The excited-state dynamics of photoexcited diethylamino hydroxybenzoyl hexyl benzoate (DHHB), a UVA absorber widely used in sunscreen formulations, are studied with transient electronic and vibrational absorption spectroscopy methods four different solvents. In the polar solvents methanol, dimethyl sulfoxide (DMSO), acetonitrile, strong stimulated emission (SE) is observed at early time delays ...

Abstract:Turmeric is a member of the ginger family (Zingiberaceae), which is extensively used as a spice, food preservative and colouring material. Curcumin is a main bioactive natural compound derived from the rhizome of this plant. Curcumin can exist in several tautomeric forms, keto and enol. The keto form is more stable than enol form. Silyl ethers have proven to be versatile substrates for...

This paper is a density functional theory (DFT) calculation of intramolecular proton transfer (IPT) in 6-hydroxypicolinic acid (6HPA, 6-hydroxypyridine-2-carboxylic acid) tautomeric forms. The transition state for the enol-to-keto transition is reported in the gas phase and in four different solvents. The planar and non-planar dimer forms of 6HPA keto and enol, respectively, were also studied i...

The title compound, C(23)H(18)N(2)O(2)·0.5H(2)O, a derivative of the biologically active compound curcumin, crystallizes with two organic mol-ecules and a solvent water mol-ecule in the asymmetric unit. Each of the two independent mol-ecules is close to being planar (the dihedral angles between the indole ring systems are approximately 9 and 12°) and each exists in the keto-enol form. There is ...

A simple explanation for the symmetry of the genetic code has been suggested. An alternative to the wobble hypothesis has been proposed. The facts revealed in this study offer a new insight into physical mechanisms of the functioning of the genetic code. The wobble hypothesis, which was first proposed more than 40 years ago [1], can explain two events: 1) formation of the uracil­guanine pair as...

Activated enol ethers derived from esters or the dinitrile of malonic acid, or from pentane-2,4-dione were treated with hydrazine hydrate. The structures of the obtained products - pyrazoles 5 - were studied with a focus on tautomerism and supramolecular structure. A reverse addition of the reagents led to the isolation of two novel products, namely bis-enehydrazines 6 with an unsymmetrical arr...

A robust method for preparing (E)and (Z)-stereodefined fully substituted enol tosylates is described. α-Substituted β-keto esters undergo (E)-selective enol tosylations using TsCl–Me2N(CH2)6NMe2 as the reagent (method A, 13 examples; 63–96%) and (Z)-selective enol tosylations using TsCl–TMEDA–LiCl as the reagent (method B, 13 examples; 62–99%). A plausible mechanism for the (E)and (Z)-enol tosy...

Enol esters of 2-substituted-3-oxoalkanoates of (Z)-configuration were reduced by bakers' yeast to chiral 2-substituted-3-hydroxyalkanoates. The sy/f-selectivities of this reaction increased compared with those of the reduction of the corresponding racemic keto esters. The reaction mayproceed via an asymmetric hydrolysis of the enol esters, followed by the reduction of the resulting carbonyl gr...

The title compound, C(18)H(23)NO(5), a potential herbicide, has an enol group that is intra-molecularly hydrogen bonded to a keto O atom. The dihedral angle between the six-membered ring formed by the enol group and the aromatic benzene ring is 53.35 (6)°.