Studies of azo–hydrazone tautomerism and H-bonding in azo-functionalized dendrimers and model compounds

Abstract A 13 C NMR and UV–visible study of the tautomeric behaviour of azo-functionalized PAMAM (polyamidoamine) dendrimers and the corresponding model compounds in a variety of solvents is reported. Results of these studies indicate that the azo-functionalized PAMAM dendrimers exist as an equilibrium mixture of azo and hydrazone tautomers. A comparison of the behaviour of the dendnmers with model compounds suggests that the dendrimer periphery affects the tautomeric equilibrium between the azo and the hydrazone forms. The results further show that the proportion of the azo tautomer increases with dendrimer generation as well as in the presence of hydrogen-bond donor solvents such as acetic acid and 2,2,2-trifluoroethanol. Results of MO calculations suggest that the more planar azo tautomer would be favored because it stacks better on the dendrimer surface, which is consistent with experimental results.

[1]  A. Burawoy,et al.  296. The effect of solvents on the tautomeric equilibria of 4-arylazo-1-naphthols and the ortho-effect , 1953 .

[2]  H. Kalinowski,et al.  Carbon 13 NMR Spectroscopy , 1988 .

[3]  J. Pitha,et al.  A COMPARISON OF OPTIMIZATION METHODS FOR FITTING CURVES TO INFRARED BAND ENVELOPES , 1966 .

[4]  P. Gregory.  Azo dyes: Structure-carcinogenicity relationships , 1986 .

[5]  A. Lyčka,et al.  15N NMR study of azo‐hydrazone tautomerism of 15N‐labelled azo dyestuffs , 1981 .

[6]  S. Jockusch,et al.  Aggregation of Methylene Blue Adsorbed on Starburst Dendrimers , 1995 .

[7]  M. Večeřa,et al.  Estimation of azo - hydrazo tautomeric equilibrium in ortho-hydroxy-azocompounds by N.M.R. , 1968 .

[8]  C. H. Nicholls,et al.  Azo-hydrazone tautomerism of hydroxyazo compounds—a review , 1982 .

[9]  Abraham Nudelman,et al.  NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities. , 1997, The Journal of organic chemistry.

[10]  S. Patai.  The chemistry of the hydrazo, azo, and azoxy groups , 1975 .

[11]  Gautam R. Desiraju,et al.  Crystal engineering : the design of organic solids , 1989 .

[12]  A. Lyčka,et al.  13C NMR spectra of non‐labelled and 15N‐mono‐labelled azo dyes , 1981 .

[13]  A. Salem,et al.  935. The nature of the internal hydrogen bond. Part I. Tautomerism of 1-arylazo-2-naphthols , 1952 .

[14]  F. Saeva.  Tautomeric Behavior Comparison of 4-Phenylazo-1-naphtol and 1-Phenylazo-2-napthol Systems by Nucear Magnetic Resonance , 1971 .

[15]  L. Antonov,et al.  Quantitative analysis of azo-quinonehydrazone tautomeric equilibrium , 1989 .

[16]  D. Fine,et al.  Studies of chelation. Part 9. Cobalt complexes of 1-[(substituted phenyl)azo]-2-naphthol and 1-[(substituted phenylimino)methyl]-2-naphthol ligands. Tautomerism and reactivity , 1981 .

[17]  J. Socha,et al.  Reactivity of organic azo-compounds. X. NMR study on azo-hydrazone tautomeric equilibrium in hydroxyazo-compounds , 1970 .

[18]  A. Goursot,et al.  Theoretical conformational analysis of some hydroxyazoic dyes , 1977 .

[19]  J. B. Flannery,et al.  Hydrogen bonding in crystalline arylazonaphthols , 1972 .

[20]  K. Pitchumani,et al.  Selectivity in bromination of aniline and N-substituted anilines encapsulated in β-cyclodextrin , 1996 .

[21]  H. Sauter,et al.  Azo—hydrazone tautomerism in azo dyes. II. Raman, NMR and mass spectrometric investigations of 1-phenylazo-2-naphthylamine and 1-phenylazo-2-naphthol derivatives , 1982 .