The secretion from the hippopotamus’ skin changes its color from colorless to red, and then brown by polymerization of its pigments. The responsible pigments for the coloring reaction were isolated and denoted as hipposudoric acid (the red pigment) and norhipposudoric acid (the orange pigment). The syntheses of these pigments and the related derivatives were performed, and the latter were of us...

Guido Krämer, Annette Oehlhof, and Herbert Meier Institute of Organic Chemistry, University of Mainz, Duesbergweg 10 – 14, 55099 Mainz, Germany Reprint requests to Prof. Dr. H. Meier. Fax: +49-(0)6131-3925396. E-mail: [email protected] Z. Naturforsch. 2009, 64b, 847 – 850; received April 8, 2009 Hydroxycycloalkanones 1 of medium ring size (8 – 10) exist in a transannular tautomeric equil...

Fluorescence imaging is used to visualize directly the transfer of two inner hydrogen atoms in single porphycene molecules. This reaction leads to a chemically equivalent but differently oriented structure and hence results in a rotation of the transition dipole moments. By probing single immobilized molecules with an azimuthally polarized laser beam in the focal spot of a confocal microscope w...

A simple approach was developed for the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates from easily available compounds, 5-methoxyisoxazoles and phenacylimidazolium salts under hybrid Fe(II)/Et3N relay catalysis. The products were easily transformed into the corresponding 3-(5-methoxycarbonyl-1H-imidazol-3-ium-3-yl)pyrrol-1-ides, which in turn can be hydrolyzed under basic conditions int...

Tautomers are often disregarded in computer-aided molecular modeling applications. Little is known about the different tautomeric states of a molecule and they are rarely registered in chemical databases. Tautomeric forms of a molecule differ in shape, functional groups, surface, and hydrogen-bonding pattern. Calculation of physical-chemical properties and molecular descriptors differ from one ...

2-Aminopurine (AP), a potent mutagenic base analogue, most frequently pairs with thymine. In the AP X T base pair, both bases adopt normal tautomeric forms. The mechanism for the mutagenic activity arises from its observed pairing with cytosine, which has been ascribed to an enhanced tendency to adopt the rare imino tautomeric form. NMR studies in H2O on all the exchangeable protons in an oligo...

the acid-base equilibria of glycine have been studied in different aqueous solutions of 1,4-dioxane(0-50 % by v/v) using potentiometric method. in this study, the macro and micro protonationconstants of the amino acid and its tautomeric constant have been determined at 25 °c and constantionic strength 0.1 mol dm-3 (nacl). the protonation and the tautomeric constants of glycine indifferent binar...

The study of tautomerics equilibria is vital importance as tautomeric compounds reactivity highly depends on the proportion each tautomer. Herein, equilibrium 3-phenyl-2,4-pentanedione was studied theoretically by b3lyp/6-31+g(d)methods. effect four solvents considered (water, methanol, carbon tetrachloride and Cyclohexane).The takes place through four-membered ring transition state. barrier he...