Imino proton NMR spectroscopy

Comparative imino proton NMR spectroscopy as described above proved a useful... 

Comparative imino proton NMR spectroscopy - assignment of the conformational equilibrium... 

Fig. 1.1.4. The RNA sequence at the top exists in a monomolecular conformational equilibrium as shown by comparative imino proton NMR spectroscopy. The references are only able to adopt a single defined fold and allow the stem-wise assignment of the NH...

Structural Probing of Small RNAs by Comparative Imino Proton NMR Spectroscopy... 

Fig. 1.1.9. Further sequence motifs of bistable RNAs. The equilibrium position was quantified by comparative imino proton NMR spectroscopy [45].

Other classical synthetic approaches to 2-furanamine have failed, including the Curtius method and Beckmann rearrangement of 2-benzoylfuran oxime. However, hydrazinolysis of AT-(2-furyl)phthalimide, obtained from phthalimide and 2,5-dimethoxy-2,5-dihy-drofuran, gives 2-furanamine which was not isolated but detected by GLC-MS and H NMR spectroscopy. The latter reveals the absence of imino tautomers (75AP713). The chemistry of 2-dialkylamino-5-phenylfurans is typical of enamines protonation occurs on carbon to produce iminium salts. They are stable to base but afford 5-phenylfuran-2(3//)-one on hydrolysis with dilute acid. 2-Morpholino-5-phenylfuran couples with diazonium salts and affords Diels-Alder adducts with maleic anhydride and IV-phenylmaleimide (73JCS(P1)2523). 

Iactone. The observed low frequency is probably caused by hydrogen bonding of the lactone carbonyl with the imino proton of the hydrazone residue on C2, as shown by NMR spectroscopy. The same low frequency band also appeared in the spectra of the bis(arylhydrazones) of other analogues (42,46) such as the phenyl analogue of DHA [4-phenyl-butano-1,4-lactone 2,3-bis(phenylhydrazone)], which cannot form a 1,5-lactone. Finally, the lactone ring size was also deduced from its chemical reactions (24). 

The formation energies of 2-aminopyridine dimer and 2-aminopyridine - 2-pyri-done complex were determined to be 6.0 and 10.6kcal/mol, respectively, in C6D6 solution by 11 NMR spectroscopy (84SA(A)623). The similar values were obtained by CNDO/2 calculations. The dynamics of amino-imino double proton-transfer tautomeric reaction of the 2-aminopyridine-acetic acid system in hexane was studied... 

Lee et al. (67) reported in 1993 that at high pH, complexes termed M-DNA form between the nucleobase pairs within calf thymus (CT), bacterial or synthetic DNA, and the divalent metal ions, Zn, Ni, or Co " ". The chemical nature of M-DNA has been investigated using methods that probe changes in DNA properties, but do not directly probe the coordination of the metal ions. Titration of a d(T-G)i5 d(C-A)i5 duplex with Zn " " at pH 8.5 monitored by NMR spectroscopy showed a decrease in the intensity of the imino peaks with the increasing concentration of Zn " " and the complete disappearance of these peaks when the Zn " " concentration became almost equal to that of the DNA base pairs (67). The transformation induced by Ni " " of B- to M-DNA for CT DNA in solutions with 1.1 mM base pair concentrations led to the release of 1.1 equiv of protons per base pair (68). Based on these results, Lee and co-workers... 

Imino IH NMR. Imino NMR spectroscopy is a powerful direct probe for the presence and nature of the base pairing in nucleic acids. As shown in Figure 6, the imino spectra for the control and the four stable a-containing duplexes exhibit resonances for the five chemically distinct imino protons in each self-complementary decamer, indicative of stable base pair formation. In addition, temperature dependent experiments showed no evidence for pre-melting of the base pairs comprising the a-nucleotides. Virtually identical NMR spectra have been obtained for the a-duplexes at optical concentrations (3 to 6 pM duplex), demonstrating that the duplex form exists under the conditions used in the thermodynamic studies. 

JA7257). The interconversion of two forms is catalyzed by H or OH and proceeds through either an intermediate cation or the anion. NMR spectroscopy determined that the monocation is formed by protonation of the IH tautomer 46a at N(5). Comparisons with the corresponding methylated derivatives in temperature-jump experiments suggested small amounts of the IH form 46c ( 10 j and 5H tautomer 46d (2 10 ). The latter in water has a partial imino structure 46e with = 10. 

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). 

An NMR study has shown that the amino form (419) is the predominant tautomer of 2-[arylamino(imino)]-4a,5,6,7,8,8a-hexahydro-(47f)-l,3,4-benzoxadiazines. The proton-transfer tautomerism of 4-azabenzimidazole, mediated by hydrogen-bonded complexes, has been studied in the ground and excited states by means of absorption and emission spectroscopy, and it has been shown that 6-nitro and 8-nitro groups in the tetrazolo[l,5-a]pyridine molecule exhibit completely different influences on the tetrazole-azide equilibrium. The solvent effect on the azo-hydrazone tautomeric equilibrium of l-phenylazo-4-naphthol has been modelled by using ab initio quantum-chemical calculations. The results have shown that the hydrazone form is more stable in water, while methanol stabilizes the azo form. ... 

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