Study of hydracids trapped in monatomic matrices. II. Intermolecular potential calculations of the structure and spectral response of polymers

Quinolone-Hydroxyquinoline Tautomerism in Quinolone 3-Esters. Preserving the 4-Oxoquinoline Structure To Retain Antimalarial Activity

Recent publications report in vitro activity of quinolone 3-esters against the bc1 protein complex of Plasmodium falciparum and the parasite. Docking studies performed in silico at the yeast Qo site established a key role for the 4-oxo and N-H groups in drug-target interactions. Thus, the possibility of 4-oxoquinoline/4-hydroxyquinoline tautomerism may impact in pharmacologic profiles and should be investigated. We describe the synthesis, structure, photochemistry, and activity against multidrug-resistant P. falciparum strain Dd2 of ethyl 4-oxo-7-methylquinoline-3-carboxylate (7Me-OQE) and ethyl 4-hydroxy-5-methylquinoline-3-carboxylate (5Me-HQE), obtained from diethyl 2-[((3-methylphenyl)amino)methylene]malonate. Theoretically (B3LYP/6-311++G(d,p)), 5Me-HQE and 7Me-OQE show clear preference for the hydroxyquinoline form. The difference between the lowest energy hydroxyquinoline and quinolone forms is 27 and 38 kJ mol(-1), for 5Me-HQE and 7Me-OQE, respectively. Calculations of aromaticity indexes show that in 5Me-HQE both rings are aromatic, while in the corresponding oxo tautomers the nitrogen-containing ring is essentially non-aromatic. The structure of monomeric 5Me-HQE was studied using matrix isolation coupled to FTIR spectroscopy. No traces of 4-oxoquinoline tautomers were found in the experimental IR spectra, revealing that the species present in the crystal, 5Me-HQE·HCl, was lost HCl upon sublimation but did not tautomerize. Continuous broadband irradiation (λ > 220 nm; 130 min) of the matrix led to only partial photodecomposition of 5Me-HQE (ca. 1/3).

Influence of a weak hydrogen bond on vibrational coherence probed by photon echoes in DCl dimer trapped in solid nitrogen

The dynamics in the ground electronic state of the two intramolecular D-Cl stretching modes of (DCl)2 in nitrogen solid has been probed by degenerate four wave mixing experiments. Accumulated photon echoes on the "free" nu1 and "bonded" nu2 modes have been performed by means of the free electron laser of Orsay (CLIO). The analysis of the time-resolved signals provides information on the various processes responsible for the loss of vibrational coherence, in particular intra- and intermolecular vibrational energy transfer and pure dephasing. The influence of the weak hydrogen bond is clearly observed on the coherence times of the two stretching modes. Whatever the temperature, the homogeneous width of nu2 lines is almost twice that of nu1 lines. Contrary to the case of isolated DCl trapped in solid nitrogen, no obvious effect of the nitrogen lattice can be extracted from the temperature dependence of the coherence times.