Resonance nucleic acid base

Nucleic Acid Base Resonances The chemical shifts of the nonexchangeable protons in poly(dA-dT), the Nuc/D = 24 complex and the Nuc/D = 8 complex in 1 M NaCl solution are plotted as a function of temperature in Figure 19. The nucleic acid nonexchangeable proton chemical shifts in the duplex state are either unperturbed (adenosine H-8, H-2, and thymidine CH3-5) or shift slightly upfield (thymidine H-6) on complex formation (Figure 19). By contrast, the thymidine H-3 exchangeable proton located in the center of the duplex resonates 0.35 ppm to higher field in the Nuc/D = 8 proflavine complex compared to its position in the... 

Base Proton Complexation Shifts The complexation shifts of certain nucleic acid base resonances of poly(dA-dT) on formation of the daunomycin neighbor exclusion complex reflect the shielding contribution due to the anthracycline ring less the contribution from one neighboring base pair which is displaced following intercalation. Thus, the adenosine H-2 resonance remains unperturbed (Figure 27) while the thymidine exchangeable H-3 proton... 

The refinement of other analytical methods, such as electrophoresis [34,36], the various techniques of optical spectroscopy [103-105], and nuclear magnetic resonance [201], is supplemented by the recent advances in real-time affinity measurements [152,202], contributing to the understanding of biomolecular reactivity. Taken together, the improvement of analytical methods will eventually allow a comprehensive characterization of the structure, topology, and properties of the nucleic acid-based supramolecular components under consideration for distinctive applications in nanobiotechnology. 

The amino groups of the nucleic acid bases may, in principle, undergo relatively free rotation. In fact, however, they must be considered as having a significant amide character as a result of a partial double-bond character of the C-N bond due to resonance structures of types 25b and 25c. 

This paper presents quantum mechanical studies of the, 5N and, 3C chemical shifts in both the N7-H and N9-H tautomeric forms of purine. Quantum mechanical calculations of the chemical shifts were used to assign the NMR resonances and the spatial orientation of the principal axes of the chemical shift tensors. Calculations in purine and in a pyridine-methanol complex model provide insights on the importance of the intermolecular interactions on the chemical shifts of the nucleic acid bases. 

W. L. Kubasek, B. Hudson, and W. L. Peticolas, Proc. Natl. Acad. Sci. 82, 2369 (1985) M. Tsuboi, Y. Nishimura, A. Hirakawa, and W. L. Peticolas, Resonance Raman spectroscopy and normal modes of nucleic acid bases, in Biological Applications of Raman Spectroscopy (T. G. Spiro, ed.), Vol. 2, John Wiley, New York, 1987. 

Buskov VI, Bushnev VN, Poltev VI (1980) Nuclear magnetic resonance study of C-H—O hydrogen bonds in nucleic acid base analogs. Mol Biol (USSR) 14 245-250 (in English)... 

Resonance structures like these are commonly cited as leading to the planar geometry of the peptide bond and nucleic acid bases. 

UV and NMR studies showed that l-methyl-A -hydroxycytosine and its methyl derivatives exist predominantly in the oxo-imino form (up to 90%) (98BPC87). A review of the structure and properties of isolated nucleic acid bases with the special attention given to metal-cation-assisted tautomerization and the solvent effects has been published (99CR3247). Tautomerism of protonated cytosine has been studied experimentally by IR and Raman spectra and theoretically by ab initio and DFT calculations (96JPC5578). Neutral and protonated forms of cytidine monophosphate have been studied by ultraviolet resonance Raman spectroscopy. The amino oxo tautomer was found to be the most stable, followed by the imino oxo form. The imino-hydroxy tautomer was determined to be the least stable one. Upon protonation, the amino-oxo structure is retained (93JA760). 

Wu X, Yang JH, Sun SN, et al. Determination of nucleic acids based on the quenching effect on resonance light scattering of the Y(III)-l,6-bi(l,-phenyl-3,-methyl-5,-pyrazolone-4 -)hexanedione system. Luminescence 2006 21 129-34. 

Using a combination of Pt and NMR, we have recently shown (23) that cis-Pt(NH3)2(H20)2 and its ethylenediamine (en) analogue react rapidly with acetamide to give a product in which the C 0 group is bound to Pt through 0 with H2O displacement. A 2 ppm shift of the NH3 or en resonance to high frequency was observed in addition to a 47 ppm Pt shift (23). We therefore sought to use similar methods to detect possible N7-06 chelation with nucleic acid bases, the subject of much speculation. 

G. Wu, S. Dong, R. Ida, N. Reen, A solid-state nuclear magnetic resonance study of nucleic acid bases, J. Am. Chem. Soc. 124 (2002) 1768. 

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