene-acrylonitrile copolymers in tetrahydrofuran have been experimentally investigated and compared with results previously reported in the literature. The behaviour of the extinction coefficient as a function of the copolymer composition is discussed in view of the information obtained from infrared and nuclear magnetic resonance measurements on the same polymers. As a result of this investigation, a quantitative correlation of the extinction coefficients of styrene-acrylonitrile copolymers with the length of the styrene sequences has been obtained which, in turn, allows for the use of UV spectrophotometers as sequence length detectors. 

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